Activated TiO2 with tuned vacancy for efficient electrochemical nitrogen reduction

We show significantly enhanced ambient electrochemical nitrogen fixation over TiO2 with tuned oxygen vacancies, providing remarkable ammonia yield rate and Faradaic efficiency in a wide potential range. [Display omitted] •We show that engineering surface oxygen vacancies of TiO2 permits significantly enhanced NRR activity−1 mgcat.−.•The yield rates and faradaic efficiencies of NH3 remain ≥ 2.0 μgNH3 h−1 mgcat.−1 and 4.9%, respectively, in a wide applied potential range −0.07 V to .•The surface oxygen vacancies in TiO2 play a role in activating the first protonation step and also increasing N2 chemisorption (relative to *H). Renewable energy-driven electrochemical N2 reduction reaction (NRR) provides a green and sustainable route for NH3 synthesis under ambient conditions but is plagued by a high reaction barrier and low selectivity. To promote NRR, modification of the catalyst surface to increase N2 adsorption and activation is key. Here, we show that engineering surface oxygen vacancies of TiO2 permits significantly enhanced NRR activity with an NH3 yield rate of about 3.0 μgNH3 h−1 mgcat.−1 and a faradaic efficiency (FE) of 6.5% at -0.12 V (vs. the reversible hydrogen electrode, RHE). Efficient conversion of N2 to NH3 is achieved in a wide applied potential range from -0.07 to -0.22 V (vs. RHE) with NH3 production rates ≥ 2.0 μgNH3 h−1 mgcat.-1 and NH3 FEs ≥ 4.9%, respectively. An NH3 FE as high as 9.8% is obtained at a low overpotential of 80 mV. Density functional theory calculations reveal that the surface oxygen vacancies in TiO2 play a vital role in facilitating electrochemical N2 reduction by activating the first protonation step and also increasing N2 chemisorption (relative to *H).