Local alkalinity enables high-performance pure water anion exchange membrane electrolysis

Anion exchange membrane water electrolyser is a highly promising electrolyser technology, but its performance in pure water is severely limited by the unsatisfactory OH^- conductivity of the membrane. To overcome this critical challenge, we develop a local alkalinity engineering strategy that employs TiO₂ nanoparticles in catalyst layers. These nanoparticles enrich OH^- in the electric double layer at both electrodes, creating self-sustaining alkaline microenvironments (pH ~ 14), as confirmed by a scanning electrochemical microscopy technique integrating pH microelectrodes. As a result, the engineered electrolyser achieves a high current density of 3.0 A cm^-2 at 2.08 V, approaching that of the precious-metal-based proton exchange membrane water electrolyser under identical conditions. In addition, the local alkalinity alleviates the degradation of non-noble metal catalysts and membrane, thus enabling the electrolyser to realise long-term stability of ~ 1400 h at 1.0 A cm^-2. We also demonstrate that this local alkalinity strategy can be readily extended to different types of membranes and scaled up, providing a universal tactic to boost the performance of anion exchange membrane water electrolysers.