Photoelectrochemical-driven nitrogen reduction to ammonia by a V_o-SnO₂/TiO₂ composite electrode

N₂ molecules with the NN triple bond structure are difficult to cleave under mild conditions to achieve the nitrogen fixation reaction. Photoelectrochemical (PEC) catalysis technology combining the advantages of photocatalysis and electrocatalysis provides the possibility of the nitrogen reduction reaction under ambient conditions. Herein, an SnO₂/TiO₂ photoelectrode was first fabricated through depositing SnO₂ quantum dots on TiO₂ nanorod arrays via a simple hydrothermal method. The oxygen vacancy (V_o) content was then induced in SnO₂ through annealing SnO₂/TiO₂ at high temperature under an inert atmosphere. The heterogeneous structure of V_o-SnO₂ quantum dots and TiO₂ nanorods boosted the separation of photocarriers. The photoelectrons generated by photoexcitation were transferred from the conduction band of TiO₂ to the conduction band of V_o-SnO₂ and trapped by V_o. V_o activates N₂ molecules adsorbed on the catalyst surface, and reacts with H⁺ in the electrolyte to generate NH₃. The nitrogen fixation yield of PEC catalysis and its faradaic efficiency can reach 19.41 μg cm^-2 h^-1, and 59.6% at -0.2 V bias potential, respectively. The heterogeneous structure of V_o-SnO₂/TiO₂, introduction of V_o and synergistic effect between light and electricity greatly promotes the PEC nitrogen reduction to NH₃.