Membraneless Cell Research Articles

High-Performance Aqueous Supercapacitors Based on a Self-Doped n-Type Conducting Polymer.

Environmentally-benign materials play a pivotal role in advancing the scalability of energy storage devices. In particular, conjugated polymers constitute a potentially greener alternative to inorganic- and carbon-based materials. One challenge to wider implementation is the scarcity of n-doped conducting polymers to achieve full cells with high-rate performance. Herein, this work demonstrates the use of a self-doped n-doped conjugated polymer, namely poly(benzodifurandione) (PBDF), for fabricating aqueous supercapacitors. PBDF demonstrates a specific capacitance of 202 ± 3 Fg-1, retaining 81% of the initial performance over 5000 cycles at 10 Ag-1 in 2m NaCl( aq ). PBDF demonstrates rate performances of up to 100 and 50 Ag-1 at 1 and 2mgcm-2, respectively. Electrochemical impedance analysis reveals a surface-mediated charge storage mechanism. Improvements can be achieved by adding reduced graphene oxide (rGO), thereby obtaining a specific capacitance of 288 ± 8 Fg-1 and high-rate operation (270 Ag-1). The performance of PBDF is examined in symmetric and asymmetric membrane-less cells, demonstrating high-rate performance, while retaining 83% of the initial capacitance after 100000 cycles at 10 Ag-1. PBDF thus offers new prospects for energy storage applications, showcasing both desirable performance and stability without the need for additives or binders and relying on environmentally friendly solutions.

Surface Spin Enhanced High Stable NiCo2S4 for Energy‐Saving Production of H2 from Water/Methanol Coelectrolysis at High Current Density (Small 2/2023)

Water/Methanol Coelectrolysis NiCo2S4 is developed through electrochemical deposition on carbon cloth, with the surface magnetism fine-tuned. The surface spin enhanced NiCo2S4 electrodes possess high stable bifunctional performance even in high current density in water/methanol coelectrolysis system. Hydrogen and value-added formate are harvested on both sides of the electrodes in the membrane-less cell, simultaneously, with energy saved. More details can be found in article number 2205257 by Xian-Zhu Fu, Jing-Li Luo, and co-workers.

Carbon Nanofibers-Sheathed Graphite Rod Anode and Hydrophobic Cathode for Improved Performance Industrial Wastewater-Driven Microbial Fuel Cells.

Carbon nanofiber-decorated graphite rods are introduced as effective and low-cost anodes for industrial wastewater-driven microbial fuel cells. Carbon nanofiber deposition on the surface of the graphite rods could be performed by the electrospinning of polyacrylonitrile/N,N-Dimethylformamide solution using the rod as nanofiber collector, which was calcined under inert atmosphere. The experimental results indicated that at 10 min electrospinning time, the proposed graphite anode demonstrates very good performance compared to the commercial anodes. Typically, the generated power density from sugarcane industry wastewater-driven air cathode microbial fuel cells were 13 ± 0.3, 23 ± 0.7, 43 ± 1.3, and 185 ± 7.4 mW/m2 using carbon paper, carbon felt, carbon cloth, and graphite rod coated by 10-min electrospinning time carbon nanofibers anodes, respectively. The distinct performance of the proposed anode came from creating 3D carbon nanofiber layer filled with the biocatalyst. Moreover, to annihilate the internal cell resistance, a membrane-less cell was assembled by utilizing a poly(vinylidene fluoride) electrospun nanofiber layer-coated cathode. This novel strategy inspired a highly hydrophobic layer on the cathode surface, preventing water leakage to avoid utilizing the membrane. However, in both anode and cathode modifications, the electrospinning time should be optimized. The best results were obtained at 5 and 10 min for the cathode and anode, respectively.

A membrane-less molten hydroxide direct carbon fuel cell with fuel continuously supplied at low temperatures: A modeling and experimental study

A molten hydroxide direct carbon fuel cell (MHDCFC) is a promising electricity generation technology. Anode behavior significantly affects the cell performance. Intermittent fuel supply is a bottleneck restricting the commercialization of the cell. An MHDCFC with fuel continuously supplied is proposed in this study. Anode structural parameters are optimized through a computational fluid dynamics (CFD) model and a current model. The optimized current collector thickness, inlet number, inlet diameter are 0.2 cm, two, and 6 mm based on reactant distribution uniformity and current. Then, a membrane-less cell is built. Influence of carbon type, particle size, carbon mass fraction, and temperature on the cell performance are investigated. The cell fueled with activated carbon holding relatively large specific surface area and high conductivity achieve a higher performance. A relative small carbon mass fraction and large particle size decrease the charge transfer resistance and improve the cell performance. The cell may obtain a higher performance at 390 ℃ comparing with that under 400 ℃. The cell exhibits a power about 21 mW when activated carbon mass fraction, particle size, and temperature are respectively of 3.33%, 0.5–0.85 mm, and 390 ℃. The model and experiment demonstrate the feasibility of a continuous MHDCFC operating at a low temperature.

Membraneless physiology of the living cell. The past and the present

Since the 1880s, the concept of compartmentalizing through membranes has taken a firm place in cell physiology and has defined the objects, methods, and goals of physiologists’ research for decades. A huge mass of biologists know about the important role of intra-membrane pumps, channels, and lipids, and various hypotheses about the origin of life often begin with explanations about how the lipid membrane occurred, without which it is impossible to imagine the origin of a living cell. Against this background, there was a dissonance of statements that there are membraneless organelles in the cell, the functions of which are rapidly expanding under our eyes. Physically, they are similar to coacervate droplets, which from time to time were used to explain the origin of life, and now the coacervates are being more and more often discussed when describing the physics of the nucleus and cytoplasm of modern cells. However, ideas about the coacervate nature of cytoplasm/protoplasm originated in the first half of the 19th Century, when the contents of cells were likened to jelly, but this approach gradually faded into the shadows. Nevertheless, limited research in this area continued and was completed in the form of a membraneless cell physiology. Now that the focus of attention has turned to membraneless compartmentalization, it’s time to remember the past. The sorption properties of proteins are the physical basis of membraneless cell because of water adsorbed by proteins changes the physical state of any biomolecular system, from supramolecular and subcellular structures to the cell as a whole. A thermodynamic aqueous phase is formed because adsorbed water does not mix with ordinary water and, in this cause, is separated from the surrounding solution in the form of a compartment. This article discusses the fundamental physical properties of such a phase – a biophase. As it turned out, the Meyer–Overton rule, which led to the idea of a lipid membrane, also applies to membraneless condensates.

Improving the configuration and architecture of a small-scale air-cathode single chamber microbial fuel cell (MFC) for biosensing organic matter in wastewater samples

Power production in microbial fuel cells has been proposed as a novel method to sense organic matter concentration in water resources. The development of microbial fuel cells as biosensors is relatively new, and still facing major issues such as response time and operation ranges. The present work aims at improving the configuration and architecture of a small-scale, air-cathode single chamber microbial fuel cell (MFC) to biosense organic matter in wastewater samples.Different MFC models were tested using CFD. The number of channels and flow disturbances was increased to minimize dead zones, increasing the Reynolds number (or shear rate), and with special emphasis on the interface between the electrodes and the substrate seeking the greatest contact. The best model obtained was built and tested with synthetic wastewater. The final Single Chamber Microbial Fuel Cell (SCMFC) version consisted of a 2 cm3 total volume as the anodic chamber. Carbon cloth was used as electrodes (4 cm2 of exposed surface area), and two different cell configurations were evaluated, a membrane cell (MFC-m) and a membrane-less cell (MFC-ml). The MFCs were tested in a Chemical Oxygen Demand (COD) range varying from 25 to 200 mg L−1. Coulombic Efficiency (CE %), sensibility, and response time were determined as comparative sensing parameters. The MFC-ml resulted in a lower CE percentage (8% vs 13 % for the MFC-m), a lower response time (45 ± 6.4 min vs 63 ± 10 min for the MFC-m), and a lower quantification difference compared to the COD traditional quantification method. Flow velocity simulation was a useful tool to improve MFC design. The MFC-ml could reduce construction costs, and enable simplification of the operation of the MFC-based sensing device, which contributes to its implementation in real water quality monitoring scenarios.

Leveraging co-laminar flow cells for non-aqueous electrochemical systems

Non-aqueous flow cells offer expanded electrochemical potential windows, which is desirable for energy storage. The performance of such electrochemical systems is however constrained by high cell resistance due to the low ionic conductivity of electrolytes and membranes in non-aqueous media. In this work, we apply membrane-less cell configurations with flow-through porous electrodes to address the ohmic losses and boost the performance of non-aqueous flow cells. Vanadium acetylacetonate redox chemistry is used as a model system and various performance aspects such as reaction kinetics, electrode wettability, cell resistance and crossover are investigated. The kinetics, measured in flow-through mode, is found competitive due to the enhanced mass transport and surface area utilization in the flow-through porous electrode. The electrode porosity is measured to be 79% and only 6.0% in acetonitrile and water, respectively, indicating superior wettability behaviour for non-aqueous electrolytes. A fully integrated co-laminar flow cell demonstrates negligible crossover and a combined ohmic cell resistance that meets techno-economic targets. Its discharge power density of 550 mW cm−2 is two orders of magnitude higher than for other non-aqueous flow cells, demonstrating that membrane-less cell designs with flow-through porous electrodes are favourable in order to overcome performance limitations in non-aqueous electrochemical systems.

Microfluidic Aluminum-air Cell with Methanol-based Anolyte

Aluminum-air cell, with trivalence redox couples, attracts a lot of interest to break the capacity limitation of conventional batteries in pursuit of higher mobility for portable devices. In order to overcome the self-discharge issue of aluminum, a microfluidic aluminum-air cell working with methanol-based anolyte was developed in this work. The operation feasibility of this membraneless cell was first proved. Then, the influences of electrolyte concentration and water content in the methanol-based anolyte on cell performances were investigated. Experimentally, a high discharge capacity density of 2507 mAh/g was achieved at a low current of 0.015mA.

Model Membrane-Free Li-S Batteries for Enhanced Performance and Cycle Life.

The success of the rechargeable Li-S cell is limited in part by the dissolution of lithium-polysulfide in the electrolyte. Remarkably, it is found that removal of the conventional membrane separator in a Li-S cell improves sulfur utilization and cycling performance, whether the sulfur is initially contained in the cathode or electrolyte. An optimized cell design yields discharge capacities as high as 980 mA h g-1 after 100 cycles.

Mixing with herringbone-inspired microstructures: overcoming the diffusion limit in co-laminar microfluidic devices.

Enhancing mixing is of uttermost importance in many laminar microfluidic devices, aiming at overcoming the severe performance limitation of species transport by diffusion alone. Here we focus on the significant category of microscale co-laminar flows encountered in membraneless redox flow cells for power delivery. The grand challenge is to achieve simultaneously convective mixing within each individual reactant, to thin the reaction depletion boundary layers, while maintaining separation of the co-flowing reactants, despite the absence of a membrane. The concept presented here achieves this goal with the help of optimized herringbone flow promoting microstructures with an integrated separation zone. Our electrochemical experiments using a model redox couple show that symmetric flow promoter designs exhibit laminar to turbulent flow behavior, the latter at elevated flow rates. This change in flow regime is accompanied by a significant change in scaling of the Sherwood number with respect to the Reynolds number from Sh ~ Re(0.29) to Sh ~ Re(0.58). The stabilized continuous laminar flow zone along the centerline of the channel allows operation in a co-laminar flow regime up to Re ~325 as we demonstrate by micro laser-induced fluorescence (μLIF) measurements. Micro particle image velocimetry (μPIV) proves the maintenance of a stratified flow along the centerline, mitigating reactant cross-over effectively. The present work paves the way toward improved performance in membraneless microfluidic flow cells for electrochemical energy conversion.

Microfluidic Redox Battery with Symmetric, Dual-Pass Architecture

Microfluidic fuel cells and microfluidic redox batteries hold promises for future power generation of portable devices. In these membrane-less cells, a co-laminar interface in the micro-channel provides the separation between the reactants whilst permitting ionic charge transfer [1]. The use of flow-through porous electrodes allowed higher power densities and increased fuel utilization [2]. Recently, a dual-pass architecture utilizing flow-through porous electrodes was reported [3]. The cell achieved power densities up to 0.3 W/cm2using vanadium redox species at high flow rates and enabled in-situ recharging. Vanadium is a special element that has four different oxidation sates. Hence, it is commonly used in both electrolytes of a redox flow battery as well as in recent microfluidic electrochemical cells [4-5]. In this study, a microfluidic redox battery (MRB) with flow-through porous electrodes and a symmetric, dual-pass design is presented. The design of the cell is capable of both recharging and regenerative use of the reactant species and therefore, maximizing the fuel utilization. The architecture presented is an extension of our previously reported work [3], with the added modification of splitting each of the two electrodes into two sections, as shown in Fig. (1a). This modification essentially divides the original MRB into a full upstream cell and a full downstream cell which can be in-situ characterized independently. The advantage of this analytical cell design is a more detailed understanding of reactant conversion in the dual-pass architecture of the MRB which will help with device optimization.The cell was fabricated using soft lithography techniques in polydimethylsiloxane (PDMS) using an SU-8 master and bonded to a glass substrate. Micro-porous carbon paper is used to make rectangular electrode strips for the device. The vanadium redox electrolytes were prepared as described elsewhere [6]. First, preliminary experiments are conducted to test the performance of the upstream cell in order to benchmark the new cell design against regular cells. The cell has an open circuit voltage around 1.51 V at a high flow rate of 100 μL/min. The full polarization and power curves for the upstream cell operated at the same flow rate is presented in Fig. (1b). These results demonstrate the successful operation of the cell in the discharge mode, where it produced up to 2.5 mW at a current of 4 mA. Moreover, the power output and the fuel utilization of the device are evaluated for both series and parallel connections of the upstream and downstream cells. These comparisons will enable quantification of the coupling between the upstream and downstream cells and evaluation of asymmetric flow separation at the downstream stagnation point of the device. Acknowledgements Funding for this research provided by the Natural Sciences and Engineering Research Council of Canada (NSERC) is highly appreciated.

Invited: From PEM Fuel Cell Design to Biological Fuel Cells: The Status of Systems Development for Biological Fuel Cells

Over the last decade, the field of biological fuel cells has expanded almost exponentially. Much of the research was originally focused on understanding fundamental principles and showing bioelectrocatalysis in a variety of environments, with a variety of biocatalysts (microbes, enzymes, mitochondria), and a variety of electrode materials, but as fundamental electrocatalysis became known, there has been a push to develop biological fuel cell systems. This paper will discuss how different applications of biological fuel cells require different cell designs. Many portable power applications utilize cell designs similar to traditional fuel cells, but many implantable applications require new membraneless cell designs, flexible cell designs, and microscale cell designs. These new cell designs will be compared with more traditional PEM fuel cell designs.

Electrical Energy Generation from a Novel Polypropylene Grafted Polyethylene Glycol Based Enzymatic Fuel Cell

A recently synthesized polypropylene-g-polyethylene glycol polymer was used for the first time as the working electrode of a fuel cell. Electrodes were prepared for unmediated and mediated enzymatic reactions including ferrocene as the mediator. Glucose oxidase and bilirubin oxidase was used as the anodic and cathodic enzymes for the working electrodes, respectively. The biofuel cell was operated using glucose as the fuel in a single-compartment and membrane-less cell. Electrochemical results demonstrated that the catalytic efficiency of the ferrocene based cathode was approximately 100-fold higher than that of an unmediated cathode. The mediated fuel cell electrodes yielded a power density of 65 nW/cm2 at a cell potential of +560 mV.

Catalytic response of microbial biofilms grown under fixed anode potentials depends on electrochemical cell configuration

In microbial electrochemical cells the anode potential can vary over a wide range, which alters the thermodynamic energy available for bacterial-electrode electron exchange (termed electroactive bacteria). We investigated how anode potential affected the microbial catalytic response of the electroactive biofilm. Microbial biofilms induced to grow on graphite electrodes by application of a fixed applied anode potential in membrane-separated and membrane-less electrochemical cells show differences in electrocatalytic response. Maximum current density is obtained using +0.2V vs. Ag/AgCl to induce biofilm growth in membrane-less cells, in contrast to a maximum achieved at lower applied potentials in a membrane-separated electrochemical cell configuration. This insight into differences in optimal applied potentials based on cell configuration can play an important role in selection of parameters required for microbial fuel cells and bio-electrochemical systems.

Controllable electrochemical generation of H2 from hydrazine together with slight power generation using a membraneless cell

The switchable generation of hydrogen from a hydrazine solution was achieved with an electrochemical cell that has a cobalt anode and a platinum cathode. The H2 generator is based on the combination of hydrazine electro-oxidation on cobalt anode and H2O electro-reduction on platinum cathode. The rate of H2 generation was regulated by switching with no power supply. Slight electricity was generated from this cell along with H2. This cell uses selective anode and cathode catalysts, and hence a membraneless (one-compartment) structure could be realized for the regulation of H2 generation.

High performance thylakoid bio-solar cell using laccase enzymatic biocathodes

Thylakoid membranes have previously been used for electrochemical solar energy conversion, but the current output and open circuit voltage are low, in part due to limitations of the cathode. In this paper, a thylakoid bioanode and laccase biocathode were combined in the construction of a bio-solar cell capable of light-induced generation of electrical power. This two-compartment cell showed a greater than 5-fold increase in short circuit current density and an open circuit voltage 0.275 V larger than that of a thylakoid bio-solar cell incorporating an air-breathing Pt cathode. The electrodes were then tested in several solutions of varying pH to evaluate the possibility of constructing a compartment-less bio-solar cell. This membrane-less cell, operating at pH 5.5, generated a short circuit photocurrent density of 14.0 ± 1.8 μA cm(-2) which is 25% larger than the two-compartment cell and a similar open circuit voltage of 0.720 ± 0.018 V.

A miniature biofuel cell operating at 0.78 V.

We report the highest voltage miniature biofuel cell to date, a membrane-less cell operating at 37 degrees C in pH 5 buffer at 0.78 V.