XII Iberian Meeting of Electrochemistry XVI Meeting of the ...

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XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society O C 05 Convolutive modelling with universal master equation of Oldham-Mahon-Myland by using Mathematica ® software. E q C i mechanism in C V at spherical electrodes. M. J. Barrera-Niebla 1 , M. R. García Hernández 2 , M. J. González Morín 1 , L.C. Fernández Mérida 1 , D.M. Grandoso Medina 1 1 Physical Chemistry Department. University of La Laguna. La Laguna 2 Consejería de Presidencia, Justicia y Seguridad. Gobierno de Canarias TENERIFE. CANARY ISLANDS. SPAIN. mbarnie@ull.es Convolutive Modelling is an important methodology of Semiintegral and Convolution Electrochemistry [1]. We model with Mathematica ® software, to overcome the advanced mathematics, I E curves for E q C i mechanism at spherical electrodes. The mechanism represented by k f k S( so ln) ne P( so ln) P( so ln) Q( so ln) (1) kb allows us to infer the following expressions for S (t) and P (t) , namely S( t) 1 1 DSt exp erfc DSt a 2 a P( t) exp kt Figure 1. Modelled voltammograms. DSt a 1 1 D t exp P erfc DPt a 2 a a electrode radius D Pt a required to apply the algorithm used to implement the master equation. A very basic program written for Mathematica ® is reported to model I E curves. We check, with SigmaPlot , these files with those obtained by digital simulation with DigiElch ® . The next figure display the comparison between convolutive modelling and digital simulation. The agreement is excellent. The 60 40 20 0 -20 -40 -60 -80 -100 -120 10 6 I/A E/V -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 (2) parameters employed were: T 298. 15K ; a 10 3 9 2 1 m ; DS DP 10 m s ; 3 CS b 1mol m 0. 5 0 4 1 k 10 m s ; E reverse 0. 5V ; (3) ; n 1 ; k 1s 1 ; 0 E 0. 0V ; 1 v 1V s ; t reverse 1s ; 3 ( sampling time) 10 s . DigiSim ® results also agree with previous files. Acknowledgements: To Professor Keith B. Oldham, Peter J. Mahon and Jan C. Myland. References [1] Barrera-Niebla, M.J.; Semiintegral and Convolution Electrochemistry. Research line. Department of Physical Chemistry. (2010). La Laguna University. Tenerife. Canary Islands. September, 811, 2010. ISEL - Lisbon 44
XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society O C 06 Electrocrystallisation of (Perylene) 2 [M(mnt) 2 ] salts Mónica Afonso, 1 Manuel J. Matos, 2,3 Rafaela A. L. Silva, 1 Quirina Ferreira, 2 Manuel Almeida 1 1 Dept. Chemistry, ITN / CFMCUL Estrada Nacional 10, P-2686-953 Sacavém, Portugal 2 IT, Av. Rovisco Pais, 1049-001 Lisboa, Portugal, 3 ISEL, Av. Emídio Navarro, 1959-007 Lisboa, Portugal mafonso@itn.pt The charge transfer salts based on perylene (Per) and transition metal bis-maleonitrile-dithiolate M(mnt) 2 with different transition metals M and general formula, (Per) 2 [M(mnt) 2 ] have attracted continued interest for more than 30 years due to unique properties derived from the existence in the same solid of two types of chains: conducting chains of partially oxidized perylene molecules (Per) 1/2+ and chains of monoanionic complexes [M(mnt) 2 ] - that depending on the metal can be either diamagnetic (M=Cu, Au, Co) or paramagnetic (M=Ni, Pd, Pt, Fe). The mutual interaction between the two type of chains, both subject to lattice instabilities typical of one-dimensional conducting and magnetic systems, leads to a very rich and unprecedented variety of physical phenomena [1,2]. However the study of these compounds has been always limited by difficulties in the growth of good quality single crystals. The situation is further complicated by the fact that the crystals can be obtained in two polymorphs, e.g. in M=Cu, Ni [3] and Pt [4] and different stoichiometries are possible for M=Co [1]. These salts have been obtained mainly by electrocrystallisation; a solution of perylene and salts of [M(mnt) 2 ] - is submitted to electrochemical oxidation which generates perylene cations to give insoluble crystals of the (Perylene) 2 M(mnt) 2 compounds growing on the anode. This electrochemical method has advantages over chemical oxidation routes yielding better quality crystals, but has also strong limitations. In this communication we report the results of our systematic investigation aiming at to establish the best conditions for the growth of single crystals of the (Per) 2 M(mnt) 2 compounds by electrocrystallisation that is constrained by the rather low solubility of perylene in appropriated solvents and the instability of the perylene radical cation. The conditions which allowed for the first time the preparation of (Per) 2 [Pd(mnt) 2 ] by electrocrystallisation are described. AFM and STM microscopy were used to monitor the early stages of crystal growth on different electrodes. The nucleation is found to occur preferentially at edge dislocations of HOPG and to be oriented along Au and Pt crystallographic axis. Acknowledgments: Work supported by F CT under contract PTDC/QUI-QUI/101788/2008. References [1] Almeida M. and Henriques R. T., in Organic Conductive Molecules and Polymers, H. S. Nalwa ed., vol. 1, chapter 2, pp. 87-149, John Wiley 1997. [2] Brooks, J.S., Graf, E.S.; Almeida, M.; R.T.; Matos, M. et al.; J. Low Temp. Phys., 2006, 142, 787. [3] Gama, V.; Almeida, M.; Henriques, R.T.; Santos, I.C.; et al. J. Phys. Chem., 1991, 95, 4263. [4] Henriques, R.T.; Sousa, I.; Almeida, M.; et al.; J. Low Temp. Physics, 2006, 142, 405. September, 811, 2010. ISEL - Lisbon 45
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