Surface Engineered Ru ₂ Ni Multilayer Nanosheets for Hydrogen Oxidation Catalysis

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLES14 Nov 2022Surface Engineered Ru2Ni Multilayer Nanosheets for Hydrogen Oxidation Catalysis Juntao Zhang†, Xing Fan†, Suling Wang, Maofeng Cao, Lingzheng Bu, Yong Xu, Haiping Lin and Xiaoqing Huang Juntao Zhang† College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 , Xing Fan† Institute of Functional Nano and Soft Materials, Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University, Suzhou 215123 , Suling Wang College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 , Maofeng Cao College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 , Lingzheng Bu College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 , Yong Xu *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Guangzhou Key Laboratory of Low-Dimensional Materials and Energy Storage Devices, Collaborative Innovation Center of Advanced Energy Materials, School of Materials and Energy, Guangdong University of Technology, Guangzhou 510006 , Haiping Lin *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] School of Physics and Information Technology, Shaanxi Normal University, Xi'an 710119 and Xiaoqing Huang *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 https://doi.org/10.31635/ccschem.022.202202269 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail The hydrogen oxidation reaction (HOR) in alkaline conditions is of great importance for the application of anion exchange membrane fuel cells (AEMFCs). However, the electrocatalysts for alkaline HOR generally suffer from the disadvantage of sluggish kinetics. Herein, we have fabricated Ru2Ni multilayered nanosheets (Ru2Ni MLNSs) in the layer-by-layer manner and engineered the surface properties via postannealing for efficient alkaline HOR. Detailed investigations reveal that such annealing at different temperatures can alter the surface properties of Ru2Ni MLNSs and thus regulate their adsorption abilities toward *H and *OH. In particular, the optimal catalyst exhibits a mass activity of 4.34 A mgRu−1 at an overpotential of 50 mV, which is 18.1 and 13.2 times higher than those of Ru/C (0.24 A mgRu−1) and Pt/C (0.33 A mgPt−1), respectively. Theoretical calculations indicate that the presence of surface O atoms can facilitate the HOR activity while the excessive coverage of O atoms on Ru2Ni surface leads to the strengthened H binding and the decay of HOR activity. This work not only provides an efficient catalyst for alkaline HOR, but it also may shed new light on the design of high-performance catalysts for electrocatalysis and beyond. Download figure Download PowerPoint Introduction Anion exchange membrane fuel cells (AEMFCs) have attracted extensive research attention by virtue of their faster oxygen reduction rate and lower dependency of noble electrocatalysts in comparison to other fuel cells.1–4 Pt has been regarded as a promising catalyst for the hydrogen oxidation reaction (HOR),5–7 a crucial half of the reaction of AEMFCs.8–12 Nevertheless, the large-scale application of Pt for HOR is limited by several drawbacks, including high cost and sluggish kinetics in alkaline conditions.13–17 Over the past decades, substantial efforts have been devoted to modifying Pt with other promoters18–22 and replacing Pt with nonnoble elements.14,23–26 Despite great progress, the performance of alkaline HOR is still far from satisfactory for practical application. It is of great importance to develop highly efficient catalysts for alkaline HOR. In principle, ideal catalysts for HOR should display appropriate energies for hydrogen binding (HBE) and hydroxide binding (OHBE).27–29 Ru has a similar HBE (65 kcal/mol) to Pt but a much lower price than Pt,30–33 for which it has been deemed a promising candidate for HOR. For instance, Wei et al.34 demonstrated that Ru clusters that confined urchin-like TiO2 crystal exhibited superior HOR activity to the commercial PtRu/C. Moreover, Ohyama and coworkers35 reported that Ru nanoparticles (NPs) with abundant unsaturated surface atoms could serve as efficient catalysts for HOR. However, the quest for highly efficient Ru-based catalysts for HOR is driven by the current drawbacks of low activity and unsatisfactory stability. It is thus highly desirable to modify Ru with other promoters to regulate HBE/OHBE and enhance HOR performance. In this work, we have fabricated Ru2Ni multilayered nanosheets (Ru2Ni MLNSs) via a facile wet-chemical method and achieved the precise surface modification via a postannealing process. Detailed studies show that Ru2Ni MLNSs are formed in the layer-by-layer manner while the postannealing process strongly varies the surface properties of Ru2Ni MLNSs, resulting in the precise regulation of the adsorption abilities toward *H and *OH. Theoretical calculations indicate that the presence of surface O atoms can facilitate the HOR activity while the excessive coverage of O atoms on a Ru2Ni surface leads to strengthened H binding and the decay of HOR activity. The optimal catalyst of Ru2Ni MLNSs-250 displays a mass activity of 4.34 A mg−1Ru at an overpotential of 50 mV for alkaline HOR, which is 18.1 and 13.2 times higher than those of commercial Ru/C (0.24 A mg−1Ru) and Pt/C (0.33 A mg−1Pt), respectively. This work not only provides an efficient catalyst for alkaline HOR, but it also sheds light on the design of high-performance catalysts for electrocatalysis and beyond. Methods Chemicals Triruthenium dodecacarbonyl (Ru3(CO)12, >98.0%) was purchased from Damas-beta (Damas International Ltd., Shanghai, China). Ruthenium chloride hydrate (RuCl3·xH2O, 99.9%) and nickel acetylacetonate (Ni(acac)2, 95.0%) were purchased from Sigma-Aldrich (Shanghai, China). Citric acid monohydrate (C6H8O7·H2O, CA, 99.5%), ethanol (C2H6O, AR), benzyl alcohol (C7H8O, AR), hexamethylene (C6H12, AR), isopropanol (C3H8O, AR), cetyltrimethylammonium bromide (C19H42BrN, CTAB, AR), acetone (C3H6O, AR), and potassium hydroxide (KOH, AR) were purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). Commercial Pt/C (20 wt %) was obtained from Johnson Matthey (JM) Corporation (Shanghai, China). Polyvinylpyrrolidone (PVP, M.W. = 58,000) was purchased from J&K Scientific Ltd. (Beijing, China). All the chemicals were used without further purification. The water (18 MΩ cm−1) used in all the experiments was obtained by passing it through an ultra-pure purification system (Aqua Solutions, RSJ, Xiamen, China). Synthesis of Ru2Ni MLNSs and Ru MLNSs In a typical synthesis of Ru2Ni MLNSs, 10 mg Ru3(CO)12, 6.6 mg Ni(acac)2, 160 mg PVP, 32 mg CTAB, 150 mg CA, and 10 mL benzyl alcohol were added into a glass vial (30 mL). The mixture solution was ultrasonicated for 1 h to obtain a homogeneous solution. The resulting homogeneous solution was heated from room temperature to 170 °C in 0.5 h and held at the same temperature for 0.5 h, which was further heated to 200 °C and held for 5 h. After cooling it to room temperature, the products were collected by centrifugation and washed with a mixture of ethanol/acetone (1/8) three times. The synthesis of Ru MLNSs was similar to that of Ru2Ni MLNSs except for the absence of Ni(acac)2. Characterizations Transmission electron microscopy (TEM) was conducted on a JEOL electron microscope (JEOL, Tokyo, Japan) at an accelerating voltage of 100 kV. High-angle annular dark-field scanning TEM (HAADF-STEM), HAADF-STEM energy-dispersive X-ray spectroscopy (HAADF-STEM-EDS), and high-resolution TEM (HRTEM) were carried out on a FEI Tecnai F30 TEM (FEI, Hillsboro, USA) at an accelerating voltage of 300 kV. Atomic force microscopy (AFM) images were obtained from a Bruker Dimension Icon, using the Peakforce Tapping model (Bruker, Karlsruhe, Germany). Scanning electron microscopy EDS (SEM-EDS) was conducted on a ZEISS Sigma (ZEISS, Oberkochen, German) at an accelerating voltage of 20 kV. The X-ray diffraction (XRD) spectroscopy was conducted on a Rigaku (Rigaku Corporation, Tokyo, Japan) with Cu Kα (λ = 1.540598 Å). X-ray photoelectron spectrum (XPS) was collected with an SSI S-Probe XPS spectrometer (Thermo Fisher Scientific, Waltham, MA, USA). The d-band centers of these samples were calculated by the equation ∫ N ( ε ) ε d ε ∫ N ( ε ) d ε in the range from 0 to 10 eV. N is the density of states. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was conducted on a Nicolet IR 380 (Thermo Fisher Scientific, Waltham, MA, USA). Electrochemical measurements All the electrochemical measurements were performed at a CHI660 electrochemical station (CH Instruments, Inc., Chenhua, Shanghai, China) in a typical three-electrode system. A glassy carbon electrode with a diameter of 5 mm, a graphite rod, and a saturated calomel electrode were used as the working electrode, the counter electrode, and the reference electrode, respectively. For the preparation of the working electrode, the Ru2Ni MLNSs were loaded on carbon black (VXC-72R) by ultrasound for about 1 h. The carbon-supported Ru2Ni MLNSs (2 mg), isopropanol (990 μL), and Nafion solution (10 μL, 5 wt %) were added into a glass vial and then ultrasonicated for 1 h to make a homogenous ink. Before the electrochemical test, the ink was ultrasonicated for 1 h to produce a homogeneous solution. The equilibrium potential was the zero point of HER/HOR by using Pt/C as the working electrode at a rotating speed of 1600 rpm in H2-saturated electrolyte. All the polarization curves were corrected by solution resistance, which was tested by AC-impedance spectroscopy from 200 kHz to 100 mHz. After 2000 cycles of HOR polarization curves of Ru2Ni MLNSs-250 in the accelerated durability test (ADT), the fresh 0.1 M KOH was used to conduct the 2001st polarization curve. The kinetic current density (jk) can be calculated by the Koutecky–Levich (K–L) equation: 1 j = 1 j k + 1 j d = 1 j k + 1 B C 0 w 1 / 2 where j, jd, B, C0, and w represent measured current, diffusional current, Levich constant, solubility of H2 in electrolyte, and angular velocity of rotating disk during the HOR measurements, respectively. The exchange current density j0 can be obtained from the Butler–Volmer (B–V) equation: j k = j o ( e α F R T η − e − ( 1 − α ) F R T η ) where α is the transfer coefficient, R is the universal gas constant, T is the temperature, and η is the overpotential, respectively. Theoretical calculations Density functional theory (DFT) calculations were performed by using the Vienna ab initio simulation packages.36,37 The electron-ion interactions were described with the projector-augmented wave potential.38,39 The exchange-correlation functional of Perdew, Burke, and Ernzerhof40,41 within the generalized gradient approximation exchange correlations potentials was used. The cutoff energy of the plane-wave basis was set to 400 eV. The NiRu catalyst was modeled with a (3 × 3) Ni doped Ru(0001) slab consisting of three and seven atomic layers for the calculations of Gibbs-free energies and search of transition states. The Brillouin zone was sampled by a 5 × 5 × 1 k-point sampling. The criterion of energy convergence was 1 × 10−4 eV. The internal coordinates of each system were fully optimized until the residual Hellmann–Feynman forces were smaller than 0.01 eV/Å per atom. A vacuum of 20 Å in the z direction was employed to avoid interactions between periodic images. The van der Waals dispersion correction was evaluated with the DFT-D3 method.42 The climbing image-nudged elastic band (CI-NEB) method and the Dimer method were used to search the minimum energy paths of the dehydrogenation of water.43–45 The change of the Gibbs-free energy (ΔG) for each elementary step at the zero potential were calculated according to the following equation: ΔG = ΔE + ΔEZPE – TΔS + ΔGpH. Where E was the total energy obtained directly from the DFT calculations. EZPE and S were the zero-point energy and the entropy, respectively. T was the temperature set as T = 298.15 K. ΔGpH was the free energy contributions related to the H+ concentration and was calculated from ΔGpH = 2.303 × KBT × pH. Results and Discussion Ru2Ni MLNSs were synthesized via a wet-chemical method, in which Ru3(CO)12/Ni(acac)2, PVP (C6H9O)n/hexadecyltrimethylammonium bromide (CTAB, C19H42BrN), CA monohydrate (C6H8O7·H2O), and benzyl alcohol (C7H8O) were added as the metal precursors, surfactants, reductant, and solvent, respectively (see details in Supporting Information). TEM and HAADF-STEM images show that hexagonal RuNi NSs with multilayered structure were obtained (Figure 1a–c). Moreover, the products were loaded on carbon powder to collect the erect TEM image for evaluating the thickness of the RuNi NSs (Figure 1d and Supporting Information Figure S1). The thickness was measured to be ∼22.3 ( Supporting Information Figure S1l), which was consistent with that from AFM ( Supporting Information Figure S2). The HRTEM image shows that the thickness of single Ru2Ni NS is ∼2.1 nm ( Supporting Information Figure S3). Furthermore, the MLNSs were confirmed by HAADF-STEM images collected by rotating from −60° to 60° (Figure 1e) and results from three-dimensional tomographic reconstruction ( Supporting Information Figure S4 and Video S1). HAADF-STEM-EDX elemental mappings indicate that Ru and Ni are uniformly distributed in products with a Ru/Ni molar ratio of 64.3/35.4 (named as Ru2Ni MLNSs, Figure 1f and Supporting Information Figure S5). In the XRD pattern, the characteristic peaks of Ru2Ni MLNSs positively shift to higher angles compared to those of Ru, which are attributed to the lattice contraction of Ru after Ni addition (Figure 1g). The lattice distance of 0.228 nm in the HRTEM image can be indexed as Ru (1010) facet (Figure 1h). The hexagonal dot pattern after fast Fourier transform (FFT) suggests the single-crystal structure of Ru2Ni MLNSs (inset of Figure 1h). Based on the above results, a scheme has been provided that vividly depicts the morphology and structure of Ru2Ni MLNSs (Figure 1i). Figure 1 | Morphology and structure of Ru2Ni MLNSs. (a) TEM image, (b) HAADF-STEM image, and (c) high-magnification TEM image of Ru2Ni MLNSs. (d) The erect TEM image of Ru2Ni MLNS on carbon powder. (e) HAADF-STEM images of Ru2Ni MLNS at different viewing angles from +60° to −60°. (f) HAADF-STEM element mappings, (g) XRD pattern of Ru2Ni MLNSs. Inset shows the typical crystallographic models of hcp structure. (h) HRTEM image of Ru2Ni MLNSs. Inset is the corresponding FFT pattern. (i) Scheme of Ru2Ni MLNSs. Download figure Download PowerPoint More experiments were conducted to study the formation mechanism of Ru2Ni MLNSs. We found that Ru MLNSs were formed in the absence of Ni(acac)2, suggesting that the growth system favours the formation of MLNSs ( Supporting Information Figure S6). No solid nanostructures were obtained in the absence of Ru3(CO)12. Meanwhile, Ru NPs were obtained when Ru3(CO)12 was replaced by Ru(acac)2, suggesting the significant role of Ru3(CO)12 in the formation of Ru2Ni MLNSs ( Supporting Information Figure S7). In the presence of Ru3(CO)12 and Ni(acac)2, single-layered NSs were already formed after 1 h (Figure 2a). The lattice distance of 0.234 nm is close to that of Ru (1010) facet (Figure 2b), further confirming the preferential formation of Ru NSs at the early stage. By prolonging the growth time to 1.5 h, multilayered structures were obtained (Figure 2c), and the lattice distance shrunk from 0.234 to 0.231 nm, which was attributed to the lattice contraction after Ni introduction (Figure 2d). When the growth time was further increased to 3 h, hexagonal Ru2Ni MLNSs with a lattice distance of 0.229 nm were formed (Figure 2e,f), suggesting that more Ni(acac)2 was reduced and alloyed with Ru. Further increase of the growth time to Ru2Ni led to negligible influences on the morphology and lattice structure (Figure 2g,h). Nevertheless, the multilayered structures of Ru2Ni were destroyed when the growth time was increased 10 h ( Supporting Information Figure S8). Moreover, we monitored the variations of Ru and Ni contents in the products collected after different growth times. The gradual decrease of Ru and increase of Ni with the increased growth time further confirm that Ru MLNSs were preferentially formed at the early stage (Figure 2i). Ni(acac)2 was subsequently reduced and alloyed with Ru to form Ru2Ni MLNSs, leading to the gradual decrease of lattice distance (Figure 2j). In addition, the corresponding XRD patterns were collected to reveal the structural evolution during growth. As shown in Figure 2k, no peaks appear in the XRD pattern of the product collected after 1 h, which may be attributed to the ultrathin nature of the single-layered nanosheet. By prolonging the growth time, the increasing peak intensities in XRD patterns demonstrate the formation of Ru2Ni MLNSs. The continuous positive shifts of peaks in XRD patterns further confirm the preferential formation of Ru NSs and the subsequent reduction of Ni(acac)2. In particular, Ru NSs are preferentially formed as the seeds, and Ni(acac)2 was subsequently reduced and then alloyed with Ru to form Ru-Ni NSs. By prolonging the growth time, more Ni(acac)2 was reduced to form hexagonal Ru2Ni NSs and finally assembled into multilayered structures in the layer-by-layer manner (Figure 2l). Figure 2 | TEM and HRTEM images of Ru2Ni MLNSs collected at (a, b) 1 h, (c, d) 1.5 h, (e, f) 3 h, and (g, h) 5 h. The variations of atomic fractions (i), lattice distance (j), and XRD patterns (k) of Ru2Ni during the formation process. (l) Schematic illustration for the formation process of Ru2Ni MLNSs. Download figure Download PowerPoint The HOR performance over Ru2Ni MLNSs was evaluated using a typical three-electrode system on rotating disk electrode (RDE) in H2-standard 0.1 M KOH electrolyte. Prior to the HOR test, Ru2Ni MLNSs were loaded on carbon powder (XC-72) with ultrasonication for 1 h and then treated in air at 250 °C (Ru2Ni MLNSs-250) and 300 °C (Ru2Ni MLNSs-300), respectively ( Supporting Information and Ru2Ni MLNSs without Ru MLNSs, commercial and commercial Pt/C were employed as for HOR. Based on the HOR polarization Ru2Ni MLNSs-250 the HOR activity the that such on Ru2Ni MLNSs strongly influences the HOR activity (Figure No current at the potential above 0 when Ru2Ni MLNSs-250 was tested in 0.1 M KOH electrolyte, suggesting that the current during HOR from hydrogen oxidation ( Supporting Information Figure Moreover, the current increased with the increased speed when Ru2Ni MLNSs-250 was used as that the HOR process was by the mass (Figure The was calculated to be by the Koutecky–Levich (inset of Figure which was close to the that the current was from H2 Based on the Ru2Ni MLNSs-250 exhibits the kinetic current those catalysts at the further confirming the superior HOR activity of Ru2Ni MLNSs-250 to other (Figure the mass activity of Ru2Ni MLNSs-250 4.34 A which is and 13.2 times higher than those of Ru2Ni MLNSs A Ru2Ni A Ru/C (0.24 A and Pt/C (0.33 A mgPt−1), respectively (Figure We that the HOR activity of Ru2Ni MLNSs-250 has Ru NPs ( Supporting Information Figure and of the reported catalysts for HOR (Figure and Supporting Information S1). In addition, the were performed for 2000 cycles to the of Ru2Ni MLNSs-250 for HOR in the range from 0 to at a rate of 100 mV As shown in Figure the HOR polarization of Ru2Ni MLNSs-250 after is with the decay of the current are for commercial Ru/C and Pt/C after 2000 Moreover, the mass of Ru2Ni MLNSs-250 by after which is much lower than those of commercial Ru/C and Pt/C ( Supporting Information Figure the current density of Ru2Ni MLNSs-250 by in H2-saturated 0.1 M KOH at an overpotential of 50 mV on after which is much lower than those of commercial Ru/C and commercial Pt/C the same conditions (Figure the morphology and structure of the Ru2Ni MLNSs-250 were ( Supporting Information that Ru2Ni MLNSs-250 can serve as a highly and catalyst for alkaline HOR. Figure 3 | (a) HOR polarization curves of Ru2Ni Ru2Ni MLNSs, Ru2Ni and Pt/C in H2-saturated 0.1 M (b) HOR polarization curves of Ru2Ni with rotating Inset is the of Ru2Ni obtained at an overpotential of 100 (c) HOR of Ru2Ni Ru2Ni Ru2Ni and (d) of Ru2Ni MLNSs, Ru2Ni Ru2Ni Ru/C and Pt/C (e) of the mass activity of reported HOR (f) curves of Ru2Ni and Pt/C and after 2000 (g) of Ru2Ni and Pt/C in H2-saturated 0.1 M KOH at an overpotential of 50 mV on Download figure Download PowerPoint The XPS of Ru2Ni MLNSs, Ru2Ni and Ru2Ni were collected to study the of temperature on the surface properties of Ru2Ni MLNSs. As shown in Figure Ru of and in these and the ratio of with the increased temperature for ( Supporting Information Figure Results from Ni XPS that the of Ru2Ni MLNSs, Ru2Ni and Ru2Ni were and respectively (Figure that Ni can facilitate the increase of surface HOR However, high temperature for to the oxidation of to which may further the *H more investigations were performed to reveal the of surface properties on the adsorption of *H and *OH. As shown in Figure the overpotential of the hydrogen peak for Ru2Ni MLNSs-250 in curves suggests the HBE compared to Ru2Ni MLNSs and Ru2Ni (Figure Moreover, the *H adsorption on Ru2Ni MLNSs-250 has been by the surface band where the d-band of Ru2Ni MLNSs-250 is much to the than those of Ru2Ni MLNSs and Ru2Ni (Figure in was conducted to the adsorption on As shown in Figure the peak at in the can be to the characteristic peak of *OH. As the temperature the to from the leading to the decrease of the peak intensities in the temperatures of for Ru2Ni MLNSs, Ru2Ni and Ru2Ni are and that Ru2Ni displays the adsorption to *OH. The above results demonstrate that the of temperature can alter the surface properties and thus regulate the adsorption abilities toward *H and *OH. to other Ru2Ni MLNSs-250 displays appropriate adsorption of *H and as a of the HOR activity. Figure | XPS of Ru (a) and Ni (c) The ratio of for Ru2Ni MLNSs, Ru2Ni and Ru2Ni (d) curves of Ru2Ni MLNSs, Ru2Ni and Ru2Ni in 0.1 M KOH with a rate of 50 mV (e) band and (f) corresponding of centers of Ru2Ni MLNSs, Ru2Ni and Ru2Ni In of (g) Ru2Ni MLNSs, (h) Ru2Ni and (i) Ru2Ni Download figure Download PowerPoint obtain into the DFT calculations were conducted to study the elementary of HOR. We (3 × 3) Ru surface consisting of 3 and atomic respectively. The ratio of was set to and the were with O atoms to the oxidation of the Ru2Ni the atomic was in structural The vacuum was 20 Å to interactions between Based on the O atoms to at the by Ni and Ru to the is a of activity in HOR, and the ideal catalyst is to display a As shown in Figure on surface O atoms are close to zero and much smaller than those on metal that surface O atoms are for HOR. We found that the increase of coverage of surface O atoms leads to the strengthened H binding and thus the decay of HOR which with In the water formation is as the step of HOR. we that the Ru2Ni surface with three layers exhibits a lower to water formation than the Ru2Ni surface with seven layers exhibits ( Supporting Information Figure further confirming that the Ru2Ni MLNSs can serve as efficient catalysts for HOR. results are consistent with the that Ni introduction can the surface O and and thus facilitate HOR Figure 5 | The calculated on Ru2Ni slab with three and seven atomic respectively. (a) NiRu are with O atom. (b) Ru2Ni are with O The atomic are the corresponding energy Download figure Download PowerPoint We have demonstrated that Ru2Ni MLNSs with surface can serve as an efficient catalyst for alkaline HOR. the Ru2Ni MLNSs were fabricated via a facile wet-chemical method and a surface modification via a postannealing process. Detailed investigations reveal that such surface can alter the surface properties and thus regulate the adsorption abilities toward *H and *OH. DFT calculations indicate that the surface O atoms facilitate HOR activity while the excessive coverage of O atoms on a Ru2Ni surface leads to strengthened H binding and the decay of HOR activity. the optimal catalyst displays a mass activity of 4.34 mgRu−1 at 50 mV, which is and 13.2 times higher than that of Ru2Ni MLNSs A Ru2Ni A Ru/C (0.24 A and Pt/C (0.33 A mgPt−1), respectively. This work the of surface to research on the design of efficient Supporting Information Supporting Information is and TEM EDS XRD and of The no The the of the Key of the of and of the of

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