Solid and acid electrolytes for Al-air batteries based on xanthan-HCl hydrogels

Journal of Solid State Electrochemistry - This paper presents first investigations on solid and strongly acid electrolytes for Al-air batteries. These electrolytes are prepared starting from a...     

Photoionization,Structures, and Energetics of Na-Doped Formic Acid–Water Clusters

The influence of formic acid on water cluster aggregation has been investigated experimentally by mass spectrometry and tunable UV laser ionization applied to Na-doped clusters formed in the supersonic expansion of water vapors seeded with formic acid (FA) as well as theoretically using high level quantum chemistry methods. The mass spectra of Na−FA(H₂O)_n clusters show an enlarging of mass distribution toward heavier clusters with respect to the Na−(H₂O)_n clusters, suggesting similar mass distribution in neutral clusters and an influence of formic acid in water aggregation. Density functional theory and coupled-cluster type (DLPNO-CCSD(T)) calculations have been used to calculate structures and energetics of neutral and ionized Na−FA(H₂O)_n as well as neutral FA(H₂O)_n. Na-doped clusters are characterized by very stable geometries. The theoretical adiabatic ionization potential values match pretty well the measured appearance energies and the calculated first six electronic excited states show Rydberg-type characters, indicating possible autoionization contributions in the mass spectra. Finally, theoretical calculations on neutral FA(H₂O)_n clusters show the possibility of similarly stable structures in small clusters containing up to n=4–5 water molecules, where FA interacts significantly with waters. This suggests that FA can compete with water molecules in the starting stage of the aggregation process, by forming stable nucleation seed.     

Dual solid electrolytes for aluminium-air batteries based on polyvinyl alcohol acidic membranes and neutral hydrogels

Water-based electrolytes are generally preferable to organic electrolytes due to their low cost and higher safety standard. However, their widespread use is generally limited by recharging issues. In the case of Al-air cells, water on the anode prevents aluminium deposition during recharging by producing hydrogen at more positive standard potentials. This promotes parasitic reactions that consume the anode and shorten the cell shelf life. On the cathode side, depending on the pH, water allows efficient oxygen reduction or oxygen evolution reactions. To produce electrolytes with different water contents on the two electrodes, we prepared solid electrolytes using polyvinyl alcohol (PVA) and aqueous HCl solutions with ionic conductivity ranging from 0.7 to 2.2 × 10⁻³ S cm⁻¹ and electrochemical windows wider than 2.2 V. The new materials resembled a thin plastic membrane (0.6–0.9 mm thick) and were able to oxidise the Al-air cell anode. We also explored the possibility of using a dual electrolyte to allow the presence of water mainly on the cathode side. Specifically, cells assembled with two electrolytes in contact, with an acidic PVA membrane as anolyte and saline hydrogel as catholyte without separator, showed discharge capacity more than one order of magnitude greater than cells with single acidic PVA electrolytes. Electrochemical impedance spectroscopy (EIS) characterisation verified that the improved cell discharge capacity was attributed to the soft aqueous catholyte on the cathode-electrolyte interface and to the membrane conductivity stabilisation during cell use through the saline gel water. Cyclic voltammetry (CV) characterisation suggested the possibility of recharging the dual electrolyte cells thanks to the substantial absence of water on the anode side.

Graphical abstract