Nickel-Based Dye-Sensitized Photocathode: Towards Proton Reduction Using a Molecular Nickel Catalyst and an Organic Dye

To construct an efficient dye-sensitized photo-electrochemical tandem cell for hydrogen production, it is crucial to understand the working principles of both the photoanode and the photocathode. Herein, the anchoring of a proton-reduction catalyst and an organic dye molecule on metal oxides is studied for the preparation of a photocathode. On TiO2, the Ni catalyst behaves as a good electrocatalyst (-250Acm(-2)) in acidic water (pH2). The Ni catalyst and the organic dye were co-immobilized on NiO to form a solely Ni-based photocathode. The electron-transfer steps were investigated by using various techniques (IR, UV/Vis, and fluorescence spectroscopy, and (photo)electrochemistry). Despite the observed successful single-electron-transfer steps between all of the components, photocatalysis did not yield any hydrogen gas. Possible bottlenecks that prevent photocatalytic proton reduction are poor electron transfer because of aggregation, charge recombination from the catalyst to the NiO, or instability of the catalyst after the first reduction.