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

The electrochemical carbon dioxide (CO₂) reduction reaction (CO₂RR) used for converting higher-value chemicals is a promising solution to mitigate CO₂ emissions. Nickel (Ni)-based catalysts have been identified as a potential candidate for CO₂ activation and conversion. However, in the CO₂RR, the size effect of the Ni-based electrocatalysts has not been well explored. Herein, the single Ni atom and the Ni₄ cluster doped nitrogen-doped carbon nanotube (Ni@CNT and Ni₄@CNT), and the Ni (110) facet were designed to explore the size effect in the CO₂RR 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 CO₂ on the Ni₄@CNT and Ni(110) facet is methane (CH₄) 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 Ni₄@CNT (0.50 V). The rate-determining step (RDS) is the formation of *CHO on the Ni₄@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 CH₄ among the three catalysts. The CO₂ reduction product changes from CO to CH₄ with the increasing size of the Ni-based catalysts. These results demonstrate that the catalytic activity and selectivity of CO₂RR highly depend on the size of the Ni-based catalysts.