Defect-engineered Cu2O/CoxO heterostructures with built-in electric fields for high-current-density alkaline water splitting

Abstract

Developing cost-effective, high-performance electrocatalysts for the oxygen evolution reaction (OER) is critical to advancing alkaline water electrolysis and renewable hydrogen production. Here, we report a heterostructured Cu₂O/Co_xO catalyst grown on nickel foam (Cu₂O/Co_xO@NF), constructed via phytic acid etching and NaBH₄-mediated reduction, which optimizes structural, electronic, and interfacial properties. The catalyst exhibits a high specific surface area of 91.76 m² g⁻¹, abundant Cu-derived defect sites, and a built-in electric field (BIEF) from the Cu₂O–Co_xO work function difference (ΔΦ = 0.13 eV). These features enhance charge separation, *OH adsorption, and the formation of active CoOOH/CuOOH phases. Cu₂O/Co_xO@NF achieves exceptionally low overpotentials of 194, 298, and 333 mV at 10, 100, and 200 mA cm⁻², outperforming Co_xO@NF, Cu₂O@NF, and commercial RuO₂. It further delivers the highest double-layer capacitance (C_dl = 296.2 mF cm⁻²), the lowest charge-transfer resistance, and early onset of CoOOH formation (1.40 V vs. RHE). In situ FTIR identifies a strong *OOH signal at ∼1130 cm⁻¹, confirming accelerated OER kinetics. During long-term testing, the catalyst maintains stable operation for 450 h at 100 mA cm⁻². In a two-electrode electrolyzer, Cu₂O/Co_xO@NF⁽⁺⁾‖Pt/C@NF⁽⁻⁾ requires only 1.77, 1.86, 1.94, and 2.01 V to reach 100–400 mA cm⁻², surpassing RuO₂@NF benchmarks. The catalyst also demonstrates a high faradaic efficiency of 98.57% and exceptional operational durability over 560 h. Finally, water splitting driven by a solar cell and a wind-powered battery demonstrates practical applicability for decentralized hydrogen production.