Editors' Choice - How the Infinitesimally Small K plus -Crossover Enables Sufficient Ionic Coupling in Ionomer-Free Thin-Form Factor Nanoelectrodes for Catholyte-Free Water Electrolysis

Abstract

Conventional anion exchange membrane (AEM) water electrolyzers are largely dependent on ionomeric binders. While ionomers provide ionic coupling and maintain the structural integrity of electrodes, they are also known to block catalytic active sites and chemically degrade with time. In this work, we present a way to operate our Ni nanomesh integrated AEM water electrolyzer with no added ionomers and without an electrolyte supply to the cathode, i.e., catholyte-free. A nanomesh is an integrated electrode comprising of billions of nanowires, horizontally and vertically crosslinked, mechanically stabilized on an open support structure. Moreover, the catholyte-free operation relies on the thin form factor of the nanomesh electrodes (4 μm) and the cross-over of potassium ions to the nanomesh cathode and supplied from the anolyte through the membrane. The thinness of the nanomesh electrodes combined with the intrinsic property of a membrane to allow tiny amounts of water to pass through it enabled the catholyte-free operation. Furthermore, for the first time, the unintended cross-over of potassium ions (K+) across an AEM is taken advantage of, to build an operando KOH environment on demand, facilitating ionic coupling in the absence of ionomers hence providing valuable insights for the optimization of AEM water electrolyzer systems.