ZIF-8-derived carbon-thin-layer protected WC/W₂₄O₆₈ micro-sized rods with enriched oxygen vacancies as efficient Pt co-catalysts for methanol oxidation and oxygen reduction

To make methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) more efficient, it is essential to explore Pt support (low Pt-loading) with desirable co-catalytic activity. Herein, tungsten carbide/tungsten oxide/zeolitic imidazolate framework-8 (ZIF-8)-derived carbon ((WC)/W₂₄O₆₈/NC_Z8) composites are prepared as Pt-supports/co-catalysts. Heating temperature is controlled to adjust structure and crystalline phases of (WC)/W₂₄O₆₈/NC_Z8. For MOR, mass activity (2492.2 mA mg⁻¹_Pt) of Pt-WC/W₂₄O₆₈/NC_Z8 (850 °C, 5.0 wt.%) is much superior to commercial Pt/C (499.2 mA mg⁻¹_Pt, 10.0 wt.%). NC_Z8-thin-layer facilitates carburization of W atoms (W₂₄O₆₈ to WC) to form WC/W₂₄O₆₈ heterojunctions. Oxygen vacancies on W₂₄O₆₈ fascinate H⁺ to encourage formation of tungsten bronze compounds (H_yWO₃, (0 < y < 1)), and reversible reaction between W₂₄O₆₈ and H_y(WO)₃ (0 < y < 1) contributes to a high MOR activity and CO resistance. Pt-WC/W₂₄O₆₈/NC_Z8 (850 °C) also exhibits a higher ORR activity (4e-) than Pt/C in acidic media. WC/W₂₄O₆₈ heterojunctions accelerate mass and charge transfer at the mixed crystal interfaces for ORR.