Synergistic coupling of a CuNi alloy with a CoFe LDH heterostructure on nickel foam toward high-efficiency overall water splitting†

Abstract

Accelerating the kinetics of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is vital for high-efficiency green hydrogen production. However, developing cost-effective and highly active bifunctional catalysts for overall water splitting electrolysis remains a huge challenge. Herein, the CuNi/CoFe LDH heterostructure is synthesized in situ on nickel foam (CuNi/CoFe LDH@NF) by a simple two-step electrodeposition process. The synergy of the CuNi alloy and CoFe LDH optimizes the electron distribution at the interface and improves the intrinsic activity of the HER/OER. Consequently, the optimal CuNi/CoFe LDH@NF bifunctional catalyst displays low overpotentials of 56 mV (10 mA cm⁻²) and 268 mV (50 mA cm⁻²) for the HER and OER, respectively, along with high stability in alkaline electrolyte. Remarkably, CuNi/CoFe LDH@NF as the cathode and anode requires a low voltage (1.49 V) to achieve 10 mA cm⁻² for overall water splitting. Meanwhile, it also displays favorable stability for operation for 17 h (50 mA cm⁻²) without obvious decline of the cell voltage. Density functional theory calculations indicate that constructing heterojunction interfaces promotes the redistribution of interface electrons and optimizes the free energy of adsorbed intermediates, thereby reducing the energy barrier of the rate-determining step (from *O to *OOH).