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Peter Single - One of the best experts on this subject based on the ideXlab platform.
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TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS 1 Compact Nonlinear Model of an Implantable Electrode Array for Spinal Cord Stimulation (SCS)
2016Co-Authors: Jonathan Scott, Senior Member, Peter SingleAbstract:Abstract—We describe the construction of a model of the electrode-Electrolyte interface and surrounding Electrolyte in the case of a platinum-electrode array intended for spinal-cord stimulation (SCS) application. We show that a finite, two-dimensional, resistor array provides a satisfactory model of the Bulk Electrolyte, and we identify the complexity required of that resistor array. The electrode-Electrolyte interface is modelled in a fashion suitable for commonly-available, compact simulators using a nonlinear extension of the model of Franks et al. [4] that incorporates diodes and a memristor. The electrode-Electrolyte interface model accounts for the nonlinear current-overpotential characteristic and diffusion-limiting effects. We characterise a commercial, implantable, electrode array, fit the model to it, and show that the model successfully predicts subtle operational characteristics. Index Terms—Electrical stimulation, Bioelectric phenomena
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Compact Nonlinear Model of an Implantable Electrode Array for Spinal Cord Stimulation (SCS)
IEEE Transactions on Biomedical Circuits and Systems, 2014Co-Authors: Jonathan Scott, Peter SingleAbstract:We describe the construction of a model of the electrode-Electrolyte interface and surrounding Electrolyte in the case of a platinum-electrode array intended for spinal-cord stimulation (SCS) application. We show that a finite, two-dimensional, resistor array provides a satisfactory model of the Bulk Electrolyte, and we identify the complexity required of that resistor array. The electrode-Electrolyte interface is modelled in a fashion suitable for commonly-available, compact simulators using a nonlinear extension of the model of Franks (IEEE Trans. Biomed. Eng., vol. 52 , no. 7 , pp. 1295-1302, Jul. 2005) that incorporates diodes and a memristor. The electrode-Electrolyte interface model accounts for the nonlinear current-overpotential characteristic and diffusion-limiting effects. We characterise a commercial, implantable, electrode array, fit the model to it, and show that the model successfully predicts subtle operational characteristics.
Dan J L Brett - One of the best experts on this subject based on the ideXlab platform.
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correlating electrochemical impedance with hierarchical structure for porous carbon based supercapacitors using a truncated transmission line model
Electrochimica Acta, 2018Co-Authors: Dina Ibrahim Abouelamaiem, Tobias P Neville, Drasti Patel, Rongfang Wang, Ivan P Parkin, Ana Belen Jorge, Mariamagdalena Titirici, Paul R Shearing, Dan J L BrettAbstract:This work considers the relationship between the morphology of porous carbon materials used for supercapacitors and the electrochemical impedance spectroscopy (EIS) response. EIS is a powerful tool that can be used to study the porous 3-dimensional electrode behavior in different electrochemical systems. Porous carbons prepared by treatment of cellulose with different compositions of potassium hydroxide (KOH) were used as model systems to investigate the form vs. electrochemical function relationship. A simple equivalent circuit that represents the electrochemical impedance behavior over a wide range of frequencies was designed. The associated impedances with the Bulk Electrolyte, Faradaic electrode processes and different pore size ranges were investigated using a truncated version of the standard transmission line model. The analysis considers the requirements of porous materials as electrodes in supercapacitor applications, reasons for their non-ideal performance and the concept of ‘best capacitance’ behavior in different frequency ranges. Graphical Abstract: The Electrolyte ions penetrate the macropores, into the mesopores and finally reach the micropores. The capacitance measured by impedance spectroscopy is a function of frequency and porous structure.
Meenesh R Singh - One of the best experts on this subject based on the ideXlab platform.
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effects of temperature and gas liquid mass transfer on the operation of small electrochemical cells for the quantitative evaluation of co2 reduction electrocatalysts
Physical Chemistry Chemical Physics, 2016Co-Authors: Peter Lobaccaro, Meenesh R Singh, Ezra L Clark, Youngkook Kwon, Alexis T Bell, J W AgerAbstract:In the last few years, there has been increased interest in electrochemical CO2 reduction (CO2R). Many experimental studies employ a membrane separated, electrochemical cell with a mini H-cell geometry to characterize CO2R catalysts in aqueous solution. This type of electrochemical cell is a mini-chemical reactor and it is important to monitor the reaction conditions within the reactor to ensure that they are constant throughout the study. We show that operating cells with high catalyst surface area to Electrolyte volume ratios (S/V) at high current densities can have subtle consequences due to the complexity of the physical phenomena taking place on electrode surfaces during CO2R, particularly as they relate to the cell temperature and Bulk Electrolyte CO2 concentration. Both effects were evaluated quantitatively in high S/V cells using Cu electrodes and a bicarbonate buffer Electrolyte. Electrolyte temperature is a function of the current/total voltage passed through the cell and the cell geometry. Even at a very high current density, 20 mA cm-2, the temperature increase was less than 4 °C and a decrease of <10% in the dissolved CO2 concentration is predicted. In contrast, limits on the CO2 gas-liquid mass transfer into the cells produce much larger effects. By using the pH in the cell to measure the CO2 concentration, significant undersaturation of CO2 is observed in the Bulk Electrolyte, even at more modest current densities of 10 mA cm-2. Undersaturation of CO2 produces large changes in the faradaic efficiency observed on Cu electrodes, with H2 production becoming increasingly favored. We show that the size of the CO2 bubbles being introduced into the cell is critical for maintaining the equilibrium CO2 concentration in the Electrolyte, and we have designed a high S/V cell that is able to maintain the near-equilibrium CO2 concentration at current densities up to 15 mA cm-2.
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an experimental and modeling simulation based evaluation of the efficiency and operational performance characteristics of an integrated membrane free neutral ph solar driven water splitting system
Energy and Environmental Science, 2014Co-Authors: Meenesh R Singh, Jian Jin, Karl Walczak, Chris Karp, Nathan S Lewis, Chengxiang XiangAbstract:The efficiency limits, gas-crossover behavior, formation of local pH gradients near the electrode surfaces, and safety characteristics have been evaluated experimentally as well as by use of multi-physics modeling and simulation methods for an integrated solar-driven water-splitting system that operates with Bulk Electrolyte solutions buffered at near-neutral pH. The integrated membrane-free system utilized a triple-junction amorphous hydrogenated Si (a-Si:H) cell as the light absorber, Pt and cobalt phosphate (Co–Pi) as electrocatalysts for the hydrogen-evolution reaction (HER) and oxygen-evolution reaction (OER), respectively, and a Bulk aqueous solution buffered at pH = 9.2 by 1.0 M of boric acid/borate as an Electrolyte. Although the solar-to-electrical efficiency of the stand-alone triple-junction a-Si:H photovoltaic cell was 7.7%, the solar-to-hydrogen (STH) conversion efficiency for the integrated membrane-free water-splitting system was limited under steady-state operation to 3.2%, and the formation of pH gradients near the electrode surfaces accounted for the largest voltage loss. The membrane-free system exhibited negligible product-recombination loss while operating at current densities near 3.0 mA cm−2, but exhibited significant crossover of products (up to 40% H2 in the O2 chamber), indicating that the system was not intrinsically safe. A system that contained a membrane to minimize the gas crossover, but which was otherwise identical to the membrane-free system, yielded very low energy-conversion efficiencies at steady state, due to low transference numbers for protons across the membranes resulting in electrodialysis of the solution and the consequent formation of large concentration gradients of both protons and buffer counterions near the electrode surfaces. The modeling and simulation results showed that despite the addition of 1.0 M of buffering agent to the Bulk of the solution, during operation significant pH gradients developed near the surfaces of the electrodes. Hence, although the Bulk Electrolyte was buffered to near-neutral pH, the electrode surfaces and electrocatalysts experienced local environments under steady-state operation that were either highly acidic or highly alkaline in nature, changing the chemical form of the electrocatalysts and exposing the electrodes to potentially corrosive local pH conditions. In addition to significant pH gradients, the STH conversion efficiency of both types of systems was limited by the mass transport of ionic species to the electrode surfaces. Even at operating current densities of <3 mA cm−2, the voltage drops due to these pH gradients exceeded the combined electrocatalyst overpotentials for the hydrogen- and oxygen-evolution reactions at current densities of 10 mA cm−2. Hence, such near-neutral pH solar-driven water-splitting systems were both fundamentally limited in efficiency and/or co-evolved explosive mixtures of H2(g) and O2(g) in the presence of active catalysts for the recombination of H2(g) and O2(g).
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an experimental and modeling simulation based evaluation of the efficiency and operational performance characteristics of an integrated membrane free neutral ph solar driven water splitting system
Energy and Environmental Science, 2014Co-Authors: Karl Walczak, Meenesh R Singh, Chris Karp, Nathan S Lewis, Chengxiang XiangAbstract:The efficiency limits, gas-crossover behavior, formation of local pH gradients near the electrode surfaces, and safety characteristics have been evaluated experimentally as well as by use of multi-physics modeling and simulation methods for an integrated solar-driven water-splitting system that operates with Bulk Electrolyte solutions buffered at near-neutral pH. The integrated membrane-free system utilized a triple-junction amorphous hydrogenated Si (a-Si:H) cell as the light absorber, Pt and cobalt phosphate (Co–Pi) as electrocatalysts for the hydrogen-evolution reaction (HER) and oxygen-evolution reaction (OER), respectively, and a Bulk aqueous solution buffered at pH = 9.2 by 1.0 M of boric acid/borate as an Electrolyte. Although the solar-to-electrical efficiency of the stand-alone triple-junction a-Si:H photovoltaic cell was 7.7%, the solar-to-hydrogen (STH) conversion efficiency for the integrated membrane-free water-splitting system was limited under steady-state operation to 3.2%, and the formation of pH gradients near the electrode surfaces accounted for the largest voltage loss. The membrane-free system exhibited negligible product-recombination loss while operating at current densities near 3.0 mA cm−2, but exhibited significant crossover of products (up to 40% H2 in the O2 chamber), indicating that the system was not intrinsically safe. A system that contained a membrane to minimize the gas crossover, but which was otherwise identical to the membrane-free system, yielded very low energy-conversion efficiencies at steady state, due to low transference numbers for protons across the membranes resulting in electrodialysis of the solution and the consequent formation of large concentration gradients of both protons and buffer counterions near the electrode surfaces. The modeling and simulation results showed that despite the addition of 1.0 M of buffering agent to the Bulk of the solution, during operation significant pH gradients developed near the surfaces of the electrodes. Hence, although the Bulk Electrolyte was buffered to near-neutral pH, the electrode surfaces and electrocatalysts experienced local environments under steady-state operation that were either highly acidic or highly alkaline in nature, changing the chemical form of the electrocatalysts and exposing the electrodes to potentially corrosive local pH conditions. In addition to significant pH gradients, the STH conversion efficiency of both types of systems was limited by the mass transport of ionic species to the electrode surfaces. Even at operating current densities of <3 mA cm−2, the voltage drops due to these pH gradients exceeded the combined electrocatalyst overpotentials for the hydrogen- and oxygen-evolution reactions at current densities of 10 mA cm−2. Hence, such near-neutral pH solar-driven water-splitting systems were both fundamentally limited in efficiency and/or co-evolved explosive mixtures of H2(g) and O2(g) in the presence of active catalysts for the recombination of H2(g) and O2(g).
Celine Merlet - One of the best experts on this subject based on the ideXlab platform.
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mesoscopic simulations of the in situ nmr spectra of porous carbon based supercapacitors electronic structure and adsorbent reorganisation effects
Physical Chemistry Chemical Physics, 2021Co-Authors: Anagha Sasikumar, Patrice Simon, Anouar Belhboub, Camille Bacon, Alexander C Forse, John M Griffin, Clare P Grey, Celine MerletAbstract:In situ NMR spectroscopy is a powerful technique to investigate charge storage mechanisms in carbon-based supercapacitors thanks to its ability to distinguish ionic and molecular species adsorbed in the porous electrodes from those in the Bulk Electrolyte. The NMR peak corresponding to the adsorbed species shows a clear change of chemical shift as the applied potential difference is varied. This variation in chemical shift is thought to originate from a combination of ion reorganisation in the pores and changes in ring current shifts due to the changes of electronic density in the carbon. While previous Density Functional Theory calculations suggested that the electronic density has a large effect, the relative contributions of these two effects is challenging to untangle. Here, we use mesoscopic simulations to simulate NMR spectra and investigate the relative importance of ion reorganisation and ring currents on the resulting chemical shift. The model is able to predict chemical shifts in good agreement with NMR experiments and indicates that the ring currents are the dominant contribution. A thorough analysis of a specific electrode/Electrolyte combination for which detailed NMR experiments have been reported allows us to confirm that local ion reorganisation has a very limited effect but the relative quantities of ions in pores of different sizes, which can change upon charging/discharging, can lead to a significant effect. Our findings suggest that in situ NMR spectra of supercapacitors may provide insights into the electronic structure of carbon materials in the future.
Patrice Simon - One of the best experts on this subject based on the ideXlab platform.
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mesoscopic simulations of the in situ nmr spectra of porous carbon based supercapacitors electronic structure and adsorbent reorganisation effects
Physical Chemistry Chemical Physics, 2021Co-Authors: Anagha Sasikumar, Patrice Simon, Anouar Belhboub, Camille Bacon, Alexander C Forse, John M Griffin, Clare P Grey, Celine MerletAbstract:In situ NMR spectroscopy is a powerful technique to investigate charge storage mechanisms in carbon-based supercapacitors thanks to its ability to distinguish ionic and molecular species adsorbed in the porous electrodes from those in the Bulk Electrolyte. The NMR peak corresponding to the adsorbed species shows a clear change of chemical shift as the applied potential difference is varied. This variation in chemical shift is thought to originate from a combination of ion reorganisation in the pores and changes in ring current shifts due to the changes of electronic density in the carbon. While previous Density Functional Theory calculations suggested that the electronic density has a large effect, the relative contributions of these two effects is challenging to untangle. Here, we use mesoscopic simulations to simulate NMR spectra and investigate the relative importance of ion reorganisation and ring currents on the resulting chemical shift. The model is able to predict chemical shifts in good agreement with NMR experiments and indicates that the ring currents are the dominant contribution. A thorough analysis of a specific electrode/Electrolyte combination for which detailed NMR experiments have been reported allows us to confirm that local ion reorganisation has a very limited effect but the relative quantities of ions in pores of different sizes, which can change upon charging/discharging, can lead to a significant effect. Our findings suggest that in situ NMR spectra of supercapacitors may provide insights into the electronic structure of carbon materials in the future.
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Confinement, Desolvation, And Electrosorption Effects on the Diffusion of Ions in Nanoporous Carbon Electrodes
Journal of the American Chemical Society, 2015Co-Authors: Clarisse Pean, Barbara Daffos, Benjamin Rotenberg, Pierre Levitz, Matthieu Haefele, Pierre-louis Taberna, Patrice Simon, Mathieu SalanneAbstract:Supercapacitors are electrochemical devices which store energy by ion adsorption on the surface of a porous carbon. They are characterized by high power delivery. The use of nanoporous carbon to increase their energy density should not hinder their fast charging. However, the mechanisms for ion transport inside electrified nanopores remain largely unknown. Here we show that the diffusion is characterized by a hierarchy of time scales arising from ion confinement, solvation, and electrosorption effects. By combining electrochemistry experiments with molecular dynamics simulations, we determine the in-pore conductivities and diffusion coefficients and their variations with the applied potential. We show that the diffusion of the ions is slower by 1 order of magnitude compared to the Bulk Electrolyte. The desolvation of the ions occurs on much faster time scales than electrosorption.
