Effect of nickel-based electrocatalyst size on electrochemical carbon dioxide reduction: A density functional theory study.

The electrochemical carbon dioxide (CO) reduction reaction (CORR) used for converting higher-value chemicals is a promising solution to mitigate CO emissions. Nickel (Ni)-based catalysts have been identified as a potential candidate for CO activation and conversion. However, in the CORR, the size effect of the Ni-based electrocatalysts has not been well explored. Herein, the single Ni atom and the Ni cluster doped nitrogen-doped carbon nanotube (Ni@CNT and Ni@CNT), and the Ni (110) facet were designed to explore the size effect in the CORR by using density functional theory (DFT) calculations. The results show that carbon monoxide (CO) is produced on the Ni@CNT with a free energy barrier of 0.51 eV. The reduction product of CO on the Ni@CNT and Ni(110) facet is methane (CH) in both cases, via different reaction pathways, and the Ni(110) facet is a more efficient electrocatalyst with a low overpotential of 0.27 V when compared to Ni@CNT (0.50 V). The rate-determining step (RDS) is the formation of *CHO on the Ni@CNT (The "*" represents the catalytic surface), while the *COH formation is the RDS on the Ni(110) facet. Meanwhile, the Ni(110) facet also has the highest selectivity of CH among the three catalysts. The CO reduction product changes from CO to CH with the increasing size of the Ni-based catalysts. These results demonstrate that the catalytic activity and selectivity of CORR highly depend on the size of the Ni-based catalysts.