Layered cesium copper titanate for photocatalytic hydrogen production

Layered cesium copper titanate as well as the unmodified cesium titanate Cs0.68Ti1.83 square O-0.17(4) (square: vacancy) were synthesized by a solution-based approach. The insertion of small amounts of copper into the vacancies of Cs0.68Ti1.83 square O-0.17(4) led to a significant red shift of the band gap energy from 3.4 eV to 2.9 eV. During photo catalytic H2 production experiments, a steady increase in the evolution rate was detected, which can be referred to the in-situ reduction of incorporated copper ions to metallic Cu. The reduced copper ions leach out of the lattice to the catalyst surface and act as co-catalyst for H2 formation, considerably exceeding the activity achieved with Cs0.68Ti1.83 square O-0.17(4) modified with 0.075 wt.-% of Rh as co-catalyst. The use of diffuse reflectance spectroscopy enabled a direct measurement of the copper nanoparticle formation by following their rising plasmon resonance at operating conditions. Characterization by X-ray diffraction (XRD) revealed a significant change in the crystal structure upon photocatalysis.