Efficient and Stable TiO2:Pt–Cu(In,Ga)Se2 Composite Photoelectrodes for Visible Light Driven Hydrogen Evolution

摘要

Novel thin film composite photocathodes based on device-grade Cu(In,Ga)Se2 chalcopyrite thin film absorbers and transparent conductive oxide Pt-implemented TiO2 layers on top are presented for an efficient and stable solar-driven hydrogen evolution. Thin films of phase-pure anatase TiO2 are implemented with varying Pt-concentrations in order to optimize simultaneously i) conductivity of the films, ii) electrocatalytic activity, and iii) light-guidance toward the chalcopyrite. Thereby, high incident-photon-to-current-efficiencies of more than 80% can be achieved over the full visible light range. In acidic electrolyte (pH 0.3), the most efficient Pt-implemented TiO2–Cu(In,Ga)Se2 composite electrodes reveal i) photocurrent densities up to 38 mA cm−2 in the saturation region (−0.4 V RHE, reversible hydrogen electrode), ii) 15 mA cm−2 at the thermodynamic potential for H2-evolution (0 V RHE), and iii) an anodic onset potential shift for the hydrogen evolution (+0.23 V RHE). It is shown that the gradual increase of the Pt-concentration within the TiO2 layers passes through an efficiency- and stability-maximum of the device (5 vol% of Pt precursor solution). At this maximum, optimized light-incoupling into the device-grade chalcopyrite light-absorber as well as electron conductance properties within the surface layer are achieved while no degradation are observed over more than 24 h of operation.