Carbon nanosheet-supported CrN nanoparticles as efficient and robust oxygen reduction electrocatalysts in acidic media and seawater Zn-air batteries

Exploring non-precious oxygen reduction reaction (ORR) catalysts is essential to fuel cells and seawater metal-air batteries. Transition metal nitrides are promising ORR catalysts with high corrosion resistance but fail to render satisfactory ORR performance. Herein, we introduce a novel method for the synthesis of carbon nanosheet-supported transition metal nitrides. Using dicyandiamine (DCDA) as the nitrogen and carbon source, we prepared carbon nanosheet-supported CrN nanoparticles (CrN/CNS) via a two-step pyrolysis method. The optimal CrN/CNS material has an ORR half-wave potential (E1/2) of 0.76 V vs. reversible hydrogen electrode (RHE) in acidic media and 0.50 V vs. RHE in simulated seawater, which is one of the best among those reported for transition metal nitrides. Furthermore, the optimal material has remarkable ORR stability in both acidic media and simulated seawater. Its ORR E1/2 shows 27 mV decay in acidic media and 20 mV increase in simulated seawater after stability tests, outperforming a commercial Pt/C catalyst and many transition metal nitrides. More importantly, the optimal CrN/CNS material-based seawater Zn-air batteries (ZABs) exhibit good stability within 200 h constant discharging. It is found that both the proportion of the Cr-N valence state and the Cr content in surfaces played a key role in the ORR activity of CrN/CNS materials. Carbon nanosheet-supported CrN nanoparticles render excellent ORR activity in acidic media and long-term stability in natural seawater Zn-air batteries.