Nickel-phosphorous Catalysts For Direct Methanol Fuel Cell Anodes In Alkaline Environments

Transitional metal phosphides are promising materials applied in various fields, especially as direct methanol fuel cell anodic catalysts, due to its low cost, high electrochemical activity, substantial storage and ease of synthesis. Nickel-phosphorous (Ni-P) composite material is fabricated by several facile and efficient methods according to porous, nano, and composite design, such as sponge-template method, electroless plating method, chemical bath deposition method, water-DMF solvothermal method. Moreover, the correlations among morphology microstructure, composition, and electrochemical performance of Ni-P composite material are studied.NiO/Ni-P composite catalysts are fabricated by the combine of sponge-template method and electroless plating method. Amorphous Ni-P is plated on sponges as precursors with different microstructures, which is modified by electroless plating time. Then, precursors are put into a 500℃muffle furnace and annealed in air to obtain NiO/Ni-P composite catalysts, which are consisted by crystalline Ni-P tubular scaffolds and NiO secondary structure with different morphology (nanoparticle, nanoflake). According to tests, NiO nanoparticle/Ni-P composite catalyst is composed of 16.2 wt.% Ni-P and 83.8 wt.% NiO, and has the biggest specific surface area (210.03 m2 g-1). Besides, NiO nanoparticle/Ni-P composite catalyst also shows the highest electro-catalytic methanol oxidation peak current density (-467 A g-1) and the best durability (≥20000 s).Water-DMF solvothermal method is used to obtain various three dimensional Ni-P-0 composite catalysts by modifying molar ratio of Ni and P in reaction systems: astrocyte network Ni-P (Ni-Pan), silkworm-like Ni-P (Ni-Psc), and microsphere-like Ni-P (Ni-Pm). Ni-Pan is composed by many amorphous nanowires with 4 nm in diameter, and possesses the biggest specific surface area (500.5 m2 g-1). Besides, Ni-Pan also shows the highest electro-catalytic methanol oxidation peak current density (1490 A g-1) in alkaline environments.Sodium hypophosphite is used as reductant and phosphorus source during water-DMF solvothermal method to fabricate Ni-Co-P-0 composite catalysts by modifying molar ratio of CoCl2·6H2O and NiCl2·6H2O. Urchin-like porous NiCoPO-2 catalyst is composed by many nanowires, and possesses the biggest specific surface area (540.5 m2 g-1). Besides, NiCoPO-2 catalyst also shows the highest electro-catalytic methanol oxidation peak current density (1567 A g-1) in alkaline environments.According to structure and composition design above, porous nanostructure catalysts all show enhanced specific surface area, which greatly increases the contact area between electrolyte and catalysts, and efficiently enhances electric catalytic activity of methanol oxidation. Besides, the combination of structure and component also make catalysts possess a better electrode accessibility, faster electron transfer and better stability (≥20000 s).