Elevating hydrogen evolution performance with plasma-induced sulfur vacancies and heteroatom doping in hollow-structured MnS–CoS catalysts

Abstract

Transition-metal sulfides doped with various elements show great promise as highly effective catalysts for the hydrogen evolution reaction (HER), potentially serving as alternatives to Pt-based electrocatalysts. Defect engineering has been identified as a key strategy to enhance the HER activity of such catalysts. This study proposes an effective strategy to generate numerous topological/geometric defects on hollow spherical Mn-doped cobalt sulfide (MnS–CoS) via plasma etching. MnS–CoS catalysts with well-defined cavity structures were successfully prepared using a combination of template-assisted and hydrothermal synthesis methods. Under plasma induction, these catalysts exhibited uniformly formed nanocavity structures with a built-in electric field, which uniformly enhanced their topological/geometric defect levels. The plasma-etched MnS–CoS catalyst demonstrated significantly enhanced HER activity, exhibiting an excellent overpotential of 172 mV at a current density of 10 mA·cm⁻2 in alkaline media and a low Tafel slope of 120 mV·dec⁻¹. These improvements can be attributed to the remarkable conductivity of Co and Mn, along with the unique hollow spherical nanostructure of the material, which contained numerous gaps that promoted electron movement and electrolyte penetration, thereby enhancing the overall catalytic performance. The synergistic effects of heteroatom doping and plasma modulation played a crucial role in achieving outstanding catalytic performance toward the HER. Density-functional theory calculations based on a structural model of MnS–CoS-p confirmed that the introduction of defects and heteroatoms reduced hydrogen adsorption: the Gibbs free energy decreased from 0.72 eV for CoS to 0.23 eV for MnS–CoS-p. The excellent HER activity of the MnS–CoS materials stemmed from the abundance of reactive heterostructured interfaces, which optimized the electronic configuration and, thus, accelerated H2O adsorption and dissociation. This study highlights the potential of combining plasma-assisted defect manipulation and transition-metal-element doping to design high-performance catalysts. The findings also offer valuable insights into the development of environment-friendly energy-conversion technologies.