Silver Sulfide-Functionalized NiFe-Layered Double Hydroxide Heterostructure as a Bifunctional Catalyst in Anode-Favoring Electrolysis

Efficient hydrogen production with minimal overall cell potential (OCP) can be aided via a rapid alternate oxidation reaction at the anode of an electrolyzer. Here, we designed a hierarchical heterostructure of two-dimensional (2D) nickel–iron layered double hydroxide (NiFe-LDH) nanosheets and zero-dimensional (0D) silver sulfide (Ag2S) nanoparticles on nickel foam via a hydrothermal approach. X-ray diffraction detects the catalytically active oxyhydroxide (−OOH) sites with Ag2S loadings >10 wt %. The optimized 15 wt % Ag2S loaded NiFe-LDH/Ag2S (or NFSS15) exhibits a 2D/0D interface, enhancing charge transport and catalytic activity. NFSS15 demonstrates η10 (overpotential to reach 10 mA/cm2) of 333, 220, and 149 mV for the oxygen evolution reaction (OER), glucose oxidation reaction (GOR), and urea oxidation reaction (UOR), respectively. For the hydrogen evolution reaction (HER), NFSS15 exhibits η10 values of 112 (alkaline water), 97 (glucose-added water), and 92 mV (urea-added water). The superior performance is attributed to Ni3+ defect sites and a high density of defective hydroxyl groups, as made evident by X-ray photoelectron spectroscopy. Remarkably, NFSS15 achieves an OCP of only 1.47 V at 10 mA/cm2 for urea-assisted water splitting with stability over 200 h. Density functional theory (DFT) calculations further support its stronger urea adsorption and reduced HER Gibbs free energy, underscoring the synergistic electrocatalytic behavior.