Single Platinum Atoms Immobilized on Monolayer Tungsten Trioxide Nanosheets as an Efficient Electrocatalyst for Hydrogen Evolution Reaction

Monolayer WO₃·H₂O (ML-WO₃·H₂O) nanosheets are synthesized via a space-confined strategy, and then a single-atom catalyst (SAC) is constructed by individually immobilizing Pt single atoms (Pt-SA) on monolayer WO₃ (ML-WO₃). The Pt-SA/ML-WO₃ retains the monolayer structure of ML-WO₃·H₂O, with a quite high monolayer ratio up to ≈ 93%, and possesses rich defects (O and W vacancies). It exhibits excellent electrocatalytic performance, with a small overpotential (η) of ? 22 mV to drive ? 10 mA cm^?2 current, a low Tafel slope of ≈ 27 mV dec^?1, an ultrahigh turnover frequency of ≈ 87 H₂ s^?1 site^?1 at η  =   ? 50 mV, and long-term stability. Of particular note, it exhibits an ultrahigh mass activity of ≈ 87 A mg_Pt^?1 at η  =   ? 50 mV, which is ≈ 160 times greater than that of the state-of-the-art commercial catalyst, 20 wt% Pt/C ( ≈ 0.54 A mg_Pt^?1). Experimental and DFT analyses reveal that its excellent performance arises from the strong synergetic effect between the single Pt atoms and the support. This work provides an effective route for large-scale fabrication of ML-WO₃ nanosheets, demonstrates ML-WO₃ is an excellent support for SACs, and also reveals the great potential of SACs in reducing the amount of noble metals used in catalysts.