Facile immobilization of polyoxometalates for low-cost molybdenum/tungsten phosphide nanoparticles on carbon black for efficient electrocatalytic hydrogen evolution

Cheap and stable earth-abundant electrocatalysts for hydrogen evolution reaction (HER) is an urgent need to realize industrial production of hydrogen. Herein, we present a "1-methylimidazole-immobilization" method to fix molybdenum and tungsten precursors simultaneously on carbon black for preparation of hybrid molybdenum/tungsten phosphide (Mo-W-P) HER catalysts. The synthesis of Mo-W-P nanoparticles on carbon black was designed as two steps: immobilization and phosphorization. The Mo/W precursors, phosphotungstic acid (H3PW12O40) and phosphomolybdic acid (H3PMo12O40) were first fixed on carbon black by 1-methylimidazole, followed by subsequent calcination in air to form the Mo-W-O precursors, which were further phosphatized with red phosphorus at 850 °C in argon atmosphere to form the Mo-W-P nanoparticles. The HER performance can be effectively tuned by changing the atomic ratio of Mo/W, where the introduction of suitable amount of W into MoP results in dramatic decrease of the overpotential. The optimized sample with Mo/W ratio of 1.8:1 showed excellent electrocatalytic performance for HER with a low onset overpotential of 92 mV, along with a low Tafel slope of 62 mV dec−1 in 0.5 M H2SO4. More importantly, at higher current density of 50 mA cm−2, the optimized Mo-W-P/CB sample showed superior overpotential (231 mV) to that of MoP/CB (287 mV) and WP/CB (333 mV). Meanwhile, the Mo-W-P/CB hybrid nanoparticles also showed good stability and durability in strong acid electrolyte. Our work provides a route for construction of efficient hybrid electrocatalysts by immobilization of inorganic complexes.