DEPARTMENT of Electrocatalysis and Electrocrystallization
Head: Prof. Konstantin Petrov
Tel.:(+359 2) 979 27 57
E-mail: kpetrov@bas.bg
Electrocatalysis
Scientific activity
Research is concentrated around two basic problems:
1. Influence of the electrode surface structure on the electrochemical double layer, adsorption and electrocatalysis.
2. New catalysts and electrodes applicable in real electrochemical systems such as: H2/O2 and direct CH3OH/O2 fuel cells, air-metal hydride (MH) rechargeable batteries, divices for
purification of flue and waste gases from SO2 as well as in
electrolysis for producing cheap hydrogen.
Current research projects:
Catalysts and electrodes for electrochemical
conversion of hydrogen and oxygen.
Aim: Research and development of low cost catalysts and electrodes that can be
used in:
- devices for recombination of hydrogen and
oxygen released during charge and operation of lead-acid and alkaline batteries;
- a hydrogen sensor for gas media, capable to
work in the concentration range 1-4 % vol. (the upper limit for safety work in
hydrogen containing atmosphere).
Bifunctional nanosized catalysts and electrodes
for electrochemical reduction and evolution of oxygen.
The primary objectives of the project are:
- synthesis and characterization of nanosized
binary oxides with spinal structure, MxCo3-xO4 and MxMn3-xO4 (where M=Cu, Ni, Mn, and Co);
- use of the developed catalysts for preparation
of rechargeable gas diffusion oxygen electrodes (ROE), applicable in air-metal
hydride or air-zinc accumulators.
- preparation of high surface area spinel oxides
by means of low temperature techniques, using inorganic and organic precursors,
- preparation of nanosized catalytic layers by
electrochemical methods or by co-condensation in vacuum of vapors of the metals
with oxides of elements from the V and VI groups on gas-diffusion layers.
Publications
1. V.Nikolova, I.Nikolov, P.Andreev, V.Naidenov, T.Vitanov, Tungsten carbide
based electrochemical sensors for hydrogen determination in gas mixtyres, J.Appl.Electrochem.,
30 (2000)705.
2. A.Stoyanova, V.Naidenov, K.Petrov, I.Nikolov, T.Vitanov, E.Budevski,
Effect of preparation conditions on the structure and catalytic activity of
carbon-supported platinum for the electrooxidation of methanol, J.Appl.Electrochem. 29:(1999)1197-1203.
3. I. Nikolov, R. Darkaoi, E. Zecheva, R. Stoyanova, N. Dimitrov, T. Vitanov
Electrocatalytic Activity of Spinel Related Cobaltites MxCO3-xO4, (M=Li, Cu, Ni) in the Oxygen Evolution Reaction, J. Electroanal. Chem.,
429(1997) 157.
4. T.Vitanov, I.Nikolov, K.Petrov, E.Zecheva, R. Stoyanova Rechargeable
oxygen electrode, Bul. Patent, 101585/61997.
5. I. Nikolov, K. Petrov, T. Vitanov, Low Temperature Electrochemical
Oxidation of Sulfur Dioxide, J. Appl. Electrochem., 26 (1996) 703.
6. I. Nikolov, V. Nikolova, T. Vitanov, Some Possibilities in Metal
Electrowining by Hydrogen Tungsten
Carbide Gas Diffusion Electrodes, Bulg. Chem. Comm., 27 (1994) 339.
7. G. Papazov, I. Nikolov, D. Pavlov, T. Vitanov, Application of WC
Electrodes in Stationary Batteries, The First International Telecomunications
Energy Special Conference, 11 - 15. 04. 94, Berlin, Telescon '94, p. 463 –
476.
8. I. Nikolov, R. Darkaui, E. Zhecheva, R. Stoyanov, N. Dimitrov, T. Vitanov,
Electrocatalytic Activity of LixNi1-x0
(0<x<0,5) Solid Solutions in the Oxigen Evolution Reaction, J. Electroanal.
Chem., 362 (1993) 119.
9. V. Nikolova, I. Nikolov, T. Vitanov, K. Wiesener, Behaviour of Tungsten
Carbide Hydrogen Gas Diffusion Electrodes in Chloride Etching
Solutions, J. Appl. Electrochem., 23 (1993) 1268.
10. I. Nikolov, G. Papazov, D. Pavlov, T. Vitanov, V. Naidenov, Tungsten
Carbide Electrodes for Gas Recombination in Lead Acid Batteries, J. Power
Sources, 31 (1990) 69.
11. T. Vitanov, E. Budevski, I. Nikolov, K. Petrov, V. Naidenov, Ch. Christov,
Electrocatalytic Oxidation of Sulphur Dioxide (the ELCOX Process), I. Chem.
E. Symposium series N 116, "Effluent Treatment and Waste Disposal", 1990,
251-260.
Electrocrystallization
Investigations on the kinetics and the mechanism of the processes of
crystallization during the electrodeposition of metals are carried out. The
electrochemical growth of individual close packed faces of silver and cadmium
single crystals in solutions of simple salts is used as a model. This unique
possibility was provided by the so-called capillary method whose development is
one of the fundamental achievements of the department. The main results of the
investigations may be summarized as follows:
The morphology and kinetics of crystal surfaces growth intersected by screw
dislocations have been studied. The morphological observations and the
experimental time and overpotential dependencies of the growth rate are in
excellent agreement with the theory of spiral growth of crystals.
Growth conditions for obtaining crystal faces free of screw dislocations were
found. On the screw-dislocation free faces the classical mechanism of crystal
growth by two-dimensional nucleation was experimentally proved and demonstrated
for the first time. The kinetics of two-dimensional nucleation were studied. The
experimental overpotential dependencies of the nucleation rate confirmed the
classical nucleation theory. Data about the time and the location of the
monatomic layer' nucleation have been obtained. The statistical analysis of
these data revealed that the nucleation process is random in time and space. A
method for studying the shape and the propagation rate of mono-layers has been
developed. The effect of the crystallographic structure on the spreading rate of
the layers was established. Kinetic constants were determined and new phenomena
associated with the elementary steps of crystallization were observed. A simple
modification of the capillary method allowed measuring the spreading rate of
poly-atomic layers and the thickness and the slope of the growth front of each
layer. An important result of these measurements served as a direct proof of the
mechanism of direct transfer of metal ions from the solution to the kink
position on the crystal surface. The growth kinetics of the screw-dislocation
free faces has been experimentally studied. The two basic growth mechanisms, i.e.
the mononuclear monolayer mechanism and the polynuclear polylayer one, predicted
by theory, have been experimentally demonstrated and the theoretical time and
overvoltage dependencies of the growth rate have been quantitatively verified.
Some theoretical investigations on the spiral growth of crystals, as well as on
the polynuclear mechanism of crystal growth were carried out.
The capillary method still offers unique possibilities of
studying the elementary processes of crystallization.
Publications
1. V.Bostanov, Electrocrystallization of silver: Growth kinetics of screw-dislocation
free (100) crystal faces, J. Crystal Growth, 42 (1977) 194.
2. V.Bostanov, E.Budevski and G.Staikov, Role of screw dislocation in the
electrolytic crystal growth, Faraday Symp. of the Chem. Soc. No 12 (1977)
p. 83.
3. E.Budevski, V.Bostanov and G.Staikov, Electrocrystallization, in “Annual Review of Materials Science” Ed. R.A.Huggins, Annual Reviews Inc.,
Vol. 10 (1980) p. 85.
4. V.Bostanov, W.Obretenov, G.Staikov, E.Budevski and D.K.Roe, Rate of
crystal growth by 2D nucleation in the case of electrocrystallization of silver, J. Crystal Growth, 52 (1981) 761.
5. V.Bostanov, W.Obretenov, G.Staikov and E.Budevski, Monolayer formation by
instantaneous two-dimensional nucleation in the case of electrolytic crystal
growth, J. Electroanal. Chem., 146 (1983) 273.
6. E.Budevski, Deposition and dissolution of metals and alloys. Part A:
Electrocrystallization, in “Comprehensive Treatise of Electrochemistry” Ed. B.E.Conway et al., Plenum Press Vol. 7 (1983) p. 399.
7. W.Obretenov, D.Kashchiev and V.Bostanov, Unified description of the rate
of nucleation-mediated crystal growth, J. Crystal Growth, 96 (1989) 843.
8. E.Budevski, G.Staikov and W. J. Lorenz, Electrochemical Phase Formation
and Growth, VCH - Weinheim ; NewYork ; Basel ; Cambridge ; Tokyo : NCH, 1996.
Materials for Metal Hydride electrodes
Research
activities
1. Investigations on the electrochemical activity, the kinetics and
mechanism of the reactions occurring in alkaline media on metal hydride
electrodes, prepared from:
- Nanoparticles, produced by means of the borohydride reduction method (with
deferent composition, (CoB):H; (CoLi):B,H; (CoMg):B,H; (SmCo):B,H; (FeLi):B,H; (NiCo):B,H; (CoVLi):B,H;
(CuB):H; LaNi5--xCox).
- Metal hydride alloys (AB5 and AB2).
- Nanoparticles as additives to metal hydride alloys.
2. Optimization on metal hydride electrodes and batteries manufacturing.
3. Research for hydrogen storage materials.
Publications
1. M.Mitov, A.Popov, I.Dragieva, "On the mechanism of reactions occurring on
CoxByHz-electrodes in alkaline media", Anal.Lab. , 6 (1997) 184.
2. M.Mitov, A.Popov, I.Dragieva, "Electrocatalytic phenomena on electrodes
prepared from hydrogen-containing nanoparticles", Bulg.Chem.Comm., 30
(1998) 441.
3. M.Mitov, A.Popov, I.Dragieva, "Nanoparticles produced by borohydride
reduction as precursors of metal hydride electrodes", J.Appl.Electrochem.,
29 (1999) 59.
4. M.Mitov, A.Popov, I.Dragieva, "Possibilities for battery application of
colloid CoxByHz particles ", Colloids and Surfaces A: Physicochem. and
Engineer.Aspects, 149 (1999) 413.
5. M.Mitov, St.Bliznakov, A.Popov, I.Dragieva, "Electrochemical properties
of colloidal powders prepared by borohydride reduction", Book of Papers of
the 16th Congress of Chemists and Technologists of Macedonia, Vol. 2, Ed. by
Fr.Popovska-Pavlovska, Faculty of Technology and Metallurgy, Skopje, 1999, p.631.
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