Electrochemical hydrogenation of mixed-phase TiO₂ nanotube arrays enables remarkably enhanced photoelectrochemical water splitting performance

We first report that photoelectrochemical (PEC) performance of electrochemically hydrogenated TiO₂ nanotube arrays (TNTAs) as high-efficiency photoanodes for solar water splitting could be well tuned by designing and adjusting the phase structure and composition of TNTAs. Among various TNTAs annealed at different temperature ranging from 300 to 700 °C, well-crystallized single anatase (A) phase TNTAs-400 photoanode shows the best photoresponse properties and PEC performance due to the favorable crystallinity, grain size and tubular structures. After electrochemical hydrogenation (EH), anatase-rutile (A-R) mixed phase EH-TNTAs-600 photoanode exhibits the highest photoactivity and PEC performance for solar water splitting. Under simulated solar illumination, EH-TNTAs-600 achieves the best photoconversion efficiency of up to 1.52% and maximum H₂ generation rate of 40.4 µmol h⁻¹ cm⁻², outstripping other EH-TNTAs photoanodes. Systematic studies reveal that the signigicantly enhanced PEC performance for A-R mixed phaes EH-TNTAs-600 photoanode could be attributed to the synergy of A-R mixed phases and intentionally introduced Ti³⁺ (oxygen vacancies) which enhances the photoactivity over both UV and visible-light regions, and boosts both charge separation and transfer efficiencies. These findings provide new insight and guidelines for the construction of highly efficient TiO₂-based devices for the application of solar water splitting.