A Hybrid Hydrogel Approach for the Design of N, S Dual-Doped Porous Carbon Electrocatalyst for Oxygen Reduction Reaction

Heteroatom-doped porous carbon materials have been largely explored as low-cost, metal-free alternatives to commercial Pt/C electrocatalysts for the oxygen reduction reaction (ORR): a key process in energy conversion and storage devices such as fuel cells and metal–air batteries. Here, we report the synthesis of a hybrid hydrogel, comprising pyrrole and thiophene monomers as a versatile precursor for the design of a N, S dual-doped porous carbon catalyst for the ORR. The unique composition and morphology of the precursor facilitate the design of a catalyst with enhanced catalytic activity and higher mass transport. The catalyst (CNS-900) with optimum N and S content demonstrates superior ORR activity in 0.1 M KOH with an onset (Eon) and a half-wave (E1/2) potential of 0.946 and 0.801 V vs reversible hydrogen electrode (RHE), respectively, close to that of Pt/C. The catalyst also demonstrates excellent short-term stability test retaining 87% of its original current in 25 h in addition to showing superior stability during the potential cycling experiment. Furthermore, the catalyst also exhibits good selectivity toward the 4e– ORR with an electron transfer number close to 4.00 and a H2O2 yield below 9.5% in the potential range 0.4–0.9 V vs RHE. This work provides a facile design approach to synthesize heteroatom-doped porous carbon catalysts using organic polymers in contrast to conventional graphene-based precursors for electrochemical applications.