They published their work on Oct. 12 in Energy Material Advances.
"The development of cost-effective and high-performance zinc-air battery cathode catalyst is imperative," said paper author Zhonghua Xiang, professor with the Beijing University of Chemical Technology. "Currently, zinc-air batteries still not occupy the market, because they are limited in both stability and in their energy density."
Xiang explained that zinc-air batteries can only work for very limited time at high current density, because there are lots of problems of its cathode, anode and electrolyte.
"The air cathode is critical to life span of ZABs." Xiang said. "The construction of the three-phase (gas–liquid–solid) interface is the key to long life span ZABs. For kinetics, a three-phase (gas–liquid–solid) reaction occurs on the air cathode, ORR need a maintain relative hydrophobicity environment and an efficient gas diffusion pathway. During long-time cycle, the ORR active sites may be flood and leads to a lower ORR activity, which leads to the decay of discharge. In contrast, the OER catalyst requires super-hydrophilicity, this means air cathode that the air cathode is more easily flooded.
The O2 bubbles generated during the OER can cause the catalyst fall off. So, it is also important to ensure that the catalyst is solidly attached to the electrode surface.
When the ZABs working at high current density, requires a large number of reactants (O2) to participate in the reaction. It means the air cathode excellent substance transport pathways are required to ensure efficient transport of reactants. The other hand, the superior dual-function catalysts are also very important, a good ZABs catalyst must exhibit excellent ΔE[E10-E1/2], outstanding stability at high current densities and a large electrochemical specific surface area and enriched pore structure. For conventional two-electrode ZABs, the air cathode must come from the bifunctional catalyst which one function for the oxygen reduction reaction (ORR) and another for the oxygen evolution reaction (OER). ORR and OER are reversible reactions, but they occur with high overpotentials. Under high voltage when OER occur, which makes ORR active decay rapidly."
"For efficient production of air cathode catalysts with superior performance. We creatively developed a pyrolysis-free strategy. The pyrolysis-free strategy can effectively avoid the structural reconfiguration during the pyrolysis process." Xiang said. "In this paper, we make more hierarchically porous structures for pyrolysis-free catalysis, which efficient boost the transport of both reactant (O2) and product (H2O)."
"Zinc-air batteries have been studied for decades, but, after a considerable amount of research, their commercialized is still not increase significantly," Xiang said. "To advance the field, we're turning to pyrolysis-free strategy. The pyrolysis-free strategy has overcome some issues of zinc-air battery cathode in resent research work, and similar work is also being carried out in our group."
