- Nano Express
- Open Access
Fabrication and Characterization of New Composite Tio2 Carbon Nanofiber Anodic Catalyst Support for Direct Methanol Fuel Cell via Electrospinning Method
© The Author(s). 2017
- Received: 26 July 2017
- Accepted: 17 November 2017
- Published: 6 December 2017
Platinum (Pt) is the common catalyst used in a direct methanol fuel cell (DMFC). However, Pt can lead towards catalyst poisoning by carbonaceous species, thus reduces the performance of DMFC. Thus, this study focuses on the fabrication of a new composite TiO2 carbon nanofiber anodic catalyst support for direct methanol fuel cells (DMFCs) via electrospinning technique. The distance between the tip and the collector (DTC) and the flow rate were examined as influencing parameters in the electrospinning technique. To ensure that the best catalytic material is fabricated, the nanofiber underwent several characterizations and electrochemical tests, including FTIR, XRD, FESEM, TEM, and cyclic voltammetry. The results show that D18, fabricated with a flow rate of 0.1 mLhr−1 and DTC of 18 cm, is an ultrafine nanofiber with the smallest average diameter, 136.73 ± 39.56 nm. It presented the highest catalyst activity and electrochemical active surface area value as 274.72 mAmg−1 and 226.75m2 g−1 PtRu, respectively, compared with the other samples.
- Carbon nanofiber
- Direct methanol fuel cell (DMFC)
- Catalyst support
Direct methanol fuel cell (DMFC) is one of the future renewable power-generating systems and very environmentally friendly. The system generates electrical energy using a liquid fuel (methanol) directly without any additional devices or combustion processes. The advantages of DMFCs are their simplicity, high specific energy, low operating temperature, and easy start-up with instant refueling . However, DMFC systems still suffer from several limitations, such as catalyst poisoning and slow reaction kinetics, which lead to the system having low performance and power output . Both of these limitations are due to the catalyst and material used in this system.
Platinum (Pt) is the common catalyst used in DMFC. However, Pt can lead towards catalyst poisoning by carbonaceous species, thus reduces the performance of DMFC. Later, platinum-ruthenium (PtRu) is introduced to increase the reaction rate, but the kinetic parameter of the catalyst is still the one of a major problem in DMFC. Therefore, the alteration towards this bimetallic catalyst starts to get placed in the field of DMFC catalyst. One of the most attractive approaches among researcher is introducing the metal oxide and nanomaterials as the side-catalyst component. Titanium dioxide (TiO2) is a metal oxide that is gaining a lot of attention from research developer. TiO2 has various beneficial properties, which is non-toxic, non-flammable, and highly resistant to corrosion , can increase the electrochemical and thermal stability , and affect the electronic properties and bifunctional mechanism of composite catalysts . Ito et al.  developed PtRu/TiO2-embedded carbon nanofiber (CNF) (PtRu/TECNF), and Ercelik et al.  presented the PtRu/C-TiO2 as an electrocatalyst in DMFC application, and the result shows that the performance of this new composite electrocatalyst is higher than PtRu catalyst.
Nanomaterial is one of the nanotechnologies that fascinated in a wide range of application including energy conversion. There are numerous types of nanomaterials in the energy conversion field, which are nanofibers, nanotubes, nanowires, nanorods, and others. This material becomes the main attraction in energy material research because of the dimensional reduction to the nanometer scale that can affect many elementary steps, including charge transfer and molecular rearrangement, as well as the surface properties to provide high interfacial volume fractions and enhanced reaction rates . This study focuses on nanofiber structures for both materials, TiO2 metal oxide and carbon. This is due to the special properties of nanofibers that can provide high surface/volume and aspect ratios , high electrical conductivity, good mechanical strength, and uniform dispersion of catalyst, which can increase the electrocatalytic activity .
This process has several parameters that can be tuned in order to obtain the optimal nanofiber structures, either for diameter or surface morphology, and the influencing parameters are different for each material. The parameters can be divided into three main categories: solution, ambient, and process parameters. This study is focused on process parameters, and solution flow rate and distance between the needle tip and the collector (DTC) were chosen as the main influencing parameters to obtain the smallest diameter. This is due to the small amount of research focused on these parameters , even though they have been considered as main variables for obtaining ultrafine nanofibers [15–18].
Thus, this study presents the composite TiO2 carbon nanofiber as catalyst support on the anode electrode. This combination of the composite is expected to increase the electrocatalytic activity and lowering the catalyst poisoning in order to boost the overall performance of DMFC. The main objectives of this study are to fabricate the smallest possible of nanofiber diameter to increase the surface area and provide more active spot for catalytic reaction and enhance the DMFC performance. The fabrication of nanofibers involves several steps, including sol-gel, electrospinning, stabilization, and carbonization processes. To obtain the smallest diameter nanofibers, the electrospinning parameters of flow rate and DTC are taken as the main variables in this study. The prepared nanofibers are characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (FESEM). All the catalyst supports with different electrospinning parameter are deposited on PtRu (PtRu/TiO2-CNF) and evaluated by electrochemical active surface area (ECSA) analysis and cyclic voltammetry (CV) to evaluate the performance and determine their potential as catalyst supports in DMFCs. The experimental results show the effect of the electrospinning parameters on the nanofiber diameter, as well as their potential in DMFC applications.
Poly(vinyl acetate) (PVAc, Mw = 500,000), dimethylformamide (DMF, 99.8%), titanium isopropoxide (TiPP, 97% content), acetic acid (99.7%), and Ru precursor (45–55% content) were obtained from Sigma-Aldrich Co., Ltd., while Pt precursor (40% content) and ethanol (99.8%) was received from Merck, Germany and R&M Chemical Reagents, respectively. All chemicals were used without any further purification. The main apparatus, electrospinning machine, is branded with Nfiber N1000, Progene Link Sdn. Bhd., and ultrasonic cell crusher INS-650Y is from INS Equipments Trading Co., Ltd., China.
Preparation of TiO2-CNF Nanofibers
The sol-gel method begins with the preparation of a polymer solution, where PVAc (11.5 wt%), as the carbon source, was dissolved in the solvent, DMF. The polymer solution was stirred at 60 °C for 1 h and then stirred overnight at room temperature. The TiO2 precursor, TiPP, and polymer solution were mixed in a 1:1 ratio, and a small amount of acetic acid and ethanol was added to the polymer solution. The mixture was homogenized by an ultrasonic cell crusher for 60 s. Then, the solution was transferred to a syringe for injection in a nanofiber electrospinning unit. The applied voltage was 16 kV, while the flow rate and DTC were manipulated in the range of 0.1–0.9 mLh−1 and 14–18 cm. The flow rate was set at 0.1, 0.5, and 0.9 mLh−1, denoted F0.1, F0.5 and F0.9, respectively. The samples with DTC values of 14, 16, and 18 cm are denoted D14, D16, and D18, respectively. The fabricated nanofiber was rested for 5 h at room temperature before being stabilized for 8 h at 130 °C. The stabilized nanofiber was carbonized at 600 °C for 2 h under a nitrogen atmosphere using a tube furnace and then crushed by mortar and pestle for 5 min before further use in this study. The mass loading for all samples is the same, which is 6.67 mgs−1.
Deposition of Catalyst
The TiO2-CNF nanofibers were added into a mixture of isopropyl alcohol (IPA) and deionized water (DI water) and sonicated in an ultrasonic bath for 20 min. The precursor of the platinum and ruthenium catalyst (20 wt% with 1:1 ratio) was mixed into the solution and stirred for 20 min. Then, the pH of the mixed solution was adjusted with NaOH solution until reaching pH 8. The temperature was raised to 80 °C, and 25 ml of 0.2 M NaBH4 was added dropwise into the mixed solution. The solution was stirred for another 1 h. The mixture was then cooled, filtered, and washed repeatedly. The catalyst powder was dried at 120 °C for 3 h and finally crushed using a mortar and pestle to obtain a fine catalyst powder that was ready for use in the performance tests.
Characterization of the Catalyst
The chemical compound in the catalyst support was identified using Fourier transform infrared spectroscopy (FTIR, PerkinElmer), and X-ray diffraction (XRD, D8 Advance/Bruker AXS, Germany) was used to analyze the pattern and crystal structure of the samples. The morphology and size distribution of the samples were analyzed by field emission scanning electron microscopy (FESEM, SUPRA 55VP). Transmission electron microscopy (TEM, Tecnai G2 F20 X-Twin) was used to observe the detailed structure and elemental distribution of the nanofibers.
Evaluation of the Electrochemical Measurement
The performance was measured for all catalysts fabricated with different parameters. The PtRu catalyst was deposited on the TiO2-CNF catalyst support for evaluation by electrochemical measurements. These measurements were obtained using a three-electrode cell system, which uses cyclic voltammetry (CV) to examine the catalyst activity in the methanol oxidation reaction (MOR) using an Autolab electrochemical workstation. The three-electrode cell system was operated at room temperature and involved a Pt, silver/silver chloride (Ag/AgCl), and glassy carbon electrode (GCE, 3 mm diameter) as the counter, reference, and working electrode. Before starting the measurement, the GCE was cleaned with alumina and polishing paper, tracing a rounded pattern resembling the number “eight,” several times. Then, the GCE was rinsed with DI water and sonicated for 30 s before use. The catalyst ink for the GCE was prepared by dispersing 15 mg of catalyst into a mixture of 400 μl DI water, 400 μl IPA, and 125 μl Nafion solution (5 wt%) for 30 min. Then, 2.5 μl of catalyst ink was coated onto the GCE using a micropipette and dried for 1 h at room temperature before being heated at 80 °C for another 30 min. The electrolyte was a solution of 0.5 M H2SO4 in 2 M methanol, and it was bubbled for 20 min with nitrogen gas to remove any oxygen. The CV measurement was performed over a potential range of − 0.1–1.1 V vs. Ag/AgCl at a scan rate of 50 mVs−1.
Effect of Flow Rate
The diameter size distribution of nanofiber for all the sample with different flow rate
Flow rate (mlhr−1)
Mean diameter, da (nm)
Std. deviation, σ (± nm)
Effect of the Distance Between the Tip and Collector
The diameter size distribution of nanofiber for all the sample with different DTC
Flow rate (mlhr−1)
Mean diameter, da (nm)
Std. deviation, σ (± nm)
The smallest mean diameter was 136.73 ± 39.56 nm (90–170 nm), belonging to D18, followed by D16 and D14 with diameters of 161.18 ± 26.08 and 189.96 ± 49.87 nm, respectively. The longer the tip-collector distances, the smaller the nanofiber diameter. This behavior is due to the deposition time and whipping instability interval during the electrospinning process. The longer distance supplies a longer deposition time, and during that period, the whipping instability phenomenon occurs, also known as the thinning and splitting mechanism. This phenomenon occurs due to interactions between charged ions and the electric field . When the electrical force applied to the nozzle tip reaches a critical value, the highly charged density and viscoelastic force split the jets into smaller jets, creating a bending, winding, and spiraling path towards the collector. When the DTC is longer, jet splitting repeatedly occurs, resulting in ultrafine and smaller diameter fibers. Therefore, the smallest diameter belongs to sample D18 with a flow rate of 0.1 mLh−1 and DTC of 18.
Comparison of the nanofiber diameter with the previous study
Type of nanofiber
Diameter of nanofiber (nm)
Flow rate (mLhr−1)
136.73 ± 39.56
Garcia-Gomez et al. 
Li et al. 
192 ± 69
Mehrpouya et al. 
Mondal et al. 
Electrochemical Characterization of the Methanol Oxidation Reaction
Diameter of nanofiber from FESEM and crystallite size of particle in catalyst from XRD data
Average diameter of nanofiber from FESEM
Crystallite size (nm)
Summary of the peak potential, current density, CO tolerance, and ECSA results for the catalyst with the different electrospinning parameter
ECSA, (m2g−1 PtRu)
Peak potential, (V vs. Ag/AgCl)
Onset potential, (V vs. Ag/AgCl)
Peak current density, (mAmg−1 PtRu)
CO tolerance, If/Ib ratio
The reverse scan in the CV curve shows a small oxidation peak at a potential of approximately 0.49–0.55 V vs. Ag/AgCl. This second oxidation peak appeared due to the incomplete removal of oxidized carbonaceous species in the forward scan . However, the ratio between the forward (If) and reversed (Ib) oxidation peak for PtRu/TiO2-CNF (D18) exceeded 3.8, which means that the electrocatalyst has high tolerance towards carbonaceous species, reducing the potential for catalyst poisoning. This result shows that the combination of metal oxide and carbon nanofibers has a good potential for use in fuel cell applications.
TiO2-CNF nanofibers can be fabricated via electrospinning, which is the main technique, and several other methods. The nanofibers are influenced by the flow rate and the DTC, which were examined as electrospinning process parameters, with three different samples for each parameter, denoted F0.1, F0.5, F0.9, D14, D16, and D18. The results showed that the TiO2-CNF (D18) sample produced the smallest average diameter of 136.73 ± 39.56 nm. TiO2-CNF was mixed with PtRu to form the composite catalyst, and its CV performance was examined. The current density of the PtRu/TiO2-CNF (D18) sample is 1.4 times higher than that of PtRu/TiO2-CNF (D14), while the ECSA of PtRu/TiO2-CNF (D18) is 10 times higher than that of the other samples. Thus, the flow rate and DTC highly affect the diameter, morphology, and performance of the nanofibers. The nanofiber performance increased with decreasing nanofiber diameter, which shows the capability of the composite nanofiber catalyst to be an upcoming anode catalyst for DMFCs.
The authors gratefully acknowledge the financial support given for this work by the Ministry of Higher Education (MOHE)-MALAYSIA under GSP/1/2015/TK01/UKM/01/1 and Universiti Kebangsaan Malaysia under DIP-2017-021.
Ministry of Higher Education (MOHE)- MALAYSIA: GSP/1/2015/TK01/UKM/01/1.
Universiti Kebangsaan Malaysia: DIP-2017-021.
All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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