Transient processes in photogalvanic cells: Part III. The alternating current photogalvanic cell

An alternating current photogalvanic cell, having a symmetrical electrode configuration, is described. It uses the Ru(bipy)₃²⁺/Fe³⁺ system. The light beam alternately illuminates the two electrodes, yielding almost rectangular current/time and voltage/time responses. The main advantage of this type of a cell is a very stable power output. Unlike other cells, mass transport from one electrode to the other is not necessary, eliminating the disadvantage of slow diffusion processes. A computer simulation of this behaviour is presented. The long-term characteristics depend on the Fe³⁺/Fe²⁺ concentration ratio.     

Transient processes in photogalvanic cells: Part II. The ru (bipy)32+/Fe3+ cell

The transient processes in photogalvanic cells using the ^*Ru(bipy)₃²⁺+Fe³⁺→Ru(bipy)₃³⁺+Fe²⁺ system are investigated by measurement of the current-time and the potential-time characteristics. Under conditions of high light intensity and low to medium workloads of the cell, a pronounced maximum in the voltage-time curve is observed. This maximum appears after some milliseconds and it amounts to four times the stationary value. The experimental results are explained and the transients simulated, using the theoretical model developed in Part I of this series.     

Survey on mass determination systems: Part I. Fundamentals and history

The influence of mass and force on the frequency of vibrating bodies today is widely applied. In Part I of the survey the historical roots are reviewed and the physical principles of the several arrangements modes of operation explained.This revised version was published online in November 2005 with corrections to the Cover Date.     

Fundamentals of lead-acid cells: Part XII. The reduction of lead sulphate

The reduction of lead sulphate grown anodically on planar and porous electrodes has been studied by a potentiostatic step technique. Both “planar” and “porous” electrodes behave in a similar manner and indicate that the electrode reduction reaction has a finite depth of penetration into the electrode. The kinetics of the formation of metallic lead on both electrodes appear to be instantaneous nucleation and two-dimensional growth processes with subsequent current limitations due to overlap and lead sulphate depletion. The current limitation processes are very complex and it has not been found possible to fit a satisfactory mathematical model.     

Bilinear modelling of batch processes. Part I: theoretical discussion

When studying the principal component analysis (PCA) or partial least squares (PLS) modelling of batch process data, one realizes that there is a wide range of approaches. In many cases, new modelling approaches are presented just because they work properly for a particular application, for example, on‐line monitoring and a given number of processes. A clear understanding of why these approaches perform successfully and which are the advantages and disadvantages in front of the others is seldom supplied. Why does modelling after batch‐wise unfolding capture changing dynamics? What are the consequences of variable‐wise unfolding? Is there any best unfolding method? When should several models for a single process be used? In this paper, it is shown how these and other related questions can be answered by properly analyzing the dynamic covariance structures of the various approaches. Copyright © 2008 John Wiley & Sons, Ltd.     

Fundamentals of lead-acid cells: Part XIII. The influence of additives on the charge and discharge processes of the negative electrode

The effects of BaSO₄ and a lignosulphonate on the normal discharge and charge processes of a porous lead electrode have been examined by the potential-step technique. Here, BaSO₄ is shown to exert a major electrochemical effect on the discharge reaction while the lignosulphate is found to increase the available active surface area of the electrode.     

Random processes in electrochemistry: Part I. Noise as an input signal

Linear and nonlinear transformation occuring when noise is fed from outside to the electrochemical interface are analysed. Expressions for the rectified components in the mean are given for both the current and potential controlled situations; these are based on the functional-method approach. It is also shown how interesting techniques based on extrinsic noise signals are possible, under Tafel-regime conditions.     

Transport and kinetics at microheterogeneous electrodes: Part II. Application to a photogalvanic cell

The transport and kinetics of photogeneted species in a proposed photogalvanic cell [1] using colloidal electrode particles are considered. Solution of the differential equations allows the conditions for an efficient cell for solar energy conversion to be found. Compared to an ordinary photogalvanic cell of the iron thionine type, the rate constant for the back reaction can be up to 10³ larger at 10⁶ dm³ mol⁻¹ s⁻¹. However, there are severe constraints on the electrochemical rate constants; the colloidal electrode particles need to be very selective. In an efficient cell the dye may become bleached. The conditions here are the same as for the ordinary photogalvanic cell and hence the dye must be sufficiently soluble to absorb the solar radiation in 10⁻⁴ cm.     

Fundamentals of lead-acid cells: Part XI. Phase formation at solid and porous lead electrodes

The development of lead sulphate on lead (charged) electrodes (massive and porous) has been examined by the potential-step technique. The behaviour of the solid electrode conforms to control by nucleation and growth processes. The exact form of the process is potential-dependent and becomes two-dimensional at more positive potentials. The behaviour of the porous electrode can be interpreted in terms of well-established theory for porous materials assuming that the same crystallisation processes are observed as for the case of solid electrodes.     

Fundamentals of lead acid cells: Part IV. The reduction of porous PbO2 electrodes in sulphuric acid

The reduction behaviour of porous lead dioxide electrodes is shown to be independent of rotation speed in a large excess of 5 M H₂SO₄. The reduction peak is broadened by the porosity. This porosity broadening is interpreted in terms of the reaction being driven more deeply into the pore structure as the front of the electrode becomes progressively more ressstive. The effect of different potential sweep rates on the current response and the effects of progressive redox cycles can be fully explained on this model.     

Derivation and experimental verification of approximate explicit equations in differential pulse polarography: Part I. First order processes

An approximate method applicable to electrochemical processes either coupled or not to first order chemical reactions in differential pulse polarography is proposed. A program has been prepared in order to enable the authors to interpret DP polarograms. The method has been tested with the aid of well-known oxidation and reduction processes. The utility of the method is shown, particularly in those cases involving overlapping DP polarographic waves. Applications to determinations of kinetic parameters and quantitative analysis have also been made.     

Automated polarographic analysis : Part I. Design of flow-through cells and deaeration unit

The design of polarographic flow-through cells for automated analysis of discrete samples is discussed. A simple way of fitting the DME capillary into the cell is described, and the problems associated with the use of a mercury pool counter electrode are discussed. A platinum wire or gauze counter electrode downstream from the DME is more satisfactory. The reference electrode may be placed outside the flow cell, e.g. in the mercury waste bottle. A new method for the deaeration of sample solutions is also described; argon is bubbled through the solutions in the sample cups just before aspiration. The effect of various experimental parameters on the deaeration is described. Pump stoppage during sample shifts is advantageous. The adaptation of the deaeration method to commercial samplers is explained. The application of the proposed automated system for the determination of chlordiazepoxide is discussed.     

Non-stoichiometric molybdenum oxides as cathodes for lithium cells: Part I. Primary batteries

Some non-stoichiometric Mo oxides have been tested as cathodes for primary Li cells. Their performance has been evaluated as a function of current density, electrolyte, temperature, cathode porosity and formulation. Specific capacities exceeding 0.4·Ah g^?1 could be reached at low rates. As found with MoO₃, these oxides give rise to the formation of ternary phases of the type Li_myMo_mO_3m?1. Li⁺ insertion in the lattices allows structure retention for Li/Mo ratios lower than 0.7–0.8, whereas higher Li⁺ contents result in the appearance of new phases.     

Amperometric enzyme electrodes: Part I. Theory

The theory of the steady state operation of an amperometric enzyme is derived. The reaction scheme includes diffusion of substrate and product through a membrane, the kinetics of the enzyme substrate reaction and the electrochemical regeneration of the enzyme. A simple diagnostic plot is derived which allows the rate limiting process to be identified, and the balance between the transport of substrate through the membrane and the enzyme and electrochemical kinetics to be determined. The effects of inhibition by the accumulation of product behind the membrane are also considered.