Covalently Bonded MoS₂–Borocarbonitride Nanocomposites Generated by Using Surface Functionalities on the Nanosheets and Their Remarkable HER Activity

In the light of the recent discovery that carbon-rich borocarbonitrides show electrocatalytic activity for generating hydrogen from water, we have synthesized nanocomposites by covalently cross-linking BC7N with MoS2 sheets to explore whether the HER activity can be significantly enhanced. In order to cross-link BC7N and MoS2 sheets, we have exploited the presence of different functional groups on the surfaces of BN (NH2) and graphene (COOH) domains of the borocarbonitride, as quantitatively determined by FLOSS. We have thus obtained two nanocomposites differing in the location of the cross-linking and these are designated as BN/BCN–MoS2 and G/BCN–MoS2, depending on which domains in the borocarbonitride participate in cross-linking. These nanocomposites were characterized by various spectroscopic methods including fluorescence labeling and their electrochemical and photochemical HER activity investigated. The composite where the graphene domains are cross-linked to MoS2 nanosheets, G/BCN–MoS2 (1:2), exhibits outstanding electrochemical HER activity with an onset potential of −30 mV (vs RHE) and a current density of 10 mA cm–2 at an overpotential of −35 mV. This performance is closely comparable to that of Pt. The composite where the BN domains were cross-linked show somewhat lower activity. The physical mixture of BCN and MoS2, on the other hand, does not display any notable HER activity. The BCN–MoS2 composites also exhibit good photochemical activity. It is noteworthy that 2H-MoS2, which does not exhibit significant catalytic activity, can be rendered highly active by cross-linking with BCN.