Efficient cathodes for quasi-solid-state aluminum-air batteries

Different commercial carbonaceous materials, two made of activated carbons and one of multiwalled nanotubes, were used to prepare cathodes for primary aluminum-air cells and compared with the more expensive platinum-dispersed carbon, usually used as cathode for many types of metal-air cells. The aluminum-air cells used in the electrochemical tests were assembled with alkaline gel polymer electrolytes without any separator. Cells with cathodes made of a cheap activated carbon showed better electrochemical performances than those obtained with platinum-based cathodes. Notably, their discharge capacities were improved and the discharge voltages were always higher than 0.2 V. These improved performances were mainly attributed to the better electrocatalytic activity of the activated carbon as it results from polarization measurements, probably due to the presence of defects, as evidenced from Raman spectra. Three-electrode discharge tests were used to measure the electrode potentials and their impact to the overall cell electrochemical performances. During the discharge, in all cases, an increase of the anodic potential towards more positive values was observed, while the cathodic potential remained almost constant. Thus, the final failure of the cells was mainly due to the degradation of the anodic interface. This indicates the possibility to further increase the cell capacity by adopting suitable mitigation strategies of anodic parasitic reaction or different electrolyte design, with the final aim to realize efficient, cheap, and eco-friendly aluminum-air cells.