Self-assembled metal cluster/perovskite catalysts for efficient acidic hydrogen production with an ultra-low overpotential of 62 mV and over 1500 hours of stability at 1 A cm<SUP>-2</SUP>

The production of green hydrogen as a promising form of clean energy via water splitting relies on the development of efficient and stable electrocatalysts for the hydrogen evolution reaction (HER). Herein, we present a new electrocatalyst, Ca2CoRuO6 (CCRO), that exhibited a record low overpotential of 62 mV at a high current density of 1 A cm-2 and the smallest Tafel slope of 10 mV dec-1 (vs. more than 400 mV at 1 A cm-2 and 29 mV dec-1 of commercial Pt/C). Moreover, the CCRO catalyst maintains stable performance for over 1500 hours in a proton exchange membrane electrolyzer operating at a current density of 1 A cm-2. In situ X-ray absorption, Raman, and X-ray diffraction spectroscopies indicated a two-step in situ transformation of CCRO. The pristine form of CCRO was reduced from Ru5+/Co3+ to Ru3+/Co2+ within the first few hours under HER conditions. Subsequently, the catalyst slowly self-assembled to form Ru metal nanoclusters doped with Co (denoted as Co-Ru) on top of the CCRO substrate (Co-Ru/CCRO). First-principles calculations revealed that the synergistic effect within the Co-Ru cluster and hydrogen spillover from the metal cluster to the interface between Co-Ru and CCRO contribute to its outstanding hydrogen production performance. This work presents a new promising HER catalyst with record HER activity and reveals an unusual in situ reconstruction process for the catalyst.