Pelletized TiO₂: Effect of Grain Size and Electrical Conductivity on Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting holds significant promise for sustainable hydrogen production. Conventional photoelectrodes typically consist of metal oxide semiconductors deposited on conductive substrates. Pelletized photoelectrodes, on the other hand, offer advantages such as facile and scalable fabrication, along with high thermal stability, but their potential and structure–property–activity relationships in PEC water splitting remain largely unexplored. In the present study, we address this gap by developing pelletized electrodes of rutile TiO2 using a powder pressing and sintering method. Increasing the sintering temperature resulted in larger grain sizes with fewer grain boundaries. The resulting TiO2 pellets were treated with a hydrogen flow at 973 K to enhance their electrical conductivity, leading to the formation of Ti3+ species. The TiO2 pellet with larger grain sizes achieved photocurrent densities of 3.8 mA cm–2 for water oxidation in neutral electrolyte (pH 6.8) under UV illumination (40 mW cm–2) at 1.23 V vs RHE, with an incident photon-to-current conversion efficiency (IPCE) of 32% at 365 nm. The analysis revealed that grain boundary density limits the performance of pelletized TiO2 electrodes, with photocurrent density increasing as electron transport resistance decreases. Fewer grain boundaries and higher donor (Ti3+) density after hydrogen treatment enhance charge transport and separation, resulting in superior PEC performance of the pelletized photoelectrode with large grains.