Interfacial Fe–Mo electronic coupling in FeMoO4/carbon hybrids for efficient and durable alkaline overall water splitting

Abstract

Biomass-derived materials have emerged as sustainable and low-cost platforms for designing next-generation electrocatalysts owing to their natural abundance, tunable porosity, and carbon-rich frameworks. In this context, water splitting demands efficient electrocatalysts capable of driving both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, we develop a biomass-oriented hybrid electrocatalyst, FeMoO₄@Ds-AC, by anchoring FeMoO₄ particles with hierarchically porous activated carbon derived from date seed waste, thereby coupling catalytic activity with sustainable material design. The FeMoO₄Ds-AC catalyst improves the OER performance in an alkaline medium, achieving a low overpotential of 334 mV at 20 mA cm⁻² and a Tafel slope of 84 mV dec⁻¹. Subsequently, it shows an effective HER activity, with an overpotential of 75 mV at 10 mA cm⁻². The catalyst splits water with a cell voltage of 1.642 V at 10 mA cm⁻². FeMoO₄@Ds-AC has outstanding long-term durability exceeding 100 hours for both the HER and OER, with low performance degradation. The enhanced activity is attributed to the synergistic interaction between redox-active FeMoO₄ and the conductive, porous carbon matrix, which accelerates charge transfer and increases active-site accessibility. Furthermore, density functional theory (DFT) calculations are performed to gain deep insights into the interfacial coupling between FeMoO₄ and Ds-AC. The lowest interaction distance between FeMoO₄ and Ds-AC confirms the strong Fe–C and Mo–C covalent bonding and large negative binding energy (−4.61 eV), representing exothermic binding. In addition, the electronic structure analysis reveals that the strong orbital hybridization between the Mo-3d, Fe-3d and C-2p states further confirms the electronic coupling bonding between the interfacial materials. Finally, the charge density difference plots reveal that the electron density redistribution between the interfaces indicates strong Fe–C and Mo–C covalent bonding. Our DFT observations clearly demonstrate that Fe–C and Mo–C coupling enhances charge transfer and influences the OER performance. This paper describes a sustainable and effective technique for developing biomass-derived bifunctional electrocatalysts for water splitting applications.