Overall Water-Splitting Enabled by Bifunctional NiPd/Pd Heterodimer Fabricated via In Situ Etching-Growth Route

The rational design of low-cost bifunctional electrocatalysts for overall water-splitting constitutes a pivotal scientific challenge on the path to carbon-neutral energy cycles. Herein, we report a unique NiPd/Pd heterodimer synthesized via an in situ etching-growth route, which functions as a highly efficient bifunctional catalyst for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). The optimized NiPd/Pd-2 heterodimer delivers exceptional activity, requiring ultralow overpotentials of only 15 mV for HER and 300 mV for OER to achieve a current density of 10 mA cm^-2, substantially outperforming the commercial Pt/C (39 mV) and RuO₂ (370 mV), respectively. Remarkably, when configured as a symmetric NiPd/Pd-2||NiPd/Pd-2 electrolyzer, it requires a cell voltage of merely 1.36 V to drive overall water splitting at 10 mA cm^-2, surpassing the performance of the Pt/C||RuO₂ couple (1.70 V). Structural and chemical characterizations after prolonged HER/OER reveal the preserved heterodimeric architecture of NiPd/Pd, with the increased content of Ni-O-O-Pd motif imparting enhanced stability in acidic conditions. Consequently, the NiPd/Pd heterodimer can maintain stable operation of HER, OER, and overall water electrolysis for 24 h without significant attenuation. Furthermore, the electrolyzer can be efficiently powered by simulated renewable sources, highlighting its great potential for sustainable energy-conversion devices.