Reduction of N2 to NH3 by TiO2-supported Ni cluster catalysts: a DFT study

Electrochemical techniques for ammonia synthesis are considered as an encouraging energy conversion technology to efficiently meet the challenge of nitrogen cycle balance. Herein, we find that TiO2(101)(-)supported Ni-4 and Ni-13 clusters can serve as efficient catalysts for electrocatalytic N-2 reduction based on theoretical calculations. Electronic property calculations reveal the formation of electron-deficient Ni clusters on the TiO2 surface, which provides multiple active sites for N-2 adsorption and activation. Theoretical calculation identifies the strongest activated configuration of N-2* on the catalysts and confirms the potential-limiting step in the nitrogen reduction reaction (NRR). On Ni-4-TiO2(101), N-2* -> NNH* is the potential-limiting step with a very small free energy increase (Delta G) of 0.24 eV (the corresponding overpotential is 0.33 V), while on Ni1(3)-TiO2(101) the potential-limiting step occurs at NH* -> NH2* with Delta G of 0.49 eV (the corresponding overpotential is 0.58 V). Moreover, the Ni-n-TiO2(101) catalyst, especially Ni-13-TiO2(101), involves in a highly selective NRR even at the corresponding NRR overpotential. This work will enlighten material design to construct metal oxide supported transition metal clusters for the highly efficient NRR and NH3 synthesis.

Automated summary

Electrochemical techniques for ammonia synthesis are considered promising for achieving nitrogen cycle balance. The study reveals that Ni clusters supported on TiO2 can serve as efficient catalysts for N-2 reduction, providing multiple active sites for N-2 adsorption and activation. This work identifies the potential-limiting steps in the nitrogen reduction reaction and suggests strategies for constructing efficient catalysts for NRR and NH3 synthesis using metal oxide supported transition metal clusters.