Plasma-assisted sulfurization of CoMoO₄ nanorods embedded in carbon nanotube sheets for enhanced hydrogen evolution reaction

Efficient hydrogen production requires cost-effective catalysts based on earth-abundant, non-noble metals. Transition metal oxides (TMOs) are promising for the oxygen evolution reaction because of their low cost, low toxicity, and structural diversity. However, their poor electrical conductivity and limited stability undermine their performance in the hydrogen evolution reaction (HER). In this work, the HER activity of TMO-based materials was enhanced via plasma-assisted sulfurization. Hydrothermally synthesized CoMoO₄ nanorods were combined with multi-walled carbon nanotubes (MWCNTs) through vacuum filtration to produce a free-standing electrocatalytic electrode. Plasma treatment of the CoMoO₄ nanorods in a mixture of H₂S and Ar partially produced 2H–MoS₂, induced a phase transformation from α-CoMoO₄ to β-CoMoO₄, and introduced sulfur dopants. Therefore, the sulfurized CoMoO₄/MWCNT exhibited a lower overpotential, a smaller Tafel slope, and good long-term stability compared with pristine CoMoO₄/MWCNT. These results highlight plasma-assisted sulfurization of free-standing CoMoO₄/MWCNT as an effective strategy for developing high-performance HER catalysts.