1D transition-metal dichalcogenides/carbon core-shell composites for the hydrogen evolution reaction

2D transition metal dichalcogenides (TMDCs) have recently been proposed as an excellent catalytic substitute for noble metals in the hydrogen evolution reaction (HER). When assembled in a 1D nanotube configuration, TMDCs show enhanced performances originating from the curved lattice strain and nanosize. However, WS₂ nanotubes (NTs) have minor electron mobility and low number of active edge sites, which hinder their effective use in electrocatalytic reactions. In this work, we present the synthesis of the core-shell structure of WS₂ NTs coated with carbon. WS₂ NTs were coated with nitrogen-doped graphitic carbon in three steps. After physical adsorption and annealing, excessive carbon was removed by CO₂ gas, which acts as a mild oxidizer. Finally, recrystallization of the carbon coating at 800 °C was done by thermal annealing in the presence of N₂. Products after each reaction step were chemically analyzed. Following the recrystallization, the heterostructure WS₂ nanotubes/carbon showed significantly improved HER performance, exhibiting an overpotential of 172 mV compared to 540 mV for the uncoated NTs. The improved activity was confirmed in different pH electrolytes. Moreover, the carbon coating significantly improved the electrochemical stability of the WS₂ by protecting it upon prolonged reductive operation. The formation of carbon-coated WS₂ NTs composite material provides a promising way to obtain a pH-universal, cost-effective electrocatalyst for energy conversion.