CuFe Bimetallic Electrocatalyst for Low-Voltage Formaldehyde-Assisted Dual Hydrogen Production

Abstract An effective strategy to lower the operating voltage and system cost of water electrolysis for green hydrogen production is to couple the hydrogen evolution reaction with a kinetically facile oxidation reaction instead of the oxygen evolution reaction. Formaldehyde oxidation reaction (FOR) is ideal for this, as it generates hydrogen molecules at the anode. In this work, boron and phosphorus are included in a copper–iron oxide-based bimetallic electrocatalyst supported on copper foam (CuFeOPB), which is developed for efficient FOR in alkaline media. The optimized CuFeOPB catalyst delivers a small FOR potential of 0.147 V at 100 mA/cm2 and exhibits excellent durability over extended operation (150 h). Structural and surface analyses reveal that iron incorporation increases the surface concentration of Cu2+ species. The coexistence of Cu2+ with Cu+ species enables synergistic enhancement of rate-limiting steps during FOR. When coupled with a selective nickel phosphoboride cathode (NiPB), the system requires a cell voltage of 0.436 V to achieve 100 mA/cm2 with an overall Faradaic efficiency of 175%. The energy consumption for hydrogen production is only 0.52 kWh/m3 of H2, which is approximately eight times lower than that of conventional alkaline water electrolysis. Product analysis confirms the formation of value-added formate with a conversion efficiency of 92%. Furthermore, a membrane-free electrolyzer configuration with a zero-gap assembly needs a cell potential of 0.352 V at 100 mA/cm2. This study demonstrates that FOR-assisted electrolysis using non-noble electrocatalysts provides a promising pathway for low-energy and cost-effective green hydrogen production.