Hydrogen production from water via electrolysis in acid is attracting extensive attention as an attractive alternative approach to replacing fossil fuels. However, the simultaneous evolution of H₂ and O₂ requires a fluorine-containing proton exchange membrane to prevent the gases from mixing while using the same space to concentrate the gases, which significantly increases the cost and reduces the flexibility of this approach. Here, a battery electrode based on the highly reversible enolization reaction of pyrene-4,5,9,10-tetraone is first introduced as a solid-state proton buffer to separate the O₂ and H₂ evolution of acidic water electrolysis in space and time, through which the gas mixing issue can be avoided without using any membrane. This process allows us to separately consider H₂ and O₂ production according to the variation in input power (e.g., the renewable energy) and/or the location for H₂ concentration, thus showing high flexibility for H₂ production.

(https://onlinelibrary.wiley.com/doi/full/10.1002/anie.201814625)