Charge Transfer in n-FeO and p-α-Fe₂O₃ Nanoparticles for Efficient Hydrogen and Oxygen Evolution Reaction

This study aims to explore the n-FeO and p-α-Fe₂O₃ semiconductor nanoparticles in hydrogen (HER) and oxygen (OER) evolution reactions and a combined full cell electrocatalyst system to electrolyze the water. We have observed a distinct electrocatalytic performance for both HER and OER by tuning the interplay between iron oxidation states Fe²⁺ and Fe³⁺ and utilizing phase-transformed iron oxide nanoparticles (NPs). The Fe²⁺ rich n-FeO NPs exhibited superior HER performance compared to p-α-Fe₂O₃ and Fe(OH)_x NPs, which is attributed to the enhancement in n-type semiconducting nature under HER potential, facilitating the electron transfer for the reduction in H⁺ ions. In contrast, p-α-Fe₂O₃ NPs demonstrated excellent OER activity. An H-cell constructed using n-FeO||p-α-Fe₂O₃ NPs as cathode and anode achieved a cell voltage of 1.87 V at a current density of 50 mA/cm². The cell exhibited remarkable stability after 30 h of activation and maintained the high current density of 100 mA/cm² for 80 h with a negligible increase in cell voltage. This work highlights the semiconducting properties of n-FeO and p-α-Fe₂O₃ for the electrochemical water splitting system using the band bending phenomenon under the applied potential.