Shuya Wei

Metal-CO₂ batteries have emerged as a promising strategy to improve energy storage technology while capturing/concentrating carbon dioxide. The Al-CO₂ battery has been previously demonstrated as a primary battery to have an excellent discharge capacity when a small amount of oxygen is introduced. Herein, we demonstrate an Al-CO₂ battery that uses a homogeneous iodine-based redox mediator to enable the reversible discharge and charge of the battery with an ultra-low overpotential of 0.05V. By replacing oxygen gas with aluminum iodide in the electrolyte of the previously primary-only configuration, the battery maintains a high discharge capacity and can be recharged for 12 cycles. Without any additive, the battery shows a negligible discharge capacity of 0.03 mAh/g when discharged at 20 mA/g to 0.5V, which is increased to 3,557 mAh/g when aluminum iodide is introduced. The capacity enhancement is present at a very low aluminum iodide concentration of 0.05M and shows low concentration dependence, indicating that the enhancement is due to a catalytic mechanism. The aluminum iodide additive also reduces stripping/plating overpotentials by 40% across a range of current rates compared to an unmodified imidazolium-based ionic liquid electrolyte. Scanning electron microscopic imaging of battery cathodes with and without aluminum iodide after discharge and charge show that the control battery without aluminum iodide does not form significant discharge products after discharge, and the discharge product remains after recharge. In contrast, the battery with added aluminum iodide shows significant discharge product formation after discharge, and that discharge product almost entirely degrades after recharge. ²⁷Al NMR spectra and TGA analysis of the discharge product confirms the discharge product to be aluminum oxalate. To achieve a higher cyclability and rate capability on Al-CO₂ batteries, modifications regarding the hydrophobicity, porosity, and high surface area of the gas diffusion electrode (GDE) have been explored. By utilizing a mixture of two-dimensional and three-dimensional high surface area carbon-based cathode materials with unique pore structures, we demonstrate that the rechargeable Al-CO₂ battery can enhance CO₂ reduction during the discharge processes.