Electrochemical Controlof Heterolytic and HomolyticHydrogenation Pathways at a Palladium Surface

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