We present a joint experimental and density functional theory (DFT) study on the effect of atomic vacancies on the restructuring of platinum—transition metal alloy nanocatalysts and the associated changes in electrocatalytic activity. Atomic vacancies were introduced into slabs composed of pure Pt monolayers, and the structures were relaxed using the Vienna ab initio simulation package code. Effects of i) the concentration and ii) the spatial distribution of atomic vacancies in the slabs on surface and bulk restructuring were investigated. Highly disordered nanostructures featuring large variations of the in‐plane and out‐of‐plane nearest‐neighbour distances around the mean were observed upon relaxation. These findings were confirmed experimentally by using hollow PtNi/C nanoparticles synthesized by a combination of galvanic replacement and the nanoscale Kirkendall effect (a vacancy‐mediated interdiffusion mechanism). The experimental results also show that hollow PtNi/C nanoparticles feature a combination of oxophilic and oxophobic catalytic sites on their surface and are thus highly active both for electrochemical oxidation and reduction reactions.
In the course of (electro)catalytic reactions, reversible and irreversible changes, namely the formation of adsorbed poisons, catalyst degradation, surface roughening, etc., take place at distinct time-scales. Reading the transformations on the catalyst surface from the measurement of the reaction rates is greatly desirable but generally not feasible. Herein, we study the effect of random surface defects on Pt(100) electrodes toward the electro-oxidation of methanol in acidic media. The surface defects are gently generated in situ and their relative magnitudes are reproducibly controlled. The system was characterized under conventional conditions and investigated under an oscillatory regime. Oscillatory patterns were selected according to the presence of surface defects, and a continuous transition from large amplitude/low frequency oscillations (type L) on smooth surfaces to small amplitude/high frequency oscillations (type S) on disordered surfaces was observed. Importantly, self-organized potential oscillations were found to be much more sensitive to the surface structure than conventional electrochemical signatures or even other in situ characterization methods. As a consequence, we proved the possibility of following the surface fine structure in situ and in a non-invasive manner by monitoring the temporal evolution of oscillatory patterns. From a mechanistic point of view, we describe the role played by surface defects and of the adsorbed and partially oxidized, dissolved species on the oscillations of type S and L.
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