Two-dimensional (2D) materials have attracted considerable attention for their unique physicochemical properties and promising applications. However, the preparation of free-standing ultrathin 2D noble metal still remains a significant challenge. Here, for the first time we report a wet-chemical method to synthesize partially hydroxylated ultrathin Ir nanosheets (Ir-NSs) with only 5∼6 atomic layer thickness. Detailed analysis indicates that the growth confinement effect of carbon monoxide and partially hydroxylated surface play a critical role in the formation of ultrathin structure. The ultrathin Ir-NSs exhibit excellent performance for both hydrogen evolution reaction and oxygen evolution reaction in a wide pH range, outperforming the state-of-the-art Pt/C and IrO2, respectively. DFT calculations reveal that the partial hydroxylation not only enhances the surface electron-transfer between Ir-sites and intermediate O-species, but also guarantees an efficient initial activation of bond cleavage of H-O-H for first-step H2O splitting. This ultimately breakthroughs barrier of full water splitting with efficient electron-transfer essentially maintained.

Oxygen evolution reaction (OER), as the primary anodic reaction, plays a critical role in many electrochemical energy conversion processes. As the state-of-the-art OER catalysts, iridium-based materials are largely hindered from practical applications mainly due to the extreme scarcity of iridium. Here we demonstrate the successful fabrication of boron-doped amorphous iridium oxide (IrO x -B) via a facile boric acid-assisted method, which realizes an ultrahigh OER mass activity of 2779 A g −1Ir at 300 mV overpotential, representing one of the best acidic OER catalysts reported so far. It is found that boric acid can not only facilitate the exposure of Ir, but also dope the amorphous IrO x with a form of metaborate, which could further modify the electronic and local ligand structure of Ir for the improved intrinsic activity. Interestingly, the reported strategy is universal that can be applied to improve other metal oxide OER catalysts, highlighting a versatile strategy for creating high-performance electrocatalysts with ultrahigh mass activity for OER and beyond.

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