Tantalum Pentoxide: From Crystal Structures to Applications in Water Splitting

The environment and energy crisis due to carbon dioxide emissions from burning fossil fuels have increased the urgency to explore sustainable energy, while hydrogen with high energy density and environmental friendliness represents a promising solution. Currently, hydrogen production from renewable-energy-driven water splitting via electrocatalytic, photocatalytic, and photoelectrochemical processes are actively investigated, where the design of stable and active earth-abundant catalysts is one of the most important scientific questions. Among the numerous metal oxide catalysts, tantalum pentoxide (Ta2O5) has recently received great attention due to its suitable band gap and high stability as an anode for water splitting. In this Review, we start with a summary of diverse Ta2O5 phases with different crystalline structures. We also summarize the experimental methods for the synthesis of different Ta2O5 phases, followed by discussions of the electronic structures of each phase from theoretical calculations. Then, we review the recent applications of Ta2O5 as the anode catalyst for the oxygen evolution reaction (OER) and the cathode catalyst for hydrogen evolution reaction (HER). Finally, we discuss the challenges and opportunities of using Ta2O5-based materials as viable catalysts for water splitting, with an emphasis on the crucial role of the synergistic effort from both theory and experiment.