Structure-optimized CoP-carbon nanotube composite microspheres synthesized by spray pyrolysis for hydrogen evolution reaction

Highlights: • Structure-optimized CoP-carbon nanotube composite microspheres are synthesized by applying spray pyrolysis process. • Macroporous structure of composite microspheres facilitates electrolyte permeation and maximize the active site exposure. • Synergistic effect between CoP nanocrystals and CNT backbone results in outstanding HER performances. CoP-carbon nanotube (CNT) composite microspheres with high porosity for hydrogen evolution reaction (HER) are synthesized by facile spray pyrolysis and subsequent low-temperature phosphidation. Highly active CoP nanocrystals are successfully decorated on conductive CNT backbone microspheres. Decomposition of polystyrene nanobeads during spray pyrolysis forms macropores over the CoP-CNT composite microspheres, which facilitate electrolyte permeation and maximize the active site exposure. In addition, such morphology not only enhances the electron transfer along the microsphere, but also minimizes the polarization of H₂ gas during HER. Due to the synergistic effect between CoP nanocrystals and CNT backbone, along with the unique morphology, the CoP-CNT composite microspheres demonstrate outstanding HER performance in an acidic electrolyte with a low overpotential of 119 mV at 10 mA cm⁻² and a small Tafel slope of 64 mV dec⁻¹. Moreover, the catalyst maintains its excellent catalytic activity over 2000 cycles. This study marks the versatility of the spray pyrolysis process for the synthesis of conductive substrate-supported electrocatalysts with a wide variety of materials and structures.