Electronic structure modulation of isolated Co-N4 electrocatalyst by sulfur for improved pH-universal hydrogen evolution reaction

Highlights: • An electronic structure modulation for accelerating the HER process was demonstrated. • The unique new Co-N3S1 system (called N-Co-S/G) was synthesized by two-step solid-state approach was established. • The HER activity of N-Co-S/G can be promoted and maintained. • The N-Co-S/G can be used in all pH and seawater hydrogen production. • The sulfur modulation eventually boosts the HER kinetics and water adsorption and activation step. Exploring an efficient platinum group metal (PGM) free electrocatalyst with superior activity and stability for hydrogen evolution reaction (HER) in a wide pH range is desirable for low-cost hydrogen production. Here, we report atomically dispersed cobalt on nitrogen and sulfur co-doped graphene (N-Co-S/G) for HER. Remarkably, the prepared N-Co-S/G electrocatalyst shows a small overpotential of 67.7 mV vs. reversible hydrogen electrode (RHE) at a current density of 10 mA cm⁻² and exceptional durability over 100 h at 10 mA cm⁻² under acidic conditions. Moreover, we found that the HER activity of N-Co-S/G is close to 20% Pt/C at all pH levels (0–14) and superior activity at high current density (>100 mA cm⁻²). Experimental and theoretical calculations reveal that the S atom in N-Co-S/G form Co-S bond, resulting new Co-N3S1 active site, which optimizes Gibbs free energy for hydrogen adsorption (∆G_H*) close to zero, while water adsorption and dissociation enhanced by S modulation for neutral and basic media HER.