Different factors contribute to the conundrum of HER activity in concentrated electrolyte solutions. It was found the onset potential of HER does not depend on the salt concentration for LiCl and LiNO 3 electrolytes. On the other hand, the distinction between free water and bound water in LiTFSI electrolyte solutions turns out to play a crucial role for the HER activity and the subsequent chemical decomposition of TFSI anions. Beside the anion type, impurities in LiTFSI electrolytes have been recently reported to have a strong inhibitory effect on HER. In addition, the same set of experiments also showed that the exchange current density for the HER is reduced by a factor of 32 when increasing the salt concentration from 1 m to 20 m, which highlights the importance of kinetic factor in the reported onset potentials.