Fe-NiO/MoO2 and in-situ reconstructed Fe, Mo-NiOOH with enhanced negatively charges of oxygen atoms on the surface for salinity tolerance seawater splitting

Abstract

Seawater electrolysis is a promising technique for H₂ production on a large scale. However, the electrocatalytic activity and stability will be deteriorated as the increase of salt concentrations which happened in the seawater splitting. Herein, through the electrodeposition and rapid Joule heating method, the Fe-NiO/MoO₂ heterostructure is designed as a highly active bifunctional electrocatalyst. During the OER possess, Fe-NiO/MoO₂ is reconstructed to the Fe, Mo-NiOOH with Fe and Mo co-doping. Based on the theoretical analysis, more electrons were transferred to the O atoms on the surface of Fe, Mo-NiOOH, thereby forming a more negatively charged surface. Moreover, that surface is found to repel Cl⁻ ions while enriching H₂O molecules to form a thin water layer on Fe, Mo-NiOOH surface based on molecule dynamics (MD) simulation, thereby improving the anti-corrosion capacity of Fe, Mo-NiOOH. The reconstructed Fe, Mo-NiOOH achieved an overpotential of 399 mV at 1000 mA cm⁻² in alkaline seawater, and the increase of overpotential for Fe, Mo-NiOOH was about 0.02 V at 500 mA cm⁻² from 0 M to 3 M NaCl in 1 M KOH electrolyte. For the HER, Fe-NiO/MoO₂ achieved an overpotential of 169 mV and 417 mV at 100 and 1000 mA cm⁻² in alkaline seawater, respectively, and the increase of overpotential for Fe-NiO/MoO₂ was about 0 mV at 500 mA cm⁻² from 0 M to 3 M NaCl in 1 M KOH electrolyte. This work sheds fresh light into the development of efficient electrocatalysts for salinity tolerance seawater splitting.