Rational Design and Synthesis of Extremely Efficient Macroporous CoSe 2 –CNT Composite Microspheres for Hydrogen Evolution Reaction

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