Oxygen vacancies enhanced cooperative electrocatalytic reduction of carbon dioxide and nitrite ions to urea

The electrochemical reduction of carbon dioxide and nitrite ions into value-added chemicals represents one of the most promising approaches to relieve the greenhouse gases, while a critical challenge is to search for a highly effective catalyst with low energy input and high conversion selectivity. In this work, we demonstrated low-valence Cu doped, oxygen vacancy-rich anatase TiO₂ (Cu-TiO₂) nanotubes as a synergetic catalyst for electrochemical co-reduction of both CO₂ and NO₂^-. The incorporation of Cu dopants in anatase TiO₂ facilitated to form abundant oxygen vacancies and bi-Ti³⁺ defect sites, which allowed for efficient nitrite adsorption and activation. The low-valence Cu dopants also served as effective catalytic centers to reduce CO₂ into CO* adsorbate. The close proximity of CO* and NH₂* intermediates was beneficial for the subsequent cooperative tandem reaction to form urea via the CN coupling. This oxygen vacancy-rich Cu-TiO₂ electrocatalyst enabled excellent urea production rate (20.8 μmol⋅h^-1) and corresponding Faradaic efficiency (43.1%) at a low overpotential of -0.4 V versus reversible hydrogen electrode, substantially superior than those of undoped TiO₂, thus suggesting an exciting approach for cooperative CO₂ and nitrogen fixation.