Application Of Bimetallic Catalysts In Li-CO₂ Batteries

With the increasingly prominent contradiction between environmental protection and energy consumption,it is necessary to find an environment-friendly energy storage conversion device.Lithium carbon dioxide(Li-CO₂)batteries have attracted extensive attention because of their high theoretical energy density and discharge potential,and their ability to capture and convert carbon dioxide into energy storage materials,which can reduce both carbon dioxide emissions and the use of fossil fuels.However,Li-CO₂ battery is still facing many problems and challenges.This is mainly due to the slow kinetics of carbon dioxide reduction reaction and carbon dioxide precipitation reaction,resulting in a series of problems such as high battery over-potential and poor cycle performance.At present,there is an urgent need to design high-efficiency cathode catalyst composites to improve the electrochemical reaction kinetics,and then improve the overall performance of the battery,which is the research hotspot and focus at present and in the next few years.Therefore,in this paper,high performance Li-CO₂ batteries were obtained by loading bimetallic catalysts on carbon nanotubes with good nanostructures.The results of relevant research are as follows:(1)A cathode/catalyst composite with ultrafine Ir-Ru alloy nanoparticles uniformly loaded on nitrogen doped carbon nanotubes(Ir Ru/N-CNTs)was synthesized by a simple solvothermal method,and further used as an efficient cathode for Li-CO₂ batteries.The Li-CO₂ battery with Ir Ru/N-CNTs cathode catalyst has large discharge capacity(6228 m Ah g^-1)and high coulomb efficiency(100%).Under the current density of 100 m A g^-1,it can keep the charging voltage below 4.2 V for 600 times,which is one of the longest cycle life reported so far.The most important thing is that after 600 times of operation,the battery can still operate 166 times with low over-potential after reassembly.Its excellent electrochemical performance can be attributed to the 3D nitrogen doped carbon nanotube matrix,highly dispersed ultrafine Ir-Ru alloy nanoparticles.The alloying effect between Ir and Ru improves the activity of CO₂RR and CO₂ER and the stability of the catalyst,and regulates the nucleation mode of the discharge products.(2)Ultra fine Ru_xIr_1-xO₂nanoparticles highly dispersed on the surface of carbon nanotubes(Ru_xIr_1-xO₂/CNTs)were synthesized by a simple hydrothermal method and further applied to Li-CO₂ batteries.The Li-CO₂ battery with Ru_xIr_1-xO₂/CNTs cathode catalyst has a large discharge capacity of 4239 m Ah g^-1,a low charging platform and over-potential(3.85V/1.22 V),and a long cycle life(6000 h/600 cycles).This is due to the fact that the three-dimensional cross-linked carbon network composed of carbon nanotubes provides a good channel for electron transport,ensures the material transfer,and provides enough space for the deposition and decomposition of discharge products.The highly dispersed Ru_xIr_1-xO₂nanoparticles increase the density of the active sites,thus enhancing the catalytic activity.Due to the synergistic catalysis of Ru O₂ and IrO₂,the morphology of discharge products is adjusted,which further promotes the formation and decomposition of discharge products.(3)The cathode/catalyst composites with IrO₂nanoparticles and NiO nanosheets on the surface of carbon nanotubes(IrO₂/NiO-CNTs)were synthesized by a simple hydrothermal method,and further used as efficient cathode for Li-CO₂batteries.The Li-CO₂ battery with IrO₂/NiO-CNTs cathode has high discharge capacity(6088 m Ah g^-1),low over-potential(0.81V)and ultra-long cycle life(5800 h/580 cycles).This is due to the three-dimensional cross-linked carbon network composed of carbon nanotubes,which ensures the transportation of CO₂,ions,electrons and electrolyte,and provides enough space for the deposition of discharge products.IrO₂/NiO-CNTs cathode catalyst combines the advantages of IrO₂nanoparticles and NiO nanosheets to greatly improve the activity of CO₂RR and CO₂ER.