Activating MoS for pH-Universal Hydrogen Evolution Catalysis.

MoS presents a promising catalyst for the hydrogen evolution reaction (HER) in water splitting, but its worse catalytic performance in neutral and alkaline media than in acidic environment may be problematic for practical application. This is because the other half reaction of water splitting, i.e., oxygen evolution reaction, often needs to be implemented in alkaline environment. Here we demonstrate a universal strategy that may be used to significantly improve the HER catalysis of MoS in all kinds of environments from acidic to alkaline, proton intercalation. Protons may be enabled to intercalate between monolayer MoS and underlying substrates or in the interlayer space of thicker MoS by two processes: electrochemically polarizing MoS at negative potentials (vs RHE) in acidic media or immersing MoS into certain acid solutions like TFSI. The improvement in catalytic performance is due to the activity enhancement of the active sites in MoS by the intercalated protons, which might be related with the effect of the intercalated protons on electrical conductance and the adsorption energy of hydrogen atoms. The enhancement in catalytic activity by the intercalated proton is very stable even in neutral and alkaline electrolytes.