Anion exchange membrane fuel cells (AEMFCs) offer several important advantages with respect to proton exchange membrane fuel cells, including the possibility of avoiding the use of platinum catalysts to help overcome the high cost of fuel cell systems. Despite such potential benefits, the slow kinetics of the hydrogen oxidation reaction (HOR) in alkaline media and limitations in performance stability (because of the degradation of the anion conducting polymer electrolyte components) have generally impeded AEMFC development. Replacing Pt with an active but more sustainable HOR catalyst is a key objective. Herein, we report the synthesis of a Pd−CeO 2 /C catalyst with engineered Pd-to-CeO 2 interfacial contact. The optimized Pd−CeO 2 interfacial contact affords an increased HOR activity leading to >1.4 W cm −2 peak power densities in AEMFC tests. This is the only Pt-free HOR catalyst yet reported that matches state-of-the-art AEMFC power performances (>1 W cm −2 ). Density functional theory calculations suggest that the exceptional HOR activity is attributable to a weakening of the hydrogen binding energy through the interaction of Pd atoms with the oxygen atoms of CeO 2 . This interaction is facilitated by a structure that consists of oxidized Pd atoms coordinated by four CeO 2 oxygen atoms, confirmed by X-ray absorption spectroscopy.

Hydride transfer changes the charge structure of the reactant and thus, may induce reorientation/reorganization of solvent molecules. This solvent reorganization may in turn alter the energetics of the reaction. In the present work, we investigate the intramolecular hydride transfer by taking Lewis acid catalyzed glucose to fructose isomerization as an example. The C2-C1 hydride transfer is the rate limiting step in this reaction. Water and methanol are used as solvents and hydride transfer is simulated in the presence of explicit solvent molecules, treated quantum mechanically and at a finite temperature, using Car-Parrinello molecular dynamics (CPMD) and metadynamics. Activation free energy barrier for hydride transfer in methanol is found to be 50 kJ mol(-1) higher than that in water. In contrast, in density functional theory calculations, using an implicit solvent environment, the barriers are almost identical. Analysis of solvent dynamics and electronic polarization along the molecular dynamics trajectory and the results of CPMD-metadynamics simulation of the hydride transfer process in the absence of any solvent suggest that higher barrier in methanol is a result of non-equilibrium solvation. Methanol undergoes electronic polarization during the hydride transfer step. However, its molecular orientational relaxation is a much slower process that takes place after the hydride transfer, over an extended timescale. This results in non-equilibrium solvation. Water, on the other hand, does not undergo significant electronic polarization and thus, has to undergo minimal molecular reorientation to provide near equilibrium solvation to the transition state and an improved equilibrium solvation to the post hydride shift product state. Hence, the hydride transfer step is also observed to be exergonic in water and endergonic in methanol. The aforementioned explanation is juxtaposed to enzyme catalyzed charge transfer reactions, where the enhanced solvation of the transition and product states by enzymes, due to electrostatic interactions, reduces the activation free energy barrier and the free energy change of the reaction. Similarly, we suggest that, in the intramolecular hydride shift, improved solvation of the transition state and of the product state by water is achieved due to minimal polarization and reorientation, and (near) equilibrium solvation.

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We use first-principles calculations to study the formation of Pt nanorafts and their oxygen reduction reaction (ORR) catalytic activity on MoC. Due to the high Pt binding energy on C atoms, Pt forms sheet-like structures on the MoC surface instead of agglomerating into particles. We find that the disordered MoC surface carbon arrangement limits the Pt sheet growth, leading to the formation of 4-6 atom Pt nanorafts. The O-O repulsion between the O atoms on the MoC and O adsorbate enhances the ORR activity by weakening the O adsorption energy. We find a significant change from the usual scaling of the energies of the intermediates in the ORR pathway and a strong interaction between the nanoraft and water that lead to a high activity of the Pt nanorafts. Fundamentally, our work demonstrates that the activity of metal catalysts can be strongly affected by manipulation of the atomic arrangement of the supporting carbide surface.

Three cobalt(III) complexes of regioisomeric trans-A 2 B-corroles were designed and efficiently synthesized. The corroles were adsorbed on smooth glassy carbon (GC) and black pearls 2000 (BP2000), high-surface-area carbon. Albeit spatially separated from the cobalt reaction center, the position of COOH group has a profound influence on the oxygen reduction reaction electrocatalytic reactivity when on GC, whereas on BP2000, a significant increase in selectivity toward the 4-electron reduction was observed in an alkaline environment. This is attributed to the wetting properties of the hydrophobic pores of BP2000, which considerably lower the dielectric constant in the pore water environment, stabilize the charged OOH − intermediate, and favor the 4-electron reduction pathway with the cobalt-bis-pentafluorophenyl (phenyl-para-carboxylic acid), when compared to analogous corroles with the COOH group at the ortho-and meta-positions.