Enhancing photoelectrochemical water oxidation efficiency via self-catalyzed oxygen evolution: A case study on TiO2

Charge injection at the semiconductor/electrolyte interface is one of critical limiting factors in achieving efficient photoelectrochemical (PEC) water splitting. Herein, we demonstrate a concept-driven strategy of self-catalyzed oxygen evolution in PEC system to realize efficient and stable charge injection by introducing oxygen vacancies (O-vac) in the nitrogen-doped TiO2 (N-TiO2) which plays dual role of light absorber and electrochemical catalyst. DFT calculation reveals the oxygen vacancies confined in the N-TiO2 films lower its adsorption energy of H2O, leading to a dramatically increase in oxygen evolution reaction (OER) efficiency. Therefore significantly improved charge injection efficiency of 94.6% at 1.23 V-RHE can be achieved for the N-TiO2 with oxygen vacancies (TiO2-N-2) films in the absence of any oxygen evolution catalyst. More interestingly, the TiO2-N-2 electrode exhibits excellent stability with negligible photocurrent decay (2%) after 4 h of PEC reaction at 1.23 VRHE under AM 1.5G illumination. Systematic studies reveal that the O vacancies in the N-TiO2 play an important role in increasing the electrochemically active surface area and the reactivity of active sites along with reduction of anodic overpotential for oxygen evolution. It is worth mentioning that, to the best of our knowledge, this is the first report on self-catalyzed oxygen evolution in PEC systems. Consequently, the strategy provides an alternative route for efficient and stable PEC water splitting.