Unlocking Scalability of overlapping electric double layers for pure water splitting

Overlapping electric double layers (EDLs) between nano-spaced cathode and anode stimulate intense, spatially pervasive electric fields, facilitating in situ ionization of water and establishing a bipolar acid-base reaction environment for pure water splitting. This membrane-free, precious-metal-free approach achieves exceptional H2 production efficiency. However, scaling up such nanoscale architecture remains challenging, requiring reconcile the effects of overlapping EDLs with practical reactor expansion. Here, we deconstruct nanoreactors into elementary components and investigate representative configurations, to quantify their impacts on both effects and scalability of overlapping EDLs. We identify an intrinsic trade-off between voltage efficiency and current efficiency that becomes increasingly pronounced upon scale-up. Meanwhile, support materials within the overlapping-EDLs region induce pseudo-currents by forming a conductive surface layer, further constraining scalability. Guided by these insights, we experimentally realize scalable overlapping EDLs by integrating the optimal components into an interdigitated reactor architecture. The resulting multi-chip system achieves projected power densities of 11.50 kW·kg-1, three orders of magnitude higher than conventional water electrolyzers. This work advances the pure water splitting toward practical H2 production, opening new possibilities for portable energy applications and renewable energy storage.