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Peak performance: Electrochemical experiments show that the oxygen reduction reaction (ORR) on platinum monolayers supported on various transition metals exhibits a volcano‐type behavior (see graph). Calculations reveal that bond‐breaking occurs more easily as bond‐making becomes harder, and why the Pd‐supported Pt monolayer (PtML/Pd(111)) has higher ORR activity than pure Pt(111).

Self-consistent periodic density functional theory calculations (GGA-PW91) have been performed to study the adsorption of O and O(2) and the dissociation of O(2) on the (111) facets of ordered Pt(3)Co and Pt(3)Fe alloys and on monolayer Pt skins covering these two alloys. Results are compared with those obtained on two Pt(111) surfaces, one at the equilibrium lattice constant and the other laterally compressed by 2% to match the strain in the Pt alloys. The absolute magnitudes of the binding energies of O and O(2) follow the same order in the two alloy systems: Pt skin < compressed Pt(111) < Pt(111) < Pt(3)Co(111) or Pt(3)Fe(111). The reduced activity of the compressed Pt(111) and Pt skins for oxygen can be rationalized as being due to the shifting of the d-band center increasingly away from the Fermi level. We propose that an alleviation of poisoning by O and enhanced rates for reactions involving O may be some of the reasons why Pt skins are more active for the oxygen reduction reaction in low-temperature fuel cells. Finally, a linear correlation between the transition-state and final-state energies of O(2) dissociation on monometallic and bimetallic surfaces is revealed, pointing to a simple way to screen for improved cathode catalysts.

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We report that the addition of alkali ions (sodium or potassium) to gold on KLTL-zeolite and mesoporous MCM-41 silica stabilizes mononuclear gold in Au-O(OH)x-(Na or K) ensembles. This single-site gold species is active for the low-temperature (<200°C) water-gas shift (WGS) reaction. Unexpectedly, gold is thus similar to platinum in creating -O linkages with more than eight alkali ions and establishing an active site on various supports. The intrinsic activity of the single-site gold species is the same on irreducible supports as on reducible ceria, iron oxide, and titania supports, apparently all sharing a common, similarly structured gold active site. This finding paves the way for using earth-abundant supports to disperse and stabilize precious metal atoms with alkali additives for the WGS and potentially other fuel-processing reactions.

The activation of dioxygen via dissociation on strained and stepped gold surfaces has been studied using periodic self-consistent (GGA-PW91) density functional theory (DFT) calculations. Although we find that molecular oxygen does not adsorb on Au(111), it does bind, albeit weakly, to an Au(111) surface stretched by 10% as well as to Au(211) surfaces both stretched and unstretched. The most stable molecular states on all three surfaces have the top-bridge-top configuration and carry about half of the magnetic moment of gas-phase O 2 . On 10%-stretched Au(111), unstretched Au(211), and 10%-stretched Au(211), the binding energies of O 2 are -0.08, -0.15, and -0.26 eV, respectively, and the activation energies of O 2 dissociation are 1.37, 1.12, and 0.63 eV. Both steps and tensile strain enhance the adsorption of atomic and molecular oxygen. A comparison between unstretched and stretched Au(211) indicates that the enhancing effect of tensile strain is less pronounced on the step edge than on the flat terrace. The magnitude of the dissociation barriers, combined with the fact that the transition states lie above the gas-phase zero on all three surfaces, suggests that O 2 dissociation remains an activated process on gold. Although additional factors may be involved in O 2 activation at low temperatures on oxide-supported Au catalysts, the present work shows that steps and tensile strain substantially facilitate O 2 activation on Au surfaces.

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Peroxidase mimics with dimensions on the nanoscale have received great interest as emerging artificial enzymes for biomedicine and environmental protection. While a variety of peroxidase mimics have been actively developed recently, limited progress has been made toward improving their catalytic efficiency. In this study, we report a type of highly efficient peroxidase mimic that was engineered by depositing Ir atoms as ultrathin skins (a few atomic layers) on Pd nanocubes (i.e., Pd-Ir cubes). The Pd-Ir cubes exhibited significantly enhanced efficiency, with catalytic constants more than 20- and 400-fold higher than those of the initial Pd cubes and horseradish peroxidase (HRP), respectively. As a proof-of-concept demonstration, the Pd-Ir cubes were applied to the colorimetric enzyme-linked immunosorbent assay (ELISA) of human prostate surface antigen (PSA) with a detection limit of 0.67 pg/mL, which is ∼110-fold lower than that of the conventional HRP-based ELISA using the same set of antibodies and the same procedure.