Iridium single-atoms anchored on a TiO₂ support as an efficient catalyst for the hydrogen evolution reaction

Single-atom catalysts (SACs) play a vital role in the hydrogen evolution reaction (HER) owing to the highly desirable atom efficiency and the minimal amount of precious metals. Herein, we use TiO₂ nanosheets to anchor stable atomically dispersed iridium (Ir) to be used as a catalyst (Ir@TiO₂) for the HER. The atomic dispersion of Ir on the TiO₂ substrate is confirmed by aberration-corrected scanning transmission electron microscopy and it is anchored by numerous surface functional groups on abundantly exposed basal planes in TiO₂. In acidic media, the Ir@TiO₂ catalyst (1.35 wt% Ir) shows a low overpotential (41 mV at 10 mA cm^-2), a small Tafel slope of 42 mV dec^-1, and a decent durability for 1000 cycles of the HER with the polarization curve having only a 1 mV shift, which are comparable with those of a commercial Pt/C catalyst with 20 wt% Pt. This work paves a way to design Ir atomically anchored catalysts with low cost and high activity.