Sub-10-nm-sized Au@Au x Ir 1- x metal-core/alloy-shell nanoparticles as highly durable catalysts for acidic water splitting.

The absence of efficient and durable catalysts for oxygen evolution reaction (OER) is the main obstacle to hydrogen production through water splitting in an acidic electrolyte. Here, we report a controllable synthesis method of surface IrO x with changing Au/Ir compositions by constructing a range of sub-10-nm-sized core-shell nanocatalysts composed of an Au core and Au x Ir 1- x alloy shell. In particular, Au@Au 0.43 Ir 0.57 exhibits 4.5 times higher intrinsic OER activity than that of the commercial Ir/C. Synchrotron X-ray-based spectroscopies, electron microscopy and density functional theory calculations revealed a balanced binding of reaction intermediates with enhanced activity. The water-splitting cell using a load of 0.02 mg Ir /cm 2 of Au@Au 0.43 Ir 0.57 as both anode and cathode can reach 10 mA/cm 2 at 1.52 V and maintain activity for at least 194 h, which is better than the cell using the commercial couple Ir/C‖Pt/C (1.63 V, 0.2 h).