Spent coffee grounds derived P, N co-doped C as electrocatalyst for supercapacitor applications

• PNDCs have been synthesized by a novel microwave-assisted method.
• PNDC-3 exhibits a high surface area of 999.64 m2 g−1.
• PNDCs exhibit micropores, mesopores and macropores with high pore volume.
• PNDC-3 exhibited a capacitance value as high as 286 F g−1 in 1 M H2SO4.
• PNDC-2 was discovered to be electrochemically stable over continuous 2000 cycles.

Spent coffee grounds, an abundant daily waste, were utilized to produce P, N co-doped C (PNDC) by a novel microwave-assisted method employing ammonium polyphosphate as the only other reactant. Different PNDCs (namely PNDC-1, PNDC-2 and PNDC-3) were synthesized by varying the ratio of spent coffee grounds to ammonium polyphosphate. The synthesized materials were found to contain spherically shaped particles as evidenced from scanning electron microscopy. X-ray photoelectron spectroscopy revealed PNDCs to contain P and N in addition to C and O. PNDC-3 was discovered to possess a surface area of 999.64 m2 g−1 with the presence of micropores, mesopores and macropores. PNDCs exhibited high specific capacitance values in acid and alkaline conditions with PNDC-3 exhibiting the highest specific capacitance value of 286 F g−1 in 1 M H2SO4. Also, PNDC-2 was observed to be highly stable under acidic and alkaline conditions with continuous cycling.

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