The Catalyst Review December 2024 - 14

Experimental Abstracts
Tailored Design of Mesoporous Nanospheres with High
Entropic Alloy Sites for Efficient Redox Electrocatalysis
High-entropy alloys (HEAs) are complex multi-element
materials with diverse applications in energy, biomedicine,
and electronics. A notable feature of HEAs is their capacity to
facilitate pH-dependent electrocatalytic processes. Herein, the
authors describe a novel wet-chemical method using a
triblock copolymer to create mesoporous PtPdRuMoNi
nanospheres. These materials demonstrated exceptional
catalytic performance in hydrogen evolution and oxidation
reactions (HER and HOR) under alkline conditions, highlighting
their potential for advanced electrocatalytic applications.
The process for designing mesoporous PtPdRuMoNi HEA
nanospheres is illustrated in (Figure 1a). Synthesis is achieved
through a simple one-pot wet chemical reduction process that
utilizes Pluronic F-127 (F127) triblock copolymer as a pore-instituting
agent. F-127 consists of a hydrophobic block at the
center, flanked by two hydrophilic blocks. When the copolymer
interacts with an aqueous medium such as water, it forms
micelles with the hydrophobic branch as the core. High-entropy
alloy (HEA) nanosphere morphology and reactivity
can be tuned by adjusting solvent composition and reaction
time. The
nanospheres
grow through
multiple
coalescence events, with their crystalline structure depending on metal
ion precursor concentration. Polymeric micelles create mesopores,
enhancing surface area, pore volume, and reactant accessibility.
The optimized mesoporous HEA nanosphere (HEA10) demonstrates
excellent hydrogen evolution and oxidation reaction activities with
faster reaction kinetics in an alkaline medium. HEA10 exhibits a mass
activity of approximately 167 (HER) and 151 A gPt -1 (HOR) at a nominal
overpotential of 30 mV, which is significantly higher than that of stateof-the-art
Pt-C-based electrocatalysts (34 and 48 A gPt −1). This high
activity is attributed to HEA10's intrinsic catalytic active nature and
tendency for faster charge transfer owing to its high entropy alloying
features, as revealed by experimental outcomes, MS analysis, and
computational insights.
Figure 1. a) Schematic illustration of mesoporous PtPdRuMoNi
HEA nanospheres formation using a one-pot wet chemical
reduction process for overall hydrogen evolution and oxidation
reactions in alkaline media. The representative b) SEM, c) TEM,
and d) HAADF-STEM images of HEA10 (mesoporous PtPdRuMoNi
HEA nanospheres). The associated e) HRTEM image, f) FT
pattern, deduced from (e), g-j) corresponding set of planes and
concomitant interplanar spacing, deduced from (e) and (f)
for HEA10.
Figure 2. Mott-Schottky plots for a) Pt-C and b) HEA10
in nitrogen purged 0.1 m KOH aqueous solution (Xintercept
in MS plot shows the respective flat band
potential (Vfb)). c) An illustration showing an upward
bending of the band edges for an n-type material at
the electrode-electrolyte interface at thermodynamical
equilibrium. (Flat band potential determines the
magnitude of band bending.) d) Calculated Gibbs free
energy profiles (in eV) for HER and HOR on the (111)
facet of HEA and Pt systems at 0.0 V versus RHE. The
brown and teal numbers correspond to the activation
free energy of the rate-determining step of HER and
HOR, respectively
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The Catalyst Review
Mott-Schottky (MS) analysis was then employed to better understand
the electrocatalysts' behavior at the electrode-electrolyte interface in an
alkaline medium (Figure 2a,b). The HEA10, with its high charge carrier
density, was expected to exhibit better space charge redistribution,
generating a stronger built-in electric field in the space charge region.
The resulting enhanced electronic interactions at the electrode-electrolyte
interface offer optimal adsorption/desorption of intermediate
species and comparatively fast charge transfer kinetics. The lower
activation energy on the HEA surface obtained in these calculations is
consistent with higher HOR kinetics than Pt-C-based
electrocatalysts. Nandan R, Nara H, Nam HN, et al. (2024) Adv. Sci.
https://doi.org/10.1002/advs.202402518
December 2024
https://www.doi.org/10.1002/advs.202402518
The Catalyst Review December 2024

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