Laser-assisted high-performance PtRu alloy for pH-universal hydrogen evolution

Abstract

Elucidating the interaction between different atomic species of bimetallic nanoparticles under reaction conditions is the key to the design of efficient catalysts. Here, we report a laser-assisted strategy towards PtRu alloys, where isolated Pt sites are anchored on the Ru host, and track the variation of the active site under electrocatalytic conditions. Operando X-ray absorption spectroscopy identified the local environment variations around Pt single atoms and revealed the increased PtRu alloying degree during the hydrogen evolution reaction (HER). Theoretical simulations confirmed that the increase of alloying extent modulates the d-band center of Ru for enhancing the activity. Surface-restructured PtRu alloy exhibited outstanding HER activity and stability under all pH values, achieving an unexpected low overpotential of only 15, 17, and 28 mV at 10 mA cm⁻² in 1 M KOH, 1 M PBS, and 0.5 M H₂SO₄, respectively. This demonstrates the feasibility of surface engineering for designing advanced bimetallic catalysts with atomic-scale platinum decoration.

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Broader context

Hydrogen is generally regarded as a crucial energy carrier for connecting intermittent renewable energy with the diverse consumer market, showing unprecedented research momentum for clean hydrogen. The design and synthesis of bimetallic electrocatalysts are critical for accelerating sustainable H₂ production and commercialization. However, during the electro-derived oxidation or reduction processes, an unignorable fact is that most nanoparticulate catalysts will undergo widely observed dynamic restructuring, while the interactions between different atoms in bimetallic catalysts remain unclear. To this end, we report a laser-assisted strategy towards PtRu alloys for highly efficient hydrogen evolution under all pH values and use operando X-ray absorption spectroscopy to investigate the surface structural reconstruction under electrocatalytic conditions. This work not only provides a novel synthetic strategy for high-performance bimetallic catalysts with precise active centers but also offers a promising approach to in situ control the interplay between different atomic species.

Alloys generally follow scaling relationships.^1,2 However, it has been predicted that the micro-alloying could induce peculiar geometric and electronic structures that could potentially provide a way to circumvent scaling relationships, owing to the isolated single-metal-site bonding environment.^2–4 Alloys hence play an increasingly significant role in the field of heterogeneous metal catalysts and have shown remarkable catalytic behavior in many chemical reactions.^4–6 Many methods, such as galvanic replacement,^7,8 sequential reduction,^9,10 electroless deposition,^11–13 co-reduction,^14,15 incipient wetness co-impregnation,^5,16,17etc., have been developed for preparing different types of alloys. However, the access to homogeneously alloyed bimetallic systems remains a grand challenge, because of the thermodynamic immiscibility of some constituent elements.^18,19 Recently, the use of laser technology to prepare nanomaterials has attracted increasing attention due to its non-equilibrium process and rapid quenching characteristics. Hence, the laser strategy is expected to overcome the inherent immiscibility of bimetallic systems, and to create novel bimetallic materials with unique properties, such as NiAu²⁰ and PtPd²¹ bimetallic nanoparticles (NPs). Moreover, in the alloy, the chemical nature and the interplay between different atomic species, would affect the binding strength of the adsorbate, ultimately determining the activity of the catalyst.^22–24 Therefore, the availability of the homogeneously alloyed bimetallic catalyst system, and the knowledge of the atomic-scale structure of the active sites, are critical for the rational design of advanced alloy catalysts.

The nanoparticulated bimetallic catalysts are known to undergo dynamic restructuring under realistic reaction conditions.^25–27 Some restructuring effects, such as phase transition,²⁸ compositional segregation,^25,29 and the accumulation of strain effects,^26,30 have been reported to be effective to boost catalytic performance. For example, the core–shell structure Ni@Au NPs dynamically transformed into NiAu alloys during the CO₂ hydrogenation process, confirming that the formation of the transient reconstructed alloy surface can promote the adsorption of CO.³¹ Also, the fact that the cationic Zn species in CuZn NPs were reduced to form CuZn alloys played a determining role in the product selectivity confirmed by the time-dependent X-ray absorption fine structure (XAFS) technique.³² However, in-depth study into the electronic and geometric properties of these bimetallic NPs is often neglected. In particular, the changes in charge states and coordination numbers (CNs) of metal atoms will greatly influence their catalytic activity.³³ In this regard, the advanced operando synchrotron-based techniques are powerful tools for revealing the local geometry of catalysts, identifying the real active sites in the alloys. Furthermore, combining with density functional theory (DFT) calculations can provide insight into the intrinsic relationship between surface structure and performance enhancement in electrocatalysis.^27,34

Herein, we employ operando XAFS to investigate the surface structural reconstruction of a well-developed PtRu alloy during the hydrogen evolution reaction (HER). The uniform PtRu alloy with isolated Pt atoms anchored on the Ru host surface was synthesized through a facile laser irradiation in liquid (LIL) strategy.^21,35–37 The PtRu alloy NPs show excellent pH-universal HER performance with extraordinarily low overpotential and robust stability. By using the operando XAFS technique, we unravel the change of surface alloying degree of bimetallic NPs under HER conditions. These experimental results are rationalized by theoretical simulations, which reveal that the high alloying degree of Pt and Ru significantly modulates the hydrogen adsorption on Pt, improves the hydroxyl adsorption, and decreases the reaction barrier for water dissociation on Ru. Therefore, our results can provide insights into the vital role of the surface alloying degree of bimetallic catalysts and develop a novel synthesis strategy for preparing alloy catalysts with extraordinary properties.

The procedures to synthesize the PtRu alloy NPs decorated on surface-modified carbon nanotube (mCNTs) catalysts (PtRu/mCNTs) are schematically shown in Fig. 1a. Typically, to obtain mCNTs, pristine CNTs (P-CNTs) were treated with conventional acidification to introduce functional groups (e.g., hydroxyl, carbonyl, and carboxyl), which can not only facilitate the dispersion of CNTs in solution but also enhance the affinity of noble metal precursors onto CNTs (see the ESI† for details).^37–39 Thus, we employed Raman spectra measurements to confirm the introduction of active sites on the mCNTs. As shown in Fig. S1 (ESI†), the I_D/I_G values of the mCNTs were significantly increased compared with those of P-CNTs, indicating the successful introduction of oxygen-containing functional groups. Then the mCNTs and metal precursors were irradiated in ethanol solution using a Nd:YAG pulsed laser (λ = 355 nm, 10 mJ) with 7 ns pulse duration. The metal precursors were reduced in situ without using an organic surfactant. After the irradiation process, bimetallic NPs can be uniformly loaded on mCNTs, demonstrating the high efficiency of using the laser-assisted method for production.

Fig. 1 (a) Schematic illustration of the manufacture of the PtRu/mCNTs catalyst. (b) TEM image and (c) HRTEM image of PtRu/mCNTs, and the inset in (b) is the size distribution of PtRu NPs. (d) HAADF-STEM, STEM-EDX elemental mapping images and (e) line-scanning profile across the PtRu NPs. (f) Pt L₃-edge XANES spectra of PtRu/mCNTs, Pt/mCNTs, Pt foil, and commercial Pt/C and PtO₂ and (g) the corresponding k²-weighted FT spectra.

The transmission electron microscopy (TEM) images revealed that the formed PtRu NPs were uniformly loaded on mCNTs with a narrow size distribution (Fig. 1b). Due to such a small particle size, only one distinct broad diffraction peak at 40.6° was distinguished from the PtRu/mCNTs XRD pattern, which can be indexed to the (111) reflections of face-centered cubic (FCC) Ru (PDF No. 88-2333) (Fig. S2, ESI†). As shown in Fig. S2 (ESI†), the peak position of PtRu NPs shifted slightly to the left side, due to the lattice expansion resulting from the incorporation of Pt atoms into the Ru lattice. The absence of monometallic Pt diffraction peaks further indicates that the PtRu NPs were well alloyed. This homogeneous dispersion is conducive to the improvement of its performance in the field of heterogeneous catalysis.^40,41 The high-resolution transmission electron microscopy (HRTEM) image in Fig. 1c shows that the measured interplanar spacing of 2.22 Å, 1.93 Å, and 1.40 Å can be assigned to the (111), (200), and (220) facets of the Ru, respectively. As a contrast, Pt/mCNTs and Ru/mCNTs were synthesized using the same method. The TEM images showed that Pt (2.16 nm) or Ru (2.29 nm) monometallic NPs were also loaded onto the mCNTs (Fig. S3 and S4, ESI†). The average spacing values of 0.227 nm and 0.206 nm correspond to the (111) facet of Pt/mCNTs and the (101) facet of Ru/mCNTs, respectively. The high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image, energy dispersive X-ray (EDX) elemental mapping, and line scan confirmed that the uniform distribution of Pt atoms cross over Ru NPs (Fig. 1d–e). The content of Pt or Ru in the different samples was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES, see Table S1, ESI†).

We employed synchrotron radiation XAFS measurements at the Pt L₃-edge of PtRu/mCNTs to confirm that Pt is atomically dispersed in the Ru lattice. Compared to the referenced Pt foil, Pt/mCNTs, and commercial Pt/C, and PtO₂, the X-ray absorption near-edge structure (XANES) characteristics of PtRu/mCNTs are distinctly different, indicating the unique local structure of Pt (Fig. 1f). Besides, the Pt L₃-edge white line intensity (H_A) corresponds to the transition from occupied Pt 2p electrons to empty 5d states and thus is indicative of 5d-band occupancy.⁴² The H_A of the Pt/mCNTs shows an increment to that of Pt foil, indicating the hybridization of Pt and other nonmetals. As for the PtRu/mCNTs sample, a further increment of the H_A can be found, implying the charge transfer from Pt to Ru after alloying. The Fourier transformed (FT) k²-weighted extended X-ray absorption fine structure (EXAFS) spectrum for the PtRu/mCNTs displays one Pt–metal coordination peak at 2.47 Å, which is shorter than the distance of the nearest coordination shells of Pt atoms in Pt foil (Fig. 1g). Meanwhile, as different coordination elements have different k space oscillation modes, it can be seen from Fig. S5 (ESI†) that the oscillation of Pt/C and Pt foil in the high-k (k > 8) part is the same (with the same coordination element Pt), while the oscillation of PtRu/mCNTs is obviously different. In other words, the coordination element in PtRu alloy is different from those of Pt/C and Pt foil. In addition, for peaks with relatively close bond distance in R space, EXAFS wavelet analysis is usually required to effectively conduct data analysis and obtain more reliable results. As can be seen from Fig. S6 (ESI†), the Pt–Pt in Pt/C appeared at R and k of about 2.6 Å and 9.0 Å⁻¹, both of which were significantly larger than those in PtRu/mCNTs. Therefore, the possible bond length contraction caused by the size effect in PtRu/mCNTs is excluded, further indicating that the peak around 2.47 Å is of a Pt–Ru bond. It also demonstrates that most Pt atoms are distributed around Ru atoms in the form of isolated atoms. The surface property was further characterized by X-ray photoelectron spectroscopy (XPS). As shown in Fig. S7 (ESI†), the Pt 4f peaks shifted toward higher binding energy, while the peak of Ru 3p shifted to the opposite direction.^43,44 The above results confirm the successful alloying of isolated Pt atoms in the Ru matrix, with a strong electronic interaction between the Pt and Ru atoms in the PtRu alloy NPs.

As the proton or hydroxide concentration will significantly affect the electrocatalytic process, the pH-universal electrocatalysts are very attractive in practical applications, especially under alkaline and neutral conditions. The HER performance of PtRu/mCNTs was first investigated in N₂-saturated 1 M KOH electrolyte. For comparison, Pt/mCNTs, Ru/mCNTs, mCNTs, and commercial Pt/C (20 wt%) were also measured under the same conditions. In Fig. 2a, PtRu/mCNTs exhibited the highest HER activity, achieving an overpotential of 15 mV at the current density of 10 mA cm⁻², which is much smaller than that of Pt/mCNTs (141 mV), Ru/mCNTs (27 mV), Pt/C (39 mV), and many other reported noble metal catalysts (Table S2, ESI†), indicating that the single-atom Pt in Ru NPs can enhance the HER activity. As shown in Fig. 2b, the Tafel slope of PtRu/mCNTs is approximately 33.5 mV decade⁻¹, which is lower than the slope values of the other control samples, implying the enhanced HER kinetics. Moreover, the mass activity is calculated according to the mass loading of the active metal, for PtRu/mCNTs (3.35 A mg⁻¹) it is about 6.8 times higher than that of the Pt/C (0.49 A mg⁻¹) catalyst at −0.1 V, indicating the high utilization efficiency of the noble metal (Fig. 2c). Besides, we further investigate the HER activity of PtRu/mCNTs in 1 M PBS and 0.5 M H₂SO₄. The PtRu/mCNTs still show remarkable HER performance with a low overpotential of 28 mV and 17 mV to achieve a current density of 10 mA cm⁻² (Fig. S8, ESI†). These values are similar to those of Pt/C under acidic and neutral conditions, but better than those of other reported noble metal electrocatalysts (Tables S3 and S4, ESI†). For a direct comparison, the overpotential at 10 mA cm⁻² of PtRu/mCNTs and those of the recently reported representative electrocatalysts are shown in Fig. 2d. The HER activity of PtRu/mCNTs under all pH ranges was superior to those of the most reported catalysts. Meanwhile, durability is another important index to evaluate the practical applications of catalysts. To assess the durability of the PtRu/mCNTs, long-term cyclic voltammetry measurements were carried out. As shown in Fig. 2e, the polarization curves of PtRu/mCNTs before and after 3,000 cycles show a small variation in the three different electrolytes. Also, the chronopotentiometry test result of the PtRu/mCNTs is presented in Fig. 2f and Fig. S8 (ESI†), showing that they maintained robust stability after 48 hours of testing in different electrolytes. All of the above results indicate that the PtRu/mCNTs have high activity and stability under a wide-pH range, which are of great significance for practical applications. It also implies that LIL is effective for the preparation of excellent bimetallic electrocatalysts.

Fig. 2 (a) HER linear sweep voltammogram curves and (b) Tafel plots for the PtRu/mCNTs as well as Pt/mCNTs, Ru/mCNTs, mCNTs and commercial Pt/C. (c) Mass activities. (d) Overpotentials of PtRu/mCNTs at 10 mA cm⁻², with those of other recently reported HER electrocatalysts. (e) Durability tests for PtRu/mCNTs (red) and Pt/C (black) in 1 M KOH, 1 M PBS, and 0.5 M H₂SO₄ before and after 3,000 cycles. (f) Chronopotentiometry test of PtRu/mCNTs at a constant current density of 10 mA cm⁻² in 1 M KOH.

Operando XAFS measurements were performed to uncover the surface reconstruction of the PtRu NPs and further understand the change of the surface alloying degree of bimetallic NPs under HER working conditions. Fig. 3a and b present a series of Ru K-edge and Pt L₃-edge XANES spectra recorded under different HER reaction conditions, the potential was applied from the open-circuit voltage (OCV) to −0.1 V. Clear evolutions can be observed in both operando XANES spectra and differential XANES (ΔXANES) spectra (Fig. S9, ESI†). In the Ru K-edge XANES spectra, compared with ex situ conditions, the absorption edge slightly shifts to the high-E side under OCV conditions (inset of Fig. 3a.), indicating an increase of the Ru oxidation state. It probably results from the adsorption of H₂O or OH⁻ on Ru atoms, resulting in the electron delocalization and the partial rearrangement of surface atoms.⁴⁵ When the applied potential shifts to +0.2 V and −0.1 V, the absorption edge gradually shifts to a low-E position, implying the lower Ru oxidation state after H₂O dissociation occurs. This may be due to the faster speed of H₂O dissociation under realistic HER conditions, which also proves that Ru has high efficiency on water dissociation.⁴⁴ To accurately calculate the Ru valence state, the fitted average oxidation states from the adsorption edge of Ru K-edge XANES are shown in Fig. S10a (ESI†). The mean valence states of Ru reduced from 2.49 to 2.14 and 2.05 under the ex situ conditions, +0.2 V and −0.1 V, respectively. On the side of the Pt L₃-edge, the mean valence states can be obtained by integrating the areas under the H_A in the ΔXANES spectra (Fig. S10b, ESI†), which show decrease from 0.90 under the ex situ conditions to 0.64 and 0.52 under the +0.2 V and −0.1 V, respectively.⁴² Note that under the operando electrochemical measurements, the bimetallic NPs will always undergo a reduction process due to the applied cathode voltage, which is mainly responsible for the decrease of valence states of Pt and Ru in the catalyst.^27,32 As shown in the inset of Fig. 3b, the main difference revealed between the ex situ and the other conditions (OCV, +0.2 V, and −0.1 V) is that the width (W_p) of the oscillation peak is widened under the HER conditions, indicating disordered structures around the decorated Pt atoms. From the perspective of thermodynamics, H* will preferentially adsorb on the Pt atom, so we attributed the width of the oscillation peak to H* spontaneously adsorbed on the Pt site, as the Pt 2p_3/2 electrons transition into unoccupied Pt–H* antibonding orbitals.⁴⁶ According to the above analysis, both Pt and Ru were reduced simultaneously under the operando working conditions. Besides, Pt is identified as the H* adsorption site, and Ru adsorbs the H₂O molecule.

Fig. 3 Operando XANES spectra at the Ru K-edge (a) and Pt L₃-edge (b). The insets show the pre-edge XANES region and the oscillation peak region, respectively. Least-squares curve-fitting analysis of operando EXAFS spectra at the Pt L₃-edge (c) and Ru K-edge (d). (e) The fitted structural parameters of PtRu/mCNTs and alloying degree under working conditions.

Then, the EXAFS spectra were analyzed to investigate the local structural evolutions of Pt and Ru. As shown in the Pt L₃-edge spectra (Fig. 3c), the Pt–Ru coordination peak at 2.47 Å enhanced gradually with the applied negative potentials, implying a possible increase of CN_Pt–Ru. A similar trend of enhanced Ru–Pt peak can also be found in the Ru K-edge spectra (Fig. 3d). Quantitatively, we carried out least-squares EXAFS curve-fitting analysis, and the corresponding structural parameters are summarized in Table S5 and Fig. S11 (ESI†). The CN_Pt–Ru for the ex situ sample was just 6.7, far less than the saturated CN of 12 for Ru foil, suggesting the existence of Pt single-atoms on the surface of PtRu NPs. Moreover, the CN_Pt–Ru increases to 7.9 and 9.1 for the catalyst at +0.2 V and −0.1 V, respectively. Combined with the TEM results, the particle size of PtRu NPs is about 2.1 nm; thus the atomic content of the surface in the particle is about half. Hence, we consider two backscattering paths, including the Ru–Pt and the Ru–Ru path for fitting the Ru K-edge, obtaining a nice fitting quality (Table S6, Fig. S12, ESI†). For the ex situ conditions, the best-fitting analyses give CNs of 8.5 and 0.7 for Ru–Ru and Ru–Pt, respectively. The CN_Ru–Ru remained nearly unchanged, while the CN_Ru–Pt increased from 0.7 to 1.3 and 1.5 with the applied potential. The above evolutions of CN between Ru and Pt suggest the increased alloying degree of PtRu under the reaction conditions, which is possibly due to the migration of Pt atoms from the surface to the interior of the alloy NPs. This point can also be reflected by the decrease of Pt–Ru bond length under operando conditions, leading to enhanced interaction between Pt and Ru.

To more accurately evaluate the alloying degree of PtRu alloy, which means that the Pt and Ru atoms are randomly distributed in the alloy NPs, we calculate the degree of alloying (J) according to the method developed by Hwang et al.⁴⁷

The J values of Pt and Ru can, respectively, give the information of their internal distribution in the alloy NPs. The parameter P_observed can be calculated as a ratio of the coordination number of scattering B atoms around absorbing A atoms (N_A–B) to the total coordination number of absorbing atoms (∑N_A–i) (P_observed = N_A–B/∑N_A–i). P_random is the parameter of perfectly alloyed bimetallic NPs, determined by the atomic ratio of A and B. The values of CN and J at different HER conditions are summarized in Fig. 3e. Due to the dynamic migration of Pt atoms, we consider that the surface atoms of PtRu NPs will become sensitive with the increase of structural disorder, as reflected by the increased disorder factor Debye–Waller factor of Ru–Pt from ∼0.008 to ∼0.010 Å⁻². Therefore, the alloying degree of Ru (J_Ru) increases significantly, from 76% under ex situ conditions to 150% under the −0.1 V conditions, indicating that the distribution of Ru atoms is disturbed by the Pt atom, and interactions between heteroatoms are increasing under the HER conditions.

We performed DFT calculations for a deep understanding of essential effects of alloying degree on the HER activity. According to the results of operando XAFS and Tafel slope, HER should follow the Volmer–Tafel process. Besides, H₂O molecules selectively adsorbed on the Ru sites at the initial stages, then H₂O* adsorbed electrons further dissociating into intermediate H_ads and OH_ads by the Volmer step. Simultaneously, the generated H_ads could be adsorbed on the Pt site and further be converted into H₂ through the Tafel step (Fig. 4a). Due to 6.7 (the fitted CN of Pt–Ru) being the closest number to the CN of the Ru (110) facet (fcc₍₁₁₁₎ = 9, fcc₍₁₀₀₎ = 8, and fcc₍₁₁₀₎ = 7), metallic Ru slabs with (110) facets are selected as possible representative surfaces for modeling the PtRu alloy. By doping a Pt atom into Ru(110) facets at the different sites, two types of models representing ex situ (PtRu_{ex situ}) and in situ (PtRu_{in situ}, −0.1 V) structures are considered to evaluate their activity toward the HER (Fig. S13, ESI†).

Fig. 4 (a) Alkaline HER mechanism on PtRu/mCNTs. The yellow, green, and red spheres represent Pt, H, and O atoms, respectively. The rest are Ru atoms. Calculated adsorption energies of H* (b), H₂O, and OH (c) on the surfaces of PtRu_{ex situ}, PtRu_{in situ}, Pt (111), Pt (110), and Ru (110). (d) PDOS of the Ru in PtRu_{ex situ}, in PtRu_{in situ}, and Ru (110) with the corresponding d-band center ε_d.

Then, we calculated the adsorption energies of H₂O, OH*, and H* at different metal sites in the PtRu_{ex situ} model to identify the discrepant metal active site. As shown in Fig. S14 (ESI†), the adsorption ability for H₂O and OH* on Ru sites is higher than on Pt, which have a better binding ability for the H* intermediate, confirming the accuracy of the operando XAFS analysis. As is known, it is well recognized that the free energy of the adsorbed hydrogen (ΔG_H*) is the major descriptor for the HER under all pH conditions.^48,49 In Fig. 4b, compared with PtRu_{ex situ} (−0.10 eV), the ΔG_H* value of the PtRu_{in situ} (−0.09 eV) is near-zero, meaning that a higher alloying degree of Pt–Ru can optimize the HER activity. Also, due to the sluggish H₂O dissociation kinetics of the Volmer step in alkaline electrolytes, the adsorption energy of oxygenated species is another HER activity descriptor. For Ru(110), the adsorption energy of OH* is −0.29 eV, while it decreases to −0.31 and −0.41 eV after the introduction of Pt atoms under the ex situ and in situ conditions (Fig. 4c), respectively, suggesting that the disassociation of H₂O has accelerated on the Ru site (corresponding to the adsorption model summarized in Fig. S15, ESI†). Meanwhile, the adsorption of OH* on Pt (110) and Pt (111) was obviously weaker than that on PtRu alloy, resulting in their HER activity being inferior to that of PtRu alloy (corresponding to adsorption model summarized in Fig. S16, ESI†). To explore the underlying reason for the above results, we further calculated projected density of states (PDOS) of d orbitals and the d-band center (ε_d) of Ru atoms (Fig. 4d). DFT calculations show an obvious up-shift of PDOS of Ru d orbitals in PtRu_{ex situ} (−2.27 eV) and PtRu_{in situ} (−2.21 eV) compared to that of pure Ru (−2.33 eV), and the corresponding ε_d values are thus closer to the Fermi level than that on pure Ru by 0.06 and 0.12 eV, respectively, implying the change of Pt coordination environment, which adjusts the d-band center of Ru. It also indicates that the antibonding energy states formed by the interaction between the adsorbate and Ru surface are heightened, illustrating that the bonding energy of H₂O/OH* is enhanced on Ru atoms, which facilitates the water dissociation. Therefore, we conclude that the Pt–Ru alloying degree increased due to the change of coordination environment of the Pt atom in the PtRu alloy under the reaction process, which not only promotes the dissociation of H₂O in alkaline media but also optimizes the binding energy of H*, resulting in an excellent HER performance.

In summary, we report an effective strategy to synthesize active and durable PtRu/mCNT catalysts for the HER using the LIL method. With the help of operando XAFS technology, we identify the surface reconstruction of PtRu NPs, which is sensitive under reduction potentials. Meanwhile, Pt atoms tend to migrate from the surface to the inner of particles, resulting in a higher alloying degree between Pt and Ru. Moreover, the geometric structure (different coordination environments) and electronic structure (d-band center up-shift) of PtRu/mCNTs are self-optimized under the working conditions, which ensures the outstanding HER performance under wide pH conditions. Finally, we hope that this work will not only promote the designed synthesis of high-performance bimetallic catalysts with precisely controlled active centers but also offer a way to in situ control the interplay between different atomic species for designing high-performance bimetallic catalysts.

Author contributions

T. Y. and C. L. conceived the idea, planned the synthesis, and analysed the results. B. P. performed the experiments. B. P. and T. Y. co-wrote the paper. X. L., W. Z., S. W., T. L., and D. L. performed the XAFS characterization and analyzed the data. T. C., X. S., T. D., and Z. L. helped in analyzing the materials. T. L. and Y. L. conducted and discussed the theoretical calculations. All the authors discussed the results and contributed to the manuscript.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the China Ministry of Science and Technology (2021YFA1600800, 2017YFA0208300, 2020YFA0710200), the National Natural Science Foundation of China (Grants No. 12025505, Grants No. 52071313), and Youth Innovation Promotion Association CAS (CX2310007007 and CX2310000091). We would like to thank NSRL and SSRF for the synchrotron beam time.

Notes and references

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/d1ee02518j

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