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A good heterogeneous catalyst for a given chemical reaction very often has only one specific type of surface site that is catalytically active. Widespread methodologies such as Sabatier-type activity plots determine optimal adsorption energies to maximize catalytic activity, but these are difficult to use as guidelines to devise new catalysts. We introduce "coordination-activity plots" that predict the geometric structure of optimal active sites. The method is illustrated on the oxygen reduction reaction catalyzed by platinum. Sites with the same number of first-nearest neighbors as (111) terraces but with an increased number of second-nearest neighbors are predicted to have superior catalytic activity. We used this rationale to create highly active sites on platinum (111), without alloying and using three different affordable experimental methods.

H2O2 is a valuable, environmentally friendly oxidizing agent, with a wide range of uses, from the provision of clean water to the synthesis of valuable chemicals. The on-site electrolytic production of H2O2 would bring the chemical to applications beyond its present reach. The successful commercialization of electrochemical H2O2 production requires cathode catalysts with high activity, selectivity and stability. In this Perspective, we highlight our current understanding of the factors that control the cathode performance. We review the influence of catalyst material, electrolyte and the structure of the interface at the mesoscopic scale. We provide original theoretical data on the role of the geometry of the active site and its influence on activity and selectivity. We have also conducted a series of original experiments on (i) the effect of pH on H2O2 production on glassy carbon, pure metals, and metal-mercury alloys, and (ii) the influence of cell geometry and mass transport in liquid half-cells in comparison to membrane electrode assemblies.

 Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Polymer electrolyte membrane fuel cells are a promising alternative for future energy provision. However, their wider utilization is hindered by the slow rate of the oxygen reduction reaction (ORR) taking place at the cathode. In order to improve the ORR kinetics, alloys of Pt with late transition metals and lanthanides have been studied extensively, as they offer enhanced activity and in some cases acceptable stability. Nevertheless, many of these alloys are far from being “model objects”; and their surface composition and structure are not stable under operating conditions in PEMFCs. The solute metal can dissolve from the surface and near-surface layers. This process often results in a structure in which several Pt-enriched layers cover the bulk alloy and protect it from further dissolution. In this work, we analyze the literature results on the properties of these alloys, from single crystals and polycrystalline materials to nanoparticles, gathered in the recent decades. As a result of this analysis, we additionally propose a relatively simple method to overview the activities of dealloyed Pt n X-type alloys toward the ORR. Given that the Pt overlayer is several atomic layers thick, the so-called strain effects should primarily determine the behavior of these catalysts. The strain in the system is the result of the differences between the lattice parameters of the alloy and Pt-rich overlayers, causing dissimilar compressive strains in the lattice of the Pt-rich layer. This causes changes in the electronic structure and, consequently, in the binding properties of the surface. We propose that the atomic radius of the solute metal can be used in some particularly complex systems (e.g., polycrystalline and nanostructured alloys) as a simple semiempirical descriptor, statistically connected to the resulting lattice strain. The implications of this phenomenon can be used to qualitatively explain the behavior of e.g. some active Pt-alloy nanoparticles so far considered “anomalous”.

The effect of Nafion on the performance of a model Cumodified Pt(111) electrocatalyst has been investigated using electrochemical techniques and density functional theory calculations. In this work, we demonstrate that Cu subsurface alloying not only increases the activity of model Pt( 111) electrodes toward the oxygen reduction reaction (ORR) but also largely prevents catalyst poisoning by electrolyte components relevant for polymer electrolyte membrane fuel cell applications. Our results indicate that specific adsorption of (bi)sulfates and sulfonates (present in Nafion membranes) on the Cu-modified Pt(111) electrocatalyst is gradually suppressed, which implies that the ORR activity in 0.05 M H 2 SO 4 electrolyte drastically increases, with a change in the corresponding pseudo-half-wave potential of ∼93 mV. Importantly, the Cu-modified Pt(111) electrocatalyst in contact with Nafion polymer shows an activity as high as that in the absence of this polymer in perchloric acid media.

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Hydrogen peroxide is a commodity chemical, as it is an environmentally friendly oxidant.