Hierarchical yolk-shell layered potassium niobate for tuned pH-dependent photocatalytic H₂ evolution

Photocatalysts and the reaction environments in which they act are crucial for improving the photocatalytic efficiency. But the pH-dependent evolution of H₂ photocatalysed using nanoscale potassium niobate particles with high surface areas has not received attention. In this study, a straightforward Ostwald ripening method was developed to synthesize KNb₃O₈ with a thin nanosheet assembled hierarchical yolk-shell structure and large surface area of 60.6 m² g^-1. The H₂ evolution from a water-methanol solution in an alkaline to neutral environment was studied. The photocatalytic H₂ evolution rates over fabricated hierarchical yolk-shell KNb₃O₈ increased when OH^- concentrations were decreased. Such behaviour implied that the concentration of H⁺ dominated the H₂ evolution over hierarchical yolk-shell KNb₃O₈ rather than the reduction ability from the conduction band, differing from the corresponding bulk material. This study demonstrated an efficient method to achieve a high H₂ evolution rate in a neutral environment through the use of photocatalysts with hierarchical structures and large surface areas.