Manganese sulfide microcubes grown on a nickel foam as an efficient binder-free and bifunctional electrocatalyst for overall water splitting in alkaline solution

Precious metal-free, binder-free, cost-effective and bifunctional electrocatalyst for the simultaneous production of hydrogen (H₂) and oxygen (O₂) by water splitting reaction under alkaline conditions is considered as the most promising approach to achieve green and sustainable energy resources to control environmental pollution and increase clean energy reservoirs. To meet this demand, manganese sulfide (MnS) microcubic material on nickel foam (NF) (denoted as MnS-x/NF, where x indicates the amount of thiourea in grams) is prepared by a simple two-step hydrothermal method as a bifunctional electrocatalyst for the first time. The high electrochemical active surface area, abundant active sites and fast charge transport ability of the MnS-0.6/NF make it a remarkable bifunctional electrocatalyst in 1 M KOH (pH = 13.5) solution, which requires only a low overpotential of 58 mV and 103 mV to provide a current density of 10 mA cm⁻² to initiate the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, outperforming most of the precious metal-free bifunctional electrocatalysts. During the electrocatalytic OER activity, MnS-0.6/NF transforms into manganese oxyhydroxide (MnOOH), which assists in the generation of bonds between oxygen atoms (O-O bonds) for better electrocatalytic activity. What's more, the application of MnS-0.6/NF for overall water splitting as an electrolyzer has shown excellent electrochemical activity and the current density of 10 mA cm⁻² is achieved at low cell voltage of only ∼1.35 V. The binder-free MnS-0.6/NF displays excellent stability after conversion to MnOOH/NF during both chronopotentiometry and amperometry tests in 1 M KOH solution, which corresponds to the strong adhesion between as-prepared microcubes and NF, fulfilling the need for a binder-free durable bifunctional electrocatalyst.