Atomic-scale self-rearrangement of hetero-metastable phases into high-density single-atom catalysts for the oxygen...

Maximizing metal-substrate interactions by self-reconstruction of coadjutant metastable phases can be a delicate strategy to obtain robust and efficient high-density single-atom catalysts. Here, we prepare high-density iridium atoms embedded ultrathin CoCeOOH nanosheets (CoCe-O-Ir_SA) by the electrochemistry-initiated synchronous evolution between metastable iridium intermediates and symmetry-breaking CoCe(OH)₂ substrates. The CoCe-O-Ir_SA delivers an overpotential of 187 mV at 100 mA cm^-2 and a steady lifespan of 1000 h at 500 mA cm^-2 for oxygen evolution reaction. Furthermore, the CoCe-O-Ir_SA is applied as a robust anode in an anion-exchange-membrane water electrolysis cell for seawater splitting at 500 mA cm^-2 for 150 h. Operando experimental and theoretical calculation results demonstrate that the reconstructed thermodynamically stable iridium single atoms act as highly active sites by regulating charge redistribution with strongly p-d-f orbital couplings, enabling electron transfer facilitated, the adsorption energies of intermediates optimized, and the surface reactivity of Co/Ce sites activated, leading to high oxygen evolution performance. These results open up an approach for engineering metastable phases to realize stable single-atom systems under ambient conditions toward efficient energy-conversion applications.