The structure–activity correlation of bifunctional MnO2 polymorphoric and MoS2-based heterostructures: a highly efficient, robust electrochemical water oxidation and reduction reaction catalyst in alkaline pH

The phase-controlled synthesis of heterostructures (X-MOMS, X = α, β, γ, and δ) derived from polymorphic MnO2 and MoS2 emerged as an advanced electrocatalyst for overall water-splitting. A two-step solvothermal synthetic approach was applied to fabricate four different novel heterostructures with tailored catalytic efficiency than the parent structure. The physicochemical and electrochemical analysis confirmed the successful formation of the heterostructure with robust oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline medium. The catalytic performance towards HER and OER depends on the electronic factor and growth mechanism of the heterostructure. The δ-MOMS exhibited improved HER performance with ∼133 mV overpotential at 10 mA cm−2 current density upon activation of the active sites of MoS2 through the heterostructure formation. Alternatively, α-MOMS offered the highest OER catalytic activity with ∼250 mV overpotential at 10 mA cm−2 current density. The higher percentage of the Mn3+ species with longer Mn–O bonds served as active sites in α-MOMS for OER. This approach helped in evaluating the selection of electrodes based on the above heterostructure for overall water splitting.