Transient, in situ synthesis of ultrafine ruthenium nanoparticles for a high-rate Li-CO₂ battery

Li-CO₂ batteries are considered promising approaches for reducing the "greenhouse effect" and taking advantage of the abundant CO₂ in the atmosphere for use in energy storage devices, due to the molecule's reversible reaction with Li. However, Li-CO₂ batteries suffer from several setbacks, such as poor rechargeability and low Coulombic efficiency. Designing and fabricating a highly efficient cathode is one of the key components to improving the electrochemical performance. For the first time, we demonstrate a transient, in situ thermal shock method combined with a three-dimensional cross-linked structure derived from CO₂ gasification to produce a high dispersion of ultrafine Ru nanoparticles on activated carbon nanofibers to serve as an efficient cathode in Li-CO₂ batteries. The interconnected channels, numerous pores, ultrafine nanoparticles, and highly crystalline structure promote the diffusion of CO₂ and the permeation of electrolyte, enhancing the catalytic decomposition of discharge products in Li-CO₂ batteries. These devices exhibit not only impressive cycling performance with a limited capacity of 1000 mA h g^-1, but also a low overpotential due to the sufficient number of active sites on the cathode. The electrode displays a low overpotential of 1.43 V after 50 cycles at 0.1 A g^-1. Furthermore, low overpotentials of 1.79 and 1.81 V can be achieved even at elevated current densities of 0.8 and 1.0 A g^-1, respectively. In comparison, the previously reported overpotentials were up to 1.95 and 1.90 V at low current densities of 0.1 and 0.2 A g^-1, respectively, indicating the Ru nanoparticles on the carbon nanofibers display excellent catalytic performance towards the reaction of Li and CO₂. Therefore, this approach offers a new pathway to high performance Li-CO₂ batteries and may spur further applications in catalysis and other renewable energy storage technologies.