Electrostatic\nAspect of the Proton Reactivity in Concentrated\nElectrolyte Solutions

Water-in-salt electrolytes with a surprisingly large\nelectrochemical\nstability window of ≤3 V have revived interest in aqueous electrolytes\nfor rechargeable lithium-ion batteries. However, recent reports of\nacidic pH measured in concentrated electrolyte solutions appear to\nbe in contradiction with the suppressed activity of the hydrogen evolution\nreaction (HER). Therefore, the fundamental thermodynamics of proton\nreactivity in concentrated electrolyte solutions remains elusive.\nIn this work, we have used density functional theory-based molecular\ndynamics (MD) simulations and the proton insertion method to investigate\nhow the HER potential shifts in concentrated LiCl solutions under\nboth acidic and alkaline conditions. Our results show that the intrinsic\nHER activity increases significantly with the salt concentration under\nacidic conditions but remains relatively constant under alkaline conditions.\nMoreover, by leverage over finite-field MD simulations, it is found\nthat a determining factor for the HER activity is the Poisson potential\nof the liquid phase, which increases in concentrated electrolyte solutions\nwith comparable values from both density functional theory and point-charge\nmodels.