(735at) Gas Diffusion Electrode Improves Kinetics of Rechargeable Aluminum-CO2 Batteries.

Aluminum (Al) is a very attractive anode material for electrochemical CO₂ conversion due to its lower cost and reactivity in comparison to other battery anode materials including lithium, sodium, potassium, etc. Additionally, the high specific energy of aluminum (2980A·hour/kg) suggests that large amounts of electrical energy are possible during the electrochemical conversion with CO₂. Primary Al-CO₂ batteries have a remarkable discharge capability with the introduction of a small amount of oxygen. Unfortunately, these batteries are not yet rechargeable. By utilizing a homogeneous iodine-based redox mediator, our group demonstrated the reversibility of the Al-CO₂ battery. This secondary battery can achieve discharge and charge with a minimal overpotential of 0.05V. The present-day rechargeable Al-CO₂ battery maintains high discharge capacity and enables the battery to be recharged for up to 12 cycles at a 20 mA/gcarbon rate.

To achieve a higher cyclability on Al-CO₂ batteries, modifications regarding the hydrophobicity, porosity, and high surface area of the gas diffusion electrode (GDE) were explored. By utilizing a mixture of two-dimensional and three-dimensional high surface area carbon-based cathode materials (Graphene and Ketjenblack EC-600JD) with unique pore structures, we demonstrate that the rechargeable Al-CO₂ battery can enhance CO₂ reduction during the discharge processes.

In addition, numerous electrochemical evaluations including cycle voltammetry (CV), impedance (PEIS), and galvanostatic charge and discharge (GCD) were conducted to examine the dependency between the active species in the electrolyte and the active cathode material. During the GCD test, an enhancement of 154 cycles at 100 mA/g was observed when doubling the electrolyte volume and incorporating an external CO₂ tank into the system. The CV examinations showed an increase in the charge and discharge from 0.4mA to 0.92mA, and 0.2mA to 0.45mA respectively. The integration of the additional electrolyte, the CO₂ external tank, and the new GDE surpasses the battery cyclability over 1250 percent in comparison to the original setup. These examinations utilizing this new cathode prove that the Al-CO₂ battery exhibits a notable cycle stability and current density improvement.