Electrochemical QCM Study of the Synthesis Process of Cobalt Nanoparticles via Electroless Deposition

2011

Self Cite

Nickel nanowires were synthesized via electroless deposition in an organic solvent (ethylene glycol) under a magnetic field. Deposition behavior of nickel particles and wires were electrochemically investigated at various concentrations of NaOH by an in-situ mixed potential measurement and voltammetry combined with quartz crystal microbalance. Based on the electrochemical investigation, a formation mechanism of nickel wires is proposed. According to the mechanism, nickel wires 100-370 nm in diameter with several dozen m of length were successfully prepared by controlling the reduction rate by varying a concentration of sodium hydroxide, trisodium citrate, and a nucleating agent, chloroplatinic acid.Nanowires of iron group metals (Fe, Co, Ni) and their alloys are attractive materials due to their magnetic properties. 1,2 Numerous synthesis methods of iron group nanowires have been reported. [3][4][5][6][7][8] In their methods, nanowires are formed by electrodeposition using templates such as anodized aluminum oxide 3-5 and polycarbonate membrane. 6-8 The methods with templates have notable advantages that highly-ordered and size-controlled nanowires can be obtained. The template methods, however, require several steps including fabrication and removal of templates in order to obtain bare nanowires. On the other hand, a self-assemble electroless deposition of ferromagnetic nanowires under a magnetic field is a relatively simple synthesis method without any templates. 9 In addition, electroless deposition is a powerful fabrication method with a wide variety of compositions and sizes in a large-scale 10,11 and thus, electroless deposition is suitable for a practical application.We have reported some studies of electrochemical approaches with in-situ mixed potential observation for the synthesis processes of copper, 12,13 cobalt, 14,15 nickel, 16 and Co-Ni alloy 17 nanoparticles, which is effective in thermodynamic oxidation-state control and analysis of the formation process of nanowires as well as nanoparticles. In the present work, the formation process of nickel nanowires via electroless deposition under a magnetic field was electrochemically investigated. In order to control the morphology of nickel deposits, the deposition behavior of nickel was studied by an in-situ mixed potential measurement; it is possible that the reduction rate of Ni(II) species affects the morphology of nickel deposits. Furthermore, the reduction rate and reduction potential of Ni(II) species were investigated by voltammetry combined with quartz crystal microbalance (QCM) as well as the oxidation rate and oxidation potential of hydrazine as a counterpart reaction. ExperimentalThe reaction solutions were prepared using nickel chloride hexahydrate (NiCl 2 Á 6H 2 O) as a source of Ni(II) ions, ethylene glycol (EG) as a solvent, and hydrazine monohydrate (N 2 H 4 Á H 2 O) as a reducing agent. Sodium hydroxide (NaOH) was added as a source of OH À ions. Trisodium citrate dihydrate (Na 3 C 6 H 5 O 7 Á 2H 2 O) and chloroplatinic acid hexahydrate ...

mentioning

confidence: 99%

Formation of Nickel Nanowires via Electroless Deposition Under a Magnetic Field

Kawamori

2011

Self Cite

“…where Co(II) represents all Co(II) species in the solution, e.g., Co 2þ , Co(OH) 2 , Co(OH) 3 , Co(OH) 4 2 , and Co(C 3 H 6 O 2 ). 25 The above reactions can be separated to cathodic (Co deposition) and anodic partial reactions (N 2 H 4 oxidation) that occur concurrently in the solution. 26 There are other cathodic partial reactions, i.e., Pt deposition and H 2 generation due to the reductive decomposition of PG.…”

Section: Discussionmentioning

confidence: 99%

“…5a, the cathodic current starts to flow when the potential is decreased below about À0.54 V vs Ag/AgCl. The measured cathodic current in a typical voltammogram is mainly a sum of the currents from all the reduction reactions, 25 i.e., Co deposition and H 2 generation due to reductive decomposition of PG. However, the onset of Co deposition observed at about À0.54 V falls within the electroinactive range of a PG solution with 0.22 M NaOH.…”

Section: Discussionmentioning

confidence: 99%

Fabrication of Cobalt Nanowires by Electroless Deposition under External Magnetic Field

Balela

2011

Self Cite

Metallic Co nanowires with a mean diameter of about 190 nm and lengths up to 160 mm are prepared by electroless deposition (solution reduction) in propylene glycol at room temperature under external magnetic field. Co deposition behavior in propylene glycol is investigated by in situ monitoring of mixed potentials in conjunction with linear sweep voltammetry and the oxidationreduction potential of the Co(II)/Co redox pair is determined to be about À0.54 V vs Ag/AgCl. When the mixed potential drops below the oxidation-reduction potential of the Co(II)/Co redox pair, small Co nanoparticles are generated in the solution and are magnetized in the presence of external magnetic field. Strong attractive dipolar interactions are induced along the magnetic field direction, which results in the assembly of Co nanoparticles to nanowires. The Co nanowires exhibit ferromagnetic properties at room temperature, with an enhanced coercivity of about 700 Oe possibly due to shape anisotropy.

“…We have extensively studied the fabrication of metallic nanoparticles such as copper, 11,12 cobalt, 13,14 nickel, 15 and Co-Ni alloy 16 by the electroless deposition method and also developed the monitoring method of the reaction process by adopting a concept of a mixed potential which is a good indicator of a reduction ability in solution. Recently, we have succeeded in a fabrication of nickel nanowires by applying this method of nanoparticles and also proposed the formation mechanism of nanowires.…”

mentioning

confidence: 99%

Iron Alloying Effect on Formation of Cobalt Nanoparticles and Nanowires via Electroless Deposition under a Magnetic Field

Kawamori

2013

Self Cite

Co-Ni nanowires 40-100 nm in diameter with several dozen μm of length were prepared via electroless deposition under a magnetic field. The formation of Co-Ni nanowires was investigated by an in-situ mixed potential measurement and a cyclic voltammetry combined with a quartz crystal microbalance electrode. These electrochemical measurements revealed that the deposition rate of nickel on nickel is lower than that of cobalt on cobalt. Nickel works as an inhibitor in a growth process of Co-Ni alloys. Thus, the thickness of Co-Ni alloy nanowires is drastically reduced by the addition of Ni(II) in solution. The morphology of Co-Ni nanowires is also strongly affected by the magnetization of Co-Ni alloy nanoparticles which are precursors in the formation of nanowires. Both the magnetization and the deposition rate in Co-Ni alloys are the key parameters to control the aspect ratio and surface morphology of nanowires.