Highly loaded fine PtCo intermetallic compounds on 3D N-doped porous graphene for enhanced and sustained efficiency in PEMFCs

Abstract

Currently, carbon supports are subject to corrosion during repetitive start-up/shut-down processes in proton exchange membrane fuel cells (PEMFCs), causing performance degradation. To address this issue, we developed highly graphitized, nitrogen-doped graphene (HGNG) through a plasma-enhanced chemical vapor deposition (PECVD) strategy, followed sequentially by high-temperature annealing and ammonia plasma activation. The HGNG features a three-dimensional hierarchical porous structure with a high specific surface area, a high degree of graphitization, and substantial nitrogen doping. This support enables the uniform distribution of a high Pt loading (45.9 wt%) of ordered face-centered tetragonal L1₀-PtCo nanoparticles (∼4.4 nm). As a result, the L1₀-PtCo/HGNG catalyst exhibits excellent oxygen reduction reaction (ORR) activity and durability in PEMFCs, exceeding the U.S. Department of Energy (DOE) 2025 targets for both catalyst and support stability. Impressively, after accelerated durability tests for the electrocatalyst and support, the L1₀-PtCo/HGNG-based membrane electrode assembly achieves a peak power density of 964 mW cm⁻² and exhibits voltage losses of only 19 mV and 17 mV at 0.8 A cm⁻² and 1.5 A cm⁻², respectively, less than the DOE target of 30 mV loss. This study demonstrates a synergistic design strategy for carbon supports, effectively reconciling the trade-off between graphitization, porosity, and surface functionality, thereby laying a foundation for designing efficient and durable catalysts for practical PEMFC applications.

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1. Introduction

Proton exchange membrane fuel cells (PEMFCs) are promising clean energy conversion devices due to their high energy density, efficiency, and zero emissions.^1–3 However, large-scale commercialization remains impeded by the triple challenges of cost, performance, and durability, among which cathode catalyst degradation constitutes a critical bottleneck.^4–7 Specifically, during start-up/shut-down events,^8–10 transient high potentials (>1.0 V) accelerate carbon support corrosion, leading to catalyst detachment and performance decay.^11,12 This highlights the critical role of carbon supports in developing stable, high-performance catalysts.^13,14

An optimal catalyst support must simultaneously fulfill three key requirements: (1) high graphitization for excellent electronic conductivity and electrochemical stability;^15,16 (2) a developed pore structure with high surface area to facilitate mass transport and provide ample sites for metal dispersion;¹⁷ and (3) heteroatom doping (e.g., N) to modulate electronic structures and enhance metal–support interactions.^18–21 However, achieving this combination is fundamentally challenging, as these properties are often mutually exclusive. Conventional high-temperature graphitization (>1500 °C) inevitably leads to pore collapse and a drastic reduction in surface area, which is detrimental to metal precursor infiltration and nanoparticle dispersion.^22–26 Conversely, highly porous carbon materials typically exhibit low graphitization degrees and poor corrosion resistance. Furthermore, while post-synthesis heteroatom doping can introduce active sites, it may also disrupt the graphitic carbon network. This “graphitization–porosity–functionality” triad of constraints constitutes a central dilemma in carbon support design.

Peer research efforts focus on improving the intrinsic activity and stability of platinum-based catalysts by forming ordered PtM intermetallic compounds (PtM-IMCs). Their synthesis, however, necessitates high-temperature annealing (>600 °C), which frequently induces significant nanoparticle coarsening—a problem exacerbated at the high metal loadings (>20 wt%) required for practical applications to reduce electrode thickness and mass transport resistance.^27,28 Recent reports on high-loading PtCo IMCs show promising activity but often lack comprehensive validation of the carbon support's long-term durability under PEMFC-relevant conditions, which is a critical gap for assessing real-world viability.²⁹

Herein, we bridge this gap through a sequential synergy strategy that integrates plasma-enhanced chemical vapor deposition (PECVD), ultra-high temperature annealing, and post-engineering plasma activation. Our approach is conceptually distinct in its purposeful order designed to overcome the classic trade-offs: First, PECVD was used to construct a robust three-dimensional graphene framework with innate porosity. Subsequent ultra-high temperature (1800 °C) annealing maximizes the graphitization degree, ensuring superior conductivity and intrinsic corrosion resistance. Finally, ammonia plasma treatment is strategically applied not only to dope nitrogen heteroatoms but also to mildly reactivate the surface and fine-tune the pore structure without compromising the graphitized backbone. This process yields a novel highly graphitized and nitrogen-doped graphene (HGNG) support. Leveraging HGNG, we achieve the uniform dispersion of a high mass loading (45.9 wt%) of ordered L1₀-PtCo nanoparticles with a small average size of 4.37 nm. The resulting L1₀-PtCo/HGNG catalyst demonstrates exceptional ORR activity and, most notably, outstanding durability exceeding DOE 2025 targets for both the catalyst and support, thereby validating our synergistic design principle.

2. Experimental section

2.1. Chemical reagents

Cobalt chloride hexahydrate (CoCl₂·6H₂O, 99%) and chloroplatinic acid hexahydrate (H₂PtCl₆·6H₂O, 99.9%) were purchased from Sigma-Aldrich. Silver nitrate solution (AgNO₃, 0.1 mol L⁻¹) and sulfuric acid (H₂SO₄) were purchased from Sinopharm Chemical Reagent Co., Ltd. The commercial Pt/C catalyst (TEC10E50E, 50 wt% Pt on carbon) was purchased from Tanaka Kikinzoku International (Japan). All chemicals were used as received without further purification.

2.2. Synthesis of GC, HGG and HGNG

Three-dimensional porous graphene carbon (GC) was synthesized via RF-PECVD at 800 °C (gases: 10 sccm CH₄, 40 sccm H₂, 5 sccm Ar, all gases are 98% pure; RF power: 300 W; deposition time: 2 h). GC was subsequently heat-treated at 1800 °C for 4 h (ramp: 10 °C min⁻¹; atmosphere: Ar) to produce highly graphitic graphene (HGG). Finally, HGG (100 g) underwent sequential plasma treatment in a fluidized bed reactor under N₂ (50 L min⁻¹), followed by (i) surface activation via O₂ plasma (500 sccm, 500 W power) and (ii) nitrogen doping via NH₃ plasma treatment for 30 min (200 sccm, 1000 W power), yielding the final nitrogen-doped graphitic graphene (HGNG).

2.3. Synthesis of Pt/HGNG

Platinum nanoparticles were deposited onto the HGNG support by EG reduction, with the mass loading of platinum controlled at ∼50 wt%. Briefly, 500 mg of prepared HGNG was ultrasonically dispersed in 100 mL of ethylene glycol for 1 h to form a homogeneous suspension. After addition of a certain amount of H₂PtCl₆·6H₂O (1 mg mL⁻¹) dissolved in EG, the mixture was stirred under N₂ bubbling for another 1 hour. The suspension was then refluxed at 150 °C for 4 h. The resulting catalyst was washed with deionized water until the pH reached neural and no chloride ions were detected in the AgNO₃ solution. The resulting catalyst was then dried in a vacuum oven at 80 °C for 12 h.

2.4. Synthesis of L1₀-PtCo/HGNG

L1₀-PtCo/HGNG was prepared by a wet impregnation strategy followed by high temperature heat treatment in a 5% H₂/Ar atmosphere. In general, CoCl₂·6H₂O and prepared Pt/HGNG were dispersed in 100 mL of deionized water with a Pt/Co molar ratio of 1 : 1 under ultrasonic agitation for 2 h. After vacuum drying and grinding, the samples were treated at 750 °C for 2 h under a 5% H₂/Ar atmosphere with a 5 °C min⁻¹ heating rate. After cooling to room temperature, the resulting powder was soaked in 0.5 M H₂SO₄ solution for 12 h to produce the final catalyst.

2.5. Electrochemical measurements

All electrochemical measurements were performed on an Autolab electrochemical workstation with a graphite rod as the counter electrode and a Hg/Hg₂SO₄ electrode as the reference electrode. The working electrode was a glassy carbon electrode (RDE, 5 mm diameter) coated with catalyst ink. For ink preparation, 4 mg of the catalyst was dispersed in 4 mL of isopropanol solution containing 30 µL of Nafion solution (5 wt%) and then sonicated for 15 min. The resulting 10 µL of ink was dropped onto a disk electrode designed to be loaded with 25 µg_Pt cm⁻² and then dried at room temperature to obtain a thin film electrode. Cyclic voltammetry (CV) curves were recorded in the potential range of 0.05–1.2 V in N₂ saturated HClO₄ solution at a scan rate of 50 mV s⁻¹, and the ECSA was calculated accordingly:

ECSA = 100 × S/(C × v × M) (1)

where S, C, v and M represent the integrated area of the hydrogen desorption peak (A V), hydroxide adsorption charge constant on the smooth Pt surface (0.21 mC cm⁻²), scan speed (mV s⁻¹) and mass of Pt on the electrode (g), respectively.

Linear sweep voltammetry (LSV) curves were recorded in an oxygen saturated HClO₄ solution at a scan rate of 10 mV s⁻¹ at 1600 rpm. Accelerated durability tests (ADTs) were used to evaluate the stability of platinum nitride (0.6–1.0 V, 100 mV s⁻¹, 25 °C) and the carbon support (1.0–1.5 V, 500 mV s⁻¹, 25 °C). All reference potentials have been converted to the reversible hydrogen electrode (RHE).

2.6. Membrane assembly electrode (MEA) preparation and single fuel cell testing

The synthesized catalyst was incorporated into a catalyst-coated membrane (CCM) by ultrasonically spraying water/n-propanol based ink onto a 12 µm Gore membrane. The Pt loading on both anode and cathode sides was 0.1 mg cm⁻² and the CCM had an active area of 5 cm². For assembling the MEA, 215 µm GDL (22BB, SGL carbon) and 140 µm gaskets were used. The cell endplates were torqued to 8 N m to achieve the desired compression ratio of approximately 22%. The H₂–air polarization curve tests were performed at 80 °C, 150 kPa_abs, and 100% relative humidity with an anode/cathode gas flow rate of 0.5/2 Liters per min H₂/air. Following DOE guidance, the low-potential catalyst ADT was subjected to trapezoidal wave cycling, with each cycle holding the MEA at 0.6 V for 3 seconds, and then at 0.95 V for 3 seconds, with H₂/N₂ flow rates of 0.2/0.075 Liters per min H₂/air at the anode and cathode, respectively. For catalyst support cycles, the triangle voltage cycling tests with a scan rate of 500 mV s⁻¹ were performed between 1.0 V and 1.5 V.

3. Results and discussion

3.1. Synthesis and characterization of the HGNG support

The synthesis process is illustrated in Fig. 1a. Briefly, a three-dimensional porous graphene carbon (GC) was obtained via PECVD.³⁰ Highly graphitized and nitrogen-doped graphene (HGNG) was subsequently fabricated through high-temperature calcination (1800 °C) followed by ammonia plasma treatment, with HGG obtained as an intermediate without the plasma step. The prepared HGG and HGNG exhibit a wrinkled three-dimensional structure of interconnected nanowalls (Fig. 1b and S1), composed of stacked, few-layer graphene nanosheets (Fig. 1c). XRD patterns show an intense graphite (002) peak for both materials, indicating high graphitization (Fig. S2). Raman spectra further confirm this, showing a sharp 2D band (Fig. S3). Notably, the I_D/I_G ratio for HGNG increases compared to HGG, which is attributed to defects introduced by nitrogen doping. This is corroborated by electron paramagnetic resonance (EPR) spectroscopy (Fig. 1d), where HGNG exhibits a significantly stronger signal, indicating the presence of paramagnetic centers associated with nitrogen dopants.^31–33

Fig. 1 (a) Schematic illustration of the synthesis procedure of L1₀-PtCo/HGNG. (b) SEM and (c) TEM image of HGNG. (d) EPR of HGG and HGNG. (e) XRD patterns of Pt/HGNG and L1₀-PtCo/HGNG. TEM image and corresponding particle size distribution (inset) of (f) Pt/HGNG and (g) L1₀-PtCo/HGNG.

XPS analysis confirms a nitrogen content of 2.58 at% in HGNG. The deconvoluted N 1s spectrum (Fig. S4) reveals the presence of pyridinic N (41.8%), pyrrolic N (24.2%), graphitic N (24.1%), and oxidized N (9.9%).³³ The abundance of pyridinic and graphitic N is crucial, as these species provide lone electron pairs that can serve as effective anchoring sites for metal nanoparticles, thereby enhancing metal–support interactions and facilitating subsequent uniform dispersion.^33–37 This is directly confirmed by a comparative Pt dispersion study (Fig. S5).

Nitrogen physisorption measurements show that HGNG possesses a large BET surface area of 554 m² g⁻¹ and a pore volume of 1.73 cm³ g⁻¹ (Fig. S6). While high-temperature treatment reduces porosity compared to the initial GC, the subsequent ammonia plasma treatment positively modifies the surface area and pore structure.³¹ The pore size distribution confirms a hierarchical porosity, with a majority of pores in the 2–20 nm mesoporous range, ideal for mass transport and metal deposition.¹⁸

3.2. Structure and composition of the L1₀-PtCo/HGNG catalyst

The L1₀-PtCo/HGNG catalyst was synthesized by annealing Co-impregnated Pt/HGNG under H₂/Ar, where the uniformly dispersed Pt nanoparticles served as seeds to guide the formation of the ordered L1₀-PtCo structure.³⁸ XRD patterns (Fig. 1e) show that all peaks for L1₀-PtCo/HGNG shift to higher angles compared to those of Pt/HGNG, indicating lattice contraction due to Co incorporation. Critically, the appearance of superlattice peaks at 24° and 33.3°, corresponding to the (001) and (110) planes of the ordered face-centered tetragonal (fct) structure, confirms the formation of the L1₀ intermetallic phase.²⁹

TEM images (Fig. 1f and g) reveal a high dispersion of nanoparticles on the graphene framework, demonstrating the efficacy of HGNG as a support in promoting uniform nanoparticle distribution. The average particle size of L1₀-PtCo is 4.37 ± 0.73 nm, larger than the ∼2.4 nm Pt seeds in Pt/HGNG due to the incorporation and ordering process. The thermogravimetric (TG) curves (Fig. S7) combined with inductively coupled plasma optical emission spectroscopy (ICP-OES) (Table S2) results determined the Pt content in Pt/HGNG and L1₀-PtCo/HGNG to be 49.8 wt% and 45.9 wt%, respectively. HR-TEM (Fig. 2a) shows lattice fringes with a d-spacing of 0.216 nm, matching the (111) plane of L1₀-PtCo.^29,38 Energy-dispersive spectroscopy (EDS) elemental mapping (Fig. 2b) and line scan profiles (Fig. 2c) demonstrate a homogeneous distribution of Pt and Co within individual nanoparticles. XPS analysis of the Pt 4f region (Fig. 2d) reveals a positive binding energy shift of 0.19 eV for L1₀-PtCo/HGNG compared to Pt/HGNG. This shift suggests an electronic interaction between the Pt nanoparticles and the N-doped carbon support, which can modulate the surface electronic structure of Pt and optimize adsorbate binding energies.¹⁸

Fig. 2 (a) HRTEM image of L1₀-PtCo/HGNG. (b) EDS elemental mapping and (c) EDS line-profile of L1₀-PtCo/HGNG. (d) XPS spectra of Pt 4f for Pt/HGNG and L1₀-PtCo/HGNG.

3.3. Electrochemical ORR performance and durability

The ORR performance was first evaluated using a rotating disk electrode (RDE). Compared to Pt/GC and Pt/HGG, Pt/HGNG exhibits the highest catalytic activity, likely owing to its three-dimensional porous architecture and abundant nitrogen doping (Fig. S8). As shown in Fig. 3a, the electrochemical-active surface area (ECSA) of the Pt/HGNG catalyst (62.5 m² g⁻¹) exceeds that of commercial Pt/C (47.2 m² g⁻¹) and L1₀-PtCo/HGNG (42.2 m² g⁻¹). Nevertheless, due to the superior intrinsic activity of L1₀-PtCo relative to pure Pt, L1₀-PtCo/HGNG is expected to exhibit enhanced ORR activity.³⁹ Indeed, as depicted in Fig. 3b, L1₀-PtCo/HGNG displays outstanding catalytic performance with a half-wave potential (E_1/2) of 0.933 V, significantly higher than those of Pt/HGNG (0.904 V) and commercial Pt/C (0.891 V). The kinetic currents of L1₀-PtCo/HGNG are also markedly greater in both high- and low-potential regions, further confirming its higher intrinsic activity (Fig. S9). To provide a more direct comparison of the electrocatalytic improvement, the specific activity (SA) and mass activity (MA) measured at 0.9 V are presented in Fig. 3c and d. L1₀-PtCo/HGNG achieves remarkable SA (1.54 mA cm_Pt⁻²) and MA (0.65 A mg_Pt⁻¹), which are 4-fold and 3.6-fold higher, respectively, than those of commercial Pt/C (0.38 mA cm_Pt⁻²; 0.18 A mg_Pt⁻¹).

Fig. 3 (a) CV curves, (b) ORR polarization curves, and (c) SA and (d) MA before and after ADT for L1₀-PtCo/HGNG, Pt/HGNG and Pt/C.

The electrochemical durability of all catalysts was evaluated by accelerated durability testing (ADT) in 0.1 M HClO₄, scanning between 0.6 and 1.0 V vs. RHE at 100 mV s⁻¹. After 30 000 potential cycles, L1₀-PtCo/HGNG retains most of its initial ECSA with only a 1.3% loss, whereas Pt/HGNG and commercial Pt/C suffer larger ECSA losses of 15.2% and 22%, respectively (Fig. S10–S12). Consistently, the L1₀-PtCo/HGNG electrode shows a minimal negative shift in E_1/2 (3 mV), while Pt/HGNG and commercial Pt/C undergo more pronounced degradation (10 mV and 41 mV shifts, respectively). After ADT, the SA and MA of L1₀-PtCo/HGNG decrease by only 11% and 12.3%, respectively. In contrast, commercial Pt/C suffers substantial losses of 66.7% in SA and 57.9% in MA (Fig. 3c and d).

Structural changes before and after ADT were further examined by TEM and XRD. For commercial Pt/C, the average nanoparticle size increases considerably from 2.58 nm to 4.0 nm, indicating significant particle agglomeration during cycling (Fig. S13). In comparison, L1₀-PtCo/HGNG exhibits negligible morphological changes; the nanoparticles remain uniformly dispersed on the HGNG support, with the average size increasing only slightly from 4.36 nm to 4.96 nm (Fig. S14). XRD patterns reveal that the L1₀-PtCo crystal structure is well preserved after cycling, as evidenced by the maintained characteristic diffraction peaks (Fig. S15), confirming the exceptional structural stability of the catalyst.⁴⁰

To evaluate the degradation of the carbon support, accelerated durability tests were performed on an RDE by cycling the catalyst between 1.0 and 1.5 V. After 5000 cycles, the ECSA retention of L1₀-PtCo/HGNG, Pt/HGNG, and Pt/C was 96.9%, 94.3%, and 88.2%, respectively (Fig. S16–S18). The lower retention of Pt/C is likely due to Pt nanoparticle growth via aggregation and/or Ostwald ripening, as supported by TEM analysis showing an increase in average particle size from 2.58 nm to 3.61 nm (Fig. S19). In contrast, both L1₀-PtCo/HGNG and Pt/HGNG showed negligible changes in nanoparticle size and distribution, with no obvious aggregation observed after testing (Fig. S20 and S21). Consistently, the LSV curves of L1₀-PtCo/HGNG and Pt/HGNG exhibited only minimal shifts, whereas commercial Pt/C displayed significant activity degradation, with an E_1/2 negative shift of 13 mV. The MA and SA retentions of L1₀-PtCo/HGNG were 90.8% and 93.9%, respectively—slightly lower than those of Pt/HGNG (96.6% and 95.7%) but substantially higher than the values for commercial Pt/C (67% and 76.3%).

Recognizing the substantial differences between conventional RDE conditions and actual fuel cell operating environments, L1₀-PtCo/HGNG was further evaluated in a MEA under realistic fuel cell conditions and compared directly with commercial Pt/C. ADTs were conducted following U.S. DOE protocols to assess electrocatalyst stability. Polarization curves recorded under H₂/air operation revealed that the MEA with an L1₀-PtCo/HGNG cathode delivered a peak power density of 964 mW cm⁻², outperforming the Pt/C-based cathode (904 mW cm⁻²) (Fig. 4a). After 30 000 potential cycles between 0.6 and 0.95 V in an H₂/N₂ atmosphere, the L1₀-PtCo/HGNG cathode exhibited negligible voltage loss across all current densities, in contrast to the significant degradation observed for commercial Pt/C (Fig. S22 and S23). Specifically, the voltage loss at 0.8 A cm⁻² was only 19 mV for L1₀-PtCo/HGNG, well below the DOE 2025 target of <30 mV. Moreover, the L1₀-PtCo/HGNG cathode retained a high ECSA with a loss of 33.2%, also meeting the DOE stability requirement of less than 40% ECSA loss (Fig. 4b and S22). In comparison, commercial Pt/C suffered a voltage loss of 54 mV at 0.8 A cm⁻² and an ECSA loss of 80.1% (Fig. 4b and S23).

Fig. 4 (a) The polarization curves of MEAs with L1₀-PtCo/HGNG, Pt/HGNG and commercial Pt/C under H₂–air conditions; (b) voltage drops and ECSA losses after the ADT; (c) comparison of the Pt content of catalysts and peak power densities for catalysts between this work and previous studies.

Conventional IMC catalysts typically contain ∼20 wt% Pt supported on carbon, which often results in thicker catalyst layers, increased mass-transfer resistance, and consequently degraded cell performance, especially at high current densities. As shown in Fig. 4c and Table S3, the present L1₀-PtCo/HGNG catalyst achieves an optimal balance between Pt loading and catalytic performance, demonstrating highly competitive ORR activity compared with many previously reported Pt-based intermetallic materials.^29,38–45

To evaluate the durability of HGNG as a catalyst support, we performed 5k ADT cycles at 1.0 to 1.5 V using fresh MEA in a H₂/N₂ environment. As shown in Fig. 5a, catalysts employing the HGNG support demonstrated outstanding stability. The voltage loss at 1.5 A cm⁻² was only 17 mV for L1₀-PtCo/HGNG and 26 mV for Pt/HGNG (Fig. S24), both well within the stringent DOE 2025 target of <30 mV. Correspondingly, the ECSA losses for L1₀-PtCo/HGNG and Pt/HGNG were 29.9% and 34.5%, respectively, also meeting the DOE stability requirement of less than 40% ECSA loss (Fig. S24 and S25). In stark contrast, the commercial Pt/C cathode suffered severe degradation under the same conditions, exhibiting a much larger voltage drop at 1.5 A cm⁻² and an ECSA loss as high as 75.9% (Fig. 5c and S26). Cross-sectional SEM analysis (Fig. 5d) offers visual proof: the catalyst layer thickness for L1₀-PtCo/HGNG and Pt/HGNG decreases only slightly (2.62 to 2.45 µm, and 2.7 µm to 2.54 µm, respectively) after cycling, whereas the Pt/C layer suffers severe thinning (2.72 to 1.51 µm). Notably, both Pt/HGNG and L1₀-PtCo/HGNG, which share the same graphitized HGNG support, showed similarly minimal corrosion, while the commercial carbon support in Pt/C severely degraded. This confirms that the corrosion resistance is an intrinsic property of the highly graphitized HGNG framework.

Fig. 5 The polarization curves of an H₂–air fuel cell with L1₀-PtCo/HGNG (a) and commercial Pt/C (b) before and after the 5k cycle ADT; (c) voltage drops and ECSA losses after the 5k cycle ADT; (d) SEM cross-section of MEAs from commercial Pt/C, Pt/HGNG and L1₀-PtCo/HGNG before and after 5k cycles of catalyst support ADT, respectively.

4. Conclusion

In summary, we have demonstrated a synergistic sequential strategy—integrating PECVD, ultra-high temperature annealing, and targeted plasma functionalization—to fabricate a novel carbon support (HGNG) that successfully reconciles the traditional conflicts between high graphitization, hierarchical porosity, and beneficial surface doping. The resultant HGNG enables the loading of a high mass fraction of uniformly dispersed, small-sized L1₀-PtCo intermetallic nanoparticles. The obtained L1₀-PtCo/HGNG catalyst exhibits outstanding ORR activity and, more importantly, exceptional durability in both half-cell and full-cell configurations, surpassing state-of-the-art commercial Pt/C and meeting stringent DOE 2025 targets. The work provides direct evidence linking nitrogen doping to enhanced metal–support interaction and high graphitization to superior corrosion resistance, offering a validated design paradigm for developing high-performance, durable electrocatalyst systems for practical energy conversion devices.

Author contributions

Zhihao Wang: conceptualization, methodology, data curation, formal analysis, writing – original draft, writing – review & editing. Huihui Jin: writing – review & editing, supervision, formal analysis. Yizhou Hao: investigation, methodology. Cheng Chen: data curation, validation. Haifeng Lv: resources, funding acquisition. Daping He: writing – review & editing, resources, funding acquisition.

Conflicts of interest

There are no conflicts to declare.

Data availability

All data needed to support the conclusions in the paper are presented in the manuscript and the supplementary information (SI). Supplementary information is available. See DOI: https://doi.org/10.1039/d5ta05492c.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (22279097 and 22279081) and the Shenzhen Science and Technology Program (Grant No. JSGGKQTD20221101115701006).

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Footnote

† These authors contributed equally to this work.

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