Carbon Nanotube-Supported MoSe₂ Holey Flake:Mo₂C Ball Hybrids for Bifunctional pH-Universal Water Splitting

Abstract

The design of cost-effective and efficient electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is pivotal for the molecular hydrogen (H₂) production from electrochemical water splitting as a future energy source. Herein, we show that the hybridization between multiple HER- and OER-active components is effective for the design and realization of bifunctional electrocatalysts for universal water splitting, i.e., in both acidic and alkaline media. Our strategy relies on the production and characterization of MoSe₂ holey flake:Mo₂C ball hybrids supported by single-walled carbon nanotube (SWCNT) electrocatalysts. Flakes of MoSe₂ are produced through hydrogen peroxide (H₂O₂)-aided liquid phase exfoliation (LPE), which promotes both the exfoliation of the materials and the formation of nanopores in the flakes via chemical etching. The amount of H₂O₂ in the solvent used for the exfoliation process is optimized to obtain ideal high ratio between edge and basal sites ratio, i.e., high-number of electrocatalytic sites. The hybridization of MoSe₂ flakes with commercial ball-like shaped Mo₂C crystals facilitates the Volmer reaction, which works in both acidic and alkaline media. In addition, the electrochemical coupling between SWCNTs (as support) and MoSe₂:Mo₂C hybrids synergistically enhances both HER- and OER-activity of the native components, reaching high η₁₀ in acidic and alkaline media (0.049 and 0.089 V for HER in 0.5 M H₂SO₄ and 1 M KOH, respectively; 0.197 and 0.241 V for OER in 0.5 M H₂SO₄ and 1 M KOH, respectively). The exploitation of the synergistic effects occurring between multicomponent electrocatalysts, coupled with the production of the electrocatalysts themselves through scalable and cost-effective solution-processed manufacturing techniques, is promising to scale-up the production of H₂ via efficient water splitting for the future energy portfolio.