Noble metal catalysts, especially Pt, have been widely used for electrochemical energy conversion, including in fuel cells, [1,2] water electrolysis, [3,4] metal-air batteries, [5] and N 2 /CO 2 to fuel conversion. [6][7][8] However, because of the scarcity of Pt, increasing its usage efficient is a significant way to reduce the cost of production. [9][10][11] An efficient strategy is to downsize catalysts, which has been regarded as one of the most effective The rational synthesis of single-layer noble metal directly anchored on support materials is an elusive target to accomplish for a long time. This paper reports well-defined single-layer Pt (Pt-SL) clusters anchored on ultrathin TiO 2 nanosheets-as a new frontier in electrocatalysis. The structural evolution of Pt-SL/TiO 2 via self-assembly of single Pt atoms (Pt-SA) is systematically recorded. Significantly, the Pt atoms of Pt-SL/TiO 2 possess a unique electronic configuration with PtPt covalent bonds surrounded by abundant unpaired electrons. This Pt-SL/TiO 2 catalyst presents enhanced electrochemical performance toward diverse electrocatalytic reactions (such as the hydrogen evolution reaction and the oxygen reduction reaction) compared with Pt-SA, multilayer Pt nanoclusters, and Pt nanoparticles, suggesting an efficient new type of catalyst that can be achieved by constructing single-layer atomic clusters on supports.

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