Understanding the Structural Evolution of IrFeCoNiCu High-Entropy Alloy Nanoparticles under the Acidic Oxygen Evolution Reaction

Abstract

High-entropy alloy (HEA) nanoparticles are promising catalyst candidates for the acidic oxygen evolution reaction (OER). Herein, we report the synthesis of IrFeCoNiCu-HEA nanoparticles on a carbon paper substrate via a microwaveassisted shock synthesis method. Under OER conditions in 0.1 M HClO 4 , the HEA nanoparticles exhibit excellent activity with an overpotential of ∼302 mV measured at 10 mA cm −2 and improved stability over 12 h of operation compared to the monometallic Ir counterpart. Importantly, an active Ir-rich shell layer with nanodomain features was observed to form on the surface of IrFeCoNiCu-HEA nanoparticles immediately after undergoing electrochemical activation, mainly due to the dissolution of the constituent 3d metals. The core of the particles was able to preserve the characteristic homogeneous single-phase HEA structure without significant phase separation or elemental segregation. This work illustrates that under acidic operating conditions, the near-surface structure of HEA nanoparticles is susceptible to a certain degree of structural dynamics.

Surface segregation in high-entropy alloys from alchemical machine learning

“…In this section, we first validate the ML potential against DFT calculations for the prototypical Cantor alloy CoCrFeMnNi and comment on the suitability of 'static' approaches to evaluate segregation patterns, which are commonly used in combination with first-principles calculations [70]. Then, we perform simulations for an IrFeCoNiCu alloy and comment on the comparison with experimental data on the surface composition from [80].…”

“…Even though obtaining a realistic description of local ordering is necessary to extract reliable estimates of thermodynamical properties, experimental conditions often require a description of kinetic effects and of the presence of a reactive environment at the surface. To investigate these effects, we consider the case of an equimolar IrFeCoNiCu HEA, for which a detailed experimental characterization of the surface composition has been recently described [80]. We first compute the Gibbs surface excess following the same protocol we used for the CoCrFeMnNi alloy.…”

“…Even though the quantitative value of the segregation enthalpy is considerably smaller, there is no indication of a major discrepancy that might alter fundamentally the trends we observe with the non-magnetic ML potential. The comparison of these results with the experimental data in [80], shown in the inset, requires a brief description of the experimental setup. First, the IrFeCoNiCu nanoparticles synthesized in that work were treated with a 0.1 M solution of perchloric acid (HClO 4 ) at room temperature under an applied voltage, which essentially washed away the outer shell of the nanoparticle.…”

Colloidal Nanoparticles of High Entropy Materials: Capabilities, Challenges, and Opportunities in Synthesis and Characterization

“…Now we turn to some current and emerging trends in the field as well as opportunities for the future. As many of the currently anticipated applications of high entropy nanoparticles are in heterogeneous catalysis, issues of bulk and surface composition as well as stability in reactive environments become increasingly important . Also important for applications in heterogeneous catalysis are a fundamental understanding and quantitative description of strain modulation throughout the particle and surface as well as of the origin and implications of synergistic effects, including electronic, magnetic, and chemical properties.…”

Enhancing oxygen evolution reactions in nanoporous high-entropy catalysts using boron and phosphorus additives

“…Recent studies have shown that HEA catalysts and related materials are promising for use in water-splitting electrodes, and ongoing research is focused on optimizing their properties for this application. 10–13 HEA catalysts have several advantages over the traditional catalysts used in water-splitting electrodes. First, the multiple metallic elements in the catalyst can work together to enhance the catalytic activity, resulting in a higher reaction rate.…”