Direct Synthesis of Earth-abundant Bifunctional Catalysts for Efficient Seawater Hydrogen Production

Practical seawater electrolysis requires bifunctional catalysts capable of driving both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) simultaneously, while also remaining resistant to chloride corrosion and free of scarce noble metals. Achieving this combination in a single earth-abundant electrode material remains a significant challenge. This thesis addresses that challenge through the design and electrochemical fabrication of a two-layer NiFe/NiFe-Cr₂O₃ architecture on nickel foam, where a Lewis acid Cr₂O₃ outer layer provides active chloride rejection and targeted molybdenum doping enhances intrinsic catalytic activity for both the HER and OER.Systematic screening across thirteen experiments revealed a threshold doping effect and, importantly, that confining Mo to the outer catalytic layer (110 mV HER overpotential at 10 mA/cm²) delivers performance comparable to dual-layer doping (105 mV) while substantially outperforming the inner-layer-only configuration (146 mV), these being best single-sample values from the placement study, and halving dopant consumption, demonstrating that Mo acts through a surface-active rather than bulk structural mechanism. The optimised catalyst achieves a reproducible HER overpotential of 116–122 mV and an OER overpotential of 277–282 mV improvement at 10 mA/cm², representing a 35% HER improvement over the undoped NiFe/NiFe-Cr₂O₃ catalyst and competitive performance against the industry standard platinum, which degrades substantially in chloride-rich media. Structural and compositional characterisation via SEM and XRD supports the proposed surface-active Mo promotion mechanism. Performance was confirmed across independent fabrication batches tested in 1M KOH (HER overpotential 116 to 122 mV; OER overpotential 277 to 282 mV).At a fraction of the cost of noble metal systems, this work demonstrates that a rationally designed, earth-abundant electrodeposition strategy can yield a genuinely bifunctional catalyst with performance relevant to practical seawater hydrogen production.