Dispersive Bonding Explains Chemical Attraction:
Significance and Impact:
Detailed description of bonding and diffusion along with measurements of electrochemical processes in this model redox system will provide a basis for understanding of proton coupled electron transfer (PCET) reactions that are crucially important in many energy related reactions
Research in the Fluid Interface Reactions, Structures and Transport (FIRST) Center is aimed at learning how reactions occur at fluid solid interfaces. Many electrochemical and photochemical reactions of energy relevance (e.g water splitting, carbon dioxide reduction, oxygen reduction) undergo stepwise or coupled electron and proton transfers, the key reactions in energy conversion. To learn how these reactions occur, researchers at FIRST Center have been studying electron/proton transfer reactions on a model redox couple, the quinone-hydroquinone conversion on carbon surfaces. Of key importance is understanding the surface bonding and interaction of the adsorbed quinone molecules at a fluid solid interface. In this work we have used inelastic neutron scattering and Raman, closely linked to density functional theory (DFT) to probe the orientation and bonding of adsorbed 9,10-phenanthrenequinone (PQ) on onion-like carbon (OLC). Electrochemical measurements demonstrated relatively strong bonding of PQ to the OLC as indicated by persistent and reversible features in the cyclic voltammetry. Spectra of bulk solid and adsorbed PQ were obtained by Inelastic Neutron Scattering (INS) and Raman spectroscopy, and the bands were compared with vibrational energies calculated from DFT. At energy losses (frequencies) above 400 cm-1, no band shifts in INS or Raman spectra were observed between bulk solid and adsorbed PQ. However, adsorption of PQ resulted in shifts in the lowest frequency modes (< 400 cm-1), compared to crystalline PQ, which could only be identified by INS. DFT calculations also provided adsorption energies and from these and comparison of computed and experimental spectra it is determined that the molecule adsorbs parallel to the onion-like carbon surface through p-p stacking interaction.
Surface Chemistry and Catalysis R&D Projects