Atomic-Scale Architectured Ir Single-Atom Catalysts for Enhanced Photoelectrochemical Water Oxidation

Here, we report an atomic-scale-architectured Ir single atoms (SAs)/NiO/Ni/ZrO2/n-Si photoanode device with drastically enhanced catalytic activity and stability. The NiO/Ni layer, intrinsically rich in Ni vacancies, stabilizes isolated Ir atoms deposited by a single-cycle atomic layer deposition (ALD), serving simultaneously as a PEC cocatalyst and an anchoring layer. Aberration-corrected STEM confirms atomically dispersed Ir, while XPS/XAS reveal Ir in +3–+4 oxidation states due to charge transfer with NiO. An ultrathin (1 nm) ZrO2 insulating layer forms an MIS junction that alleviates Fermi level pinning and enlarges photovoltage. The Ir SAs/NiO/Ni/ZrO2/n-Si achieves a photocurrent density of 27.7 mA cm−2 at 1.23 V versus RHE and 130 h stability. IMPS and EIS show that Ir SAs suppress surface recombination and enhance charge transport, delivering the highest charge transfer efficiency and lowest interfacial resistance compared with Ir nanoclusters and films. DFT indicates isolated Ir sites lower the OER thermodynamic barrier (PDS: O* → OOH*) and facilitate hole transfer to OH adsorbates. This work demonstrates the large potential of single-atom Ir to boost photogenerated charge-carrier kinetics in PEC water oxidation.