Atomic Layer Deposition of Pd: Schottky Junction Construction on CoP-Co <b> ₂ </b> P for Efficient Hydrogen Evolution

Cobalt phosphide (CoP)-based electrocatalysts have emerged as promising alternatives to noble metals for alkaline hydrogen evolution reactions (HER), despite their inherent structural instability. In this study, we construct a Schottky junction of Pd@CoP-Co₂P on nickel foam (NF) via atomic layer deposition (ALD), achieving an ultralow Pd loading of 0.06 wt %. The optimized electrocatalyst exhibits a significantly reduced HER overpotential of 55 mV at 10 mA cm^-2 and exceptional long-term stability over 300 h, much superior than the unmodified CoP-Co₂P/NF (66 mV, 12 h). X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) investigations reveal that the enhanced performance is attributed to the physical barrier effect of Pd and the electronic structure modulation of CoP-Co₂P, facilitated by the formation of a metal-semiconductor Schottky junction. This modulation effectively upshifts the d-band center, optimizing the Gibbs free energy value while concurrently mitigating P leaching and Co(OH)₂ formation. Furthermore, the electrocatalyst showcases remarkable oxygen evolution reaction (OER) activity, achieving 177 mV at 10 mA cm^-2 with 300 h of stability, underscoring its bifunctional prowess. This work highlights the transformative potential of ALD in engineering durable transition metal phosphide electrocatalysts through strategic interface design.