Stable CuO with variable valence states cooperated with active Co 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 CoO@NPC/CuO composites as catalysts for ORR and Pt supports/co-catalysts for MOR. The ORR activity (E = 0.83 V) and long-term stability (activity retention of 85.5% after 30,000 s) of CoO@NPC/CuO-400 (400 °C) dodecahedron are better than those of commercial Pt/C (10 wt%) in alkaline electrolytes. The surface CuO with variable valence states (Cu and Cu) can be used as both the active component for ORR and the protective layer for CoO to enhance catalytic stability. Partial removal of CoO from carbon framework promotes the exposure of highly active sites (Co) on the CoO. For MOR, the mass activity of Pt-CoO@NPC/CuO-400 (5 wt%) (1947 mA mg) is much higher than that of Pt/C (751 mA mg), mainly attributing to that the Pt active sites are uniformly dispersed on CoO@NPC/CuO support. The strong interaction between Pt and CuO can reduce the bond strength of Pt-CO to enhance CO resistance. CoO can activate HO 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.