Transition metal-based bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries

Abstract

Zinc-air batteries (ZABs) have been regarded as one of the most promising next-generation energy conversion devices due to their high theoretical energy density. However, the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during the discharging and charging process severely limit the commercial application of ZABs. Pt-based electrocatalysts exhibit high ORR activities, while Ru- and Ir-based are excellent OER electrocatalysts, but natural scarcity, high cost, and poor durability seriously reduce the commercial competitiveness of rechargeable ZABs. Therefore, the development of cost-effective, and highly efficient non-precious metal bifunctional electrocatalysts is important for the commercialization of rechargeable ZABs. Firstly, I report a bifunctional oxygen electrocatalyst consisting of ZIF-derived carbon-anchored Fe/Fe₃C nanoparticles and Fe single atoms, which are crosslinked by carbon nanotube (denoted as CNT@Fe/Fe₃C FeNC). Benefiting from the synergetic effect of Fe/Fe₃C nanoparticles, Fe-N_x active sites, and the 3D interpenetrating network structure, CNT@Fe/Fe₃C FeNC shows a low ΔE of 0.671 V. Furthermore, Ni was doped into the system to enhance the OER activity of the catalysts. ZIF-derived carbon-anchored Fe/Ni single atoms and graphene supported FeNi nanoparticle was successfully integrated into a hybrid catalyst (denoted as Fe/Ni-NC FeNi@G). Synergizing highly active Fe single atoms for ORR and FeNi alloy nanoparticles for OER, the as-constructed Fe/Ni-NC FeNi@G exhibits an ultra-low ΔE of 0.618 V. Although Fe/Ni-NC FeNi@G exhibits outstanding bifunctionality, its practical application in ZAB still needs improving. Finally, bamboo-like carbon nanotubes and N-doped porous carbon nanosheets-encapsulated Co/Co₇Fe₃ interfacial nanoparticles composite electrocatalyst is synthesized (denoted as Co/Co₇Fe₃@BCNT/NPCN). Co/Co₇Fe₃@BCNT/NPCN demonstrates a low ΔE of 0.658 V and the assembled rechargeable ZAB exhibits a remarkable peak power density of 203 mW cm^–2 and robust cycling stability, enduring up to 900 h. This thesis provides valuable insights into the design of high-performance bifunctional ORR/OER electrocatalysts and makes non-precious metal electrocatalysts assembled ZABs close to achieving commercial applications.

Date of Award	2024
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Minhua SHAO (Supervisor) & Ping GAO (Supervisor)