Electrochemical control of heterolytic and homolytic hydrogenation pathways at a palladium surface

Here, we use a palladium membrane reactor to investigate hydrogen transfer pathways at a palladium surface. The palladium membrane reactor uses electrochemistry to facilitate the controlled adsorption of hydrogen, sourced from water, into one face of a palladium foil. This hydrogen permeates through the palladium and reacts with unsaturated species in the opposing compartment. The amount of hydrogen loaded into the palladium can be controlled electrochemically to form a well-defined and static PdHx ratio for studying chemical hydrogenation. These static PdHx ratios are otherwise difficult to achieve. We show a preference for homolytic pathways at low current densities and heterolytic hydrogen transfer pathways at higher current densities. We also show reaction conditions that favor hydrogen reacting as either hydrogen radical (H●), proton (H+), or hydride (H–).