On-top hydrogen on a Pd cathode (Pd–H) was observed for the first time by operando infrared (IR) spectroscopy at 2030 cm−1, being stabilized by co-adsorbed solvent (n-alkane) molecules. A proton-exchange membrane (PEM) reactor with Pt/C (anode) and Pd/C (cathode) catalysts was modified to transmit an infrared (IR) beam for operando observation. Pd–H species was observed when 1) H+ was supplied to the cathodic chamber through the PEM, 2) solvent was flowed at the cathode, and 3) an appropriate bias was applied to the cathode. Because atomic H on Pd surfaces interacts with multiple Pd atoms, on-top Pd–H is proposed to be stabilized by co-adsorbed solvent molecules. Spectra of the solvent were deformed when Pd–H species were present: the peak intensity increased and nonfundamental bands at 2800–2500 cm−1 became pronounced. The intensification of these bands was caused by resonance with free-electron absorption bands in the IR region.
Supporting Information for Pd–H species on electrode stabilized by solvent co-adsorption: observation by operando IR spectroscopy
Contents of Supporting Information are Experimental, Materials, Assembly of PEM reactor for operando IR observation, Measurement of IR spectra of MEA, NMR analysis of reaction products, and Figures S1–S6.