Prof. Charles T. Campbell
Title: Effects of solvents and electric fields on the surface chemistry of catalysis and electrocatalysis
Bio:
Prof. Charles T. Campbell is Professor Emeritus in Chemistry at the University of Washington, where he is also Adjunct Professor of Chemical Engineering and of Physics, and the Rabinovitch Endowed Chair in Chemistry. He received his BS (1975) and PhD (1979, under JM White) degrees at the University of Texas at Austin in Chemical Engineering and Chemistry, then did postdoctoral research in Germany with Gerhard Ertl (2007 Nobel Prize Winner) and was a staff member at Los Alamos National Lab (1981-1986). He is the author of over 370 publications and two patents on surface chemistry, catalysis, physical chemistry and biosensing. He is an elected Fellow of the ACS, the AVS and the AAAS, Honorary Fellow of the Chinese Chemical Society, and Member of the Washington State Academy of Sciences. He received the Arthur W. Adamson Award of the ACS, the ACS Award for Colloid or Surface Chemistry, the ACS Gabor Somorjai Award for Creative Research in Catalysis, the ACS Catalysis Award for Exceptional Achievements, the Gerhard Ertl Lecture Award, the Robert Burwell Award/Lectureship of the North American Catalysis Society, the Medard W. Welch Award of the AVS, the Gauss Professorship of the Göttingen Academy of Sciences, the Ipatieff Lectureship of Northwestern University and an Alexander von Humboldt Research Award. He serves as Editor-in-Chief of Surface Science Reports and Catalysis Reviews in Science and Engineering, and on the boards of Catalysis Letters, Surface Science and Topics in Catalysis. He previously served as Editor-in-Chief of Surface Science for over ten years.
Abstract:
Understanding how liquid solvents affect the adsorption energies of catalytic reaction intermediates on transition metal surfaces, compared to their better-known values in gas phase, is crucial for understanding liquid-phase catalysis and electrocatalysis. For neutral adsorbates, the dominant effect is a decrease in adsorption energy compared to the gas phase by an amount equal to the solvents’ adhesion energy to the solid multiplied by the surface area of the solid (that is blocked from solvent adsorption) per mole of adsorbed reactant. However, the electric field near the surface also has a strong effect on adsorption energies. When thermal catalytic or electrocatalytic reactions occur on metal surfaces in liquid solvents like water, an electrical double layer develops near the metal surface with a large electric field which changes with reaction conditions. This electric field affects the energies of adsorbed reaction intermediates and transition states, and therefore reaction rates. I will review what is known from ultrahigh vacuum (UHV) surface science studies regarding the effects of electric fields on the energies of adsorbed catalytic reaction intermediates, and show how that can guide predictions about how changes in electric fields from the double layer affect adsorbate energies on metal surfaces in liquids. In UHV, the electric field felt by an adsorbate can be strongly tuned by the addition of another adsorbed species nearby. Alkali adatoms exert a very strong change in electric field near the metal surface, which changes the energies of coadsorbed catalytic reaction intermediates, their electronic character and their reaction rates, as has been studied extensively in UHV. Assuming that changes in the field have only small effects on the strength of the weak attractions between adsorbate and solvent, the change in adsorbate energy with local electric field in a liquid is the same as in UHV. This approach explains the well-known observation that the binding energy of hydrogen adatoms (Had) to many late transition metal surfaces, as probed by cyclic voltammetry in water, increases with increasing pH. This change in Had energy in turn explains pH-induced changes in thermal catalytic and electrocatalytic hydrogenation reaction rates whereby Had must add to another species.
Keywords: Heterogeneous catalysis, electrocatalysis, surface chemistry, clean energy technologies
Host: Prof. Marcel Schreier