Rational Design and Synthesis of Extremely Efficient Macroporous CoSe₂–CNT Composite Microspheres for Hydrogen Evolution Reaction

Uniquely structured CoSe₂–carbon nanotube (CNT) composite microspheres with optimized morphology for the hydrogen-evolution reaction (HER) are prepared by spray pyrolysis and subsequent selenization. The ultrafine CoSe₂ nanocrystals uniformly decorate the entire macroporous CNT backbone in CoSe₂–CNT composite microspheres. The macroporous CNT backbone strongly improves the electrocatalytic activity of CoSe₂ by improving the electrical conductivity and minimizing the growth of CoSe₂ nanocrystals during the synthesis process. In addition, the macroporous structure resulting from the CNT backbone improves the electrocatalytic activity of the CoSe₂–CNT microspheres by increasing the removal rate of generated H₂ and minimizing the polarization of the electrode during HER. The CoSe₂–CNT composite microspheres demonstrate excellent catalytic activity for HER in an acidic medium (10 mA cm⁻² at an overpotential of ≈174 mV). The bare CoSe₂ powders exhibit moderate HER activity, with an overpotential of 226 mV at 10 mA cm⁻². The Tafel slopes for the CoSe₂–CNT composite and bare CoSe₂ powders are 37.8 and 58.9 mV dec⁻¹, respectively. The CoSe₂–CNT composite microspheres have a slightly larger Tafel slope than that of commercial carbon-supported platinum nanoparticles, which is 30.2 mV dec^–1.