Li-CO2/O2 battery operating at ultra-low overpotential and low O2 content on Pt/CNT catalyst

Abstract

Li-CO2/O2 battery presents a promising solution to combine CO2 utilization and electrochemical energy storage. Herein, Pt nanoparticles (NPs) of 2.5 nm in mean size loaded uniformly on carbon nanotubes (Pt/CNT) were synthesized and served as cathodic catalysts. The Li-CO2/O2 battery with Pt/CNT catalyst were investigated in mixture gas of CO2 and O2 with O2 content varying from 0% to 20%. It has revealed that the Li-CO2/O2 (2% O2) battery, i.e., operating with 2% O2 content, displays a minimum overpotential of 0.31 V and a cycling stability of 127 cycles, which are significantly superior to the Li-CO2/O2 (20% O2) battery (0.51 V, 90 cycles) and the Li-CO2 battery (0% O2 content) (0.44 V, 110 cycles). Results of in-situ Fourier transform infrared (FTIR) spectroscopy have demonstrated the complete decomposition of Li2CO3 at 3.2 V in the Li-CO2/O2 (2% O2) battery. However, density function theory (DFT) calculations indicate that the decomposition energy barrier of Li2CO3 in Li-CO2/O2 (2% O2) battery is higher than that in Li-CO2 battery. SEM characterizations revealed a localized growth mechanism when O2 content is between 2% and 6% during the initial cycling, in which the Li2CO3 tends to form inside the Pt/CNT catalyst layer, rather than it distributes uniformly on both sides of the Pt/CNT catalyst layer with 0% or 20% O2 content. Such a growth mechanism ensures a better contacting interface between the Pt/CNT catalyst and Li2CO3, which plays a key role in optimal battery performance.