Flowerlike NiCo₂S₄ Hollow Sub-Microspheres with Mesoporous Nanoshells Support Pd Nanoparticles for Enhanced Hydrogen Evolution Reaction Electrocatalysis in Both Acidic and Alkaline Conditions

Flowerlike NiCo₂S₄ hollow sub-microspheres are synthesized through Cu₂O templates to support Pd nanoparticles as high-efficiency catalysts for the hydrogen evolution reaction (HER). The diameter and shell size of NiCo₂S₄ hollow sub-microspheres are about 400 and 16 nm, respectively. In addition, the surface of the shells is constructed by petallike nanosheets. About 3 nm Pd particles uniformly incorporate with the flowerlike NiCo₂S₄ hollow sub-microsphere to form the NiCo₂S₄/Pd heterostructure. The NiCo₂S₄/Pd catalysts exhibit significantly lower overpotential of only 87 and 83 mV at 10 mA/cm² for the HER in both acidic and alkaline conditions, respectively, relative to NiCo₂S₄ (247, 226 mV) and Pd (175, 385 mV) catalysts. Besides, the NiCo₂S₄/Pd catalysts also exhibit excellent stability of HER in these two conditions. The superior HER performance of NiCo₂S₄/Pd might be resulted from the unique architecture of metal nanoparticles anchored on the bimetallic sulfide flowerlike hollow sub-microspheres, which could provide high surface area, lots of active sites, strong synergetic effect, and stable structure.