The activity evidence of Ti defect towards electrocatalytic N2 reduction

Abstract

Electrochemical N2 reduction reaction (NRR) for NH3 synthesis, which usually needs highly-efficient electrocatalysts for N2 activation, is a carbon-neutral alternation compared to the traditional Haber–Bosch process. Although Ti-based compounds is widely used as electrocatalysts, what Ti defect affects NRR activity is still illusive. In this work, our systematic density functional calculations on Ti defect-decorated titanium oxide disclose that the unsaturated-Ti with the orbital splitting of defect electron states is the necessary feature for N2 binding and activation, which can be further enhanced by increasing the splitting degree. The bonding/antibonding orbital population and projected density of states indicate that the nature of N2 binding and activation on Ti-defect site is attributed to the elimination of the bonding orbital population in the conduction bands and the formation of * π back-bonding in the valence bands. For the whole NRR process, the synergy of Ti-defect and oxygen vacancy (VO) promotes N2 reduction, and the required maximum energy input scales quite well with the adsorption strength of *NNH. Finally, the formed volcano shape successfully predicts new candidate catalysts for ammonia synthesis, such as TiO2 combined VO with Ti interstitial or H atom. This work provides disclosure of the key elements on the rational design of Ti-based nanomaterial electrocatalysts for artificial N2 fixation.