The sluggish kinetics associated with the oxygen reduction reaction (ORR) at the proton exchange membrane fuel cell cathode leads to high overpotentials and limits fuel cell performance. Although significant progress has been made in first-principles modeling of the ORR, the complexity of the electrified aqueous/metal interface has limited advances in the use of theory to elucidate the influence of electrode potential on the mechanism and kinetics. The first reduction step of adsorbed molecular oxygen has been speculated to be the rate-determining step in the ORR. Periodic density functional theoretical calculations are carried out with the double-reference method developed by Filhol and Neurock [ Angew. Chem. Int. Ed. , 45 , 402 (2006)] to determine the potential dependence of the reaction energy and activation barrier for the reduction of <mml:math display="inline"><mml:msubsup><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mo>*</mml:mo></mml:msubsup></mml:math>O2* to <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">O</mml:mi><mml:mi mathvariant="normal">O</mml:mi><mml:msup><mml:mi mathvariant="normal">H</mml:mi><mml:mo>*</mml:mo></mml:msup></mml:mrow></mml:math>OOH* on the fully hydrated Pt(111) surface. This method allows for tuning the electrode potential with a slab representation of the electrode surface. Electron transfer is found to precede the protonation of the adsorbed <mml:math display="inline"><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>O2 molecule, occurring with the proton formally residing as an <mml:math display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub><mml:msup><mml:mi mathvariant="normal">O</mml:mi><mml:mo>+</mml:mo></mml:msup></mml:mrow></mml:math>H3O+ species connected to the adsorbed <mml:math display="inline"><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>O2 molecule by hydrogen bonding through two additional water molecules. The importance of the periodic representation of the metal electronic structure and the inclusion of extended solvation in considering the elementary kinetics is discussed.

We report calculated oxygen reduction reaction energy pathways on multi-metal-atom structures that have previously been shown to be thermodynamically favorable. We predict that such sites have the ability to spontaneously cleave the O₂ bond and then will proceed to over-bind reaction intermediates. In particular, the *OH bound state has lower energy than the final 2 H₂O state at positive potentials. Contrary to traditional surface catalysts, this *OH binding does not poison the multi-metal-atom site but acts as a modifying ligand that will spontaneously form in aqueous environments leading to new active sites that have higher catalytic activities. These *OH bound structures have the highest calculated activity to date.

First-principles calculations based on the projector augmented-wave (PAW) technique have been applied to the prediction of materials properties of $\alpha$-uranium and its (001) surface. The results of the PAW calculations are shown to be comparable in accuracy to the full-potential calculations reported elsewhere. In addition to calculating lattice constants and elastic moduli, the vacancy formation energy $\left(1.95\mathrm{eV}\right)$, (001) surface relaxation ($-3.5\%$ for ${\delta }_{12}$ and $+1.2\%$ for ${\delta }_{23}$), (001) surface energy $(1.4\mathrm{J}∕{\mathrm{m}}^2)$, and (001) work function $\left(3.6\mathrm{eV}\right)$ were also obtained. The overall agreement with experiment is satisfactory. Using an elastic model for brittle-crack failure, a yield stress of $430\mathrm{MPa}$ was estimated. Further exploration of materials failure modes (such as plastic deformation) awaits a larger-scale atomistic treatment. Full spin-orbit and scalar relativistic calculations were shown to give results with similar levels of accuracy compared to experiment.

Parabolic rate constants, k_p, were collected from published reports and calculated from corrosion product data (sample mass gain or corrosion product thickness) and tabulated for 75 alloys exposed to temperatures between ~800 and 2000 K (~500–1700 ^oC; 900–3000 ^oF). Data were collected for environments including lab air, ambient and supercritical carbon dioxide, supercritical water, and steam. Materials studied include low- and high-Cr ferritic and austenitic steels, nickel superalloys, and aluminide materials. A combination of Arrhenius analysis, simple linear regression, supervised and unsupervised machine learning methods were used to investigate the relations between composition and oxidation kinetics. The supervised machine learning techniques produced the lowest mean standard errors. The most significant elements controlling oxidation kinetics were Ni, Cr, Al, and Fe, with Mo and Co composition also found to be significant features. The activation energies produced from the machine learning analysis were in the correct distributions for the diffusion constants for the oxide scales expected to dominate in each class.