Fig. 4.

Multi-hierarchy monolayer MoS₂ catalysts for HER. a Schematic structure of the multi-hierarchy MoS₂ catalysts with both high density of domain and phase boundaries. b Polarization curves for pristine type-II samples, pristine type-III samples, a series of heterophase type-III samples with different phase boundary densities and Pt. c Tafel plots of the corresponding curves in b. d HER performance of a multi-hierarchy MoS₂ catalyst in 0.5-M H₂SO₄ (red curve) and 1-M KOH (purple curve). e Time-dependent current density curve for a multi-hierarchy MoS₂ catalyst under static overpotential of 150 mV for 200 h. f Demonstration of the catalytic HER activity in 0.5 M H₂SO₄ from a multi-hierarchy MoS₂ catalyst with a size of 4 inches in diameter. Inset: photograph of pristine as-grown wafer-scale MoS₂ on sapphire substrate