Understanding the electrochemical reaction mechanisms of precious metals Au and Ru as cathode catalysts in Li–CO2 batteries

Abstract

The electrochemical reaction mechanisms of Au and Ru as cathode catalysts in Li–CO₂ batteries are firstly studied by first-principles density functional theory (DFT) calculations. During the discharge process, the free energy changes of different intermediates during the nucleation processes of lithium oxalate (Li₂C₂O₄) and lithium carbonate (Li₂CO₃) are systematically investigated, showing that on both Au and Ru surfaces, Li₂C₂O₄ nucleations are kinetically favorable for the discharge intermediate product. However, Li₂CO₃ nucleations are thermodynamically favorable for the final discharge product, and Li₂C₂O₄ cannot be stabilized as the final product anymore and has to decompose into Li₂CO₃ as the final discharge product. During the charging process, the Li₂CO₃ decomposition mechanism is also studied on both Au and Ru surfaces, showing that the discharge products of Li₂CO₃ and carbon can be much more reversibly decomposed on the Ru catalyst than on the Au surface. The electrochemical free energy diagrams are also introduced to identify the overpotentials compared with the experimental results. A series of electrochemical reaction pathways proposed here can effectively evaluate the catalytic activity of the catalysts toward the discharging and charging processes, thereby providing more insights into the design and optimization cathode catalysts for Li–CO₂ batteries.