Rationally designed oxygen vacant TiO2 decorated with covalent organic framework for enhanced electrocatalytic nitrogen reduction to ammonia

This study focuses on the rational design of uniformly distributed oxygen vacant TiO_2−x nanoparticles supported on an anthraquinone-based covalent organic framework (TiO_2−x@COF-Aq), aiming to address the challenges of Haber-Bosch process. The N-philic nature of Ti and the presence of abundant oxygen vacant sites on the TiO_2−x@COF-Aq promote the adsorption of nitrogen, facilitating the electrocatalytic NRR process. The theoretical study reveals that TiO_2−x@COF-Aq suppresses the H⁺ adsorption, facilitates oxygen vacancy formation and favors the N₂ adsorption at oxygen vacant sites. The synthesized nanocatalyst exhibits many folds higher electrochemical NRR activity than bulk oxygen vacant TiO_2−x with an ammonia yield of ∼30 μg mg^-1 h^–1 and ∼16% Faradaic efficiency. Long term stability study manifests the robustness and industrial significance of the catalyst. The overall synergism between the stabilized nanoparticle and functionalized COF has established the fundamental understanding of the proton coupled electron transfer for N₂ fixation through experiments and theoretical findings.