Efficient hydrogen evolution reaction with platinum stannide PtSn4 via surface oxidation

By means of surface-science experiments, electrochemical tests and density functional theory, we assess the suitability of PtSn4 for catalysis. Through an investigation of the surface chemical reactivity toward CO, H2O, O2 molecules at room temperature and, moreover, of surface stability in air, we show that the catalytic activity of PtSn4 is determined by the atomic tin layer constituting its surface termination. The PtSn4 surface is not affected by CO poisoning, although it evolves into a tin-oxide skin in ambient atmosphere. We demonstrate that hydrogen evolution reaction for PtSn4 can be modelled by the combination of two steps, i.e. Volmer and Tafel reactions. Surprisingly, surface oxidation induces a reduction of the energy barrier for the Tafel reaction, so that oxidized PtSn4 behaves similarly to Pt(111), in spite of the reduced amount of Pt in the alloy and without available over-surface Pt sites. Correspondingly, we observe in electrochemical experiments a Tafel slope of 86 mV dec-1 and an onset potential similar to pure Pt. Our results indicate PtSn4 as a promising novel material for electrocatalytic reactions, whose performance could be further tuned by surface treatments.