Solid Polymer Electrolyte-Coated Macroporous Titania Nanotube Photoelectrode for Gas-Phase Water Splitting.

Photoelectrochemical (PEC) water vapor splitting by using n-type semiconductor electrodes with a proton exchange membrane (PEM) enabled pure hydrogen production from humidity in ambient air. We proved a design concept that the gas-electrolyte-semiconductor triple-phase boundary on a nanostructured photoanode is important for the photoinduced gas-phase reaction. A surface coating of solid-polymer electrolyte on a macroporous titania-nanotube array (TNTA) electrode markedly enhanced the incident photon-to-current conversion efficiency (IPCE) at the gas-solid interface. This indicates that proton-coupled electron transfer is the rate-determining step on the bare TNTA electrode for the gas-phase PEC reaction. The perfluorosulfonate ionomer-coated TNTA photoanode exhibited an IPCE of 26 % at an applied voltage of 1.2 V under 365 nm ultraviolet irradiation. The hydrogen production rate in a large PEM-PEC cell (16 cm2 ) was 10 μmol min-1 .