Layer Control of Tubular Graphene for Corrosion Inhibition of Nickel

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Layer Control of Tubular Graphene for Corrosion Inhibition of Nickel Wires An T. Nguyen, Wei-Cheng Lai, Bao Dong To, Duc Dung Nguyen, YaPing Hsieh, Mario Hofmann, Hung-Chih Kan, and Chia Chen Hsu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 09 Jun 2017 Downloaded from http://pubs.acs.org on June 9, 2017

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ACS Applied Materials & Interfaces

Layer Control of Tubular Graphene for Corrosion Inhibition of Nickel Wires An T. Nguyenꜝ, Wei-Cheng Laiꜝ, Bao Dong Toꜝ, Duc Dung Nguyenꜝꜝ, Ya-Ping Hsiehꜜ, Mario Hofmannꜛ, Hung-Chih Kanꜝ, Chia-Chen Hsuꜝ´ ⃰ ꜝDepartment of Physics, National Chung Cheng University, Ming-Hsiung, Chia-Yi, Taiwan 62102, ꜝꜝDepartment of Materials Science and Engineering, National Tsing-Hua University, Hsinchu, Taiwan 30010, ꜜGraduate Institute of Opto-Mechatronics, National Chung Cheng University, Ming-Hsiung, Chia-Yi, Taiwan 62102, ꜛ Department of Physics, National Taiwan University, Taipei, Taiwan 10617

Keywords: nickel wire, graphene tube, graphene layer, anti-corrosion, thermal annealing ABSTRACT: Corrosion protection of complex surface is an active area of research due to its importance to commercial applications such as electrochemical fabrication. However, conventional coatings exhibit limited conductivity, thermal stability, and durability and are thus not suitable. Recent work has shown the potential of graphene, a two-dimensional carbon allotrope, for corrosion protection. The studies, however, limited themselves to simple planar geometries that provide limited insight in the applicability to relevant morphologies, such as mesh electrodes and roughened surfaces. We here study the corrosion protection ability of tubular graphene (TG) on Ni-wires as a model system for such complex geometries. TG-covered Ni wires of approximately 50 µm diameters were produced by the annealing of cellulose acetate (CA) on Ni. The high quality of the TG coating was confirmed by Raman spectroscopy, scanning electron microscopy, and electrical measurements. We show that the graphene layer number could be controlled by adjusting the CA membrane quantity. We found a direct relation between the degree of corrosion inhibition with the variation of graphene layer number. The increase of graphene layers on a Ni surface could enhance its corrosion inhibition in acidic, basic, and marine environments which shows the potential of our approach for future applications.

Introduction Due to the limited resistance of metals under harsh environments, metallic corrosion, which annually costs US$300 billion in the United States, 1 is a serious concern for many fields such as marine industry, pipelines, automotive transportation, construction industries, etc. Corrosion reaction is inevitable and more intense for any exposed metal parts. To protect various metals from corrosion, their surfaces are usually coated with paints or galvanized layers, or decorated with oxide layers, 2 organic layers, 3 and polymers. 4 However, thermal and electrical conductivities of metal are unfortunately decreased after the coating; the physical properties, such as appearance, and optical property, are changed due to the thickness of the coating. To overcome these drawbacks, recently, graphene is applied as corrosive protecting layers on various metal substrates through the incorporation with paints 5-8 or wet-transferred graphene films on Cu and Ni foils. 9,10 Because of its remarkably chemical inertness, ultrathin nanostructures, and stability up to 400 ºC in an ambient atmosphere, graphene demonstrates excellent performance for anticorrosion and antioxidation in marine or saline environment. 11-14 Indeed, graphene coated metal foils exhibit a corrosion rate that is several times slower compared with their corresponding bare counterparts. The graphene surface acts as an ultrathin impermeable barrier, thus physically preventing direct interaction between the protected metal and reactants. However,

these studies limited themselves to planar structures that are not directly applicable to many important conditions. For example, wire-mesh structures are commonly employed to provide large surface-area electrodes and filtering membranes. However, it is unclear if the contact points between neighboring wires will be reliably covered by graphene or act as weak spots in the corrosion barrier. Ni wires exhibit superior properties such as high corrosion resistance, improved lubrication and hardness, which can be suitably used in electronic components, transport and storage, temperature sensors, electrical resistance, thermometers, etc. However, the enhancement of corrosion protection is necessary to extend the lifetime of Ni. 1517 Previous studies on the use of graphene, as a protecting layer of Cu or Ni foils from the harsh environment, were mainly focused on material synthesized by chemical vapor deposition (CVD). 18,19 The CVD, a popular graphene fabrication process, usually takes several hours in a tube furnace at around 1000 °C that may restrict the anticorrosive application potential of graphene. We herein present a simple process to fabricate tubular graphene (TG)covered interwoven Ni wires at the macroscopic scale based on rapid thermal annealing of cellulose acetate (CA, C045A047A, Advantec) on Ni at a low vacuum condition. Compared with other typical methods, this approach is safer because it can avoid the hazards of using explosive gaseous materials or toxic chemicals. Furthermore, it has advantages like less power consumption, and shorter pro-

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cessing time. Ni exhibits a melting point of 1455°C, which is much higher than the temperature of graphene growth (950°C). Therefore, the macroscopic Ni wires used in our study can absolutely endure the high annealing temperature of graphene fabrication. In this work, we first demonstrated the number of TG layers could be controlled by adjusting the CA quantity. Then we investigated the degree of corrosion inhibition with the variation of graphene layer number. We found that the increase of graphene layers on a Ni wire surface could enhance its corrosion inhibition by serving as an ultrathin impermeable barrier, and making more tortuous pathway of permeating solution. Experimental Fabrication of TG-covered Ni wires The TG-covered Ni wires (GNi) were fabricated by a thermal annealing technique as reported in our previous works. 20,21 Ni was used as a transition metal catalyst for the surface precipitation of carbon atoms. First, a piece of commercial interwoven Ni wires was cleaned by acetone and rolling-pressed with different amounts of CA membrane (a solid carbon precursor). Note that the layers of TGs were controlled by adjusting the CA membrane quantity (CA to Ni mesh area ratios (CA/Ni area ratio) of 1:16, 1:50, and 1:400); the GNi samples are subsequently denoted by GNi–1/16, GNi–1/50, and GNi–1/400, respectively. Subsequently, the sample was annealed to 950ºC at a heating rate of 15.0°C/s in an infrared lamp annealing system; this temperature was maintained for 8 min at a pressure of 0.6–0.8 × 10-3Torr. The sample was then cooled to 500 °C at a cooling rate of 5.6°C/s, and from 500 °C to room temperature at a cooling rate of 0.48°C/s for yielding the TG-covered Ni wires. 2

The chamber size of our annealing system is 2×2 cm . Consequently, that is the largest size of TG mesh that we can fabricate. However, it is possible to fabricate larger graphene films if bigger furnace is employed. Characterizations A scanning electron microscope (SEM, Hitachi, S-3000H) was used to examine the morphologies and dimensions of the TG meshes; while a Raman spectroscope (Horiba, XploRA ONE), and an atomic force microscope (AFM, XE70) were used to investigate the crystallographic and layered structures of the TGs. An ultrahigh resolution analytical electron microscope operated at 200 kV (HRAEM, JEOL-2100F) was used to determine the number of graphene layers. The sheet resistance of the samples was measured using a four-point probe instrument at room temperature. The energy-dispersive X-ray (EDX) of the FESEM (JSM-6500F) was used to analyze elemental composition of the woven TGs. The X-ray photoelectron spectroscopy (XPS) was used to analyze the surface chemical properties of the TG. Electrochemical measurement Ni is inert in neutral and alkaline environments because of the passivation of the Ni surface through an outgrowing NiO layer 15. This passive film is dissolved when immersed in acidic environment. Therefore, HCl was chosen

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in this study as an appropriate solution for investigating the corrosion resistance of TG-covered nickel instead of Na2SO4, or O2 as previously reported. 18,22,23 Nevertheless, we also determined the corrosion behavior of all the samples in 3.5% NaCl, and 0.5M KOH solutions for further understanding the role as a protective barrier of TG. Electrochemical measurements of the TG-covered Ni meshes were conducted in a three-electrode cell, containing a working electrode, a Pt-mesh counter electrode, and an Ag/AgCl/KCl reference electrode. The corrosion resistances of the TGs were analyzed in acidic (0.05M, 0.1M, and 0.5M HCl), basic (0.5M KOH) and salty (3.5% NaCl) environments. The Tafel plots, the logarithm of the current density (log i) vs. the electrode potential, were recorded by a Jiehan 5600 electrochemical workstation with a scan rate of 20 mV/s. The scan was repeated 3 times to check the reproducibility. All three polarization curves of each sample in 0.5M HCl solution were shown in Fig S1 for reference. The second and third scans of each electrode were almost overlapped, indicating the repeatability of the measurement. Therefore, the third polarization curves of the four electrodes in different environments were chosen for further study. Besides, the corrosion relative parameters, such as corrosion current density (icorr), corrosion rate (CR), and corrosion potential (Ecorr) of different samples were obtained on the basis of the Tafel plots and corrosion theory. 10,24,25 Icorr was determined indirectly from the intersection point of the asymptotic lines of both anodic and cathodic curves. The anodic oxidation and cathodic reduction reactions are as follows:

Ni → Ni + 2e

(1)

O + 2H O + 4e → 4OH

(2)

The CR was calculated through the corrosion current density using the following formula [10]:

CR =

× × ×

(3)

where K is a corrosion rate constant (3272 mm per A per cm per year), EW is the equivalent weight (29 g for Ni), ρ is the density (8.9 g/cm3 for Ni), and A is the sample area (1×2 cm2). Results and Discussion The thickness and quality of graphene synthesized on interwoven meshes were characterized after removal of the Ni (the details on the removal process can refer to [20,21]). The morphology of the TG grown on the Ni mesh at 950 °C, with a 1:50 area ratio of CA membrane to Ni mesh, was examined using the FESEM at different magnifications, as displayed in Fig. 1a–c. The TGs maintained the woven structure of the Ni template, and fully covered the Ni wires without containing any void. The graphene tubes had diameters of approximately 50µm, and were constructed of continuous micron-sized graphene domains, which can be clearly observed on the surface of both TG and GNi (see Fig. 1a, S2a). Small wires remained in the core of every graphene tube were caused by carbon impurities formed during the annealing process. 21 The


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EDX analysis revealed the complete removal of the Ni core after the etching process; the compositions of the TG mesh were carbon (89.3wt.%) and oxygen (10.7wt.%).

Fig. 1. (a−c) SEM images at different magnifications of the o TG sample annealed at 950 C with CA/Ni area ratio of 1:50, (d) the sheet resistance dependence of TGs on the initial CA quantity; the insets show the optical images of the TG–1/50 and TG–1/16 meshes, (e) C 1s scan and the deconvolution of 2 3 the TG-1/50 show sp , sp bonding and oxygen-attached carbon functional groups.

We also carried out EDX analysis on the GNi and found its oxygen concentration is quite low (0.16 wt.%) (see Fig. S2c). The abundant oxygen (10.7 wt.%) found in the TG sample is due to the wet etching process of Ni wires. Since we only used GNi samples for electrochemical measurements, the low concentration of oxygen should have minor effect on the anti-corrosion property of the TG. Note that the CA membrane quantity was adjusted to vary the layer numbers of TGs. Specifically, the CA/Ni area ratio was chosen to be 1:16, 1:50, and 1:400, and the three samples were denoted by TG–1/16, TG–1/50, and TG–1/400, respectively. The electron transparency of the TG structures shown in Fig. 1c and S3 indicates that the walls of the graphene tubes are thin. The optical images of the TG–1/50, and TG–1/16 meshes (see the insets of Fig. 1d) demonstrated free-standing, and great flexibility of the TGs. The TG–1/16, which more CA membrane was used, is darker than the TG–1/50, representing that more graphene layers are formed under these conditions. Another evidence to support this inference is the sheet resistance measurement results of three TG meshes shown in Fig. 1d. The sheet resistance of the TG mesh slightly decreased with the increase of CA/Ni area ratio. Since the sheet resistance is inversely proportional to the thickness of graphene layers, the result indicates thicker graphene layers was formed under higher CA/Ni area ratio. 26 The C 1s XPS spectrum of graphene tubes (TG-1/50) displayed in Fig. 1e can be deconvoluted into four components corresponding to the following chemical states: the components at 284.5 eV, and 285.4 eV are respectively assigned to the carbon sp2, and sp3; the components at 286.0 eV, and 288.7 eV correspond to the O–C–O, and O– C=O functional groups, respectively. The TG exhibited a high sp2/sp3 ratio of 6, further presenting good structural quality of graphene lattices. 27

Fig. 2. (a) Typical Raman spectra obtained from the surface of the three TG samples; Raman maps of I2D/IG ratio of the three samples annealed with different CA/Ni area ratios of (b) 1:16, (c) 1:50, and (d) 1:400.

Fig. 2a shows the typical Raman spectra of the TG meshes annealed at 950 oC with different CA/Ni area ratios. In addition, Fig. S4 displays Raman spectra of these meshes randomly obtained from 15 points on the surface of each sample. All three samples exhibited extremely weak D peaks at〜1335 cm-1 indicating negligible defects on the TGs surfaces. Moreover, two characteristics peaks of graphene (G peak at〜1584 cm-1 and 2D peak at〜2671 cm-1) were clearly observed. The intensity ratio of 2D peak to G peak (I2D/IG) decreased with increase of CA/Ni area ratio. The same trend was also observed in the Raman spectral mapping of I2D/IG intensity ratio taken from three samples in a 50x50 µm2 region as displayed in Fig. 2b-d. It implies more graphene layers were formed in the TGs if larger quantity of CA was used. 28,29 To determine the wall thicknesses of TGs, AFM technique was employed. An unzipped TG was firstly obtained by O2 plasma technique (illustrated in Fig. S5a) because of the nature of hollow tubular structure. The upper half TG was oxidized and removed away while the bottom half graphene was kept unchanged. The unzipped TG was formed and laid on a silica substrate after the Ni etching process. Fig. 3a-c show the AFM results measured at one position of three unzipped TGs; the wall thicknesses were determined to be 1.8 nm, 1.3nm and 1.0 nm for TG-1/16, TG-1/50 and TG-1/400, respectively. To systematically investigate the effect of the CA/Ni area ratio on the layer thickness of the TG, wall thicknesses at 10 random positions of each TG sample were measured by AFM and their results are plotted in Fig. S5b-d. Fig. 3d plots the average and standard deviation of wall thickness of each TG sample versus the CA/Ni area ratio determined from Fig. S5b-d. As expected, the average thickness of the TG increased when more CA was used for the growth of the TG.



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Fig. 3. AFM measurements of the unzipped TG samples fabricated with CA/Ni area ratio of (a) 1:16, (b) 1:50, (c) 1:400. The corresponding insets at the bottom of each image show the thickness difference of two selected points (graphene edge thickness); (d) the TG wall thickness of the TG samples fabricated with different CA amounts; HRAEM images with magnified parts in the insets taken on the wall-edges of the TGs fabricated with CA/Ni area ratio of (e) 1:16, (f), 1:50 and (g) 1:400 .

Fig. 4. (a), (b), (c) The potentiodynamic polarization curves of the bare Ni and GNi samples in 0.05M HCl, 0.1M HCl, and 0.5M HCl, respectively; (d) the corresponding corrosion rates of the Ni and GNi extracted from the Tafel plots.

Furthermore, HRAEM taken on the wall-edge areas allows directly determination of the graphene layer number as displayed in Fig. 3e-g. The TG wall of the TG-1/16 consisted of 8 graphene layers, while they were 5 layers, and 3-4 layers for the TG-1/50, and TG-1/400 samples, respectively. The results provided strong evidence of graphene layered structure, and the finding is consistent with those of Raman spectra, AFM and sheet resistance results. Anti-corrosion capability Chloride ions, which exhibit a very strong corrosion capability, were used to study the anti-corrosion properties of

the TGs in this study. Fig. 4a−c show the Tafel polarization curves of the graphene-coated Ni wire samples measured in different HCl concentrations (0.05M, 0.1M, and 0.5M). Bare Ni mesh was used for comparison. Note that the number of graphene layers was controlled by adjusting the amount of CA as aforementioned. The Tafel plots of the GNi samples exhibited a clear decrease in both anodic and cathodic reaction rates, especially for the strongest acid solution (0.5M), suggesting that the graphene layer has the capability to inhibit corrosion caused by chloride ions by slowing down the ionic diffusion and reaction with the Ni surface. The CR values of all the samples (see Fig. 4d) in different concentrations of acid solutions were calculated by using formula (3). All the samples exhibited low CR in the lowest concentration of 0.05 M. Nevertheless, the GNi samples still had lower CR compared with that of the bare Ni; e.g. it is 4.55 × 10-12 m/s for the GNi-1/400 sample, about 0.38 times of the bare Ni (11.97 × 10-12 m/s). While the CR values of the GNi–1/50, and GNi–1/16 samples were slightly lower than that of the GNi-1/400. The increase of graphene layers can indeed promote the corrosion protection property of TGs as evidenced by the lower values of CR. The corrosion behaviors in the 0.1 M and 0.5 M HCl solutions followed a similar trend like in the 0.05M HCl, except CR values of samples increased with the increase of the acidic concentration. In the highest concentration (0.5M), the GNi-1/16 sample indeed exhibited the strongest anticorrosion performance compared with the other three samples. Note that the bare Ni sample was corroded very quickly, about 4.9 times faster than that of the GNi–1/16.


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Table 1. Polarization parameters of the bare Ni, GNi-1/400, GNi-1/50, GNi-1/16 in the different environments at 300K Sample

Ni

GNi-1/400

CR (m/s) -11

HCl 0.05M

1.2×10

HCl 0.1M

1.22×10-11

HCl 0.5M

-11

NaCl 3.5% KOH 0.5M

3.01×10 1.0×10

4.55×10

-12

2.08×10

CR (m/s)

-13

-12

8.1×10-12 11.4×10

-12

4.15×10 1.25×10

-13

-13

GNi-1/50 PE (%)

CR (m/s) -12

62.0

3.15×10

33.9

3.7×10-12

62.0

-12

58.3 39.7

7.9×10 3.0×10 8.1×10

-13

-14

GNi-1/16 PE (%)

CR (m/s) -12

PE (%)

73.7

2.87×10

69.8

2.74×10-12

77.6

-12

79.6

-13

73.1

73.7 69.8 61.1

6.14×10

2.68×10 6.4×10

-14

76

69.1

Fig. 5. (a), (b) Potentiodynamic polarization curves of the graphene/Ni and bare Ni samples in 3.5% NaCl and 0.5M KOH , respectively; (c) the corresponding corrosion rates of the samples extracted from the Tafel plots, (d) the corrosion current densities vs. the number of graphene layers in the different environments; (e), (f) the Nyquist, and Bode plots, together with their corresponding fitting curves (solid lines), obtained in 0.1M HCl electrolyte for the Ni (black), and GNi-1/16 (red) samples, respectively.

We also measured the Tafel polarization curves of the GNi samples in 3.5% NaCl solution to investigate the corrosion inhibition property of the TG coating in a marine environment. As expected, the icorr values of all the samples followed a similar trend (the GNi samples exhibited lower icorr compared with that of the bare Ni), but were much lower than those in the HCl solution (see Fig. 5a, d). This is reasonable because of the strong oxidation of Ni in acidic environment. Furthermore, as indicated in Fig. 5c, the CR values of the GNi meshes decreased with the increase of thickness of the TGs and they were lower than that of the bare Ni mesh, suggesting the TG coating indeed improved anticorrosion capability of the Ni mesh. We also investigated the anticorrosion property of the TG coating in 0.5M KOH solution (see Fig. 5b-d). Note that the CR values of

all the samples were two-order magnitude lower than those of obtained in HCl solutions because of the inertness of Ni in the basic environment. A passive film formed on Ni surface in alkaline environments prevented Ni from further corrosion. However, this passive film will be dissolved when it is immersed in acidic environment, resulting in the high CR values of Ni in the HCl solutions. In the KOH solution, the increase of graphene layers still slightly increased the anti-corrosion capability as evidenced by the lower values of corrosion rate and corrosion current. The corrosion potentials (Ecorr), typically referred to the pitting point, of the GNi–1/400, GNi–1/50, and GNi–1/16 samples shifted toward more negative values, whereas the corresponding icorr values were few times decrease, compared with those of the bare Ni. This indicates the gra-

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phene is primarily playing a role as an inhibitor of the cathodic reactions, i.e. O + 2H O + 4e → 4OH . 30,31 The corrosion protection efficiency (PE) of each GNi sample was determined by using the formula (4) and the result was used to evaluate the effectiveness of the corrosion inhibition of each sample,

PE % =

× 100%

(4)

where i0corr is the corrosion current density of bare Ni, and iccorr is the corrosion current density of the GNi mesh. Table 1 summarizes CR and PE values of all the samples studied in this work obtained under HCl (with different solution concentrations), KOH and NaCl solutions. As revealed in Table 1, the PE values increased with increase of thickness of the TGs in aforementioned solutions. The highest PE values obtained were approximately 76–80% from the GNi–1/16 sample in HCl, which are comparable to that of the graphene-covered steel as reported. 11 To investigate the stability of graphene coating, SEM images of the Ni, and GNi-1/50 before and after the corrosion test in HCl solution were obtained and are displayed in Fig. S6a, and b, respectively. The morphology of the bare Ni was clearly corroded and became rough after the corrosion test, while the morphology of the GNi-1/50 remained unchanged. Furthermore, Raman spectra randomly obtained at 5 points on the sample surface are shown in Fig. S6c,which were comparable to those of the freshly prepared counterpart (see Fig. S4b), indicating the absence of damage to the graphene after corrosion measurements. Moreover, the GNi-1/50 was immersed in 3.5% NaCl solution for 8 months to investigate long-term stability of the graphene coating. As shown in the Fig S7a, b, the morphology of the sample preserved that of the fresh sample (see Fig. S6b). Fig. S7c displays Raman spectra randomly obtained at five points on the sample surface; low D peaks indicated negligible defects for this sample. The Tafel plots of the sample in acidic and marine electrolytes were measured in comparison with the freshly prepared counterpart (see Fig. S8). The corrosion current densities of two curves in both environments were only slightly different. These results displayed long-term stability of the graphene coatings in corrosion environment. Overall, the icorr of a GNi sample was smaller than that of the counterpart Ni, indicating that the TG coating indeed enhances its corrosion resistance. The GNi–1/16 exhibited the lowest icorr in different environments (see Fig. 5d), representing its best corrosion resistance. Note that the GNi–1/16 has the thickest graphene layers among all the samples. By contrast, the GNi–1/400 with the thinnest graphene layers exhibited the highest icorr compared with the other two GNi samples. This trend can be additionally evidenced by the I–V curves in the different environments as shown in Fig. S9, with a suppression of ionic conduction through the TG coating. The impermeability of the

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TGs makes them serve as excellent barriers against the diffusion of ions such as H+, OH—, and Cl—. Besides, more graphene layers can lead to more tortuous pathway of permeating water. The electrochemical impedance spectroscopy (EIS) EIS, measured by a CHI660E electrochemical workstation, was used to evaluate the anticorrosion mechanism of TG. Under EIS examination, a small sinusoidal perturbation was applied to the sample, and the impedance modulus |Z| was recorded as a function of frequency ω, which allows further analysis of the anticorrosion behavior of the TG layers; the Bode (or Nyquist) plot generally offers the information on the corroding surface, since the electrochemical impedance includes a complex number with a real component (Zreal) and an imaginary component (Zimaginary). The Nyquist and Bode plots obtained in 0.1M HCl electrolyte for the Ni, and GNi-1/16 samples are shown in Fig. 5e, and 5f, respectively. The larger impedance modulus of the GNi-1/16 in the Bode plot indicates the increase of Ni corrosion resistance by graphene coating, and are consistent with the behavior of a graphene-protected metal with minor defects in the protective coating. 10,11 The Nyquist plot of the two samples consisted of two different regions: a semicircle which is attributed to the total charge transfer capacity between Ni and its oxide films, and a linear region which is related to the resistance against the diffusion of corrosive species. By fitting the data to an equivalent circuit model (illustrated in the inset of Fig. 5f), 18,31 the corrosion behavior of bare Ni and graphene-covered Ni samples can be quantitatively calculated. Table 2: Equivalent circuit parameters of the Ni, and GNi1/16 in 0.1M HCl solution -5

-7

Cdl×10

-2 n

-2

CPE×10 -1

R2

R1

Rcorr

(Fcm ) (Ωcm2) (Ωcm2) (Ωcm2)

(Ω cm s )

n

Ni

9.85

0.87

4.06

56.64

29.02

GNi-1/16

3.11

0.96

3.59

145.5

36.83 182.3

Sample

85.7

The graphene-covered Ni electrode exhibited lower electrolyte/metal interface capacitance (Cdl, 35.9 µFcm-2) compared to that of the bare Ni (see table 2). This implies the effectiveness of the graphene coating in providing separation between the Ni and the corrosive environment. Since the capacitance is inversely proportional to the distance of charge separation, lower Cdl of the graphene-covered Ni refers to a lower exposure of Ni surface to active species. The corrosion resistance (Rcorr) can be estimated as the sum of resistance (R1) against electrolyte exposure to graphene (or oxide) through defects, and interface resistance (R2) between the electrolyte and graphene/Ni (or oxide/Ni). 31 A corrosion resistance of 182.3 Ωcm2 was found for the GNi-1/16, 2.1 times larger than that of the bare Ni.

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The exponent of constant phase element (CPE), n, of the GNi is 0.96, closer to 1 compared to that of the bare Ni, indicating capacitor behavior (resistor behavior if n is close to 0). Overall, the EIS results, together with the potentiodynamic polarization results, indicate the graphene coatings as an excellent barrier layer that prevents direct contact between Ni and corrosive environment, resulting in the decrease of the anodic reaction rate. Conclusions The layers of the TGs were controlled by adjusting the CA membrane quantity during the thermal annealing process. The increase of graphene layers was observed when more CA was used for the growth of graphene, evidenced by the Raman, AFM, and HRAEM results. The wall thickness of TGs can be reduced to approximately 1.0 nm (corresponding to 2–3 graphene layers) when the CA/Ni area ratio was reduced to 1/400. We investigated the corrosion resistance of the TG-covered Ni in the acidic (HCl), marine (3.5% NaCl), and basic (0.5M KOH) environments for further understanding the role as a protective barrier of the TGs. In the different solutions, the icorr of a GNi sample was smaller than that of bare Ni, exhibiting the protecting capability of graphene against corrosion. The GNi–1/16, which has the thickest graphene layers among all the samples, exhibited the lowest icorr and CR values in different environments, indicating its best corrosion resistance. By contrast, the GNi–1/400 with the thinnest graphene layers showed the highest icorr and CR values compared with the other two GNi samples. Furthermore, larger impedance values in EIS analysis were found for the graphene-covered Ni sample. Long-term stability of the graphene coatings in corrosion environment was also investigated by characterizing the sample immersed in 3.5% NaCl for 8 months. The EIS results, together with the potentiodynamic polarization results, indicate that graphene acts as an impermeable barrier against the diffusion of corrosive agents; thicker graphene layers can make more tortuous pathway of permeating water.

AUTHOR INFORMATION Corresponding Author ⃰ Corresponding author. Tel: +886-5-2720411 ext.66305 E-mail address: [email protected]

ACKNOWLEDGMENT This study was financially supported by the Ministry of Science and Technology (MOST) of the Republic of China (Taiwan) (MOST 104-2112-M-194-002-MY3). Dr. An T. Nguyen acknowledges the support of postdoctoral fellowships from MOST, Taiwan.

REFERENCES (1) (2)

(3)

(4)

(5)

(6)

(7)

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ASSOCIATED CONTENT Supporting information: Potentiodynamic polarization curves of the graphene/Ni samples in 0.5M HCl which repeated 3 times for each sample; SEM images of the TG samples annealed at 950 ºC with different CA/Ni area ratios; Raman spectra randomly measured at 15 points on the surface of the samples annealed with different CA/Ni area ratios; the distribution of TG wall thickness obtained from different positions of the un-zipped TG samples; SEM, and Raman results of the Ni, and GNi before and after corrosion measurements; SEM, and Raman results of the GNi immersed in 3.5% NaCl for 8 months; Tafel plots of the GNi immersed in NaCl for 8 months in acidic and marine environments; current density vs voltage curves of the bare Ni and Ni coated by variety layers of graphene in different einvoronments. This material is available free of charge via the Internet at http://pubs.acs.org.

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Böhm, S. Graphene Against Corrosion. Nat. Nanotech. 2014, 9, 741-742. Mittal, V.K.; Bera, S.; Saravanan, T.; Sumathi, S.; Krishnan, R.; Rangarajan, S.; Velmurugan, S; Narasimhan, S.V. Formation and Characterization of Bi-layer Oxide Coating on Carbon-Steel for Improving Corrosion Resistance. Thin Solid Films 2009, 517, 1672-1676. Appa Rao, B.V.; Yakub Iqbal, Md.; Sreedhar, B. Selfassembled Monolayer of 2-(octadecylthio) Benzothiazole for Corrosion Protection of Copper. Corros. Sci. 2009, 51, 1441-1452. Redondo, M.I.; Breslin, C. B. Polypyrrole Electrodeposited on Copper from an Aqueous Phosphate Solution: Corrosion Protection Properties. Corros. Sci. 2007, 49, 1765-1776. Mo, M.; Zhao,W.; Chen, Z.; Liu, E.; Xue, Q. Corrosion Inhibition of Functional Graphene Reinforced Polyurethane Nanocomposite Coatings with Regular Textures. RSC Adv. 2016, 6, 7780-7790. Yu, Y. H; Lin, Y.-Y.; Lin, C-H.; Chan, C.-C.; Huang, Y-C. High-Performance Polystyrene/Graphene-based Nanocomposites with Excellent Anti-corrosion Properties. Polym. Chem. 2014, 5, 535-550. Jiang, K.; Lia, J.; Liu, J. Electrochemical Codeposition of Graphene Platelets and Nickel for Improved Corrosion Resistant Properties. RSC Adv. 2014, 4, 36245-36252. Sun, W.; Wang, L.; Wu, T.; Wang, M.; Yang, Z.; Pan, Y.; Liu, G. Inhibiting the Corrosion-Promotion Activity of Graphene. Chem. Mater. 2015, 27, 2367-2373. Li, X.; Cai, W.; An, J.; Kim, S.; Nah, J.; Yang, D.; Piner, R.; Velamakanni, A.; Jung, I.; Tutuc, E.; Banerjee, S. K.; Colombo, L.; Ruoff R. S. Large-area Synthesis of High-quality and Uniform Graphene Films on Copper Foils. Science 2009, 324, 1312-1314. Prasai, D.; Tuberquia, J. C.; Harl, R. R.; Jennings, G. K.; Bolotin. K. I. Graphene: Corrosion-Inhibiting Coating. ACS Nano 2012, 6, 1102-1108. Atta, N. F.; Amin, K. M.; Abd El-Rehimb, H. A.; Galal, A. Graphene Prepared by Gamma Irradiation for Corrosion Protection of Stainless Steel 316 in Chloride Containing Electrolytes. RSC Adv. 2015, 5, 71627-71636. Dumée, L. F.; He, L.; Wang, Z.; Sheath, P.; Xiong, J.; Feng, C.; Tan, M. Y.; She, F.; Duke, M.; Gray, S.; Pacheco, A.; Hodgson, P.; Majumder, M.; Kong, L. Growth of Nanotextured Graphene Coatings across Highly Porous Stainless Steel Supports towards Corrosion Resistant Coatings. Carbon 2015, 87, 395-408. Pu, N.-W.; Shi, G.-N.; Liu, Y.-M.; Sun, X.; Chang, J.-K.; Sun, C.-L.; Ger, M.-D.; Chen, C.-Y.; Wang, P.-C.; Peng, Y.-Y.; Wu, C.-H.; Lawes S. Graphene Grown on Stainless Steel as a

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(14)

(15)

(16)

(17)

(18)

(19)

(20)

(21)

High-Performance and Ecofriendly Anti-corrosion Coating for Polymer Electrolyte Membrane Fuel Cell Bipolar Plates. J. of Power Sources 2015, 282, 248-256. Stoot, A. C.; Camilli, L.; Spiegelhauer, S.-A.; Yu, F.; Bøggild, P. Multilayer Graphene for Long-term Corrosion Protection of Stainless Steel Bipolar Plates for Polymer Electrolyte Membrane Fuel Cell. J. of Power Sources 2015, 293, 846-851. Ye, X. H.; Yu, F.; Curioni, M.; Lin, Z.; Zhang, H. J.; Zhu, H. W.; Liu, Z.; Zhong, M. L. Corrosion Resistance of Graphene Directly and Locally Grown on Bulk Nickel Substrate by Laser Irradiation. RSC Adv. 2015, 5, 35384-35390. Jeong, N.; Jwa, E.; Kim, C.; Hwang, K. S.; Park, S.; Jang, M. S. Characterization and Anticorrosion Properties of Carbon Nanotubes Directly Synthesized on Ni Foil Using Ethanol. Appl. Sur. Sci. 2016, 376, 199-208. Roy, A.; Kumar, M.K. P.; Srivastava, C. Graphene as a Diffusion Barrier for Isomorphous Systems: Cu–Ni System. Chem. Phys. Lett. 2016, 646, 158-161. Hsieh, Y.-P.; Hofmann, M.; Chang, K.-W.; Jhu, J. G.; Li, Y.Y.; Chen, K. Y.; Yang, C. C.; Chang, W.-S.; Chen, L.-C. Complete Corrosion Inhibition through Graphene Defect Passivation. ACS Nano 2014, 8, 443-448. Zhu, M.; Du, Z.; Yin, Z.; Zhou, W.; Liu, Z.; Tsang, S. H.; Teo, E. H. T. Low-temperature in situ Growth of Graphene on Metallic Substrates and its Application in Anticorrosion. ACS Appl. Mater. Interfaces 2016, 8, 502-510. Nguyen, D. D.; Suzuki, S.; Kato, S.; To, B. D.; Hsu, C. C.; Murata, H.; Rokuta, E.; Tai, N.-H.; Yoshimura, M. Macroscopic, Freestanding, and Tubular Graphene Architectures Fabricated via Thermal Annealing. ACS Nano 2015, 9, 32063214. Nguyen, A. T.; Lai, W.-C.; Tran, V. V; Nguyen, D. D.; Kan, H.-C.; Hsu, C. C. Tubular Graphene Architectures at the Macroscopic Scale: Fabrication and Properties. Adv. Device Mater. 2016. 2, 23-29.

Page 8 of 9

(22) Zhou, F.; Li, Z.; Shenoy, G. J.; Li, L.; Liu, H. Enhanced Room-Temperature Corrosion of Copper in the Presence of graphene. ACS Nano 2013, 7, 6939-6947. (23) Yi, M.; Shen, Z.; Zhao, X.; Liu, L.; Liang, S.; Zhang, X. Exploring Few-layer Graphene and Graphene Oxide as Fillers to Enhance the Oxygen-Atom Corrosion Resistance of Composites. Phys. Chem. Chem. Phys. 2014, 16, 11162-11167. (24) Nine, M. J.; Cole, M. A.; Johnson, L.; Tran, D. N. H.; Losic, D. Robust Superhydrophobic Graphene-based Composite Coatings with Self-cleaning and Corrosion Barrier Properties. ACS Appl. Mater. Interfaces 2015, 7, 28482-28493. (25) Qiu, Z.; Wang, R.; Wu, J.; Zhang, Y.; Qu, Y.; Wu, X. Graphene Oxide as a Corrosion-Inhibitive Coating on Magnesium Alloys. RSC Adv. 2015, 5, 44149-44159. (26) Chen, T.-W.; Hsieh, Y.-P.; Hofmann, M. Ad-layers Enhance Graphene's Performance. RSC Adv. 2015, 5, 93684-93688. (27) Seo,D. H.; Pineda, S.; Fang, J.; Gozukara, Y.; Yick, S.; Bendavid, A.; Lam, S. K. H.; Murdock, A. T.; Murphy, A. B.; Han, Z. J.; Ostrikov, K. Single-step Ambient-air Synthesis of Graphene from Renewable Precursors as Electrochemical Genosensor. Nat. Comm. 2017, DOI: 10.1038/ncomms14217. (28) Graf, D.; Molitor, F.; Ensslin, K.; Stampfer, C.; Jungen, A.; Hierold, C.; Wirtz, L. Spatially Resolved Raman Spectroscopy of Single- and Few-layer Graphene. Nano Lett. 2007, 7, 238-242. (29) Nguyen, D. D.; Tiwari, R. N.; Matsuoka, Y.; Hashimoto, G.; Rokuta, E.; Chen, Y.-Z.; Chueh, Y.-L.; Yoshimura, M. Low Vacuum Annealing of Cellulose Acetate on Nickel towards Transparent Conductive CNT−graphene Hybrid Films. ACS Appl. Mater. Interfaces 2014, 6, 9071-9077. (30) Kirkland, N.T.; Schiller, T.; Medhekar, N.; Birbilis, N. Exploring Graphene as a Corrosion Protection Barrier. Corros. Sci. 2012, 56, 1-4. (31) Huh, J.-H.; Kim, S. H.; Chu, J. H.; Kim, S. Y.; Kim, J. H.; Kwon, S.-Y. Enhancement of Seawater Corrosion Resistance in Copper Using Acetone-derived Graphene Coating. Nanoscale 2014, 6, 4379-4386.

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Layer Control of Tubular Graphene for Corrosion Inhibition of Nickel

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