Heterostructure Fe₇S₈/Mn(OH)₂ of incomplete sulfurization induces Mn atoms with high density of states for enhancing oxygen evolution reaction and supercapacitor electrochemical performance

Heterostructures and the introduction of heterogeneous elements have been regarded as effective strategies to promote electrochemical performance. Herein, sulfur species are introduced by a simple hydrothermal vulcanization method, which constructs the open heterostructure Fe₇S₈/Mn(OH)₂ as a bifunctional material. The open cordyceps-like morphology can make the material contact more sufficiently with the electrolyte, exposing a large number of reaction sites. Furthermore, the introduction of the heterogeneous element S successfully constructs a heterogeneous interface, the interface-modulated composite material consists of Mn atoms contributing the main density of states (DOS) near the Fermi energy level from the density functional theory (DFT) calculations, which optimizes the adsorption energy of oxygen-containing intermediates during the oxygen evolution reaction (OER) process and reduces the reaction energy barrier, being conducive to the improvement of the material's electrochemical properties. As predicted, the Fe₇S₈/Mn(OH)₂ material exhibits remarkable electrochemical properties, such as an overpotential of 202 mV at 10 mA cm⁻² for the oxygen evolution reaction and even a specific capacitance of 2198 F g⁻¹ at 1 A g⁻¹. This work provides new insights into the role of introducing sulfur species and controlling the structure of the material, and exemplifies novel design ideas for developing bifunctional materials for energy storage and conversion.