Effect of Intercalated Metals on the Electrocatalytic Activity of 1T-MoS₂ for the Hydrogen Evolution Reaction

We show that intercalation of cations (Na⁺, Ca2⁺, Ni2⁺, and Co2⁺) into the interlayer region of 1T-MoS2 is an effective strategy to lower the overpotential for the hydrogen evolution reaction (HER). In acidic media the onset potential for 1T-MoS₂ with intercalated ions is lowered by ~60 mV relative to that for pristine 1T-MoS₂ (onset of ~180 mV). Density functional theory (DFT) calculations show a lowering in the Gibbs free energy for H-adsorption (ΔGH) on these intercalated structures relative to intercalant-free 1T-MoS₂. The DFT calculations suggest that Na⁺ intercalation results in a $ΔG_H$ close to zero. Consistent with calculation, experiments show that the intercalation of Na⁺ ions into the interlayer region of 1T-MoS₂ results in the lowest overpotential for the HER.