In Situ Creation of Surface Defects on Pd@NiPd with Core–shell Hierarchical Structure Toward Boosting Electrocatalytic Activity

A deep insight into surface structural evolution of the catalyst is a challenging issue to reveal the structure–activity relationship. In this contribution, based on a surface alloying strategy, the dual-functional Pd@NiPd catalyst with a unique core–shell hierarchical structure is developed through selective crystal growth, surface cocrystallization, directional self-assembly, and reduction process. The surface defects are created in situ on the outer NiPd alloy layer in the electrochemical redox processes, which endow the Pd@NiPd catalyst with excellent electrocatalytic activity of hydrogen generation reaction (HER) and oxygen generation reaction (OER) in alkaline media. The optimal Pd@NiPd-2 catalyst requires an overpotential of only 18 mV that is far lower than Pt/C benchmark (43 mV) at the current density of 10 mA cm–2 for the HER, and 210 mV that is far lower than RuO2 benchmark (430 mV) at 50 mA cm–2 for the OER. Density functional theory (DFT) calculations reveal that the outstanding electrocatalytic activity is originated from the creation of surface defect structure that induces a significant reduction in the adsorption and dissociation energy barriers of H2O molecules in the HER and a decrease in the conversion energy from O* to OOH* that resulted from the synergy of two adjacent Pd sites by forming O-bridge. This work affords a typical paradigm for exploiting efficient catalysts and investigating the dependence of electrocatalytic activity on the surface structural evolution.