Mongolian Academy of Sciences Mongolian Journal of Chemistry Institute of Chemistry & Chemical Technology Mongolian Journal of Chemistry 16 (42), 2015, 13-17 The mathematical stability study for the system of the CoO(OH) – overoxidized polypyrrole composite synthesis in the presence of fluor ions V.Tkach 1,2* , S.C.de Oliveira 2 , R.Ojani 3 , P.I.Yagodynets´ 1 , U.Páramo-García 4 1 Chernivtsi National University, Kotsjubynskyi street 2, Chernivtsi 58012, Ukraine 2 Universidade Nacional de Mato Grosso do Sul, Brazil 3 University of Mazandaran, Islamic Republic of Iran 4 Instituto Tecnológico de Ciudad Madero, Mexico ARTICLE INFO: Received 17 May 2015; revised 03 January 2016; accepted 07 January 2016 Abstract: The potentiostatic synthesis of CoO(OH) – Overoxidized polypyrrole composite in the presence of fluor ions has been investigated mathematically. The corresponding mathematical model was described and analyzed by means of linear stability theory and bifurcation analysis. The steady-state stability requirements, like also oscillatory and monotonic instability conditions are derived. Keywords: Cobalt oxide-hydroxide, overoxidized polypyrrole, composite, fluoride, steady-state stability INTRODUCTION Oxy-hydroxycompound of cobalt, described by the formula of CoO(OH), is a very interesting material [1- 3], that is viewed as an alternative to titanium dioxide in photo- and photoelectrocatalysis, for LEDs, and other optical devices, due to its intensively black color. It may also be used in corrosion-protecting coatings on some metal surfaces. On the other hand, the conducting polymers (CP) are another class of attractive materials, extensively investigated during the last 5 decades [4-10], due to their capability to combine the properties of plastics with metal conductivity and facility in modification. They also have vast and rich use spectrum, beginning on corrosion protection and ending with sensors and biosensors [11-20]. So, the composite of CoO(OH) with conducting polymers must have interesting optical, electroanalytic and catalytic (including electrocatalytic) properties. One of negative sides of the electrochemical synthesis of CoO(OH) from cobalt salts may be the Co 2+ oxidation potential, superior to the overoxidation potential of some conducting polymers, like some polypyrroles, by the scheme: Other negative side of the use of CoO(OH) is its instability in the presence of fluoride ions, which form the complex ions by reaction: CoO(OH) + 6HF  H 3 [CoF 6 ] +2H 2 O (3) The synthesis may also be affected by electrochemical instabilities, accompanying both the synthesis of conducting polymers [21-30] and of CoO(OH) [31-32], like oscillations, represented in Figures1-4. In the most part of reported works, these phenomena received purely phenomenological explanation, which besides of being logically argued, didn’t have strong theoretical base, which may only be given by development and analysis of a mathematical model, capable to describe adequately the system´s behavior. This modeling is also capable to describe the behavior of relative systems and also compare it with the *corresponding author: e-mail: nightwatcher2401@gmail.com DOI: http://dx.doi.org/10.5564/mjc.v16i0.663 (1) (2) Fig. 1. The oscillatory behavior during the anodic electropolymerization of thiophene with two different background electrolytes-4-TSS (argentum 4-tolylsulphate) (a) and ZnSO 4 (c) and corresponding morphological changes (b,d). Reproduced from [22] with the permission of IN-SCAR, India