RESEARCH ARTICLE
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A High-Entropy Oxyhydroxide with a Graded Metal Network
Structure for Eﬃcient and Robust Alkaline Overall Water
SplittingChen-Xu Zhang, Di Yin, Yu-Xuan Zhang, Yu-Xiang Sun, Xiao-Jin Zhao, Wu-Gang Liao,*
and Johnny C. Ho*

Designing high-entropy oxyhydroxides (HEOs) electrocatalysts with
controlled nanostructures is vital for eﬃcient and stable water-splitting
electrocatalysts. Herein, a novel HEOs material (FeCoNiWCuOOH@Cu)
containing ﬁve non-noble metal elements derived by electrodeposition on a
3D double-continuous porous Cu support is created. This support, prepared
via the liquid metal dealloying method, oﬀers a high speciﬁc surface area andrapid mass/charge transfer channels. The resulting high-entropy
FeCoNiWCuOOH nanosheets provide a dense distribution of active sites. The
heterostructure between Cu skeletons and FeCoNiWCuOOH nanosheets
enhances mass transfer, electronic structure coupling, and overall structural
stability, leading to excellent activities in the oxygen evolution reaction (OER),
hydrogen evolution reaction (HER), and water splitting reaction. At
10 mA cm−2 , the overpotentials for OER, HER, and water splitting in 1.0 m
KOH solution are 200, 18, and 1.40 V, respectively, outperforming mostcurrent electrocatalysts. The catalytic performance remains stable even after
operating at 300 mA cm−2 for 100, 100, and over 1000 h, correspondingly.
This material has potential applications in integrated hydrogen energy
systems. More importantly, density functional theory (DFT) calculations
demonstrate the synergy of the ﬁve elements in enhancing water-splitting
activity. This work oﬀers valuable insights for designing industrial waterelectrolysis systems.

C.-X. Zhang, Y.-X. Sun, X.-J. Zhao, W.-G. Liao
State Key Laboratory of Radio Frequency Heterogeneous Integration(Shenzhen University)
College of Electronics and Information Engineering
Shenzhen 518060, China
E-mail: wgliao@szu.edu.cn

The ORCID identiﬁcation number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/advs.202406008© 2024 The Author(s). Advanced Science published by Wiley-VCH
GmbH. This is an open access article under the terms of the Creative
Commons Attribution License, which permits use, distribution andreproduction in any medium, provided the original work is properly cited.

1. Introduction
Hydrogen energy is one of the most promising ways to achieve decarbonization goals,
owing to its sustainability, high energy
density, and environmentally friendly attributes. Electrocatalytic water splitting has
become an ideal strategy for converting intermittent renewable energy into hydrogenfuel.[1–4] Despite the current prominenceof catalysts containing precious metals likePt and Ir for this process, their scarcity
and high cost severely constrain theirwidespread practical applications. Consequently, extensive research eﬀorts are directed toward developing low-cost and efﬁcient electrocatalysts based on transition
metals abundant in the Earth’s crust.[5–7]Single transition metals (Fe, Co, Ni, W, Mo,
Cu, etc.) typically exhibit moderate catalytic
activity, whereas alloys comprising these elements can modulate the number of active
site moles (geometric eﬀects) and electronic
structures (electronic eﬀects),[8–13] thereby
generating an ideal catalytic transition statewith the minimum energy barrier, continuously improving the performance of electrocatalytic water splitting.

C.-X. Zhang, D. Yin, Y.-X. Zhang, J. C. Ho
Department of Materials Science and Engineering
City University of Hong Kong
Hong Kong, SAR 999077, P. R. China
E-mail: johnnyho@cityu.edu.hk
J. C. Ho
State Key Laboratory of Terahertz and Millimeter Waves
City University of Hong Kong
Hong Kong, SAR 999077, P. R. China
J. C. Ho
Institute for Materials Chemistry and Engineering
Kyushu University
Fukuoka 816-8580, Japan

DOI: 10.1002/advs.202406008

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HEOs are a class of emerging materials composed of ﬁve
or more primary metallic elements.[14–16] They consist of oxyhydroxides and high-entropy structures. Oxyhydroxides exhibit
diversity in elemental composition, ﬂexibility in structure,and simplicity in preparation, making them one of the mosteﬀective electrocatalysts for water splitting.[17,18] High-entropy
engineering holds promise for further enhancing the electrocatalytic water-splitting performance of oxyhydroxides.[19,20]
Through the synergistic eﬀect of multiple metal components,
precise control of geometric morphology, optimized electronic
structure, and outstanding chemical and thermal stability,[21–23]
HEOs demonstrate enormous potential in energy storage andelectrocatalysis.
In addition to selecting electrocatalytic water-splitting materials with high intrinsic activity, facilitating the adsorption, reaction, and desorption of reactants with a large speciﬁc surface area
is crucial for eﬀectively harnessing the high catalytic activity ofhigh-entropy materials.[24–26] Apart from widely studied particle
catalysts, nanoporous metals, serving as structure-function integrated materials, possess a 3D double-continuous open porous
structure, high speciﬁc surface area, and high conductivity, which
promote mass transfer within internal porous channels.[27–29]
Moreover, nanoporous matrices readily integrate with other active substances, enabling template strategies to precisely control
the loading amount and interface structure, further enhancing
catalytic performance.[30]Herein, we have developed a novel FeCoNiWCuOOH@Cu
heterostructure HEOs material, leveraging the structural advantages of 3D double-continuous pores and the dual-component
design concept of HEOs, exhibiting high catalytic activity andlong-term stability for eﬃcient electrocatalytic alkaline water
splitting reactions. The optimized FeCoNiWCuOOH@Cu
electrode demonstrated an excellent performance in the
OER/HER/water splitting reactions with overpotentials of200, 18, and 1.40 V, respectively, at 10 mA cm−2 in KOH (1 m)solution. Notably, at a high current density of 300 mA cm−2 , itexhibited remarkable durability and stability, operating for 100,
100, and 1000 h or more. Among them, the Cu carrier, preparedusing the liquid dealloying method, features a 3D doublecontinuous porous structure, providing advantages such as highconductivity, high speciﬁc surface area, and rapid charge/masstransfer. By leveraging the structural advantages of Cu carriers,
FeCoNiWCuOOH NS growth was suﬃciently promoted, ensuring the enrichment and widespread distribution of multiple
active sites. The high-entropy “cocktail” eﬀect, arising from themulti-element composition and unique microstructure of HEOs,
led to unexpected nonlinear results. The entropy stabilizationeﬀect near the surface eﬀectively countered the inﬂuence of surface electrochemical oxidation-reduction, resulting in long-term
stable activity. Further, DFT calculations demonstrated that thesynergistic eﬀect of the ﬁve elements enhanced the electrocatalytic water-splitting activity of the catalyst. The rich selectivityof elements and precise regulation of nanostructures injected
new vitality into the industrial application of high-entropy catalysts in long-term and eﬃcient electrocatalytic water-splitting
reactions.

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2. Results and Discussion
2.1. Synthesis and Structural Characterization of
FeCoNiWCuOOH@Cu System Electrocatalysts
The FeCoNiWCuOOH@Cu catalyst was synthesized using asimple and scalable alloy-dealloying method combined with
an electrodeposition technique (see Experimental Section,
Figure 1a; Figure S1, Supporting Information, for details). The
preparation of AlCu alloy was achieved through suﬃcient mixing of liquid metals using the high-temperature alloying method.
X-ray diﬀraction (XRD), scanning electron microscope (SEM),
and Brunauer-Emmett-Teller (BET) tests (Figure S2, Supporting
Information) conﬁrmed that the AlCu alloy is an intermetallic
compound composed of Al and Al2 Cu, featuring a dense structure without voids, resulting in a speciﬁc surface area of only
0.882 m2 g−1 . Subsequently, upon chemical dealloying of Al element with 2 m hydrochloric acid solution, the intermetallic
compound gradually transformed into a double-continuous poreCu framework with interconnected large channels and small
nanopores. Notably, chloride ions played a crucial role in promoting the surface diﬀusion of Cu, facilitating the formation of larger
ligaments, and enhancing anti-coarsening stability.[31] To further
improve activity and stability, chemically active 3D transition
metals such as Fe, Co, Ni, and 5d metal W were introduced into
Cu. FeCoNiWCuO was in situ grown on the Cu framework using
the electrochemical deposition method, and FeCoNiWCuOOH
NS were generated through electrochemical oxidation. The double hydroxide layer on the surface played a vital role in enhancing anti-coarsening stability by reducing surface energy.[31] Cu,
CuOOH@Cu, FeCuOOH@Cu, FeWCuOOH@Cu, and FeNiWCuOOH@Cu samples were prepared separately using thesame method.
The SEM images of FeCoNiWCuOOH@Cu (Figure 1b) reveal a typical hierarchical porous structure consisting of interpenetrating large channels and small nanopores within interconnected Cu ligaments. From the enlarged view in Figure 1b, many
nanoparticles (NPs) can be observed forming the skeleton of thiscontinuous channel structure, ﬁlled with secondary nanoporous
structures. These structures are beneﬁcial for increasing the speciﬁc surface area, facilitating the widespread distribution of active
sites, and promoting electrolyte diﬀusion, thereby enhancing effective electrochemical reactions on the catalyst surface.[32,33] In
the transmission electron microscope (TEM) image (Figure 1c),the loose porous surface of the FeCoNiWCuOOH@Cu catalyst
is observed to be ﬁlled with ultra-thin NS structures, identiﬁed
as FeCoNiWCuOOH NS formed through the electrochemical
reduction process. This ultrathin NS structure eﬀectively optimizes the diﬀusion distance and charge transfer rate between
reactants and products, thereby accelerating mass/charge transfer during the catalytic process. Notably, the surface-distributed
small nanopores have an average size of ≈10 nm and are evenly
distributed on the surface of the Cu framework.[34] The type III
nitrogen adsorption/desorption isotherm of the hierarchicallyporous FeCoNiWCuOOH@Cu catalyst exhibits accelerated adsorption characteristics. The nanopore size distribution shows© 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH21983844, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202406008 by Johnny Ho - City University Of Hong Kong , Wiley Online Library on [13/09/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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Figure 1. Microstructure properties of FeCoNiWCuOOH@Cu. a) Synthesis diagram, b) SEM, and c) TEM images, the inset of (b) and (c) are the enlarged
view of the corresponding positions, respectively, d) HRTEM image, e,f) strain distribution along Exy of (d), the compressive strain showed a shift fromgreen to dark blue, and the tensile strain showed a shift from bright yellow to red, g,h) the measured interplanar distances, i,j) FFT patterns, and k)
HAADF-STEM image and its corresponding EDS elemental mappings of FeCoNiWCuOOH@Cu.

a distinct peak centered at ≈11.85 nm, indicative of a typical
nanopore structure formed by Cu NPs (Figure S3, Supporting
Information).
High-resolution TEM (HR-TEM) was employed to investigate the detailed atomic structure of FeCoNiWCuOOH@Cu(Figure 1d). A distinct heterostructure between Cu NPs and FeCoNiWCuOOH NS is observed, indicating a continuous andstable heterostructure with strong coupling eﬀects. This facilitates eﬃcient charge transfer and further enhances the activ-

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ity and stability of the system through synergistic eﬀects.[35,36]
Furthermore, the high-temperature melting reaction produces
short- and long-range ordering of Cu ligaments. Due to themismatch in element mass, size, and bond state, severe lattice distortion occurs, leading to short-range disordered latticestripes in the FeCoNiWCuOOH material. This is conﬁrmed by
the geometric phase analysis (GPA) image (Figure 1e) obtained
from Figure 1d, further conﬁrming the multi-element solid solution structure of FeCoNiWCuOOH.[37] Comparing HRTEM© 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH21983844, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202406008 by Johnny Ho - City University Of Hong Kong , Wiley Online Library on [13/09/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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Figure 2. Chemical characterization. a) XRD patterns, b) Raman patterns, c) in situ Raman spectroscopy, and d) XPS spectra of O 1s of diﬀerent samples.

with GPA images (Figure 1f), it is evident that lattice strain primarily occurs in the FeCoNiWCuOOH structure, whereas lattice strain is less evident in the Cu skeleton. This diﬀerenceis also a contributing factor to the high activity of FeCoNiWCuOOH. Additionally, the stability of the FeCoNiWCuOOH
material’s structure maintains orderly long-range atom arrangements, thereby sustaining a stable charge transport structure.
HR-TEM images of Cu NPs and FeCoNiWCuOOH NS reveal
lattice fringes with spacings of 1.27 (Figure 1d,g,i), 1.227, and1.267 Å (Figure 1d,h,j), respectively, corresponding to the (220),(222), and (004) diﬀraction facets of Cu, Cu2 O, and CuO. This
indicates that FeCoNiWCuOOH NS grows on the Cu skeleton
composed of Cu NPs, and the high-entropy NS structure still
mainly exhibits a copper oxide crystal structure. The atomic ratios of various elements in the FeCoNiWCuOOH@Cu catalyst(Fe/Co/Ni/W/Cu/O = 4.05/5.52/5.29/0.01/43.89/41.24) were analyzed using TEM-related energy dispersive X-ray spectroscopy(EDS) (Figure S4, Supporting Information). The high content of
Cu and O indicates the generation of a certain amount of copper oxide in the system. Aberration-corrected high-angle annulardark-ﬁeld scanning transmission electron microscopy (HAADFSTEM) image and related EDS elemental imaging distribution
diagrams (Figure 1k) demonstrate a uniform distribution of Fe,
Co, Ni, W, Cu, and O elements in the FeCoNiWCuOOH@Cu catalyst. Additionally, Analysis of the HRTEM and corresponding
GPA images (Figure S5, Supporting Information) reveals that theformation of a hydroxide oxide layer on the Cu substrate surface
enhances its resistance to coarsening. As the number of metal elements increases, the hydroxide oxide layer exhibits more kinks
and step sites, leading to more grain boundaries and defects. This
is indicative of the strain and cocktail eﬀects. Moreover, SEM
morphology, EDS element distribution, and atomic ratios of Cu(Figure S6, Supporting Information), CuOOH@Cu (Figure S7,Adv. Sci. 2024, 2406008

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Supporting Information), FeCuOOH@Cu (Figure S8, Supporting Information), FeWCuOOH@Cu (Figure S9, Supporting Information) and FeNiWCuOOH@Cu (Figure S10, Supporting Information) exhibit similar characteristics.

2.2. Phase Structure and Electronic State Analysis of
FeCoNiWCuOOH@Cu System Electrocatalysts
The composition of the FeCoNiWCuOOH@Cu system was further characterized by X-ray diﬀraction (XRD) patterns (Figure2a). The results reveal that the primary structure of the doublecontinuous pore framework consists of Cu elements. However,the presence of Cu2 O was observed due to the weak oxidation of the Cu framework by oxygen in both air and solution. Following the electrochemical hydroxylation process, Cu2 O
gradually oxidizes to CuO, as evidenced by the appearance ofCuO diﬀraction peaks in the XRD curves of CuOOH@Cu, FeCuOOH@Cu, FeWCuOOH@Cu, FeNiWCuOOH@Cu, and FeCoNiWCuOOH@Cu. Moreover, due to the amorphous natureof the hydroxyl oxide formed on the surface of the Cu skeleton,
no corresponding diﬀraction peaks are observed in the XRD pattern. Hence, Raman spectroscopy testing (Figure 2b) was conducted to detect the presence of hydroxyl oxides. The results
indicate the detection of not only CuO and Cu2 O after electrochemical hydroxylation but also the presence of CuOOH and 𝛾NiOOH/CoOOH.[38–41] To monitor real-time changes in crystal
structure during the electrochemical hydroxylation process, insitu electrochemical Raman spectroscopy testing was performedon FeCoNiWCuOOH@Cu (Figure 2c; Figure S11, Supporting
Information). The ﬁndings reveal a gradual weakening of the
Cu2 O peak and an increase in the CuO peak as the electrochemical hydroxylation process progresses, suggesting the progressive© 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH21983844, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202406008 by Johnny Ho - City University Of Hong Kong , Wiley Online Library on [13/09/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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oxidation of Cu2 O to CuO. Additionally, the peak corresponding
to CuOOH and 𝛾-NiOOH/CoOOH increases gradually during
the electrochemical process, indicating the gradual formation ofan amorphous metal hydroxyl oxide layer on the surface of theCu skeleton. In the high wavenumber range of the Raman plot
(Figure S12, Supporting Information), no peaks corresponding
to common intercalated anions (e.g., NO3 − ,[42] CO3 2- .[43] ) wereobserved. This conﬁrms that the generated structure is a MetalOOH rather than a layered double hydroxide. Inert gas ion bombardment was utilized to sequentially etch the surface of the FeCoNiWCuOOH@Cu sample layer by layer, and the X-ray photoelectron spectroscopy (XPS) spectra of O 1s after each etching
step were examined (Figure 2d). The results indicate a gradualdisappearance of the metal hydroxide peak with increasing etching depth, while the metal oxide peak still exists. This further conﬁrms the transformation of the metal oxide layer on the sample’s
surface into a metal oxide/metal hydroxyl oxide layer during theelectrochemical hydroxylation process. Based on comprehensive
XRD, Raman, in−situ electrochemical Raman, and XPS analyses,
it can be concluded that FeCoNiWCuO gradually transforms into
FeCoNiWCuOOH during the electrochemical hydroxylation process, rendering it suitable for subsequent electrocatalytic testing.
XPS was utilized to investigate the near-surface electronic
structure and oxidation state of all samples. The XPS wide scanmeasurement spectrum conﬁrmed the presence of Fe, Co, Ni, W,
Cu, and O elements (Figure S13, Supporting Information). Highresolution XPS spectra (Figures S14–S19, Supporting Information) of corresponding O 1s, Cu 2p, Fe 2p, W 4f, Ni 2p, and Co 2p
for Cu, CuOOH@Cu, FeCuOOH@Cu, FeWCuOOH@Cu, FeNiWCuOOH@Cu, and FeCoNiWCuOOH@Cu were collected. The
O 1s spectra consist of metal oxide peaks attributed to Cu2 O/CuO
and metal hydroxide peaks attributed to Cu(OH)2 . Cu 2p spectra
can be indexed as the Cu0 peak of the Cu skeleton, the Cu1+ peakof Cu2 O, and the Cu2+ peak of CuO. Fe 2p spectra can be deconvoluted into two pairs of Fe2+ and Fe3+ , along with a pair of satellite peaks. The W 4f spectra can be attributed to W6+ , while Ni
2p spectra can be indexed as the Ni2+ peak and a pair of satellite
peaks. Co 2p spectra can be deconvoluted into two pairs of Co2+
and Co3+ , along with a pair of satellite peaks. Due to the inﬂuence of electrochemical deposition and hydroxylation reactions,
all metal elements in FeCoNiWCuOOH@Cu mainly exist in highoxidation states, which is beneﬁcial for alkaline OER to exhibit
high electrocatalytic activity. Additionally, oxygen-related species
in FeCoNiWCuOOH@Cu are often considered active sites forcatalyzing OER.[44] Comparing the XPS ﬁne spectra of Cu 2p before and after the hydroxylation process (Figure S20, Supporting
Information), it can be seen that after electrochemical hydroxylation, the Cu2+ peak of Cu in XPS shifts to a higher energy level,
indicating the formation of CuOOH.[45]2.3. OER Activity of FeCoNiWCuOOH@Cu System
Electrocatalysts
The electrocatalytic activity for alkaline OER of FeCoNiWCuOOH@Cu system catalysts in 1 m KOH electrolyte
was evaluated using linear sweep voltammetry (LSV) in athree-electrode system, with commercial RuO2 /Cu catalysts
measured and studied for comparison. From the polarization

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curves depicted in Figure 3a,b, it is evident that the FeCoNiWCuOOH@Cu sample exhibits superior OER performance.
At a current density of 10 mA cm−2 , FeCoNiWCuOOH@Cu
requires an overpotential of only 200 mV, which is notably
better than FeNiWCuOOH@Cu (279 mV), FeWCuOOH@Cu(315 mV), FeCuOOH@Cu (290 mV), CuOOH@Cu (341 mV),and RuO2 /Cu (240 mV) catalysts. The corresponding Tafel curves(Figure 3c) further indicate that FeCoNiWCuOOH@Cu possesses a lower Tafel slope of 24 mV dec−1 , signiﬁcantly smaller
than FeNiWCuOOH@Cu (23 mV dec−1 ), FeWCuOOH@Cu(23 mV dec−1 ), FeCuOOH@Cu (52 mV dec−1 ), CuOOH@Cu(50 mV dec−1 ), and RuO2 /Cu (38 mV dec−1 ) catalysts.
This highlights the rapid OER kinetic charge transfer of
FeCoNiWCuOOH@Cu.[46] Furthermore, the double-continuous
pore structure of the FeCoNiWCuOOH@Cu catalyst not only
utilizes industrially scalable preparation methods (produced
using industrial-scale metallurgical techniques (ranging fromtons to millions of tons) but also employs simple dealloying andelectrochemical deposition processes to achieve OER activity).
Its performance signiﬁcantly surpasses other noble metal andnon-noble metal-based electrocatalysts (Figure 3d; Table S1,
Supporting Information), demonstrating its enormous potential
for near-term commercialization.[47] In addition, we conducted
the electrochemical tests of the catalysts before and after theelectrochemical activation process (hydroxylation) (Figure S21,
Supporting Information). The results showed that due to theintroduction of high-entropy structures, the active sites of thecatalysts gradually increased (lattice distortion led to many
kinks, step edges, and grain boundaries), resulting in a gradualimprovement in electrochemical performance.
Subsequently, the OER electrochemical active surface area
(ECSA) of the catalyst was measured using double-layer capacitance (Cdl ) to gain a deeper understanding of the intrinsic catalytic activity of the FeCoNiWCuOOH@Cu system. The Cdl isderived from the cyclic voltammetry (CV) curve (Figure S22,
Supporting Information). According to calculations, the ECSA
value of FeCoNiWCuOOH@Cu can reach 1812 cm2 (Figure 3e),≈1.61, 1.32, 1.33, and 1.16 times that of CuOOH@Cu, FeCuOOH@Cu, FeWCuOOH@Cu, and FeNiWCuOOH@Cu, respectively. The large ECSA value of FeCoNiWCuOOH@Cu indicates that owing to the porous double-continuous pore structure and various metal components, it not only provides a sizeable electrochemical interface and more active sites but alsoenhances the availability of active sites in electrocatalytic reactions and promotes the adsorption of water molecules andclose contact with electrolytes. The intrinsic activity of FeCoNiWCuOOH@Cu was evaluated using the ECSA normalized LSV
curves, as shown in Figure S23 (Supporting Information). FeCoNiWCuOOH@Cu exhibits signiﬁcant intrinsic activity, requiring only 256 mV of overpotential to achieve a normalized current
density of 0.01 mA cm−2 for ECSA. This value is signiﬁcantly
lower than CuOOH@Cu (377 mV), FeCuOOH@Cu (331 mV),
FeWCuOOH@Cu (342 mV), and FeNiWCuOOH@Cu (316 mV).
The results indicate that the high-entropy structure, heterostructure, and double-continuous pore structure can all improve catalytic performance, with the ﬁrst two enhancing intrinsic catalytic activity and the latter signiﬁcantly increasing available active sites.[48–50] To further evaluate the intrinsic activity of the catalyst, the O2 turnover frequency (TOF) of FeCoNiWCuOOH@Cu© 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH21983844, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202406008 by Johnny Ho - City University Of Hong Kong , Wiley Online Library on [13/09/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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Figure 3. Electrochemical characterization on OER properties. a) Polarization curves, b) corresponding overpotentials, and c) Tafel slopes of diﬀerent
samples in 1 m KOH solution. d) Overpotentials at 10 mA cm−2 of the as-obtained FeCoNiWCuOOH@Cu electrocatalyst in comparison with reported
related electrocatalysts. e) ECSA histograms of diﬀerent samples. f) TOF pattern of the as-obtained FeCoNiWCuOOH@Cu electrocatalyst in contrast
with reported related electrocatalysts. g) EIS curves of other samples. h) Contact angle photos of FeCoNiWCuOOH@Cu. i) Constant current curve of
FeCoNiWCuOOH@Cu at 300 mA cm−2 current density for 100 h.

was calculated (Figure S24, Supporting Information) and compared with recently reported related catalysts (Figure 3f; Table
S2, Supporting Information). The results show that FeCoNiWCuOOH@Cu has excellent TOF values. At overpotentials of
200 and 300 mV, the TOF values are 0.764 and 5.806 s−1 , respectively, better than those of the recently reported related catalysts.
In addition, more evaluations were conducted using mass activity analysis. The results indicate that the mass activity of FeCoNiWCuOOH@Cu is the highest, reaching 150.08 A g−1 at 300 mV(Figure S25, Supporting Information).
The Nyquist plots obtained through electrochemical
impedance spectroscopy (EIS) illustrate the corresponding
charge transfer resistance (Rct ) semicircles, thereby investigating
the electron transfer kinetics at the catalyst/electrolyte interface.
As depicted in Figure 3g, the EIS spectrum of the nanoporous
FeCoNiWCuOOH@Cu electrode displays two characteristic

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semicircles in the mid to low-frequency range, aligned with theconstant phase element (CPE), representing Rct and pore resistance (Rp ), respectively.[51,52] At higher frequencies, the real axis
intercept denotes the intrinsic resistance (RI ) of the electrodeand electrolyte. Based on the equivalent circuit of these universal
descriptors (illustrated in Figure 3g), the Rct value of nanoporous
FeCoNiWCuOOH@Cu is determined to be ≈3.7 Ω, signiﬁcantly lower than that of nanoporous CuOOH@Cu (≈94.29 Ω),
FeCuOOH@Cu (≈22.48 Ω), FeWCuOOH@Cu (≈14.36 Ω),
and FeNiWCuOOH@Cu (≈13.31 Ω) (Figure S26, Supporting
Information). The RI and Rp values of FeCoNiWCuOOH@Cu
are ≈2.19 and 0.97 Ω, respectively, comparable to those of
nanoporous CuOOH@Cu (≈2.06 and 0.79 Ω), FeCuOOH@Cu(≈2.78 and 4.89 × 10−4 Ω), FeWCuOOH@Cu (≈2.21 and 0.14 Ω),
and FeNiWCuOOH@Cu (≈3.13 and 0.97 Ω). This suggests thatthe high-entropy structure has minimal impact on the intrinsic© 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH21983844, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202406008 by Johnny Ho - City University Of Hong Kong , Wiley Online Library on [13/09/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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resistance and pore resistance of the system, possibly due tothe stable heterostructure formed between the Cu skeleton andthe high-entropy structure. Consequently, the entire systemdemonstrates the lowest responsive charge transfer resistanceand faster electron transfer process, consistent with its excellent
OER catalytic performance. Further insights into the adsorption
strength of the catalyst for water molecules were obtained
through contact angle testing. As depicted in Figure 3h, thenanoporous FeCoNiWCuOOH@Cu catalyst achieves nearly
instantaneous (0.36 s) overall inﬁltration and adsorption of watermolecules (≈0°), indicating the loose and porous characteristicsof the double-continuous pore structure and the high adsorption
capacity of the high-entropy structure for water molecules,
thereby facilitating the adsorption of water molecules andsubsequent decomposition reactions. Moreover, nanoporous
CuOOH@Cu, FeCuOOH@Cu, FeWCuOOH@Cu, and FeNiWCuOOH@Cu also exhibit excellent hydrophilicity (Figure S27,
Supporting Information), highlighting the unique advantageof the sample preparation method in the electrocatalytic water
splitting reaction.
Durability stands as a key indicator in designing practical
OER electrocatalysts. The durability of FeCoNiWCuOOH@Cu
was assessed through extended timed current testing (Figure 3i).
Under the alkaline condition with a ﬁxed current density of
300 mA cm−2 , following a prolonged 100 h OER reaction, thecurrent density of FeCoNiWCuOOH@Cu merely decreased by
6%. This outcome indicates the excellent stability of the FeCoNiWCuOOH@Cu electrode. To investigate changes in the FeCoNiWCuOOH@Cu crystal structure pre- and post-stability experiments, XRD and Raman spectroscopy analyses were conducted.
As depicted in Figure S28a (Supporting Information), the persistence of both the Cu skeleton and its surface oxides is evident.
Post-stability testing shows a gradual increase in the peak intensity of the oxides, indicating further enhancement in surface Cu
oxidation. This is further corroborated by the enhanced CuOOH
peak in the Raman spectrum (Figure S28b, Supporting Information). Moreover, diverse elements and diﬀraction peaks in the
XPS spectrum (Figure S29, Supporting Information) imply that
post-stability experiments, the crystal structure and elemental valence states of FeCoNiWCuOOH@Cu have undergone negligible changes. Furthermore, to study morphological changes in FeCoNiWCuOOH@Cu, SEM images were examined post-stability
testing. Figure S30 (Supporting Information) illustrates that thenanoporous double-continuous pore structure remains intact,with a relatively uniform distribution of various elements. Thismay be attributed to the entropy stabilization eﬀect of the highentropy surface, which prevents electrochemical redox near thesurface. At the same time, FeCoNiWCuOOH@Cu heterostructure stabilizes the connection, ensuring system stability. Theseﬁndings indicate the remarkable structural stability of FeCoNiWCuOOH@Cu during prolonged electrochemical OER processes, demonstrating its potential as an eﬃcient OER catalyst.

2.4. HER Activity of FeCoNiWCuOOH@Cu System
Electrocatalysts
The HER performance of FeCoNiWCuOOH@Cu system catalysts featuring a double-continuous pore structure was in-Adv. Sci. 2024, 2406008

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vestigated under alkaline conditions. Analysis of the polarization curves depicted in Figure 4a reveals that compared to CuOOH@Cu (72 mV), FeCuOOH@Cu (53 mV),
FeWCuOOH@Cu (43 mV), and FeNiWCuOOH@Cu (28 mV),the FeCoNiWCuOOH@Cu catalyst exhibits the lowest overpotential of 18 mV, enabling a current density of 10 mA cm−2 , which
is notably lower than the 33 mV overpotential of commercial
Pt/C/Cu (Figure 4b). Remarkably, the FeCoNiWCuOOH@Cu
catalyst achieves a substantial overpotential of 115 mV at
100 mA cm−2 , signiﬁcantly lower than CuOOH@Cu (330 mV),
FeCuOOH@Cu (206 mV), FeWCuOOH@Cu (216 mV), FeNiWCuOOH@Cu (176 mV), and Pt/C/Cu (223 mV). To further delve into the HER reaction kinetics, the Tafel slope wasderived from the corresponding polarization curves. As illustrated in Figure 4c, the Tafel slope value provided by FeCoNiWCuOOH@Cu stands at 14 mV dec−1 , substantially smaller
than that of CuOOH@Cu (105 mV dec−1 ), FeCuOOH@Cu(25 mV dec−1 ), FeWCuOOH@Cu (52 mV dec−1 ), FeNiWCuOOH@Cu (17 mV dec−1 ), and Pt/C/Cu (60 mV dec−1 ). Thissuggests that the rapid HER kinetics of FeCoNiWCuOOH@Cu
are rooted in the Volmer–Tafel mechanism, dominated by the
Tafel step under the alkaline condition. Additionally, by comparing the electrochemical test results before and after the electrochemical activation process (hydroxylation) (Figure S31, Supporting Information), we found that the catalyst activity is further
enhanced after hydroxylation. Metal-hydroxide oxide (M-OOH)
can further improve water electrolysis activity. To elucidate theoutstanding performance achieved by the nanoporous doublecontinuous pore structure of FeCoNiWCuOOH@Cu, a comparison was made with numerous recently reported excellent HER
electrocatalysts (Figure 4d; Table S3, Supporting Information),including Fe, Co, Ni, multiple metals, and noble metal-based materials. It was observed that the FeCoNiWCuOOH@Cu catalyst
exhibits excellent HER activity with a lower Tafel slope. Additionally, the H2 TOF of FeCoNiWCuOOH@Cu was assessed to further elucidate its intrinsic activity. The results (Figure 4e; Table
S4, Supporting Information) demonstrate that at overpotentials
of 50, 100, and 200 mV, the TOF values stand at 5.166, 12.766,
and 41.292 s−1 , respectively. These values surpass those of mostrecently reported related catalysts, indicating that high-entropy
structures enhance intrinsic activity. Consistent with the HER polarization curve results, the FeCoNiWCuOOH@Cu catalyst displayed the highest mass activity value (55.77 A g−1 at −50 mV) inthe samples (Figure S32, Supporting Information). This meansthat the excellent HER performance of FeCoNiWCuOOH@Cu
under alkaline conditions may be attributed to the synergistic effect of multiple nonprecious metal components.
As is well known, exceptional electrocatalysts typically exhibit
sustained durability over prolonged periods or under highcurrent densities. The stability of the catalyst was assessed via
chronoamperometry, as depicted in Figure 4f. At a high current
density of 300 mA cm−2 , FeCoNiWCuOOH@Cu demonstrates
the ability to maintain a stable current output for a minimumof 100 h, with a current density of 98% and almost no activity
decay, demonstrating good durability. The crystal structure andmorphology changes of the FeCoNiWCuOOH@Cu catalyst postdurability testing were evaluated using XRD, Raman, and SEM
techniques. XRD patterns of the FeCoNiWCuOOH@Cu catalyst
pre- and post-durability testing were analyzed (Figure S33a,© 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH21983844, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202406008 by Johnny Ho - City University Of Hong Kong , Wiley Online Library on [13/09/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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Figure 4. Electrochemical characterization on HER properties. a) Polarization curves, b) corresponding overpotentials, c) Tafel slopes of diﬀerent samples in 1 m KOH solution. d) Overpotentials at 10 mA cm−2 and e) TOF pattern of the as-obtained FeCoNiWCuOOH@Cu electrocatalyst compared with
reported related electrocatalysts. f) Constant current curve of FeCoNiWCuOOH@Cu at 300 mA cm−2 current density for 100 h.

Supporting Information). A comparison reveals that following
the 100-h stability test, the peak intensity of CuO gradually
weakens while that of Cu2 O strengthens. This phenomenon is
attributed to the reduction reaction occurring at the cathode,leading to the gradual transition of Cu from a high valence
state to a low valence state. This transition is further evident in
the weakened Cu2 O and 𝛾-NiOOH/CoOOH peaks observed in
the Raman spectrum (Figure S33b, Supporting Information).
SEM analysis (Figure S34, Supporting Information) reveals that
following the 100-h durability test, the FeCoNiWCuOOH@Cu
catalyst retains its nanoporous double-continuous pore structure composed of nanoparticles, with no signiﬁcant changes
observed in the corresponding element mappings and EDS
spectra. This indicates the excellent structural stability of the
FeCoNiWCuOOH@Cu catalyst, with changes post-long-term
durability testing deemed negligible.

2.5. Water Splitting Activity of FeCoNiWCuOOH@Cu System
Electrocatalysts
Due to its dual activity in both OER and HER, FeCoNiWCuOOH@Cu electrode sheets were directly utilized asboth anode and cathode catalysts, and an overall water-splitting
device was assembled in a 1.0 m KOH electrolyte to explore
practical applications.[53] As depicted in Figure 5a,b, the FeCoNiWCuOOH@Cu||FeCoNiWCuOOH@Cu system requires
only a battery voltage of 1.40 V to achieve a current density of
10 mA cm−2 , signiﬁcantly lower than the overpotential needed
for the Pt/C/Cu||RuO2 /Cu system (1.52 V @ 10 mA cm−2 ),consistent with the reported results.[54] This performance sur-Adv. Sci. 2024, 2406008

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passes the recently reported noble or non-noble metal-based
catalysts (Figure 5d; Table S5, Supporting Information). Furthermore, H2 and O2 generated during the reaction process inthe electrolytic cell were collected using a drainage method.[55]The molar–time curves (Figure 5c) indicate that the actual
volume ratio of collected H2 and O2 closely approximates thetheoretical volume ratio of 2:1 in the electrocatalytic watersplitting reaction. This suggests that the Faraday eﬃciencyof the overall water-splitting reaction is close to 100%. Theseﬁndings undoubtedly demonstrate FeCoNiWCuOOH@Cu
as a promising alkaline water-splitting catalyst. Additionally,
the
FeCoNiWCuOOH@Cu||FeCoNiWCuOOH@Cu
system exhibits remarkable durability. Following continuous electrolysis for 1000 h at 300 mA cm−2 , the FeCoNiWCuOOH@Cu||FeCoNiWCuOOH@Cu system can stillsustain 96% of the initial current density, with negligible performance degradation. Additionally, the FeCoNiWCuOOH@Cu||FeCoNiWCuOOH@Cu system demonstrates
stable water splitting performance for over 500 h at a highcurrent density of 500 mA cm−2 , showcasing its strong competitiveness (Figure S35, Supporting Information). In comparison
with the most advanced noble and non-noble metal-based catalysts previously reported (Table S5, Supporting Information),the prepared nanoporous double-continuous pore structure
Cu catalyst continues to demonstrate excellent water splitting
stability, making it one of the best electrocatalysts for achieving overall water splitting. Evaluating the activity and stabilityof catalysts under practical application conditions is of greatsigniﬁcance. Therefore, we reassessed the water electrolysis
activity of the catalyst in a real water electrolyzer equippedwith an anion exchange membrane. The results (Figure S36,

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Figure 5. Electrochemical performance in alkaline water electrolyzer. a) Polarization curves and b) corresponding overpotentials at 10 mA cm−2 ofdiﬀerent samples in 1 m KOH aqueous electrolyte. c) FE of H2 and O2 generated over FeCoNiWCuOOH@Cu electrode at 10 mA cm−2 for 600 min.
d) Overpotentials of the as-obtained FeCoNiWCuOOH@Cu electrocatalyst at 10 mA cm−2 compared to reported related electrocatalysts. e) Constantcurrent curve of FeCoNiWCuOOH@Cu||FeCoNiWCuOOH@Cu at 300 mA cm−2 for 1 000 h; the inset is the SEM image after the stability test. f–i) Actual
operation diagram of water splitting powered by wind, lithium cell, thermal, and sunlight.

Supporting Information) show that the water electrolyzer assembled with FeCoNiWCuOOH@Cu maintained good activity(1.532 V@10 mA cm−2 ) under the conditions of 30 wt.% KOH
electrolyte and 60 °C and could run stably for at least 100 h at
500 mA cm−2 . These results indicate that our catalyst exhibits acceptable performance and durability under practical application
conditions.
After 1000 h of water splitting reaction, XRD, Raman, and SEM
characterization were conducted to deepen the understanding of
the stability of the catalytic system and the electrocatalytic reaction mechanism. XRD analysis (Figure S37a, Supporting Infor-

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mation) indicates that the peaks corresponding to the Cu skeleton in the XRD components notably decreased following the reaction. In contrast, the peak intensities related to Cu2 O and CuO
signiﬁcantly increased. This suggests that after 1000 h of stability testing, the oxidation degree of the Cu skeleton has substantially improved. The apparent enhancement of Cu2 O and CuO
peaks in the Raman spectrum (Figure S37b, Supporting Information) further supports this observation. Subsequently, structuralchanges in the FeCoNiWCuOOH@Cu catalyst were analyzed via
SEM analysis. It was observed (Figure S38, Supporting Information) that the FeCoNiWCuOOH@Cu catalyst maintained its© 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH21983844, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202406008 by Johnny Ho - City University Of Hong Kong , Wiley Online Library on [13/09/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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nanoporous double-continuous pore structure while developing
a nanosheet-like secondary structure on its surface. This phenomenon arises from the prolonged oxidation reaction of the
FeCoNiWCuOOH@Cu electrode sheet, leading to further oxidation of the surface Cu skeleton. Additionally, the FeCoNiWCuO
layer undergoes in situ oxidation to generate a highly active hydroxyl oxide protective layer, thereby preserving the nanoporous
double-continuous pore structure of the Cu skeleton.[56] Subsequent element mapping and EDS spectra conﬁrmed the relative
stability of the overall element distribution and content in the FeCoNiWCuOOH@Cu electrode. These ﬁndings conﬁrm the potential of the FeCoNiWCuOOH@Cu system as a comprehensive
electrocatalyst for overall water splitting.
Establishing an eﬀective external water-splitting system isparamount in collecting, storing, and converting energy in thenatural environment. Such a system not only helps reduce energy
consumption and break free from dependence on electricity supply but also facilitates low-cost, pollution-free, and sustainable hydrogen production, which is signiﬁcant.[57,58] Thus, a green energy hydrogen production system was introduced, wherein FeCoNiWCuOOH@Cu electrode sheets serve as components of
OER/HER catalysts. As illustrated in Figure 5f–i, wind energy,lithium batteries, thermal energy, and solar energy were harnessed as driving forces for water electrolysis to generate hydrogen. Furthermore, the dynamic processes of eﬃcient water
splitting and gas accumulation, as demonstrated in Videos S1–S4 (Supporting Information), clearly demonstrate the excellent
hydrogen production outcomes achieved by these green energyhydrogen production systems. These results indicate the broad
application prospects of FeCoNiWCuOOH@Cu water-splitting
electrocatalysts in hydrogen production.

2.6. Catalytic Activity Mechanism
In order to further elucidate the OER and HER mechanisms inalkaline FeCoNiWCuOOH@Cu solution, DFT calculations wereconducted. For better representativeness, we used a CuOOH
structure model with a size of 1.5 × 5 × 2 as the basis and additionally constructed four theoretical models with FeCuOOH,
FeWCuOOH, FeNiWCuOOH, and FeCoNiWCuOOH (Figure
S39, Supporting Information) to investigate the Gibbs free energy (ΔG) and local density of states (PDOS) of intermediates
in OER and HER electroatalytic reactions. The ﬁrst step for
the OER and HER processes is to consider various sites to infer the most probable H2 O adsorption sites on the samples.
The results (Table S6, supporting information) indicate that Cu
sites on CuOOH and FeCuOOH surfaces, as well as W sites on
FeWCuOOH, FeNiWCuOOH, and FeCoNiWCuOOH surfaces,
have the strongest adsorption energy for H2 O. Therefore, thefree energy evolution of the corresponding metal sites on theelectrocatalyst surface for OER and HER was explicitly studied. As shown in Figures 6a–d and S40 (Supporting Information), schematic diagrams of the OER and HER mechanisms
and corresponding free energy in the proposed alkaline electrolyte are presented. The adsorption energy barriers of four
essential intermediates (OH* , O* , OOH* , and H* ) were analyzed through DFT calculations. For the OER process, the results in Figure 6c indicate that under the imposed potential ofAdv. Sci. 2024, 2406008

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1.23 V, the rate-determining step (RDS) in the four-electron process of CuOOH@Cu and FeWCuOOH@Cu is the formationof O* . At the same time, the RDS for FeCuOOH@Cu, FeNiWCuOOH@Cu, and FeCoNiWCuOOH@Cu is the adsorptionof OH− . In addition, compared with CuOOH@Cu (1.33 V), FeCuOOH@Cu (0.55 V), FeWCuOOH@Cu (0.67 V), and FeNiWCuOOH@Cu (0.47 V), FeCoNiWCuOOH@Cu displays thelowest theoretical overpotential (0.23 V). For the HER process, compared with CuOOH@Cu (−1.61 V), FeCuOOH@Cu(1.20 V), FeWCuOOH@Cu (−0.89 V), and FeNiWCuOOH@Cu(−0.83 V), the hydrogen adsorption Gibbs free energy (ΔGH* )of FeCoNiWCuOOH@Cu is closer to the thermal neutral value(−0.73 V).[36,59,60] These results indicate that the formation ofhigh-entropy structures is conducive to lowering their Gibbs
free energy, thereby exhibiting signiﬁcant dual functionality inpromoting alkaline overall water splitting, consistent with theexperimental results showing the optimal activity of FeCoNiWCuOOH@Cu (Figures 3a and 4a).
In order to determine the actual active sites of HER and OER,
we conducted an in-depth analysis of the results. A detailed
analysis of the free energy diagram for OER (Figure 6c) reveals
that in the 4OH− → OH* process, CuOOH@Cu and FeCoNiWCuOOH@Cu require relatively low energy absorption (0.24
and 0.23 eV). In comparison, FeCuOOH@Cu requires the highest energy absorption (0.55 eV). FeWCuOOH@Cu and FeNiWCuOOH@Cu require moderate energy absorption (0.34 and0.44 eV), indicating that Co and Cu ions favor OH− adsorption,
while W and Ni show moderate performance, and Fe performs
the worst. In the OH* → O* process, FeNiWCuOOH@Cu, and
FeCoNiWCuOOH@Cu exhibit the lowest energy transition (0.17
and 0.22 eV), suggesting that Ni and Co facilitate OH* dissociation. In the O* → OOH* process, FeCoNiWCuOOH@Cu has
already achieved energy reduction (−0.07 eV), indicating that Co
promotes the conversion of O* to OOH* . Although CuOOH@Cu
shows greater energy reduction (−0.51 eV) during this reaction,
the high energy barrier in the OH* → O* process (1.33 eV)
hinders the further OER process of Cu. Considering the ratedetermining steps and required energy for each catalyst, Co is
the primary active element in the OER process. Cu contributes
more to OH− dissociation, while Ni facilitates OH* dissociation. An in-depth study of the free energy diagram for HER(Figure 6d) reveals that CuOOH@Cu and FeCuOOH@Cu exhibit the most extreme ΔGH* values (−1.61 and 1.20 eV). In
contrast, FeWCuOOH@Cu, FeNiWCuOOH@Cu, and FeCoNiWCuOOH@Cu have more moderate ΔGH* values (−0.89, −0.83,
and −0.73 eV). Additionally, we calculated the adsorption energies of H2 O for each sample (Figure S41, Supporting Information). The results show that CuOOH@Cu has the best H2 O adsorption performance (−4.89 eV), leading to more incredible difﬁculty in subsequent reactions. While FeCuOOH@Cu has themost suitable water adsorption energy (−1.52 eV), its high water
dissociation barrier limits its activity. FeWCuOOH@Cu, FeNiWCuOOH@Cu, and FeCoNiWCuOOH@Cu have moderate water adsorption energies (−1.83, −1.52, and −1.74 eV), which are
beneﬁcial for the subsequent processes. These results indicatethat W, Ni, and Co are conducive to the overall HER reaction,
while Cu plays a signiﬁcant role in H2 O adsorption.
Further calculations were conducted to determine the density of states (DOS) for each sample (Figure 6h). The results© 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH21983844, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202406008 by Johnny Ho - City University Of Hong Kong , Wiley Online Library on [13/09/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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Figure 6. a,b) Schematic diagrams depicting the proposed mechanisms for (a) OER and (b) HER of FeCoNiWCuOOH@Cu. c,d) Free energy proﬁlesfor (c) OER with the set potential of 1.23 V and (d) HER. e) PDOS results for various samples.

revealed that CuOOH@Cu exhibited a lower d-band center(𝜖 d ) value (−2.610 eV). Upon introduction of Fe atoms, the 𝜖 dvalue increased to −1.610 eV (FeCuOOH@Cu sample). With theintroduction of W atoms (FeWCuOOH@Cu sample), 𝜖 d fell to−1.882 eV. The subsequent introduction of Ni and Co atoms resulted in varying degrees of increase in 𝜖 d (FeNiWCuOOH@Cu
sample: −1.669 eV, FeCoNiWCuOOH@Cu sample: −1.651 eV).
A deeper analysis of this trend of change was inﬂuenced byatomic radii. Due to the introduction of various metal elements(Fe, Co, Ni, and W), diﬀerent degrees of increased/decreased

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bond length and strain occurred within the CuOOH structure(Figure S42, Supporting Information), leading to the narrowing/widening of 𝜖 d . Consequently, the occupation of antibonding
orbitals weakened/enhanced, aﬀecting the adsorption strengthof reaction intermediates.[61] According to the 𝜖 d theory,[62] 𝜖 dvalues indicating moderate adsorption strength suggest morefavorable adsorption/desorption, thus facilitating rapid overallwater splitting. The moderate 𝜖 d value of FeCoNiWCuOOH@Cu
is beneﬁcial for enhancing the catalytic performance of both OER
and HER. This also suggests that HEO catalysts with optimal© 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH21983844, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202406008 by Johnny Ho - City University Of Hong Kong , Wiley Online Library on [13/09/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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adsorption energy can be designed by introducing diﬀerent
metal elements.

3. Conclusions
In summary, a novel strategy combining liquid metal dealloying and electrodeposition has been developed to design FeCoNiWCuOOH@Cu heterostructure HEOs nanocomposite dualfunctional electrocatalysts with a double-continuous pore structure. The optimized FeCoNiWCuOOH@Cu electrode demonstrates excellent activity in both OER and HER, achieving a current density of 10 mA cm−2 with ultra-low overpotentials of only
200 and 18 mV, respectively. The corresponding Tafel slopes are
as low as 24 and 14 mV dec−1 , respectively. Moreover, the overall water splitting device assembled with FeCoNiWCuOOH@Cu
electrode sheets operates at a low battery voltage of 1.40 V, achieving a current density of 10 mA cm−2 , and exhibits high stability
for over 1000 h of operation at 300 mA cm−2 . Notably, the formation of the double-continuous pore structure enhances the exposure of active sites, while high-entropy engineering enhances theintrinsic activity of the catalysts. The synergistic eﬀect of multiple
elements and the precise regulation of nanostructures provide
new impetus for improving the performance of high-entropy catalysts. Furthermore, the HEO layer formed on the surface of theCu skeleton eﬀectively isolates atomic diﬀusion, endowing the
FeCoNiWCuOOH@Cu electrode sheets with long-term durability. DFT calculations also elucidate the strong coupling eﬀect ofmulti-element interactions on OER/HER activity. The successful demonstration of green energy hydrogen production systems
opens up new possibilities for the practical large-scale application of electrocatalytic water splitting technology. This work is
expected to advance the development of externally driven largecurrent water-splitting systems.

4. Experimental Section
Materials: Cu (99.9%) and Al (99.9%) were obtained from Beijing
Zhongke Yannuo New Materials Technology Co., Ltd. Hydrochloric acid
(HCl, 37 wt.%) was purchased from Honeywell International Inc. Iron chloride (FeCl3 , A.R.) was provided by Advanced Technology & Industrial Co.,
Ltd. Cobaltous nitrate hexahydrate (Co(NO3 )2 ·6H2 O, A.R.), anhydrous citric acid (C6 H8 O7 , A.R.), Pt/C (A.R.), potassium hydroxide (KOH, A.R.) andpotassium phosphate dibasic anhydrous (K2 HPO4 , A.R.) were purchasedfrom Shanghai Meryer Chemical Technology Co., Ltd. Nickel chloride hexahydrate (NiCl2 ·6H2 O, A.R.) was obtained from Beijing InnoChem Science & Technology Co., Ltd. Sodium tungstate dihydrate (Na2 WO4 ·2H2 O,
A.R.) and ruthenium oxide (RuO2 , A.R.) were provided by Shanghai Aladdin Biochemical Technology Co., Ltd. Naﬁon solution (5%) and sodium
phosphate monobasic dihydrate (NaH2 PO4 ·2H2 O, A.R.) were purchasedfrom Sigma–Aldrich, USA. Ethanol (C2 H6 O, A.R.) was provided by Anaqua
Global International Inc. Limited. Deionized (DI) water was obtained froman OmniaLab ED+ 40 Ultrapure water system.
Synthesis of FeCoNiWCuOOH@Cu System Electrocatalysts: A precursor of Cu20 Al80 alloy sheet with a 1 cm × 1 cm × 250 μm thickness was
prepared by arc melting Cu and Al metals in N2 atmosphere, followed bycooling and cutting procedures. Then, it was immersed in a 2 m HCl solution for 4 h for chemical dealloying to remove Al. The dealloyed sample wasrinsed with ultrapure water to remove residual chemicals in the nanopores
and obtain a nanoporous Cu framework. FeCl3 (1 mmol), Co(NO3 )2 ·6H2 O(1 mmol), NiCl2 ·6H2 O (1 mmol), and 5 mmol anhydrous citric acid weredissolved in 30 mL of solution (15 mL of H2 O and C2 H6 O each), de-Adv. Sci. 2024, 2406008

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noted as solution A. Na2 WO4 ·2H2 O (3.5 mmol) was dissolved in 20 mL
of H2 O, denoted as solution B. Solution B was added to solution A to obtain the electroplating solution. A three-electrode system was assembled
using the cleaned sample, the graphite rod electrode, and the saturated
calomel electrodes as working, counter, and reference electrodes, respectively. At a potential of −4 V (relative to the saturated calomel electrode),
FeCoNiWCuO NS were electrodeposited on a nanoporous Cu framework.
Subsequently, a three-electrode system was assembled using a Hg/HgO
electrode as the reference electrode and 1 m KOH solution as the electrolyte. FeCoNiWCuO NS were subjected to 10 times CV tests at a scanning rate of 20 mV s−1 in the potential range of 0–1.5 V, and the FeCoNiWCuOOH@Cu catalyst was ultimately obtained. Only the relevant composition of the electroplating solution is modiﬁed in the preparation processof FeCuOOH@Cu, FeWCuOOH@Cu, and FeNiWCuOOH@Cu catalysts,
and the other preparation processes are the same as those of the FeCoNiWCuOOH@Cu catalyst. The electroplating process is eliminated in the
preparation process of the CuOOH@Cu catalyst, and other processes are
the same as those of the FeCoNiWCuOOH@Cu catalyst. By mixing commercially available Pt/C and RuO2 nanocatalysts and Naﬁon in a solution
containing ethanol (20%) and water (80%) and dropwise coating them
onto the nanoporous Cu framework, Pt/C and RuO2 electrodes loaded on
the nanoporous Cu framework were prepared, respectively.
Characterization: TEM, HRTEM, SAED, and EDX analyses were conducted with JEOL JEM-2100F equipment. The surface morphologies wereobserved by SEM (S-4800) equipped with an EDS detector at 5 and 30 kV
acceleration voltages. The crystal structures of the alloy sheets were analyzed by a D2 PHASER XE-T X-ray Diﬀractometer System equipped with Cu
K𝛼 radiation (𝜆 = 1.5406 Å). Raman spectroscopy was employed in a WITecalpha 300 R Raman System with a 532 nm laser excitation source. The XPS
data were collected by PHI 5000 Versaprobe system with a monochromatic
Al K𝛼 radiation source. All binding energies were calibrated by shifting the
C 1s peak to 284.8 eV. The contact angles of electrode tabs were tested
by DataPhysics Contact Angle Tester. The speciﬁc surface area of the catalysts was obtained through BET testing using the 3FLEX 3500 Multi-Port
High-Throughput Gas Adsorption Analyzer.
Electrochemical Measurements: All electrochemical tests were conducted in a standard three-electrode system connected to the Chenhua
CHI760E electrochemical workstation. The reference electrode was calibrated before the performance testing. All potentials have undergone 80%
iR correction. Before LSV testing, 20 CV cycles were performed at a scanning rate of 5 mV s−1 to remove the passivation surface of the working
electrode. A Hg/HgO electrode and graphite rod electrode are used as thereference and counter electrodes in 1 m KOH solution. For HER, OER, andwater splitting experiments, LSV scans were performed at a scan rate of
5 mV s−1 and potential intervals from −1.6 to −0.9 V, 0 to 1.5 V, and 0
to 1.5 V, respectively. The potentials in 1 M KOH solution were converted
to the corresponding potentials versus reversible hydrogen electrode (vsRHE) using Equation (1):ERHE = EHg∕HgO + 0.098 + 0.059 × pH

(1)

where ERHE and EHg/HgO are the potentials versus RHE and measured potentials versus Hg/HgO reference electrode, respectively.
The ECSAs of the catalysts were calculated from the Cdl proﬁles using
Equation (2):[63,64]
ECSA = (Cdl ∕ Cs )Ageo(2)

where Cs = 0.040 mF cm−2 and Ageo (0.5 cm2 ) is the actual geometric areaof the alloy sheets exposed to the electrolyte.
First, The currents without the Faradaic process were measured. Then,Cdl values were calculated from the half slope of the linearly ﬁtted curvesof the capacitive current and plotted as a function of the scan rate.[65]To calculate TOF values of the catalysts, CV scans were performed in
1 m phosphate buﬀer saline (PBS) solution with a scanning voltage of© 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH21983844, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202406008 by Johnny Ho - City University Of Hong Kong , Wiley Online Library on [13/09/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

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50 mV s−1 from −0.2 to 0.6 V (vs RHE). The TOF values were calculated
based on Equations (3) and (4):[66]TOF = I ∕ 2nF(3)n = Q ∕ 2F

(4)(Grant No. 2023C008) and the National Natural Science Foundation ofChina (Grant No. 61904110), Shenzhen Strategic Emerging Industry Support Plan (Grant No. F-2023-Z99-509043). The authors also acknowledge
the support from the Instrumental Analysis Center of Shenzhen University(Xili Campus).

Among them, I refers to the current (in A) during the LSV measurement process, n represents the number of active sites (in mol), F is the
Faraday constant (in 96 500 C mol−1 ), and Q is the number of voltammetric charges (in C).
The EIS measurements were conducted at open circuit potential in thefrequency range from 100 kHz to 0.01 Hz.
Computational Methods: The electronic optimizations were achievedby employing spin-polarized DFT calculations using a facet-wave method
implemented in the Vienna Ab Initio Simulation Package (VASP) code.[67]The core-valence interaction was described using the projection augmented wave (PAW) method. At the same time, the electron exchange andcorrelation energy were accounted for using generalized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE) function.[68] A cutoﬀ energy of 450 eV was chosen, and spin-polarization calculations were
performed for all structural optimizations. Using Löwdin-orthogonalizedatomic projectors, calculations were carried out at the GGA+U level with
the Hubbard U correction. The U values applied were 3 eV for Co, 4 eV forCu, and 8 eV for both Ni and Fe.[20]The OER/HER free energy diagrams of the FeCoNiWCuOOH systemwere calculated, and the total OER/HER equations were acquired by Equations (5)–(9):For OER:

Conﬂict of Interest

4OH− → OH∗ + 3OH− + e−

(5)→ O∗ + H2 O + 2OH− + 2e−(6)→ HOO∗ + H2 O + OH− + 3e−(7)→ O2 + 2H2 O + 4e−(8)[1] H. Dotan, A. Landman, S. W. Sheehan, K. D. Malviya, G. E. Shter, D.
A. Grave, Z. Arzi, N. Yehudai, M. Halabi, N. Gal, Nat. Energy 2019, 4,
786.
[2] J. Kibsgaard, I. Chorkendorﬀ, Nat. Energy 2019, 4, 430.
[3] V. R. Stamenkovic, D. Strmcnik, P. P. Lopes, N. M. Markovic, Nat.
Mater. 2017, 16, 57.
[4] H. Zhang, S. Zuo, M. Qiu, S. Wang, Y. Zhang, J. Zhang, X. W. Lou, Sci.
Adv. 2020, 6, eabb9823.
[5] J. Wang, Y. Gao, H. Kong, J. Kim, S. Choi, F. Ciucci, Y. Hao, S. Yang,
Z. Shao, J. Lim, Chem. Soc. Rev. 2020, 49, 9154.
[6] Q. Gao, W. Zhang, Z. Shi, L. Yang, Y. Tang, Adv. Mater. 2019, 31,
1802880.
[7] K. Hu, T. Ohto, L. Chen, J. Han, M. Wakisaka, Y. Nagata, J.-i. Fujita, Y.
Ito, ACS Energy Lett. 2018, 3, 1539.
[8] Q. Lu, G. S. Hutchings, W. Yu, Y. Zhou, R. V. Forest, R. Tao, J. Rosen,
B. T. Yonemoto, Z. Cao, H. Zheng, Nat. Commun. 2015, 6, 6567.
[9] J. Chen, Y. Ge, Q. Feng, P. Zhuang, H. Chu, Y. Cao, W. R. Smith, P.
Dong, M. Ye, J. Shen, ACS Appl. Mater. Interfaces 2019, 11, 9002.
[10] H. Shi, Y.-T. Zhou, R.-Q. Yao, W.-B. Wan, X. Ge, W. Zhang, Z. Wen,
X.-Y. Lang, W.-T. Zheng, Q. Jiang, Nat. Commun. 2020, 11, 2940.
[11] M. Jakšić, Electrochim. Acta 1984, 29, 1539.
[12] H. Xin, A. Vojvodic, J. Voss, J. K. Nørskov, F. Abild-Pedersen, Phys.
Rev. B 2014, 89, 115114.
[13] W.-J. Jiang, T. Tang, Y. Zhang, J.-S. Hu, Acc. Chem. Res. 2020, 53, 1111.
[14] H. Wu, Q. Lu, Y. Li, M. Zhao, J. Wang, Y. Li, J. Zhang, X. Zheng, X.
Han, N. Zhao, J. Li, Y. Liu, Y. Deng, W. Hu, J. Am. Chem. Soc. 2023,
145, 1924.
[15] L. Zhang, W. Cai, N. Bao, Adv. Mater. 2021, 33, 2100745.
[16] Z. Zhu, Y. Zhang, D. Kong, N. He, Q. Chen, Small 2023, 2307754.
[17] L. Hui, Y. Xue, B. Huang, H. Yu, C. Zhang, D. Zhang, D. Jia, Y. Zhao,
Y. Li, H. Liu, Y. Li, Nat. Commun. 2018, 9, 5309.
[18] P. Zhai, M. Xia, Y. Wu, G. Zhang, J. Gao, B. Zhang, S. Cao, Y. Zhang,
Z. Li, Z. Fan, C. Wang, X. Zhang, J. T. Miller, L. Sun, J. Hou, Nat.
Commun. 2021, 12, 4587.
[19] Q. Hu, S. Qi, Q. Huo, Y. Zhao, J. Sun, X. Chen, M. Lv, W. Zhou, C.
Feng, X. Chai, J. Am. Chem. Soc. 2023, 146, 2967.

For HER:
H+ + e− → 1∕2H2(9)The free energy (chemical potential) of each hydrogen atom in the initial
and ﬁnal states was considered equal in the equilibrium state. The free energies of OER/HER intermediates were computed based on Equation (10):ΔG = ΔE + ΔZPE − TΔS(10)where ΔG, ΔS, and ΔZPE represent the binding energy, entropy change,
and zero-point energy change at 298.15 K, respectively.[69]Supporting Information
Supporting Information is available from the Wiley Online Library or fromthe author.

Acknowledgements
The work was partially supported by ﬁnancial support from the
Guangdong Basic and Applied Basic Research Foundation (Grant No.
2023A1515010693), partially by the Shenzhen Science and Technology Program (Grant No. ZDSYS20220527171402005 and 20220809125959001),
Research Team Cultivation Program of Shenzhen University (Grant No.
2023QNT010), Shenzhen University 2035 Program for Excellent Research

Adv. Sci. 2024, 2406008

2406008 (13 of 14)

The authors declare no conﬂict of interest.

Data Availability Statement
The data that support the ﬁndings of this study are available from the corresponding author upon reasonable request.

Keywords
graded metal network, heterostructure, high-entropy oxyhydroxide, longterm stability, water splitting
Received: July 1, 2024
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www.advancedscience.com[20] S. Qi, Z. Lei, Q. Huo, J. Zhao, T. Huang, N. Meng, J. Liao, J. Yi,
C. Shang, X. Zhang, H. Yang, Q. Hu, C. He, Adv. Mater. 2024, 36,2403958.
[21] G. M. Tomboc, X. Zhang, S. Choi, D. Kim, L. Y. S. Lee, K. Lee, Adv.
Funct. Mater. 2022, 32, 2205142.
[22] H. Wang, Q. He, X. Gao, Y. Shang, W. Zhu, W. Zhao, Z. Chen, H.
Gong, Y. Yang, Adv. Mater. 2024, 36, 2305453.
[23] Y. Zhai, X. Ren, B. Wang, S. Liu, Adv. Funct. Mater. 2022, 32, 2207536.
[24] R. Song, J. Han, M. Okugawa, R. Belosludov, T. Wada, J. Jiang, D. Wei,
A. Kudo, Y. Tian, M. Chen, Nat. Commun. 2022, 13, 5157.
[25] H. Shi, X.-Y. Sun, Y. Liu, S.-P. Zeng, Q.-H. Zhang, L. Gu, T.-H. Wang,
G.-F. Han, Z. Wen, Q.-R. Fang, X.-Y. Lang, Q. Jiang, Adv. Funct. Mater.
2023, 33, 2214412.
[26] H. Shi, X.-Y. Sun, S.-P. Zeng, Y. Liu, G.-F. Han, T.-H. Wang, Z. Wen,
Q.-R. Fang, X.-Y. Lang, Q. Jiang, Small Struct 2023, 4, 2300042.
[27] C. Zhu, Z. Qi, V. A. Beck, M. Luneau, J. Lattimer, W. Chen, M. A.
Worsley, J. Ye, E. B. Duoss, C. M. Spadaccini, Sci. Adv. 2018, 4,
eaas9459.
[28] X. Wang, M. Luo, J. Lan, M. Peng, Y. Tan, Adv. Mater. 2021, 33,
2007733.
[29] R.-Q. Yao, Y.-T. Zhou, H. Shi, W.-B. Wan, Q.-H. Zhang, L. Gu, Y.-F. Zhu,
Z. Wen, X.-Y. Lang, Q. Jiang, Adv. Funct. Mater. 2021, 31, 2009613.
[30] J.-S. Sun, Z. Wen, L.-P. Han, Z.-W. Chen, X.-Y. Lang, Q. Jiang, Adv.
Funct. Mater. 2018, 28, 1706127.
[31] Y. Gao, Y. Ding, Chem. - Eur. J. 2020, 26, 8845.
[32] H. Liang, A. N. Gandi, D. H. Anjum, X. Wang, U. Schwingenschlögl,
H. N. Alshareef, Nano Lett. 2016, 16, 7718.
[33] S. Chu, W. Chen, G. Chen, J. Huang, R. Zhang, C. Song, X. Wang, C.
Li, K. K. Ostrikov, Appl. Catal. B-Environ. 2019, 243, 537.
[34] F. Lin, F. Lv, Q. Zhang, H. Luo, K. Wang, J. Zhou, W. Zhang, W. Zhang,
D. Wang, L. Gu, Adv. Mater. 2022, 34, 2202084.
[35] Y. Dong, Z. Deng, H. Zhang, G. Liu, X. Wang, Nano Lett. 2023, 23,9087.
[36] Q. Yu, X. Liu, G. Liu, X. Wang, Z. Li, B. Li, Z. Wu, L. Wang, Adv. Funct.
Mater. 2022, 32, 2205767.
[37] X. Cui, Y. Liu, X. Wang, X. Tian, Y. Wang, G. Zhang, T. Liu, J. Ding, W.
Hu, Y. Chen, ACS Nano 2024, 18, 2948.
[38] L. Zhang, C. Ye, X. Li, Y. Ding, H. Liang, G. Zhao, Y. Wang, Nano-Micro
Lett. 2018, 10, 1.
[39] Z. Zhang, C. Feng, D. Wang, S. Zhou, R. Wang, S. Hu, H. Li, M. Zuo,
Y. Kong, J. Bao, Nat. Commun. 2022, 13, 2473.
[40] R. Qin, P. Wang, Z. Li, J. Zhu, F. Cao, H. Xu, Q. Ma, J. Zhang, J. Yu, S.
Mu, Small 2022, 18, 2105305.
[41] B. Wu, S. Gong, Y. Lin, T. Li, A. Chen, M. Zhao, Q. Zhang, L. Chen,
Adv. Mater. 2022, 34, 2108619.
[42] H. Sun, L. Chen, Y. Lian, W. Yang, L. Lin, Y. Chen, J. Xu, D. Wang, X.
Yang, M. H. Rümmerli, J. Guo, J. Zhong, Z. Deng, Y. Jiao, Y. Peng, S.
Qiao, Adv. Mater. 2020, 32, 2006784.
[43] P.-J. Deng, Y. Liu, H. Liu, X. Li, J. Lu, S. Jing, P. Tsiakaras, Adv. Energy
Mater. 2024, 14, 2400053.
[44] K. Miao, W. Jiang, Z. Chen, Y. Luo, D. Xiang, C. Wang, X. Kang, Adv.
Mater. 2024, 36, 2308490.

Adv. Sci. 2024, 2406008

2406008 (14 of 14)[45] X. Pang, H. Bai, H. Zhao, W. Fan, W. Shi, ACS Catal. 2022, 12, 1545.
[46] H. H. Pham, M.-J. Cheng, H. Frei, L.-W. Wang, ACS Catal. 2016, 6,
5610.
[47] Z. Jia, K. Nomoto, Q. Wang, C. Kong, L. Sun, L. C. Zhang, S. X. Liang,
J. Lu, J. J. Kruzic, Adv. Funct. Mater. 2021, 31, 2101586.
[48] P. Yin, G. Wu, X. Wang, S. Liu, F. Zhou, L. Dai, X. Wang, B. Yang, Z.-Q.
Yu, Nano Res. 2021, 14, 4783.
[49] W. J. Liu, X. Hu, H. C. Li, H. Q. Yu, Small 2018, 14, 1801878.
[50] S. Chen, Z. Kang, X. Hu, X. Zhang, H. Wang, J. Xie, X. Zheng, W. Yan,
B. Pan, Y. Xie, Adv. Mater. 2017, 29, 1701687.
[51] B. Geng, F. Yan, X. Zhang, Y. He, C. Zhu, S. L. Chou, X. Zhang, Y. Chen,
Adv. Mater. 2021, 33, 2106781.
[52] H. Jiang, M. Sun, S. Wu, B. Huang, C. S. Lee, W. Zhang, Adv. Funct.
Mater. 2021, 31, 2104951.
[53] Y. Lu, K. Huang, X. Cao, L. Zhang, T. Wang, D. Peng, B. Zhang, Z. Liu,
J. Wu, Y. Zhang, Adv. Funct. Mater. 2022, 32, 2110645.
[54] A. Kumar, S. K. Purkayastha, A. K. Guha, M. R. Das, S. Deka, ACS
Catal. 2023, 13, 10615.
[55] P. Wang, J. Qi, X. Chen, C. Li, W. Li, T. Wang, C. Liang, ACS Appl. Mater.
Interfaces 2019, 12, 4385.
[56] Y. Zhang, S. Lee, S. Jeong, E. Son, J. M. Baik, Y. K. Han, H. Park, Adv.
Funct. Mater. 2024, 34, 2309250.
[57] D. Chen, Z. Pu, R. Lu, P. Ji, P. Wang, J. Zhu, C. Lin, H. W. Li, X. Zhou,
Z. Hu, Adv. Energy Mater. 2020, 10, 2000814.
[58] P. Wang, J. Zhu, Z. Pu, R. Qin, C. Zhang, D. Chen, Q. Liu, D. Wu, W.
Li, S. Liu, Appl. Catal. B-Environ. 2021, 296, 120334.
[59] T. Gu, R. Sa, L. Zhang, D.-S. Li, R. Wang, Appl. Catal. B-Environ. 2021,
296, 120360.
[60] Y. Liu, G. Yu, G. D. Li, Y. Sun, T. Asefa, W. Chen, X. Zou, Angew. Chem.
2015, 127, 10902.
[61] Z. Hou, C. Cui, Y. Li, Y. Gao, D. Zhu, Y. Gu, G. Pan, Y. Zhu, T. Zhang,Adv. Mater. 2023, 35, 2209876.
[62] L. Zhang, Y. Zhu, Z. Nie, Z. Li, Y. Ye, L. Li, J. Hong, Z. Bi, Y. Zhou, G.
Hu, ACS Nano 2021, 15, 13399.
[63] C. C. L. McCrory, S. Jung, J. C. Peters, T. F. Jaramillo, J. Am. Chem.
Soc. 2013, 135, 16977.
[64] Y. L. Wu, X. F. Li, Y. S. Wei, Z. M. Fu, W. B. Wei, X. T. Wu, Q. L. Zhu,
Q. Xu, Adv. Mater. 2021, 33, 2006965.
[65] H. Zhang, X. Li, A. Haehnel, V. Naumann, C. Lin, S. Azimi, S. L.
Schweizer, A. W. Maijenburg, R. B. Wehrspohn, Adv. Funct. Mater.
2018, 28, 1706847.
[66] X. Shang, Z. Z. Liu, S. S. Lu, B. Dong, J. Q. Chi, J. F. Qin, X.
Liu, Y. M. Chai, C. G. Liu, ACS Appl. Mater. Interfaces 2018, 10,43561.
[67] S. Q. Chen, N. J. Zhang, C. W. N. Villarrubia, X. Huang, L. Xie, X. Y.
Wang, X. D. Kong, H. Xu, G. Wu, J. Zeng, H. L. Wang, Nano Energy
2019, 66, 104164.
[68] L. Zhang, Y. Jia, G. Gao, X. Yan, N. Chen, J. Chen, M. T. Soo, B. Wood,
D. Yang, A. Du, X. Yao, Chem 2018, 4, 285.
[69] J. Yang, B. Chen, X. Liu, W. Liu, Z. Li, J. Dong, W. Chen, W. Yan, T. Yao,
X. Duan, Y. Wu, Y. Li, Angew. Chem., Int. Ed. 2018, 57, 9495.

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