Seebeck coefficients of cells with lithium carbonate and gas electrodes

AbstractThe Seebeck coefficient is reported for thermoelectric cells with gas electrodes and a molten electrolyte of one salt, lithium carbonate, at an average temperature of 750°C. We show that the coefficient, which is 0.88mVK−1, can be further increased by adding an inorganic oxide powder to the electrolyte. We interpret the measurements using the theory of irreversible thermodynamics and find that the increase in the Seebeck coefficient is due to a reduction in the transported entropy of the carbonate ion when adding solid particles to the alkali carbonate. Oxides of magnesium, cerium and lithium aluminate lead to a reduction in the transported entropy from 232±12 to around 200±4JK−1mol−1. This is of importance for design of thermoelectric converters

CAPMIX -Deploying Capacitors for Salt Gradient Power Extraction

AbstractThe process of mixing sea and river water can be utilised as a power source. At present, three groups of technology are established for doing so; i) mechanical; Pressure Retarded Osmosis PRO, ii) electrochemical reactions; Reverse ElectroDialysis (RED) and Nano Battery Electrodes (NBE) and iii) ultra capacitors; Capacitive Double Layer Expansion (CDLE) and Capacitors charge by the Donnan Potentials (CDP). The chemical potential for salt gradient power systems is only limited by the feed solution concentrations and is the same for all types of salt power branches, but the electric work to the grid, however, relies on the route of conversion and means chosen therein. The CAPMIX project is a joint project to develop and explore ultra capacitors for doing so.Ultra-capacitor materials can interact with sea and river water in order to be deployed as an electricity source. The author consortium is currently exploring two routes to extract the potential free energy from mixing sea and river water by such means. These two routes are the Capacitive Double Layer Expansion (CDLE) and Capacitors charge by the Donnan Potentials (CDP), which are both recently reported, since 2009. The denominator of the two processes is the porous carbon capacitors constituting the capacitors where the chemical energy is converted into electric energy (current). The CDP differs from the CDLE mainly because it includes the use of membranes in addition to the capacitor materials

Improved reverse electro-dialysis using membranes with integrated spacers

Reverse Electro-Dialysis, RED, utilises the energy of mixing between two solutions of different salinity by allowing ionic current to pass through the membranes and the two solutions such that cations are transport to the cathode and anions to the anode. [1-4] The ionic current is converted to electronic current by red-ox reactions at the cathode and the anode. The membranesapplied in this process are ionic selective, traditionally of uniform thickness and separated by a non-conductive spacer [5, 6]. Traditionally, non-conductive spacers have been deployed as eddy promoters and membrane spacers in salinity difference power extraction systems, such as Pressure Retarded Osmosis (PRO) and Reverse Electro-Dialysis (RED)

Regeneration of the ionic liquid tetraoctylammonium oleate after metal extraction

Ionic liquids (ILs) have been presented as suitable candidates for metal extraction in the hydrometallurgy. It has already been proven that they have an adjustable selectivity towards metal ions. However, industrial applications of ILs are often limited due to their high price. Therefore, regeneration and reuse of ILs is necessary. In this study the regeneration of the fatty acid based IL tetraoctylammonium oleate was investigated, because in previous study excellent metal salt extraction efficiencies were obtained with this benign IL. Two methods for regeneration were investigated, i.e. electro-deposition and chemical regeneration. Electro-deposition turned out to be unfeasible for this IL. Chemical regeneration showed that the metal ions (Zn, Co and Mn) can be selectively back-extracted, so that metals can also be separated from each other in this step. The best stripping solution was aqueous sodium oxalate, which allowed the IL to be reused with no further treatment

Seawater electrodialysis with preferential removal of divalent ions

In this work desalination of a ternary salt mixture and at North Sea water is studied with a lab scale electrodialysis stack, which was used in a recycling batch mode. During desalination samples were taken and the ionic composition of the dilute stream was determined. The effect of applied current density (10-300 A/m(2)) On this composition was investigated. A clear effect of applied current density was observed. A lower applied current density leads to a more complete reduction in concentration of divalent ions, in an earlier extent of desalination. This influence of the applied current density could be related to the concentration polarization effects that occur in the diffusional boundary layer and are explained with a model based on the Nernst-Planck flux equation. It was found that the lower initial ion concentration of Ca2+, Mg2+ but also of K+ and SO42- compared to respectively Na+ and Cl-, leads to stronger depletion of these ions in the transport layer adjacent the membrane. These boundary layer effects are more pronounced at higher applied current densities, resulting in reduced transport of ions with a low initial concentration. High monovalent over divalent ion ratios can be found at low applied current. (C) 2013 Elsevier By. All rights reserved

Extraction of Energy from Small Thermal Differences near Room Temperature Using Capacitive Membrane Technology

Extracting electric energy from small temperature differences is an emerging field in response to the transition toward sustainable energy generation. We introduce a novel concept for producing electricity from small temperature differences by the use of an assembly combining ion exchange membranes and porous carbon electrodes immersed in aqueous electrolytes. Via the temperature differences, we generate a thermal membrane potential that acts as a driving force for ion adsorption/desorption cycles within an electrostatic double layer, thus converting heat into electric work. We report for a temperature difference of 30 degrees C a maximal energy harvest of similar to 2 mJ/m(2), normalized to the surface area of all the membranes

Impact of Wire Geometry in Energy Extraction from Salinity Differences Using Capacitive Technology

Energy extraction based on capacitive Donnan potential (CDP) is a recently suggested technique for sustainable power generation. CDP combines the use of ion-exchange membranes and porous carbon electrodes to convert the Gibbs free energy of mixing sea and river water into electric work. The electrodes geometry has a relevant impact on internal resistance and overall performance in CDP. In this work, we present the first effort to use wire shaped electrodes and its suitability for improving CDP. Analytical evaluation and electrical measurements confirm a strong nonlinear decrease in internal resistance for distances between electrodes smaller than 3 mm. We also demonstrated that we get more power per material invested when compared to traditional flat plate designs. These findings show the advantages of this design for further development of CDP into a mature technology

Faster Time Response by the Use of Wire Electrodes in Capacitive Salinity Gradient Energy Systems

Capacitive energy extraction based on Donnan potential (CDP) and capacitive energy extraction based on double layer expansion (CDLE) are novel electroctrochemical processes to convert the potential free energy of mixing sea and river water into electric work. This is done by the use of supercapacitor electrodes with and without ion exchange membranes. Currently, these techniques rely on improved mass transport in order to become more efficient and give higher power output. In this paper we evaluate the transport phenomena by diffusion and the electrode geometry when switching between sea and river water at open circuit potential (OCP). By changing the electrode geometry from a flat plate to a cylindrical one, experiments and analytical models in combination show that mass transport by diffusion is increased. This is demonstrated without any changes in the hydrodynamic conditions. Improving mass transport without changing the hydrodynamic conditions breaks with what has been the convention in the scientific community of salinity gradient power. Moreover, in sea water the transport phenomena appear to be controlled by diffusion, and the response time for building open circuit potential in CDP and CDLE under this condition is reduced by a factor of 2 when using wire electrodes instead of flat plate electrodes. In river water, the trend is similar though the response time is generally larger