Cation Effects on the Acidic Oxygen Reduction Reaction at Carbon Surfaces

Hydrogen peroxide (H2O2) is a widely used green oxidant. Until now, research has focused on the development of efficient catalysts for the two-electron oxygen reduction reaction (2e- ORR). However, electrolyte effects on the 2e- ORR have remained little understood. We report a significant effect of alkali metal cations (AMCs) on carbons in acidic environments. The presence of AMCs at a glassy carbon electrode shifts the half wave potential from -0.48 to -0.22 VRHE. This cation-induced enhancement effect exhibits a uniquely sensitive on/off switching behavior depending on the voltammetric protocol. Voltammetric and in situ X-ray photoemission spectroscopic evidence is presented, supporting a controlling role of the potential of zero charge of the catalytic enhancement. Density functional theory calculations associate the enhancement with stabilization of the *OOH key intermediate as a result of locally induced field effects from the AMCs. Finally, we developed a refined reaction mechanism for the H2O2 production in the presence of AMCs.

Reaction mechanism of dimethyl ether carbonylation to methyl acetate over mordenite – a combined DFT/experimental study

Dimethyl ether carbonylation to methyl acetate over mordenite was studied theoretically with density functional theory calculations and experimentally in a fixed bed flow reactor. A new reaction path to methyl acetate entirely in the 8 membered ring was discovered.

Mechanistic insights into nitrogen fixation by nitrogenase enzymes

Biological nitrogen fixation by nitrogenase enzymes is a process that activates dinitrogen (N2) one of the most inert molecules in nature, within the confines of a living organism and at ambient conditions. Despite decades of study, there are still no complete explanations as to how this is possible. Here we describe a model of N2 reduction using the Mo-containing nitrogenase (FeMoco) that can explain the reactivity of the active site via a series of electrochemical steps that reversibly unseal a highly reactive Fe edge site. Our model can explain the 8 proton-electron transfers involved in biological ammonia synthesis within the kinetic scheme of Lowe and Thorneley, the obligatory formation of one H2 per N2 reduced, and the behavior of known inhibitors.

Scaling properties of adsorption energies for hydrogen-containing molecules on transition-metal surfaces

Density functional theory calculations are presented for CHx, x=0,1,2,3, NHx, x=0,1,2, OHx, x=0,1, and SHx, x=0,1 adsorption on a range of close-packed and stepped transition-metal surfaces. We find that the adsorption energy of any of the molecules considered scales approximately with the adsorption energy of the central, C, N, O, or S atom, the scaling constant depending only on x. A model is proposed to understand this behavior. The scaling model is developed into a general framework for estimating the reaction energies for hydrogenation and dehydrogenation reactions.