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• Oxygen reduction reaction (ORR) is a critical process in proton exchange membrane fuel cells (PEMFCs), metal-air batteries, and other electrochemical energy conversion technologies [1,2]. The development of efficient electrocatalysts for the ORR is of paramount importance to enhance the performance and affordability of these devices, which are keys to a sustainable and clean energy future [3–5]. Pt and its alloys have long been regarded as highly effective electrocatalysts for the ORR, due to their exceptional electrocatalytic activity and stability [6]. Nevertheless, the high cost and limited availability of Pt have impeded its large-scale deployment. To address these challenges, researchers have explored the incorporation of transition metals, such as Co, into Pt-based catalysts, which can sustain the intrinsic ORR activity of Pt while modifying the electronic structure through the introduction of Co [7]. The synergistic effect of Pt and Co not only improves the catalytic reaction rate and stability of catalysts, but also reduces the overall Pt loading, rendering PEMFCs more economically viable. Efforts have been spent to manipulating the surface electronic structure, controlling the preparation processes and tuning the atomic structures of low-Pt catalysts [8].

  Crystallinity engineering holds immense importance to rational design advanced catalysts [9–12]. By atomic-scaled modification of the crystalline structure of catalysts, the specific surface structures, disordered regions, atomic steps and high-index facets can be introduced, all of which can profoundly create additional active sites for the reactant adsorption and facilitate the electron-hole charge transfer, resulting in the improved catalytic kinetics [13–16]. Furthermore, the controlled introduction of disordered sites and variation of bonding energy can enhance the stability of the catalysts, making it more resistant to degradation under harsh operating conditions. Consequently, crystallinity engineering not only boosts the overall electrocatalytic activity but also extends the lifespan of catalysts, making it a pivotal strategy in the quest for more efficient, durable, and cost-effective catalysts. The ultrafast high temperature shock (HTS) technique based on Joule heating, proposed by Chen and Hu et al. in 2016 [17,18], has been demonstrated a variety of applications in manufacturing of micro-/nano- catalysts including single metals, multimetallic metals (e.g., high entropy alloys), metal compounds like oxides, carbides, nitrides and sulfides, etc. [19–23]. The non-equilibrium HTS method showed great potential for crystallinity engineering of well-dispersed, uniform, stable, and ultrafine nanocatalysts due to its kinetic advantages such as ultrafast heating/cooling rates (~10⁵ K/s), short dwelling time, and the generation of high local temperature (up to 3000 K) [24,25]. Due to the ultrafast cooling rate, HTS can freeze the high-temperature phase within nanostructures, thus capturing the Gibbs free energy [26]. This is particularly vital for the ORR, which involves multiple intermediate steps and the adsorption of oxygen species on the surface of catalysts. Materials with high Gibbs free energy shows a greater propensity to facilitate these interactions, ultimately leading to improved ORR performance. Furthermore, the superhigh synthesis temperatures in the HTS process with high energy input enable the rational tuning of chemical bonds and local electronic configuration, generating more active sites and enhancing interface effects and synergistic effects among various elements in nanoalloys [27,28]. The aforementioned characteristics collectively promote the adsorption and activation of oxygen species, reducing the energy barriers of intermediates for ORR, resulting in lower overpotentials and faster reaction kinetics.

  Herein, two types of PtCo₃ nanoalloys, both anchored on the carbon black support, were manufactured using the HTS technique based on instant Joule heating. The average size of these nanoalloys is 6 nm. They were prepared using two different modes: high temperature shock, and Joule heating for 2 s, resulting in PtCo₃HTS and PtCo₃HT-2 s, respectively. PtCo₃HTS showed lower crystallinity and longer metal bonds, as compared to PtCo₃HT-2 s. Detailed XRD and XAFS analyses provide robust evidence of the crystallinity variation between these two nanostructures. Both nanoalloys outperform the commercial 20 wt% Pt/C catalyst for ORR, which can be ascribed to the synergistic effects between Pt and Co. Note that the remarkable overpotential and durability of PtCo₃HTS may be attribute to its higher Gibbs free energy, variation in chemical bond, lower crystallinity, and more active electronic structures. The emergence of crystallinity engineering by efficient HTS method offers a new kinetic dimension control over the catalyst design and interface modulation for optimal catalytic activity. This strategy offers a promising avenue to make clean energy technologies more accessible and environmentally sustainable.

  PtCo₃ nanoalloys on carbon black support, referred to as PtCo₃/C, were synthesized via an ultrafast HTS method at about 1173 K under an argon (Ar) atmosphere in the presence of metal precursors like chloroplatinic acid hexahydrate (H₂PtCl₆·nH₂O) and cobalt (II) nitrate hexahydrate (Co(NO₃)₂·6H₂O), along with XC72R carbon black as support. The synthetic process of PtCo₃/C was illustrated in Fig. 1. Firstly, the metal precursors mixed with the carbon support were uniformly dispersed in aqueous solvent under sonication and magnetic stirring, adjusting the pH value around 9 using ammonium hydroxide. Owing to the electrical charge effect, metal ions prefer to be adsorbed on carbon black particles. After centrifugation, the dried powder was subsequently been treated by instant Joule heating under an Ar atmosphere. The high temperature shock mode, involving a single pulse of electrical heating, was utilized for the preparation of PtCo₃HTS. PtCo₃HT-2 s was obtained, when Joule heating lasts for 2 s. During Joule heating process, the metal precursors decomposed into Pt and Co atoms, undergoing rapid condensation and crystallization within milliseconds. For the PtCo₃HT-2 s, the extended high temperature maintenance can provide additional energy, potentially enhancing the nucleation and growth process, and improving crystallinity. Note that both heating modes can reach high heating rate of about 700 K/s, with the cooling rate of HTS mode slightly higher at 600 K/s, compared to 400 K/s for the HT-2 s mode. The rapid quenching process may induce the freezing of high-temperature state atoms, leading to a more randomly arranged structure with high Gibbs free energy. Temporal evolutions of both modes are shown in Fig. S1 (Supporting information). Further experimental details are described in Supporting information.

  Figure 1

  

  Figure 1.  Schematic illustration of the manufacturing of PtCo_3–HTS and PtCo_3–HT-2 s via HTS technique.

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  The representative transmission electron microscopy (TEM) showed that the as-obtained PtCo₃HTS, with a relatively uniform size of 5.4 nm, is well-dispersed on carbon black (Fig. 2a). Due to the pre-mixing of metal precursors and carbon black in aqueous solution before HTS process, the uniform dispersion and refined particle size are guaranteed. According to the high-resolution TEM (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image (Figs. 2b and c), PtCo₃HTS mainly showed a single crystalline structure. The lattice fringe exhibits an interplanar crystal spacing of 0.21 nm, corresponding to the (111) planes of the face-centered cubic (fcc) phase. Due to the orientation, only the (111) planes are visible in Fig. 2c, and the axis cannot be defined in the inset fast Fourier transform (FFT) pattern. In addition, the atomic-thin carbon layer coating on PtCo₃HTS can effectively prevent the particle aggregation as well as enhance its stability. Importantly, the lattice spacing is corroborated by the pixel intensity calculation (Fig. S2 in Supporting information) taken from the red rectangular region in Fig. 2c. The HAADF-STEM and corresponding EDS elemental mapping images display the uniform dispersion of Pt and Co elements (Pt/Co ratio of 24.7/75.3) within PtCo₃HTS (Figs. 2d-g and Fig. S3 in Supporting information).

  Figure 2

  

  Figure 2.  Electron microscopic characterization and analysis for PtCo_3–HTS. (a) TEM image and the inset particle size distribution diagram of PtCo_3–HTS. (b) HRTEM and (c) HAADF-STEM images of PtCo_3–HTS. Inset in (c) is the corresponding FFT pattern of the yellow dash square area. (d) HAADF-STEM and (e-g) the corresponding EDS elemental mapping of PtCo_3–HTS.

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  As shown in Fig. 3a, PtCo₃HT-2 s exhibits a similar uniform dispersion on carbon black. The average diameter of PtCo₃HT-2 s is 6.4 nm, slightly larger than that of PtCo₃HTS. The size difference can be attributed to the continuously nucleation and grain growth during the longer high-temperature reaction of PtCo₃HT-2 s. Note that some nanoparticles of PtCo₃HT-2 s display a multi-crystalline structure (Fig. 3b). According to the HAADF-STEM image and corresponding FFT pattern (Fig. 3c), the crystallinity of PtCo₃HT-2 s is clear shown as fcc phase with a lattice spacing of 0.211 nm and 0.183 nm, corresponding to the (111) and (002) planes with the axis along [110], which is also consistent with the lattice fringe measured by integrated pixel intensity (yellow line in Fig. S2). The relatively longer high-temperature treatment reinforced the crystallinity of PtCo₃HT-2 s. Moreover, the carbon layer of some nanoparticles even showed crystallinity (Fig. S4 in Supporting information). The Pt/Co atomic ratio of PtCo₃HT-2 s was quantified as 23.2/76.8 according to the EDS elemental mapping (Figs. 3d-g and Fig. S5 in Supporting information). PtCo₃HT-2 s also showed uniform dispersion of Pt and Co elements.

  Figure 3

  

  Figure 3.  Electron microscopic characterization and analysis for PtCo_3–HT-2 s. (a) TEM image and the inset particle size distribution diagram of PtCo_3–HT-2 s. (b) HRTEM and (c) HAADF-STEM images of PtCo_3–HT-2 s. Inset in (c) is the corresponding FFT pattern of the yellow dash square area. (d) HRTEM and (e-g) the corresponding EDS elemental mapping of PtCo_3–HT-2 s.

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  The structural analysis of PtCo₃/C alloys is presented by XRD characterization, as shown in Fig. S6 (Supporting information). The XRD peaks for both PtCo₃/C samples align with those of the fcc PtCo alloy (PDF#71–7411), showing a positive shift compared to pure Pt, indicative of the alloying effect [29]. Notably, according to the Scherrer formula and XRD peak profiles, the average particle sizes of PtCo₃HTS and PtCo₃HT-2 s are determined to be 5.7 nm and 6.9 nm, respectively, aligning with the size statistics based on TEM images. Moreover, normalized XRD profiles reveal that PtCo₃HT-2 s exhibits a narrower full width at half maximum (FWHM) of the main peak, as compared to PtCo₃HTS, which might suggest the higher crystallinity for PtCo₃HT-2 s [30]. This is rationalized by the extended heat treatment at high temperature during the synthesis of PtCo₃HT-2 s, promoting enhanced nucleation, atomic arrangement, and grain growth. Impressively, compared to traditional heat treatment method via a tube furnace, the Joule heating approach can prepare PtCo₃/C with a significant refined grain size (Fig. S7 in Supporting information).

  To investigate the local atomic structure of PtCo₃HTS and PtCo₃HT-2 s, the X-ray absorption fine structure (XAFS) measurements were performed. Note that the Pt L₃-edge white line peaks in the X-ray absorption near-edge structure (XANES) spectra for PtCo₃HTS and PtCo₃HT-2 s are slightly stronger than that of Pt foil, indicating a lower level of occupation in the Pt 5d-band orbitals in PtCo₃ alloys (Fig. 4a) [31]. The decrease in the Pt 5d-orbital occupation may be influenced by the electronic configuration of the alloying element [32]. The main peak (2.2 Å) in the Fourier transform of extended X-ray absorption fine structure (FT-EXAFS) spectra for PtCo₃HTS and PtCo₃HT-2 s (Fig. 4b) represents the nearest coordination shells of Pt atoms, which is smaller than that of the Pt foil (2.4 Å). This shorter radial distance suggests a shorter bond length than that of Pt foil, attributed to heteroatomic interaction in such alloy structures [33]. Impressively, PtCo₃HTS displays a much lower intensity of this main peak compared to PtCo₃HT-2 s, indicating its lower crystallinity.

  Figure 4

  

  Figure 4.  XAFS analysis of PtCo_3–HTS, PtCo_3–HT-2 s, Pt foil, and Co foil. (a) XANES and (b) FT-EXAFS spectra for Pt L₃-edge. (c) XANES and (d) FT-EXAFS spectra for Co K-edge.

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  XANES spectra of Co K-edge for Co foil, PtCo₃HTS and PtCo₃HT-2 s are shown in Fig. 4c. The white line intensity of PtCo₃HTS is slightly larger than that of PtCo₃HT-2 s. This implies that Co atoms in PtCo₃HTS possess fewer electrons than those in PtCo₃HT-2 s, suggesting a much more positive charge on Co^δ+ in PtCo₃HTS. Moreover, the white line intensities for PtCo₃HTS and PtCo₃HT-2 s are significantly larger than for Co foil, suggesting the presence of some oxidation form of Co in both PtCo₃/C catalysts. From the FT-EXAFS spectra, larger radial distances are observed in both PtCo₃HTS (2.2 Å) and PtCo₃HT-2 s (2.3 Å), as compared to Co foil (2.1 Å), indicating the alloying effect of such alloys and the slight oxidation of PtCo₃HTS (Fig. 4d). This slight oxidation, which might due to the improper storage before XAFS analysis, is also evidenced by both the height of the white line and the diminishment of the pre-edge at around 7709 eV. Similarly, the lower main peak intensity of PtCo₃HTS represents its lower crystallinity compared to PtCo₃HT-2 s. The synergistic effect between Pt and Co in such alloy nanostructures can tune the electronic structures, enhancing catalytic performance. The low crystallinity in PtCo₃HTS indicates the suspension of the high-temperature phase, lower energy barriers, and the provision of more active sites for electrocatalysis [27].

  The electrocatalytic capacities of PtCo₃HTS and PtCo₃HT-2 s were evaluated as catalysts for electrocatalytic ORR in 0.1 mol/L KOH aqueous solution. The commercial Pt/C (20 wt%) catalyst was used for comparison. Using a rotating disk electrode (RDE), cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were conducted to evaluate the oxygen reduction reaction (ORR) activity of PtCo₃ catalysts. In a N₂-saturated 0.1 mol/L KOH electrolyte, CV tests were performed at a scan rate of 50 mV/s. The CV of commercial Pt/C, PtCo₃HTS, and PtCo₃HT-2 s to some extent illustrate their catalytic performance (Fig. 5a). The ORR peak appears at approximately 0.75 V vs. RHE. In this potential range, the ORR region of PtCo₃HTS shifts to higher potentials, indicating weaker binding strength with adsorbed intermediates, favorable for catalytic reactions. Additionally, the Pt-O reduction peak position of PtCo₃HTS in the CV graph is similar to that of PtCo₃HT-2 s, suggesting comparable binding energies with oxygen-containing intermediates. Therefore, the superior catalytic performance of PtCo₃HTS mainly depends on the weak binding strength of adsorbed intermediates in the ORR region. As shown in Fig. 5b, LSV curves were tested in O₂-saturated 0.1 mol/L KOH solution at 1600 rpm with a scan rate of 10 mV/s to investigate their ORR performance. PtCo₃HTS exhibited a significantly higher onset potential (E_onset) than PtCo₃HT-2 s and commercial Pt/C. The half-wave potential (E_1/2) of PtCo₃HTS was 0.897 V, 25 mV higher than PtCo₃HT-2 s and 50 mV higher than commercial Pt/C, indicating the optimal ORR catalytic activity of PtCo₃HTS. Intrinsic activity of the catalyst is also a crucial indicator. As shown in Fig. 5c, by calculating the mass activity (MA) and specific activity (SA) at 0.9 V, PtCo₃HTS exhibited MA (2.08 A/mg_Pt) and SA (2.87 mA/cm²) values far exceeding commercial Pt/C, being 13.87 times and 7.36 times higher, respectively, demonstrating the outstanding intrinsic catalytic activity of PtCo₃HTS. By comparison, MA (1.01 A/mg_Pt) and SA (2.01 mA/cm²) of PtCo₃HT-2 s showed 6.7 times and 5.15 times of those of commercial Pt/C. In addition, the MA of PtCo₃HTS significantly surpasses the target (0.44 A/mg_Pt at 0.90 V) set by the U.S. Department of Energy (DOE, 2020–2025) [31,34]. Detailed data can be found in Table S2 (Supporting information).

  Figure 5

  

  Figure 5.  (a) CV curves, (b) ORR polarization curves, (c) MA and SA at 0.9 V, (d) Tafel curves of the PtCo_3–HTS, PtCo_3–HT-2 s, and Pt/C in 0.1 mol/L KOH. (e) The initial LSV curves and the corresponding LSV curves after 50, 000 cycles for PtCo_3–HTS PtCo_3–HT-2 s, and Pt/C, respectively. (f) Comparison of the mass activity of PtCo_3–HTS and previously reported electrocatalysts for ORR.

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  The ORR kinetics of the three samples were analyzed by Tafel curves (Fig. 5d). Notably, the Tafel slopes of PtCo₃HTS and PtCo₃HT-2 s were 23.9 mV/dec and 33.7 mV/dec, respectively, both lower than the commercial Pt/C with a Tafel slope of 59.5 mV/dec. This indicates that PtCo₃HTS and PtCo₃HT-2 s have favorable ORR kinetic processes. Catalyst stability is also a crucial evaluation factor. Using the accelerated durability test (ADT) method, stability was tested by cycling between 0.055 V and 1.015 V at a speed of 200 mV/s for 50, 000 cycles in O₂-saturated 0.1 mol/L KOH electrolyte. Fig. 5e shows the LSV curves of PtCo₃HTS, PtCo₃HT-2 s, and commercial Pt/C before and after cyclic tests. The E_1/2 of PtCo₃HTS showed a slight decrease, indicating its excellent stability. Fig. S8 (Supporting information) shows the morphology of PtCo₃HTS after stability testing, revealing minimal changes, no apparent aggregation, and dissolution, confirming its good stability. To investigate the ORR reaction pathway, LSV curves of PtCo₃HTS were measured at different speeds between 400 rpm and 2500 rpm at a scan rate of 10 mV/s, providing corresponding Koutecky-Levich (K-L) plots (Fig. S9 in Supporting information). During the ORR process, the electron transfer number of the PtCo₃HTS catalyst ranged from 4.2 to 4.3, between 0.35 V and 0.70 V, indicating that O₂ reduction is mainly achieved through a four-electron reaction mechanism [35]. The ORR reaction process mainly has two pathways: one is a two-electron reaction where O₂ is incompletely reduced, generating unstable H₂O₂ and OH⁻, thereby slowing down the reaction [36]. The second is a four-electron reaction where O₂ is directly reduced to H₂O, facilitating the progress of ORR. As shown in Fig. S9, PtCo₃HTS follows the four-electron reaction mechanism, which is one of the reasons for its outstanding catalytic performance. Compared with previously reported Pt-based catalysts, PtCo₃HTS still exhibits top-tier catalytic performance (Fig. 5f and Table S3 in Supporting information).

  The superior electrocatalytic performance of PtCo₃HTS can be attributed to several factors. Firstly, the PtCo₃HTS, prepared by instant Joule heating, exhibits a clean surface due to the ultrahigh treating temperature [37]. Additionally, the strong bonding between PtCo₃ and carbon black support contributes to the stability of electrocatalytic ORR [38,39]. The thin carbon layer on PtCo₃HTS may also facilitate electron transfer through a synergistic effect. Secondly, the catalytic performance of nanocatalysts can be rationally modified through crystallinity engineering [40]. The lower crystallinity of PtCo₃HTS plays a crucial role in optimizing the electronic structure of active sites. This results in a reduction of the oxygen binding energy on Pt, enhancing the surface reactivity of metallic nanostructures and improving their activity for ORR. Thirdly, the synergistic structural and electronic effects between Pt and Co further reinforce the electrocatalytic activity of PtCo₃HTS for ORR [41]. The alloying of Pt with transition metals, such as Co, can modify the electronic structure of Pt, contributing to the overall improvement of electrocatalytic activity [42].

  In summary, the non-equilibrium and energy-efficient HTS method has been successfully applied for the crystallinity engineering of PtCo₃/C nanocatalysts. This innovative approach, featured with ultrahigh temperature, ultrafast heating and cooling rates, short dwelling time, and kinetic modulation of reaction system, allows for the rational modification of the nucleation and grain growth processes of nanoalloys, by tuning the Joule heating parameters such as heating duration and power input. Impressively, PtCo₃HTS, obtained through the shock mode, shows outstanding electrocatalytic activity and stability for ORR, with an E_1/2 of 0.897 V and a long-term duration after 50, 000 cycles. This work introduces a novel strategy with potential applications in industrial manufacturing and catalyst development.

  Declaration of competing interest

  The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

  Acknowledgment

  This study was financially supported by the National Natural Science Foundation of China (No. 12205165).

  Supplementary materials

  Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2024.110069.

  
  
• 1. [1]

     M. Liu, Z. Zhao, X. Duan, Y. Huang, Adv. Mater. 31 (2019) 1802234.

  2. [2]

     G.L. Chai, K. Qiu, M. Qiao, et al., Energy Environ. Sci. 10 (2017) 1186–1195.

  3. [3]

     Y. Qiu, Z. Hu, H. Li, et al., Chem. Engin. J. 430 (2022) 132769.

  4. [4]

     L. Cui, K. Fan, L. Zong, et al., Energy Storage Mater. 44 (2022) 469–476.

  5. [5]

     Q. Lu, H. Wu, X. Zheng, et al., Adv. Sci. 8 (2021) 2101438.

  6. [6]

     Y. Bing, H. Liu, L. Zhang, D. Ghosh, J. Zhang, Chem. Soc. Rev. 39 (2010) 2184–2202. doi: 10.1039/b912552c

  7. [7]

     J.D. Lee, D. Jishkariani, Y. Zhao, et al., ACS Appl. Mater. Interfaces 11 (2019) 26789–26797. doi: 10.1021/acsami.9b06346

  8. [8]

     Y.X. Wang, T.H. Chen, Chin. Chem. Lett. 25 (2014) 907–911. doi: 10.1109/CISP.2014.7003907

  9. [9]

     Y. Chen, Z. Lai, X. Zhang, et al., Nat. Rev. Chem. 4 (2020) 243–256.

  10. [10]

      F. Saleem, X. Cui, Z. Zhang, et al., Small 15 (2019) 1903253.

  11. [11]

      F. Saleem, Z. Zhang, X. Cui, et al., J. Am. Chem. Soc. 141 (2019) 14496–14500. doi: 10.1021/jacs.9b05197

  12. [12]

      Z. Zhang, G. Liu, X. Cui, et al., Scie. Adv. 7 (2021) eabd6647.

  13. [13]

      X. Wang, Z. Chen, X. Zhao, et al., Angew. Chem. 130 (2018) 1962–1966. doi: 10.1002/ange.201712451

  14. [14]

      J. Liang, F. Ma, S. Hwang, et al., Joule 3 (2019) 956–991.

  15. [15]

      Y. Yao, Z. Huang, P. Xie, et al., ACS Appl. Mater. Interfaces 11 (2019) 29773–29779. doi: 10.1021/acsami.9b07198

  16. [16]

      X. Cui, Z. Zhang, Y. Gong, et al., CCS Chem. 2 (2020) 24–30.

  17. [17]

      Y. Chen, G.C. Egan, J. Wan, et al., Nat. Commun. 7 (2016) 1–9.

  18. [18]

      Y. Chen, Y. Li, Y. Wang, et al., Nano Lett. 16 (2016) 5553–5558. doi: 10.1021/acs.nanolett.6b02096

  19. [19]

      S. Dou, J. Xu, X. Cui, et al., Adv. Energy Mater. 10 (2020) 2001331.

  20. [20]

      R. Jiang, Y. Da, Z. Chen, et al., Adv. Energy Mater. 12 (2022) 2101092.

  21. [21]

      R. Jiang, Y. Da, X. Han, et al., Cell Rep. Phys. Sci. 2 (2021) 100302.

  22. [22]

      Y. Li, Y. Chen, A. Nie, et al., Adv. Energy Mater. 7 (2017) 1601783.

  23. [23]

      Y. Yao, Z. Huang, T. Li, et al., Proc. Nat. Acad. Sci. U. S. A. 117 (2020) 6316–6322. doi: 10.1073/pnas.1903721117

  24. [24]

      Y. Liu, X. Tian, Y.C. Han, Y. Chen, W. Hu, Chin. J. Catal. 48 (2023) 66–89.

  25. [25]

      Y. Yao, Q. Dong, L. Hu, Matter 1 (2019) 1451–1453.

  26. [26]

      Y. Yao, Z. Huang, P. Xie, et al., Science 359 (2018) 1489–1494. doi: 10.1126/science.aan5412

  27. [27]

      S. Liu, Z. Hu, Y. Wu, et al., Adv. Mater. 32 (2020) 2006034.

  28. [28]

      C. Liu, W. Zhou, J. Zhang, et al., Adv. Energy Mater. 10 (2020) 2001397.

  29. [29]

      J.E. Lim, U.J. Lee, S.H. Ahn, et al., Appl. Catal. B: Environ. 165 (2015) 495–502.

  30. [30]

      S. Yu, Z. Liu, N. Xu, J. Chen, Y. Gao, Anal. Sci. 36 (2020) 947–951. doi: 10.2116/analsci.19p427

  31. [31]

      C. Jin, Q. Wang, J. Liu, Nano Res. 17 (2024) 2462–2472. doi: 10.1007/s12274-023-6151-7

  32. [32]

      F. Jiang, F. Zhu, F. Yang, et al., ACS Catal. 10 (2019) 604–612. doi: 10.1364/ao.58.000604

  33. [33]

      S. Mukerjee, S. Srinivasan, M.P. Soriaga, J. McBreen, J. Electrochem. Soc. 142 (1995) 1409. doi: 10.1149/1.2048590

  34. [34]

      C. Zhang, Z. Chen, H. Yang, et al., J. Colloid Interface Sci. 652 (2023) 1597–1608.

  35. [35]

      Y. Ma, A.N. Kuhn, W. Gao, et al., Nano Energy 79 (2021) 105465.

  36. [36]

      L. Zhang, S. Jiang, W. Ma, Z. Zhou, Chin. J. Catal. 43 (2022) 1433–1443.

  37. [37]

      W. Cai, Y. Han, Y. Pan, et al., J. Mater. Chem. A 9 (2021) 13483–13489. doi: 10.1039/d1ta02720d

  38. [38]

      S. Dou, J. Xu, D. Zhang, et al., Angew. Chem. 135 (2023) e202303600.

  39. [39]

      S. Liu, Y. Shen, Y. Zhang, et al., Adv. Mater. 34 (2022) 2106973.

  40. [40]

      H. Cheng, N. Yang, X. Liu, et al., Adv. Mater. 33 (2021) 2007140.

  41. [41]

      M. Shao, Q. Chang, J.P. Dodelet, R. Chenitz, Chem. Rev. 116 (2016) 3594–3657. doi: 10.1021/acs.chemrev.5b00462

  42. [42]

      V.R. Stamenkovic, B.S. Mun, K.J. Mayrhofer, P.N. Ross, N.M. Markovic, J. Am. Chem. Soc. 128 (2006) 8813–8819. doi: 10.1021/ja0600476

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  Figure 1  Schematic illustration of the manufacturing of PtCo_3–HTS and PtCo_3–HT-2 s via HTS technique.

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  Figure 2  Electron microscopic characterization and analysis for PtCo_3–HTS. (a) TEM image and the inset particle size distribution diagram of PtCo_3–HTS. (b) HRTEM and (c) HAADF-STEM images of PtCo_3–HTS. Inset in (c) is the corresponding FFT pattern of the yellow dash square area. (d) HAADF-STEM and (e-g) the corresponding EDS elemental mapping of PtCo_3–HTS.

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  Figure 3  Electron microscopic characterization and analysis for PtCo_3–HT-2 s. (a) TEM image and the inset particle size distribution diagram of PtCo_3–HT-2 s. (b) HRTEM and (c) HAADF-STEM images of PtCo_3–HT-2 s. Inset in (c) is the corresponding FFT pattern of the yellow dash square area. (d) HRTEM and (e-g) the corresponding EDS elemental mapping of PtCo_3–HT-2 s.

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  Figure 4  XAFS analysis of PtCo_3–HTS, PtCo_3–HT-2 s, Pt foil, and Co foil. (a) XANES and (b) FT-EXAFS spectra for Pt L₃-edge. (c) XANES and (d) FT-EXAFS spectra for Co K-edge.

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  Figure 5  (a) CV curves, (b) ORR polarization curves, (c) MA and SA at 0.9 V, (d) Tafel curves of the PtCo_3–HTS, PtCo_3–HT-2 s, and Pt/C in 0.1 mol/L KOH. (e) The initial LSV curves and the corresponding LSV curves after 50, 000 cycles for PtCo_3–HTS PtCo_3–HT-2 s, and Pt/C, respectively. (f) Comparison of the mass activity of PtCo_3–HTS and previously reported electrocatalysts for ORR.

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