Disposition of Iridium on Ruthenium Nanoparticle Supported on Ketjenblack: Enhancement in Electrocatalytic Activity toward the Electrohydrogenation of Toluene to Methylcyclohexane.

Electrohydrogenation of toluene (TL) to methylcyclohexane (MCH) has been recognized as a promising technology for the hydrogenation process in the organic hydride hydrogen storage system. Recently, we found that the Ketjenblack (KB)-supported Ru-Ir alloy electrocatalyst showed a high electrocatalytic activity for the electrohydrogenation of TL to MCH, and there was the synergy of Ir electrocatalysis for the formation of adsorbed hydrogen species (H) (H + e → H) and Ru catalysis for hydrogenation of TL (6H + TL → MCH). In this paper, the Ir-modified Ru nanoparticle supported on KB (Ir/Ru/KB) electrocatalyst was synthesized by using a modified spontaneous deposition method. The method enables to control the surface structure of Ru-Ir nanoparticles. The Ir/Ru/KB cathode showed higher electrohydrogenation activity than the Ru-Ir alloy/KB cathodes even at lower loadings of precious Ir. Characterization studies using a scanning-transmission electron microscope with an energy-dispersive X-ray spectrometer and X-ray absorption fine structure proved selective and uniform modification of Ru nanoparticle with Ir. Cyclic voltammetry measurements in HSO aqueous solution indicated higher electrochemical active surface areas of Ir at the Ir/Ru/KB electrocatalysts than that at the Ru-Ir alloy/KB electrocatalysts, which is the reason for the strong synergy of Ru and Ir for the electrohydrogenation of TL to MCH.