Titanium Nitride As a Conducting Interfacial Layer between Hydrogen Evolution Catalysts and Silicon Photocathodes for Stable Solar-to-Hydrogen Water Splitting Devices

The development of a solar-driven water splitting device that replaces costly noble metal electrodes, while achieving high performance and stable operation, is a major challenge. Transition metal phosphides (TMP) are being developed as low-cost hydrogen evolution reaction (HER) catalysts, but no reports have demonstrated their successful integration with a photoabsorber achieving stable performance in liquid junction electrolytes. Here, we report on a monolithic junction consisting of cubic-NiP2 HER catalyst : TiN ultrathin-film : Si photoabsorber. Crystalline TiN creates an electron conducting, near-transparent film that effectively hinders atomic diffusion during fabrication and maintains stable interfaces. Crystalline cubic-NiP2 on TiN/n+p-Si retains 97% of the bare Si’s photovoltage, a comparable Jsc to bare Si, and achieves a turnover frequency of 1.04 H2 site-1s−1 at −100 mV applied electrical potential. When used in 0.5 M H2SO4 it requires only −150 mV overpotential beyond Pt/TiN/n+p-Si benchmark to reach an HER photocurrent density of −10 mA/cm2. This photocathode maintains a stable H2 photocurrent (±10%) for at least 125 hours, the duration of test. Transmission electron microscopy, voltammetry, ion scattering, AFM and XPS give information on the physical properties responsible for the observed activity and stable performance of these interfaces.