Graphite-Supported Pt_n Cluster Electrocatalysts: Major Change of Active Sites as a Function of the Applied Potential

Abstract

The oxygen reduction reaction (ORR) plays a key role in renewable energy transformation processes. Unfortunately, it is inherently sluggish, which greatly limits its industrial application. Sub-nano-cluster-decorated electrode interfaces are promising candidate ORR electrocatalysts. However, understanding the nature of the active sites on these catalysts under electrocatalytic conditions presents a formidable challenge for both experiment and theory, due to their dynamic fluxional character. Here, we combine global optimization with the electronic Grand Canonical DFT to elucidate the structure and dynamics of subnano Pt n clusters deposited on electrified graphite. We show that, under electrochemical conditions, these clusters exist as statistical ensembles of multiple states, whose fluxionality is greatly affected by the applied potential, electrolyte, and adsorbate coverage. The results reveal the presence of potential-dependent active sites and, hence, reaction energetics.

Electrocatalytic Hydrogen Evolution at Full Atomic Utilization over ITO-Supported Sub-nano-Ptn Clusters: High, Size-Dependent Activity Controlled by Fluxional Pt Hydride Species

“…In the presence of CO, Au 2 on ceria dissociates, whereas Au 3 survives. Reorganization of supported clusters under electrochemical potential and adsorbates of oxygen reduction reaction was also recently reported. , …”

“…In the presence of CO, Au 2 on ceria dissociates, whereas Au adsorbates of oxygen reduction reaction was also recently reported. 8,10 While small, electrode-supported Pt clusters allow reactant access to all the Pt atoms, it is unclear how cluster size affects reactivity of the atoms. The hydrogen adsorption energy is a key reactivity descriptor for HER, and extended Pt surfaces, such as Pt(111), have H binding energies that are slightly more negative but close to the theoretical optimum (ΔG ads ≈ 0 eV).…”

“…Due to their unique topologies and electronic properties, which are crucial to understanding their chemisorption properties, small nanoclusters are also interesting from a fundamental perspective. There may be substantial adsorbate-induced reconstructions for such a small cluster, altering the geometry and electronic structure of the active sites during the reaction, − maybe for the better. There is also the possibility for adsorbate- or potential-induced sintering or cluster disintegration, modifying the catalyst properties and possibly reducing the catalyst lifetime .…”

Corrosion of Electrochemical Energy Materials: Stability Analyses Beyond Pourbaix Diagrams

“…(Photo)­electrochemical processes may lead to the destabilization of thermodynamically stable materials and facilitate the formation of metastable phases. Depending on working conditions, these metastable phases may be short- or long-lived and even define the overall interfacial activity and stability. ,− Thus, in some cases, material interfaces can be in constant state of dynamic metastability making it challenging to analyze their properties based solely on equilibrium Pourbaix diagrams. Metastable phases may exhibit catalytic activity much higher than that of their thermodynamically stable parent structures, albeit often at the expense of their stability.…”

“…This also assumes that even if the electrode potential changes, it does so in a quasi-equilibrium fashion. This is not always the case in practice due to the transient operating conditions of many energy conversion devices including fuel cells and electrolyzers. − Moreover, the cycling between reducing and oxidizing potentials can be deliberately employed to steer reactivity of electrocatalysts . It was demonstrated, however, that such potential fluctuations may result in transient dissolution, i.e., dissolution during a transition between two thermodynamically stable phases.…”