72 research outputs found
Waste heat to Hydrogen using Reverse Electrodialysis
No full textIn current times the research across the globe is focused on carbon-free energy sources that can drive the economy in future. One of the promising ways to achieve this is to have demand-based sustainable energy storage powered by renewable energy sources. The use of excess renewable energy to produce chemicals or storing energy in the form of chemicals is the point of focus. This shows that we are transitioning towards power to chemical-based future energy system. Hydrogen is one such chemical. However, renewable energy sources such as solar and wind are intermittent. Sectors such as chemical industries, transportation are found to have potential. More than 40% of the total industrial energy use is being wasted by dumping it in the surrounding. We propose a salinity gradient-based energy system known as Reverse electrodialysis (RED) to solve these problems. Here, the driving force is concentration difference across an ion exchange membrane that causes a flow of ions in a specific direction. This flux of ions can be converted either into electrical current or produce gas such as hydrogen depending on the appropriate choice of electrode-electrolyte system. The RED system does not produce any toxic waste when in operation; it can be up-scaled to Mega-Watts size. Closed-loop RED systems use Mechanical or thermal energy to reuse the solutions exiting from the system. This heat can be at a temperature lower than 373 K. Thus leading to a stand-alone system independent of the geographical constraints for the source of the feed solutions.
A thermolytic salt- ammonium bicarbonate can use the low-grade waste heat (less than 373 K) to restore the concentration to initial. A thermodynamic model developed provides insight into the different parameters such as operating conditions- concentration of feed solutions, temperature; system parameters such as inter-membrane distance or channel thickness; residence time of feed solutions in the RED stack; and membrane properties such as permselectivity and area-specific membrane resistance. The system’s performance is evaluated based on hydrogen production rate normalised over membrane area, waste heat required to produce unit kilograms of hydrogen and cost incurred to produce one kilogram of hydrogen if the system is to be operated for 20 years levelised cost of hydrogen (LCH).
The concentration of concentrate solution increases the hydrogen production rate and reduces the levelised cost of hydrogen. The theoretical maximum concentration of concentrate solution is 2.6 M, whereas, in practice, it is 2M at room temperature. There is an optimal dilute solution concentration; any deviation decreases the hydrogen production rate and increases the levelised cost of hydrogen. However, with the increase in the concentration of feed solutions, the waste heat required to restore the concentration increases. This increase in the waste heat required increases the levelised cost of hydrogen. Hence to achieve low LCH, there is an optimum value of dilute solution concentration. This optimum was found to be ± 0.1 M. The increase in operating temperature increases the open circuit potential, increases ionic mobility, i.e. solution conductivity and thus the hydrogen production and lowers the LCH.
Assuming negligible resistance due to the electrical double layer and diffusion boundary layer, the increase in the inter-membrane distance or channel thickness decrease the hydrogen production rate due to increased channel ohmic resistance. The increase in the intermembrane distance decreases waste heat required per unit volume due to the reduced salt flux through the membrane but increases the total waste heat required due to the increased amount of volume flowing through the channel. An increase in residence time decreases pressure drop and thus the pumping power required. The amount of salt diffusing through the membrane increases, which increases the waste heat per unit volume. However, as the volume flow rate decreases, the total heat required to restore the concentrations decreases.
The economic study suggests that in the present scenario, capital expenses (CAPEX) and waste heat required contributes to more than 75% of the LCH. Regeneration system and membranes contribute more than 80% to the CAPEX. Hence it is essential to optimize regeneration system and membranes to achieve market competitive LCH. In the present and future scenario for a euro increase in the membrane cost, the LCH increases by 0.055 and 0.01 C kg−1 H2 . And for a 0.001 C kWh−1 increase in the cost of waste heat, the LCH increases by 4.02 and 1.78 C kg−1 H2 .
Membrane properties such as permselectivity and membrane resistance of ten commercial membranes were studied. In general, the anion exchange membranes (AEM) showed lower conductivity at different concentration and elevated temperatures when compared to the cation exchange membrane (CEM). The membranes with high conductivity (CMF- CEM; APSAEM) and low area-specific membrane resistance (CSO- CEM; FAS- AEM) were compared based on hydrogen production rate, specific waste heat required, energy efficiency and LCH. The highest performance was achieved with a stack made of FAS and CSO, producing hydrogen at 8.48· 10−7 kgm−2mems−1 with a waste heat requirement of 344kWhkg−1 hydrogen. This yielded an operating energy efficiency of 9.7% and a levelised cost of 7.80 C kg−1H2 . Permselectivity of the best performing membranes was studied at different concentrations; the AEM- FAS had lower permselectivity values than CEM- CSO. The concentration of ammonium bicarbonate solutions in the salt bridge influences the junction potential measurements without any clear trend. The estimated values for hydrogen production rate, thermodynamic efficiency, specific waste heat and the levelised cost of hydrogen for RED stack with CSO/FAS are 8.05·10−7 kgm−2s−1, 9.1%, 365.87kWhkg−1H2 , 10.132 C kg−1 H2 respectively. Finally, membrane area-specific resistance lower than 1·10−4 m−2 and permselectivity higher than 0.9 at membrane cost lower than 10 Cm−2 and waste heat cost of 0.005 CkWh−1 will make ammonium bicarbonate RED competitive with the current renewable source-based hydrogen-producing technologies
Faster Time Response by the Use of Wire Electrodes in Capacitive Salinity Gradient Energy Systems
No full textCapacitive 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
Impact of Wire Geometry in Energy Extraction from Salinity Differences Using Capacitive Technology
No full textEnergy 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 in 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 designs. Analytical evaluation and electrical measurements confirm a strong non-linear
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
Understanding Transport Phenomena in Membrane Systems for Waste Utilisation: Electrodialysis Concepts for Waste Heat to Hydrogen and Lithium-Ion Battery Recycling
No full textThe overall aim of this thesis is the development of useful and sustainable applications of ion-exchange membranes, with a focus on methods for understanding the fundamental transport processes taking place in the electrochemical cell. A deeper insight into the fundamentals may aid in the design and development of both new ion-exchange membranes and process applications. This approach is applied to the modeling of electrodialysis and reverse electrodialysis for use in battery recycling and hydrogen production, respectively.
First, models for the ion-exchange membrane fluxes and permselectivity were derived for an aqueous KCl mixture using non-equilibrium thermodynamics. The established relations were used to model the state of a unit cell during steady state reverse electrodialysis operation, and a stack of unit cells, each with an electric potential contribution due to the salinity gradient, was used to drive water electrolysis. The spent electrolyte mixtures exiting each unit cells could subsequently be regenerated by distillation using industrial waste heat, restoring the salinity gradient and creating a closed-loop system for hydrogen production. Simulations indicated a hydrogen production of 0.38 gH2 m−2h−1, a waste heat requirement of 1.7 kWh g−1 H2 , and a system efficiency of 2 % is possible with a saturated feed mixture and a draw mixture of 0.2 mol kg−1. The permselectivity model showed that the transference of water has a significant impact on the unit cell electric potential and therefore also on the system performance. Furthermore, it depends on the magnitude of the coupling between electric current and water flux, but also on the thermodynamic state of the two electrolyte mixtures. Factors such as the water transference coefficient, membrane and mixture resistance, cell geometry and the choice of electrolyte have been identified as important parameters which can be optimised to improve the system performance.
Next the permselectivity model was verified experimentally for two commercial ionexchange membranes, the Selemion CMVN cation-exchange membrane (CEM) and the Selemion AMVN anion-exchange membrane (AEM). It was determined that the model could accurately describe the statistically significant trends in the electric potential measurements of ion-exchange membranes subject to a salinity gradient. It was also verified that the electric potential contribution of one membrane was more easily accessed by using bare Ag/AgCl electrodes compared to commercial reference electrodes with filling solutions and porous junctions. The porous junction of the reference electrode showed an electric potential contribution to the total voltage compatible with a K+ transport number of tK+ = 0.494 ± 0.008 and no significant net transference of water. This is congruent with literature values of measured transport numbers for K+ in bulk aqueous KCl. The Selemion CMVN CEM was characterised by tK+ = 0.996 ± 0.006 and a constant water transference coefficient of tw = 3.69 ± 0.40. The Selemion AMVN was well described by tK+ = −0.002±0.004 and tw = −3.75±0.27, and therefore tCl– = 1−tK+ = 1.002±0.004. In other words, the two membranes appear to be perfectly selective to the target ion, but each ion carries around 4 water molecules through the membrane as part of the charge migration process. This is shown to have a beneficial effect on the energy requirement of electrodialysis, but a negative effect on the available work from a reverse electrodialysis cell.
The permselectivity model was then extended to ternary mixtures of KCl, H2O and ethanol (EtOH). A computational model was created to explore the state of a unit cell in electrodialysis, for the purpose of extracting salt and water from a saturated feed mixture and leaving purified EtOH behind. To do so, the ionexchange membranes must be highly selective towards salt along with a significant amount of water co-transport, while restricting co-transport of EtOH. In a case of individual ion-exchange membranes with tw = 15 and ta = 0, the EtOH solvent weight fraction was increased from ωa,in = 0.7 to ωa,out = 0.81. This required around 73 kWh m−3 EtOH, and could serve as the basis for a salt precipitation process with an energy requirement of 0.161 kWh mol−1 KCl. The concept may be of use in the recycling of batteries if ion-exchange membranes with negligible EtOH co-transport are identified or developed in the future.
For the analysis of measurements and construction of models related to the ternary mixture, thermodynamic data is necessary. The collected data was combined and critically analysed with a focus on the reference state of the salt. Notably, a constant reference state was used, in contrast to the variable salt reference state often used for mixed solvent electrolyte mixtures. Empirical regression models were then formulated for the activity coefficients of H2O and EtOH, and KCl was subsequently expressed as a function of those two models via Gibbs Duhem’s equation. This procedure yielded a thermodynamically consistent model which could be regarded as a useful low-complexity mixed solvent electrolyte model.
Lastly, we extended the permselectivity measurements to the ternary mixture for the determination of ion-exchange membrane transference coefficients. Significant variance was present in the measurements, but the permselectivity of the Selemion CMVN cation-exchange membrane was well described by a constant tK+ = 0.98 ± 0.01, a constant water transference coefficient of tw = 2.81 ± 0.42. The EtOH transference was characterized by the ratio of the transference coefficient to the thermodynamic activity, ta/aa, which was determined as a function of the mean thermodynamic activities of EtOH and salt in combination with a constant regression coefficient χ = 1.38 ± 0.40. EtOH transference coefficients of up to 2 were calculated based on this model. These results suggest that up to 2 molecules of EtOH can be carried along with K+ as the electric current passes through the CEM. The established permselectivity expressions and experimental methods are general and can be extended to other mixtures of interest
Testing Lithium-ion batteries thermal conductivity
No full textVarmeproduksjon og batteriets indre temperatur har stor innvirkning på ytelse og aldring av litium-ion batteri (LIB). Derfor spiller batteriets termiske styringssystem en avgjørende rolle for å redusere disse effektene i løpet av batteriets levetid. Å forstå de termiske ledningsevnene til batterikomponentene og de faktorene som påvirker disse evnene, vil bidra til mer nøyaktig temperaturforutsigelse inne i cellen og vil bidra til å forbedre strategiene for termisk styring i disse batterier.
Denne oppgaven rapporterer termisk ledningsevne til en FS3006-25 separator og kommersielle elektroder fra to LIB-celler. En celle som bruker LCO som katode og grafittanode, den andre cellen bruker en NMC katode og grafittanode. Materialene har målt under forskjellige trinn av komprimeringstrykk. I tillegg ble effekten av elektrolyttløsningsmidlet, celle aldring og termisk grensesnittmotstand mellom cellelagene undersøkt. Til slutt ble effekten av disse faktorene på den termiske varmetransporten inne i batteriet bestemt ved hjelp av en enkel endimensjonal termisk modell som simulerte temperaturfordelingen inne i batteriet.
Separatorens varmeledningsevne varierte fra 0.116 til 0.124 W/k m for et påført trykk fra 2,7 til 11,6 bar. NMC-katodens varmeledningsevne varierte fra 0,35 til 0,38 W/k m, mens LCO-katoden varierte fra 0,51 til 0,65 W/k m. Når det gjelder anoder, varierte varmeledningsevnen fra 0,427 til 0,597 W/k m. Tilsetning av elektrolyttløsningsmidlet økte materialers varmeledningsevne med en faktor på 2, 3 og 4.
De termiske modellene viste at tilsetning av elektrolyttløsningsmidlet tilLIB-cellelagene senker temperaturen i senteren av batteriet med 0,8 K for den NMC cellen (30 A/m ^2 current density), mens den LCO (13,1 A/m ^2 current density) temperaturen i senteren av batteriet redusert med 0,08 K. Videre, elektroder fra batteriet ved (beginning of life BOL) varmeledningsevne har målet og sammenlignet med (fresh) elektroder (aldri vært i batteri før). BOL NMC katode måling viste rundt 35 % lavere varmeledningsevneverdier enn (fresh) katoden.
Til slutt, den termisk kontaktmotstand mellom LIB-cellelagene ble målet. Resultatene viste en termisk kontaktmotstand på 4,3 E-5 K m ^2 w ^- 1 for LCO-katoden og 2,1 E-5 K m ^2 w ^- 1 for NMC-katoden. Anodenes termiske kontaktmotstand mot separatoren har målet på omtrent 6.5 E-5 K m ^2 w ^- 1. Tilsetning av elektrolyttløsningsmidlet reduserte termisk kontaktmotstand med en faktor på ca. 2 for katodene og ca. 7 for anodene
Testing Lithium-ion batteries thermal conductivity
No full textVarmeproduksjon og batteriets indre temperatur har stor innvirkning på ytelse og aldring av litium-ion batteri (LIB). Derfor spiller batteriets termiske styringssystem en avgjørende rolle for å redusere disse effektene i løpet av batteriets levetid. Å forstå de termiske ledningsevnene til batterikomponentene og de faktorene som påvirker disse evnene, vil bidra til mer nøyaktig temperaturforutsigelse inne i cellen og vil bidra til å forbedre strategiene for termisk styring i disse batterier.
Denne oppgaven rapporterer termisk ledningsevne til en FS3006-25 separator og kommersielle elektroder fra to LIB-celler. En celle som bruker LCO som katode og grafittanode, den andre cellen bruker en NMC katode og grafittanode. Materialene har målt under forskjellige trinn av komprimeringstrykk. I tillegg ble effekten av elektrolyttløsningsmidlet, celle aldring og termisk grensesnittmotstand mellom cellelagene undersøkt. Til slutt ble effekten av disse faktorene på den termiske varmetransporten inne i batteriet bestemt ved hjelp av en enkel endimensjonal termisk modell som simulerte temperaturfordelingen inne i batteriet.
Separatorens varmeledningsevne varierte fra 0.116 til 0.124 W/k m for et påført trykk fra 2,7 til 11,6 bar. NMC-katodens varmeledningsevne varierte fra 0,35 til 0,38 W/k m, mens LCO-katoden varierte fra 0,51 til 0,65 W/k m. Når det gjelder anoder, varierte varmeledningsevnen fra 0,427 til 0,597 W/k m. Tilsetning av elektrolyttløsningsmidlet økte materialers varmeledningsevne med en faktor på 2, 3 og 4.
De termiske modellene viste at tilsetning av elektrolyttløsningsmidlet tilLIB-cellelagene senker temperaturen i senteren av batteriet med 0,8 K for den NMC cellen (30 A/m ^2 current density), mens den LCO (13,1 A/m ^2 current density) temperaturen i senteren av batteriet redusert med 0,08 K. Videre, elektroder fra batteriet ved (beginning of life BOL) varmeledningsevne har målet og sammenlignet med (fresh) elektroder (aldri vært i batteri før). BOL NMC katode måling viste rundt 35 % lavere varmeledningsevneverdier enn (fresh) katoden.
Til slutt, den termisk kontaktmotstand mellom LIB-cellelagene ble målet. Resultatene viste en termisk kontaktmotstand på 4,3 E-5 K m ^2 w ^- 1 for LCO-katoden og 2,1 E-5 K m ^2 w ^- 1 for NMC-katoden. Anodenes termiske kontaktmotstand mot separatoren har målet på omtrent 6.5 E-5 K m ^2 w ^- 1. Tilsetning av elektrolyttløsningsmidlet reduserte termisk kontaktmotstand med en faktor på ca. 2 for katodene og ca. 7 for anodene.Heat generation and cell internal temperature have a large impact on Lithium-ion battery (LIB) cell performance and ageing mechanisms. Therefore, the battery thermal management system plays a critical role in mitigating all these effects during the battery life cycle. Understanding the thermal conductivities of the battery components and the factors that affect these values will help predict the temperature inside the cell, further improve the thermal management system.
This thesis reports the thermal conductivity of an FS3006-25 separator and commercial electrodes from two LIB cells. One cell utilizing LCO as the cathode and graphite as the anode, the other cell utilizing an NMC cathode and graphite anode. The materials are measured at different compaction pressure steps. In addition, the effect of the electrolyte solvent, cell assembly and thermal interface resistance between the cell layers were investigated. Finally, the effect of these factors on the heat transport inside the battery was determined using a simple one-dimensional thermal model simulating the temperature distribution inside the battery.
The thermal conductivity of the separator ranged from 0.116 to 0.124 W k^-1m^-1 for an applied pressure from 2.7 to 11.6 bar. NMC cathode thermal conductivity ranged from 0.35 to 0.38 W k^-1 m^-1 while the LCO cathode ranged from 0.51 to 0.65 W k^-1m^-1. In the case of anodes, the thermal conductivity ranged from 0.427 to 0.597 W k^-1m^-1. Adding the electrolyte solvent increased the thermal conductivity of the measured materials by a factor of 2 to 4.
In addition, the thermal models showed that adding the electrolyte to the cell layers decreases the centre temperature by 0.8 K for the NMC cell (30 A/m^2 charging current density), while the LCO cell (13.1 A/m^2 charging current density) centre temperature decreased by 0.08 K. Furthermore, electrodes at beginning of life (BOL) thermal conductivity are measured and compared to fresh electrodes. The BOL NMC cathode measurement showed around 35 % lower thermal conductivity values compering to the fresh cathode.
Finally, the thermal interface resistance between the LIB cell layers is measured. Results showed a thermal contact resistance of 4.3 E-5 K m^2 w^-1 for the LCO cathode and 2.1 E-5 K m^2 w^-1 for the NMC cathode. Anode thermal contact resistance to the separator is measured at about 6.5 E-5 K m^2 w^-1. Adding the electrolyte solvent decreased the thermal contact resistance by a factor of about 2 for the cathodes and about 7 for the anode
Waste heat to Hydrogen using Reverse Electrodialysis
No full textIn current times the research across the globe is focused on carbon-free energy sources that can drive the economy in future. One of the promising ways to achieve this is to have demand-based sustainable energy storage powered by renewable energy sources. The use of excess renewable energy to produce chemicals or storing energy in the form of chemicals is the point of focus. This shows that we are transitioning towards power to chemical-based future energy system. Hydrogen is one such chemical. However, renewable energy sources such as solar and wind are intermittent. Sectors such as chemical industries, transportation are found to have potential. More than 40% of the total industrial energy use is being wasted by dumping it in the surrounding. We propose a salinity gradient-based energy system known as Reverse electrodialysis (RED) to solve these problems. Here, the driving force is concentration difference across an ion exchange membrane that causes a flow of ions in a specific direction. This flux of ions can be converted either into electrical current or produce gas such as hydrogen depending on the appropriate choice of electrode-electrolyte system. The RED system does not produce any toxic waste when in operation; it can be up-scaled to Mega-Watts size. Closed-loop RED systems use Mechanical or thermal energy to reuse the solutions exiting from the system. This heat can be at a temperature lower than 373 K. Thus leading to a stand-alone system independent of the geographical constraints for the source of the feed solutions.
A thermolytic salt- ammonium bicarbonate can use the low-grade waste heat (less than 373 K) to restore the concentration to initial. A thermodynamic model developed provides insight into the different parameters such as operating conditions- concentration of feed solutions, temperature; system parameters such as inter-membrane distance or channel thickness; residence time of feed solutions in the RED stack; and membrane properties such as permselectivity and area-specific membrane resistance. The system’s performance is evaluated based on hydrogen production rate normalised over membrane area, waste heat required to produce unit kilograms of hydrogen and cost incurred to produce one kilogram of hydrogen if the system is to be operated for 20 years levelised cost of hydrogen (LCH).
The concentration of concentrate solution increases the hydrogen production rate and reduces the levelised cost of hydrogen. The theoretical maximum concentration of concentrate solution is 2.6 M, whereas, in practice, it is 2M at room temperature. There is an optimal dilute solution concentration; any deviation decreases the hydrogen production rate and increases the levelised cost of hydrogen. However, with the increase in the concentration of feed solutions, the waste heat required to restore the concentration increases. This increase in the waste heat required increases the levelised cost of hydrogen. Hence to achieve low LCH, there is an optimum value of dilute solution concentration. This optimum was found to be ± 0.1 M. The increase in operating temperature increases the open circuit potential, increases ionic mobility, i.e. solution conductivity and thus the hydrogen production and lowers the LCH.
Assuming negligible resistance due to the electrical double layer and diffusion boundary layer, the increase in the inter-membrane distance or channel thickness decrease the hydrogen production rate due to increased channel ohmic resistance. The increase in the intermembrane distance decreases waste heat required per unit volume due to the reduced salt flux through the membrane but increases the total waste heat required due to the increased amount of volume flowing through the channel. An increase in residence time decreases pressure drop and thus the pumping power required. The amount of salt diffusing through the membrane increases, which increases the waste heat per unit volume. However, as the volume flow rate decreases, the total heat required to restore the concentrations decreases.
The economic study suggests that in the present scenario, capital expenses (CAPEX) and waste heat required contributes to more than 75% of the LCH. Regeneration system and membranes contribute more than 80% to the CAPEX. Hence it is essential to optimize regeneration system and membranes to achieve market competitive LCH. In the present and future scenario for a euro increase in the membrane cost, the LCH increases by 0.055 and 0.01 C kg−1 H2 . And for a 0.001 C kWh−1 increase in the cost of waste heat, the LCH increases by 4.02 and 1.78 C kg−1 H2 .
Membrane properties such as permselectivity and membrane resistance of ten commercial membranes were studied. In general, the anion exchange membranes (AEM) showed lower conductivity at different concentration and elevated temperatures when compared to the cation exchange membrane (CEM). The membranes with high conductivity (CMF- CEM; APSAEM) and low area-specific membrane resistance (CSO- CEM; FAS- AEM) were compared based on hydrogen production rate, specific waste heat required, energy efficiency and LCH. The highest performance was achieved with a stack made of FAS and CSO, producing hydrogen at 8.48· 10−7 kgm−2mems−1 with a waste heat requirement of 344kWhkg−1 hydrogen. This yielded an operating energy efficiency of 9.7% and a levelised cost of 7.80 C kg−1H2 . Permselectivity of the best performing membranes was studied at different concentrations; the AEM- FAS had lower permselectivity values than CEM- CSO. The concentration of ammonium bicarbonate solutions in the salt bridge influences the junction potential measurements without any clear trend. The estimated values for hydrogen production rate, thermodynamic efficiency, specific waste heat and the levelised cost of hydrogen for RED stack with CSO/FAS are 8.05·10−7 kgm−2s−1, 9.1%, 365.87kWhkg−1H2 , 10.132 C kg−1 H2 respectively. Finally, membrane area-specific resistance lower than 1·10−4 m−2 and permselectivity higher than 0.9 at membrane cost lower than 10 Cm−2 and waste heat cost of 0.005 CkWh−1 will make ammonium bicarbonate RED competitive with the current renewable source-based hydrogen-producing technologies
Emptiness, Membership and Regular Expressions for Tree Homomorphic Feature Structure Grammars
No full textTree Homomorphic Feature Structure Grammar is a feature structure grammar formalism based on Lexical-Functional Grammar (LFG). It has a strong restriction on the syntax of the equation schemata, but does not have the off-line parsability constraint. In this paper we use modal logic to show that the emptiness and membership problems are decidable for this grammar formalism. We also show that we may allow regular expressions in the feature structure equations without changing the class of languages described. 1 Introduction and some definitions Feature structure grammars are widely used in computational linguistics. They are grammar formalisms that use feature structures as (one of) their main data structure(s), sometime together with some phrase structure backbone. Feature structures and the way they may be specified are very flexible, but this flexibility has its drawback: the formalisms become almost too powerful in the sense that the membership problem for these grammars in their m..
Thermal conductivity and temperature profiles in carbon electrodes for supercapacitors
No full textThe thermal conductivity of supercapacitor film electrodes composed of activated carbon (AC), AC with 15 mass% multi-walled carbon nanotubes (MWCNTs), AC with 15 mass% onion-like carbon (OLC), and only OLC, all mixed with polymer binder (polytetrafluoroethylene), has been measured. This was done for dry electrodes and after the electrodes have been saturated with an organic electrolyte (1 M tetraethylammonium–tetrafluoroborate in acetonitrile, TEA–BF4). The thermal conductivity data was implemented in a simple model of generation and transport of heat in a cylindrical cell supercapacitor systems. Dry electrodes showed a thermal conductivity in the range of 0.09–0.19 W K−1 m−1 and the electrodes soaked with an organic electrolyte yielded values for the thermal conductivity between 0.42 and 0.47 W K−1 m−1. It was seen that the values related strongly to the porosity of the carbon electrode materials. Modeling of the internal temperature profiles of a supercapacitor under conditions corresponding to extreme cycling demonstrated that only a moderate temperature gradient of several degrees Celsius can be expected and which depends on the ohmic resistance of the cell as well as the wetting of the electrode materials.submittedVersionThis is a submitted manuscript of an article published by Elsevier Ltd in Journal of Power Sources, 25 July 2013
Thermal conductivity and temperature profiles in carbon electrodes for supercapacitors
No full textThe thermal conductivity of supercapacitor film electrodes composed of activated carbon (AC), AC with 15 mass% multi-walled carbon nanotubes (MWCNTs), AC with 15 mass% onion-like carbon (OLC), and only OLC, all mixed with polymer binder (polytetrafluoroethylene), has been measured. This was done for dry electrodes and after the electrodes have been saturated with an organic electrolyte (1 M tetraethylammonium–tetrafluoroborate in acetonitrile, TEA–BF4). The thermal conductivity data was implemented in a simple model of generation and transport of heat in a cylindrical cell supercapacitor systems. Dry electrodes showed a thermal conductivity in the range of 0.09–0.19 W K−1 m−1 and the electrodes soaked with an organic electrolyte yielded values for the thermal conductivity between 0.42 and 0.47 W K−1 m−1. It was seen that the values related strongly to the porosity of the carbon electrode materials. Modeling of the internal temperature profiles of a supercapacitor under conditions corresponding to extreme cycling demonstrated that only a moderate temperature gradient of several degrees Celsius can be expected and which depends on the ohmic resistance of the cell as well as the wetting of the electrode materials
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