Silicon protected with atomic layer deposited TiO2: durability studies of photocathodic H2 evolution

Abstract

The semiconducting materials used for photoelectrochemical (PEC) water splitting must withstand the corrosive nature of the aqueous electrolyte over long time scales in order to be a viable option for large scale solar energy conversion. Here we demonstrate that atomic layer deposited titanium dioxide (TiO₂) overlayers on silicon-based photocathodes generate extremely stable electrodes. These electrodes can produce an onset potential of +0.510 V vs. RHE and a hydrogen evolution saturation current of 22 mA cm⁻² using the red part of the AM1.5 solar spectrum (λ > 635 nm, 38.6 mW cm⁻²). A PEC chronoamperometry experiment was carried out for 2 weeks under constant illumination at +0.300 V vs. RHE with negligible degradation (<5%). Further testing showed slight degradation, but the re-addition of catalyst recovered the activity. These results show that properly processed TiO₂ overlayers may have the potential to be stable for the long time frames that will be necessary for commercial devices.