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thTUNISIAN CRYSTALLOGRAPHIC MEETING –TCM5–
Hammamet / TUNISIA /March 20-24, 2016
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TWO-STEP ELECTROLESS SYNTHESIS OF A COPPER/SILVER COMPOSITE FILM FOR ELECTROCATALYTIC OXIDATION
OF FORMALDEHYDE
Dehchar Charif 1, 2, Kherrat Rochdi 2
1 Research Center in Industrial Technologies (CRTI, ex-CSC), Thin Films and Applications Unit (UDCMA), Setif, Algeria
2 Laboratory of Environmental Engineering, Faculty of Engineering Sciences, Badji Mokhtar
University, Annaba, Algeria E-mail: [email protected]
I. INTRODUCTION
Recently, a number of different types of modified electrodes made from noble metal composites have emerged among various research groups and employed in several applications like sensors, electrolysis, medical and analytical devices, etc. This interest is due to their enhanced physicochemical properties, high efficiency, long-time stability and also to their effective catalytic ability for various electrochemical reactions [1-3].
In this study, we report a two-step electroless plating process for preparing a copper/silver composite film on a Resin Epoxy (RE) substrate. The electrochemical reactivity of the prepared copper/silver composites was investigated towards the electrochemical oxidation of formaldehyde. The electrochemical measurements were performed in 0.01 M, pH 7.0 phosphate buffer as supporting electrolyte using cyclic voltammetry technique. Scanning electron microscopy of the composites showed a porous microstructure with uniform surface morphology. The presence of silver and copper onto the RE surface was confirmed by energy dispersive X-ray analysis. The formaldehyde oxidation peak on the copper/silver electrode is obtained at -0.3 V/SCE. The electrode showed a significant electrocatalytic activity with good repeatability and stable electrochemical response.
2 II. EXPERIMENTAL
II.1. Chemicals
All reagents used were of analytical grade. Distilled water was used as solvent for preparing all solutions throughout this study. Silver nitrate and copper sulphate were purchased from Prolabo and were used as metal source for the electroless synthesis of silver and copper films, respectively. Other chemicals were from Sigma-Aldrich.
II.2. Apparatus and materials
All experiments were carried out at ambient temperature. Silver (Ag) film and copper/silver (Cu/Ag) composite film were synthesized by chemical bath deposition method. The morphology of films were investigated using a JEOL JSM 6830 scanning electron microscope with accelerating voltage of 25 kV coupled with energy dispersive X-ray elemental analysis (EDX).
The electrochemical reactivity of the prepared composites was investigated in 0.01 M, pH 7.0 phosphate buffer using a Voltalab PGZ 301 potentiostat-galvanostat. A standard electrochemical cell was employed: a platinum (Pt) wire and a saturated calomel electrode were used as counter and reference electrode, respectively. The working electrode was the prepared Ag/RE and Cu/Ag/RE modified electrodes with the dimensions of 1 × 2 cm2.
III. RESULTS AND DISCUSSION
III.1. Deposition of silver film
Before we proceed with the deposition of silver film, RE substrate was first cleaned thoroughly using 55 % NaOH solution and then distilled water. Secondly, the cleaned substrate was sensitized in a stannous chloride solution for 5 min, and then rinsed by distilled water. Finally, sensitized substrate was immersed for 10 min into silvering bath previously prepared by dissolving silver nitrate into ammonia solution.
Once the silver films have been deposited, the coated-RE substrate was removed from the solution, well rinsed by distilled water and dried.
Fig 1 shows a SEM pattern of silver film prepared by this method. The obtained Ag film presents a homogeneous and porous morphology. This morphology was widely found in literature and is suitable to support another film to form composite material. The EDX spectrum confirms the deposition of silver film.
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Fig 1. Silver film deposited on RE substrate. (a) SEM image. (b) EDX spectrum of the corresponding film.
III.2. Deposition of copper film
After the deposition of silver film, copper was deposited from a separate electrolyte solution containing: 35 g copper sulphate, 50 g sodium hydroxide, 25 g sodium carbonate, and 20 g EDTA. This solution was heated up to the boiling point (95 °C); this temperature has been maintained all through the deposition process. Formaldehyde at 37 % was added to the solution and was used as reducing agent of copper ions.
Copper film was deposited by the reduction of copper ions (Cu2+) on the silver film. Such reduction occurs according to the following equation:
Cu2+ + 2 e- = Cu
Fig 2a shows the SEM image of the resulting copper/silver composite film. It is possible to observe a change in the coating morphology coming from the deposition of copper film. This film is preferentially composed of aggregates of average size about 1 µm.
The obtained film was evaluated by EDX analysis. Fig 2b shows the result of this analysis.
Only the copper element has been detected, this indicates that copper was homogeneously covered all through the silver film and copied its morphology.
a b
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Fig 2. Copper film deposited on Ag/RE electrode. (a) SEM image. (b) EDX spectrum of the corresponding film.
III.3. Electrochemical behavior of Cu/Ag composites
The electrocatalytic activity of copper/silver composites was evaluated by cyclic voltammetry technique for formaldehyde oxidation.
Fig 3 represents cyclic voltammogram recorded for the copper/silver modified electrode in 0.01 M, pH 7.0 phosphate buffer solution in presence and absence of formaldehyde. In the absence of formaldehyde no obvious redox activity is observed during positive scan over most of the potential range, while in the presence of formaldehyde, an increase in current density is observed on about -0.3 V. This peak is attributed to the oxidation of formaldehyde. During the sweep return, the cathodic waves which appeared on about -0.6 and -1 V are matched well with the electrolyte and proton reduction, respectively.
-1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6
-6 -4 -2 0 2 4
0 µL 100 µL
Current density /mA cm-2
Potential /V vs SCE
Fig 3. Cyclic voltammogram of copper/silver electrode recorded in 0.01 M PBS in presence and absence of formaldehyde.
a b
5 The ability of the composite film to oxidize formaldehyde was evaluated by varying the concentration of this analyte. The electrode response towards the successive additions of formaldehyde is shown in Fig 4.
-1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6
-6 -4 -2 0 2 4
100 µL 150 µL 200 µL 250 µL 300 µL 350 µL
Current density /mA cm-2
Potential /V vs SCE
Fig 4. Cyclic voltammograms of copper/silver electrode recorded in 0.01 M PBS in the presence of different concentrations of formaldehyde.
According to the curves, it can be seen that oxidation current peaks are observed at the same potential (around -0.3 V). However the current densities increase by increasing the concentration of formaldehyde. This reveals that the prepared electrode has a significant catalytic activity towards the electrochemical oxidation of formaldehyde. This activity is at first view due to the high surface area of the deposited copper film.
CONCLUSION
Composite material based on copper/silver films was prepared at room temperature by chemical reduction of metal precursor and reducing agent from two-separated solutions. It was found that the pre-deposition of silver film, characterized by a porous microstructure, provides an efficient route for deposition of copper film.
Electrochemical measurements clearly demonstrated that this procedure allows preparation of catalysts for the electrochemical oxidation of formaldehyde.
REFERENCES
1. Seungmin Yoo, Jung-In Lee, Seunghee Ko, and Soojin Park. Nano Energy (2013) 2, 1271–
1278
2. Zhiqiang Li, Xing Lu, Boqiong Li, Lu Bai, and Qi Wang. ECS Electrochemistry Letters, (2015) 4 (6) H24-H27
3. Dan-Ling Zhou, Qian-Li Zhang, Zhang-Ying Lv, Wan-Yi Chen, Xiang-Feng Liu, Ya-Hui Lu, Ai-Jun Wang and Jiu-Ju Feng. Microchim Acta (2013) 180:1495–1500
