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Electrochemistry Communications 6 (2004) 1029–1031

Nickel-coated carbon nanofibers prepared by electroless deposition

Susumu Arai a,*, Morinobu Endo b, Shinji Hashizume c, Yasuho Shimojima c

a Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University, 4-17-1 Wakasato,

Nagano-shi, Nagano 380-8553, Japanb Department of Electrical and Electronic Engineering, Faculty of Engineering, Shinshu University, 4-17-1 Wakasato,

Nagano-shi, Nagano 380-8553, Japanc Tsukada Riken Industry Co. Ltd., 16397-5 Akaho, Komagane-shi, Nagano 399-4117, Japan

Received 31 July 2004; accepted 3 August 2004

Available online 27 August 2004

Abstract

Nickel-coated carbon nanofibers have been prepared by an electroless deposition process. The carbon nanofibers were pre-trea-

ted prior to the nickel electroless deposition. Polyacrylic acid was used to disperse carbon nanofibers in the pre-treatment solutions.

The carbon nanofibers were coated homogeneously with nickel by the electroless deposition process using an electroplating bath

containing sodium hypophosphite as a reducing agent. The process resulted in a powdery-nickel-coated carbon nanofiber material.

� 2004 Elsevier B.V. All rights reserved.

Keywords: Carbon nanofibers; Nickel; Composite; Electroless deposition; Powder; Polyacrylic acid

1. Introduction

Carbon nanotubes and nanofibers [1,2] have excellent

mechanical characteristics, including high tensile

strength and high elastic modulus, as well as high ther-

mal and electrical conductivities. Research for practical

applications of carbon nanotubes and nanofibers has

been actively pursued recently. In particular, metal com-posites incorporating these nanosized materials show

promise as new materials offering improved and unique

functionality. Powder carbon nanofiber–metal compos-

ites represent promising raw materials for powder metal-

lurgical processing, including powder rolling, powder

flame spraying, and powder forging.

We have earlier reported that copper–carbon nanofi-

ber composite powder with a sea urchin shape was ob-tained using an electrodeposition method [3,4]. Also,

1388-2481/$ - see front matter � 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.elecom.2004.08.001

* Corresponding author. Tel.: +81 026 269 5413; fax: +81 026 269

5432.

E-mail address: araisun@gipwc.shinshu-u.ac.jp (S. Arai).

nickel–carbon nanofiber composite powder with a skew-

ered dumpling shape was obtained using an electrodep-

osition method [5]. It is generally known that electroless

depositon method is a very useful technique for the for-

mation of metal-covered minute particles [6]. In the pre-

sent study, we have examined the electroless plating

technique to fabricate powdery nickel-coated carbon

nanofibers.

2. Experimental

The carbon nanofibers used are commercially availa-

ble carbon nanofibers (Showa Denko Co. Ltd.) which

corresponds to the multi-walled carbon nanotubes.

These are vapor-grown carbon nanofibers (VGCFs) ob-tained via catalyst assisted CVD [7], and heat treated at

2800 �C in Ar for 30 min. The carbon nanofibers were

typically 100–200 nm in diameter and 10–20 lm in

length. Prior to electroless plating, the VGCFs needed

to be pre-treated. As the VGCFs were not hydrophilic

and did not disperse homogeneously into the pre-treated

Table 1

Composition of the electroless nickel plating bath

Reagent Concentration (mol dm�3)

NiSO4 Æ 6H2O 0.08

NaPH2O2 Æ H2O 0.2

C6H5Na3O7 Æ 2H2O 0.08

1030 S. Arai et al. / Electrochemistry Communications 6 (2004) 1029–1031

solutions, first the VGCFs were made hydrophilic. We

have earlier reported that polyacrylic acid was very

effective to make the VGCFs hydrophilic and disperse

them into aqueous solutions [3–5]. To make the VGCFs

hydrophilic, 0.2 g dm�3 VGCFs were placed in a

2 · 10�5 mol dm�3 polyacrylic acid solution and sub-jected to stirring and ultrasonic irradiation. The VGCFs

were dispersed homogeneously into the solution. The

VGCFs were then filtered using a paper filter and rinsed

with pure water. They were then put in a 4.4 · 10�2

mol dm�3 SnCl2 Æ 2H2O + 0.12 mol dm�3 HCl solution

for 5 min at 25 �C under ultrasonic irradiation to adsorb

Sn2+ ions on the VGCFs. After the filtration and rins-

ing, the VGCFs were placed in a 5.6 · 10�4 mol dm�3

PdCl2 + 0.12 mol dm�3 HCl solution for 5 min at 25

�C under ultrasonic irradiation to form palladium cata-

lytic nuclei on the VGCFs. After filtration and rinsing,

the VGCFs were placed in a nickel electroless plating

bath. The composition of the nickel electroless plating

bath is shown in Table 1 and it contains sodium hypo-

phosphite and sodium citrate as a reducing agent and

a complexing agent of nickel, respectively. The pH ofthe bath was adjusted to nine by the addition of NH3

solution. Electroless plating was performed for 15 min

at 35 �C under ultrasonic treatment. After filtration

and rinsing, electroless plated VGCFs were dried for

60 min at 90 �C. The material deposited by the electro-

Fig. 1. SEM images of (a) raw VGCFs and (b) nickel-coated VGCFs obtain

(b) are shown in (c) and (d), respectively.

less process was then examined using field-emission

scanning electron microscope (FE-SEM: Hitachi S-

4100 and Hitachi S-5200). The composition of the

deposited material on the VGCFs was analyzed using

an electron probe X-ray microanalyzer (EPMA: Shi-

mazu Seisakusho EPMA-1610).

3. Results and discussion

The raw VGCFs were black and powdery. After the

electroless nickel plating, the color of the VGCFs chan-

ged to gray and it remained powdery. Fig. 1 shows SEM

micrographs of the raw VGCFs ((a), (c)) and the electro-

less nickel-plated VGCFs ((b), (d)). Nickel was depos-

ited on all the VGCFs homogeneously, resulting innickel-coated VGCF powder, as shown in Fig. 1(b).

The thickness of the nickel coating was about 25–50

ed by electroless deposition. Enlarged images corresponding to (a) and

Fig. 2. EPMA compositional mapping image. (a) SEM image of nickel-coated VGCFs obtained by electroless deposition. (b) Distribution of

phosphorus in the same area as (a).

S. Arai et al. / Electrochemistry Communications 6 (2004) 1029–1031 1031

nm and the morphology of the nickel coating was not

smooth, as seen in Fig. 1(d).

EPMA qualitative analysis showed that phosphorus,

about 2–3 wt%, was present in the nickel coatings on theVGCFs. It is well known that phosphorus is involved in

the electroless nickel plating film when a electroless plat-

ing bath containing sodium hypophosphite as a reducing

agent is used [8]. It has been reported that the content of

phosphorus in the electroless nickel plating film varies

from 1 to 14 wt% depending on the conditions such as

the pH of the bath and a nickel plating with lower phos-

phorus content (1–4 wt%) is obtained from an ammoniaalkaline electroless nickel plating bath [9], as used in the

present study. Thus, the phosphorus content in the elec-

troless nickel film on the VGCFs nearly corresponds to

the previously reported value. Fig. 2 shows the results of

the EPMA mapping analysis of nickel-coated VGCFs.

Fig. 2(a) shows the SEM micrograph of nickel-coated

VGCFs and Fig. 2(b) shows the distribution of phos-

phorus in the same area as in Fig. 2(a). Phosphoruswas clearly distributed homogeneously in the nickel

films on the VGCFs. Therefore, it can be asserted that

VGCFs coated with a Ni–P alloy film can be fabricated

by the electroless deposition process, as demonstrated in

the present study.

4. Conclusions

Nickel-coated VGCF powder was successfully fabri-

cated using the electroless plating process. Polyacrylic

acid was used to disperse VGCFs in the pre-treatment

solutions. Nickel was deposited homogeneously on the

VGCFs, resulting in nickel-coated VGCF powder. The

nickel deposit contained 2–3 wt% phosphorus. Since

the VGCFs possess excellent characteristics, such as ahigh elastic modulus and high thermal conductivity, in

combination with nickel, which also has good character-

istics such as magnetic properties, the nickel-coated

VGCF powder obtained in the present study is expected

to be a promising raw material for various composite

materials.

Acknowledgements

This research was supported by the CLUSTER of the

Ministry of Education, Culture, Sports, Science and

Technology, Japan.

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