The electrochemistry of [PtH(PEt3)3]+; inverted and amplified cyclic voltammetric waves and catalytic hydrogen production at a mercury electrode

Abstract

Inverted and amplified waves in cyclic voltammograms of [PtH(PEt₃)₃]⁺ at a sitting mercury drop electrode are interpreted in terms of catalytic cycles for hydrogen production from water involving adsorbed species. The adsorption step on the cathodic sweep involves a two-electron reduction to the catalytically inactive species [PtH(PEt₃)₃]^–(ads.). On the reverse (anodic) sweep, a reductive catalytic cycle is initiated by oxidation to [PtH(PEt₃)₃]˙(ads.) and stops when the potential is insufficiently negative to reduce [Pt(PEt₃)₃]˙⁺(ads.){or [PtH₂(PEt₃)₃]˙⁺(ads.)}. In second and subsequent forward scans the catalytic cycle restarts when the potential is sufficiently reducing to reduce [Pt(PEt₃)₃]˙⁺(ads.) or [PtH₂(PEt₃)₃]˙⁺(ads.) and terminates when [PtH(PEt₃)₃]˙(ads.) is reduced to [PtH (PEt₃)₃]^–(ads.). Variations in peak shape and position with [PtH(PEt₃)₃]⁺(aq.) concentration are interpreted in terms of partial or full desorption of [Pt(PEt₃)₃](ads.) or [PtH(PEt₃)₃]˙(ads.) during the catalytic cyclic under certain conditions. Catalysis of hydrogen production at a mercury drop electrode with catalyst turnover numbers up to 2 × 10⁵ h^–1 for > 16 h is also described.