Functional integration of Ni-Mo electrocatalysts with Si microwire array photocathodes to simultaneously achieve high fill factors and light-limited photocurrent densities for solar-driven hydrogen evolution

An n(+)p-Si microwire array coupled with a two-layer catalyst film consisting of Ni-Mo nanopowder and TiO2 light-scattering nanoparticles has been used to simultaneously achieve high fill factors and light-limited photocurrent densities from photocathodes that produce H-2(g) directly from sunlight and water. The TiO2 layer scattered light back into the Si microwire array, while optically obscuring the underlying Ni-Mo catalyst film. In turn, the Ni-Mo film had a mass loading sufficient to produce high catalytic activity, on a geometric area basis, for the hydrogen-evolution reaction. The best-performing microwire array devices prepared in this work exhibited short-circuit photocurrent densities of -14.3 mA cm(-2), photovoltages of 420 mV, and a fill factor of 0.48 under 1 Sun of simulated solar illumination, whereas the equivalent planar Ni-Mo-coated Si device, without TiO2 scatterers, exhibited negligible photocurrent due to complete light blocking by the Ni-Mo catalyst layer.