Electrode materials for supercapacitors

Electrode materials for supercapacitors based on carbon / sulfide or metal oxides nanocomposites

Duration of the project: August 2016 –December 2016

Project executor: Vasyl Stefanyk Precarpathian National University (Grant President of Ukraine, Project of the Ministry of Education and Science of Ukraine)

Project goals: The development and testing of experimental methods of carbon/ MoS2 and carbon/Fe2O3 (FeOOH, LiFePO4) nanocomposite obtaining with optimized structural, morphological and electrophysical parameters as hybrid supercapacitor electrode.

Project objectives: The establishment of regularities of the structuralmorphological, magnetic and electrical properties of metal sulfide / carbon and metal oxides / carbon nanocomposites; the investigation of electrochemical properties of these materials at charge-discharge cycling

Project results :

  1. Multilayer nanoparticles with the sizeof 40–70 nm are synthesized by hydrothermal synthesis using cations of the cetyltrimethylammonium bromide as micelle-forming agent. The resulting material has a double- hierarchical structure in which MoS 2 layers alternate with carbon. It has reported about the growth of the interatomic distances of obtained nanostructured MoS2within the (001).
  2. Spherical nanoparticles with alternating MoS2 and C layers synthesized by hydrothermal method were studied as an electrode base for Li power sources. It was deter- mined that the obtained values of specific capacity (3700, 1390, and 790 A h kg−1 at currents 0.1, 0.3, and 0.5 C, respectively) are caused by synergetic ef fect of the following factors: (i) deformation, expanding, and breaches of MoS2 crystal structure as a result of carbon layers’ presence and thermal treatment; (ii) conductivity growth for MoS2 /C nanocomposite comparatively to bulk materials; and (iii) combination both faradaic and pseudocapacitive non-faradaic mechanisms of charge accumulation. The conductivity character of the obtained MoS2 /C composite is being changed after thermal treatment from typical for crystalline MoS2 to symmetric hopping or random barrier model. The conductivity saturation point, observed in the annealed material, is balancing between temperature and frequency of applied field and decreasing at higher temperatures. Without modifying the 2H structure of MoS2 , the anneal- ing has introduced a number of defects – the supplemen tary active sites—where the redox reactions occur. This together with spherical hollow structure of MoS2/C nanoparticles affected the results of galvanostatic and potentiodynamic studies.
  3. The combination of a large surface area of mesoporous carbon and fast Faradic processes in MoS 2 is a good solution for improving the working characteristics of supercapacitors. Despite that the surface area of the nanocomposite is much smaller than that of mesoporous carbon (430 and 2200 m2 g–1 , respectively), due to redox reactions occurrence in MoS 2 , the resulting specific capacity of the nanocomposite is twice higher in comparison with just carbon. In addition, the synergetic effect between C and MoS2 increases the electric conductivity of the synthesized material, because of the sum of hopping charge transfer mechanism on Mo atoms and additional electron donation by carbon atoms. In general, a simple and cheap method of MoS2/C nanocomposite obtainment and a relatively good electrochemical performance made it a promising electrode material for supercapacitors.
  4. The variation of precursor’s (FeCl3×6H2O) molar concentration during ultrafine β-FeOOH sol-gel synthesis allow to obtain the mesoporous superparamagnetic materials. The growth of precursor’s molarity from 0.10 M to 0.55 M leads to average particle sizes decreasing and enlarging BET specific surface area in a range 138-190 m2 /g. The pore size distributions and mesopore relative content depend on the precursor’s molarity. The synthesized materials can be represented as systems of mono­do­main clusters with fluctuated mag­netic mo­ments. The obtained results are probably caused by transitions from diffusion limited aggregation reaction to limited cluster slow aggregation. The specific capacitances of β-FeOOH samples (calculated from the CVA data) are about 26-29 F/g. Li+ ions diffusion coefficient slightly depends on the scan rate and changes in a the range of (1.0- 3.0)·10-13 cm2∙s-1.

Contact person and project manager at Vasyl Stefanyk Precarpathian National University:Volodymyr KOTSYUBYNSKY, Ph.D., Professor, e-mail: kotsuybynsky@gmail.com