Ni–deficient NiO/downsized RuO2 composite catalyst with rivalrous size evolution for rechargeable Li–CO2 batteries

Abstract

Lithium–carbon dioxide (Li–CO2) batteries utilize a lightweight and environmentally impactful CO2 gas as a cathode and offer a high energy density (1876 Wh kg−1). However, the thermodynamically stable discharge product, Li2CO3, necessitates the use of catalysts to facilitate reversible reaction kinetics, underscoring the importance of developing efficient catalysts to overcome this bottleneck. In this study, we fabricate nanofiber NiO–RuO2 composite oxide catalysts (nf–NRO) to utilize the synergistic effect of the two oxides. In particular, we spotlight a critical phenomenon–rivalrous grain growth between two oxide components–as a strategy for catalyst optimization, balancing cost–effectiveness and catalytic performance. We observe rivalrous particle size changing behavior, where increasing the RuO2 ratio in the composite oxide leads to RuO2 downsizing and NiO coarsening. To elucidate this phenomenon, we propose expected mechanisms supported by DFT calculations; 1) Band bending between metallic oxide and p–type semiconductor, 2) Interfacial redox reactions driven by differences in the reduction potentials of the NiO and RuO2 nanoparticles, 3) Acceleration of NiO growth due to the oxygen donor effect of RuO2 coupled with surface energy–driven growth mechanisms. Accordingly, the catalytic property of nf–NRO55 is maximized by downsizing RuO2 and Ni3+–rich NiO. The Li–CO2 battery with nf–NRO exhibits lower charge platform and superior cycle stability over 120 cycles. As a result, the correlation between the material properties of the nf–NRO and their electrochemical performance is identified.