Hierarchical Nanoboxes Composed of Co₉ S₈ -MoS₂ Nanosheets as Efficient Electrocatalysts for the Hydrogen Evolution...

The development of hydrogen evolution catalysts based on nonprecious metals is essential for the practical application of water-splitting devices. Herein, the synthesis of Co₉ S₈ -MoS₂ hierarchical nanoboxes (HNBs) as efficient catalysts for the hydrogen evolution reaction (HER) is reported. The surface of the hollow cubic structure was organized by CoMoS₄ nanosheets formed through the reaction of MoS₄^2- and Co²⁺ released from the cobalt zeolite imidazole framework (ZIF-67) templates under reflux in a mixture of water/ethanol. The formation process for the CoMoS₄ HNB structures was characterized by TEM images recorded at various reaction temperatures. The amorphous CoMoS₄ HNBs were converted through sequential heat treatments into CoS_x -MoS₂ and Co₉ S₈ -MoS₂ HNBs. Owing to their unique chemical compositions and structural features, Co₉ S₈ -MoS₂ HNBs have a high specific surface area (124.6 m²  g^-1 ) and superior electrocatalytic performances for the HER. The Co₉ S₈ -MoS₂ HNBs exhibit a low overpotential (η₁₀ ) of 106 mV, a low Tafel slope of 51.8 mV dec^-1 , and long-term stability in an acidic medium. The electrocatalytic activity of Co₉ S₈ -MoS₂ HNBs is superior to that of recently reported values, and these HNBs prove to be promising candidates for the HER.