Deciphering Electrochemical Generation, Transport, and Reactivity of Hydrogen Species in the Electrochemical Palladium Membrane Reactor.

Electrochemical palladium membrane reactor (ePMR) enables hydrogenation chemistry by mechanically separating, but (electro)chemically coupling reduction and chemical hydrogenation by transporting hydrogen species through a dense Pd membrane, yet the identity and transport mechanism of the reactive hydrogen species remain underdefined. Here, we disentangled the roles of hydrogen species, including hydrogen atoms and molecules for both electrochemical and chemical compartments using 1hexyne electrochemical hydrogenation reaction as a model reaction. Tafel analysis with H/D electrolytes, isotopic effects, and quantification of products show that the apparent kinetics were strongly affected by the electron transfer kinetics and hydrogen permeation through the Pd membrane. Furthermore, mathematical description of hydrogen atom transport through the Pd membrane provided qualitative model framework. Electrochemically deposited Pd, Rh, and PdRh layers with controlled thickness and morphology tuned the reaction pathway of hydrogen atom vs. H