Green synthesis of N, P-co doped porous reduced graphene oxide as an active metal-free electrocatalyst toward oxygen reduction reaction

Abstract

Developing high-efficient and price-friendly novel cathode catalysts to substitute commercial Pt/C catalyst is extremely vital for the future of fuel cells system, because the oxygen reduction reaction (ORR) is the cornerstone of diverse sustainable energy-conversion technologies. Metal-free heteroatom-doped carbons as ORR catalysts have attracted worldwide attentions. Herein, low-cost and easily available inorganic fertilizers are utilized as heteroatom precursors, successfully fabricating the N, P-co doped porous reduced graphene oxide (NP-PrGO) with the help of ascorbic acid, and the ORR performance of NP-PrGO samples at diverse pyrolysis temperatures are further studied in detail. The physical characterizations illustrate that all products exhibit loose and porous three-dimensional structures, large surface area, abundant defects and excellent electrocatalytic activity. Particularly, the optimal NP-PrGO-1100 (the pyrolysis temperature is 1100 °C) displays a great positive ORR onset potential (0.913 V vs. RHE) and half-wave potential (0.819 V vs. RHE), as well as a large current density at 0.2 V (vs. RHE, −5.48 mA cm−2). Furthermore, it also shows superb methanol tolerance and extraordinary electrochemical stability, which is better than that of Pt/C. The origin of enhanced ORR performance for NP-PrGO-1100 can be attributed to its porous structure, large surface area (202.02 m2 g−1) and highest amount of active N species (pyridinic N and graphitic N, 82%). These glorious properties make the NP-PrGO-1100 a promising metal-free ORR catalyst for replacing Pt/C in fuel cells.