Svetlozar Ivanov

Influence of copper anion complexes on the incorporation of metal particles in polyaniline. Part I: Copper citrate complex

Copper electrodeposition in polyaniline-coated electrodes is studied using copper citrate complex anions as reducing species. Use of these complex anions allows shifting the potential window for metal deposition in the negative direction and resolving the polymer and metal reduction processes. As shown by galvanostatic experiments and SEM photographs, copper electrodeposition from citrate solution is highly inhibited and results in a small number (3.6 × 106 cm−2) of large hemispherical crystals located mainly on top of the polymer layer. Statistical analysis of distances between neighbouring crystals shows a random surface distribution of the copper hemispheres. Thus, the low number of crystals obtained cannot be related to the appearance and overlap of nucleation exclusion zones partly blocking the electrode surface. It is likely connected to the specific role of the metal anion complexes in the deposition process and more precisely to the inhibited diffusion of both the copper complex anions and the released (after reduction) citrate anions in and out of the polymer structure.

Role of polymer synthesis conditions for the copper electrodeposition in polyaniline

Abstract Polyaniline (PAN) layers are electrochemically synthesised by three different procedures – potentiostatic (PS), potentiodynamic (PD) and pulse potentiostatic (PP). Galvanostatic copper deposition and subsequent oxidation of copper species are studied on the three types of PAN layers. A marked difference in the deposition/dissolution behaviour is found depending on the type and redox state of PAN. Copper reduction is easily initiated at low overpotentials at oxidised PS and PP PAN specimens, whereas for oxidised PD layers copper deposition needs higher overpotentials. This difference is discussed in terms of various reduction behaviours of the three types of PAN. In general reduced PANs strongly inhibit copper nucleation and growth. Still a marked difference in the metal deposition on reduced PD and PP PANs on the one hand and reduced PS PAN on the other exists. This difference is related to the varying amount of defects in the three polymer structures, evidenced by SEM observation of Cu/PAN-coated electrodes.

Electroanalytical applications of nanocomposites from conducting polymers and metallic nanoparticles prepared by layer-by-layer deposition*

Layer-by-layer (LbL) deposition is a convenient technique for the formation of ultra-thin nanocomposite layers containing metallic nanoparticles (NPs) and conducting polymers (CPs). The advantages of this approach for producing composite layers suitable for electroanalytical applications are discussed. Examples of electroanalytical applications of LbL-deposited composites are presented. Composite layers consisting of polyaniline (PANI) and Pd NPs are used for hydrazine oxidation. The PANI–Au NPs system is applied for dopamine (DA) and uric acid (UA) oxidation.

Polyaniline doped with poly(acrylamidomethylpropanesulphonic acid): electrochemical behaviour and conductive properties in neutral solutions

Poly(2-acrylamido-2-methyl-1-propanesulphonic acid) (PAMPSA)-doped polyaniline (PANI) layers are synthesised in the presence of sulphuric and perchloric acids. The effects of the inorganic acid as well as of the electrochemical synthetic procedure (potentiostatic and potentiodynamic deposition) and thickness of the polymer layers are studied. The focus is directed towards the pH dependence of the electrochemical redox activity and conductivity of the PAMPSA-doped PANI layers obtained under different conditions. Ascorbic acid oxidation is used as a test reaction to study the electrocatalytic behaviour of various PAMPSA-doped PANI layers in neutral solution. It is found that the type of inorganic component present in the polymerisation solution has a marked effect on the extent of doping in acidic solutions as well as on the redox electroactivity in neutral solutions. A comparison between potentiostatically and potentiodynamically synthesised layers at pH 7 shows a markedly lower conductance and lower extent of redox charge preservation in the case of potentiodynamic synthesis. The PANI electrocatalytic activity for ascorbic acid oxidation is also dependent on the polymer electrodeposition procedure, with potentiostatically synthesised layers exhibiting better electrocatalytic performance.

Thin-film calorimetry: In-situ characterization of materials for lithium-ion batteries

Abstract Thin-film calorimetry allows for qualitative and quantitative in-situ analysis of thermodynamic properties of thin films and thin-film systems from room temperature up to 1000 °C. It is based on highly sensitive piezoelectric langasite resonators which serve simultaneously as planar temperature sensors and substrates for the films of interest. Generation or consumption of heat during phase transformations of the films cause deviations from the regular course of the resonance frequency. Thermodynamic data such as phase transformation temperatures and enthalpies are extracted from these deviations. Thin-film calorimetry on Sn and Al thin films is performed to prove the concept. The results demonstrate high reproducibility of the measurement approach and are in agreement with literature data obtained by established calorimetric techniques. The calibration of the system is done in different atmospheres by application of defined heat pulses via heating structures. The latter replace the films of interest and simulate phase transformations to provide detailed analysis of the heat transfer mechanisms occurring in the measurement system. Based on this analysis, a data evaluation concept is developed. Application-relevant studies are performed on thin films of the lithium-ion battery materials NMC(A), NCA, LMO, and MoS2. Their phase transformation temperatures and enthalpies are evaluated in oxidizing and reducing atmospheres. Furthermore, their thermodynamic stability ranges are presented. Finally, measurements on all-solid-state thin-film batteries during electrochemical cycling are performed. They demonstrate the suitability of the system for in-situ investigations.

Effect of synthesis conditions and composition modification on the structural and electrochemical properties of layered transition metal oxide cathode materials

Novel and promising layered oxide cathode materials Li(Ni,Mn,Co)O2, with improved capacity and high stability during cycling, were obtained by cationic substitution and by optimization of the synthesis conditions. These cathode materials were prepared by self-combustion method using metal nitrates and sucrose as fuel. Synthesis was then followed by annealing at 900°C during 1h. The temperature and annealing plateau were optimized in order to adjust the average particle size and size distribution. Two annealing atmospheres (argon and air) were used as well to investigate their effect on the structure and morphology of the NMC material. The time between synthesis and annealing was also varied in order to study the aging effect. X-ray diffraction was carried out as first step and showed that all the obtained materials crystallize in the rhombohedral system (α-NaFeO2 type structure). The obtained results through scanning electron microscopy and galvanostatic cycling proved that the best performances were obtained for the substituted materials that were annealed directly after synthesis, under air atmosphere.