Stable CuO with variable valence states cooperated with active Co2+ as catalyst/co-catalyst for oxygen reduction/methanol oxidation reactions

Catalysts/co-catalysts for cathodic oxygen reduction and anodic methanol oxidation reactions (ORR/ MOR) play the major roles in promoting the commercialization of direct methanol fuel cells. Herein, bimetallic zeolite-imidazolate-frameworks (CoZn-ZIFs) is used as precursor to synthesize Co3O4@NPC/CuO composites as catalysts for ORR and Pt supports/co-catalysts for MOR. The ORR activity (E-1/2 = 0.83 V) and long-term stability (activity retention of 85.5% after 30,000 s) of Co3O4@NPC/CuO-400 (400 degrees C) dodecahedron are better than those of commercial Pt/C (10 wt%) in alkaline electrolytes. The surface CuO with variable valence states (Cu-0 and Cu2+) can be used as both the active component for ORR and the protective layer for Co3O4 to enhance catalytic stability. Partial removal of CoOx from carbon framework promotes the exposure of highly active sites (Co2+) on the Co3O4. For MOR, the mass activity of Pt-Co3O4@NPC/CuO-400 (5 wt%) (1947 mA mg(Pt)(-1)) is much higher than that of Pt/C (751 mA mg(Pt)(-1)), mainly attributing to that the Pt active sites are uniformly dispersed on Co3O4@NPC/CuO support. The strong interaction between Pt and CuO can reduce the bond strength of Pt-CO to enhance CO resistance. Co3O4 can activate H2O molecules to provide sufficient OH- species to promote MOR. This study provides a new idea for preparation of active ORR catalysts and MOR co-catalyst from bimetallic ZIFs. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

The study utilized bimetallic ZIFs to synthesize new catalysts for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR), with Co3O4@NPC/CuO-400 composites showing superior performance compared to commercial Pt/C in alkaline electrolytes. The interaction between Pt and CuO in the composites enhances catalytic activity and stability for MOR, while Co3O4 activates H2O molecules to provide OH- species.