Open-Circuit Voltage Comes from Non-Equilibrium Thermodynamics

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Diego del Olmo ◽  
Michal Pavelka ◽  
Juraj Kosek
Keyword(s):  
Open Circuit Voltage ◽  
Open Circuit ◽  
Electrochemical Reactions ◽  
Equilibrium Thermodynamics ◽  
Nernst Equation ◽  
Vanadium Redox ◽  
Mixed Potentials ◽  
Thermodynamic Derivation ◽  
Zinc Air Batteries ◽  
Non Equilibrium

AbstractOriginally derived by Walther Nernst more than a century ago, the Nernst equation for the open-circuit voltage is a cornerstone in the analysis of electrochemical systems. Unfortunately, the assumptions behind its derivation are often overlooked in the literature, leading to incorrect forms of the equation when applied to complex systems (for example, those with ion-exchange membranes or involving mixed potentials). Such flaws can be avoided by applying a correct thermodynamic derivation independently of the form in which the electrochemical reactions are written. The proper derivation of the Nernst equation becomes important, for instance, in modeling of vanadium redox flow batteries or zinc-air batteries. The rigorous path towards the Nernst equation derivation starts in non-equilibrium thermodynamics.

Photometrical Determination of the State-of-Charge in Vanadium Redox Flow Batteries Part II: In Combination with Open-Circuit-Voltage

2019 ◽  
Vol 233 (12) ◽  
pp. 1695-1711 ◽  
Author(s):  
Jan Geiser ◽  
Harald Natter ◽  
Rolf Hempelmann ◽  
Bernd Morgenstern ◽  
Kaspar Hegetschweiler
Keyword(s):  
Open Circuit Voltage ◽  
Open Circuit ◽  
The State ◽  
State Of Charge ◽  
Vanadium Redox Flow Battery ◽  
Term Operation ◽  
Partial State ◽  
Set Up ◽  
Vanadium Redox

AbstractBy means of in-situ UV/Vis/NIR spectrometry, separately both in the anolyte as well as in the catholyte of a vanadium redox flow battery (single cell) partial state-of-charge values are determined online. The UV/Vis/NIR spectroscopic experimental set-up is calibrated using the state-of-charge value determined from measurements of the open-circuit-voltage (OCV) in the pristine state of the battery which is related to Nernst’s equation taking into account also H+ formation/consumption during the V4+/V5+ redox process. The comparison of both partial state-of-charge values indicates a possible imbalance of the battery, which can occur after long-term operation.

scholarly journals Thermodynamically Rigorous Description of the Open Circuit Voltage of Redox Flow Batteries

2021 ◽  
Author(s):  
Nicolas Hayer ◽  
Maximilian Kohns
Keyword(s):  
Activity Coefficients ◽  
Open Circuit Voltage ◽  
Renewable Energy Sources ◽  
Measurement Data ◽  
Open Circuit ◽  
Power Grids ◽  
Nernst Equation ◽  
Rigorous Approach ◽  
Redox Flow Batteries ◽  
Flow Batteries

Redox flow batteries (RFBs) are considered an outstanding candidate for the integration of renewable energy sources into the existing power grids. A key property of RFBs is the open circuit voltage (OCV) corresponding to the currentless equilibrium state. In the literature, the Nernst equation describing this property is often simplified by neglecting the activity coefficients. In this work, using a thermodynamically rigorous approach, we show that activity coefficients have a significant influence on the OCV of the Iron-Cadmium and All-Vanadium RFBs. Moreover, this influence varies with the state of charge. Therefore, activity coefficients should not be neglected in the Nernst equation. We show that when doing so, the resulting offset in OCV is actually comparable to typical voltage losses occurring during operation. Hence, fitting kinetic parameters to measurement data of voltage losses can lead to ambiguous results if only the idealized OCV, obtained by neglecting the activity coefficients, is used in that evaluation. Therefore, the implementation of a thermodynamically rigorous model has the potential to significantly improve state-of-the-art models for RFBs.

Microcrystalline (Si,Ge):H Solar Cells

2003 ◽  
Vol 762 ◽  
Author(s):  
Jianhua Zhu ◽  
Vikram L. Dalal
Keyword(s):  
Solar Cells ◽  
Buffer Layer ◽  
Quantum Efficiency ◽  
Fill Factor ◽  
Open Circuit Voltage ◽  
Defect Density ◽  
Cell Structure ◽  
Open Circuit ◽  
Base Layer ◽  
Ecr Plasma

AbstractWe report on the growth and properties of microcrystalline Si:H and (Si,Ge):H solar cells on stainless steel substrates. The solar cells were grown using a remote, low pressure ECR plasma system. In order to crystallize (Si,Ge), much higher hydrogen dilution (∼40:1) had to be used compared to the case for mc-Si:H, where a dilution of 10:1 was adequate for crystallization. The solar cell structure was of the p+nn+ type, with light entering the p+ layer. It was found that it was advantageous to use a thin a-Si:H buffer layer at the back of the cells in order to reduce shunt density and improve the performance of the cells. A graded gap buffer layer was used at the p+n interface so as to improve the open-circuit voltage and fill factor. The open circuit voltage and fill factor decreased as the Ge content increased. Quantum efficiency measurements indicated that the device was indeed microcrystalline and followed the absorption characteristics of crystalline ( Si,Ge). As the Ge content increased, quantum efficiency in the infrared increased. X-ray measurements of films indicated grain sizes of ∼ 10nm. EDAX measurements were used to measure the Ge content in the films and devices. Capacitance measurements at low frequencies ( ~100 Hz and 1 kHz) indicated that the base layer was indeed behaving as a crystalline material, with classical C(V) curves. The defect density varied between 1x1016 to 2x1017/cm3, with higher defects indicated as the Ge concentration increased.

Reducing recombination and enhancing open circuit voltage by Strontium-alloying in multiple cation perovskite solar cells

2017 ◽  
Author(s):  
Pietro Caprioglio ◽  
Fengshuo Zu ◽  
Christian M. Wolff ◽  
Martin Stolterfhot ◽  
Norbert Koch ◽  
...  
Keyword(s):  
Solar Cells ◽  
Open Circuit Voltage ◽  
Perovskite Solar Cells ◽  
Open Circuit
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