F-Doped Graphene Composites as

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Energy, Environmental, and Catalysis Applications

Rhodium Nanoparticles/F-Doped Graphene Composites as Multifunctional Electrocatalyst Superior to Pt/C for Hydrogen Evolution and Formic Acid Oxidation Reaction Wen Shen, Lei Ge, Yuyang Sun, Fan Liao, Lai Xu, Qian Dang, Zhenhui Kang, and Mingwang Shao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b09297 • Publication Date (Web): 07 Sep 2018 Downloaded from http://pubs.acs.org on September 7, 2018

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ACS Applied Materials & Interfaces

Rhodium Nanoparticles/F-Doped Graphene Composites as Multifunctional Electrocatalyst Superior to Pt/C for Hydrogen Evolution and Formic Acid Oxidation Reaction Wen Shen†, Lei Ge†, Yuyang Sun, Fan Liao, Lai Xu*, Qian Dang, Zhenhui Kang*, Mingwang Shao* Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou 215123, PR China. KEYWORDS: Rh nanoparticle; F-doped graphene; Hydrogen evolution reaction; Formic acid oxidation reaction; proton-adsorption

ABSTRACT High-efficient electrocatalysis for clean, efficient and sustainable energy supply, such as hydrogen evolution reaction (HER) and formic acid oxidation reaction (FAOR), has drawn enthusiastic and worldwide attention. Universal and efficient electrocatalysts for these reactions are essential elements for the development of renewable and clean energy technologies. Herein, we show the design and fabrication of the rhodium nanoparticles modified fluorinedoped graphene (Rh/F-graphene) catalyst using silicon nanowires (SiNWs) as the sacrifice template. The optimized Rh/F-graphene catalyst (Rh/F-graphene-2) has a low Rh mass fraction 1 Environment ACS Paragon Plus

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of 9.4% and F doping of 4.0%. The mean diameter of Rh is 9.39 nm. Rh/F-graphene-2 serves as a proton-adsorption-dominated multifunctional electrocatalyst for both HER and FAOR with performance superior to 20 wt% Pt/C in acidic solution. In addition, due to the doping of fluorine, the stability of Rh/F-graphene-2 catalyst greatly improves and is the best among all the compared electrocatalysts. This design for multifunctional catalysts could greatly increase the utilization ratio of Rh, which may provide a new avenue for the preparation of other noble metal-based catalysts.

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INTRODUCTION Hydrogen evolution reaction (HER)

1

and formic acid oxidation reaction (FAOR)

2

are the

cornerstones for the production of clean, efficient and sustainable energy, which have drawn enthusiastic and worldwide attention. High efficient electrocatalysts are desperately needed for these reactions although the mechanisms of these reactions are not same. Various noble-metalfree catalysts are developed in order to decrease the cost;3, 4 however, it would be hard to deny that noble metals, in particular the Pt-based catalysts (such as commercial Pt/C) still dominate the commercialization and industrialization at current stage. The noble metal catalysts always exhibit high catalytic activity and can be universally used in the energy synthesis reactions as mentioned above.5, 6 The biggest obstacles for noble metal catalysts are their rare reserves and low durability, which both lead to the high cost.7,

8

To overcome these drawbacks, we need to tailor the

architecture of nanostructures, reduce the usage and enhance the stability of the noble metals.9-11 Currently the high surface area and stable silicon and carbon nanomaterial supports, such as silicon nanowires (SiNWs),11 carbon black

12

and doped graphene,13 are the most promising

candidates to design the high-efficient noble metal-based catalysts. For example, numerous studies regarding the heteroatoms-doped (such as N, B, S and P) graphene have been explored.1417

The increase of the catalytic activity is attributed to the formation of charged sites originated

from the different electronegativity values between carbon and heteroatom dopants.18 Fluorine (F) is an element with the largest electronegativity (δ = 4.0) than other heteroatoms, which may induce delocalization of charges to the great extent, change charge distributions of graphene, and thus facilitate the adsorption performances. This can explain why the F-doped graphene can effectively enhance the electrocatalytic activity towards oxygen reduction reaction.



19

F doping can also enlarge the interlayer distance and increase disorders of the catalysts,

overcoming the agglomeration of graphene. The strong electrophilic ability of F may suppress the carbon corrosion and increase the stability of the carbon-based catalysts. The electrical conductivity and electron transport can be improved at the same time.20 Nevertheless, the Fdoped graphene loaded with noble metals employed as catalysts for HER, alcohol electrooxidation and formic acid electrooxidation reactions were rarely reported and F-doped materials are much less explored than other heteroatoms doped materials. The high cost and toxicity of fluorinating agents (such as F2, XeF2, SF6 and so on) and the extreme synthesis conditions (like high temperature and high pressures) have limited the progress of F-doped materials.21 Thus, the development of an easy route to prepare a catalyst doped by F with desirable electrocatalytic performance has been expected. Herein, we attempt to design a multifunctional noble metal / F-doped graphene electrocatalyst using SiNWs as a sacrifice template. Accompanied with hydrofluoric acid, noble metal ions can be reduced at room temperature and SiNWs can be etched under hydrothermal condition with temperature of 120 oC. With the mild solution method, we can obtain F-doped graphene and uniform rhodium nanoparticles modified on it (Rh/F-graphene). According to the volcano plot,22 rhodium shows a negative Gibbs free energy of the hydrogen adsorption (ΔGH*) value. The ΔGH* value is considered as an important descriptor of the catalytic activity and it is well known that the near zero ΔGH* value of Pt leads to its superior activity in electrocatalysis. The F-doped graphene has a positive ΔGH* value.17 The synergistic effect between Rh and F-doped graphene leads to a proper ΔGH* value. In addition, the strong proton adsorption of the F atom due to its highest electronegativity is beneficial to improve the catalytic activity, which would result in a multifunctional catalyst with higher electrocatalytic performance including low onset


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overpotentials and longer durability than 20 wt% Pt/C in acidic solution. This phenomenon means that the strong proton adsorption ability would promote the electrocatalytic performance, as reported in the previous work.23 The experimental results show that the optimized catalyst is Rh/F-graphene-2 with component of Rh : F : graphene = 9.4 wt% : 4.0 wt% : 86.6 wt%. The mean diameter of Rh is 9.39 nm. The proton absorption capability of Rh/F-graphene-2 is about 4.28 mg·g-1 (based on HCl), which is almost twice as 20wt% Pt/C (2.19 mg·g-1) and more than four times as the undoped Rh/graphene. For HER, the Rh/F-graphene-2 catalyst exhibited remarkable performance for its lower overpotential of 46 mV @ -10 mA·cm-2, lower Tafel slope of 30 mV·dec-1 and larger current densities at higher potentials that even overwhelmed the performance of 20 wt% commercial Pt/C in acidic solution (0.5 M H2SO4). The theoretical calculations, showing much more nearzero hydrogen adsorption free energy value (ΔGH* = −0.02 eV) on rhodium/F-doped graphene than that on rhodium/graphene (ΔGH* = −0.31 eV), demonstrate that the doping of fluorine could be in favor of HER performance. For FAOR, the Rh/F-graphene-2 catalyst also reveals excellent performance with low onset potential and high anodic mass activities, which is superior to that of 20 wt% Pt/C in 0.5 M H2SO4 solutions as well. Moreover, Rh/F-graphene-2 catalyst also shows the highest stability because of the doped F, which makes it a promising multifunctional catalyst in energy conversion reaction.

RESULTS AND DISCUSSION Characterization. Figure 1A reveals the whole synthesis process of Rh/F-graphene-2 catalysts. The X-ray powder diffraction (XRD) patterns of the Rh/F-graphene-2, Rh/graphene, pure Fgraphene catalysts and graphene oxide (GO) are shown in Figures 1B and S1 (Supporting



Information). The characteristic XRD peak at around 2θ of 10°in GO disappeared in F-graphene, Rh/F-graphene-2 and Rh/graphene catalysts, which proves the reduction of GO to reduced graphene oxide. In addition, the broad peaks, which are located at 2θ values of ~24 and 43°, could be attributed to graphene. Moreover, other new diffraction peaks, appearing at 41.07, 47.78, 69.87 and 84.39°, could be assigned to (111), (200), (220) and (311) crystal planes of cubic Rh (JCPDS data No. 05-0685), respectively, indicating the high purity of the as-prepared catalysts. The Raman spectra of the GO, F-graphene, Rh/F-graphene-2 and Rh/graphene catalysts were shown in Figure S2 (Supporting Information). The two main peaks at about 1335 and 1600 cm−1 could be ascribed to the typical D and G bands, respectively. The intensity ratio of D band to G band of GO, F-graphene, Rh/F-graphene-2 and Rh/graphene are 0.96, 1.26, 1.41 and 1.37, respectively. The enlarged ratio for the Rh/F-graphene-2 implied the enhanced disorder of the graphene due to the interactions among graphene, F and Rh, which may be beneficial to the electrocatalysis. Figures 1C and S3A (Supporting Information) reveal the Transmission electron microscope (TEM) image of the Rh/F-graphene-2 catalysts. Also, the TME images for Rh/F-graphene catalysts with different reaction time (2, 10 and 20 h) are shown in Figure S4 (Supporting Information). As observed, many Rh nanoparticles are uniformly dispersed on the surface of Fgraphene when the reaction time is smaller than 10 h. However, when the reaction time is 20 h, the Rh nanoparticles aggregate partly. The insets in Figure 1C and Figure S4 (Supporting Information) show the diameter distribution of 100 Rh nanoparticles, indicating that mean diameters of the Rh nanoparticles of Rh/F-graphene-2h, Rh/F-graphene-2, Rh/F-graphene-10h and Rh/F-graphene-20h are 8.86, 9.39, 13.28 and 16.18 nm, respectively. In addition, the TEM


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images of Rh/graphene and 20 wt% Pt/C are also shown in Figures S3B and S3C (Supporting Information). The high resolution TEM (HRTEM) in Figure 1D shows the lattice spacing of 0.22 and 0.19 nm, corresponding to the cubic Rh (111) and (200) planes (JCPDS 05-0685) along the [01-1] crystal axis and indicating its high crystallinity. The selected-area electron diffraction (SAED) patterns (Figure 1E and Figure S5, Supporting Information) display concentric rings formed by bright discrete diffraction spots, which may be indexed as (111), (200), (220) and (311) diffraction planes of Rh. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) image of Rh/F-graphene-2 catalysts is shown in Figure 1F and the corresponding energy dispersive spectroscopy (EDS) mapping images(Figures 1G-1J) reveal the elemental distribution of carbon (red), fluorine (yellow) and rhodium (green), respectively, confirming the doping of F and existence of Rh nanoparticles as well.



Figure 1. (A) The illustration of preparation of Rh/F-graphene-2 catalysts; (B) XRD patterns of F-graphene, Rh/F-graphene-2 and Rh/graphene catalysts; (C) TEM image of Rh/F-graphene-2, the inset being the diameter distribution of 100 Rh nanoparticles; (D) HRTEM image of Rh/Fgraphene-2 with the [01-1] crystal axis; (E) SAED pattern of Rh/F-graphene-2; (F) HAADFSTEM image of Rh/F-graphene-2; and (G-J) its corresponding EDS mapping for the distribution of C, F and Rh elements.

The chemical states of C, F and Rh in the as-prepared catalysts were characterized by X-ray photoelectron spectroscopy (XPS). The full scan spectra (Figures S6A-S6C, Supporting Information) verify the high purity of all catalysts as well and the high resolution spectra of Rh/graphene, F-graphene and GO are shown in Figures S6D-S6J (Supporting Information). The XPS spectra of Rh/F-graphene-2 given in Figures 2A-2C clearly show the high resolution C 1s, F 1s and Rh 3d spectra, demonstrating the doping of F atoms by the mild solution synthesis. The oxygen functionalities and their distributions on the surface of Rh/F-graphene could be identified by deconvoluting the C1s peak into the relative components (Figure 2A). Three main peaks located at 284.6, 286.1 and 289 eV correspond to C-C, C-O and C=O, respectively.24 Besides those oxygen functionalities, the semiionic C–F peak (~288.2 eV) can be certainly identified at the C1s peak of Rh/F-graphene.25 The reduction level of the GO can be determined by XPS from the relative ration of peak area of C-O and C=O bonds to C-C bonds, shown in Table S1. Furthermore, the comparison of high-resolution F 1s spectra between Rh/F-graphene-2 (Figure 2B) and Rh/graphene (Figure S6E, Supporting Information) could further demonstrate the F heteroatom doping of graphene under the solution synthesis. The high-resolution F 1s spectrum of Rh/F-graphene-2 exhibits one peak located at 687.9 eV, indicating the nearly semi-ionic


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fluorine atoms.26 Moreover, the semiionic C−F bond is more active than covalent C−F bond. As a result, the high content of semiionic C−F bond may contribute to the high electrocatalytic performance of Rh/F-graphene-2.27 In addition, the content of F was determined to be 4.0%. The Rh 3d spectrum in Figure 2C shows two kinds of Rh with peaks of Rh0 at ~307.5 eV (3d5/2) and 312.3 eV (3d3/2) and those of RhIII at ~308.6 eV (3d5/2) and 313.3 eV (3d3/2).

Figure 2. (A-C) XPS spectra for Rh/F-graphene-2 catalysts of C 1s, F 1s and Rh 3d, respectively; and (D) dependence of contact time on the removal of H+ by Rh/F-graphene-2, Rh/graphene and 20 wt% Pt/C catalysts.



The proton adsorption experiments of as-prepared catalysts were performed to determine the strong proton (H+) adsorption property of Rh/F-graphene-2. The amount of adsorbed HCl (Q, mg·g-1), could be obtained by the equation: 𝐐=

(𝑪𝟎 −𝑪𝒆 )𝑽 𝟏𝟎𝟎𝟎 𝑾

(1)

where C0 is the initial concentration (mg·L-1), Ce is the equilibrium concentration (mg·L-1), V is the volume of HCl (mL) and W is the weight (g) of the catalysts. Figure 2D reveals the dependence on contact time of the removal of H+ by different catalysts. It can be verified that 15 min is the equilibrium time during the adsorption experiment due to the constant amount of H+ after 15 min of adsorption. The amount of adsorbed H+ (based on the quantity of HCl) is determined to be 4.28 mg·g-1 for Rh/F-graphene-2, which is much larger than those of Rh/graphene and 20 wt% Pt/C. It should be pointed that such high hydrogen adsorption mainly results from F-graphene with large exposured surface, which is in favor of the electrocatalytic process. Hydrogen evolution reaction. The electrocatalytic HER performance of all catalysts were measured by linear sweep voltammetry (LSV) in O2 free 0.5 M H2SO4 with a scan rate of 5 mV·s-1. In Figure 3A and Figure S7 (Supporting Information), the commercial 20 wt% Pt/C and the blank F-graphene were tested as a comparison. The Pt/C shows excellent HER performance with an expected theoretical onset potential and high current density, while the F-graphene exhibits a negligible HER activity. It is noted that the HER activity of Rh/F-graphene-2 catalysts is comparable to the commercial 20 wt% Pt/C with the same overpotential of 46 mV @ -10 mA·cm-2 and even surpasses that of the 20 wt% Pt/C at high overpotentials with larger current density. By comparing the HER performance of Rh/F-graphene-2 and F-graphene, it can be demonstrated that the active sites of Rh/F-graphene-2 are Rh nanoparticles. Interestingly, the


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Rh/graphene shows the overpotential of 66 mV @ -10 mA·cm-2, much larger than Rh/Fgraphene-2 with the similar Rh content, indicating that the doping of F will significantly enhance the HER activity due to its derived strong proton adsorption capacity. In addition, the LSV curves in terms of mass activity and current per mole are also displayed in Figure S8 (Supporting Information). As observed, the Rh/F-graphene-2 shows the largest mass activities among them. Furthermore, the current per mole of Rh/F-graphene-2 is also the highest among them at higher overpotentials, suggesting that the activity per atom of Rh in Rh/F-graphene-2 is much larger than that of Pt in 20 wt% Pt/C and Rh in Rh/graphene, which further demonstrate the better HER performance of Rh/F-graphene-2 catalysts than that of 20 wt% Pt/C. Figure S9 (Supporting Information) explores the optimal dosage of the Rh/F-graphene catalysts. It can be clearly observed that the HER performance improves firstly with the increasing content of Rh and reach a peak at the Rh content of 9.4 wt%. However, a further increase of Rh content goes against the HER performance. Taking the utilization of the Rh into consideration, the mass activity of all catalysts was appraised showing in Figure 3B and Figure S10 (Supporting Information), which reveals that the mass activities of Rh/F-graphene-2 are the highest among all the catalysts at the overpotentials of 30, 40, 50 and 60 mV. The Tafel plots of 20 wt% Pt/C, Rh/graphene and different Rh/F-graphene catalysts derived from the polarization curves are shown in Figure 3C, Figures S11 and S12 (Supporting Information). And the Tafel slopes were obtained by fitting the linear regions of Tafel plots to the Tafel equation (ƞ = a + b Log (-j)), where ƞ is the overpotential, b the Tafel slope and j the current density) to illuminate the catalytic kinetics for the HER. The Tafel slopes of 20 wt% Pt/C, Rh/graphene, Rh/F-graphene-1, Rh/F-graphene-2, Rh/F-graphene-3 and Rh/F-graphene-4 catalysts were calculated to be 30, 39, 52, 30, 30 and 32 mV·dec-1, respectively. The comparable



Tafel slope with Pt/C indicates the remarkable HER catalytic performance of Rh/F-graphene-2 and the Tafel slope of Rh/F-graphene-2 reveals that it belongs to a Volmer-Tafel mechanism.28 Moreover, the HER performance of various catalysts are listed in Table S2 (Supporting Information). The overpotential @ -10 mA·cm-2 and Tafel slope for Rh/F-graphene-2 are the smallest among the other Rh-based catalysts, indicating the excellent HER performance of the as-prepared catalysts. The exchange current density (-j0) values, determined by Tafel equation, are listed in Table S3 (Supporting Information). The -j0 value of Rh/F-graphene-2 catalysts (0.300 mA·cm-2) is the highest among all the listed Rh-based catalysts, which is also comparable to that of the 20 wt% Pt/C (0.303 mA·cm-2). The calculated TOF (Table S3, Supporting Information) of Rh/F-graphene-2 is 0.502 H2 Rh-1 s-1 at -46 mV (vs. RHE), largest among all the listed catalysts including 20 wt% Pt/C, demonstrating the superior HER performance of Rh/F-graphene-2. Electrochemical impedance spectroscopy (EIS), indicating the HER kinetics at the electrode/electrolyte interface of the Rh/F-graphene catalysts, was investigated at the overpotential of 46 mV with the frequency ranging from 0.1 Hz to 10000 Hz (Figure S13, Supporting Information). It could be obtained that the Rct of Rh/F-graphene-2 is only 12.02 Ω (Table S3, Supporting Information), being the smallest among all the catalysts including 20 wt% Pt/C, indicating the fast electron transfer rate and exhibiting an outstanding HER performance. The HER activities of Rh/F-graphene-2h, Rh/F-graphene-2, Rh/F-graphene-10h and Rh/Fgraphene-20h are also tested to evaluate the influence of the size of Rh nanoparticles. As shown in Figure S14 (Supporting Information), the Rh/F-graphene-2 with a relatively smaller mean Rh diameter of 9.39 nm shows the best HER performance due to its larger specific surface area.


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However, the Rh/F-graphene-2h with the minimum mean Rh diameter of 8.86 nm shows relatively poor HER performance, which may be caused by lower exposed coverage of the Rh nanoparticles on the surface of the electrode. Figure S15 (Supporting Information) shows the HER performance of the Rh/F-graphene-5 catalysts with the F doping of 6.9% to investigate the effect of the amount of F doping. By comparing the HER activities of Rh/graphene, Rh/F-graphene-2 and Rh/F-graphene-5 catalysts, it can be obviously determined that the optimum content of F doping is 4% for HER.

Figure 3. HER performance: (A) Polarization curves of Rh/F-graphene-2 and 20 wt% Pt/C catalysts in oxygen-free 0.5 M H2SO4; (B) The mass activities of pure metal for 20 wt% Pt/C, different Rh/F-graphene and Rh/graphene catalysts at different overpotentials; (C) The corresponding Tafel plots showing Tafel plots of 20 wt% Pt/C and Rh/F-graphene-2 catalysts



derived from (A); and (D) the stability of 20 wt% Pt/C and Rh/F-graphene-2 catalysts by the chronopotentiometry technique @ -10 mA·cm-2. Chronopotentiometry technique @ -10 mA·cm-2 was tested to evaluate the stability of the catalysts for HER (Figure 3D and Figure S16, Supporting Information). During the whole process, it could be obviously observed that there is only a slight potential increase (34 mV) after 10 h for Rh/F-graphene-2, while the Rh/graphene and Pt/C both reveal apparent increases in potentials (61 mV for Pt/C, 154 mV for Rh/graphene), indicating a better durability than Pt/C and Rh/graphene in acidic solutions, which may be attributed to the doping of F atoms. The TEM images before and after stability tests (Figure S3, Supporting Information) reveal that the Rh/Fgraphene-2 catalysts could maintain its morphology after durability tests, while the Rh/graphene and Pt/C catalysts both have obvious agglomeration, demonstrating that fluorination of graphene should provide the maximum charge polarization for achieving excellent electrode stability. DFT calculations were adopted to explicate the phenomenon that the HER performance of Rh/F-graphene-2 surpasses that of the Rh/graphene catalysts due to the F doping. The models were all shown in Figure S17 (Supporting information) with the hydrogen doped Rh (111) on the surface of graphene layers with or without F doping. Figure 4 reveals the changes of Gibbs free energy of upon H adsorption (ΔGH*) at the interface of Rh/F-doped graphene and Rh/graphene catalysts. It can be obviously observed that the value of Rh/F-doped graphene (ΔGH* = -0.02 eV) is much closer to zero than that of Rh/graphene (ΔGH* = -0.31 eV), indicating that the interaction between adsorbed H atom and Rh/F-doped graphene was optimized by F doping. Therefore, Rh/F-graphene possesses more thermodynamically catalytic active sites for HER.


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Figure 4. Theoretical calculations: The Gibbs free energy profile of hydrogen adsorption for HER on Rh/F-doped graphene and Rh/graphene catalysts.

Formic acid oxidation reaction. The electrocatalytic FAOR activities were also performed by cyclic voltammograms (CVs) to evaluate the catalysts (Figure 5). Figures 5A and S18 (Supporting Information) show the FAOR performance of Rh/F-graphene-2, Rh/graphene and 20 wt% Pt/C catalysts in the mixture of 0.5 M H2SO4 and 0.5 M HCOOH with a scan rate of 50 mV·s−1. During the forward scan, it can be observed that the onset potentials of the FAOR peaks locate at 0.59, 0.61 and 0.83 V for Rh/F-graphene-2, Rh/graphene and 20 wt% Pt/C catalysts, respectively. In addition, FAOR produces a prominent anodic peak with mass activity maximum of 335.6, 152.3 and 102.3 A/g for Rh/F-graphene-2, Rh/graphene and 20 wt% Pt/C catalysts, respectively. An obvious negative shift of the onset potential and high anodic mass activity maximum of Rh/F-graphene-2 indicate it highest electrocatalytic activities. Figure S19 shows the FAOR activities for different Rh/F-graphene catalysts. To intuitively compare the performance of different catalysts, the histogram of the peak values of the anodic



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mass activities of different Rh/F-graphene, Rh/graphene and 20 wt% Pt/C catalysts for FAOR is displayed in Figure 5B, showing that the mass activity of the formic acid oxidation for Rh/Fgraphene-2 in the forward potential scan is the largest among them. In addition, the FAOR performances of Rh/F-graphene-2h, Rh/F-graphene-2, Rh/F-graphene10h and Rh/F-graphene-20h are shown in Figure S20 (Supporting Information). Obviously, the Rh/F-graphene-2 with a mean Rh diameter of 9.39 nm shows the best FAOR performance due to its larger specific surface area, suggesting that the reaction time of 4 h is optimal. Also, the influence of the amount of F doping was investigated in Figure S21 (Supporting Information). The FAOR performance of the Rh/F-graphene-5 catalysts with the F doping of 6.9% is inferior to Rh/F-graphene-2. It can be obviously determined that Rh/F-graphene-2 with an optimum F doping of 4% exhibits best FAOR performance. To determine the influence of the scan rate for FAOR, CVs of the Rh/F-graphene-2 catalysts with different scan rates of 5, 10, 20, 30, 40, 50 mV·s-1 in the mixture of 0.5 M H2SO4 and 0.5 M HCOOH were shown in Figure S22 (Supporting Information). As observed, the anodic peak current density and peak potential both increase with the increase of scan rate. Additionally, Figure S22B indicates the linear relationship between the square root of scan rate and anodic peak current density, which demonstrates that the whole process of FAOR is controlled by the diffusion of formic acid from the bulk solution to the electrode surface. Figures 5C and S23 (Supporting Information) show the stability of the Rh/F-graphene-2, Rh/graphene and 20 wt% Pt/C catalysts for FAOR in N2-saturated 0.5 M H2SO4 and 0.5 M HCOOH solutions with a sweep rate of 100 mV·s-1. After 100 cycles, the peak values of the anodic current density of Rh/F-graphene-2 maintain 65% of the previous value, while


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Rh/graphene and 20 wt% Pt/C decrease to 61 % and 40% of their previous values, suggesting the relatively higher durability of the Rh/F-graphene-2 catalysts due to the doping of F. Moreover, Table S4 (Supporting Information) reveals the FAOR performance of various Rhbased catalysts, with the Rh/F-graphene-2 being the best, indicating the excellent formic acid oxidation performance of the as-prepared catalysts, which may be attributed to the high proton (H+) adsorption capacity of Rh/F-graphene-2 catalysts.

Figure 5. (A) Metal-mass normalized CV curves of Rh/F-graphene-2 and 20 wt% Pt/C catalysts in 0.5 M H2SO4 + 0.5 M HCOOH with a scan rate of 50 mV·s−1; (B) histogram of mass activities at anodic peaks of different Rh/F-graphene, Rh/graphene and 20 wt% Pt/C catalysts for FAOR in 0.5 M H2SO4; and (C) electrochemical performance of Rh/F-graphene-2 and 20 wt% Pt/C catalysts in solutions with 0.5 M H2SO4 and 0.5 M HCOOH over 100 circles, where the potential related to current is the potential at the forward oxidation current peak in CV curves at the sweep rate of 100 mV·s-1.

Methanol oxidation reaction (MOR). To verify the fact that the high proton (H+) adsorption capacity of Rh/F-graphene catalysts could contribute to the excellent HER and FAOR performance in acidic solutions, the MOR performance of Rh/F-graphene-2 and Rh/graphene catalysts were tested by CVs in acidic (0.1 M HClO4), neutral (0.1 M K2SO4) and basic (1 M KOH) solutions with the addition of 1 M CH3OH at a sweep rate of 50 mV·s-1 (Figure 6).



As shown in Figure 6A, the MOR performances for Rh/F-graphene-2 and Rh/graphene catalysts are similar with almost the same anodic peak current densities. Because of the strong proton-adsorption-dominated property, the active sites in Rh/F-graphene-2 are covered with hydrogen and hinder the oxidation reaction. It is a reasonable assumption that in neutral and basic solutions with limited H+, the MOR performance will be promoted, which is demonstrated by following test. Figures 6B and 6C display the CVs of Rh/F-graphene-2 and Rh/graphene catalysts in neutral and basic solutions respectively. It could be obviously observed that the Rh/F-graphene-2 exhibits larger mass activities between them, indicating better MOR performance of the Rh/F-graphene-2 than Rh/graphene in neutral and basic solutions. It is worth mentioning that the MOR performance of Rh/F-graphene-2 catalyst in basic solution is pretty good with two obvious oxidation peaks: one for the oxidation of the methanol, and the other for the oxidation of the adsorbed intermediate species. The influence of the scan rate for MOR in 1 M KOH and 1 M CH3OH is tested (Figure S24, Supporting Information), indicating that the whole process is diffusion controlled.

Figure 6. (A) CVs for Rh/F-graphene-2 and Rh/graphene catalysts in N2-saturated 0.1 M HClO4 with 1 M CH3OH; (B) CVs for Rh/F-graphene-2 and Rh/graphene catalysts in N2-saturated 0.1 M K2SO4 with 1 M CH3OH; and (C) CVs for Rh/F-graphene-2 and Rh/graphene catalysts in N2saturated 1 M KOH with 1 M CH3OH.


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CONCLUSIONS In conclusion, we display a simple fabrication of Rh/F-graphene catalyst using silicon nanowires (SiNWs) as the sacrifice template and HF as the introducer of F atoms. The Fgraphene as a good carrier with large surface area can anchor the Rh nanoparticles and avoid the aggregation of catalysts. At the same time, the introducing of F atoms could affect the electronic structure and show a strong proton-adsorption-dominated property, which may be in favor of high electrochemical performance and excellent stability. The optimized Rh/F-graphene-2 catalyst has a low Rh mass fraction of 9.4% and the F doping of 4.0%. The mean diameter of Rh is 9.39 nm. When the Rh/F-graphene-2 catalyst serves as a proton-adsorption-dominated multifunctional electrocatalyst, it displays remarkable HER and FAOR performance, surpassing that of the 20 wt% Pt/C in acidic solutions. For HER, it exhibits low overpotential of 46 mV (vs. RHE) @ -10 mA·cm-2 and small Tafel slope of 30 mV·dec-1 in 0.5 M H2SO4 solutions. In addition, the TOF value is up to 0.502 H2 Rh-1 s-1 (at 46 mV vs. RHE), which is larger than that of the 20 wt% Pt/C (0.447 H2 Pt-1 s-1) and the mass activity of Rh/F-graphene-2 is also larger than Pt/C, indicating the brilliant HER performance. The density functional calculations also demonstrate F doping could be beneficial to the HER performance due to the smaller thermodynamical hydrogen adsorption free energy for Rh/F-doped graphene-2 (ΔGH* = −0.02 eV). For FAOR, it displays performance superior to 20 wt% Pt/C with higher mass activity maximum and lower onset potential (0.78 V) in the anodic scan in 0.5 M H2SO4 solutions, which may be put down to its high proton adsorption capacity. Moreover, the Rh/F-graphene reveals remarkable stability in all electrocatalysis due to the doping of F, which is better than Rh/graphene and 20 wt% Pt/C in 0.5 M H2SO4 solutions. In addition, the performance of alcohol eletrooxidation reaction in acidic, neutral and basic solution could also demonstrate the



importance of the proton adsorption abilities, which further illustrates the excellent HER and FAOR performance of Rh/F-graphene-2 catalysts in acidic solution. This strategy could dramatically improve the utilization of the noble metal and exhibit multifunctional and excellent electrochemical performance at the same time, which provides a platform for the development of noble metals.

Methods Synthesis of the Rh/F-graphene, F-graphene and Rh/graphene catalysts. The synthetic procedures of Rh/F-graphene catalysts were similar to our previous work.29 In detail, SiNWs (30 mg), synthesized via the high temperature method,30 and GO (10 mg) were dispersed in 70 mL H2O. And then different amount of RhCl3·3H2O solution (10 mg·mL-1) was added dropwise and stirred for about 4 h. Afterwards, 10 mL HF aqueous solution (2%) was added into above mixture with vigorous stirring for 1 h. Finally, the above mixture was transferred into a 100 mL Teflon-lined stainless steel autoclave, maintained at 120 ºC for 4 h, and cooled down naturally. The products were washed and dried via a freeze-drying method. Then the Rh/F-graphene catalysts (Rh/F-graphene-1 to Rh/F-graphene-4) with different Rh contents were synthesized. The preparation of the F-graphene was similar to that of the Rh/F-graphene catalysts except that no RhCl3·3H2O solution was added during the whole process. The Rh/F-graphene-5 was synthesized by the pretreatment of GO with 5% HF. The Rh/F-graphene catalysts with different particle size were synthesized with tuning the reaction time to 2, 10 and 20 h, denoted as Rh/Fgraphene-2h, Rh/F-graphene-10h and Rh/F-graphene-20h, respectively. The Rh/graphene catalysts were also synthesized by the hydrothermal method with ethylene glycol as the reductant. The GO (10 mg) were dispersed in 40 mL pure ethylene glycol, and the RhCl3·3H2O solution


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(10 mg·mL-1) was added dropwise. The above mixture was then transferred into 100 mL Teflonlined stainless steel autoclave, maintained at 180 ºC for 12 h, and cooled down naturally. The products were obatained after washing with acetone, ethanol and double distilled water for several times and drying via a freeze-drying method. Table S5 and Table 1 show the raw materials and Rh, C, F and Si contents of all Rh-based catalysts.

Table 1. The Rh, C, F and Si contents in as-prepared catalysts. Catalysts Rh/F-graphene-1 Rh/F-graphene-2 Rh/F-graphene-3 Rh/F-graphene-4 Rh/F-graphene-5 Rh/F-graphene-2h Rh/F-graphene-10h Rh/F-graphene-20h Rh/graphene

Rh (wt%)

C (wt%)

F (wt%)

Si (wt%)

5.1 9.4 14.9 19.5 9.5 8.3 10.1 10.3 10.2

90.8 86.6 81.4 77.0 83.6 87.9 85.6 85.4 89.8

4.1 4.0 3.7 3.5 6.9 3.8 4.3 4.3 0

BDL BDL BDL BDL BDL BDL BDL BDL \

Note: BDL is Below Detectable Level. DFT calculations. The VASP (which is the abbreviation of the Vienna ab initio simulation package) was used to perform DFT calculations by using plane wave technology.31 The ion electrons were described in the plane wave pseudopotentials that are added to the projector, and the plane wave cut off energy of 450 eV was used in the calculation.32 The GGA-PBE was employed to describe the exchange-correlation energy, a vacuum region of around 22 Å was set along the z direction to avoid interaction between periodic images, and the Irreducible Brillouin zone was sampled using a 1×1×1 gamma centered grid for all calculations.33 The convergence threshold was set as 10-5 eV in energy and 0.05 eV/Å in force. There are a widely-accepted HER



mechanism: 𝐻 + + 𝑒 − + 𝑅ℎ → 𝐻 − 𝑅ℎ, 2H − Rh → 𝐻2 ↑ +2𝑅ℎ. In this calculation, we used 12 H (one monolayer) absorbed in the surface of the Rh, and the integral adsorption energy is 𝑛

1

defined by ∆E = 𝑛 (𝐸(𝑠𝑢𝑟𝑓 + 𝑛𝐻) − 𝐸(𝑠𝑢𝑟𝑓) − 2 𝐸(𝐻2 )), where n represents the number of H atom.34 We doped F atoms in the middle of layers of graphene, and also compared with the case where no F atoms doped between the layers. The change in the amount of adsorption energy doped with a small amount of F, was compared with the case for the graphene without F doping. Here, 𝐸(𝑠𝑢𝑟𝑓 + 𝑛𝐻) represents the energy when the hydrogen atom is adsorbed on the Rh surface, while 𝐸(𝑠𝑢𝑟𝑓) represents the energy when no H is adsorbed. The aim of this calculation is to compare the adsorption energy difference between the sandwich with F doping (Rh/F-doped graphene) and without F doping (Rh/graphene). All the calculations were done on graphene added with a layer of Rh. The free energy of the adsorbed state was calculated as: ∆𝐺𝐻 ∗ = ∆𝐸𝐻 + ∆𝐸𝑍𝑃𝐸 − 𝑇∆𝑆𝐻 ,35 where ∆𝐸𝑍𝑃𝐸 is the difference in zero point energy between the adsorbed and the gas phase and ∆𝐸𝐻 is the hydrogen chemisorption energy above which can be calculated directly by VASP. The structural optimization was carried out before the energy calculation and the convergence accuracy was achieved.

ASSOCIATED CONTENT Supporting Information. DFT calculations, the structural characterization, electrochemical performances and stability of the catalysts.

AUTHOR INFORMATION Corresponding Author


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E-mail: [email protected] (L Xu), [email protected] (ZH Kang), and [email protected] (MW Shao)

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. W Shen and L Ge contributed equally. Notes The authors declare no competing financial interests. ACKNOWLEDGMENT The project was supported by the National Key Research and Development Program of China (2017YFA0204800), the 111 Project, Collaborative Innovation Center of Suzhou Nano Science & Technology, the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), the National Natural Science Foundation of China (Grant No. 51725204, 51572179, 21471106, 21771132, 21501126, 21603155), Six Talent Peak Project in Jiangsu Province (Grant No.XNY-042), and Innovative and Entrepreneurial Doctor (World-Famous Universities) in Jiangsu Province. REFERENCES 1. Jaramillo, T. F.; Jorgensen, K. P.; Bonde, J.; Nielsen, J. H.; Horch, S.; Chorkendorff, I. Identification of Active Edge Sites for Electrochemical H2 Evolution from MoS2 Nanocatalysts. Science 2007, 317, 100-102.



2. Qiu, X. Y.; Zhang, H. Y.; Wu, P. S.; Zhang, F. Q.; Wei, S. H.; Sun, D. M.; Xu, L.; Tang, Y. W. One-Pot Synthesis of Freestanding Porous Palladium Nanosheets as Highly Efficient Electrocatalysts for Formic Acid Oxidation. Adv. Funct. Mater. 2017, 27, 1603852. 3. Zheng, Y.; Jiao, Y.; Jaroniec, M.; Qiao, S. Z. Advancing the Electrochemistry of the Hydrogen-Evolution Reaction through Combining Experiment and Theory. Angew. Chem. Int. Ed. 2015, 54, 52-65. 4. Shi, Y. M.; Zhang, B. Recent Advances in Transition Metal Phosphide Nanomaterials: Synthesis and Applications in Hydrogen Evolution Reaction. Chem Soc Rev 2016, 45, 1529– 1541. 5. Jiang, K. Z.; Bu, L. Z.; Wang, P. T.; Guo, S. J.; Huang, X. Q. Trimetallic PtSnRh Wavy Nanowires as Efficient Nanoelectrocatalysts for Alcohol Electrooxidation. ACS Appl. Mater. Interfaces 2015, 7, 15061–15067. 6. Durst, J.; Siebel, A.; Simon, C.; Hasché, F.; Herranz, J.; Gasteiger, H. A. New Insights into the Electrochemical Hydrogen Oxidation and Evolution Reaction Mechanism. Energy Env. Sci 2014, 7, 2255–2260. 7. Fei, H. L.; Dong, J. C.; Arellano-Jiménez, M. J.; Ye, G. L.; Kim, N. D.; Samuel, E. L. G.; Peng, Z. W.; Zhu, Z.; Qin, F.; Bao, J. M.; Yacaman M. J.; Ajayan P. M.; Chen D. L.; Tour J. M. Atomic Cobalt on Nitrogen-Doped Graphene for Hydrogen Generation. Nat. Commun. 2015, 6, 8668. 8. Choi, S. I.; Shao, M. H; Lu, N.; Ruditskiy, A.; Peng, H. C.; Park, J.; Guerrero, S.; Wang, J. G; Kim, M. J.; Xia, Y. N. Synthesis and Characterization of Pd@Pt–Ni Core–Shell Octahedra with High Activity toward Oxygen Reduction. ACS Nano 2014, 8, 10363–10371.


Page 24 of 29

Page 25 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


9. Xia, B. Y.; Wu, H. B.; Li, N.; Yan, Y.; Lou, X. W. D.; Wang, X. One-Pot Synthesis of Pt-Co Alloy Nanowire Assemblies with Tunable Composition and Enhanced Electrocatalytic Properties. Angew. Chem. Int. Ed. 2015, 54, 3797–3801. 10. Ye, W.; Chen, S. M.; Ye, M. S.; Ren, C. H.; Ma, J.; Long, R.; Wang, C. M.; Yang, J.; Song, L.; Xiong, Y. J. Pt4PdCu0.4 Alloy Nanoframes as Highly Efficient and Robust Bifunctional Electrocatalysts for Oxygen Reduction Reaction and Formic Acid Oxidation. Nano Energy 2017, 39, 532-538. 11. Zhu, L. L.; Lin, H. P.; Li, Y. Y.; Liao, F.; Lifshitz, Y.; Sheng, M. Q.; Lee, S. T.; Shao, M. W. A Rhodium/Silicon Co-Electrocatalyst Design Concept to Surpass Platinum Hydrogen Evolution Activity at High Overpotentials. Nat. Commun. 2016, 7, 12272. 12. Gunji, T.; Noh, S. H.; Tanabe, T.; Han, B.; Nien, C. Y.; Ohsaka, T.; Matsumoto, F. Enhanced Electrocatalytic Activity of Carbon-Supported Ordered Intermetallic Palladium–Lead (Pd3Pb) Nanoparticles toward Electrooxidation of Formic Acid. Chem. Mater. 2017, 29, 2906–2913. 13. Cheng, N. C.; Stambula, S.; Wang, D.; Banis, M. N.; Liu, J.; Riese, A.; Xiao, B. W.; Li, R. Y.; Sham, T. K.; Liu, L. M.; Botton G. A.; Sun X. L. Platinum Single-Atom and Cluster Catalysis of the Hydrogen Evolution Reaction. Nat. Commun. 2016, 7, 13638. 14. Lin, Z. Y.; Waller, G. H.; Liu, Y.; Liu, M. L.; Wong, C. P. Nitrogen-Doped Graphene Prepared by Pyrolysis of Graphene Oxide with Polypyrrole for Electrocatalysis of Oxygen Reduction Reaction. Nano Energy 2013, 2, 241-248. 15. Jia, J.; Xiong, T. L.; Zhao, L. L.; Wang, F. L.; Liu, H.; Hu, R. Z.; Zhou, J.; Zhou, W. J.; Chen, S. W. Ultrathin N-Doped Mo2C Nanosheets with Exposed Active Sites as Efficient Electrocatalyst for Hydrogen Evolution Reactions. ACS Nano 2017, 11, 12509–12518.



16. Jiao, Y.; Zheng, Y.; Davey, K.; Qiao, S. Z. Activity Origin and Catalyst Design Principles for Electrocatalytic Hydrogen Evolution on Heteroatom-Doped Graphene. Nat. Energy 2016, 1, 16130. 17. Zheng, Y.; Jiao, Y.; Li, L. H.; Xing, T.; Chen, Y.; Jaroniec, M.; Qiao, S. Z. Toward Design of Synergistically Active Carbon-Based Catalysts for Electrocatalytic Hydrogen Evolution. ACS Nano 2014, 8, 5290–5296. 18. Shahzad, F.; Zaidi, S. A.; Koo, C. M. Synthesis of Multifunctional Electrically Tunable Fluorine-Doped Reduced Graphene Oxide at Low Temperatures. ACS Appl. Mater. Interfaces 2017, 9, 24179–24189. 19. Jiang, S.; Sun, Y. J. ; Dai, H. C.; Hu, J. T.; Ni, P. J.; Wang, Y. L.; Li, Z.; Li, Z. Nitrogen and Fluorine Dual-Doped Mesoporous Graphene: A High-Performance Metal-Free ORR Electrocatalyst with a Super-Low HO2− Yield. Nanoscale 2015, 7, 10584–10589. 20. An, H. R.; Li, Y.; Gao, Y.; Cao, C.; Han, J. K.; Feng, Y. Y.; Feng, W. Free-Standing Fluorine and Nitrogen Co-Doped Graphene Paper as a High-Performance Electrode for Flexible Sodium-Ion Batteries. Carbon 2017, 116, 338–346. 21. Lee, W. H.; Suk, J. W.; Chou, H.; Lee, J. H.; Hao, Y. F.; Wu, Y. P.; Piner, R.; Akinwande, D.; Kim, K. S.; Ruoff, R. S. Selective-Area Fluorination of Graphene with Fluoropolymer and Laser Irradiation. Nano Lett. 2012, 12, 2374–2378. 22. Trasatti, S. Work Function, Electronegativity, and Electrochemical Behaviour of Metals: III. Electrolytic Hydrogen Evolution in Acid Solutions. J. Electroanal. Chem. 1972, 39, 163–184. 23. Ma, Y. Y.; Wu, C. X.; Feng, X. J.; Tan, H. Q.; Yan, L. K.; Liu, Y.; Kang, Z. H.; Wang, E. B.; Li, Y. G. Highly Efficient Hydrogen Evolution from Seawater by a Low-Cost and Stable CoMoP@C Electrocatalyst Superior to Pt/C. Energy Environ. Sci. 2017, 10, 788–798.


Page 26 of 29

Page 27 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


24. Wu, P.; Qian, Y. D.; Du, P.; Zhang, H.; Cai, C. X. Facile Synthesis of Nitrogen-Doped Graphene for Measuring the Releasing Process of Hydrogen Peroxide from Living Cells. J. Mater. Chem. 2012, 22, 6402. 25. Huang, S. Z.; Li, Y.; Feng, Y. Y.; An, H. R.; Long, P.; Qin, C. Q.; Feng, W. Nitrogen and Fluorine Co-Doped Graphene as a High-Performance Anode Material for Lithium-Ion Batteries. J. Mater. Chem. A 2015, 3, 23095–23105. 26. Zhang, J. T.; Dai, L. M. Nitrogen, Phosphorus, and Fluorine Tri-Doped Graphene as a Multifunctional Catalyst for Self-Powered Electrochemical Water Splitting. Angew. Chem. Int. Ed. 2016, 55, 13296–13300. 27. Sun, X. J.; Zhang, Y. W.; Song, P.; Pan, J.; Zhuang, L.; Xu, W. L.; Xing, W. Fluorine-Doped Carbon Blacks: Highly Efficient Metal-Free Electrocatalysts for Oxygen Reduction Reaction. ACS Catal. 2013, 3, 1726–1729. 28. Cao, X.; Han, Y.; Gao, C. Z.; Xu, Y.; Huang, X. M.; Willander, M.; Wang, N. Highly Catalytic Active PtNiCu Nanochains for Hydrogen Evolution Reaction. Nano Energy 2014, 9, 301–308. 29. Jiang, B. B.; Liao, F.; Sun, Y. Y.; Cheng, Y. F.; Shao, M. W. Pt Nanocrystals on NitrogenDoped Graphene for Hydrogen Evolution Reaction Using Si Nanowires as a Sacrifice Template. Nanoscale 2017, 9, 10138–10144. 30. Shao, M. W.; Shan, Y. Y.; Wong, N. B.; Lee, S. T. Silicon Nanowire Sensors for Bioanalytical Applications: Glucose and Hydrogen Peroxide Detection. Adv. Funct. Mater. 2005, 15, 1478–1482. 31. Kresse, G.; Furthmuller, J. Efficiency of Ab-Initio Total Energy Calculations for Metals and Semiconductors Using a Plane-Wave Basis Set. Comput. Mater. Sci. 1996, 6, 15–50.



32. Kresse, G.; Furthmuller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B 1996, 54, 11169–11186. 33. Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865–3868. 34. Nørskov, J. K.; Bligaard, T.; Logadottir, A.; Kitchin, J. R.; Chen, J. G.; Pandelov, S.; Stimming, U. Trends in the Exchange Current for Hydrogen Evolution. J. Electrochem. Soc. 2005, 152, J23–J26. 35. Greeley, J.; Nørskov, J. K.; Kibler, L. A.; El-Aziz, A. M.; Kolb, D. M. Hydrogen Evolution over Bimetallic Systems: Understanding the Trends. ChemPhysChem 2006, 7, 1032–1035.


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Table of Contents graphic


F-Doped Graphene Composites as

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