Fast formation of thin TiO_x layer on titanium surface enabling a broadband light capture and fast charge carrier transfer

Improving light absorption and conversion ability is essential to improving the performance of photoelectrochemical (PEC) cells in converting and storing solar radiation into chemical energy. As part of this, realizing broadband light absorption in the wavelength of 250–2500 nm is promising to improve solar energy utilization. Previous studies have typically relied on noble metal functional materials to realize visible light harvesting over broadband light capture in PEC water splitting (WS) cells. Here, we report an electrochemical oxidation method to prepare thin TiO_x layer on a Ti-foil surface. A nanostructured film is formed within 10–60 s with a tunable absorption range between 250 and 2500 nm, going beyond the 420 nm absorption edge of TiO₂. In addition to superior light capture ability, the film shows a 10-fold enhancement in the charge carrier transfer rate under AM 1.5 G light compared to that measured under dark conditions. The method proposed is simple, fast, and low-cost, and it has potential for large-area PEC cells with promoted charge carriers’ transfer.