Ni–CoS2/WS2/MoS2 hollow cuboids as noble metal-free bifunctional catalysts for highly efficient photovoltaics and electrochemical hydrogen production

Abstract

Transition metal compounds, especially NiS2, CoS2, WS2, and MoS2 as noble metal-free catalyst materials, are widely applied to replace Pt in the fields of dye-sensitized solar cells (DSSCs) and hydrogen evolution reactions (HER). Meanwhile, hollow structures have large specific surface area and their large void spaces can also effectively reduce ion migration resistance and diffusion length. In this work, Ni–CoS2/WS2 and Ni–CoS2/MoS2 hollow cuboids have been successfully synthesized and applied as promising bifunctional electrocatalysts in high-efficiency DSSCs and HERs. In detail, nickel-cobalt hydroxide cuboids were prepared and served as self-sacrificing templates to react with (NH4)2WS4 or (NH4)2MoS4 at room temperature, and then mixed with sulfur powder for annealing treatment. Besides, Ni–CoS2 hollow cuboids were synthesized as a reference. Profiting from the stable hollow structure, large specific surface area, abundant effective active sites exposed by WS2, and synergistic effect of multiple elements, Ni–CoS2/WS2 hollow cuboids manifested a preeminent performance. Compared with Pt (8.06%), the conversion efficiency of Ni–CoS2/WS2 hollow cuboids had reached 9.41% as counter electrode for DSSCs. As for HER, it exhibited the lowest overpotential of 72.4 mV@10 mA cm−2 and had the minimum Tafel slope (56.1 mV dec−1) compared with Ni–CoS2/MoS2 and Ni–CoS2.