Open Access

Influence of the nanofibrous morphology on the catalytic activity of NiO nanostructures: an effective impact toward methanol electrooxidation

Nanoscale Research Letters20138:402

DOI: 10.1186/1556-276X-8-402

Received: 7 September 2013

Accepted: 23 September 2013

Published: 28 September 2013


In this study, the influence of the morphology on the electrocatalytic activity of nickel oxide nanostructures toward methanol oxidation is investigated. Two nanostructures were utilized: nanoparticles and nanofibers. NiO nanofibers have been synthesized by using the electrospinning technique. Briefly, electrospun nanofiber mats composed of polyvinylpyrolidine and nickel acetate were calcined at 700°C for 1 h. Interestingly, compared to nanoparticles, the nanofibrous morphology strongly enhanced the electrocatalytic performance. The corresponding current densities for the NiO nanofibers and nanoparticles were 25 and 6 mA/cm2, respectively. Moreover, the optimum methanol concentration increased to 1 M in case of the nanofibrous morphology while it was 0.1 M for the NiO nanoparticles. Actually, the one-dimensional feature of the nanofibrous morphology facilitates electrons' motion which enhances the electrocatalytic activity. Overall, this study emphasizes the distinct positive impact of the nanofibrous morphology on the electrocatalytic activity which will open a new avenue for modification of the electrocatalysts.


Methanol electrooxidation NiO nanofibers Electrospinning Direct methanol fuel cells


In the last decades, nanostructural materials have been intensively investigated because of their high surface area which strongly affects their physicochemical characteristics. Of the reported nanostructures shapes, special attention has been paid to the one-dimensional forms such as nanorods, nanowires, and nanofibers. This is due to their potential applications in nanodevices [13]. Nanofibers (NFs) received special consideration due to their high axial ratio, good mechanical properties, and easy manageability. Compared to nanoparticles (NPs), nanofibers have small surface area which might have a negative impact upon using them as catalyst in the chemical reactions. However, it was reported that the axial ratio distinctly enhances the catalytic performance, especially in case of electrons' transfer-based processes. For instance, in the photocatalysis, the nanofibrous morphology strongly modifies the performance [35].

Direct methanol fuel cells (DMFCs) received much attention during the last decade because methanol is an inexpensive, readily available, and easily stored and transported liquid fuel [6]. DMFCs do not have the fuel storage problem because methanol has a higher energy density than hydrogen - though less than gasoline or diesel fuel. Methanol is also easier to supply to the public using our current infrastructure. In the DMFCs, methanol is directly oxidized to carbon dioxide and water, providing a new way to store and convey the energy [79]. The electrocatalysts are the backbone not only of the DMFCs but also of any kind of fuel cells. The successful commercialization is quite dependent on the cost, activity, and durability of the electrocatalysts [9, 10]. At present, almost all pre-commercial low-temperature fuel cells use Pt-based electrocatalysts [1114]. Accordingly, the manufacturing cost is relatively high which constrains wide applications. Moreover, the catalyst poisoning by CO or CHO species is another real problem facing most of the Pt-based electrocatalysts [9, 15, 16].

To develop new non-precious electrocatalysts, most of the researchers focus only on modifying the composition and ignore the morphology impact. Therefore, many transition metal NPs were introduced as alternative non-precious electrocatalysts to replace the Pt-based materials. However, those NPs suffer from low chemical stability which keeps non-stop research activities to improve the performance as well as the stability.

Compared to metals, it is known that metal oxides have higher chemical stabilities in various media. Accordingly, metal oxides are good candidates as electrocatalysts if the performance could be improved. Recently, NiO nanoparticles deposited on carbon nanotubes showed good behavior toward methanol electrooxidation [17]. In this study, the electrocatalytic activity of NiO toward methanol oxidation could be improved by modification of its nanomorphology. Interestingly, compared to NiO NPs, NiO NFs which were synthesized by the electrospinning process revealed higher performance.

Main text

Experimental section

To prepare NiO NFs, a sol–gel composed of nickel acetate tetra-hydrate (NiAc, 1 g, 98% assay Junsei Chemical Co., Ltd, Japan), polyvinylpyrolidine (PVP 1 g, molecular weight = 1,300,000 g/mol, Sigma-Aldrich Corporation, St. Louis, MO, USA) and ethanol (10 g) was electrospun at 10 kV and feeding rate of 0.05 ml/min. The electrospun mat was first vacuously dried and then sintered in air at 700°C. The utilized NiO NPs were synthesized from the same mixture; however, instead of spinning, the solution was dried, grinded and sintered at the same conditions. The electrochemical measurements were performed in a 1 M KOH solution at room temperature. Preparation of the working electrode was carried out by mixing 2 mg of the functional material, 20 μL Nafion solution (5 wt.%) and 400 μL isopropanol. The slurry was sonicated for 30 min at room temperature. Fifteen microliters from the prepared slurry was poured on the active area of the glassy carbon electrode which was then subjected to drying process at 80°C for 20 min. The measurements were performed on VersaSTAT 4 (Oak Ridge, TN, USA) electrochemical analyzer and a conventional three-electrode electrochemical cell. A Pt wire and an Ag/AgCl electrode were used as the auxiliary and reference electrodes, respectively. Surface morphology was studied by scanning electron microscope (SEM; JEOL JSM-5900, JEOL Ltd., Tokyo, Japan) and field-emission scanning electron microscope equipped with EDX analysis tool (FESEM; Hitachi S-7400, Hitachi Ltd., Chiyoda, Tokyo, Japan). Information about the phase and crystallinity was obtained by using Rigaku X-ray diffractometer (XRD, Rigaku Corporation, Tokyo, Japan) with Cu Kα (λ = 1.540 Å) radiation over Bragg angle ranging from 10° to 90°.

Results and discussion

The simplicity of the electrospinning process, the diversity of the electrospinnable materials, and the unique features of the obtained electrospun nanofibers provide especial interest for both of the technique and the resultant products. Various polymers have been successfully electrospun into ultrafine fibers in recent years mostly in solvent solution and some in melt form. Moreover, functional inorganic nanofibers can be produced by using sol–gel composed of metal(s) precursor(s) and proper polymer(s). In the field of metallic nanofibers, electrospinning process has a good contribution as it has been invoked to produce several pristine metallic nanofibers [1821]. Beside the metal alkoxides, metal acetates have been widely utilized as metal precursors, as these promising salts have a good tendency for polycondensation to form electrospinable sol-gels with the proper polymers [22]. The polycondensation reaction can be explained as follows [22]:
where M is Ni. Accordingly, the prepared NiAc/PVP solution produced good morphology, smooth and beads-free electrospun nanofibers, as shown in Figure 1A. Due to the polycondensation characteristic, the calcination of the prepared electrospun nanofibers did not affect the nanofibrous morphology as shown in Figure 1B. Figure 1C represents the SEM image for the synthesized NiO NPs. From Figures 1B and C, it can be concluded that the average diameters of the synthesized NFs and NPs are approximately 70 nm.
Figure 1

SEM images of electrospun PVP/NiAc electrospun nanofibers (A), synthesized NiO nanofibers (B), and NPs (C). SEM images of the electrospun PVP/NiAc nanofiber mats (A) and after calcination at 700°C (B). SEM image of the synthesized NiO NPs (C). Scale bar = 200 nm.

It was expected that the calcination of the prepared NiAc/PVA nanostructures in air will lead to eliminate the polymer and decompose the metallic precursor to the oxide form; this hypothesis was affirmed by using the XRD analysis. As shown in Figure 2, the XRD spectra of the synthesized NiO NPs and NFs are similar and match the standard spectra of NiO (JCPDS number 44–1159). From the obtained XRD spectra, the grain size could be estimated using Scherrer equation [23]. The determined sizes were 36 and 37 nm for the NPs and NFs, respectively.
Figure 2

XRD analyses for the prepared NiO nanofibers and nanoparticles.

Due to its surface oxidation properties, nickel reveals good performance as electrocatalyst. Many materials involving nickel as a component in their manufacture could be used as catalysts in fuel cells. Nickel is commonly used as an electrocatalyst for both anodic and cathodic reactions in organic synthesis, water electrolysis, and electrooxidation of alcohols [2426]. Surface activation of the nickel-based materials is an important step to create NiOOH compound on the surface and initiate the electrochemical activity. For instance, NiOOH compound has to be originated on the surface to initiate the electrochemical activity. Similarly, the investigated NiO nanostructures in this study were activated by applying cyclic voltages for 50 times in 1 M KOH electrolytes (the utilized scan rate was 100 mV/s). The cyclic voltammetric behaviors of NiO NPs and NFs are shown in Figure 3. In the voltammograms of the nickel oxide nanoparticles and nanofibers, the cathodic and anodic peaks corresponding to Ni(II)/Ni(III) couple are observed at about 0.35 and 0.42 V (vs. Ag/AgCl), respectively. As the chemical composition and the grain size are similar in both nanostructures, the same behavior was obtained as shown in the figure. Typically, these peaks refer to the formation of NiOOH in accordance with these reactions [2729]:
NiO + H 2 O Ni OH 2
Ni OH 2 + O H NiOOH + H 2 O + e
Figure 3

Consecutive cyclic voltammogram of the synthesized NiO NPs and NFs in 1 M KOH at scan rate of 50 mVs −1 .

Increasing the number of potential sweeps results in a progressive increase of the current density values of the cathodic peak because of the entry of OH into the surface layer, which leads to the progressive formation of a thicker NiOOH layer corresponding to the NiO/NiOOH transition [24]. It is noteworthy mentioning that the formed NiOOH layer is responsible for the electrocatalytic activity of nickel-based electrocatalysts [17, 24].

The linear scan voltammograms for the methanol oxidation on the NiO NPs and NFs surfaces in different methanol concentrations are shown in Figure 4. The methanol-containing electrolyte was previously purged with argon. The onset potential is an important indicator among the invoked parameters to demonstrate the electrocatalytic activity. The onset potential indicates the electrode overpotential. In other words, the onset potential can be utilized to evaluate the efficacy of the electrocatalyst. In methanol electrooxidation, more negative onset potential indicates high activity and less overpotential. Generally, the main reason behind increasing the onset potential is the OH and CO adsorbed layer on the surface of the electrodes, this gas layer leads to overpotential [30]. Sometimes, carbon monoxide is an intermediate compound in the methanol electrooxidation; it accumulates on the surface of the electrode until further oxidation step to carbon dioxide occurs. Usually, adsorption of CO appears to take place with the formation of islands of adsorbate [31], and electroactivity appears to be restricted to the outsides of these islands. Accordingly, good catalytic activity is related with the rate of CO removal and/or skipping formation of CO intermediate. From the obtained results, the onset potentials are 0.37 and 0.39 V (vs. Ag/AgCl) for the NiO NPs and NFs, respectively; these values are good compared with many reported materials.
Figure 4

Linear scan voltammograms for the methanol oxidation on the NiO NPs and NFs surfaces. Cyclic voltammograms at a scan rate of 50 mVs−1 and 25°C for NiO NPs and NFs in 1 M KOH and different methanol concentrations.

Two important findings can be observed in Figure 4: First, the nanofibrous morphology strongly enhances the electrocatalytic activity as the maximum current density significantly increased from 6 (in case of NPs) to 25 mA/cm2 (in case of NFs). Second, the optimum methanol concentration increased from 0.1 M in case of nanoparticulate morphology to 1 M in case of the nanofibers. Actually, concentrated methanol solution is a target fuel in the DMFCs to reduce the volume. However, increasing of methanol concentration can have a negative influence on the current density, so each electrocatalyst corresponds to a certain methanol concentration. The obtained good performance of the nanofibrous morphology can be assigned to the influence of the one-dimensional feature which facilitates the electron transfer through the electrocatalyst. It is expected that the electron paths through the nanoparticles will be corrugated; however, as the nanofibers have very high axial ratio, almost straight paths are expected. Moreover, within the nanoparticles, the electrons pass through several contact points as they have to move through many nanoparticles; this adds more constraints for the electrons transfer which distinctly affects the catalyst performance. Figure 5 shows a conceptual illustration for the electrons paths through the nanofibrous and nanoparticulate electrocatalysts.
Figure 5

Schematic diagram showing the electron paths in case of NiO nanofibers and nanoparticles.


Electrospinning technique can be utilized to fabricate NiO nanofibers from PVP and nickel acetates sol–gel. The morphology has a distinct influence on the electrocatalytic activity of the nickel oxide nanostructures toward methanol oxidation. Compared to the nanoparticles, the nanofibrous morphology facilitates the electrons' motion which positively affects the performance. It is expected that the good impact of the nanofibrous morphology is a common feature, so it can be utilized with other electrocatalytic materials.



This research was supported by NPST program by King Saud University project number 11-ENE1721-02. Also, this work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (no. 2012R1A2A2A01046086).

Authors’ Affiliations

Department of Organic Materials and Fiber Engineering, College of Engineering, Chonbuk National University
Faculty of Engineering, Chemical Engineering Department, Minia University
Department of Chemistry, College of Science, King Saud University


  1. Barakat NAM, Abadir MF, Nam KT, Hamza AM, Al-Deyab SS, Baek W-I, Kim HY: Synthesis and film formation of iron-cobalt nanofibers encapsulated in graphite shell: magnetic, electric and optical properties study. J Mater Chem 2011, 21(29):10957–10964. 10.1039/c1jm00052gView ArticleGoogle Scholar
  2. Barakat NAM, Khil MS, Sheikh FA, Kim HY: Synthesis and optical properties of two cobalt oxides (CoO and Co3O4) nanofibers produced by electrospinning process. J Phys Chem C 2008, 112(32):12225–12233. doi: 10.1021/jp8027353 doi: 10.1021/jp8027353 10.1021/jp8027353View ArticleGoogle Scholar
  3. Kanjwal M, Barakat N, Sheikh F, W-i B, Khil M, Kim H: Effects of silver content and morphology on the catalytic activity of silver-grafted titanium oxide nanostructure. Fibers Polym 2010, 11(5):700–709. doi: 10.1007/s12221–010–0700-x doi: 10.1007/s12221-010-0700-x 10.1007/s12221-010-0700-xView ArticleGoogle Scholar
  4. Barakat NA, Kanjawal MA, Chronakis IS, Kim HY: Influence of temperature on the photodegradation process using Ag-doped TiO2 nanostructures: negative impact with the nanofibers. J Mol Catal A Chem 2012, 336(1):333–340.Google Scholar
  5. Barakat NA, Kanjwal MA, Al-Deyab SS, Chronakis IS, Kim HY: Influences of silver-doping on the crystal structure, morphology and photocatalytic activity of TiO2 nanofibers. Mater Sci Appl 2011, 2(9):1188–1193.Google Scholar
  6. Prakash J, Tryk DA, Yeager EB: Kinetic investigations of oxygen reduction and evolution reactions on lead ruthenate catalysts. J Electrochem Soc 1999, 146: 4145–4151. 10.1149/1.1392605View ArticleGoogle Scholar
  7. Guo YG, Hu JS, Wan LJ: Nanostructured materials for electrochemical energy conversion and storage devices. Adv Mater 2008, 20(15):2878–2887. 10.1002/adma.200800627View ArticleGoogle Scholar
  8. Tian ZQ, Jiang SP, Liang YM, Shen PK: Synthesis and characterization of platinum catalysts on multiwalled carbon nanotubes by intermittent microwave irradiation for fuel cell applications. J Phys Chem B 2006, 110(11):5343–5350. 10.1021/jp056401oView ArticleGoogle Scholar
  9. Shen J, Hu Y, Li C, Qin C, Ye M: Pt-Co supported on single-walled carbon nanotubes as an anode catalyst for direct methanol fuel cells. Electrochim Acta 2008, 53(24):7276–7280. 10.1016/j.electacta.2008.04.019View ArticleGoogle Scholar
  10. Shao Y, Sui J, Yin G, Gao Y: Nitrogen-doped carbon nanostructures and their composites as catalytic materials for proton exchange membrane fuel cell. Appl Catal, B 2008, 79(1):89–99. 10.1016/j.apcatb.2007.09.047View ArticleGoogle Scholar
  11. Ren X, Zelenay P, Thomas S, Davey J, Gottesfeld S: Recent advances in direct methanol fuel cells at Los Alamos National laboratory. J Power Sources 2000, 86(1):111–116.View ArticleGoogle Scholar
  12. Liu Z, Ling XY, Su X, Lee JY: Carbon-supported Pt and PtRu nanoparticles as catalysts for a direct methanol fuel cell. J Phys Chem B 2004, 108(24):8234–8240. 10.1021/jp049422bView ArticleGoogle Scholar
  13. Mu Y, Liang H, Hu J, Jiang L, Wan L: Controllable Pt nanoparticle deposition on carbon nanotubes as an anode catalyst for direct methanol fuel cells. J Phys Chem B 2005, 109(47):22212–22216. 10.1021/jp0555448View ArticleGoogle Scholar
  14. Li W, Zhou W, Li H, Zhou Z, Zhou B, Sun G, Xin Q: Nano-structured Pt-Fe/C as cathode catalyst in direct methanol fuel cell. Electrochim Acta 2004, 49(7):1045–1055. 10.1016/j.electacta.2003.10.015View ArticleGoogle Scholar
  15. Yen CH, Shimizu K, Lin YY, Bailey F, Cheng IF, Wai CM: Chemical fluid deposition of Pt-based bimetallic nanoparticles on multiwalled carbon nanotubes for direct methanol fuel cell application. Energy Fuels 2007, 21(4):2268–2271. 10.1021/ef0606409View ArticleGoogle Scholar
  16. Frackowiak E, Lota G, Cacciaguerra T, Béguin F: Carbon nanotubes with Pt-Ru catalyst for methanol fuel cell. Electrochem Commun 2006, 8(1):129–132. 10.1016/j.elecom.2005.10.015View ArticleGoogle Scholar
  17. Tong X, Qin Y, Guo X, Moutanabbir O, Ao X, Pippel E, Zhang L, Knez M: Enhanced catalytic activity for methanol electro-oxidation of uniformly dispersed nickel oxide nanoparticles - carbon nanotube hybrid materials. Small 2012, 8(22):3390–3395. doi: 10.1002/smll.201200839 doi: 10.1002/smll.201200839 10.1002/smll.201200839View ArticleGoogle Scholar
  18. Graeser M, Bognitzki M, Massa W, Pietzonka C, Greiner A, Wendorff JH: Magnetically anisotropic cobalt and iron nanofibers via electrospinning. Adv Mater 2007, 19(23):4244–4247. 10.1002/adma.200700849View ArticleGoogle Scholar
  19. Wu H, Zhang R, Liu X, Lin D, Pan W: Electrospinning of Fe, Co, and Ni nanofibers: synthesis, assembly, and magnetic properties. Chem Mater 2007, 19(14):3506–3511. 10.1021/cm070280iView ArticleGoogle Scholar
  20. Barakat NA, Woo K-D, Kanjwal MA, Choi KE, Khil MS, Kim HY: Surface plasmon resonances, optical properties, and electrical conductivity thermal hysteresis of silver nanofibers produced by the electrospinning technique. Langmuir 2008, 24(20):11982–11987. 10.1021/la802084hView ArticleGoogle Scholar
  21. Barakat NA, Farrag TE, Kanjwal MA, Park SJ, Sheikh FA, Yong Kim H: Silver nanofibres by a novel electrospinning process: nanofibres with plasmon resonance in the IR region and thermal hysteresis electrical conductivity features. Eur J Inorg Chem 2010, 2010(10):1481–1488. 10.1002/ejic.200900453View ArticleGoogle Scholar
  22. Yousef A, Barakat NAM, Amna T, Unnithan AR, Al-Deyab SS, Yong Kim H: Influence of CdO-doping on the photoluminescence properties of ZnO nanofibers: effective visible light photocatalyst for waste water treatment. J Lumin 2012, 132(7):1668–1677. doi: 10.1016/j.jlumin.2012.02.031 doi: 10.1016/j.jlumin.2012.02.031 10.1016/j.jlumin.2012.02.031View ArticleGoogle Scholar
  23. Patterson A: The Scherrer formula for X-ray particle size determination. Phys Rev 1939, 56(10):978. 10.1103/PhysRev.56.978View ArticleGoogle Scholar
  24. Rahim A, Abdel Hameed R, Khalil M: Nickel as a catalyst for the electro-oxidation of methanol in alkaline medium. J Power Sources 2004, 134(2):160–169. 10.1016/j.jpowsour.2004.02.034View ArticleGoogle Scholar
  25. Fan C, Piron D, Sleb A, Paradis P: Study of electrodeposited nickel-molybdenum, nickel-tungsten, cobalt-molybdenum, and cobalt-tungsten as hydrogen electrodes in alkaline water electrolysis. J Electrochem Soc 1994, 141(2):382–387. 10.1149/1.2054736View ArticleGoogle Scholar
  26. Raj IA, Vasu K: Transition metal-based hydrogen electrodes in alkaline solution - electrocatalysis on nickel based binary alloy coatings. J Appl Electrochem 1990, 20(1):32–38. 10.1007/BF01012468View ArticleGoogle Scholar
  27. Fleischmann M, Korinek K, Pletcher D: The oxidation of organic compounds at a nickel anode in alkaline solution. J Electroanal Chem Interfacial Electrochem 1971, 31(1):39–49. 10.1016/S0022-0728(71)80040-2View ArticleGoogle Scholar
  28. Vuković M: Voltammetry and anodic stability of a hydrous oxide film on a nickel electrode in alkaline solution. J Appl Electrochem 1994, 24(9):878–882. 10.1007/BF00348775View ArticleGoogle Scholar
  29. Enea O: Molecular structure effects in electrocatalysis - II. oxidation of d-glucose and of linear polyols on Ni electrodes. Electrochim Acta 1990, 35(2):375–378. 10.1016/0013-4686(90)87014-SView ArticleGoogle Scholar
  30. Geng D, Lu G: Dependence of onset potential for methanol electrocatalytic oxidation on steric location of the active center in multicomponent electrocatalysts. J Phys Chem C 2007, 111(32):11897–11902. 10.1021/jp0709510View ArticleGoogle Scholar
  31. Shukla A, Christensen P, Hamnett A, Hogarth M: A vapour-feed direct-methanol fuel cell with proton-exchange membrane electrolyte. J Power Sources 1995, 55(1):87–91. 10.1016/0378-7753(94)02150-2View ArticleGoogle Scholar


© Barakat et al.; licensee Springer. 2013

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.