Chain-ordered Pt atoms with delocalized electronic structure for improved hydrogen production

Domain: physics
Published: 2025-11-29
Editorial outcome: major_revision

Abstract
As the smallest one-dimensional structure, single-atom chains exhibit many one-dimensional quantized behaviors, such as Tomonaga-Luttinger liquid behavior, high-temperature superconductivity, and fluctuations. In contrast to single-atom catalysts, there is growing interest in exploring whether and how the point-to-point interaction occurs between neighboring metal atoms in 1D chains. Here, we controllably fabricate Pt chains and single atoms in MoS2 films with similar coordination environments and conduct model studies on their catalytic behaviors in hydrogen production. Combining calculations with field effect transistor and micro-electrochemical measurements, we reveal that the chains exhibit significant delocalized electron densities, which underpins their metallic behavior and engenders a fascinating center site with lower Gibbs free energy than that of single atoms. Notably, we demonstrate that the chain density can be well-tuned, achieving a maximum of 2.82 Pt/nm2, which enables a competitive turnover frequency and wafer-scale hydrogen production. This work offers insights into our understanding of the possible synergistic effect between metal atoms in a 1D arrangement for electrocatalysis.

Introduction
With the development of advanced fabrication methods and atomic-imaging techniques over the past few decades, it is now possible to tailor nanomaterials down to an atomic scale. For instance, 0D single atoms have been dispersed on substrates, and both 1D single-atom chains and 2D single-atom layers have been realized. For example, graphene and hexagonal boron nitride (h-BN) are representative single-atom layer materials in which atoms are arranged in two-dimensional (2D) honeycomb lattices, showing promising applications1,2. Another example is single-atom catalysts, where metals are dispersed as isolated atoms, demonstrating high activity and selectivity in heterogeneous catalysis3–7. Compared with the structures mentioned above, single-atom chains made up of metal-atom strings are considered the most straightforward 1D system, attracting intense attention in the physical field. For example, previous studies have reported that they could serve as ideal model systems for investigating condensed matter theories (e.g., high-temperature superconductivity8, topological phases9, and quantum spin Hall effect10) as well as complex phenomena in many-body systems (e.g., Aubry-type leptonics11, the final state12, Majorana fermions13, and chiral solitons14,15).

However, despite extensive research on single-atom catalysts, few studies have focused on single-atom chains in catalysis. This is primarily due to the formidable challenge of precisely arranging single atoms into 1D arrays, which often limits their catalytic potential. Although a series of fabrication methods, e.g., mechanically controllable breaking junction (MCBJ)16–20, twisted 2D bilayer materials21, self-assembly22–27, and ligand-assisted synthesis28–33, have been developed, these approaches require strict growth conditions that greatly restrict their catalytic applicability. For example, single-atom chains prepared via MCBJ typically suffer from short length (<5 atoms in length) and structural fragility, while self-assembled atom wires are extremely unstable in an atmosphere.

In our recent work, we reported a wafer-scale network of Pt single-atom chains in transition metal dichalcogenides (TMDCs) films grown by a chemical vapour co-deposition method34. The obtained atomic chains have an average length of up to ~17 nm and are highly stable in air and solution. Encouragingly, this strategy is expected to offer a promising opportunity to study the catalytic behavior of single-atom chains. More importantly, compared with single-atom catalysts with isolated single atoms, this system can serve as an ideal 1D model for exploring potential point-to-point interaction between neighboring metal atoms along 1D chains, thereby clarifying how their synergistic mechanism arises. Furthermore, it could help guide the design of 1D-arranged active sites to improve catalytic performance.

In this work, we conducted model studies to investigate how the catalytic behavior of Pt chains differs from that of Pt single atoms, and then explored their potential toward hydrogen production. First, we performed density functional theory (DFT) calculations to examine their electronic structures and screen their possible active sites, demonstrating the strong electronic delocalization of Pt atoms in chains. Next, using a mass flow-controlled chemical vapor deposition (CVD) method, we precisely controlled the formation of Pt chains and isolated single atoms with similar coordination environments. This approach enabled a detailed investigation of their electronic and catalytic properties through field-effect transistors (FET) and micro-electrochemical devices. Finally, we tuned and optimized the chain density to a maximum of 2.82 Pt/nm2, yielding numerous vertex structures that further contributed to hydrogen evolution reaction (HER) performance, that is, an overpotential of less than 10 mV at the current density of 10 mA/cm2.

Results
We began investigating the potential for catalytic and electronic behaviors between isolated single Pt atoms (Fig. 1a) and their 1D-arrayed chains (Fig. 1e) in MoS2 using density functional theory (DFT) calculations; see Methods for details. We here first calculated all possible active sites for H atom adsorption on Pt atom-MoS2 and Pt chain-MoS2 (Fig. 1b and f), respectively. In the Pt atom-MoS2 system, the active sites are sulfur atoms adjacent to the isolated Pt; among these, the S-3 site (labeled in a blue rectangular box in Fig. 1b) exhibits the lowest adsorption Gibbs free energy (ΔGH* = 0.25 eV, Fig. 1c). Interestingly, in the Pt chain-MoS2 system, we found that the H atom preferentially adsorbs at the center of Pt-adjacent atoms (red box in Fig. 1f), as well as at the S-side and S-top (grey boxes in Fig. 1f). Detailed structural analysis suggest that the center sites show ΔGH* for hydrogen adsorption as low as 0.18 eV, which is consistent with an improved HER activity compared to the Pt atom-MoS2 (Fig. 1g). Notably, this type of center site for Pt chains has not been widely reported. In addition, we also calculated the catalytic activities of the S sites located at the second and third nearest positions to the Pt chain (Supplementary Fig. 1). Both of them turn out the Gibbs free energy as high as about 1.79 eV, much higher than that of the S site adjacent to Pt (site 1: 0.81 eV), suggesting that the MoS2 near the Pt chains remains inactive.

To comprehend the origin of those active sites, we further calculated their band structures and projected densities of states (DOS), as shown in Fig. 1d and h. In the Pt atom-MoS2 system, introducing isolated single atoms in the MoS2 lattice appears to create new defect energy levels near the Fermi level35, thereby lowering the position of the conduction band edge and consequently reducing the overall band gap to 0.47 eV (Fig. 1d). By contrast, when Pt atoms are arranged into 1D chains in MoS2, we observed significant delocalized electron densities between adjacent Pt atoms, which increases the DOS across the band gap and imparts metallic behavior to the Pt chains (Fig. 1h). Consequently, the electron state near the Fermi level could provides an abundant supply of electrons for proto-hydrogen adsorption36–38. Besides, the partial charge densities indicate the considerable interaction of Pt-Pt and Pt-S for the Pt chain-MoS2 system (Supplementary Fig 2). Therefore, compared with isolated Pt atoms, 1D-arrayed Pt chains display pronounced electronic delocalization, which significantly modifies the electronic structure of Pt-MoS2 systems, correlating with enhanced HER activity.

Pt chains and isolated single atoms in MoS2 were synthesized using a mass flow-controlled CVD method (Supplementary Fig 3). The typical procedure comprises two steps: i) pre-deposition of Pt atomic clusters on the SiO2/Si substrate by electron beam evaporation, forming Pt nanoclusters with sizes ranging from 0.6 to 1.5 nm dispersed across the SiO2/Si substrate (Supplementary Fig 4); ii) the fabrication of either 1D Pt chains or isolated Pt atoms can be obtained by growing MoS2 on those substrates at different metal precursor mass fluxes. For 1D Pt chains, the growth process is similar to our previous work34, where MoO3 was used as metal precursors to facilitate a “surf-zip” growth mechanism. However, for isolated Pt atoms, salt (e.g., NaCl in our experiment) was added to generate volatile MoOCl4 precursors, which significantly increased the MoS2 growth rate and thereby inhibited the above “surf-zip” kinetic process39,40. As a result, Pt atoms were randomly isolated within the MoS2 lattices.

Figure 2a and c displays optical images of as-grown Pt chain-MoS2 and Pt atom-MoS2 samples on SiO2/Si substrates, respectively, revealing uniform and continuous films. This is further supported by the scanning electron microscope (SEM) images (Supplementary Fig 5), showing a complete film grown on the SiO2/Si substrate. X-ray photoelectron spectroscopy (XPS) measurements show two identical types of Pt(II) in the Pt 4f region for both samples, indicating similar Pt coordination environments (Fig. 2b and d)41–43. The absence of metallic Pt peaks at 71.3 eV suggests that all Pt atoms are bonded to S atoms following our CVD growth34,41. Additionally, the Raman spectra show that the E2g/A1g intensity ratio in Pt chain-MoS2 is lower than that of Pt atom-MoS2 (Supplementary Fig. 6a and c and Table 1), indicating that the former has a polycrystalline-rich structure due to high-density grain boundaries44. Furthermore, the absence of the characteristic 780 nm MoS2 photoluminescence peak in Pt chain-MoS2 (Supplementary Fig 6b) suggests a charge transfer process between Pt chains and MoS245, which results from the chain-induced electronic delocalization behavior as discussed above in the DFT results (Fig. 1h).

To probe the atomic structures of Pt chain-MoS2 and Pt atom-MoS2 samples, we employed scanning transmission electron microscopy (STEM) in combination with energy-dispersive X-ray spectroscopy (EDS) mapping. We observed a uniform distribution of Pt, S, and Mo in both films (Fig. 2e and f), confirming the incorporation of Pt in both samples. Furthermore, the EDS data clearly demonstrate a Mo/S atomic ratio of approximately 1:2 (Supplementary Table 2). Figure 2g shows that Pt chains have lengths ranging from 1.2 to 5.3 nm, and their angles are close to 60° (Supplementary Fig 7), consistent with the rotation of the MoS2 crystal structure (Supplementary Fig 8). The distance between adjacent Pt atoms is around 3.4 Å (right in Fig. 2g), a value larger than that of the conventional Pt–Pt bonds (e.g., 2.78 Å in Pt (111) surface46). In contrast, Pt atoms in the Pt atom-MoS2 sample are uniformly dispersed without a chain-like arrangement (Fig. 2h). Notably, the Pt intensity profiles measured are similar to the Pt atom-MoS2 sample, suggesting their identical Pt-S bonds. This conclusion could be rationalized by our simulation analysis of annular dark-field scanning transmission electron microscopy (ADF-STEM) imaging, confirming that the Pt atoms in the Pt chain-MoS2 are embedded within the MoS2 film and bonded to S atoms (Supplementary Fig 9a). In contrast, the Pt atoms in the Pt atom-MoS2 sample occupy Mo vacancies while similarly bonding to adjacent S atoms (Supplementary Fig 9b). Therefore, the coordination environments of Pt atoms in both samples are similar, and their STEM signal intensities are comparable (Fig. 2g and h). Together, these results indicate that our mass flow-controlled CVD method enables the growth of Pt chains and isolated Pt atoms in MoS2 films with similar Pt coordination, providing a platform to study distinct properties solely based on their 1D atomic arrangement.

Next, we fabricated FET devices based on Pt chain-MoS2 and Pt atom-MoS2 samples (Fig. 3a and Supplementary Fig 10). The resulting Ids–Vds curves are linear and symmetrical, reflecting good electrical contact between the Cr/Au electrode and the films (Fig. 3b). As shown in Fig. 3c, pure MoS2 displays n-type semiconducting behavior, in agreement with previous FET measurements42,47, whereas Pt atom-MoS2 reveals weak p-type modulation, implying that the introduction of Pt atoms significantly modifies the electronic structures of the MoS2 host materials. Furthermore, despite similar Pt content, the Pt chain-MoS2 device demonstrates higher conductance and markedly reduced modulation compared to the Pt atom-MoS2 counterpart. These findings indicate the metallic nature of Pt chains in MoS2, consistent with our DOS analysis from the theoretical calculations presented above.

Micro-electrochemical devices were also used to evaluate the HER activity of Pt atom-MoS2 and Pt chain-MoS2 with the same Pt loading (0.1 Pt/nm2), as illustrated in Fig. 3d. To eliminate the interference from the contact barrier between the Au electrode and MoS2, a CVD-grown graphene layer was employed as the electron-injection substrate, ensuring reliable microcell measurements43,44,48–51. The fabrication procedures of the micro-electrochemical device are shown in Supplementary Fig 11. Figure 3e and f present the typical linear sweep voltammetry (LSV) polarization curves and the corresponding Tafel slopes, respectively. It is evident that the Pt chain-MoS2 delivers an overpotential of 155 mV at 10 mA cm-2 and Tafel slope of 84 mV dec-1, demonstrating enhanced HER activity over Pt atom-MoS2 and pure MoS2 (Pt atoms: η10 is 320 mV, Tafel slope is 123 mV dec-1; pure MoS2: η10 is 389 mV, Tafel slope is 135 mV dec-1). These results confirm that the center sites located at the Pt chains exhibit an optimized Gibbs free energy for HER, as predicted by the theoretical calculations above. By combining experimental measurements with theoretical calculations, we demonstrate that point-to-point interactions between neighboring metal atoms along 1D chains contribute to metallic behavior and enhanced catalytic activity compared to isolated atom structures.

Building on the insights gained from the above model studies on single-atom and chain systems, we now aim to increase the density of Pt chains for practical HER applications. Although a higher density typically requires a greater amount of Pt atomic precursors, prolonged deposition times result in precursor aggregation into large nanoparticles that are detrimental to Pt chain formation. To obtain high-density, small-size nanoclusters, we adopted several strategies: i) lowering the substrate temperature (nearly at 15°C) during the deposition process in our e-beam setup; ii) shortening the deposition time to 1 min while increasing the evaporation cycles to 5-10 times, thereby facilitating secondary nucleation of Pt nanoclusters on the substrate. As a result, the as-deposited Pt precursors with different densities could be distributed uniformly without forming large clusters, as confirmed by our high-angle angular dark field-scanning transmission electron microscopy (HAADF-STEM) imaging (Supplementary Fig 13). In contrast, suboptimal deposition conditions produced large clusters during growth (Supplementary Fig 12). Benefiting from the above strategies, the density of Pt chains could be effectively controlled (Fig. 4a), achieving a high density of up to 2.82 Pt/nm2, corresponding to an atom ratio of 3.96%, as confirmed by STEM and EDS analyses (Supplementary Fig 14). Notably, an increase in the density not only lengthens the chains (Fig. 4b) but also, more importantly, increases the number of chain vertices in the samples (Fig. 4c and Supplementary Fig 15). These vertices may serve as additional active sites to enhance HER performance, as discussed in the following.

To investigate the catalytic contribution of these vertex sites, we constructed a model to analyze their detailed structures based on the STEM images, as shown in Fig. 4d. Our analysis indicates a vertex angle of 60°, and the coordination of Pt atoms at those sites differs from that within the chain structure. Specifically, the two S atoms connected to the Pt atom at the vertex form a smaller angle in the first coordination shell, leading to a higher concentration of delocalized electrons at the vertex compared with straight chains, as shown in Fig. 4e. We further examined the catalytic activities at the vertex, with the corresponding ΔGH* contour plot presented in Fig. 4f. Interestingly, these vertices exhibit a ΔGH* as low as only 0.06 eV, lower than that of Pt chains above. Then, to evaluate their thermal stability, we performed the ab initio molecular dynamics (AIMD) simulation using the NVT ensemble, where the simulation was run at 1000 K and the time step was set to 1 fs over 10 ps. As shown in Supplementary Fig 16, the resulting energy evolution and final structure confirm the good thermal stability of Pt-chain vertices. Therefore, these results suggest that the point-to-point interactions between neighboring metal atoms along the 1D chains are particularly pronounced at the vertex, supporting a potential synergistic catalytic effect between neighboring metal atoms52.

Figure 5a and b shows the polarization curves and the corresponding Tafel plots for samples with varied Pt densities measured in 0.5 M H2SO4. It is clear that as the Pt density increases from 0.11 to 2.82 Pt/nm2, the HER catalytic activity of Pt chain-MoS2 gradually approaches that of Pt metal. Specifically, the overpotential at 10 mA cm−2 decreases from 615 mV to 9.98 mV (Fig. 5a), and the Tafel slope declines from 138 mV dec⁻¹ to 58 mV dec⁻¹ (Fig. 5b). Furthermore, the turnover frequency (TOF) for H2 evolution, normalized by the number of Pt atoms, is shown in Fig. 5c (see calculation details in Supplementary Note 1). Remarkably, a higher density of Pt chains delivers an improved TOF at a lower potential, which can be attributed to two factors: i) the increased number of vertex sites and ii) the enhanced conductance of the films (Supplementary Fig 17)53. Finally, as a proof-of-concept for hydrogen generation, a centimeter-scale high-chain-density film was transferred onto an Au substrate for mass production of hydrogen, as shown in Fig. 5d. A large amount of H2 bubbles was produced during the reaction, demonstrating the tantalizing potential of Pt chain catalysts for practical hydrogen production. In summary, we have both theoretically predicted and experimentally confirmed that Pt chains show distinct catalytic behavior compared to single atoms, and further applied these Pt chains for wafer-scale hydrogen production. These chain and single-atom structures, grown using a mass flow-controlled CVD method, share similar coordination environments, as supported by our complementary characterizations. Combined device measurements and DFT calculations suggest that Pt chains exhibit metallic behavior and feature fascinating center sites with competitive Gibbs free energy compared to single atoms, potentially linked to the substantial delocalized electron densities in the chains. Notably, the chain density can be tuned to a maximum value up to 2.82 Pt/nm2, forming numerous vertex sites that significantly contribute to improved HER activity. This work deepens our understanding of the catalytic properties of 1D-arrayed Pt single-atom chains and highlights the importance of the synergistic effect between neighboring metal atoms in electrocatalysis.

Methods
Growth of Pt chain-MoS2 and Pt atom-MoS2
Synthesis of Pt chain-MoS2 films. Pt nanoclusters were deposited on clean SiO2/Si substrates using e-beam evaporation with a rate of 0.01 Å/s for deposition times of 20 s, 50 s, 100 s, and 300 s, respectively. These Pt-coated SiO2/Si substrates were then employed in the chemical vapor deposition (CVD) of MoS2 films. In this process, substrates were placed in a face-down configuration on an aluminum oxide boat containing MoO3 powders (AR, 99.5%, Aladdin) at the center of a quartz tube reaction chamber, while sulfur powders (CP, 99.5%, Changlian Shanghai) were loaded in another crucible upstream in the tube. After purging the CVD system with 200 sccm of Ar for 5 minutes, the center of the furnace was heated from room temperature (25 °C) to growth temperature at a rate of ~50 °C/min under continuous 60 sccm of Ar flow. The Pt chain-MoS2 films are synthesized by maintaining a temperature of 650 °C for 4 minutes for the Mo sources, while the S sources are maintained at around 230 °C. Finally, the furnace cools naturally under the protective argon atmosphere.

Synthesis of Pt atom-MoS2 films. The Pt nanoclusters are deposited on clean SiO2/Si substrates using e-beam evaporation with a speed of 0.01 Å/s for 100 s. The as-prepared Pt-coated SiO2/Si substrates are used as the substrate for the chemical vapor deposition (CVD) of MoS2 films, facing down on an aluminum oxide boat containing mixtures (MoO3 powders and NaCl powders (AR, 99.5%, G reagent) in the center of a quartz tube reaction chamber, and sulfur powders are loaded in another crucible upstream in the tube. After purging the CVD system with a 200 sccm argon flow for 5 minutes, the center of the furnace was heated from room temperature (25 °C) to growth temperature at a rate of ~50 °C/min under continuous argon gas flow of 60 sccm. The Pt atom-MoS2 films are synthesized by maintaining a temperature of 650 °C for 4 minutes in the Mo source, while the S source is kept at approximately 230 °C. The furnace cools naturally under the protective argon atmosphere.

Device fabrication
SiO2/Si chips (15 mm × 15 mm, with a 285 nm SiO2 layer) with 32 pre-patterned Au contact pads were fabricated by a conventional photolithography or a peelable-resist PDMS-assisted dry-transfer lithography. The fabrication steps included: i) a mask aligner (JD6S-A47P) with UV exposure to define the electrode geometry; ii) the resulting resist mask was transferred onto the target chip using a PDMS-assisted stamping technique, followed by metal deposition via thermal evaporation. iii) the resist and excess metal were then removed through tape-based dry stripping, yielding clean and well-defined 32-channel Au electrode arrays. Next, the as-prepared samples were transferred onto the chips using a polymethylmethacrylate (PMMA)-assisted method. Electron-beam lithography (TESCAN VEGA4) was then used to define the metal electrodes on the samples, which were followed by the thermal evaporation of 5 nm Cr and 60 nm Au. Finally, the device chips were coated with a 1 μm PMMA resist layer (ALLRESIST 950K A8 2500 rpm 60 s), and windows were patterned in the PMMA by electron-beam lithography (Raith 150 Two) to expose the designated regions on the samples. After development (1 min in 1:3 methyl isobutyl ketone (MIBK)/international phonetical alphabet (IPA) solution and 1 min in IPA), the micro-electrochemical devices were dried with Ar gas.

Electronic measurements
Following the device fabrication of the Pt chain-MoS2 and Pt atom-MoS2 on SiO2/Si, the samples were loaded into a vacuum probe station (≈1×10⁻⁴ Torr) at 25 °C. Electrical measurements were then carried out in a SEMISHARE CG-O-4 cryogenic probe station configured with two Keithley 2450 source meters53.

Micro-electrochemical measurements
A three-electrode configuration was employed for the in-situ electrochemical measurement (see the micro-cell schematic in Fig. 3d). All tests were carried out in 0.5 M H2SO4 (PH≈0, electrolyte freshly prepared from ultrapure water prior to each experiment). An Ag/AgCl reference electrode (filled with 3 M KCl) and a high-purity graphite counter electrode were used44. The other electrode in the three-electrode configuration connected to the films served as the working electrode (tungsten needle). Throughout all experiments, catalytic activity was restricted to the exposed regions of the films (60 μm2), with the remaining electrolyte-contacted areas passivated by a PMMA coating. The electrochemical current density was obtained by normalizing the measured current to the reaction window area51. All measured potentials were converted to the reversible hydrogen electrode (RHE) according to the following equation44:

ERHE = EAg/AgCl + 0:219 V (1)

Prior to electrochemical testing, the 0.5 M H2SO4 electrolyte was degassed by purging with pure Ar gas for 30 minutes for achieving saturation. Linear sweep voltammetry (LSV) was performed under quasi-equilibrium conditions at a scan rate of 5 mV/s, using a Keithley 2450 source meter to record the measurements54.

HER turnover frequency calculation
TOF of Pt chain-MoS2 was calculated using the equation:

TOF = Number of H2 produced per geometric area / Number of active sites per geometric area (2)

Then the number of H2 molecules produced per geometric area can be calculated using the equation.

Turnover = j (mA cm−2) × 10−3 A mA−1 × 1 s / (2 × 1.602 × 10−19 C) × 1 mol / NA (3)

Here, j is the current density (mA cm−2), z is the number of electrons involved in the reaction (for HER, z = 2), and NA is the Avogadro constant (6:02×1023). Using the current density at an overpotential of 10 mV, the H2 TOF for Pt chain-MoS2 with different densities can be calculated.

Number of active sites per nm2 = 0.11, 0.41, 0.61, 1.15, 2.82, as shown in Fig. 4a.

Using the methods described above, the TOF values of Pt chain-MoS2 with densities were calculated, as shown in Fig. 5c.

Theoretical calculations
All the theoretical calculations were performed with the Vienna Ab-initio Simulation Package55–57. The structural optimizations were carried out using the generalized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE) exchange-correlation functional, along with projector-augmented wave (PAW) potentials58. The electronic wavefunctions were expanded in a plane wave basis set with a kinetic energy cutoff of 500 eV. The electronic wavefunctions were expanded using a plane-wave basis set with a kinetic energy cutoff of 500 eV. For Brillouin zone sampling, a 1 × 10 × 1 Monkhorst–Pack k-point mesh was adopted for the Pt single-atom chain model, and a 5 × 5 × 1 mesh was used for the Pt single-atom model. The electronic iteration convergence threshold was set at 10⁻⁵ eV. All structures were fully relaxed until each atom’s force was < 0.01 eV Å−1. A vacuum layer of approximately 15 Å was included in the models to avoid spurious interactions between periodic images. We considered the van der Waals (vdW) interaction using the DFT-D3 method59. The implicit solvent model was considered using VASPsol to describe the adsorption strength in solvent systems60.

The hydrogen adsorption energy is defined as:

ΔEH* = EH*Slab − ESlab − 1/2EH2 (4)

where EH*Slab is the energy of the Pt/MoS2 system with a H atom adsorbed, ESlab is that of the Pt/MoS2 system without adsorbed H, and EH2 is that of the gas phase H2 molecule.

The Gibbs free energy ΔGH* was defined as:

ΔGH* = ΔEH* + ΔEZPE − TΔS (5)

where ΔEH* is the hydrogen adsorption energy, ΔEZPE is the zero-point energy difference, T is the temperature, and ΔS is the entropy difference for hydrogen between the adsorbed state and the gas phase.

Material characterization
The micromorphology and atomic structure of samples were characterized by an optical microscope (NM910-TR, NEXCOPE), a field-emission scanning electron microscope (SEM, TESCAN MIRA3), and transmission electron microscopes equipped with energy-dispersive X-ray spectroscopy (TEM, FEI Tecnai F30, operated at 300 kV and Talos F200S operated at 200 kV). Scanning transmission electron microscopy (STEM) was performed using JEOL ARM-200F (equipped with CEOS CESCOR aberration corrector, operated at 80 kV) and a Thermo Scientific Themis Z (operated at 300 kV). In EDS analysis, JEOL’s certified database and ZAF correction models were employed, where Pt Lα is used as the primary reference peak to calculate the Pt mass and atomic ratios. The atomic-resolution HAADF images were deconvoluted using the Richard-Lucy method to enhance the contrast. STEM simulations were performed by the Prismatic Software package61,62. Molecular vibrations and chemical compositions were examined using micro-Raman spectroscopy (Raman, Jobin-Yvon LabRam HR800, 532 nm YAG laser) and X-ray photoelectron spectroscopy (XPS, Kratos AXIS Ultra, Al Kα source, 1486.6 eV), respectively.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript demonstrated fabricated Pt chains and single atoms in MoS2 films with similar coordination environments and conducted model studies on their catalytic behaviors in hydrogen production. The authors provide both theoretical and experimental evidence showing that the single-atom chain system exhibits metallic characteristics and superior catalytic hydrogen evolution performance compared to single-atom systems. By modulating the atomic chain density, they achieved enhanced catalytic activity. Furthermore, their study reveals that increased atomic chain density correlates with a more significant number of vertex Pt atoms, which exhibit hydrogen adsorption free energy comparable to that of metallic Pt. Generally, this work is impressive and presents novel insight into catalysis, especially for synergistic effects between single atoms. Also, some issues need to be addressed before acceptance by Nature Communications.\n1.The authors mention that reducing the size of Pt precursors is beneficial. What is the specific rationale for minimizing precursor dimensions? Additionally, while extended deposition durations yield larger Pt configurations, how do these enlarged dimensions influence the regulation of atomic chain density?\n2.A notable inconsistency exists between the Pt nanocluster size distribution reported in Fig. S3 (0.6–2.2 nm) and the 0.6–1.5 nm range described on page 5 in the main text. Could the authors address this discrepancy?\n3.In the second paragraph of page 6, the authors assert that “the Raman spectra shows that the E2g/A1g intensity ratio in Pt chains-MoS2 is lower than that of Pt atoms-MoS2.” Quantitative peak intensity ratio data should be provide to substantiate this comparison. Furthermore, while the text identifies 780 nm as MoS2’s PL peak, Fig. S3 shows emission near 680 nm.\n4.The elemental composition analysis in Fig. 2e and 2f suggests comparable Mo and Pt content. Is this observation due to abbreviated elemental acquisition durations during characterization, or are other factors responsible?\n5.Fig. 2g “Pt interatomic spacing of 3.4 Å, notably larger than conventional Pt-Pt bonds (e.g., 2.78 Å in Pt(111) surfaces)”. What structural implications does this expanded spacing convey? The authors correlate equivalent Pt signal intensities in atomic chains and Pt atoms-MoS2 samples with Pt-S bonding. What complementary characterizations substantiate this bonding configuration conclusion?\n6.Are the Pt chains in Fig. 4a grown from the precursors shown in Fig. S11? If so, please explain the mechanism by which larger Pt nanoparticles (>1 nm) can evolve into atomically discrete chains. If not, please provide size distribution data for the precursor Pt clusters associated with the monoatomic chains in Fig. 4a.\n7.Why does the TOF curve for 0.11 Pt/nm² in Fig. 5c show significant oscillations?\n8.Formatting and terminology revisions required\na) Nomenclature consistency: Standardize “Pt chain-MoS2” vs. “Pt chains-MoS2” throughout the text and figure captions.\nb) Abbreviations: Define TMDC, CVD, HAADF-STEM, IPA, and MIBK at first mention.\nc) Units: Correct “1um” to “1 μm” (on page 10)\n9.The statement on page 5, line 12 – “the electron state near the Fermi level provides an abundant supply of electrons for proto-hydrogen adsorption” – requires supporting references.", "reviewer_2": "In this manuscript, the authors predicted the excellent catalytic activity of the single-metal-atom-chains (SMACs) through DFT calculations and conducted experiments for synthesis and verification. They successfully synthesized Pt SMACs with varying densities and conducted detailed characterization, yielding a superior HER performance with an overpotential below 10 mV at 10 mA/cm2. Through a comparison of the electrical and electrochemical properties with single-atom samples, this manuscript elucidates the significant impact of the synergistic interactions between metal atoms on the performance of the samples. They explained the enhancement of the catalytic activity originated from the delocalized electron density and metallic behavior in the Pt chains through DFT calculations. This work demonstrates the great potential of one-dimensional structures in electrocatalysis and provides excellent insights. Thus, I recommend this manuscript to be accepted after following questions and concerns have been addressed.\n(1) The incorporation of Pt atoms not only affects the charge distribution of the SMACs, but should also influence the charge distribution of nearby MoS2. However, the authors only calculated the catalytic activity on the Pt chains. Whether the MoS2 near the Pt chains also has catalytic activity or not?\n(2) The SMACs are more like the grain boundary. So, if Pt atoms do not exist, what would be the Gibbs free energy of the typical intrinsic MoS2 grain boundaries?\n(3) The author mentioned that the corner structure has more superior catalytic activity. Then, should the stability of this corner structure be investigated? AIMD simulations should be provided.\n(4) Is the SMACs structure synthesized monolayer or multi-layer? If it is multi-layered, does there exist interaction between layers?\n(5) In Figure 2, the notation for the micrometer unit (μm) is not standardized. It is recommended that the authors revise the unit formatting to ensure consistency with international convention.", "reviewer_3": "Sang et al. described the synthesis of 1D-Pt chains on MoS2 and compared their properties with single atom Pt deposited on MoS2 in the submitted paper. Here, I will mainly comment on the electron microscopy results. In general, the aberration-corrected images support their assertion of forming 1D chains, but I have significant issues with the STEM-EDS data presented.\nFor one, the maps in Figure 2 indicate a clear deficiency in their synthesized samples where S is generally found all over the support, whereas Mo map shows up much more sparsely in comparison. This issue is also reflected in the quantification shown in Figure S7, where the ratio of S to Mo is almost 4:1 in both cases and not 2:1 that is typical for MoS2.\nI also have my concerns about the EDS spectra shown in S7. Particularly, the S-K peak looks abnormal with the peak profile is partially filled at the bottom but open under the line at the top. We do typically get profiles that look like that with EDS. Some peak labels are also truncated, i.e. t-N and u-N (there are also no N lines).\nFurthermore, the authors should provide STEM-EDX data for all the samples described in the paper, not just 2. The changes in Pt density should be quantifiable with EDS."}, "author_response": "Our Response to the Reviewer’s Comments\nContents\nReviewer #1........................................................................................................................................... 2\nReviewer #2........................................................................................................................................... 8\nReviewer #3......................................................................................................................................... 12\nReferences ........................................................................................................................................... 15\nThis manuscript demonstrated fabricated Pt chains and single atoms in MoS films with similar coordination\n2\nenvironments and conducted model studies on their catalytic behaviors in hydrogen production. The authors\nprovide both theoretical and experimental evidence showing that the single-atom chain system exhibits metallic\ncharacteristics and superior catalytic hydrogen evolution performance compared to single-atom systems. By\nmodulating the atomic chain density, they achieved enhanced catalytic activity. Furthermore, their study reveals\nthat increased atomic chain density correlates with a more significant number of vertex Pt atoms, which exhibit\nhydrogen adsorption free energy comparable to that of metallic Pt. Generally, this work is impressive and\npresents novel insight into catalysis, especially for synergistic effects between single atoms. Also, some issues\nneed to be addressed before acceptance by Nature Communications.\nResponse: We greatly thank for the Reviewer’s positive comments on our work.\nComment 1.1. The authors mention that reducing the size of Pt precursors is beneficial. What is the specific\nrationale for minimizing precursor dimensions? Additionally, while extended deposition durations yield larger\nPt configurations, how do these enlarged dimensions influence the regulation of atomic chain density?\nResponse: We first appreciate the Reviewer’s constructive suggestions. The rationale for minimizing precursor\ndimensions lies in two aspects: i) lowering the substrate temperature (nearly at 15°C) during the deposition\nprocess in our e-beam setup, which can prevent atom migrations and aggregation on the SiO /Si substrate; ii\n2\nshortening the deposition time to 1 min while increasing the evaporation cycles to 5-10 times, thereby\nfacilitating secondary nucleation of Pt nanoclusters on the substrate. Based on these strategies, the as-deposited\nPt precursors with different densities could be distributed uniformly without large clusters, as confirmed by\nHAADF-STEM images in Figure R1.\nIn contrast, suboptimal deposition conditions could lead to the formation of large clusters during the deposition\nprocess (Supplementary Figure 12). Those large clusters are not conducive to the growth of high-density Pt\nchains in the film, as they cannot form liquid (or molten) droplets according to the platinum’s melting point-\ndiameter relationship1. In our experiment, whether liquid Pt nanodroplets form is a critical factor in determining\nthe formation of Pt chains. The reason is that the liquid nanodroplets facilitate the diffusion of platinum atoms,\nwhich are further captured by MoS domains to form thermodynamically stable Pt-chain structures. We added\n2\nthe corresponding HAADF-STEM images of Pt precursors in Supplementary Figure 13.\n2\nof Pt precursors on MoS without large cluster formation. These precursors were subsequently used to grow Pt\n2\nchains with densities ranging from 0.11 to 2.82 Pt/nm2.\nComment 1.2. A notable inconsistency exists between the Pt nanocluster size distribution reported in Fig. S3\n(0.6–2.2 nm) and the 0.6–1.5 nm range described on page 5 in the main text. Could the authors address this\ndiscrepancy?\nResponse: Thank the reviewer very much for his/her carefulness, and we have revised them accordingly.\nComment 1.3. In the second paragraph of page 6, the authors assert that “the Raman spectra shows that the\nE /A intensity ratio in Pt chains-MoS is lower than that of Pt atoms-MoS .” Quantitative peak intensity ratio\n2g 1g 2 2\ndata should be provided to substantiate this comparison. Furthermore, while the text identifies 780 nm as MoS ’s\nResponse: This is a good suggestion. We quantitatively extracted the E /A intensity ratio and FWHM from\n2g 1g\nthose two samples in Table R1, confirming that the ratio for Pt chain-MoS is lower than that for Pt atom-MoS .\n2 2\nThis is attributed to the fact that the highly dense platinum nanoclusters facilitate the growth of high-density\nMoS nanograins, which provide abundant one-dimensional channels for Pt atoms incorporation to form chains.\nSupplementary Table 1.\nFor the second comment, we double-checked the PL peaks and identified this as a typographical error. We have\ncorrected it to 680 nm.\nTable R1. Comparison of Raman spectra between Pt chain-MoS and Pt atom-MoS . Pt chain-MoS\n2 2 2\nexhibits a lower E /A intensity ratio and a broader FWHM of the E mode, indicating reduced crystallinity\n2g 1g 2g\ncompared to Pt atom-MoS .\n2g 1g 2g\n2\n2\nIs this observation due to abbreviated elemental acquisition durations during characterization, or are other\nfactors responsible?\nResponse: We appreciate the reviewer’s insightful suggestions. After re-examing the initial EDS data, we\nrealized that the elemental composition analysis was affected by peak overlap between Mo and S. To address\nthis issue, we re-collected the EDS data under optimized acquisition and analysis conditions, as shown in Figure\nR2. The results clearly demonstrate uniform distribution of Pt, S, and Mo across the films, with a Mo/S atomic\nratio close to 2:1. We have updated those mapping results in Figures 2e and 2f of the revised manuscript, and\nadded the table in Supplementary Table 2.\nFigure R2. EDS elemental mapping and atomic ratios of Pt chain-MoS (top) and Pt atom-MoS (bottom).\n2 2\na, Elemental maps of Pt chain-MoS and Pt atom-MoS , showing uniform distributions of S, Pt, and Mo. b,\n2 2\nAtomic ratios of Pt chain-MoS and Pt atom-MoS , showing similar Pt content and the S: Mo ratio close to 2:1.\n2 2\nComment 1.5. Fig. 2g “Pt interatomic spacing of 3.4 Å, notably larger than conventional Pt-Pt bonds (e.g., 2.78\nÅ in Pt(111) surfaces)”. What structural implications does this expanded spacing convey? The authors correlate\nequivalent Pt signal intensities in atomic chains and Pt atoms-MoS samples with Pt-S bonding. What\n2\ncomplementary characterizations substantiate this bonding configuration conclusion?\nResponse: Thank the reviewer for their suggestions on the Pt chain structures. Following the suggestions, to\ninvestigate the local environment surrounding the Pt atoms, we performed a detailed analysis on STEM data, as\nshown in Figure R3. The results reveal that in chain configurations, Pt atoms are primarily bonded to S atoms.\nThis Pt-S bonding induces an elongated Pt-Pt bond length, significantly exceeding the atomic spacing in bulk\nPt (111). These observations could be rationalized by our simulation analysis of ADF-STEM imaging (Figures\n2\nbonded to S atoms. In contrast, the Pt atoms in the Pt atom-MoS sample occupy Mo vacancies while similarly\n2\nbonding to adjacent S atoms. Therefore, the coordination environments of Pt atoms in both samples are similar,\nand their STEM signal intensities are comparable (Figures 2g and 2h). We have added these STEM results in\nSupplementary Figure 9 and the corresponding discussions in the revised manuscript. Please see it below.\n“This conclusion could be rationalized by our simulation analysis of annular dark-field scanning transmission\nelectron microscopy (ADF-STEM) imaging, confirming that the Pt atoms in the Pt chain-MoS₂ are embedded\nwithin the MoS film and bonded to S atoms (Supplementary Figure 9a). In contrast, the Pt atoms in the Pt\n2\natom-MoS sample occupy Mo vacancies while similarly bonding to adjacent S atoms (Supplementary Figure\n2\n9b).”\nFigure R3. Structural models of Pt atoms with different structures in MoS . a, False-colored HAADF-\n2\ncolored HAADF-STEM image of Pt atoms in MoS (left) and corresponding simulated ADF-STEM image\n2\n(right). c, Optimized structural models of a Pt chain (top) and a Pt atom (bottom) integrated into the MoS .\nthe mechanism by which larger Pt nanoparticles (>1 nm) can evolve into atomically discrete chains. If not,\nplease provide size distribution data for the precursor Pt clusters associated with the monoatomic chains in Fig.\n4a.\nResponse: The Pt chains in Figure 4a were not grown from the precursors shown in Supplementary Figure\n11 (in Supplementary Figure 12 of the revised manuscript). Those precursors formed under suboptimal\ndeposition conditions, which lead to large Pt clusters that are detrimental for the growth of chains. In our\nresponse to Comment 1.1, such large clusters cannot generate liquid (or molten) droplets, thereby making it\nimpossible to form the chains.\nthe Pt precursor clusters used for Pt chain growth (Figure 4a). Through optimizing the deposition conditions,\nPt precursors with different densities could be distributed uniformly without large clusters in our experiment.\nComment 1.7. Why does the TOF curve for 0.11 Pt/nm² in Fig. 5c show significant oscillations?\nResponse: We appreciate this insightful question. The oscillations observed in the original TOF curve at low\ncurrent densities arise from our weak-current measurements (nA level), which are close to the detection limit\nof the source meter and susceptible to environmental disturbance. Given the ~10-11A background noise threshold,\nwe optimized the measurement conditions, e.g., by using a Faraday shield to collect more reproducible and\nreliable data, as shown in Figure R4. We have updated the original curve in the revised manuscript (Figures\n5a-c).\nFigure R4. Improvement of HER performance for Pt chain-MoS . a-b, Polarization curves (a) and the\n2\ncorresponding Tafel plots (b) of Pt chains with varied vertices in 0.5 M H SO . c, Potential-dependent TOF\n2 4\ncurves derived from (a) and (b).\nComment 1.8. Formatting and terminology revisions required\na) Nomenclature consistency: Standardize “Pt chain-MoS2” vs. “Pt chains-MoS2” throughout the text and\nfigure captions.\nb) Abbreviations: Define TMDC, CVD, HAADF-STEM, IPA, and MIBK at first mention.\nc) Units: Correct “1um” to “1 μm” (on page 10)\nResponse: We sincerely appreciate the reviewer’s meticulous attention to detail. We have conducted a\ncomprehensive review of the entire manuscript, including all figures, captions, and supplementary materials, to\nensure all identified errors have been corrected.\nsupply of electrons for proto-hydrogen adsorption” – requires supporting references.\nResponse: Following the reviewer’s valuable suggestion, we added related references to substantiate the\nrelationship between the electronic states near the Fermi level and hydrogen adsorption behavior in HER\ncatalysts. The added references are listed below.\n1. Greeley J, Jaramillo TF, Bonde J, Chorkendorff I, Nørskov JK. Computational high-throughput screening\nof electrocatalytic materials for hydrogen evolution. Nat. Mater. 5, 909-913 (2006).\n2. Nørskov JK, et al. Trends in the Exchange Current for Hydrogen Evolution. J. Electrochem. Soc. 152, J23\n(2005).\n3. Hammer B, Nørskov JK. Electronic factors determining the reactivity of metal surfaces. Surf. Sci. 343, 211-\n220 (1995).\nIn this manuscript, the authors predicted the excellent catalytic activity of the single-metal-atom-chains (SMACs)\nthrough DFT calculations and conducted experiments for synthesis and verification. They successfully\nsynthesized Pt SMACs with varying densities and conducted detailed characterization, yielding a superior HER\nperformance with an overpotential below 10 mV at 10 mA/cm . Through a comparison of the electrical and\n2\nelectrochemical properties with single-atom samples, this manuscript elucidates the significant impact of the\nsynergistic interactions between metal atoms on the performance of the samples. They explained the\nenhancement of the catalytic activity originated from the delocalized electron density and metallic behavior in\nthe Pt chains through DFT calculations. This work demonstrates the great potential of one-dimensional\nstructures in electrocatalysis and provides excellent insights. Thus, I recommend this manuscript to be accepted\nafter following questions and concerns have been addressed.\nResponse: We highly appreciate the reviewer’s positive comments on our work.\nComment 2.1. The incorporation of Pt atoms not only affects the charge distribution of the SMACs, but should\nalso influence the charge distribution of nearby MoS . However, the authors only calculated the catalytic activity\n2\non the Pt chains. Whether the MoS near the Pt chains also has catalytic activity or not?\nadditional calculations on the hydrogen evolution activity of S sites at varying distances from Pt chains (Figure\nR5a). Remarkably, both sites 2 and 3 turn out the Gibbs free energy as high as about 1.79 eV (Figure R5b),\ncomparable to that of pristine MoS₂ and much higher than that of previously-calculated S site adjacent to Pt\n(site 1: 0.81 eV).\nThis finding indicates that the Pt chains only influence adjacent S atoms (sites 1) but have a negligible impact\non the more distant S atoms (sites 2 and 3), suggesting that the MoS near the Pt chains remains inactive. We\n2\nadded the data in Supplementary Figure 1 and the corresponding discussions in the revised manuscript. Please\nsee it below.\n“In addition, we also calculated the catalytic activities of the S sites located at the second and third nearest\npositions to the Pt chain (Supplementary Figure 1). Both of them turn out the Gibbs free energy as high as about\n1.79 eV, much higher than that of the S site adjacent to Pt (site 1: 0.81 eV), suggesting that the MoS near the\nmodel, including three sites near the Pt chain. b, Gibbs free energy of H adsorption at these three sites.\nComment 2.2. The SMACs are more like the grain boundary. So, if Pt atoms do not exist, what would be the\nGibbs free energy of the typical intrinsic MoS grain boundaries?\nthe most stable grain boundaries ending with S-oriented (S-4|4a) and Mo-oriented (Mo-4|8), as shown in\nFigures R6a and b, respectively. Their corresponding Gibbs free energy of the optimal adsorption sites is\npresented in Figure R6c. It was found that the S-4|4a grain boundary gives a Gibbs free energy of 1.33 eV while\nthe Mo-4|8 grain boundary has 0.67 eV, both of which are much higher than the Pt chain foamed at grain\nboundaries (0.18 eV).\nFigure R6. Grain boundary structures and hydrogen adsorption energy of grain boundaries in MoS . a-\n2\nb, The atomic structure model of H adsorption for the S-4|4a grain boundary (a) and the Mo-4|8 grain boundary\n(b). c, The Gibbs free energies calculated for two grain boundaries.\nComment 2.3. The author mentioned that the corner structure has more superior catalytic activity. Then, should\nthe stability of this corner structure be investigated? AIMD simulations should be provided.\nResponse: Based on the Reviewer’s invaluable comments, we performed the AIMD simulation to evaluate the\nthermal stability of the Pt chain-MoS vertex structure using the NVT ensemble. The simulation was run at 1000\nstructural configuration confirm excellent thermal stability. We have added the data in Supplementary Figure\n16 to the Supplementary Information and included the corresponding discussion in the revised manuscript.\n“Then, to evaluate their thermal stability, we performed the ab initio molecular dynamics (AIMD) simulation\nusing the NVT ensemble, where the simulation was run at 1000 K and the time step was set to 1 fs over 10 ps.\nAs shown in Supplementary Figure 16, the resulting energy evolution and final structure confirm the good\nthermal stability of Pt-chain vertices..”\nFigure R7. Investigation of thermal stability using AIMD simulation. a-b, The structure of Pt chain-MoS\n2\nvertex before (a) and after (b) the AIMD simulation. c, Total energy evolution of Pt chain-MoS vertex system\n2\nthroughout a 10 ps AIMD simulation at 1000 K.\nComment 2.4. Is the SMACs structure synthesized monolayer or multi-layer? If it is multi-layered, does there\nexist interaction between layers?\nResponse: We thank the reviewer for this insightful suggestion. In our experiment, we could also observe the\nSMACs structure synthesized in the multi-layers, as shown in Figure R8. It can be seen that Pt-chains are\nsubstantially located at the top layer. Regarding to the question “does there exist interaction between layers?”,\nwe carried out DFT calculations to probe the charge density difference of the Pt chain-bilayer MoS structure\n2\n(Figure R8). It was found that the two layers are connected by van der Waals interaction, with substantial\ncharge transfer occurring between them (Figure R9).\nMoS structure, together with the corresponding plane-averaged profiles.\nthat the authors revise the unit formatting to ensure consistency with international convention.\nResponse: Following the suggestions, we have carefully checked the entire manuscript and revised the notation\nof the micrometer unit to “μm” in accordance with the international standard throughout the text and all figure\ncaptions, including Figure 2. All units are now consistently formatted in the revised manuscript.\nSang et al. described the synthesis of 1D-Pt chains on MoS and compared their properties with single atom Pt\n2\ndeposited on MoS in the submitted paper. Here, I will mainly comment on the electron microscopy results. In\n2\ngeneral, the aberration-corrected images support their assertion of forming 1D chains, but I have significant\nissues with the STEM-EDS data presented.\nResponse: We are grateful for the reviewer’s comments and concerns raised regarding the STEM-EDS data. In\nthe revised manuscript, we have tried our best to do more experiments to address those issues.\nComment 3.1: For one, the maps in Figure 2 indicate a clear deficiency in their synthesized samples where S\nis generally found all over the support, whereas Mo map shows up much more sparsely in comparison. This\nissue is also reflected in the quantification shown in Figure S7, where the ratio of S to Mo is almost 4:1 in both\ncases and not 2:1 that is typical for MoS .\nthat the elemental composition analysis is not accurate due to overlap peaks between Mo and S. To address\nthis issue, we re-collected the EDS data under optimized acquisition and analysis conditions, as shown in Figure\nR2. It can be seen that Pt, S, and Mo are uniformly distributed in those films, and the atom% of Mo/S is close\nto 2. We updated those mapping results in Figures 2e and f in the revised manuscript and added the table in\nSupplementary Table 2.\nFigure R2. EDS elemental mapping and atomic ratios of Pt chain-MoS (top) and Pt atom-MoS (bottom).\n2 2\na, Elemental maps of Pt chain-MoS and Pt atom-MoS , showing uniform distributions of S, Pt and Mo. b,\n2 2\nAtomic ratios of Pt chain-MoS and Pt atom-MoS , showing similar Pt content and the S: Mo ratio close to 2:1.\n2 2\nabnormal with the peak profile is partially filled at the bottom but open under the line at the top. We do typically\nget profiles that look like that with EDS. Some peak labels are also truncated, i.e. t-N and u-N (there are also\nno N lines).\nFurthermore, the authors should provide STEM-EDX data for all the samples described in the paper, not just 2.\nThe changes in Pt density should be quantifiable with EDS.\nResponse: The review is right. The original version contained abnormal S-K peak profiles and truncated peak\nlabels (e.g., “t-N” and “u-N”), which we acknowledge were caused by improper export settings. The appearance\nof “N” labels was due to default software labeling errors during export. In the revised manuscript, we have\ncorrected the parameters and re-exported the EDS spectra, which now display proper peak shapes and accurate\nelement labels.\nFor the reviewer’s suggestions on STEM-EDX data and Pt density, we have performed additional STEM-EDS\nmeasurements on all samples described in the manuscript to investigate Pt distribution and density variations.\nAs shown in Figure R10, those samples exhibit a uniform distribution of Pt element, with measured atomic\nratios of 0.53%, 0.85%, 1.41%, 2.59%, and 3.96%. We added these data to Supplementary Figure 14.\nFigure R10. EDS mappings of Pt chains with various densities. a-e, Elemental maps and corresponding EDS\nprofiles for the Pt chain-MoS samples with atomic ratios of 0.53%, 0.85%, 1.41%, 2.59%, and 3.96%, showing\n2\nuniform distributions.\nquality and the completeness of our characterization.\n1. Nanda, K.K., Sahu, S.N. & Behera, S.N. Liquid-drop model for the size-dependent melting of\nlow-dimensional systems. Physical review A 66, 013208 (2002).\n2. Guo, S. et al. Direct growth of single-metal-atom chains. Nature Synthesis 1, 245-253 (2022).\nContents\nReviewer #3 ........................................................................................................................................... 2\nReferences ............................................................................................................................................. 4\nIn this case, I am still concerned about the EDS results. For one, I have no idea what are the Pt Mr and Pt Mz\npeaks labelled in the spectrum. That is not standard nomenclature. It is also concerning that the authors were\nable to address the mismatch I highlighted by using a different fitting procedure that accounts for peak overlap.\nHere, it would fine if the authors showed clear spectra of the peaks and the decomposed peaks from the fitting\nresults but all they show is very low resolution and pixelated data. In view of these issue, l suggest that the\nauthors approach colleagues with more experience in EDS analysis as I am not confident at all with the\nreliability of their analysis.\nResponse: We appreciate the reviewer’s constructive suggestions on the Pt Mr and Pt Mz peaks in the spectrum\nand our fitting procedure. We first apologize for our improper labeling in the original spectrum. For the Pt M\nζ\nand M , their transitions exhibit much weaker intensities compared to the principal emission lines (i.e., K , K ,\nγ α β\nand L ). Therefore, they cannot be used for quantitative fitting of mass or atomic ratios.\nα\nAfter consulting with our colleagues experienced in EDS analysis, we confirmed that our labeling procedure\nfollows the Siegbahn notation system established by Manne Siegbahn in 1916 for X-ray spectral line\nidentification1, which is widely used in recent articles2-7. Specifically, our quantification procedure was carried\nout as follows: i) the quantification process utilized JEOL’s certified database and ZAF correction models;\nii)\nprincipal reference peaks (O K and Pt L ) were employed for cross-verification. Given the overlap among Pt\nα α\nM, Mo L , and S K , the peak of Pt L is employed to reliably determine the Pt mass and atomic ratios, which\nα α α\nis shown in Figure R1.\nWe have added the results in Supplementary Figure 14 and updated the corresponding discussions in the\nMethods in the revised manuscript. Please see it below.\n“In EDS analysis, JEOL’s certified database and ZAF correction models were employed, where Pt Lα\nis used as the primary reference peak to calculate the Pt mass and atomic ratios.”\nprofiles for the Pt chain-MoS samples with atomic ratios of 0.53%, 0.85%, 1.41%, 2.59%, and 3.96%, showing\n2\nuniform distributions.\n1. Siegbahn, M. Relations between the K and L Series of the High-Frequency Spectra. Nature 96\n(1916).\n2. Kim, I. et al. Unveiling the reconstruction of copper bimetallic catalysts during CO2\nelectroreduction. Nature Catalysis, 1-17 (2025).\n3. Zhang, T. et al. High-entropy alloy enables multi-path electron synergism and lattice oxygen\nactivation for enhanced oxygen evolution activity. Nature Communications 16, 3327 (2025).\n4. He, L. et al. Single-atom Mo-tailored high-entropy-alloy ultrathin nanosheets with intrinsic\ntensile strain enhance electrocatalysis. Nature Communications 15, 2290 (2024).\n5. Kohlrausch, E.C. et al. One-Size-Fits-All: A Universal Binding Site for Single-Layer Metal\nCluster Self-Assembly. Advanced Science, e08034 (2025).\n6. Balena, A. et al. Deterministic Fabrication of Plasmonic Nanostructures on Optical Nanofibers\nvia Blurred Electron Beam Deposition. Advanced Science, e07004 (2025).\n7. Brunnengräber, K., Jeschonek, K., George, M., Zhang, G.-R. & Etzold, B.J.M. Ionic Liquid\nModified Electrocatalysts: a STEM-EDX Approach for Identification of Local Distributions\nwithin Ionomer Containing Catalysts Layers. Chemistry–Methods 3, e202200084 (2023).\n4"}, {"round": 2, "reviewer_comments": {"reviewer_1": "authors have well addressed the questions, my suggestion is that the present manuscript could be accepted and published in NC.", "reviewer_2": "The authors have made point-to-point response to my comments, and the revised manuscript has been improved greatly. I recommend the publication of this work with the current form.", "reviewer_3": "In this case, I am still concerned about the EDS results. For one, I have no idea what are the Pt Mr and Pt Mz peaks labelled in the spectrum. That is not standard nomenclature. It is also concerning that the authors were able to address the mismatch I highlighted by using a different fitting procedure that accounts for peak overlap. Here, it would fine if the authors showed clear spectra of the peaks and the decomposed peaks from the fitting results but all they show is very low resolution and pixelated data. In view of these issue, I suggest that the authors approach colleagues with more experience in EDS analysis as I am not confident at all with the reliability of their analysis."}, "author_response": "Our Response to the Reviewer’s Comments\nContents\nReviewer #3 ........................................................................................................................................... 2\nReferences ............................................................................................................................................. 4\nIn this case, I am still concerned about the EDS results. For one, I have no idea what are the Pt Mr and Pt Mz\npeaks labelled in the spectrum. That is not standard nomenclature. It is also concerning that the authors were\nable to address the mismatch I highlighted by using a different fitting procedure that accounts for peak overlap.\nHere, it would fine if the authors showed clear spectra of the peaks and the decomposed peaks from the fitting\nresults but all they show is very low resolution and pixelated data. In view of these issue, l suggest that the\nauthors approach colleagues with more experience in EDS analysis as I am not confident at all with the\nreliability of their analysis.\nResponse: We appreciate the reviewer’s constructive suggestions on the Pt Mr and Pt Mz peaks in the spectrum\nand our fitting procedure. We first apologize for our improper labeling in the original spectrum. For the Pt M\nζ\nand M , their transitions exhibit much weaker intensities compared to the principal emission lines (i.e., K , K ,\nγ α β\nand L ). Therefore, they cannot be used for quantitative fitting of mass or atomic ratios.\nα\nAfter consulting with our colleagues experienced in EDS analysis, we confirmed that our labeling procedure\nfollows the Siegbahn notation system established by Manne Siegbahn in 1916 for X-ray spectral line\nidentification1, which is widely used in recent articles2-7. Specifically, our quantification procedure was carried\nout as follows: i) the quantification process utilized JEOL’s certified database and ZAF correction models;\nii)\nprincipal reference peaks (O K and Pt L ) were employed for cross-verification. Given the overlap among Pt\nα α\nM, Mo L , and S K , the peak of Pt L is employed to reliably determine the Pt mass and atomic ratios, which\nα α α\nis shown in Figure R1.\nWe have added the results in Supplementary Figure 14 and updated the corresponding discussions in the\nMethods in the revised manuscript. Please see it below.\n“In EDS analysis, JEOL’s certified database and ZAF correction models were employed, where Pt Lα\nis used as the primary reference peak to calculate the Pt mass and atomic ratios.”\nprofiles for the Pt chain-MoS samples with atomic ratios of 0.53%, 0.85%, 1.41%, 2.59%, and 3.96%, showing\n2\nuniform distributions.\n1. Siegbahn, M. Relations between the K and L Series of the High-Frequency Spectra. Nature 96\n(1916).\n2. Kim, I. et al. Unveiling the reconstruction of copper bimetallic catalysts during CO2\nelectroreduction. Nature Catalysis, 1-17 (2025).\n3. Zhang, T. et al. High-entropy alloy enables multi-path electron synergism and lattice oxygen\nactivation for enhanced oxygen evolution activity. Nature Communications 16, 3327 (2025).\n4. He, L. et al. Single-atom Mo-tailored high-entropy-alloy ultrathin nanosheets with intrinsic\ntensile strain enhance electrocatalysis. Nature Communications 15, 2290 (2024).\n5. Kohlrausch, E.C. et al. One-Size-Fits-All: A Universal Binding Site for Single-Layer Metal\nCluster Self-Assembly. Advanced Science, e08034 (2025).\n6. Balena, A. et al. Deterministic Fabrication of Plasmonic Nanostructures on Optical Nanofibers\nvia Blurred Electron Beam Deposition. Advanced Science, e07004 (2025).\n7. Brunnengräber, K., Jeschonek, K., George, M., Zhang, G.-R. & Etzold, B.J.M. Ionic Liquid\nModified Electrocatalysts: a STEM-EDX Approach for Identification of Local Distributions\nwithin Ionomer Containing Catalysts Layers. Chemistry–Methods 3, e202200084 (2023).\n4"}, {"round": 3, "reviewer_comments": {"reviewer_3": "This is much better. I have no further comments."}, "author_response": ""}]

Decision letter