The electrochemical irreversibility of the Zn anode and degradation of the air cathodes in alkaline electrolytes have long been a barrier to the practical application of rechargeable zinc-air batteries (ZABs), resulting in poor cycle life and low cell voltage.
For the reversibility of ZABs to be enhanced, exhaustive measures have been made to utilize highly feasible catalysts for the air cathode while lessening the corrosion of the Zn anode via electrolyte additives or electrode design. Such strategies could ease but not entirely overcome the core difficulties linked to the powerfully alkaline electrolyte.
A research group headed by Xinbo Zhang from the Changchun Institute of Applied Chemistry (CIAC) of the Chinese Academy of Sciences recently came up with a high-voltage, stable hybrid ZAB by making use of an acidic cathode, a dual-hydrophobic-induced, a neutral Zn anode, and proton-shuttle-shielding membrane to isolate the two electrodes.
Their study outcomes were reported in the journal Joule.
The scientists discovered that highly reversible Zn plating or stripping could be obtained in neutral electrolytes, while acidic electrolytes are necessary for making the air cathode immune to CO2 poisoning problems. Hence, a hybrid ZAB by decoupling the functional environments of the neutral Zn anode and acidic air cathode was suggested by the scientists.
But the necessary prerequisite for the long-time operation of a hybrid ZAB is that the two electrodes tend to function separately in their respective surroundings, thus entirely and permanently preventing the proton crossover caused from catholyte to anolyte.
Depending on this prerequisite, the scientists suggested a proton-shuttle-shielding, hydrophobic-ion-conducting membrane to make this hybrid system feasible.
Remarkably, this hybrid cell allows the improved redox chemistry of both the air cathode and Zn anode. This allows stable Zn stripping or plating in the neutral electrolyte and the high voltage of the oxygen redox reaction present in the acidic electrolyte. Consequently, the hybrid ZAB displays a high working voltage of around 1.5 V and long cycle life of 2000 hours.
Zhang and his research group suggested two kinds of hybrid cell prototypes that would be applicable for the proton-shuttle-shielding, hydrophobic-ion-conducting strategy. However, both the hybrid Zn-Br battery and hybrid Zn-Mn battery are anticipated to display a long cycle life and high voltage. This shows the likelihood of utilizing such hybrid cells to make high-energy-density aqueous batteries.
The rise of a hybrid ZAB might also stimulate the development of many burgeoning areas, such as acidic ORR/OER in proton-exchange membrane fuel cells and electrolyzers.
Xinbo Zhang, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences
Cui, Y.-F., et al. (2022) A high-voltage and stable zinc-air battery enabled by dual-hydrophobic-induced proton shuttle shielding. Joule. doi.org/10.1016/j.joule.2022.05.019.