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 nanotubes (SWCNT) electrocatalysts. Flakes of MoSe2 are produced through hydrogen peroxide (H2O2)-aided liquid phase exfoliation (LPE), which promote 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 enhance both HER- and OER-activity of the native components, reaching remarkable ƞ10 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 V and 0.241 V for OER in 0.5 M H2SO4, and 1 M KOH, respectively). The exploitation of the synergistic effects occurring between multi-component 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.