Solvent-controlled O2 diffusion enables air-tolerant solar hydrogen generation

Abstract

Solar water splitting into H₂ and O₂ is a promising approach to provide renewable fuels. However, the presence of O₂ hampers H₂ generation and most photocatalysts show a major drop in activity in air without synthetic modification. Here, we demonstrate efficient H₂ evolution in air, simply enabled by controlling O₂ diffusion in the solvent. We show that in deep eutectic solvents (DESs), photocatalysts retain up to 97% of their H₂ evolution activity and quantum efficiency under aerobic conditions whereas in water, the same catalysts are almost entirely quenched. Solvent-induced O₂ tolerance is achieved by H₂ generation outcompeting O₂-induced quenching due to low O₂ diffusivities in DESs combined with low O₂ solubilities. Using this mechanism, we derive design rules and demonstrate that applying these rules to H₂ generation in water can enhance O₂ tolerance to >34%. The simplicity and generality of this approach paves the way for enhancing water splitting without adding complexity.