Substrate diffusion electrodes allow for the electrochemical hydrogenation of concentrated alkynol substrate feeds

Electrosynthesis has the potential to revolutionize industrial organic synthesis sustainably and efficiently. However, high cell voltages and low stability often arise due to solubility issues with organic solvents, while protic electrolytes restrict substrate options. We present a three-layered electrode design that enables the use of concentrated to neat substrate feeds. This design separates the organic substrate from the aqueous electrolyte using layers with varying porosity and hydrophilicity, ensuring precise reactant transport to the catalyst layer while minimizing substrate and electrolyte crossover. We demonstrate its effectiveness by semi-hydrogenating three alkynols with different hydrophobicities. For the semi-hydrogenation of 3-methyl-1-pentyn-3-ol in pure form, we achieved 65% faradaic efficiency at 80 mA cm^-2. Additionally, semi-hydrogenation of neat 2-methyl-3-butyn-2-ol on palladium showed a faradaic efficiency for semi-hydrogenation of 36%, that was stable for 22 h. This design could be pioneering the electrochemical valorization of neat substrates, reducing the need for extensive downstream processing.