Microcrystalline cellulose-derived porous carbons with defective sites for electrochemical applications

Abstract

An approach for producing defect-containing porous carbon from microcrystalline cellulose is proposed. A sample with intrinsic defects and a low level of nitrogen doping prepared at a carbonisation temperature of 600 °C followed by thermal treatment in a reducing environment exhibited excellent performance both as a supercapacitor electrode and oxygen reduction reaction (ORR) electrocatalyst. With 1 M H₂SO₄ aqueous electrolyte, it delivered a specific capacitance of 426 F g⁻¹ at a current density of 0.25 A g⁻¹ or 177 F g⁻¹ at 100 A g⁻¹ measured using a three-electrode system. About 90% of its original capacitance was retained after 60 000 cycles at 5 A g⁻¹ measured in a symmetric supercapacitor cell. In addition, the electrode with a mass loading of 12 mg cm⁻² exhibited areal capacitances of 2518 and 1128 mF cm⁻² at current densities of 0.5 and 50 mA cm⁻², respectively, along with a good cycling stability. Three-electrode system electrochemical analysis reveals that the porous structure and low amount of N/O doping of the sample were more fully and efficiently utilised for charge storage via electrical double-layer and pseudocapacitive mechanisms, respectively, as the presence of intrinsic defects further changed its electronic structure. A symmetric supercapacitor assembled with this carbon electrode in 1 M LiCl electrolyte exhibited an energy density of 20.7 W h kg⁻¹ at a power density of 426 W kg⁻¹. This sample also demonstrated good performance in the ORR due to the presence of intrinsic defects, which promoted electron transfer. It was observed that increasing the thermal treatment temperature is favourable for further improving the ORR activity.