A spinel based high entropy oxide (Co, Fe, Mn, Ni, Li)3O4 and reduced graphene oxide composite anode for seawater electrolysis

Abstract

Electrolysis of seawater by renewable energy has emerged as a promising alternative for production of green hydrogen. However, the presence of multiple ions in seawater and the competing chlorine evolution reaction at the anode pose a major challenge. Herein, we report a novel electrocatalyst based on composite of spinel high entropy oxide (S-HEO), (Co, Fe, Mn, Ni, Li)₃O₄ and reduced graphene oxide (rGO), synthesized by facile one-step solvothermal technique towards selective oxygen evolution reaction (OER) at the anode. To alleviate the problem of corrosion of metal supports in seawater, carbon paper is used as a catalyst support. The composite exhibited a low overpotential of 346.28 mV at 10 mA cm⁻² and a low overall seawater splitting voltage of 1.85 V at a current density of 10 mA cm⁻² with a remarkable stability of 100 hours in alkaline seawater. Further, the composite exhibits a high turnover frequency (TOF) of 0.66 s⁻¹. The presence of multiple cations in S-HEO offers abundant catalytic sites and high intrinsic activity. In addition to selectivity towards OER, the electrocatalyst exhibits corrosion resistance and suppresses hypochlorite formation. Post-stability investigations reveal the synergistic catalytic effects arising from multiple cations in S-HEO, contributing to optimal performance of the composite. This work demonstrates the potential of high entropy oxides towards seawater electrolysis.