Advanced water electrolysers represent a new direction in the field of low-cost green hydrogen production. However, the high cost of precious metal-catalysts in proton-exchange-membranes electrolysers, the high gas permeation of porous diaphragms and the alkaline instability at elevated temperatures (< 60°C) of anion-exchange-membranes in alkaline electrolysers remarkably limit their operational flexibility. Here, we demonstrate a different class of alkaline-water-electrolyser based on

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... able oxindole/KOH complex ion pairs in poly(oxindole biphenylene) ion-solvating-membranes that can bridge the gap in existing water electrolysis technologies by enabling the use of non-precious metal-catalysts (Ni, Ni/Fe) and broadening operation temperature range (-35 ~ 120°C), in combination with ultralow gas permeation and thus low-transient-response times (< 1 s). These ISMs exhibit inspiring alkaline stability at 80°C with a negligible conductivity decay of more than 15000 h and thus allow durable alkaline electrolysis over 2500 h even at elevated temperatures and high operating voltages of 2.3 V.