Single Cobalt Atoms Immobilized on Palladium‐Based Nanosheets as 2D Single‐Atom Alloy for Efficient Hydrogen Evolution Reaction

Abstract Single‐atom alloys (SAAs) display excellent electrocatalytic performance by overcoming the scaling relationships in alloys. However, due to the lack of a unique structure engineering design, it is difficult to obtain SAAs with a high specific surface area to expose more active sites. Herein, single Co atoms are immobilized on Pd metallene (Pdm) support to obtain Co/Pdm through the design of the engineered morphology of Pd, realizing the preparation of ultra‐thin 2D SAA. The unsaturated coordination environments combined with the unique geometric and electronic structures realize the modulation of the d‐band center and the redistribution of charges, generating highly active electronic states on the surface of Co/Pdm. Benefiting from the synergistic interaction and spillover effect, the Co/Pdm electrocatalyst exhibits outstanding hydrogen evolution reaction (HER) performance in both acid and alkaline solutions, especially with a Tafel slope of 8.2 mV dec −1 and a low overpotential of 24.7 mV at 10 mA cm −2 in the acidic medium, which outperforms commercial Pt/C and Pd/C. This work highlights the successful preparation of 2D ultra‐thin SAA, which provides a new strategy for the preparation of HER electrocatalyst with high efficiency, activity, and stability.