Molecular Transformations in Solid Polymer Electrolyte Reactors

This is the authors' abstract. We don't add key points for this paper.

Solid polymer electrolyte (SPE) reactors based on membrane-electrode assemblies (MEAs) provide a scalable platform for organic electrosynthesis by enabling electrolyte-free operation and high current densities in a zero-gap configuration. A defining feature of SPE reactors is the triple-phase boundary, where electron transfer, ion transport, and substrate mass transfer are coupled within a porous catalyst/ionomer architecture. This review summarizes our recent advances in reaction design using proton-exchange-membrane (PEM) and anion-exchange-membrane (AEM) reactors. In PEM systems, electrocatalytic hydrogenation proceeds predominantly via adsorbed hydrogen (Hads), allowing safe, H2-free operation and tunable selectivity; we demonstrate highly diastereoselective hydrogenation of cyclic ketones under continuous flow and selective semihydrogenation of alkynes. In AEM reactors, we achieve additive-free hydrogenation of N-heteroarenes (e.g., pyridines to piperidines) by steering the pathway from outer-sphere electron transfer to surface electrocatalysis on Rh-based cathodes. We also describe selective oxidation of primary alcohols to aldehydes by spatially confining effective basicity near the anodic surface while keeping the bulk solution near-neutral, thereby suppressing over-oxidation. Finally, operando IR/XAFS are highlighted as powerful tools to identify surface intermediates and active metal states.