Field of the disclosure

[0001] The present disclosure broadly relates to a process for converting flexible printed circuit boards into activated carbon, and the use of the activated carbon produced as an electrode material.

Background of the disclosure

[0002] Any discussion of the prior art throughout this specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.

[0003] There are significant financial and environmental benefits associated with solid-waste recycling. However, available recycling technologies for electronic waste (e-waste) are limited, as e-waste has the complex intrinsic property of combined metals and non-metals embedded in the same waste stream.

[0004] Flexible printed circuit boards (FPCBs) are a common component for the manufacture of small and flexible electronic devices. These devices have a very short lifespan, which creates a large volume of e-waste. When FPCBs are tailored to electronic devices of various shapes and sizes they are punched and cut to measure, which generates a significant number of offcuts. The number of offcuts increases with production volume. FPCBs typically contain a polyamide (PA) and/or polyimide (Pl)-based substrate where the circuits are interconnected by metal foils, such as copper. The inks used to print the circuits contain mainly Ag, Au, Sn, Ni and Zn-based alloys.

[0005] The present inventors have developed an efficient process to transform FPCBs into materials that can be used as a feedstock for other manufacturing processes. The process opens up new pathways for the recovery and development of high-performance, green materials from waste products.

Summary of the disclosure

[0006] In a first aspect there is provided a process for preparing an activated, doped, porous carbon from FPCBs comprising metal and a polymer, the process comprising, consisting of, or consisting essentially of: (a) heating the FPCBs so as to provide a mixture comprising the metal and char;

(b) separating the metal and the char; and

(c) contacting the char with carbon dioxide under conditions effective to activate the char so as to provide the activated, doped, porous carbon.

[0007] The FPCBs may be waste FPCBs.

[0008] The waste FPCBs may be, or may comprise, off-cuts.

[0009] Step (a) may be performed in an inert atmosphere, such as for example a nitrogen atmosphere.

[0010] In step (a) the FPCBs may be heated at a temperature that is below the melting point of the metal.

[0011] In step (a) the FPCBs may be heated to a temperature between about 600 °C and about 1000 °C, or to a temperature between about 600 °C and about 900 °C, or to a temperature between about 650 °C and about 850 °C, or to a temperature between about 650 °C and about 750 °C, or to a temperature of about 700 °C.

[0012] In step (a) the heating may be performed for a period of time between about 5 minutes and about 2 hours, or for a period of time between about 15 minutes and about 45 minutes, or for about 30 minutes.

[0013] Step (b) may be performed by gravity separation, such as for example gravity separation in an aqueous medium.

[0014] The process may further comprise drying the char following step (b).

[0015] The process may further comprise grinding the char prior to step (c).

[0016] The char may be ground into a powder.

[0017] The char may be ground using a ball mill.

[0018] Step (c) may comprise heating the char in an atmosphere of carbon dioxide to a temperature between about 600 °C and about 1000 °C, or to a temperature between about 600 °C and about 900 °C, or to a temperature between about 700 °C and about 900 °C, or to a temperature between about 750 °C and about 850 °C, or to a temperature of about 800 °C, so as to provide the activated, doped, porous carbon. [0019] Step (c) may be performed for a period of time between about 30 minutes and about 3 hours, or for a period of time between about 30 minutes and about 1.5 hours, or for about 1 hour.

[0020] The FPCBs may comprise both metallic and non-metallic portions.

[0021] The FPCBs may be used in the process without undergoing any separation into constituent components.

[0022] The FPCBs may be used in the process without being separated into metallic and non- metallic parts.

[0023] No other carbon source besides the FPCBs may be present in heating step (a).

[0024] Prior to step (a), the FPCBs may undergo no pre-treatment or pre-processing.

[0025] The process may not involve cryomilling of the FPCBs.

[0026] The char may not be subjected to oxidation in air.

[0027] The activated, doped, porous carbon may not be subjected to oxidation in air.

[0028] The polymer may be a nitrogen-containing polymer.

[0029] The nitrogen-containing polymer may be a polyamide, a polyimide, a polyaniline, a poly(nitroaniline) or a polyvinyl tetrazole.

[0030] The nitrogen-containing polymer may be a polyamide or a polyimide.

[0031] Following separation in step (b), the metal may be recovered in a purity of greater than 95%, 96%, 97%, 98%, 99%, or greater than 99.5%.

[0032] The metal may catalyse conversion of the polymer to the char.

[0033] The metal may be copper.

[0034] The activated, doped, porous carbon may be O- and N-doped.

[0035] Besides carbon dioxide, the process may involve no addition of activating agents in step (c).

[0036] The process may be performed in a furnace. [0037] The activated, doped, porous carbon may be for use in, or suitable for use in, an electrode.

[0038] The activated, doped, porous carbon may be for use in, or suitable for use in, a supercapacitor electrode.

[0039] In a second aspect there is provided an activated, doped, porous carbon whenever prepared by the process of the first aspect.

[0040] In a third aspect there is provided an activated, doped, porous carbon comprising:

• a surface area between about 900 m ² /g and about 1100 m ² /g by BET ; and/or

• an average pore diameter between about 2 nm and about 3 nm; and/or

• a micropore volume between about 0.3 cm ³ /g and about 0.5 cm ³ /g; and/or

• a mesopore volume between about 0.3 cm ³ /g and about 0.5 cm ³ /g; and/or

• a total pore volume between about 0.50 cm ³ /g and about 1.0 cm ³ /g; and/or

• between about 9 wt% and about 11 wt% N, between about 11 wt% and about 14 wt% O, and between about 73 wt% and about 77 wt% C; and/or

• a specific capacitance between about 230 Fg ^-1 and about260 Fg ^-1 in 0.5M KOH and at a scan rate of 5 mV s ^-1 .

[0041] In an embodiment of the third aspect there is provided an activated, doped, porous carbon comprising:

• a surface area between about 900 m ² /g and about 1000 m ² /g by BET; and/or

• an average pore diameter between about 2 nm and about 3 nm; and/or

• a micropore volume between about 0.3 cm ³ /g and about 0.5 cm ³ /g; and/or

• a mesopore volume between about 0.3 cm ³ /g and about 0.5 cm ³ /g; and/or

• a total pore volume between about 0.60 cm ³ /g and about 0.90 cm ³ /g; and/or

• between about 9 wt% and about 10 wt% N, between about 11.5 wt% and about 13.5 wt% O, and between about 74 wt% and about 76 wt% C; and/or a specific capacitance between about 235 Fg ^-1 and about250 Fg ^-1 in 0.5M KOH and at a scan rate of 5 mV s ^-1 .

[0042] In another embodiment of the third aspect there is provided an activated, doped, porous carbon comprising:

• a surface area between about 950 m ² /g and about 1000 m ² /g by BET; and/or

• an average pore diameter between about 2 nm and about 2.75 nm; and/or

• a micropore volume between about 0.32 cm ³ /g and about 0.48 cm ³ /g; and/or

• a mesopore volume between about 0.32 cm ³ /g and about 0.48 cm ³ /g; and/or

• a total pore volume between about 0.65 cm ³ /g and about 0.85 cm ³ /g; and/or

• between about 9 wt% and about 10 wt% N, between about 12.5 wt% and about 13.5 wt% O, and between about 74.5 wt% and about 76 wt% C; and/or

• a specific capacitance between about 235 Fg ^-1 and about250 Fg ^-1 in 0.5M KOH and at a scan rate of 5 mV s ^-1 .

[0043] In a further embodiment of the third aspect there is provided an activated, doped, porous carbon comprising:

• a surface area between about 960 m ² /g and about 990 m ² /g by BET; and/or

• an average pore diameter between about 2.10 nm and about 2.60 nm; and/or

• a micropore volume between about 0.32 cm ³ /g and about 0.48 cm ³ /g; and/or

• a mesopore volume between about 0.32 cm ³ /g and about 0.48 cm ³ /g; and/or

• a total pore volume between about 0.70 cm ³ /g and about 0.85 cm ³ /g; and/or

• between about 9.5 wt% and about 10 wt% N, between about 12.5 wt% and about 13.25 wt% O, and between about 74.5 wt% and about 75.5 wt% C; and/or

• a specific capacitance between about 238 Fg ^_1 and about248 Fg ^_1 in 0.5M KOH and at a scan rate of 5 mV s ^_1 . [0044] In yet another embodiment of the third aspect there is provided an activated, doped, porous carbon comprising:

• a surface area between about 970 m ² /g and about 980 m ² /g by BET; and/or

• an average pore diameter between about 2.10 nm and about 2.40 nm; and/or

• a micropore volume between about 0.30 cm ³ /g and about 0.45 cm ³ /g; and/or

• a mesopore volume between about 0.30 cm ³ /g and about 0.45 cm ³ /g; and/or

• a total pore volume between about 0.70 cm ³ /g and about 0.82 cm ³ /g; and/or

• between about 9.65 wt% and about 10 wt% N, between about 12.75 wt% and about 13.25 wt% O, and between about 74.75 wt% and about 75.25 wt% C; and/or

• a specific capacitance between about 240 Fg ^-1 and about248 Fg ^-1 in 0.5M KOH and at a scan rate of 5 mV s ^-1 .

[0045] In still a further embodiment of the third aspect there is provided an activated, doped, porous carbon comprising:

• a surface area between about 970 m ² /g and about 980 m ² /g by BET; and/or

• an average pore diameter between about 2.20 nm and about 2.40 nm; and/or

• a micropore volume between about 0.32 cm ³ /g and about 0.45 cm ³ /g; and/or

• a mesopore volume between about 0.32 cm ³ /g and about 0.45 cm ³ /g; and/or

• a total pore volume between about 0.72 cm ³ /g and about 0.82 cm ³ /g; and/or

• between about 9.65 wt% and about 10 wt% N, between about 12.75 wt% and about 13.25 wt% O, and between about 74.75 wt% and about 75.25 wt% C; and/or

• a specific capacitance between about 240 Fg ^_1 and about248 Fg ^_1 in 0.5M KOH and at a scan rate of 5 mV s ^_1 .

[0046] In yet another embodiment of the third aspect there is provided an activated, doped, porous carbon comprising: a surface area between about 970 m ² /g and about 980 m ² /g by BET; and/or • an average pore diameter between about 2.25 nm and about 2.35 nm; and/or

• a micropore volume between about 0.35 cm ³ /g and about 0.45 cm ³ /g; and/or

• a mesopore volume between about 0.32 cm ³ /g and about 0.42 cm ³ /g; and/or

• a total pore volume between about 0.72 cm ³ /g and about 0.80 cm ³ /g; and/or

• between about 9.75 wt% and about 10 wt% N, between about 12.75 wt% and about 13.25 wt% O, and between about 74.75 wt% and about 75.25 wt% C; and/or

• a specific capacitance between about 240 Fg ^_1 and about248 Fg ^_1 in 0.5M KOH and at a scan rate of 5 mV s ^_1 .

[0047] In a further embodiment of the third aspect there is provided an activated, doped, porous carbon comprising:

• a surface area between about 970 m ² /g and about 980 m ² /g by BET; and/or

• an average pore diameter between about 2.25 nm and about 2.35 nm; and/or

• a micropore volume between about 0.37 cm ³ /g and about 0.42 cm ³ /g; and/or

• a mesopore volume between about 0.35 cm ³ /g and about 0.43 cm ³ /g; and/or

• a total pore volume between about 0.75 cm ³ /g and about 0.80 cm ³ /g; and/or

• between about 9.75 wt% and about 10 wt% N, between about 12.75 wt% and about 13.25 wt% O, and between about 74.75 wt% and about 75.25 wt% C; and/or

• a specific capacitance between about 241 Fg ^_1 and about247 Fg ^_1 in 0.5M KOH and at a scan rate of 5 mV s ^_1 .

[0048] In yet another embodiment of the third aspect there is provided an activated, doped, porous carbon comprising:

• a surface area of about 975 m ² /g by BET ; and/or

• an average pore diameter of about 2.3 nm; and/or a micropore volume of about 0.4 cm ³ /g; and/or a mesopore volume of about 0.38 cm ³ /g; and/or • a total pore volume of about 0.78 cm ³ /g; and/or

• about 9.8 wt% N, about 13 wt% O, and about 75 wt% C; and/or

• a specific capacitance of about 244 Fg ^_1 in 0.5M KOH and at a scan rate of 5 mV s’ ¹ .

[0049] In the third aspect and embodiments thereof, the activated, doped, porous carbon may be O- and N- doped.

[0050] In the third aspect and embodiments thereof, the activated, doped, porous carbon may be polyamide-derived.

[0051] In the third aspect and embodiments thereof, the activated, doped, porous carbon may be in the form of an electrode.

[0052] The electrode may have a stability greater than about 90% after 2000 cycles.

[0053] The electrode may have a stability of -97% after 2000 cycles.

[0054] The electrode may have a stability of greater than 80% after 10,000 cycles.

[0055] The electrode may have a stability of -87% after 10,000 cycles.

[0056] In a fourth aspect there is provided a supercapacitor comprising the activated, doped porous carbon of the second or third aspects.

[0057] The supercapacitor may comprise an electrode, wherein the electrode comprises, consists of, or consists essentially of the activated, doped, porous carbon.

[0058] The electrode may be an anode or cathode.

[0059] The supercapacitor may further comprise an electrolyte, a separator and/or a current collector.

[0060] The supercapacitor may be in operable connection with an electrical circuit.

[0061] The supercapacitor may be in operable connection with a printed circuit board.

[0062] In a fifth aspect there is provided a method for capturing carbon dioxide, the method comprising contacting the carbon dioxide with the activated, doped, porous, carbon of the second or third aspects. [0063] In a sixth aspect there is provided a carbon dioxide capture device comprising the activated, doped, porous carbon of the second or third aspects.

Definitions

[0064] The following are some definitions that may be helpful in understanding the description of the present disclosure. These are intended as general definitions and should in no way limit the scope of the present disclosure to those terms alone, but are put forth for a better understanding of the following description.

[0065] Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0066] The terms "a" and "an" are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.

[0067] In the context of this specification the term "about" is understood to refer to a range of numbers that a person of skill in the art would consider equivalent to the recited value in the context of achieving the same function or result.

[0068] Any numerical range recited herein is intended to include all sub-ranges of the same numerical precision subsumed within the recited range. For example, a range of 1.0 to 5.0 is intended to include all sub-ranges between (and including) the recited minimum value of 1.0 and the recited maximum value of 5.0, that is, having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 5.0, such as 2.1 to 4.5. Any maximum numerical limitation recited herein is intended to include all lower numerical limitations subsumed therein and any minimum numerical limitation recited herein is intended to include all higher numerical limitations subsumed therein.

Brief Description of the Drawings

[0069] Figure 1 : Schematic illustration of a process in accordance with one embodiment of the invention in which waste FPCBs are used to prepare O- and N-doped activated carbon suitable for use as a supercapacitor electrode.

[0070] Figure 2: (a) Thermogravimetric analysis with derivatives of the FPCBs (black line) and raw polyamide (blue line) (b) Off-gas analysis of FPCBs and raw polyamide at 700 °C by I R gas analyser; (c) TGA-FTIR off-gas analysis of FPCBs under different thermal conditions; (d) TGA-FTIR off-gas analysis of raw polyamide under different thermal conditions.

[0071] Figure 3: a) X-ray diffractogram of recovered Cu; and (b) Characteristic XPS of recovered Cu.

[0072] Figure 4: (a) Raman spectroscopy of carbons with and without activation; (b) N ₂ adsorption/desorption isotherms of activated carbon; (c) subsequent distribution of the pore size of the activated carbon; (d), (e) and (f) are the high-resolution XPS activated spectra of C1s, O1s, and N1s respectively of the activated carbon.

[0073] Figure 5: Nano SEM image of the polyamide-derived carbon (a) without activation, (b) with activation; (c) and (d) is the high-resolution TEM image of the activated carbon showing a clear porous structure; (e) STEM image of the activated carbon sample, elementary mapping of activated carbon sample; (f) carbon; (g) oxygen; (h) nitrogen.

[0074] Figure 6: Electrochemical performance of the activated carbon derived from polyamide; (a) CV curves, (b) galvanostatic charge-discharge curves, and (c) retention rate at 1 Ag- ¹ current density.

[0075] Figure 7: Electrochemical impedance spectra for the activated carbon (a) Nyquist plot (b) bode impedance plot.

Detailed Description

[0076] In one aspect of the disclosure there is provided a process for preparing an activated, doped, porous carbon from FPCBs comprising metal and a polymer, the process comprising, consisting of, or consisting essentially of:

(a) heating the FPCBs so as to provide a mixture comprising the metal and char;

(b) separating the metal and the char; and

(c) contacting the char with carbon dioxide under conditions effective to activate the char so as to provide the activated, doped, porous carbon.

[0077] Typically, the FPCBs are waste FPCBs, such as for example off-cuts. In other embodiments, the waste FPCBs are end-of-life FPCBs.

[0078] In some embodiments, step (a) is performed in an inert atmosphere, such as for example a nitrogen or an argon atmosphere. [0079] In step (a) the FPCBs may be heated to a temperature between about 600 °C and about 1000 °C, or to a temperature between about 600 °C and about 950 °C, or to a temperature between about 600 °C and about 925 °C, or to a temperature between about 600 °C and about 900 °C, or to a temperature between about 625 °C and about 875 °C, or to a temperature between about 625 °C and about 850 °C, or to a temperature between about 650 °C and about 825 °C, or to a temperature between about 650 °C and about 800 °C, or to a temperature between about 650 °C and about 775 °C, or to a temperature between about 650 °C and about 750 °C, or to a temperature between about 650 °C and about 725 °C, or to a temperature between about 675 °C and about 725 °C, or to a temperature between about 685 °C and about 715 °C, or to a temperature of about 700 °C. Typically, step (a) is performed at a temperature that is below the melting point of the metal.

[0080] In step (a) the heating may be performed for a period of time between about 5 minutes and about 2 hours, or for a period of time between about 5 minutes and about 90 minutes, or for a period of time between about 10 minutes and about 90 minutes, or for a period of time between about 10 minutes and about 60 minutes, or for a period of time between about 10 minutes and about 45 minutes, or for a period of time between about 15 minutes and about 45 minutes, or for a period of time between about 5 minutes and about 45 minutes, or for about 30 minutes.

[0081] Step (a) may be carried out by heating the FPCBs without conducting any pre- treatment or pre-processing of the FPCBs. In the context of this specification, "pre-treatment" and "preprocessing" include any and all steps that either partially or completely breakdown, disassemble, dismantle, take apart or otherwise degrade the FPCBs from their assembled working state. Examples of pre-treatment and pre-processing include, but are not limited to, any separation of the FPCBs into their constituent parts (such as for example, separation of the FPCBs into metallic and non-metallic parts), any chemical treatments and milling of the FPCBs.

[0082] In some embodiments, step (b) may be performed by gravity separation, such as for example gravity separation in water. Gravity separation is well known amongst those skilled in the art.

[0083] In some embodiments the process further comprises drying the char obtained following step (b). Drying may be carried out for example, by heating the char in an oven at about 100 [0084] In some embodiments, the process may further comprise grinding the char prior to step (c). The char may be ground into a powder. In some embodiments the powder may have an average particle size of less than about 200 .m. In alternative embodiments, the powder may have an average particle size between about 150 .m and about 200 .m. Methods for grinding the char will be well known to those skilled in the art and include, for example, a ball mill.

[0085] Typically, the char is ground after being dried.

[0086] Step (c) comprises contacting the char with carbon dioxide under conditions effective to activate the char so as to provide the activated, doped, porous carbon. The conditions may comprise heating the char in the presence of carbon dioxide.

[0087] Step (c) may comprise heating the char in an atmosphere of carbon dioxide to a temperature between about 600 °C and about 1000 °C, or to a temperature between about 600 °C and about 950 °C, or to a temperature between about 625 °C and about 950 °C, or to a temperature between about 650 °C and about 900 °C, or to a temperature between about 650 °C and about 875 °C, or to a temperature between about 675 °C and about 875 °C, or to a temperature between about 700 °C and about 875 °C, or to a temperature between about 700 °C and about 850 °C, or to a temperature between about 700 °C and about 825 °C, or to a temperature between about 725 °C and about 825 °C, or to a temperature between about 750 °C and about 850 °C, or to a temperature between about 775 °C and about 825 °C, or to a temperature between about 785 °C and about 815 °C, or to a temperature between about 790 °C and about 810 °C, or to a temperature between about 795 °C and about 805 °C, or to a temperature of about 800 °C, so as to provide the activated, doped, porous carbon.

[0088] Step (c) may be performed for a period of time between about 5 minutes and about 3 hours, or for a period of time between about 10 minutes and about 3 hours, or for a period of time between about 15 minutes and about 3 hours, or for a period of time between about 20 minutes and about 3 hours, or for a period of time between about 30 minutes and about 3 hours, or for a period of time between about 45 minutes and about 3 hours, for a period of time between about 5 minutes and about 2 hours, or for a period of time between about 10 minutes and about 2 hours, or for a period of time between about 15 minutes and about 2 hours, or for a period of time between about 20 minutes and about 2 hours, or for a period of time between about 30 minutes and about 2 hours, or for a period of time between about 45 minutes and about 2 hours, or for a period of time between about 5 minutes and about 1.5 hours, or for a period of time between about 10 minutes and about 1 .5 hours, or for a period of time between about 15 minutes and about 1 .5 hours, or for a period of time between about 20 minutes and about 1.5 hours, or for a period of time between about 30 minutes and about 1.5 hours, or for a period of time between about 45 minutes and about 1.5 hours, or for a period of time between 45 minutes and about 75 minutes, or for a period of time between about 55 minutes and about 65 minutes, or for a period of time of about 1 hour.

[0089] In some embodiments, neither the char nor the activated, doped, porous carbon are subjected to oxidation in air.

[0090] In some embodiments the polymer may be a nitrogen-containing polymer, such as for example, a polyamide, a polyimide, a polyaniline, a poly(nitroaniline) or a polyvinyl tetrazole.

[0091] FPCBs typically contain a polyamide-based or polyimide-based substrate in which the circuits are interconnected by metal foils, such as copper. Accordingly, in some embodiments the polymer is a polyamide or a polyimide, and the metal is copper.

[0092] In some embodiments, besides carbon dioxide, the process may involve no addition of activating agents (such as for example, calcium chloride, phosphoric acid, zinc chloride and/or hydroxides) in step (c). Typically, activating agents are dehydrating agents and/or oxidizing agents.

[0093] In another aspect, there is provided an activated, doped, porous carbon whenever prepared by the process of the present disclosure. The activated, doped, porous carbon may find use in a number of areas, such as for example, as an electrode, or as a medium to capture carbon dioxide.

[0094] In another aspect there is provided an activated, doped, porous carbon having one or more of the following properties listed in paragraphs [0095] to [0101]:

[0095] A surface area between about 850 m ² /g and about 1050 m ² /g by BET, or between about 875 m ² /g and about 1025 m ² /g by BET, or between about 900 m ² /g and about 1025 m ² /g by BET, or between about 915 m ² /g and about 1000 m ² /g by BET, or between about 945 m ² /g and about 1000 m ² /g by BET, or between about 955 m ² /g and about 995 m ² /g by BET, or between about 965 m ² /g and about 985 m ² /g by BET, or between about 970 m ² /g and about 980 m ² /g by BET, or about 975 m ² /g by BET.

[0096] An average pore diameter between about 1 nm and 4 nm, or between about 1.2 nm and about 3.8 nm, or between about 1.2 nm and about 3.6 nm, or between about 1.4 nm and about 3.6 nm, or between about 1 .4 nm and about 3.4 nm, or between about 1.5 nm and about 3.3 nm, or between about 1.6 nm and about 3.2 nm, or between about 1.7 nm and about 3.1 nm, or between about 1.8 nm and about 2.9 nm, or between about 1 .9 nm and about 2.7 nm, or between about 2.0 nm and about 2.6 nm, or between about 2.1 nm and about 2.5 nm, or between about 2.2 nm and about 2.4 nm, or between about 2.25 nm and about 2.35 nm, or between about 2.27 nm and about 2.32 nm, or about 2.3 nm.

[0097] A micropore volume between about 0.05 cm ³ /g and about 2 cm ³ /g, or between about 0.07 cm ³ /g and about 1.5 cm ³ /g, or between about 0.09 cm ³ /g and about 1 .3 cm ³ /g, or between about 0.1 cm ³ /g and about 1.1 cm ³ /g, or between about 0.12 cm ³ /g and about 0.9 cm ³ /g, or between about 0.14 cm ³ /g and about 0.7 cm ³ /g, or between about 0.16 cm ³ /g and about 0.5 cm ³ /g, or between about 0.2 cm ³ /g and about 0.5 cm ³ /g, or between about 0.25 cm ³ /g and about 0.45 cm ³ /g, or between about 0.3 cm ³ /g and about 0.45 cm ³ /g, between about 0.35 cm ³ /g and about 0.45 cm ³ /g, or between about 0.38 cm ³ /g and about 0.42 cm ³ /g, or about 0.4 cm ³ /g.

[0098] A mesopore volume between about 0.05 cm ³ /g and about 2 cm ³ /g, or between about 0.07 cm ³ /g and about 1.5 cm ³ /g, or between about 0.09 cm ³ /g and about 1 .3 cm ³ /g, or between about 0.1 cm ³ /g and about 1.1 cm ³ /g, or between about 0.12 cm ³ /g and about 0.9 cm ³ /g, or between about 0.14 cm ³ /g and about 0.7 cm ³ /g, or between about 0.16 cm ³ /g and about 0.5 cm ³ /g, or between about 0.2 cm ³ /g and about 0.5 cm ³ /g, or between about 0.25 cm ³ /g and about 0.45 cm ³ /g, or between about 0.3 cm ³ /g and about 0.45 cm ³ /g, or between about 0.35 cm ³ /g and about 0.45 cm ³ /g, or between about 0.35 cm ³ /g and about 0.40 cm ³ /g, or about 0.38 cm ³ /g.

[0099] A total pore volume between about 0.05 cm ³ /g and about 2 cm ³ /g, or between about 0.07 cm ³ /g and about 1.9 cm ³ /g, or between about 0.09 cm ³ /g and about 1 .7 cm ³ /g, or between about 0.13 cm ³ /g and about 1.5 cm ³ /g, or between about 0.23 cm ³ /g and about 1.3 cm ³ /g, or between about 0.33 cm ³ /g and about 1.1 cm ³ /g, or between about 0.43 cm ³ /g and about 1.0 cm ³ /g, or between about 0.53 cm ³ /g and about 0.95 cm ³ /g, or between about 0.58 cm ³ /g and about 0.90 cm ³ /g, or between about 0.63 cm ³ /g and about 0.90 cm ³ /g, or between about 0.68 cm ³ /g and about 0.85 cm ³ /g, or between about 0.73 cm ³ /g and about 0.85 cm ³ /g, or between about 0.76 cm ³ /g and about 0.8 cm ³ /g, or about 0.78 cm ³ /g.

[00100] C, N and O content as follows: between about 8 wt% and about 11.5 wt% N, between about 11 wt% and about 14.8 wt% O, and between about 73 wt% and about 76.8 wt% C; or between about 8.2 wt% and about 11.3 wt% N, between about 11.2 wt% and about 14.6 wt% O, and between about 73.2 wt% and about 76.6 wt% C; or between about 8.4 wt% and about 11.1 wt% N, between about 11.4 wt% and about 14.4 wt% O, and between about 73.4 wt% and about 76.4 wt% C; or between about 8.6 wt% and about 10.9 wt% N, between about 11.6 wt% and about 14.2 wt% O, and between about 73.6 wt% and about 76.2 wt% C; or between about 8.8 wt% and about 10.7 wt% N, between about 11.8 wt% and about 14.0 wt% O, and between about 73.8 wt% and about 76 wt% C; or between about 9.0 wt% and about 10.5 wt%

N, between about 12 wt% and about 13.8 wt% O, and between about 74 wt% and about 75.8 wt% C; or between about 9.2 wt% and about 10.3 wt% N, between about 12.2 wt% and about 13.6 wt% O, and between about 74.2 wt% and about 75.6 wt% C; or between about 9.4 wt% and about 10.2 wt% N, between about 12.4 wt% and about 13.5 wt% O, and between about 74.4 wt% and about 75.4 wt% C; or between about 9.5 wt% and about 10.1 wt% N, between about 12.5 wt% and about 13.4 wt% O, and between about 74.5 wt% and about 75.3 wt% C; or between about 9.6 wt% and about 10.0 wt% N, between about 12.6 wt% and about 13.3 wt% O, and between about 74.6 wt% and about 75.2 wt% C; or between about 9.7 wt% and about 9.9 wt% N, between about 12.7 wt% and about 13.2 wt% O, and between about 74.7 wt% and about 75.15 wt% C; or between about 9.75 wt% and about 9.85 wt% N, between about 12.8 wt% and about 13.1 wt% O, and between about 74.8 wt% and about 75.1 wt% C; or between about 9.8 wt% and about 9.9 wt% N, between about 12.9 wt% and about 13 wt%

O, and between about 74.9 wt% and about 75 wt% C.

[00101] A specific capacitance between about 220 and about 270, or between about 222 and about 268, or between about 224 and about 266, or between about 226 and about 264, or between about 228 and about 262, or between about 230 and about 260, or between about 232 and about 258, or between about 234 and about 256, or between about 236 and about 254, or between about 238 and about 252, or between about 240 and about 250, or between about 242 and about 248, or between about 242 and about 246, or about 244, each in 0.5M KOH and at a scan rate of 5 mV s’ ¹ .

[00102] It will be understood that the present disclosure contemplates any and all combinations of the above ranges for each different property of the activated, doped, porous carbon.

[00103] The use of electrochemical supercapacitors as energy storage devices has drawn considerable attention as a result of their high power density, fast charge/discharge rate, long cycle lifetime and wide operating temperatures. Activated carbons are typically used as electrode materials for commercial electrical double layer capacitors (EDLCs) due to their large surface area and adequate pore size, which are basic requirements for creating accessible paths for ionic transport and double layer formation. Activated carbon produced in accordance with the present disclosure demonstrated extraordinary specific capacitance (244 F g' ¹ at a scan rate of 5 mV s ^_1 ), thereby establishing its potential as a highly effective electrode material for application in supercapacitors. Accordingly, in a further aspect of the disclosure there is provided a supercapacitor comprising the activated, doped, porous carbon of the second or third aspects. [00104] The supercapacitor may comprise an electrode, wherein the electrode comprises, consists of, or consists essentially of the activated, doped, porous carbon. The electrode may be an anode or a cathode.

[00105] The supercapacitor may further comprise an electrolyte, a separator and/or a current collector. The supercapacitor may be in operable connection with an electrical circuit. In alternative embodiments the supercapacitor may be in operable connection with a printed circuit board.

[00106] Activated carbons have also gained attention in recent years as gas storage/separation sorbents. As such, in yet another aspect there is provided a method for capturing carbon dioxide, the method comprising contacting the carbon dioxide with the doped, porous, carbon of the second or third aspects. The carbon dioxide may be present in flue gas, exhaust gas, ambient air or landfill gas.

[00107] In still a further aspect of the disclosure there is provided a carbon dioxide capture device comprising the activated, doped, porous carbon of the second or third aspects.

Examples

[00108] The present disclosure is further described below by reference to the following nonlimiting examples.

Example 1 - Preparation of activated carbon from multilayer waste FPCBs and the characterisation thereof

Materials and methods

[00109] Multilayer waste FPCBs comprising copper and polyamide were provided by TES- AMM (Thailand) Co., Ltd. and cut into small pieces having an average size of 2cm x 2cm. Heating was performed in a horizontal tube furnace equipped with a high-quality infrared camera and gas analyser.

[00110] The FPCBs were subjected to a range of different conditions (i.e. from 650 °C to 900 °C, with a holding time from 5 to 30 minutes) in order to identify the optimum conditions in which to generate carbon and copper without melting the copper. The infrared gas analyser was used to analyse gas emissions resulting from carbonisation of the plastics. The spectra of CO, CO2, and CH4 were identified by decomposition of polyamide and epoxy.

[00111] The waste FPCBs were introduced into the furnace after the set temperature was reached. Introduction of the FPCBs to the furnace was designed in such a way as to avoid oxidation. Air from the furnace chamber was removed via a constant supply of inert gas (N2: 1 L/min). The waste FPCBs were placed on a graphite crucible and slowly inserted into the hot zone of the furnace. After heating, the crucible was removed from the hot zone and introduced into a low temperature zone (having a temperature between about 200 °C and about 250 °C) for about 5 minutes. Finally, when the sample temperature was reduced to about 200 °C to about 250 °C it was removed from the furnace. A char/copper mixture was produced by the thermal delamination and carbonisation of the layered structure of polyamide and copper. The char and copper were separated from the mixture using gravity separation in a water medium.

[00112] Following separation, the resulting char was dried in an oven at 100 °C and ground in a ball mill. The ball mill was operated at 100 rpm for 30 minutes to produce a fine carbon powder. This fine carbon powder was then thermally activated at 800 °C for 1 hour in a carbon dioxide atmosphere to introduce porosity and increase the surface area. During this thermal activation, carbon dioxide acts as an oxidising agent that reacts with surface carbon thereby creating a porous skeleton throughout the material. The porous carbon was utilised as an electrode material in a three-electrode system for a supercapacitor application.

[00113] To evaluate the thermal characteristics of the waste FPCBs at different temperatures, a thermogravimetric analysis (TGA) was carried out. The temperature was varied from room temperature to 900 °C at a 20 °C/min heating rate. N2 gas was purged to create an inert environment.

[00114] To evaluate the catalytic effect of the embedded metal substrate on the carbonisation of the polyamide contained in the FPCBs two different samples were analysed. One was a FPCB in which polyamide was laminated on the metallic foils, the other was the same polyamide without metal laminating (referred to as "raw PA").

Characterisation methods

[00115] TGA was performed using a PerkinElmer STA 8000 instrument. The elemental composition of the recovered copper co-product was characterised with inductively-coupled, plasma-based optical emission spectroscopy (ICP-OES) with a Perkin Elmer OPTIMA 7300 after digestion in nitric acid. The phase and elemental information were confirmed with a PANalytical X’Pert Pro multipurpose machine, where the X-ray diffraction (XRD) pattern was collected by using copper source radiation (A=1.54 A). The software used to identify phases and components was X’Pert High Score Plus. The composition of the carbon and copper was confirmed with X-Ray Photoelectron Spectroscopy (XPS) analysis, which was carried out in a Thermo Scientific ESCALAB250Xi machine using an Al Ka X-ray source. For the XPS analysis, a spot size of 500 micrometres was chosen for both copper and carbon. The oil collected from the thermal processing of the FPCBs was analysed using gas chromatographymass spectrometry (GC-MS). The microstructural characterisation of the carbon was carried out with a field emission scanning electron microscope (FE-SEM) - FEI Nova NanoSEM 450 FE-SEM. Renishaw inVia coupled with a microscope was used for Raman spectroscopy of the carbonaceous materials. An argon-ion laser of 514 nanometres was used for this work. The pore size, pore-volume, and surface area of the activated carbon were measured through N ₂ absorption/disabsorption on a Micromeritics Tristar II Plus absorption analyser using Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) models.

Results and discussion

[00116] The thermal characteristics of the waste FPCBs and raw PA are shown in Figure 2a. The FPCB sample contains two prominent degradation zones at 420 °C and 620 °C. The first peak at 420 °C is ascribed to the early volatilisation state of polyamide and the binder, and the peak at 620 °C is also due to the mass decomposition of polyamide at a relatively higher temperature. A -17% loss in the weight of the FPCB was observed at 700 °C and remained approximately constant above this temperature. In contrast, when the raw PA was analysed, the two prominent degradations were observed at slightly higher temperatures: 460 °C and 695 °C. The calculated weight loss was -15% for the entire process, and the curve of the weight loss did not reach a constant profile. This indicated that carbonisation was not completed during the process.

[00117] An off-gas analysis was also conducted using Fourier-transform infrared spectroscopy (FTIR) to evaluate the quality of the gas emissions at different temperatures and identify the gas components of the FPCBs and raw PA (see Figures 2c and d). In both cases, similar absorption spectra were observed. These spectra can be divided into several segments, attributed to the chemical bonds of several functional groups. Peaks between 3700 to 3300 cm ^-1 can be attributed to intermolecular single bonds of O and H molecules - which can be ascribed as the functional groups of O-H stretching. The peaks between 3200 and 2600 crrr ¹ indicate the presence of stretching vibrations of intense, moderate and weak bonds of C-H which can be attributed to the alkane group. In the peak range from 2600 to 2000 cm ^-1 , a strong peak was identified at 2357 cm ^-1 , which can be attributed to the asymmetric bond of O=C=O. A number of minor peaks were observed between 2000 cm ^-1 and 750 cm ^-1 , due to the stretching of C=C and C-H bending vibrations. The major peak observed at 1760 cm ^-1 resulted from the stretching vibration of C=O bonds. A number of minor peaks with a distinctive peak at 671 cm ^-1 were observed during the thermal process, which can be attributed to C-H bonds and the out-of-plane bending vibration of aromatic hydrocarbons. The overall process is associated with the ejection of aromatic hydrocarbons, and CO _X gases due to the evaporation of water vapour and the decomposition of epoxy and polyamide. Likewise, FTIR spectra showed that the decomposition of the polyamide started rapidly when the metal was embedded with polyamide (indicated by the red circle in Figures 2c and d for FPCB and raw PA respectively). This may be attributed to the catalytic effect of the metallic content of the FPCB, which likely promoted low-temperature carbonisation over a short time period.

[00118] As a result of the observed catalytic effect, the optimum conditions in which to generate char and copper from waste FPCBs without melting the copper were found to be 700 °C for 30 minutes in a nitrogen atmosphere. This represents a substantial decrease in the energy input for Cu recovery compared to current industrial smelting processes from waste sources, which require temperatures in the order of 1250 °C. It is therefore clear that using waste FPCBs instead of raw polyamide plastic to generate activated carbon is more cost- effective because of the ability to employ lower carbonisation temperatures and shorter reaction times.

[00119] The quality of the surface of the recovered Cu was characterised using XPS and XRD analysis, and the composition of the recycled metals was measured by ICP-OES analysis. The results of the ICP-OES analysis are presented below in Table 1. The purity of the recycled Cu was -99.6% with some minor trace elements. These trace elements may have existed in the basic composition of the metal, or alternatively may be derived from the polymers or interfaces between the polymers and metals.

Table 1 : ICP elemental composition of the recovered metals in weight percentage after heating of the FPCBs

[00120] The phase characterisation of the Cu was investigated by XRD analysis, showing pure peaks of FCC Cu at 43.1 °, 50.3°, 73.9°, 89.7°, and 94.1 ° (see Figure 3a). X-ray diffraction patterns show clear copper peaks with no trace elements. The patterns indicate 100% pure copper because the trace elements in this sample were less than 1 % (which was beyond determination by the XRD pattern).

[00121] Figure 3b shows the XPS spectra of the major components detected on the surface of the recycled Cu. The Cu 2p3 (Figure 3) spectrum had two significant peaks at 932.66 eV and 934.74 eV with no evidence of satellite peaks from oxides. The large amount of carbonaceous materials resulted from degradation of the polyamide. This residual carbon protected the Cu from oxidation by constraining the approach of oxygen towards Cu due to the oxygen molecules being trapped on the residual carbon. The XPS spectra obtained are summarised in Table 2.

Table 2: Elemental compositions on the metallic surfaces of recycled Cu

[00122] Activated carbon was prepared from the char by heating at a temperature of 800°C in a CO2 atmosphere for 1 hour. The weight loss was observed as less than 10% for this activation temperature. When thermal activation was carried out, partial gasification of the char took place in the CO2 atmosphere. During this process, disorganised carbons are removed first, with a subsequent increase in pore volume. This ongoing process exposes the elementary crystallites to the activating agent (CO2) which creates greater porosity and enlarges the pore size and generates more off gas. The average recovery of the activated carbon per gram was 0.13 gm, which equates to 130 gm/kg. This was calculated by the weight of the FPCBs used as raw material and the activated carbon derived therefrom.

[00123] Raman spectroscopy was collected for wavenumbers in the range of 1000-1800 cm ^-1 and the results are shown in Figure 4a. Two distinct peaks were evident for all carbon samples: a D-band peak at -1340 cm ^-1 , and a G-band peak at -1590 cm ^-1 . The D-band peak can be attributed to the degree of defects in the carbon structure, and the G-band peak can be attributed to E2g vibrations and sp2 hybridised carbon. The comparative intensities of D and G bands (ID/IG) can provide information about material defects and graphitisation, where an intense D-band peak specifies more disordered carbon atoms. As shown in Figure 4a, there are dissimilarities in the Raman spectra of the raw PA and FPCB samples. The ratio (ID/IG) was calculated to be 0.84 before activation, and 1.08 after activation of the polyamidederived carbon. Generally, porous carbon structures have a greater ID/IG ratio than non-porous structures due to the higher degree of disorientation in the carbon structure. A Gaussian function was used to perform curve fitting for the spectra to determine full width at half maximum value (FWHM) values of the G band. In the case of the activated carbon, the FWHM value was calculated to be 88 cm ^-1 , which is significantly higher than the value for graphitic carbon. The FWHM value for the G band of pyrolytic graphitic carbon is from 15 to 23 cm ^-1 . This indicates that the activated carbon has a highly disordered atomic structure which could be the consequence of the high specific surface area. The specific surface area of the carbon samples was measured by BET analysis as shown in Figures 4b and 4c, and in Table 3. Table 3: BET surface area, pore volume and pore diameter of the polyamide-derived carbon with and without activation

[00124] A high specific surface area can enhance the performance of electrode materials in electrostatic double-layer capacitors. The volume and size distribution of pores in the electrode material is also important for performance. The polyamide-derived activated carbon samples were characterised by BET analysis in order to identify the pore size, volume and specific surface area of the activated carbon. The pore size distribution and the corresponding isotherms demonstrated an abrupt rise in N2 absorption for the activated, polyamide-derived carbon. This can be ascribed to the higher level of microporosity, as shown in Figure 4b. The large volume of micropores can increase the specific surface area significantly, which can provide more sites for charge storage. In contrast, mesopores have a larger diameter, which is favourable for infiltration of electrolytes and ion transportation at low resistance. Micropores are mainly created by the removal of disordered carbon, while mesopores are created by the reaction and phase separation between carbon and CO2. The specific surface area of the activated carbon was measured as 975 m ² /g by BET analysis (Table 3). The porosity of the polyamide-derived activated carbon was observed though N ₂ uptake at 77 K, which indicates a wide range for the pore distribution. The pore volume distribution indicated that micropores made up -60% of the sample’s porosity, and the proportion of mesopores was -40% (Figure 4c). Interconnected meso-microporous carbon with a high specific surface area has favourable characteristic for electrode materials.

[00125] The textural characteristics of the activated carbon materials are listed in Table 3. From Table 3 it can be seen that the surface area of the polyamide-derived activated carbon had a maximum value of 975 m ² g ^-1 , with an average pore size of 2.0 nm. Thermal transformation at 700 °C converts the FPCBs into a stable and heat-resistant compound that comprises mainly carbon. The primary off-gas contains mainly oxygen and hydrogen, leaving a carbonaceous-solid skeleton with a low surface area. Thermal activation at 800 ⁰ C in a CO2 atmosphere promotes the reaction of CO2 with carbon via the reaction C + CO2 2CO. This reaction causes the gasification of carbon and creates pores in the surface. Continuous CO2 supply drills through the carbon skeleton which deepens, clears out and volatilises impurities. This gasification process develops porosity by eliminating carbon atoms from the solid framework, while active carbon is produced. Through this gasification process, numerous types of carbon can be produced by varying the treatment time and temperature to give the end-product a range of adsorption capacities. The optimum activation temperature and time were determined to be 800 °C for 1 hour.

[00126] The surface chemical composition of the polyamide-derived activated carbon was determined by XPS analysis and the observed characteristics are presented in Figures 4 d, e and f. Along with C, the major elements detected were O, N, Si, and Cu. The Cu metal came from the metallic part of the FPCB sample. The Cu spectra show the association of several components of pure copper and CuO (Table 4). The evaluation of the spectra for the N and C components is difficult, owing to several bonding combinations present between the components, which increased with the association of the O functional group. Pyridinic N is bonded to two carbon atoms, while the graphitic N is bonded to three carbon atoms. The peak at 398.1 eV has been identified as the C=N-C bond for Pyridinic N. The peak for the N1s spectra in the region between 399 and 400 eV could be attributed to the nitrile group and could be associated with the triple-bond to a single carbon atom (identified as an N-C=N bond). The energy peak at 402.3 eV could partially originate from graphitic N and is labelled as N-(C)3. Polyamide is very rich in nitrogen, which remains after the activation process. However, the activated carbon could be less rich in nitrogen compared to the original composition because nitrogen could be one sacrificial element in the initial 700 °C heating process, forming nitriles and escaping the carbon structure.

Table 4: Elemental compositions of the activated carbon by XPS survey scan

[00127] The XPS spectrum for the carbon molecules is associated with four different energy peaks for C1s at around 284.8, 286.26, 287.8 and 289.22 eV. The highest emission at 284.8 eV is for sp2 carbon (C=C). The peak at 286.5 eV could have arisen due to hydroxyl (C-O) and/or N-(C)s bonds. The peak at 287.8 eV is from the carboxyl (C=O) and/or C=N-C bonds, and the peak at 288.41 eV is from the carboxyl (O-C=O) bonded carbon or the sp2-hybridized carbon in the aromatic ring (N-C=N). These results confirmed the in-situ nitrogen doping. The detected O (~12 at%) is associated with thermally-stable groups and caused mainly by absorption in the carbon material during the thermal process. The energy peak of O1s can be deconvoluted into three peaks at 530.97 eV, 532.36 eV and 533.84 eV, and are ascribed to hydroxyl (C-O) and carboxyl (C=O). Carbon-containing oxygen functional groups can enhance supercapacitor performance by increasing the specific capacitance of the surface. This can promote pseudocapacitance, which is favourable for energy storage and can also improve pore access by increasing the wettability of the carbon electrode. The C, N, H, and S compounds in the activated carbon were also investigated by XRF analysis, which is presented in Table 5. The XRF analysis also shows a significant amount of N and O content in the activated carbon. A slight amount of S content was also detected. The synthetic resin which may be used as a glue could contain S. Also, the solder mask could contain S which comes from the fire-retardant elements.

Table 5: C, N, H, O and S analysis of the poly-amide derived carbon samples by XRF

[00128] To observe the surface morphology, SEM and TEM analysis were performed on the surface of the carbon materials. The results are shown in Figure 5. Figure 5a and b show SEM images of the polyamide-derived carbon before and after activation. It is noted that both before and after activation, the samples have regular spherical particles. However, before activation, agglomeration was observed (Figure 5a). As shown in Figure 5b, the activated carbon particles have defects on their surface, less spherical morphology, but are well dispersed. When the surface tension decreases with thermal activation due to decreased cohesive forces, the increase in molecular thermal activity may decrease the cross-linking density between adjoining carbon particles. This could result in well-dispersed carbon spheres. An etching effect was also observed in the carbon particles due to the reaction of surface carbon with CO2. This reaction created defects on the carbon surface. This kind of defect is beneficial for energy storage applications. The clear pore structure is evident in the HR-TEM image in Figures 5c and d. This image demonstrates a mainly microporous structure, which can provide a greater interface for energy conversion which leads to a high specific capacitance. The elementary mapping images detected evenly distributed traces of nitrogen (Figure 5h) and oxygen (Figure 5g).

Example 2 - Electrochemistry of the activated carbon

Electrochemical measurements

[00129] The FPCB-derived activated carbon’s performance was evaluated using a standardised three-electrode system. The film for the supercapacitor was produced by dropcasting 10 pL of conductive ink on a platinum electrode. The platinum electrode had an inner and outer diameter of 3 mm and 6 mm respectively. Prior to drop-casting, the platinum electrode was polished and cleaned with soapy water, deionised water and acetone. T o make the conductive ink, 5 ± 0.5 mg of active materials were added to 150 pL of deionised water. The binder used in this solution was 15 pl of Nation. After preparation of the suspension, the tube containing the suspension was sealed. The tube was then sonicated for 30 minutes and stirred for 12 hours.

[00130] The reference electrode was a saturated calomel (Hg ₂ Cl2) along with a counter electrode made of platinum wire. The working electrode in the three-electrode system contained the synthesised activated carbon. The electrolyte used in the system was 0.5 mole of KOH in an aqueous solution. Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) were performed at room temperature utilising an electrochemical workstation (Biologic VSP-300). The potential range was chosen to be from -1 to +0.1 V at various scan rates, such as 5, 10, 50,100, 150 mV.S’ ¹ . For the GCD analysis, the current density was chosen at 1 , 3, 6, 10, 15 A. g- ¹ , respectively. Supercapacitance performance was measured with both CV and GCD analysis. The specific capacitance was measured using the following equation:

I dV

Csp = f &VxVxM (1)

The galvanostatic capacitance was evaluated using the following equation:

I x At

Csp =

AV xM (2)

[00131] Csp denotes the specific capacitance in F.g ^-1 , I (A) is the current read by the equipment, AV is the voltage difference for the potential window of the scan in mV.s ^-1 , and M is the mass in grams of activated carbon deposited on the electrode. Electrochemical results and analysis

[00132] The cyclic voltammetry (CV) curves for the activated carbon electrode (Figure 6a), show similar, almost rectangular-shaped profiles at all scan rates from 5 to 150 mV s’ ¹ . This indicates that there is fast-ion transportation inside the porous structure of the carbon which could be made possible by the meso- and micropores present in the carbon surfaces. It is evident that at a particular scan rate, the activated carbon displays superior current densities and charge storage capacity compared to non-activated carbon over a range of scan rates. The capacitance value decreased with an increased scan rate. For example, the capacitance value dropped by 80 F.g ^_1 (from 244 F.g ^_1 to 164 Fg ^_1 ) when the scan rate was increased from 5 mV.s’ ¹ to 150 mV.s’ ¹ . This can be explained by the fact that, when scan rates are lower, ions from the electrolyte have more time to be stored within the pores of the activated carbon. However, for faster scan rates, the ions have less time for infiltration and are therefore aggregated on the outer surface of the electrode. As a result, higher scan rates give a lower capacitance value. The superior capacitance of the sample is associated with its higher specific surface area of 975 m ² .g' ¹ . As a result of a large number of pore sites, the activated carbon has more ion-accessible trap sites, hence enabling more energy storage capacity via faster transportation of electrolytes and diffusion of ions.

[00133] Figure 6b shows the galvanostatic charge-discharge (GCD) curves of the sample at several current densities. The discharge counterparts follow triangular charging-discharging attributes due to quick-charge transmission, along with an ohmic drop in the conductive ink. The charge-discharge curves show an approximately symmetrical pattern, attributed to a very good capacitance of EDLC capacitance and a small amount of pseudo-capacitance. As calculated from the GCD curves, the activated carbon had a specific capacitance of 250 F g ^-1 at 1 A g' ¹ and displayed a specific capacitance of 148.6 F g ^-1 even at 15 A g- ¹ , which indicates a reasonable energy storage capacity at high current density. The lower capacitance at higher current densities can be attributed to inadequate ion diffusion of the electrolytes into the carbon’s pores. This was because the activated carbon had -60% micropores, making it difficult for the ions to be stored on these sites at higher current densities. This phenomenon reduces the stored ions into the interface of the electrode which further reduces specific capacitance. The effect of heteroatom implantation and a meso-microporous structure could maintain a higher specific capacitance. The surface functionalities and incorporation of N and O hetero atoms in the activated carbon (which were confirmed by XPS analysis) might correspondingly be responsible for the high pseudocapacitance.

[00134] The enduring cyclic stability is an important characteristic of electrode materials for energy storage applications. Figure 6(c) illustrates the cyclic stability of the activated carbon samples at 1 Ag ^-1 current density in 0.5 M KOH, through charge-discharge attributes. The carbon electrode demonstrated acceptable retention after 2000 cycles of charge-discharge by maintaining -97% of the initial specific capacitance, suggesting that the fabricated electrode had good cycle stability, which could lead to longer operational life. A slight deterioration in capacitance over cycles could arise because of the mechanically expanded conductive ink, through the dissolution of carbon in the aqueous electrolyte and ion-penetration process. After 10,000 cycles the stability of the electrode was -87%. The capacitance value decays with increasing scan rates. When the scan rate is low, the electrolyte ions get enough time to penetrate the pores of the carbons. In contrast, when we increase the scan rate the electrolytes accumulate only on the surface of the carbon. The potential window of the GCD mainly depends on the scan rate. Normally for activated carbon the potential window will be sharp on the tip and the GCD cycles will be shorter compared to the other kinds of materials used in supercapacitors, such as oxide materials. In ideal conditions, the capacitive performance decays rapidly in the case of activated carbons.

[00135] Electrochemical impedance spectroscopy (EIS) is important in the analysis of electrochemical kinetics. Figure 7 shows EIS Nyquist and bode impedance plots. Reference to Figure 7a shows that the Nyquist plot exhibited a vertical line characteristic at the middle and lower end, and partial semicircular characteristics at the higher frequencies. This phenomenon could be described as the resistive behaviour for transferring charge by the activated carbon at higher frequencies. As no conductive carbon was used to measure the performance of the activated carbon derived from the FPCBs, this kind of charge resistivity occurred due to the presence of functional groups in the activated carbon, such as N and O. A diagonal line in a -45° angle is detected at the middle range of the frequency. This occurred at the interface of electrode and electrolyte due to where the effect of ion diffusion is visible. This kind of phenomenon is ascribed as the Warburg impedance. The double-layer charge storage is dominating in this system which is ascribed by the straight line at the lower frequencies. Therefore, activated carbon derived from FPCBs demonstrates good conductivity, despite the fact that no conductive carbon was used during preparation of the electrode.

[00136] A bode plot was also considered to observe the frequency response of the system (see Figure 7b). When the frequency is more than 1 Hz, a constant impedance is observed. At this stage, the impedance was at its minimum level. As the frequency range went below 1 Hz, the impedance level increased gradually by a concurrent rise in the phase shift, suggesting the growth of the charge accumulation on the carbon surface. At frequencies lower than 0.01 Hz, a -70° phase angle was achieved which becomes approximately constant. This indicates that a predominant capacitive behaviour instead of series resistance is present at this frequency range. The rise in the impedance higher than the frequency of 0.01 Hz is indicative of the developed resistance of the diffusion layer on the surface of the activated carbon.

[00137] The meso- and micropores and heteroatom induced carbon result in a high specific surface area which is a favourable quality for materials used in supercapacitor applications. Two dominant charge-storage mechanisms are present: EDLC and pseudocapacitance. These two mechanisms work concurrently and are reliant on the material, specific surface area, morphology and the voltage applied to the electrodes. The conductivity of the fabricated carbon was improved by the in situ doping of the activated carbon with hetero N and O atoms. The N and O functional groups enhanced the wettability of the porous, activated-carbon surface by the electrolyte. N- and O-doping can also promote extra pseudocapacitance effects due to the Faradaic redox reactions in the active sites.

[00138] Table 6 below compares activated carbon materials obtained from other carbon sources with the activated carbon prepared in accordance with the present disclosure. The commercial Nomex aramid fiber derived activated carbon via chemical and CO2 activation shows a specific capacitance of 175 F g- ¹ , and chemically modified graphene shows 135 F g- ¹ . Even after pre-impregnation by a pore-forming agent, banana fibers and pistachio nutshell derived activated carbon show capacitance values of 74 and 45 F g ^_1 respectively. The high surface area activated carbon produced from electronic waste and waste compact discs demonstrates a specific capacitance of 52 F g ^_1 at a scan rate of 10 mV s' ¹ . Activated carbon produced from waste FPCBs shows extraordinary specific capacitance (244 F g ^_1 at a scan rate of 5 mV s-1), which is promising as an electrode material for application in supercapacitors.

Table 6: Performance comparison of the activated carbon derived from waste FPCBs and other sources.

[00139] The process of the present disclosure offers many advantages. For example, the process allows recycling of waste FPCBs "as is", without any pre-treatment or pre-processing. This permits fewer process steps thereby increasing efficiency and lowering cost.

[00140] The metal component of the FPCBs catalyses conversion of the non-metallic component of the FPCBs (for example polyamide) to char which permits carbonisation to occur at a lower temperature and faster rate, thereby further increasing the economic feasibility of the process. The process also allows recovery of carbon and highly pure metal simultaneously.

[00141] Typically, resource recovery from printed circuit boards is limited to metallic components, the non-metallic components being disposed of as slag or residue. The present process allows recovery of metallic and non-metallic components of FPCBs simultaneously.

[00142] N- and O- doped activated carbon may be prepared from carbonised FPCBs using only carbon dioxide as an activating agent. Other activating agents, such as hydroxide, H3PO4, ZnCl2 and the like, and any other compounds for achieving N- and O- doping are not required. Carbon dioxide activation alone is beneficial because it does not deplete nitrogen content. Alternative methods employ expensive activating agents that reduce the natural nitrogen content of the carbon precursors and also require washing to maintain the pH balance. This results in the generation of wastewater.

[00143] Activated carbon produced in accordance with the disclosure exhibits excellent electrochemical performance and shows promise as a highly effective electrode material in supercapacitor applications.

[00144] Those skilled in the art will appreciate that the disclosure described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the disclosure includes all such variations and modifications. The disclosure also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of an two or more of said steps, features, compositions and compounds.