Electrolyte Distribution Research Articles

(Invited) Smart Electrolyte Matrix for Enhanced Carbonate Fuel Cell Life

Introduction The electrolyte matrix plays a pivotal role on electrolyte management, gas sealing efficiency and durability of molten carbonate fuel cells (MCFCs). The matrix is manufactured by tape casting a slurry of ultrafine particles of LiAlO2 and large size (>10µm) alumina crack arrestors to form a well-packed fine-pore microstructure. The electrolyte distribution and electrodes polarization in MCFC are controlled by the balance in capillary forces among the porous cell components. The electrolyte matrix needs to remain completely filled; therefore, its pores need to be stable and significantly finer than the electrodes to exert sufficient capillary force to prevent electrolyte loss and gas cross-over during endurance operation. A well balanced cell-component pore structure offers stable low cell resistance and enhanced triple phase boundary (TPB) in the electrodes. Accelerated tests and long-term operations of FCE’s internal-reforming MCFC (Direct Fuel Cell, DFC®) stacks demonstrated that the baseline electrolyte matrix meets the requirement for life greater than 5 years. However, development of more stable matrix and advanced electrolyte management designs are required to further extend cell life and enable accelerated MCFC deployment. This paper will review baseline matrix stability in stack endurance tests and the progress on developing a unique matrix design that offers significant enhanced pore and material stabilities. Parameters affecting particles coarsening and phase transformation under reducing environment will be presented. Experimental Experiments were performed in 30W single cells (250 cm2) and 30 kW technology stacks. Each cell consisted of a porous Ni-alloyed anode, a porous in-situ lithiated NiO cathode and a porous matrix (LiAlO2) filled with the alkali carbonate electrolyte. Tests were performed at different temperatures and gas atmospheres to investigate parameters and processes affecting matrix stability. Different techniques such as XRD, XPS, SEM, Mercury porosimetry, AC-impedance and steady-state polarization were carried out to evaluate and characterize matrix stability under DFC operating conditions. Results and Discussion Literature reported that matrix material LiAlO2 coarsening increases with higher temperature, lower CO2 partial pressure and in strong basic melt (1,2). Post-test analysis of accelerated FCE endurance single cell tests showed that the baseline matrix coarsening is more pronounced at the anode/matrix interface, whereas much slower at the center and the cathode side. A series of single cell tests were performed to investigate the benefits of newly developed “Smart” matrix in terms of pores and particles stability. Results showed that the advanced matrix offers >60% reduction of particles coarsening in anode side compared to the baseline (Figure 1). Porosimetry analysis showed essentially no pore-structure change (up to 6,000 hours). This improvement enables enhanced gas sealing efficiency, reduced electrolyte loss and extended cell life. Solubility and phase stability studies under different conditions will be also reported. Acknowledgement The advanced matrix research is funded by the Office of Energy Efficiency and Renewable Energy (EERE), U.S. Department of Energy, under Award Number DE-EE0006606 1. S. Terrada, K. Higaki, I. Nagashima, Y. Ito, J. Power Sources, 83, 227 (1999). 2. K. Takizawa, A. Hagiwara , J. Power Sources, 109, 127 (2002). Figure 1

(Invited) The Effect of Heat-Treatment on Mechanical Property and Wetting Behavior of α-LiAlO2

α-LiAlO2 is widely used as membrane structural material to support electrolyte in molten carbonate fuel cell (MCFC) stacks. The α-LiAlO2 electrolyte matrix always experiences mechanical and thermal stress during the initial start-up and operation (550-650oC) due to (1) insufficient mechanical strength of non-sintered α-LiAlO2, (2) thermal expansion coefficient difference between the α-LiAlO2 matrix and carbonate electrolyte, and (3) high capillary force, which may cause cracking of the matrix. A non-sintered/heat-treated pure α-LiAlO2 matrix has low mechanical strength. In this study, heat-treatment was used to enhance the mechanical strength of the α-LiAlO2 matrix. It has been found that the mechanical strength of the α-LiAlO2 matrix was increased four folds (2.72MPa) after heat-treated at 800oC for 5h to that of pure α-LiAlO2 matrix (0.57MPa). The porosity of those matrices was not changed significantly after the heat-treatment. The XRD results showed that the crystal structure of α-LiAlO2 did not change during the heat-treatment at 800oC. The wetting behavior and carbonate electrolyte distribution of those pure α-LiAlO2 matrix and heat-treated α-LiAlO2 matrix was investigated. Non-heat-treated and heat-treated α-LiAlO2 matrices were all completely wetted by liquid carbonate electrolyte. Non-heat-treated α-LiAlO2 sample cracked during the melting and wetting process of carbonate electrolyte, however, the heat-treated α-LiAlO2 matrices did not crack due to enhanced mechanical strength.

SEDIMENTATION OF ULTRADISPERSED DIAMONDS IN CITRATE COPPER PLATING ELECTROLYTE

The processes of aggregation and sedimentation of ultradispersed diamonds (UDD) in citrate copper plating electrolyte used for obtaining composite electrochemical coatings was investigated. The study of sedimentation and aggregation resistance was carried out for the purpose of selecting the concentration of UDD in citrate copper plating electrolyte. It was necessary to obtain composite copper plating featuring advanced operational properties (increased hardness, wear resistance, corrosion resistance), as well as to attain new properties (antifriction, catalytic). UDD content in electrolyte varied from 0,2 to 2,0 g/l. UDD particle size distribution in electrolyte was determined using the Malvern Mastersizer 2000 laser diffraction analyzer both as soon as suspension had been prepared and after 10-day holding. Aggregation and sedimentation resistance of UDD suspension in citrate copper plating electrolyte was investigated gravimetrically with a continuously weighed quartz cup immersed into the above mentioned suspension. The quartz cup was connected to the Sartorius R200D analytical balance by quartz fiber. The above experiment resulted in obtaining the relationship between the mass of UDD debris and the time Q = f(t).The obtained relationship was used to determine the relative particle size distribution. Sedimentation resistance has been proved to be greatly affected by the process of particle aggregation intensified by means of diamond concentration strengthening. Appropriate aggregation and sedimentation resistance results were derived from UDD suspension in citrate copper plating electrolyte at a concentration of 1,0 g/l. In this case the combination of high disperse phase content and aggregation and sedimentation resistance produced copper composite coatings with enhanced operational properties.

Advanced porous electrodes with flow channels for vanadium redox flow battery

Abstract Improving the overall energy efficiency by reducing pumping power and improving flow distribution of electrolyte, is a major challenge for developers of flow batteries. The use of suitable channels can improve flow distribution through the electrodes and reduce flow resistance, hence reducing the energy consumption of the pumps. Although several studies of vanadium redox flow battery have proposed the use of bipolar plates with flow channels, similar to fuel cell designs, this paper presents the use of flow channels in the porous electrode as an alternative approach. Four types of electrodes with channels: rectangular open channel, interdigitated open cut channel, interdigitated circular poked channel and cross poked circular channels, are studied and compared with a conventional electrode without channels. Our study shows that interdigitated open channels can improve the overall energy efficiency up to 2.7% due to improvement in flow distribution and pump power reduction while interdigitated poked channel can improve up to 2.5% due to improvement in flow distribution.

A circular stacking strategy for microfluidic fuel cells with volatile methanol fuel

Microfluidic fuel cell (MFC) stacking is a prerequisite to improve its power output for practical applications. Unlike the stacking of membrane-based fuel cells, MFC stacking generally involves complex fluidic management, such as anolyte and catholyte distribution, and spent electrolyte collection, which greatly increases the system’s complexity. In addition, the operational robustness of MFC stacks is generally sensitive to the electrolyte flow rate, which imposes stringent requirements on the precision of the electrolyte distributor and the stability of the environment where the MFC stack works. To deal with these issues, a circular MFC stacking strategy is proposed in this paper, which is especially suitable for volatile hydrocarbon fuels. In such an MFC stack, anolyte is no longer needed because fuel is stored outside the MFC in neat form, which evaporates into vapor form and diffuses into the MFC anodes, while oxidant is directly obtained from the ambient air. In this manner, only one electrolyte flow is needed for each single cell, which greatly simplifies the fluidic management system. Moreover, the stack performance is also found to be flow rate insensitive, ensuring a much improved operational robustness. Experimental results of a six-cell stack prototype (connected in series) have demonstrated an OCV of 5–5.5V, indicating a very effective electrolyte distribution and, therefore, fuel crossover suppression. A peak power density of 108.7mWcm−2 can be achieved at 60°C with 3M KOH as electrolyte. Moreover, stacking efficiency as high as 98.4% was obtained, which could be attributed to both the effective inhibition of shunt currents and the limited performance difference among the single cells.

A high-performance aluminum-feed microfluidic fuel cell stack

Abstract In this paper, a six-cell microfluidic fuel cell (MFC) stack is demonstrated. Low-cost aluminum is fed directly to the stack, which produces hydrogen fuel on site, through the Al-H 2 O reaction. This design is not only cost-efficient, but also eliminates the need for hydrogen storage. Unlike the conventional MFC stacks which generally require complex electrolyte distribution and management, the present Al-feed MFC stack requires only a single electrolyte stream, flowing successively through individual cells, which is finally utilized for hydrogen generation. In this manner, the whole system is greatly simplified while the operational robustness is also improved. With 2 M sodium hydroxide solution as electrolyte and kitchen foil Al as fuel, the present six-cell stack (in series) exhibits an open circuit voltage of nearly 6 V and a peak power density of 180.6 mWcm −2 at room temperature. In addition, an energy density of 1 Whg −1 (Al) is achieved, which is quite high and comparable with its proton exchange membrane-based counterparts. Finally, pumpless operation of the present stack, together with its practical applications are successfully demonstrated, including lightening LED lights, driving an electric fan, and cell phone charging.

Thermal Contact Resistance Measurements of Compressed PEFC Gas Diffusion Media

Localized temperature gradients in a polymer electrolyte fuel cell (PEFC) are known to decrease the durability of the polymer membrane. The most important factor in controlling these temperature gradients is the thermal contact resistance at the interface of the gas diffusion layer (GDL) and the bipolar plate. Here, we present thermal contact resistance measurements of carbon paper and carbon cloth GDLs over a pressure range of 0.7–14.5 MPa. Contact resistances are highly dependent upon the clamping pressure applied to a fuel cell, and in the present work, contact resistances vary from 3.5 × 10−4 to 2.0 × 10−5 m2 K/W, decreasing nonlinearly over the pressure range for each material tested. The contact resistances of carbon cloth GDLs are two to four times higher than contact resistances of carbon paper GDLs throughout the range of pressures tested. The data presented here also show that the thermal resistance of the sample is negligible in comparison to the thermal contact resistance. Controlling temperature gradients in a fuel cell is desirable, and the measurements presented here can be used to more accurately predict temperature distribution in a polymer electrolyte fuel cell.

Performance Analysis with Various Amounts of Electrolyte in a Molten Carbonate Fuel Cell

The effect of initial electrolyte loading (IEL) on cell performance in a coin-type molten carbonate fuel cell (MCFC) was investigated in this work. Since the material of MCFC depends on the manufacturer, optimisation requires experimental investigation. In total, four IEL values, 1.5, 2.0, 3.0, and 4.0 g, were used, corresponding to a pore filling ratio (PFR) of 38, 51, 77, and 102%, respectively. The cell performance with respect to the PFR was analysed via steady-state polarisation, step-chronopotentiomtery, and impedance methods. The electrochemical analyses revealed that internal resistance and overpotential of the cell decreased with increasing PFR, and a large overpotential was observed when the PFR was 102%, probably due to the flooding phenomenon. After operation, cross-section of the cell was analysed via surface analysis of SEM and EDS methods, and the remaining electrolyte was estimated by dissolution of the cell in 10 wt% acetic acid. A linear relationship between IEL and the weight reduction ratio by dissolution was obtained. Thus, the remaining amount of electrolyte could be measured after operation. The results of SEM and EDS showed that a PFR of 38 and 102% showed a lack and flooding of electrolytes at the cell, respectively, which led to a large overpotential. This work reports that MCFC performance is allowed only in the narrow range of PFR. Keywords: Molten carbonate fuel cell, Pore filling ratio, Electrolyte distribution, Overpotential, Post analysis

All-Solid-State Li Battery with Sulfur Composite Cathode

All-solid-state batteries were fabricated using lithium silicide anodes (Li4.4Si), sulfide-based glass electrolyte (Li2S-P2S5), and sulfur composite cathodes. Sulfur cathode was prepared by various methods; ① Hand mixing by mortar, ② Ball milling at 370rpm for 15min and ③ Secondary ball milling(planetary ball mill) at 700rpm for 10min after completing the method ②. It was found that the method ② improved distribution of sulfur, carbon and solid electrolyte(S.E) particles. The method ③ increased interfacial area(reduced particle size) as well as improved distribution of electrode component particles. BET(Burnauer-Emmett-Teller) adsorption, EDS(Energy Dispersive Spectroscopy) mapping and GITT(Galvanostatic Intermittent Titration Test) were conducted on the cell with three types of composite cathode, to investigate the effect of preparation methods on particle size(S, C, S.E), particle distribution and interfacial area, respectively. This effect was reflected in charge-discharge tests on the full cell with the method ③ cathode, resulting in higher capacities. Thus, the present work indicates why preparation method of sulfur composite electrode layers is a critical factor in determining the performance of all-solid-state Li-S batteries.

Simulation of Lithium-Ion Conduction and Deposition with Heterogeneous Porous Structure of Electrode Layers and Separators

Recently, innovative design of electrode structure on the basis of kinetics and transport phenomena of ion is needed in order to increase the high-rate performance. Especially, its local ion flux distribution relates ununiformed reaction distribution and local Li metal deposition. So, the relationship between heterogeneous porous structure and its mass transport and reaction phenomena has to be known well to increase cell performance and durability. In our previous study, we focused on the actual heterogeneous structure and the Li ion and electron conductivity was evaluated by the effective conductive path with the actual reconstruction electrode structure of LiCoO2 cathode and graphite anode [1], [2]. Furthermore, the effect of volume expansion of charge-discharge state was evaluated by using simulation with structure change based on the actual porous electrode structure, and the relationship between structural change and battery performance was considered. In this study, Li deposition phenomena was modeled and combined to our previous simulation. And, the effect of porous separator structure on its phenomena was examined. Firstly, actual separator structure was reconstructed by focused-ion beam scanning electron microscopy (FIB-SEM: Helios NanoLab 600, FEI). In this study, Cryo-FIB-SEM with the function of frozen-cutting was used to prevent polymer material from melting by beam damage. The slice pitch was 20 nm in 200 slices. The validity of this structure was checked by comparing pore size distribution. Furthermore, in order to compare between the property of actual structure and theoretical physical limiting, various simulated structure were made by simulation, such as biaxial stretching structure, fibrous structure and foam structure. In simulation structure, the resolution is 0.1 mm/mesh, the porosity is 0.5, the thickness is 20 mm, and the size is (50 mm)2. Figure 1 shows reconstructed and simulated structure, Li+ flux distribution, standardized statistics of local Li+ flux and relative conductivity. In this figure, it was found that Li flux distribution of actual separator was not uniform. Comparing actual structure and foam structure, the relative conductivity of actual separator which was defined by the ratio between porosity and tortuosity can be increased 1.7 times, and the local flux can be uniformed with optimal structure. With these structures, the reaction and mass transfer in these reconstructed electrode structure and simulated separator structure were simulated by multi-block method [3] which is the method of coarse graining to keep the information of heterogeneous structure. Li concentration and potential distribution in active material (AM) and electrolyte (EL) were calculated with Butler-Volmer equation as the boundary condition of the interface between AM and EL. In addition, Li metal deposition reaction model and structural change effect were included our previous simulation. It was assumed that temperature is constant and that the formation of SEI is ignored. Figure 2 shows the example of Li metal deposition distribution in separator. Moreover, the relationship between porous structure of separator and deposition structure was examined.

Developing Cobalt Doped Pr0.5Ba0.5MnO3-δ Electrospun Nanofiber Bifunctional Catalyst for Oxygen Reduction Reaction and Oxygen Evolution Reaction

The development of energy storage and conversion devices provides a beneficial approach for the renewable energy application, which can help relieve the severe reliance on fossil fuels and also address problems related to global climate change. Currently, the efficiencies of energy conversion devices such as the metal–air batteries and fuel cells are mainly limited by the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) processes. Developing catalytically active and cost effective catalyst for the ORR and OER is of prime importance. So far, noble metals and their alloys, such as Pt and Pt-Pd, have been exclusively used as electrochemical bifunctional catalyst in ORR and OER due to their superior catalytic activity. However, the high cost, limited availability, poor durability and sluggish electron transfer kinetics of noble metal based bifunctional catalysts have impeded the practical application of metal-air batteries. Therefore, the discovery of cost effective, catalytically active alternative bifunctional catalyst such as non-precious metals, carbonaceous materials, and transition metal oxides is highly desirable. Perovskite oxide (ABO3) possesses a unique electronic structure and chemical defect properties, and has been demonstrated to be a promising non-precious metal catalyst among the transition metal oxides in the application of metal air batteries and alkaline fuel cells. It is known that the intrinsic electrochemical catalytic activity is mainly determined by the B site cation in perovskite oxide. Extensive research conducted by Yang et al. demonstrated that the ORR and OER catalytic activities of perovskite oxides follow a volcanic relationship with the filling of electrons in antibonding orbitals [1]. Among the typical LaMO3 (M= Mn, Co, Fe, Ni, Cr), LaMnO3 and LaCoO3 have exhibited highest ORR and OER catalytic activities, respectively. In addition, due to the desirable electronic properties of the perovskite oxides, strategies such as cation partial substitution and oxygen non-stoichiometry formation could, therefore, be utilized as the effective approaches to fine-tune the catalytic properties and to achieve a better bifunctional activity [2,3]. To enhance the bifunctional catalytic performance, improved specific surface area as well as enhanced oxygen channel are desired. Researchers have found that electrochemical catalysts with porous nanofiber structures could favor the ORR and OER pathways by providing uniform O2 electrolyte distribution, and beneficial oxygen diffusion channels. Zhao et al. have synthesized mesoporous La0.5Sr0.5CoO2.91 nanowires through the multistep microemulsion method, showing significant enhanced catalytic performance [4]. Xu et al. have demonstrated that the porous La0.75Sr0.25MnO3 nanotube catalyst fabricated through facile electrospinning technologies provides favorable advantages to the availability of the catalytic active sites in the organic solvent electrolyte in Li-O2 batteries [5].Herein, we developed a bifunctional perovskite catalyst towards both ORR and OER in alkaline solution. Cobalt cations were doped into Pr0.5Ba0.5MnO3-δ perovskite to achieve the higher intrinsic ORR and OER activities by engineering the structure symmetry, electronic and the oxygen vacancy defects of the material. The bifunctional catalyst with a unique porous nanofiber structure was fabricated by electrospinning technology (Figure.1). A single phase perovskite oxide Co doped Pr0.5Ba0.5MnO3-δ was obtained after sintering the electrospun precursor at high temperature. The ORR and OER activities of the composite catalysts consisting 50 wt% of the as-synthesized perovskite oxides and 50 wt% carbon black were investigated in 0.1 KOH with rotating disk electrode (RDE). Significant enhancement in ORR and OER performance was achieved via using the composite catalyst with Co doped Pr0.5Ba0.5MnO3-δ nanofiber/carbon black with respect to the reduced overpotential and improved current density. In particular, the Co doped Pr0.5Ba0.5MnO3-δ nanofiber/carbon black composite demonstrated enhanced electron transfer number in the ORR process, indicating preferable dominance of four electron transfer pathway. Moreover, the Co doped Pr0.5Ba0.5MnO3-δ composite exhibited high stability during the cycling tests, indicating its promising applications in metal-air batteries.

Electrochemical Performance of All-Solid-State Batteires Using Size Controlled Sulfide Based Solid Electrolyte

Since large-sized energy storage systems with high energy density such as electric vehicles and smart-grid systems has been intensive attention. Lithium ion batteries have been considered as one of realistic candidates. Nevertheless, the more energy demand the more focus on safety issues of because of ignite liquid electrolytes. To resolve this problem, all-solid-state batteries with solid electrolytes have been researched as next generation of lithium ion batteries. Even though all-solid-state batteries have better safety, main huddle of all-solid-state batteries is energy density of composite electrode in all-solid-state batteries which include solid electrolytes different from lithium ion batteries with liquid electrolyte. In spite of solid electrolytes act as important role for composite electrode in all-solid-state batteries due to create lithium ion path in the composite electrode, solid electrolyte don’t contribute to capacities of batteries. Therefore, Solid electrolyte in composite electrode for all-solid-state batteries are need to be minimized without sacrifice electrochemical performances. In order to find optimal composition of composite electrode for all-solid-state batteries, size of solid electrode powder were controlled to maximize the energy density of all-solid-state batteries. In this research, size of sulfide based solid electrolytes were controlled via wet ball milling and ultra-sonication process with increasing milling time. Composite cathodes of all-solid-state batteries were produced with three different ratio of active materials and solid electrolyte for each sizes of solid electrolyte. To obtain composite cathode, the cathode materials, conductive additive and glass-ceramics solid electrolyte powders were mixed by dry mixing method using an agate mortar and pestle with hand. All-solid-state cells were constructed by uniaxial cold pressing method. Morphology of solid electrolyte were measured with FE-SEM. Size distribution of solid electrolyte were measured by Particle Size Analyzer. Microstructure and electrochemical properties of fabricated composite cathodes with different size of solid electrolyte were characterized. Sizes of sulfide solid electrolyte showed drastically decrease and uniform distribution after wet ball milling process. Morphology of sulfide based solid electrolyte particle became irregularity and agglomeration shape to uniform and spherical shape. Therefore, electrochemical performance wet ball milled solid electrolyte showed better electrochemical performance at every cathode ratio of all-solid-state cells because of lithium ion paths are constructed by size controlled solid electrolyte particles. Improved electrochemical performances are indicating that size and morphology of solid electrolyte particle act as very important role in all-solid-state batteries. In addition, considerable electrochemical performance at cathode ratio over 90% can be achieved by more refined size and morphology of solid electrolyte particle in the future. Figure 1

High-performance membrane-electrode assembly with an optimal polytetrafluoroethylene content for high-temperature polymer electrolyte membrane fuel cells

Although high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) have a high carbon monoxide tolerance and allow for efficient water management, their practical applications are limited due to their lower performance than conventional low-temperature PEMFCs. Herein, we present a high-performance membrane-electrode assembly (MEA) with an optimal polytetrafluoroethylene (PTFE) content for HT-PEMFCs. Low or excess PTFE content in the electrode leads to an inefficient electrolyte distribution or severe catalyst agglomeration, respectively, which hinder the formation of triple phase boundaries in the electrodes and result in low performance. MEAs with PTFE content of 20 wt% have an optimal pore structure for the efficient formation of electrolyte/catalyst interfaces and gas channels, which leads to high cell performance of approximately 0.5 A cm−2 at 0.6 V.

Electrostatic interaction of charged surfaces with semipermeable membranes

We have investigated the ion density distribution and electrostatic disjoining pressure of the size-asymmetric electrolytes in the gap between the semipermeable membranes and the charged surface by using the density functional theory. The present theory is in reasonably good agreement with the simulation data whereas the Poisson-Boltzmann equation does not describe the electrostatic properties of the electrolytes near a charged surface. The ion density distribution and the electrostatic disjoining pressure depend strongly on the size-asymmetric electrolytes in charge and size as well as the ion density of the electrolyte. The finite size of the ions leads to a large repulsive electrostatic disjoining pressure in the gap. However, the effect of the gap width on the repulsive electrostatic disjoining pressure is very small. The repulsive electrostatic disjoining pressure increases with increasing or decreasing surface charge density with its having a minimum value near a neutral surface. The surface charge amplification and the charge reversal phenomenon are observed for a neutral semipermeable membrane with a charged surface. A positively charged surface enhances the charge surface amplification whereas a negatively charged surface enhances the charge reversal phenomenon.

Early diabetic kidney maintains the corticomedullary urea and sodium gradient.

Early diabetic nephropathy is largely undetectable before substantial functional changes have occurred. In the present study, we investigated the distribution of electrolytes and urea in the early diabetic kidney in order to explore whether pathophysiological and metabolic changes appear concomitantly with a decreased sodium and urea gradient. By using hyperpolarized 13C urea it was possible to measure the essential intrarenal electrolyte gradients and the acute changes following furosemide treatment. No differences in either intrarenal urea or sodium gradients were observed in early diabetes compared to healthy controls. These results indicate that the early metabolic and hypertrophic changes occurring in the diabetic kidney prelude the later functional alterations in diabetic kidney function, thus driving the increased metabolic demand commonly occurring in the diabetic kidney.

The Mechanical Insights into Proton/Electron Transfer in Cytochrome C Oxidase Revealed by Direct Modeling of Voltage Changes in Response to Charge Separation

The use of electrometric techniques to study time-dependent membrane potential has been used to elucidate charge motions in membrane proteins, thereby offering mechanistic insights into the function of membrane-bound pumps and transporters. The mean field macroscopic continuum approach is a usual choice of computational methods that allows one to connect the observed voltage changes to the dielectric distance obtained by solving the voltage Poisson-Boltzmann (PB-V) equation. However, correlating the observed voltage changes with the number of transferred charges and distances is challenging since the nature of the dielectric response in a protein-membrane system is complex. Recently, we introduced a new semi-microscopic coarse-graining (CG) of the voltage coupling for membrane proteins, which include the compete electrode, electrolyte, protein, membrane systems. The CG model evaluates the electrogenic events by directly simulating the external charge that flows through electrolyte solution, considering “the changes in the electrolyte distributions” between initial and final configuration of membrane proteins. This model has also provided a new avenue to measure voltage changes in Bacetrial Reactio Center by computing “the changes in electrode potentials” upon electron/proton transfer [Kim I, Charkrabarty S, Brzeninski P and Warshel A (2014) PNAS 111, 11353]. Here, we employs our CG model to give mechanical insights into electron/proton translocation within membrane in Cytochrome c Oxidase. It is found that different proton pathways can give the same elctrogenic results, and the available measurements cannot distinguish between different feasible proton/electron paths in CcO. However, consistency with the paths available upon mutations can provide a powerful insight.

A numerical investigation of serpentine flow channel with different bend sizes in polymer electrolyte membrane fuel cells

Bipolar plates are one of the key parts of a PEMFC (polymer electrolyte membrane fuel cell). The flow fields of the bipolar plates distribute reactant gasses on the electrode surfaces. The flow channels should have an appropriate design to decrease the mass transport loss at a minimum pressure drop. Among different flow channels, serpentine flow channel received considerable attention for application in electrochemical cells. In this work, a three-dimensional numerical model is proposed and applied for studying the effect of bend sizes on a PEM (polymer electrolyte membrane) fuel cell. The obtained results show that as bend size increases from 1 mm to 1.2 mm, not only does the over potential reduce significantly but temperature gradient is also alleviated. These welcome effects are largely due to a more even distribution of electrolytes over the electrode surface which eventually increases the power density of the fuel cell about 1.78% compared to channels with 0.8 mm square bend size. Moreover, it is shown that the serpentine flow channels with 1.2 mm square bend size act successfully in preventing secondary flows internal thereby decreasing pressure drop about 90.6% compared to serpentine flow channels with a bend size of 0.8 mm.

Electrochemical Machining of Multiple Slots with Low-frequency Tool Vibrations

In electrochemical machining (ECM) of multiple slots, the electrolytic flow field distribution is a critical factor to the process stability, which may draw unwanted abnormal phenomena such as short-circuits. Using finite element method, the flow field distribution in ordinary ECM method of multiple slots was calculated. The simulation results revealed that most of the electrolyte will drain away from the channels between cathode tools. The electrolyte velocity in the machining gap will be reduced and hardly remove the electrolytic products in time. This paper suggested a method for ECM of multiple slots with low-frequency tool vibrations to improve the electrolyte velocities in machining gaps. Tool vibration will improve the refresh of electrolyte in the machining gap and promote the removal rate of electrolytic products. For higher electrolyte velocities, the relationship between section area ratio (SAR) and electrolyte velocities was discussed. The optimized tools height with best SAR was suggested. Experiments were carried out to evaluate the process stability of the ordinary and suggest method. The results verified that electrolyte velocities were improved significantly with low-frequency tool vibrations and promoting SAR. A specimen with 30 slots was fabricated in ECM with low frequency tool vibrations and optimized tools height.

Water distribution in high temperature polymer electrolyte fuel cells

In this work a high temperature polymer electrolyte fuel cell based on a phosphoric acid doped polybenzimidazole membrane is operated at 160 °C on dry air and dry hydrogen. The anodic stoichiometry was varied to resemble typical operation with pure hydrogen or reformate gas. At the outlet of the fuel cell liquid water was collected by condensers. The resulting amounts of liquid water from cathode and anode were computationally analyzed. The results yielded an effective diffusion coefficient of water vapor of D≈2.7⋅10−7 m2 s−1, which is the average value for the cell based on the water partial pressures at the outlets. From the calculated water partial pressures at the anode and cathode it can be concluded that the concentration of phosphoric acid differs significantly within catalyst layer of the anode and cathode. Finally, the crossover of hydrogen and oxygen was shown to depend on the swelling of the membrane.

Investigation of pulse electrochemical sawing machining of micro-inner annular groove on metallic tube

Pulse electrochemical sawing micro-machining (PECSM) is a non-conventional process. Having features of no tool wear, no cutting force, and good surface quality, this process is suitable for machining micro-grooves on the inner wall of hole. The rotating dentate cathode (RDC) is beneficial for the distribution of electrolyte and electrolytic products removal, thus reducing the effects of concentration polarization on the electrochemical reaction. This study focuses on the PECSM of micro-inner annular groove on 304 stainless steel tube using a pH-neutral NaClO3 electrolyte. To study the effects of RDC on the process, the bubble layer structure (BLS) adhered to the surface of RDC was photographed using a high-speed camera. Under the condition of immersion, the symmetric distribution of two kinds of BLS adhered to the RDC surface. The four selected parameters (radius of dentate cathode, rotational speed of RDC, initial gap, feed rate) with different levels were carried out to study the process of PECSM micro-inner annular grooves on 304 stainless steel tube. Experimental results indicate that PECSM has high potential for machining micro-inner annular groove on metallic tube. A micro-inner annular groove that is 340μm in depth and 263μm in width was fabricated on a 304 stainless steel tube.