Optimizing Ru Metallene Catalytic Cathodes via Compressive Strain Engineering for an Improved Li–CO₂ Battery

Ru-based catalysts have already shown potential advantages in Li-CO2 batteries. The strain regulation strategy has been widely used in various catalysts to achieve catalytic activity enhancement. In this study, seven different strained RuX metallenes were systemically researched by first-principles calculations, where X = ±6, ±4, ±2, and 0%. The structure and electronic properties of RuX metallenes were investigated as well as adsorption energies of reactants, reaction thermodynamics, and electrochemical performance. The results showed that lattice expansion contributed to an upward shift in the d-band center, which enhanced the strength of the CO2 adsorption on RuX. A linear relationship between CO2 activation and lattice strain was demonstrated by analyzing the bond lengths, bond strengths of C-O, and bond angles of CO2. Specifically, under tensile strain, the CO2 activation on RuX was gradually improved. Among all RuX, Ru-2 metallene with an appropriate CO2 adsorption energy exhibited the lowest reaction energy (0.93 eV) for the rate-determining step of Li2CO3 and C formation and the lowest overpotential (0.85 V), demonstrating its excellent catalytic performance in Li-CO2 batteries. This work elucidated the electrochemical mechanism of strain regulation on RuX metallenes as cathode catalysts for Li-CO2 batteries and provided valuable insights for designing metal catalysts with improved catalytic activity.