# Solar Hydrogen Production with Metal/III–V Semiconductor Junction Monolithically Integrated on Si

Hanh Vi Le, Rozenn Bernard, Ludovic Largeau, Gilles Patriarche, Sylvain Febvre, Fatima Merhi, Bienvenu Boulingui Koumba, Antoine Létoublon, Christophe Levallois, Fauzia Jabeen, et al.

► To cite this version:

Hanh Vi Le, Rozenn Bernard, Ludovic Largeau, Gilles Patriarche, Sylvain Febvre, et al. Solar Hydrogen Production with Metal/III–V Semiconductor Junction Monolithically Integrated on Si. Chem-ElectroChem, 2025, 10.1002/celc.202500251. [https://hal.science/hal-05334599v1](https://hal.science/hal-05334599v1)

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# Solar Hydrogen Production with Metal/III–V Semiconductor Junction Monolithically Integrated on Si

Hanh Vi Le, Rozenn Bernard, Ludovic Largeau, Gilles Patriarche, Sylvain Febvre, Fatima Merhi, Bienvenu Boulingui Koumba, Antoine Létoublon, Christophe Levallois, Fauzia Jabeen, Sylvie Harel, Angus Rockett, Xerxes K. Steirer, Tony Rohel, Karine Tavernier, Julie Le Pouliquen, Yoan Léger, Nicolas Bertru, Bruno Fabre, Gabriel Loget,* and Charles Cornet*

GaAs is an excellent candidate for high-performance photoelectrochemical water splitting due to its appropriate band-edge and bandgap energies, as well as its excellent transport properties. The most significant limitations of GaAs for photoelectrochemical applications are its instability against corrosion, the high substrate cost, and the huge overpotentials required for triggering water electrolysis. The monolithic epitaxial integration of GaAs thin films directly on the Earth-abundant Si fundamentally limits the costs associated with the substrate fabrication. Herein, photocathodes made of 1 µm thick GaAs layers epitaxially grown on p-doped Si substrates are developed and their performances are compared

to those of bare p-doped GaAs electrodes. Sulfur passivation and standard interfacing with Pt catalyst are applied and analyzed for both series of photocathodes. A massive onset potential shift of 0.63 V is demonstrated for GaAs/Si photocathodes after electroless Pt deposition and sulfur passivation, reaching an onset potential of 0.4 V versus the reversible hydrogen electrode. The stability of the Pt/GaAs/Si photocathode is finally assessed over more than 112 h. These findings are essential for further development toward the fabrication of cost-efficient and stable unassisted photoelectrochemical cells for green hydrogen production.

## 1. Introduction

One of the most important problems facing humanity nowadays is the production and storage of clean, renewable, and low-cost energy. Similar to photosynthesis, which converts solar energy into

chemical energy, solar photoelectrochemical (PEC) cells directly store solar energy in the form of hydrogen fuel, which could potentially solve the aforementioned issues.[1–3] Developing stable, cost-efficient, and high-yield photoelectrodes for PEC cells is thus an essential step of this research field. Among the promising materials

H. V. Le, R. Bernard, S. Febvre, B. B. Koumba, A. Létoublon, C. Levallois,

F. Jabeen, T. Rohel, K. Tavernier, J. L. Pouliquen, Y. Léger, N. Bertru,

C. Cornet

Univ Rennes

INSA Rennes

CNRS

Institut FOTON–UMR – UMR 6082

F-35000 Rennes, France

E-mail: charles.cornet@insa-rennes.fr

L. Largeau, G. Patriarche

Center for Nanoscience and Nanotechnology

C2N UMR 9001

CNRS

Université Paris Saclay

91120 Palaiseau, France

F. Merhi, G. Loget

University of Bordeaux

Bordeaux INP

ISM

UMR CNRS 5255

33607 Pessac, France

E-mail: gabriel.loget@cnrs.fr

S. Harel

Nantes Université

Institut des Matériaux de Nantes-Jean Rouxel (IMN) CNRS UMR6502

2 rue de la Houssinière BP 32229, 44322 Nantes Cedex3, France

A. Rockett

Department of Metallurgical and Materials Engineering

Colorado School of Mines

1500 Illinois Street, Golden, CO 80401, USA

X. K. Steirer

Department of Physics

Colorado School of Mines

1500 Illinois Street, Golden, CO 80401, USA

B. Fabre

Univ Rennes

CNRS

ISCR (Institut des Sciences Chimiques de Rennes) –UMR6226

F-35000 Rennes, France

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Supporting information for this article is available on the WWW under https://doi.org/10.1002/celc.202500251

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© 2025 The Author(s). ChemElectroChem published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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for photoelectrodes, group III–V semiconductors are quite appealing, as they have been variously studied in photovoltaic and photonic applications. Monolithic multijunction III–V solar cells have already demonstrated record conversion efficiencies.[4–6] This success is due to their remarkable physical properties, i.e., their direct bandgap, appropriate and tunable band-edges,[7] excellent transport properties, and high quantum yield.[8] For this reasons, III–V semiconductors are also excellent candidates for unassisted PEC water splitting, where the PEC cell operates under illumination without requiring an external bias, setting solar-to-hydrogen efficiencies above 10%.[9,10] Growing III–V semiconductors on Si wafers provides an economically appealing approach for solar devices[11] since III–V substrates are 10 times more expensive than common Si wafers. Monolithic III–V-on-silicon solar cells have converted 33.3% of the AM1.5G photon energy into electricity even though structural defects mitigate the photovoltaic performance.[5] Recent work has improved the understanding of heterogeneous III–V/Si integration with achievements of high-quality GaAs/Si epilayers within small deposition thicknesses.[12] The integration of III–V nanowires on Si for PEC applications was also attempted, as they can help avoid the formation of numerous crystal defects. However, the performance of III–V/Si nanowire-based photocathodes remains limited (<5 mA cm⁻² at 0 V vs reversible hydrogen electrode [RHE]), especially due to their complex geometry and high surface state density.[13,14] Planar III–V/Si epilayers have recently been considered for developing high-yield and cost-effective photoelectrodes.[15] Photoanodes, such as (In, Ga)N/Si,[16] Ga(P, Sb)/Si,[17] or Ga(As, P)/Si,[18–20] have been studied. These systems highlight the benefits of using midgap III–V absorbers to better match the solar spectrum. However, they still face challenges related to stability and to improving the onset potential (Vonset). This parameter is crucial for the development of unassisted water splitting since both the cathode and anode must generate enough potential difference to drive the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) without external bias. A common strategy to increase the photovoltage (Vph) and improve Vonset is to use a p–n junction. Following this strategy, high-performance Si photocathodes (Table S1, Supporting Information in Ref. [21]) have been achieved by combining n⁺–p-processed Si substrates with optimized protection and catalyst coatings. However, this also adds another degree of complexity and cost to the process. Zeng et al. addressed this by using epitaxial planar wurtzite GaN as a protective wide-bandgap layer on n⁺–p Si photocathodes, together with Pt as a catalyst to reduce overpotentials, reaching a Vonset of 0.3 V versus the RHE.[21] The first demonstration of a smaller bandgap planar Ni-coated III–V semiconductors on Si photocathode was demonstrated very recently reaching onset potentials of 0.25 V versus RHE.[22] Nevertheless, in these earlier works, the individual roles of the light absorber, the catalyst, and the p–n-junction-induced Vph in performance improvement were not clearly distinguished. Furthermore, the integration of smaller bandgap planar III–V semiconductors on Si for photocathode applications has not yet been explored.

In this work, we comparatively apply sulfur passivation (S-passivation) and standard Pt catalyst strategies to GaAs:p and nonintentionally doped (nid) GaAs/Si:p thin-film photocathodes

to assess the potential of the latter. To isolate the intrinsic physical limitations, this study deliberately excludes any p–n engineering strategies and novel catalyst developments. We demonstrate that a simple and cost-efficient unintentionally doped GaAs thin film grown on a bare Si:p wafer can achieve efficient and stable solar hydrogen production, provided the surface is adequately passivated and charge transfer to the electrolyte is activated, despite its much lower crystal quality. The specific contributions of surface/interface states and catalysts to the overpotential reduction are highlighted. As a result, we demonstrate a surface-passivated and charge-activated GaAs/Si:p photocathode with a Vonset of 0.4 V versus RHE, achieved without any intentional p–n junction, and assess its stability over 112 h. To further elucidate the underlying processes, we employ advanced structural, surface, optical, and PEC characterization techniques to analyze the surface electrochemical reactions and solid-state band bending in photocathodes made of GaAs:p wafers, and GaAs/Si:p epitaxial layers during PEC water splitting.

## 2. Results and Discussion

### 2.1. GaAs:p and GaAs/Si:p-Based Photocathodes

As discussed in the literature,[23] GaAs has attractive band positions for both HER and OER. In the following, performance and structural characterizations of GaAs/Si:p photocathodes will be systematically compared to those of photocathodes made of bare GaAs wafers. The stability of GaAs photoelectrodes has been investigated in the literature. Results suggest that GaAs generally undergoes active corrosion under anodic conditions,[19,24,25] while GaAs photocathodes remain relatively stable. For example, unmodified GaAs:p photocathodes have been shown to operate for more than 70 h at a bias of –0.6 V versus RHE in H₂SO₄ 1 M,[26] or even 120 h in H₂SO₄ 3 M.[27] Still, one of the most significant drawbacks of GaAs for HER is its huge overpotential. An excessively high overpotential of the photocathode results in an undesirably low Vonset. One solution to improve Vonset is by optimizing the Vph generated by the photocathode, as demonstrated in p–n junction GaAs-based photoelectrodes.[28,29] However, this approach is technologically complex, requiring precise optimization during the growth procedure. Managing the interplay between surface recombination and catalytic effects is another possible route. Several studies have investigated the passivation and catalytic behavior of GaAs:p, but these two processes and their combined effects remain poorly understood. It has been shown that by depositing a catalyst on GaAs:p, Vonset can shift to a more positive value,[26,30–32] this was observed, e.g., with Au where a Vonset shift from –0.2 to 0.09 V versus RHE was reported.[33] Obviously, several groups have been investigating the catalytic effects of Pt on GaAs:p deposited by different methods such as sputtering, electron beam deposition, electrodeposition, and electroless deposition. In this case, a positive shift in Vonset can indeed be expected since Pt is a good catalyst for HER.[30,32] However, Pt deposition on GaAs surfaces can also generate elemental As, which produces midgap surface states that act as recombination centers of photocarriers. This increases carrier
<figure><img src="image_5.png" /></figure>

recombination and strongly limits the benefits of the catalyst.[26,34–36] In all reported cases, the best V onset obtained for Pt-coated GaAs:p photocathodes reached 0.25 V versus RHE (see Table S1, Supporting Information).[31] On the other hand, S-passivation of III–V semiconductors has been extensively reported to reduce surface states by filling dangling bonds and removing the oxides and elemental As from the surface, thereby enhancing the performance of photonic devices.[37–39] Yet, relatively few studies have examined the impact of S-passivation on electrochemical applications. H. Lim et al.[40] demonstrated that passivating a nanostructured GalnP surface with (NH₄)₂S significantly decreased surface recombination of photogenerated carriers and also enhanced photoelectrode stability to over 124 h. In the following, we investigate the effects of both surface passivation and catalyst deposition on the performance of commercial GaAs:p wafers and epitaxial GaAs/Si:p photocathodes.

**Figure 1a** illustrates the structure of the GaAs/Si:p photocathode under scrutiny, with a cross-sectional transmission electron microscopy (TEM) image showing each layer of the sample. A 1 µm thick, nonintentionally doped GaAs epilayer was grown by molecular beam epitaxy (MBE) on a bare p-type Si substrate (B-doped, 10¹⁶ cm⁻³). Atomically thin S-passivation and/or a 3 nm Pt coating by electroless deposition[³¹,⁴¹] were then realized on the sample surface. Details of the deposition procedures are provided in the Experimental Section. As evident from the TEM image,

structural defects are present in the epitaxial GaAs layer, which are expected to reduce its transport properties compared to bulk GaAs. Figure 1b schematically summarizes the two distinct phenomena that may occur at the photocathode surface: electrons may either transfer to the electrolyte (green arrow) to react with the redox couple and produce H₂, or can get trapped by surface states, where they are more likely to recombine with majority carriers (red arrows).[42] Each process occurs with a certain probability, corresponding to a transfer or recombination rate. For GaAs, one of the key limitations is the large overpotential, arising from the low electron transfer rate to the electrolyte relative to the recombination rate. To address this, we adopt a dual strategy: 1) Pt-catalyst electroless deposition, referred to as activation of the photoelectrode, to increase the electron transfer rate from the semiconductor to the electrolyte and 2) (NH₄)₂S chemical surface passivation, referred to as passivation of the photoelectrode, to suppress surface recombination channels.[37–39]

Structural characterization of the epitaxial GaAs/Si:p sample was performed by X-ray diffraction (XRD) in the conventional ω/2θ mode and compared with a commercial GaAs:p wafer (Figure S1a, Supporting Information). The GaAs:p wafer shows a thin Bragg peak at 66.03°, attributed to the signal of the GaAs (004). For the GaAs/Si:p sample, a sharp peak at 69.14° is observed, corresponding to the signal of the Si (004), originating from the Si substrate. Unlike the GaAs wafer, the GaAs (004) peak

<figure><img src="image_6.png" /><figcaption>**Figure 1.** a) Cross-sectional TEM image and schematic of the Pt/GaAs/Si:p sample with a 1 µm-thick GaAs layer. b) Illustration of carrier dynamics in a photocathode (SS: surface states). c) Absorption coefficient of GaAs as a function of photon energy for the GaAs/Si:p photocathode compared with a commercial GaAs:p wafer.</figcaption></figure>
<figure><img src="image_7.png" /></figure>

of the epitaxial layer is broadened, with a full width at half maximum of 0.47°, much larger than that of the GaAs:p wafer (0.025°). This broadening indicates that the epitaxial layer contains more defects than the reference GaAs wafer, consistent with the TEM analysis (Figure 1a) and previous studies.[19] These defects—namely, dislocations, antiphase boundaries, and microtwins—have been widely reported in the literature,[19,43] especially in the case of GaAs epitaxially grown on Si. Atomic force microscopy (AFM) of the as-grown GaAs/Si:p sample (Figure S1b, Supporting Information) reveals a root-mean-square (rms) roughness of 6.9 nm, and the topology is attributed to the emergence of antiphase boundaries.[44] Ellipsometry measurements were performed for both GaAs/Si:p sample and GaAs:p wafer and the individual absorption coefficients of the GaAs epilayer and bulk GaAs were extracted and compared in Figure 1c for the two cases. Both samples exhibit similar absorption coefficients, despite the presence of crystal defects in the epilayer, which, in turn, indicate that the photogeneration of carriers is comparable from one sample to the other.

## 2.2. PEC Properties of Bare, Catalytically Activated, and Passivated GaAs/Si:p and GaAs:p Wafer Photocathodes

The PEC characteristics of GaAs:p wafer-based and GaAs/Si:p-based photocathodes for HER were evaluated in the cathodic regime, in a three-electrode cell configuration in 0.2 M H₂SO₄ under simulated AM1.5G solar illumination (1000 W m⁻²). This configuration is optimized for strongly acidic media, where

GaAs shows relatively high stability.[26] Figure 2 shows the current density-potential (J-V) curves of GaAs:p wafer-based (Figure 2a) and GaAs/Si:p-based (Figure 2b) photocathodes prepared with different surface treatments. The corresponding color codes are shown in Figure 2c. The maximum photocurrent density (Jmax) of GaAs-based photocathodes are measured at -15 mA cm⁻², comparable to those determined in previous reports.[26,27,30-33] This value is higher than that of the GaAs/Si:p-based photocathodes, where Jmax is measured at around -4.5 mA cm⁻². The impeded carrier transport at the GaAs/Si:p interface,[45] due to traps and band misalignment/band bending issues, is believed to be responsible for this trend. A detailed analysis of the spectral response and band bending is given in Figure S2 and S3, Supporting Information. Despite this difference, both photocathodes show comparable Vonset (orange J-V curves, Figure 2a,b) with Vonset values measured for bare GaAs:p and epitaxial GaAs/Si:p photocathodes of -0.19 and -0.23 V versus RHE, respectively. Sulfur passivation alone (green J-V curves, Figure 2a,b) slightly enhances Vonset for both photocathodes by a few mV to a few tens of mV. In contrast, when a single 3 nm thick Pt coating is applied (red J-V curves, Figure 2a,b), the Vonset of GaAs:p and GaAs/Si:p photocathodes is improved massively by 340 and 560 mV, respectively, in comparison with the corresponding untreated electrodes. Beyond this catalytic enhancement of charge transfer rate at the semiconductor/electrolyte interface, it is noteworthy that applying a large negative potential activates the bulk Si, allowing it to contribute to the overall photocurrent. This is evidenced in the incident-photon-to-current efficiency

<figure><img src="image_8.png" /><figcaption>**Figure 2.** Current density-potential J-V curves measured in a three-electrode configuration for a) GaAs:p and b) GaAs/Si:p photocathodes subjected to different surface treatments under chopped AM1.5G illumination. The scan rate was 50 mV s⁻¹. c) Schematic of the surface preparation steps with corresponding color codes used to plot the J-V curves in panels a and b.</figcaption></figure>
<figure><img src="image_9.png" /></figure>

spectra (Figure S2, Supporting Information) of GaAs/Si:p photo-
cathodes before and after Pt catalyst deposition. At a low applied
potential (−1.26 V vs RHE), a strong electric field in the Si region
enables photogenerated electrons in Si to cross into GaAs layer
and contribute to photocurrent, resulting in spectral response
below the GaAs bandgap (1.42 eV). The detailed explanation is
provided in Figure S2, Supporting Information. It is interesting
to note that the situation is probably more complex in reality,
as spectral response of photoelectrodes have been shown to
be different in anodic or cathodic regimes, and depend on the
III-V thickness and the potential applied to the system.[19,22]
Further, band engineering could most likely optimize the Si
and GaAs contributions to the photocurrent even at more posi-
tive bias. The Pt coating also increases the Schottky barrier height
by at least 0.2 V, as shown by the open-circuit potential (OCP) in
Figure S3, Supporting Information. The V onset of GaAs/Si:p is
even improved further by 30 mV, at 0.4 V versus RHE, when
S-passivation is applied on the Pt-coated samples (blue J–V
curves, Figure 2a,b). The Mott–Schottky plots at 1 kHz (Figure S4,
Supporting Information) for a bare GaAs:p before and after treat-
ment by (NH₄)₂S confirm that sulfur passivation reduces surface/
interface states. However, exposure to the electrolyte progres-
sively degrades the passivation effect. Nevertheless, the achieved
V onset of 0.4 V versus RHE remains significantly higher than
previously reported values for costly GaAs-based Schottky-like
photocathodes.[26,27,30–33]

The effect of S-passivation on both samples (GaAs:p and GaAs/Si:p) is thus modest. Besides, our results indicate that the S-passivation is not fully stable. Previous works have shown that the passivation effect vanishes within minutes of electrolyte immersion.[46] In contrast, Pt deposition produces a strong improvement in V onset, with a significantly greater enhancement for GaAs:p-based photocathodes despite their higher density of crystal defects. To better understand this behavior, we further investigated Pt/GaAs:p and Pt/GaAs/Si:p samples using scanning transmission electron microscopy (STEM) with energy-dispersive - X-ray spectroscopy (EDX) to unveil compositional differences between these two electrodes. **Figure 3a** shows the cross-sectional TEM image and corresponding EDX mappings of Ga, As, O, and Pt elements across the surface for the Pt/GaAs:p sample. In this case, the crystalline GaAs is conformally covered by an amorphous layer with a thickness of ≈4.5 nm. The EDX mappings reveal a continuous Pt layer and a continuous oxide layer. Figure 3b shows the cross-sectional TEM image and corresponding EDX mappings for the Pt/GaAs/Si:p sample. The overall structure is similar to that of the Pt/GaAs:p sample, except that the Pt layer on GaAs/Si:p is discontinuous and forms clusters, as clearly visible in the high-angle annular dark field (HAADF) panel. These observations are consistent with scanning electron microscopy (SEM) images of both samples (**Figure 4c** for the Pt/GaAs/Si:p and Figure S5, Supporting Information, for the Pt/GaAs:p). The survey X-ray photoelectron spectroscopy (XPS) spectra (Figure S6, Supporting Information) confirm this morphological difference: the Ga 2p peak at 1145 eV is clearly detected in Pt/GaAs/Si:p but absent in Pt/GaAs:p spectrum, where the continuous Pt film attenuates the Ga 2p signal arising from the GaAs (the

Ga 2p photoelectron mean free path $\lambda$ in Pt being $\lambda \approx 0.6$ nm,[47]
thus the thickness of the conformal Pt layer is equal or greater
than the information depth ID (ID $\approx 3\lambda$) of 2 nm). From the
extracted EDX atomic fraction line scans (Figure S7, Supporting
Information) of Pt/GaAs:p, the compound composition as a func-
tion of the position was estimated, considering the possible pres-
ence of GaAs, elemental As, $Ga_2O_3$, $As_2O_3$, and Pt. Strictly, the
matrix describing this transformation is singular, and we made
the following local assumptions: 1) between 10 and 13 nm, enter-
ing the amorphous region, it is hypothesized that $Ga_2O_3$ is pref-
erentially formed over $As_2O_3$ due to the low oxygen content;[48]
2) between 13 nm and the electrode surface, we consider that the
GaAs content becomes negligible and that $As_2O_3$ forms as oxy-
gen increases. Notably, the disappearance of GaAs in this region
is consistent with the profile calculated in the deeper region.
While more complex oxides may exist—as suggested by the
As 3d XPS spectra (Figure S8, Supporting Information)—the dom-
inant presence of elemental As⁰ remains clear, being more pro-
nounced in Pt/GaAs:p than in Pt/GaAs/Si:p after Pt deposition.
Consequently, for the sake of simplicity, only $Ga_2O_3$ and $As_2O_3$
are considered in this analysis. Overall, the calculated compound
fraction profiles for Pt/GaAs:p sample are given in Figure 3c. We
observe that in the transition region from crystalline to amor-
phous material (10–13 nm), the formation of $Ga_2O_3$ coincides with
elemental As⁰ in a relatively high fraction approaching 60%. The
$Ga_2O_3$ peak reaches a maximum at around 14.5 nm and then
decreases, competing with $As_2O_3$ formation. However, the ele-
mental As⁰ fraction remains high in this region, with a maximum
of 64% in the Pt coating region (>16 nm). Identical assumptions
were made for the Pt/GaAs/Si:p sample with an $As_2O_3$-free region
between 9 and 12 nm and a GaAs-free region above 12 nm. The
computed compound fraction profiles for this sample are pre-
sented in Figure 3d. Qualitatively, elemental As⁰ fraction remains
high near the GaAs/oxide interface but decreases significantly
toward the electrode surface, unlike in Pt/GaAs:p. The Pt/
GaAs/Si:p sample contains slightly more total oxides ($Ga_2O_3$
and $As_2O_3$), but much less elemental As⁰ overall compared to
Pt/GaAs:p. This difference is attributed to the discontinuity of
the Pt layer on Pt/GaAs/Si:p, which favors the solubilization
of elemental As⁰ during the Pt electroless deposition. Since elec-
troless deposition is highly sensitive to doping type and concen-
tration,[49,50] the difference on the morphology of the Pt layer
between the two types of photocathodes is thus linked to
the different dopant concentrations of the substrates: GaAs:p
wafers are doped at $2 \times 10^{17} \text{ cm}^{-3}$, while the GaAs epilayer
on Si is not intentionally doped. Pt morphology therefore plays
a critical role in controlling defect states—particularly elemental
As⁰—at the metal–insulator–semiconductor (MIS) interface. The
continuous Pt film on GaAs:p retains more elemental As⁰ in the
MIS electrode, reducing catalytic activity, as compared to GaAs/
Si:p. In the latter case, the clustered Pt morphology promotes
elemental As⁰ removal from the interface during the electrode
preparation and simultaneously promotes the pinch-off
effect,[31] thereby improving catalyst performance (Figure S9,
Supporting Information).
<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /><figcaption>**Figure 3.** High-resolution HAADF images and corresponding STEM-EDX elemental mappings (Ga, As, O, Pt) across the surface of a) Pt/GaAs:p and b) Pt/GaAs/Si:p. Compound fraction profiles as a function of position along the growth axis for c) Pt/GaAs:p and d) Pt/GaAs/Si:p.</figcaption></figure>

## 2.3. Stability of Pt/GaAs/Si:p during Solar H₂ Production

A key prerequisite for the effective use of semiconductor photo-electrodes in solar H₂ production is the long-term preservation of the material properties and catalytic performance of the photo-electrode itself. In this regard, the stability of Pt/GaAs/Si:p photocathode was evaluated at 0 V versus RHE in 0.2 M H₂SO₄ (aq) under simulated 1-sun illumination. Figure 4a shows the current density measured for the Pt/GaAs/Si:p photocathode as a function of the electrolysis time. As shown by this chronoamperogram, during operation at 0 V versus RHE, the photocurrent decreases by 50% in the first 4 h (from 4 to 2 mA cm⁻²) and then stabilizes up to 90 h. After 112 h of operation, the photocurrent remains at 1.7 mA cm⁻². According to Pourbaix diagrams of GaAs,[⁵¹] at 0 V versus RHE and pH ≈ 0.7, elemental As⁰ is formed and stabilizes the photoelectrode surface. This observation is

consistent with previous reports[²⁷] and explains the long operational lifetime exceeding 112 h. The initial photocurrent decay aligns with the negative Vonset shift observed in the illuminated J-V curves of the Pt/GaAs/Si:p photocathode (Figure 4b). To further investigate this degradation, SEM images were collected before and after chronoamperometry (CA) operation (Figure 4c-f). Prior to CA, we observed a high density of small Pt clusters (diameter ≈ 2 nm) on the surface (Figure 4c). The observed trenches on the GaAs surface are characteristics of emerging anti-phase boundaries.[¹⁸] After 2.5 h of operation, several darker areas appeared on the surface (Figure 4d) where Pt particles had been completely removed (Figure 4f), while in other areas, the Pt particles coalesced into larger clusters with diameter larger than 3 nm (Figure 4e). This morphological evolution correlates with the generation of excess elemental As⁰ during operation, which promotes Pt particle coalescence. In addition to altering the Pt
<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /><figcaption>**Figure 4.** a) CA curve of the Pt/GaAs/Si:p photocathode at 0 V versus RHE in H₂SO₄ 0.2 M under 1 sun illumination; the inset shows the evolution during the first 4 h, where the photocurrent decreases. b) J-V curves recorded for the Pt/GaAs/Si:p photocathode during the potentiostatic experiment shown in (a) (scan rate: 50 mV s⁻¹). SEM images of the Pt/GaAs/Si:p photocathode: c) before CA, d) after 2.5 h of CA, e) magnified view of the bright region in (d) (red square), and f) magnified view of the dark region in (d) (yellow square).</figcaption></figure>

distribution, elemental As⁰ can, furthermore, adversely affect interfacial charge transfer process in the photocathode (the detailed explanation is given hereafter).[26] Overall, the gradual deactivation of the Pt/GaAs/Si:p photocathode is attributed to both partial Pt removal (observed by SEM) and the excess generated elemental As⁰ during operation. In this context, employing physical deposition methods for Pt could be a promising strategy to enhance the long-term stability of these photoelectrodes.

## 2.4. PEC Processes

As widely reported in the literature,[30-32] Pt deposition strongly increases the catalytic activity of GaAs-based photocathodes. In this study, however, we show that the catalytic performance is strongly influenced by the oxide layer formed at the semiconductor-metal interface, which, in turn, strongly depends on the deposition method. In this work, the electroless deposition

process is largely influenced by the doping level of the semiconductor layer. Using this procedure, a large accumulation of elemental As⁰ occurs within the oxide layer, due to the continuity of the Pt/GaAs:p electrodes, resulting in the trapping of photo-generated carriers. A large band bending is then required to separate efficiently the charges in order to obtain a significant photocurrent (Figure 5a). In contrast, for samples where the Pt deposit is discontinuous such as observed with the Pt/GaAs/Si:p photoelectrodes, elemental As⁰ can be more efficiently removed from the oxide during electroless deposition, reducing overall recombination. As a result, a smaller degree of band bending is sufficient to sustain comparable photocurrent densities (Figure 5b). The modest V-onset improvement observed with S-passivated Pt/GaAs/Si:p electrodes (Figure 2b) suggests that post-deposition passivation only weakly mitigates the effect of elemental As identified by STEM-EDX. This limited effect is likely due to the inability of sulfur treatment to modify the deeper oxide

<figure><img src="image_14.png" /><figcaption>**Figure 5.** Schematic illustration of PEC operation processes for a) Pt/GaAs:p photocathode and b) Pt/GaAs/Si:p photocathode; red dots within the cyan layer indicate defect states (DS). Dashed lines delineate the components of three layers displayed in gray, cyan, and light pink. Green arrows represent electron transfer processes, while red arrows denote recombination pathways.</figcaption></figure>
<figure><img src="image_15.png" /></figure>

regions.[52] Nonetheless, the Pt-coated GaAs/Si:p photocathode demonstrates clear advantages over a dark Pt cathode. Gas evolution analysis indicates a H₂ production rate of ≈0.02 µmol cm⁻² s⁻¹ which is comparable to values reported for Si-based photocathodes.[53] Additional details on the catalytic efficiency of the studied photoelectrodes are provided in Figure S10 and S11, Supporting Information. Overall, this work not only shows the whole potential of planar III–V/Si photoelectrodes for industrial solar hydrogen production but also highlights the need to consider less expensive adapted catalysts and explore the interplay between catalysts morphologies and surface states.[54]

### 3. Conclusion

In summary, we demonstrated an activated and passivated III–V/Si Schottky-based photocathode that addresses the main limitations of conventional III–V systems, namely, cost, overpotential, and durability. GaAs/Si:p photocathodes were benchmarked against commercial GaAs:p photocathodes, the latter serving as a reference. Following electroless Pt deposition and S-passivation, the GaAs/Si:p photocathodes exhibited a remarkable positive shift (0.63 V) in onset potential, achieving 0.4 V versus RHE. Notably, this improvement exceeded that of the less-defective GaAs reference, a trend attributed to differences in Pt film morphology arising during electroless deposition. In addition, the underlying Si substrate was shown to contribute directly to the overall photocurrent, confirming its photoactivity. The stability of Pt/GaAs/Si:p photocathodes was assessed, demonstrating a positive onset potential after 112 h of operation, without evidence of GaAs corrosion. Overall, this study shows the potential of planar III–V/Si photoelectrodes as a cost-effective and high-performance platform for solar-driven hydrogen production.

### 4. Experimental Section

P-type GaAs (100) substrates (Zn-doped, 0.72–2.8 × 10¹⁷ cm³) and 1 µm thick GaAs layers (non-intentionally doped) grown by MBE on a p-doped Si substrate (B-doped, 10¹⁶ cm⁻³, with a miscut of 6° off along [110]) were used as the light absorbers and were cut into small 0.2–0.3 cm² pieces. Ohmic back contact was formed by scratching the backside of Si wafer, applying a droplet of gallium–indium eutectic (99.99%, Alfa Aesar), then covering with silver paste (Electron Microscopy Sciences).

#### Electrochemical Characterization

The PEC cell used was a three-electrode cell, with the light absorber employed as the working electrode, a graphite rod as the counter electrode, and an Ag/AgCl as the reference electrode. The used electrolyte was H₂SO₄ 0.2 M. An Autolab electrochemical analyzer (PGSTAT 20 potentiostat/galvanostat from Eco Chemie B.V.) was used to control the experiments. All measurements were performed at room temperature, at scan rate of 50 mV s⁻¹ and were conducted under AM1.5G (100 mW cm⁻²) conditions using a solar simulator (LS0106, LOT Quantum Design). All potentials reported in this article are referred to RHE. The V-onset of all of the J–V curves was determined at a threshold of –0.25 mA cm⁻².

#### Sulfur Passivation

The bare samples were first dipped in HCl 10% aqueous solution for 1 min, followed by (NH₄)₂S 20% aqueous solution for 1 h. After treatment, the samples were dried with N₂ gun. The Pt-coated samples were only dipped in (NH₄)₂S 20% for 1 h, followed by drying with N₂ gun.

#### Platinum Electroless Deposition

Samples were dipped in a solution containing hydrogen fluoride HF at 4.6 M and chloroplatinic acid H₂PtCl₆ at 1 mM for 10 s. Samples were then rinsed with ultrapure water and dried with N₂ gun.

#### Ellipsometry

The ellipsometry measurements were performed at room temperature using a Horiba Jobin-Yvon UVisel 2 phase-modulated ellipsometer. The data in the range 1.39–6.20 eV were measured with an incidence angle of 70°.

#### AFM

The AFM images were obtained using an Innova Bruker AFM microscope, which is a high-resolution scanning probe microscope. The microscope has been used in the tapping mode with a standard non-contact probe.

#### XRD

XRD was performed on a D8 Discover Bruker XRD diffractometer. A 2 bounce Ge (220) asymmetric monochromator with 2 reflectors was used for line scan XRD. The beam height was 1.2 mm and the detector model was Dectris 250 K, allowing a collection angle of 2.6° over 2θ.

#### STEM-EDX

The STEM high-resolution imaging and EDX line-scan were obtained by using a 200 kV ThermoFisher Titan TEM/STEM equipped with a probe aberration corrector allowing atomic-scale resolution images in Z-contrasted HAADF mode and four silicon drift detectors for EDX. Since the region of interest (top surface of the semiconducting material partly oxidized) was sensitive to the beam irradiation, the gun was set to GunLens = 5 giving a low probe current of 80 pA avoiding any degradation during the EDX analyses. The cross-sectional TEM lamellae were prepared by focused ion beam.

#### SEM

The SEM images were obtained using an Apreo2 Thermofisher scanning electron microscope. The working distance was around 2 mm. T2 detector was used which is sensitive to the chemical composition and surface of the samples.

#### XPS

XPS measurements were performed with a HiPP lab system Scienta Omicron spectrometer using monochromatic Al Kα (1486.6 eV) X-ray
<figure><img src="image_16.png" /></figure>

source. Survey scans were collected in the range of 0–1400 eV. The raw data were processed using CASA XPS software.

## Acknowledgements

The authors acknowledge RENATECH (French Network of Major Technology Centers) within Nanorennes and C2N-PANAM platform for technological support. This research was supported by the "France 2030" program of the French National Research Agency, NAUTILUS Project (grant no. ANR-22-PEHY-0013), the EQUIPEX NANOFUTUR (ANR-21-ESRE-0012), Rennes Métropole, and Région Bretagne. H.V.L., Y.L., N.B., B.F., G.L., and C.C. conceived the idea and designed the experiments. H.V.L., S.F., T.R., R.B., K.T., N.B., and C.C. conceived and realized the samples. H.V.L., G.L., L.L., G.P., A.L., C.L., B.B.K., S.H., A.R., K.S., and J.L.P. characterized the samples. H.V.L., G.L., B.F., F.M., L.L., F.J., R.B., Y.L., N.B., and C.C. analyzed the data. H.V.L., Y.L., and C.C. wrote the article. All authors reviewed and commented on the manuscript.

## Conflict of Interest

The authors declare no conflict of interest.

## Author Contributions

**Hanh Vi Le**: data curation (lead); formal analysis (equal); investigation (lead); methodology (supporting); visualization (equal); writing—original draft (lead); writing—review and editing (equal). **Rozenn Bernard**: data curation (equal); formal analysis (supporting); investigation (supporting); resources (supporting). **Ludovic Largeau**: data curation (equal); formal analysis (supporting); investigation (supporting); resources (equal); writing—review and editing (supporting). **Gilles Patriarche**: data curation (supporting); formal analysis (supporting); funding acquisition (supporting); investigation (supporting); resources (equal); writing—review and editing (supporting). **Sylvain Febvre**: methodology (equal). **Fatima Merhi**: formal analysis (supporting). **Bienvenu Boulingui Koumba**: data curation (supporting); investigation (supporting). **Antoine Letoublon**: data curation (equal); formal analysis (equal); investigation (supporting); methodology (equal); writing—review and editing (supporting). **Christophe Levallois**: data curation (supporting); formal analysis (supporting). **Fauzia Jabeen**: data curation (supporting); formal analysis (supporting). **Sylvie Harel**: data curation (equal); formal analysis (supporting); investigation (equal); methodology (equal); resources (supporting); writing—review and editing (supporting). **Angus Rockett**: data curation (supporting); investigation (supporting); resources (supporting). **Xerxes K. Steirer**: data curation (supporting); formal analysis (supporting); resources (supporting). **Tony Rohel**: data curation (equal); investigation (supporting). **Karine Tavernier**: data curation (equal); investigation (supporting). **Julie Le Pouliquen**: data curation (supporting); investigation (supporting). **Yuan Léger**: conceptualization (equal); data curation (equal);

formal analysis (lead); funding acquisition (supporting); investigation (lead); methodology (equal); resources (equal); software (supporting); supervision (equal); validation (lead); writing—review and editing (equal). **Nicolas Bertru**: conceptualization (equal); data curation (equal); formal analysis (lead); funding acquisition (supporting); investigation (lead); resources (supporting); supervision (equal); validation (equal); writing—review and editing (equal). **Bruno Fabre**: data curation (equal); formal analysis (equal); investigation (equal); methodology (equal); resources (equal); supervision (supporting); validation (supporting); writing—review and editing (equal). **Charles Cornet**: conceptualization (lead); data curation (equal); formal analysis (lead); funding acquisition (lead); investigation (lead); methodology (equal); project administration (lead); resources (lead); supervision (lead); validation (equal); writing—original draft (supporting); writing—review and editing (lead).

## Data Availability Statement

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

**Keywords:** epitaxy · GaAs/Si · photocathodes · solar water splitting

[1] A. Fujishima, K. Honda, *Nature* **1972**, *238*, 37.

[2] M. G. Walter, E. L. Warren, J. R. McKone, S. W. Boettcher, Q. Mi, E. A. Santori, N. S. Lewis, *Chem. Rev.* **2010**, *110*, 6446.

[3] F. Lin, S. W. Boettcher, *Nature Mater.* **2014**, *13*, 81.

[4] J. F. Geisz, R. M. France, K. L. Schulte, M. A. Steiner, A. G. Norman, H. L. Guthrey, M. R. Young, T. Song, T. Moriarty, *Nat. Energy* **2020**, *5*, 326.

[5] R. Cariou, J. Benick, F. Feldmann, O. Höhn, H. Hauser, P. Beutel, N. Razek, M. Wimplinger, B. Bläsi, D. Lackner, M. Hermle, G. Siefer, S. W. Glunz, A. W. Bett, F. Dimroth, *Nat. Energy* **2018**, *3*, 326.

[6] M. Bosi, C. Pelosi, *Prog. Photovoltaics Res. Appl.* **2007**, *15*, 51.

[7] S. Tiwari, D. J. Frank, *Appl. Phys. Lett.* **1992**, *60*, 630.

[8] G. Siddiqi, Z. Pan, S. Hu, in *Semiconductors and Semimetals*, (Eds: Z. Mi, L. Wang, C. Jagadish), Elsevier, Amsterdam, Netherlands **2017**, pp. 81–138

[9] J. Tournet, Y. Lee, S. K. Karuturi, H. H. Tan, C. Jagadish, *ACS Energy Lett.* **2020**, *5*, 611.

[10] W.-H. Cheng, M. H. Richter, M. M. May, J. Ohlmann, D. Lackner, F. Dimroth, T. Hannappel, H. A. Atwater, H.-J. Lewerenz, *ACS Energy Lett.* **2018**, *3*, 1795.

[11] T. Ramsden, D. Steward, J. Zuboy, Technical Report NREL/TP-560-46267, September **2009**.

[12] A. Gilbert, M. Ramonda, L. Cerutti, C. Cornet, G. Patriarche, É. Tournié, J. Rodriguez, *Adv. Opt. Mater.* **2023**, *11*, 2203050.

[13] J. Wu, Y. Li, J. Kubota, K. Domen, M. Aagesen, T. Ward, A. Sanchez, R. Beanland, Y. Zhang, M. Tang, S. Hatch, A. Seeds, H. Liu, *Nano Lett.* **2014**, *14*, 2013.

[14] T. Dursap, M. Fadel, P. Regreny, C. T. Garcia, C. Chevalier, H. S. Nguyen, E. Drouard, S. Brottet, M. Gendry, A. Danescu, M. Koepf, V. Artero, M. Bugnet, J. Penuelas, *ACS Appl. Mater. Interfaces* **2023**, *15*, 53446.

[15] I. Lucci, S. Charbonnier, M. Vallet, P. Turban, Y. Léger, T. Rohel, N. Bertru, A. Létoublon, J.-B. Rodriguez, L. Cerutti, E. Tournié, A. Ponchet, G. Patriarche, L. Pedesseau, C. Cornet, *Adv. Funct. Mater.* **2018**, *28*, 1801585.
<figure><img src="image_17.png" /></figure>

[16] P. Kumar, P. Devi, R. Jain, S. M. Shivaprasad, R. K. Sinha, G. Zhou, R. Nötzel, *Commun. Chem.* **2019**, *2*, 1.

[17] M. Alqahtani, S. Sathasivam, L. Chen, P. Jurczak, R. Piron, C. Levallois, A. Létoublon, Y. Léger, S. Boyer-Richard, N. Bertru, J.-M. Jancu, C. Cornet, J. Wu, I. P. Parkin, *Sustainable Energy Fuels* **2019**, *3*, 1720.

[18] L. Chen, Y. Léger, G. Loget, M. Piriyev, I. Jadli, S. Tricot, T. Rohel, R. Bernard, A. Beck, J. L. Pouliquen, P. Turban, P. Schieffer, C. Levallois, B. Fabre, L. Pedesseau, J. Even, N. Bertru, C. Cornet, *Adv. Sci.* **2022**, *9*, 2101661.

[19] M. Piriyev, G. Loget, Y. Léger, L. Chen, A. Létoublon, T. Rohel, C. Levallois, J. L. Pouliquen, B. Fabre, N. Bertru, C. Cornet, *Solar Energy Mater. Solar Cells* **2023**, *251*, 112138.

[20] M. Piriyev, G. Loget, Y. Léger, H. V. Le, L. Chen, A. Létoublon, T. Rohel, C. Levallois, J. L. Pouliquen, B. Fabre, N. Bertru, C. Cornet, *J. Mater. Chem. C* **2024**, *12*, 1091.

[21] G. Zeng, T. A. Pham, S. Vanka, G. Liu, C. Song, J. K. Cooper, Z. Mi, T. Ogitsu, F. M. Toma, *Nat. Mater.* **2021**, *20*, 1130.

[22] F. Merhi, B. B. Koumba, R. Bernard, A. Létoublon, P. Huillery, Y. Léger, N. Bertru, C. Cornet, P. Garrigue, B. Fabre, G. Loget, *J. Phys. Chem. C* **2025**, *129*, 11290.

[23] C. G. Van de Walle, J. Neugebauer, *Nature* **2003**, *423*, 626.

[24] K. Walczak, Y. Chen, C. Karp, J. W. Beeman, M. Shaner, J. Spurgeon, I. D. Sharp, X. Amashukeli, W. West, J. Jin, N. S. Lewis, C. Xiang, *ChemSusChem* **2015**, *8*, 544.

[25] E. Verlage, S. Hu, R. Liu, R. J. R. Jones, K. Sun, C. Xiang, N. S. Lewis, H. A. Atwater, *Energy Environ. Sci.* **2015**, *8*, 3166.

[26] W. Yu, M. H. Richter, E. Simonoff, B. S. Brunschwig, N. S. Lewis, *J. Mater. Chem. A* **2021**, *9*, 22958.

[27] J. L. Young, K. X. Steirer, M. J. Dzara, J. A. Turner, T. G. Deutsch, *J. Mater. Chem. A* **2016**, *4*, 2831.

[28] D. Kang, J. L. Young, H. Lim, W. E. Klein, H. Chen, Y. Xi, B. Gai, T. G. Deutsch, *J. Yoon, Nat. Energy* **2017**, *2*, 1.

[29] W. Yu, P. Buabthong, J. L. Young, Z. P. Ifkovits, S. T. Byrne, M. A. Steiner, T. G. Deutsch, N. S. Lewis, *ACS Appl. Mater. Interfaces* **2022**, *14*, 26622.

[30] M. Khader, *Int. J. Hydrogen Energy* **1996**, *21*, 547.

[31] K. Choi, K. Kim, I. K. Moon, I. Oh, J. Oh, *ACS Appl. Energy Mater.* **2019**, *2*, 770.

[32] S. Cao, Z. Kang, Y. Yu, J. Du, L. German, J. Li, X. Yan, X. Wang, Y. Zhang, *Adv. Energy Mater.* **2020**, *10*, 1902985.

[33] K. Choi, K. Kim, I. K. Moon, J. Bang, J. Oh, *Nanoscale* **2019**, *11*, 15367.

[34] K. Uosaki, Y. Shigematsu, S. Kaneko, H. Kita, *J. Phys. Chem.* **1989**, *93*, 6521.

[35] T. Suzuki, K. Iizuka, in *Proc. of the Symposium on Photoelectrochemistry and Electrosynthesis on Semiconducting Materials*, (Eds: D. S. Ginley, K. Honda, A. Nozik, A. Fujishima, N. Armstrong, T. Sakata, T. Kawai), *Electrochemical Society, Pennington, USA 1988*.

[36] K. Uosaki, Y. Shigematsu, H. Kita, *Chem. Lett.* **1988**, *17*, 1815.

[37] M. Rebaud, M.-C. Roure, V. Loup, P. Rodriguez, E. Martinez, P. Besson, *ECS Trans.* **2015**, *69*, 243.

[38] B. Brennan, M. Milojevic, C. L. Hinkle, F. S. Aguirre-Tostado, G. Hughes, R. M. Wallace, *Appl. Surface Sci.* **2011**, *257*, 4082.

[39] Z. L. Yuan, X. M. Ding, H. T. Hu, Z. S. Li, J. S. Yang, X. Y. Miao, X. Y. Chen, X. A. Cao, X. Y. Hou, E. D. Lu, S. H. Xu, P. S. Xu, X. Y. Zhang, *Appl. Phys. Lett.* **1997**, *71*, 3081.

[40] H. Lim, J. L. Young, J. F. Geisz, D. J. Friedman, T. G. Deutsch, J. Yoon, *Nat. Commun.* **2019**, *10*, 3388.

[41] N. D. Pham, S. J. Park, J. P. Lee, I. Oh, *J. Chem.* **2014**, *2014*, 1.

[42] Y. Zhao, J. Descamps, S. Ababou-Girard, J.-F. Bergamini, L. Santinacci, Y. Léger, N. Sojic, G. Loget, *Angew. Chem. Int. Ed.* **2022**, *61*, e202201865.

[43] I. Lucci, S. Charbonnier, L. Pedesseau, M. Vallet, L. Cerutti, J.-B. Rodriguez, E. Tournié, R. Bernard, A. Létoublon, N. Bertru, A. L. Corre, S. Rennesson, F. Semond, G. Patriarche, L. Largeau, P. Turban, A. Ponchet, C. Cornet, *Phys. Rev. Mater.* **2018**, *2*, 060401.

[44] C. Cornet, S. Charbonnier, I. Lucci, L. Chen, A. Létoublon, A. Alvarez, K. Tavernier, T. Rohel, R. Bernard, J.-B. Rodriguez, L. Cerutti, E. Tournié, Y. Léger, M. Bahri, G. Patriarche, L. Largeau, A. Ponchet, P. Turban, N. Bertru, *Phys. Rev. Mater.* **2020**, *4*, 053401.

[45] S. Hu, C.-Y. Chi, K. T. Fountaine, M. Yao, H. A. Atwater, P. D. Dapkus, N. S. Lewis, C. Zhou, *Energy Environ. Sci.* **2013**, *6*, 1879.

[46] M. S. Carpenter, M. R. Melloch, T. E. Dungan, *Appl. Phys. Lett.* **1988**, *53*, 66.

[47] S. Tanuma, C. J. Powell, D. R. Penn, *Surf. Interface Anal.* **1994**, *21*, 165.

[48] J. Li, L. M. Peter, *J. Electroanal. Chem. Interfacial Electrochem.* **1986**, *199*, 1.

[49] S. Chattopadhyay, X. Li, P. W. Bohn, *J. Appl. Phys.* **2002**, *91*, 6134.

[50] H. Cachet, M. Froment, E. Souteyrand, C. Dennig, *J. Electrochem. Soc.* **1992**, *139*, 2920.

[51] K. Murase, *Rev. Polarogr.* **2014**, *60*, 35.

[52] R. H. Wilson, *J. Appl. Phys.* **1977**, *48*, 4292.

[53] A. Jena, C.-J. Chen, H. Chang, S.-F. Hu, R.-S. Liu, *J. Mater. Chem. A* **2021**, *9*, 3767.

[54] A. Kazemi, F. Manteghi, Z. Tehrani, *ACS Omega* **2024**, *9*, 7310.

Manuscript received: June 19, 2025

Revised manuscript received: September 4, 2025

Version of record online: