Researchers from China's Ningbo University and Chinese Academy of Sciences (CAS) have developed a universal thermal reduction method to convert spent cobalt-based perovskites into high-performance bifunctional oxygen catalysts for zinc-air batteries (ZABs), achieving high-efficient Cobalt (Co) recovery and re-utilization.
Cobalt is widely used in energy storage and conversion devices, although its content on our planet is not sufficient. Therefore, recycling it from spent Co-enriched materials is very valuable. Co-based perovskites, which contain abundant Co, are extensively utilized in solid oxide fuel cells, three-way catalysts, and oxygen-permeable membranes, and the recovery of Co from the spent Co-based perovskites is necessary to meet the long-term requirement of Co.
The scientists explained that at high temperatures, melamine and dopamine hydrochloride were transformed into carbon nanotubes, C3N4 and reducing gases (such as NH3 and H2). Simultaneously, the metal elements in the spent Co-based perovskites were converted into nano-scale alloy particles and metal nitrides. Then, the phase structures, micromorphology, and element valences of the obtained multiphase oxygen catalyst (SNCF–Ni-PM) were characterized by X-ray diffraction, scanning/transmission electron microscopy, and X-ray photoelectron spectroscopy, respectively.
The electrochemical properties, including oxygen catalytic activities and stability, of SNCF-Ni-PM were measured by linear sweep voltammetry, chronopotentiometry, chronoamperometry, and cyclic voltammetry methods. Considering the practical applications, the aqueous and solid-state ZABs were assembled and measured.
The results reportedly demonstrate that the multiphase SNCF-Ni-PM mainly includes carbon nanotubes, C3N4 nanosheets, and FeNiN or CoFe nanoparticles.
Moreover, SNCF-Ni-PM exhibits excellent bifunctional oxygen catalytic activity, with an oxygen evolution reaction (OER) potential at 10 mA cm−2 of 1.51 V and an oxygen reduction reaction (ORR) half-wave potential of 0.77 V, outperforming most of the reported oxygen catalysts.
Using SNCF-Ni-PM, the aqueous and solid-state ZABs can achieve high power densities of 295.9 and 228.4 mW cm−2, respectively, being superior to most ZABs.
In addition, the aqueous ZAB with SNCF-Ni-PM can operate stably for 300 h with a slight degradation.
This work provides a feasible method for effectively recycling Co from the spent Co-based perovskites.
