A newly hierarchically porous pyrolysis-free bifunctional catalyst to boost ultralong lifespan zinc-air batteries

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-E_1/2], 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."

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Reference
Authors: TENGGE CHEN, DI LIU, XUELI LI , MENGQING SHI, AND ZHONGHUA XIANG

Title of original paper: A Mass Transfer-Enhanced Pyrolysis-Free Bifunctional Catalyst to Boost Ultralong Lifespan Zinc-Air Batteries

Journal: Energy Material Advances

DOI: 10.34133/energymatadv.0061

Affiliations: State Key Laboratory of Organic-Inorganic Composites; Beijing University of Chemical Technology, Beijing 100029, PR China.

About the Author: Zhonghua Xiang is a professor and director of the Molecular Energy Materials R&D Center at Beijing University of Chemical Technology (BUCT). He received his B.S. in Xiangtan University in 2007, Ph.D. in 2013 at BUCT and was a postdoctoral researcher at Case Western Reserve University (2013–2014). His research interests are focused on the design and synthesis of molecular energy materials, mainly including covalent-organic frameworks (COPs) for fuel cells and flow battery. He has published over 100 SCI articles in J. Am. Chem. Soc., Angew. Chem. Int. Ed., Sci. Adv., Nat. Commun., Adv. Mater. et al., and authorized 19 invention patents, 6 of which have been successfully transferred to the enterprise; He led and presided over the National Key Research and Development Program of China, the key international cooperation projects of the National Fund Commission, National Science Fund for Outstanding Young Scholars, Beijing National Science Fund for Distinguished Young Scholars, PetroChina and other enterprises; He won the First Prize (Natural Science) of Scientific and Technical Awards of Ministry of Education of China as a second winner; the Hou Debang Chemical Science and Technology Award for young scientists; the China Renewable Energy Society Excellent Science and Technology Talent Award; He was an associate board members of Next Mater., and young board members of Green Chem. Eng., eScience, Chinese Chem. Lett. He was appointed as the Deputy Director of the Youth Working Committee of China Renewable Energy Society, member of the Hydrogen Energy Professional Committee of China Renewable Energy Society, and member of the International Academic Exchange Working Committee of China Chemical Society.