Coupling low platinum and tungsten carbide supported on ZIFs-Derived porous carbon for efficient hydrogen evolution

Critical Review, Recent Updates on Zeolitic Imidazolate Framework-67 (ZIF-67) and Its Derivatives for Electrochemical Water Splitting

Design and construction of low-cost electrocatalysts with high catalytic activity and long-term stability is a challenging task in the field of catalysis. Metal-organic frameworks (MOF) are promising candidates as precursor materials in the development of highly efficient electrocatalysts for energy conversion and storage applications. This review starts with a summary of basic concepts and key evaluation parameters involved in the electrochemical water-splitting reaction. Then, different synthesis approaches reported for the cobalt-based Zeolitic imidazolate framework (ZIF-67) and its derivatives are critically reviewed. Additionally, several strategies employed to enhance the electrocatalytic activity and stability of ZIF-67-based electrocatalysts are discussed in detail. The present review provides a succinct insight into the ZIF-67 and its derivatives (oxides, hydroxides, sulfides, selenides, phosphide, nitrides, telluride, heteroatom/metal-doped carbon, noble metal-supported ZIF-67 derivatives) reported for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting applications. Finally, this review concludes with the associated challenges and the perspectives on developing the best economic, durable electrocatalytic materials.

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 °C) dodecahedron are better than those of commercial Pt/C (10 wt%) in alkaline electrolytes. The surface CuO with variable valence states (Cu⁰ 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 CoO_x 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.