An improvement on the electrocatalytic performance of ZIF-67 byin situself-growing CNTs on surface.

Efficient and robust oxygen reduction reaction (ORR) catalysts are essential for the development of high-performance anion-exchange membrane fuel cells (AEMFC). To enhance the electrochemical performance of metal-organic frameworks of cobalt-based zeolite imidazolium skeleton (ZIF-67), this study reported a novel ZIF-67-4@CNT byin situgrowing carbon nanotubes (CNTs) on the surface of ZIF-67 via a mild two-step pyrolysis/oxidation treatment. The electrochemical results showed that the as-prepared ZIF-67-4@CNT after CTAB modification exhibited excellent catalytic activity with good stability, with Eonset, E1/2, and Ilimit, respectively were 0.98 V (versus RHE), 0.87 V (versus RHE) and 6.04 mA cm-2@1600 rpm, and a current retention rate of about 94.21% after polarized at 0.80 V for 10 000 s, which were all superior to that of the commercial 20 wt% Pt/C. The excellent ORR catalytic performance was mainly attributed to the large amount of thein situgrowing CNTs on the surface, encapsulated with a wide range of valence states of metallic cobalt.

The chemical state of iron species influence on the performance of Fe-N-C bifunctional electrocatalyst for Zn-air batteries.

Fe-N-C materials have emerged as promising alternatives to precious metals foroxygen reduction reaction/oxygen evolution reaction (ORR/OER). In this study, astrategy is presented to investigate the influence of different chemical states of ironspecies in Fe-N-C materials on their electrocatalytic performance. Three Fe-N-Ccatalysts, containing either zero-valent Fe or Fe3O4 nanoparticles, aresynthesized using acid pickling, high-speed centrifugation and ultrasound-assisted hydrothermal methods, respectively. The findings manifest that the chemical state of iron significantly affects the electrocatalytic activity of Fe-NX active sites, namely zero-valent Fe enhancing Fe- NXactivity while Fe3O4weakening its activity. Notably, the Fe@FeNC catalyst containing only zero-valent iron, demonstrates the only 0.621 V potential difference between the ORR half-wave potential and the OER potential at 10 mA cm-2. Furthermore, the rechargeable Zn-air battery assembled with Fe@FeNC as the air cathode exhibits a remarkable peak power density of 179.0 mW cm-2, excellent cycling stability over 210 h (with a cycle frequency of one every 10 minutes), and the minimal voltage gap of 0.710 V. These results reveal the significance of different chemical statesof metal-based nanoparticles in Fe-NX activity of Fe-N-C catalysts and offer insights .