Chitosan-derived carbon sphere with self-activating behavior for stable oxygen reduction reaction in acid and alkaline media

Abstract

Utilizing shrimp waste-derived Chitosan as biomass source, we developed metal-free nitrogen and sulfur-doped porous carbon (NSPC) with a high specific surface area of 609.53 m2/g as a remarkable electrocatalyst for oxygen reduction reaction (ORR), surpassing benchmark Pt/C with half-wave (0.8574 V) and onset (0.9573 V) potentials in alkaline (0.1 M KOH) media. Besides high electrocatalytic activity, NSPC-800 showed excellent methanol tolerance ability and significantly low hydrogen peroxide yields (H2O2) of 5 % and 8 % in 0.1 M KOH and 0.5 M H2SO4, which is comparably lower than the previously reported chitosan based non-precious catalysts. Interestingly NSPC-800 displays robust stability in 0.1 M KOH electrolyte, improving the current retention rate from 89.17 % to 95.18 % over an increased operation period, evidencing its self-activating characteristics. This self-activating stability is also mirrored in 0.5 M H2SO4 where both fresh and recycled (after 5000 CV cyles) NSPC-800 catalysts retained more than half of their initial current. Additionally, to identify the nature of the active sites, the ORR measurements were correlated with ex-situ spectroscopy for post-stability of fresh and recycled NSPC-800 catalysts revealed dynamic reconfiguration of nitrogen, sulfur, and oxygen active sites evidenced compared to the pre-stability elemental surface, indicating an adaptive response of the catalyst to the harsh operating environment. In the future, our biomass-derived NSPC-800 will pave the way to develop cost-effective and highly efficient catalysts from waste to energy devices promising a twin-goal approach, contributing to the circular economy and sustainable development goals.