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 .