Aluminum-air batteries with acidic bio-polymer gel electrolytes and wood-derived metal-free cathodes

Aluminum-air batteries with acidic xanthan-based gel polymer electrolytes and metal-free cathodes made of wood-derived activated carbons have been prepared and their electrochemical performances have been compared with those of the same cells assembled with benchmark platinum/carbon cathodes. Three-electrode electrochemical tests made possible to decouple the anodic and cathodic contributions during the functioning of the cells, allowing unambiguous interpretations of the electrode processes. Compared to the platinum/carbon cathodes, the cathodic potentials of the cheaper wood-derived cathodes show higher values, responsible for the enhanced cell potentials. The galvanostatic impedance spectroscopy carried out at different discharge currents and during discharge tests highlighted a lower impedance for both the charge transfer reaction and the mass transport phenomena of the activated carbon compared to the platinum/carbon one. We found that cells made with xanthan-based polymer gel electrolyte and wood-derived activated carbon have stable potentials at around 1 V @ 1 mA cm⁻², moderate capacity of about 25 mAh cm⁻² and gravimetric capacities that can reach the outstanding value of 2682 mAh g⁻¹ even at low discharge currents.