Cathode Compartment Research Articles

Boosting Electrocatalytic CO 2 Reduction with Conjugated Bimetallic Co/Zn Polyphthalocyanine Frameworks

Boosting Electrocatalytic CO ₂ Reduction with Conjugated Bimetallic Co/Zn Polyphthalocyanine Frameworks

Deeper Understanding of Ternary Eutectic Carbonates/Ceria-Based Oxide Composite Electrolyte through Thermal Cycling

Due to a high conductivity of about 0.1 S·cm−1, Li-Na-K carbonate eutectic and Sm-doped ceria composite material is a good electrolyte candidate for hybrid fuel cells operating between 500 °C and 600 °C. The present paper aims at a deeper understanding of the species and mechanisms involved in the ionic transport through impedance spectroscopy and thermal analyses, in oxidizing and reducing atmospheres, wet and dry, and during two heating/cooling cycles. Complementary structural analyses of post-mortem phases allowed us to evidence the irreversible partial transformation of molten carbonates into hydrogenated species, when water and/or hydrogen are added in the surrounding atmospheres. Furthermore, this modification was avoided by adding CO2 in anodic and/or cathodic compartments. Finally, a mechanistic model of such composite electrical behavior is suggested, according to the surrounding atmospheres used. It leads to the conclusions that cells based on this kind of electrolyte would preferably operate in molten carbonate fuel cell conditions, than in solid oxide fuel cell conditions, and confirms the name of “Hybrid Fuel Cells” instead of Intermediate Temperature (or even Low Temperature) Solid Oxide Fuel Cells.

Parametric study to optimize proton exchange membrane electrolyzer cells

Proton exchange membrane electrolyzer cells (PEMECs) are a promising system that can produce high purity hydrogen without any carbon emissions through a water splitting process. Yet, with more robust configurations and optimal operating conditions, PEMECs can potentially be utilized in energy and cost-effective practical applications. In this study, we conducted a parametric study to explore the optimal operating conditions that improve the performance and efficiency of PEMECs for the production of high purity hydrogen. Our experimental results show the high reliability of WSe2 in the oxygen evolution reaction as an anodic catalyst that improved the electrolysis performance of 29.1% in terms of a current density at an applied potential of −3 V compared to the conventional novel catalyst Pt/C 20%. Furthermore, a higher current density up to 17.2% was obtained by supplying sulfuric acid (H2SO4) into the cathode compartment of the PEMECs. The cell performance was also affected by the H2SO4 flow direction inside the PEMECs, and an average higher current density was improved by 4.1% when the H2SO4 flowed from the bottom side to the top of the electrolyzer cell. In addition, a faster flow rate delivered a higher current density up to 49.9% than a slower flow rate at a reduction potential of 1.8 V. Finally, the flow path coating of the catalysts provided a higher current density by 26.1% on average compared to the use of a gas diffusion electrode (GDE). This study provides a way to utilize PEMECs in commercial applications for high purity hydrogen production with high efficiency in the future.

Sequential anaerobic-aerobic treatment of rice mill wastewater and simultaneous power generation in microbial fuel cell

Microbial fuel cells (MFCs) have attracted widespread interest due to their capability to generate power while treating wastewater. In the present investigation, rice mill wastewater (RMW) was treated in a dual-chamber MFC with a biological cathode (MFCB), in which anaerobic treatment was provided in the anode compartment, and aerobic treatment was enployed in the cathode compartment. The performance was compared with an identical MFC with an abiotic cathode (MFCA). During continuous operation, the hydraulic retention time (HRT) of the anode compartments of both MFCs was kept at 12 h. The maximum volumetric power density obtained in MFCB (379.53 mW/m3) was lower than MFCA (791.72 mW/m3). Similarly, the maximum open-circuit voltage (OCV) and operating voltages were 0.519 V and 0.170 V for MFCB, while for the MFCA, they were 0.774 V and 0.251 V, respectively. The internal resistance of MFCA was 372.34 Ω while the MFCB showed a higher internal resistance of 533.89 Ω. The linear sweep voltammetry and cyclic voltammetry also demonstrated high electrochemical activity in MFCA compared to MFCB. However, MFCB has shown a higher chemical oxygen demand (COD) removal efficiency (96.8%) than MFCA (88.4%) under steady-state conditions. Both anaerobic and aerobic degradation of organic substrates significantly reduced the COD of RMW. Furthermore, the absence of an expensive catalyst in the cathode substantially reduces the cost of the system. The electrical performance of the system can be enhanced by employing novel cathode material with surface modification.

Accumulation of Inert Impurities in a Polymer Electrolyte Fuel Cell System with Anode Recirculation and Periodic Purge: A Simple Analytical Model

Anode recirculation with periodic purge is commonly used in polymer electrolyte fuel cell systems to control the accumulation of nitrogen, water, and other impurities that are present in the fuel or diffuse through the membrane from the cathode compartment. In this work, we develop a simple, generalized analytical model that simulates the time dependence of the accumulation of inert impurities in the anode compartment of such a system. It is shown that, when there is transport out of the anode chamber, the inert species is expected to accumulate exponentially until equilibrium is reached when the rate of inert entering the anode in the fuel supply and/or via crossover from the cathode is balanced by the rate of leakage and/or crossover to the cathode. The model is validated using recently published experimental data for the accumulation of N2, CH4, and CO2 in a recirculated system. The results show that nitrogen accumulation needs to be taken into account to properly adjust system parameters such as purge rate, purge volume, and recirculation rate. The use of this generalized analytical model is intended to aid the selection of these system parameters to optimize performance in the presence of inerts.

Rare Earth Elements Partition and Recovery During Electrodialytic Treatment of Coal Fly Ash

Rare earth elements (REE) recovery from waste (end-of-line, reusable, recyclable, etc.) should become an essential stream of REE for current demands. Methods to achieve this recovery are then paramount. This study uses the electrodialytic remediation (EDR) as an REE extraction method from coal fly ashes. We used different chemicals to assist REE extraction during EDR: distilled water, 0.01 mol l−1 NaNO3, 0.4 mol l−1 Sodium acetate in 1.0 mol l−1 Acetic acid, and 0.5 mol l−1 Citric acid. Citric acid achieved the highest REE extraction/recovery from the four studied solutions: up to 40%. This represents a total recovery of 148 g REE from 1 ton of coal ashes. The citric acid experiment also proved to be energy efficient, using 70 Wh per 100 g of treated coal ash. The acidic environment provided by the citric acid supplies higher REE migration rates towards the cathode. Once at the cathode compartment, REEs then precipitate at the cathode complexed as Ca- and P-bearing minerals.

Microbial Fuel Cell Based on Nitrogen-Fixing Rhizobium anhuiense Bacteria.

In this study, the nitrogen-fixing, Gram-negative soil bacteria Rhizobium anhuiense was successfully utilized as the main biocatalyst in a bacteria-based microbial fuel cell (MFC) device. This research investigates the double-chambered, H-type R. anhuiense-based MFC that was operated in modified Norris medium (pH = 7) under ambient conditions using potassium ferricyanide as an electron acceptor in the cathodic compartment. The designed MFC exhibited an open-circuit voltage (OCV) of 635 mV and a power output of 1.07 mW m−2 with its maximum power registered at 245 mV. These values were further enhanced by re-feeding the anode bath with 25 mM glucose, which has been utilized herein as the main carbon source. This substrate addition led to better performance of the constructed MFC with a power output of 2.59 mW m−2 estimated at an operating voltage of 281 mV. The R. anhuiense-based MFC was further developed by improving the charge transfer through the bacterial cell membrane by applying 2-methyl-1,4-naphthoquinone (menadione, MD) as a soluble redox mediator. The MD-mediated MFC device showed better performance, resulting in a slightly higher OCV value of 683 mV and an almost five-fold increase in power density to 4.93 mW cm−2. The influence of different concentrations of MD on the viability of R. anhuiense bacteria was investigated by estimating the optical density at 600 nm (OD600) and comparing the obtained results with the control aliquot. The results show that lower concentrations of MD, ranging from 1 to 10 μM, can be successfully used in an anode compartment in which R. anhuiense bacteria cells remain viable and act as a main biocatalyst for MFC applications.

Semi-continuous anolyte circulation to strengthen CO2 bioelectromethanosynthesis with complex organic matters as the e-/H+ donor for simultaneous biowaste refinery

• The effect of anolyte circulation in microbial electrolysis cell was investigated. • Semi-continuous anolyte circulation increased CH 4 yield by 5.4 times. • PEM fouling impeding the transfer of proton led to low performance. • Semi-continuous anolyte circulation enhanced the transfer of electron and proton. • Enrichment of electroactive and methanogenic microorganism occurred. CO 2 bioelectromethanosynthesis represents a promising strategy for the capture and utilization of CO 2 . In such process, the continuous generation of electron (e - ) and proton (H + ) in anodic oxidation are of prime importance for the efficient cathodic CO 2 electroreduction and process stability. Proton transfer, however, is very easy to be hindered due to the fouling of proton exchange membrane (PEM). In this study, an artificial channel in microbial electrolysis cell (MEC) was proposed to strengthen the transport of protons from anodic to cathodic compartment, and H + -rich anolyte was semi-continuously circulated to the cathodic chamber to provide protons for CO 2 electroreduction. The results indicated that the daily CH 4 yield in cathode with anolyte circulation (18.5 mL/d·L-reactor) was 5.4-fold higher than that without circulation (2.9 mL/d·L-reactor). Meanwhile, efficient anodic biodegradation of organic components was observed with COD, proteins and polysaccharides removal of up to 95.6 ± 1.9%, 96.3 ± 3.7% and 99.1 ± 0.2% respectively, which supplied a continuous e - /H + donor for CO 2 electroconversion. 16S rRNA gene pyrosequencing analysis identified a large number of proteins-utilizing Bacteroidetes (14.11%) and polysaccharides-consuming Thermotogae (18.49%) in anodic biofilm, conductive to the biodegradation of organic components. Moreover, a high abundance of Methanobacterium (81.07%) was detected to prevail in cathodic biofilm, demonstrating the occurrence of highly enhanced CH 4 bioelectrosysthesis. The syntrophic and symbiotic relationship was established in the dual-bioelectrode system, creating a beneficial environment and an energy-efficient approach for biowaste refinery and CO 2 electromethanosynthesis.

The different behaviour of Thermotoga neapolitana in the anodic and cathodic compartment of a bioelectrochemical system

Thermotoga neapolitana is a hyperthermophilic bacterium that can metabolize glucose and several organic wastes in hydrogen and lactate at a temperature of 80°C. Their high performance in producing hydrogen at so high a temperature as 80°C suggests a potential energy application of them where hydrogen is an important element of the process. In this view, experimentation of a T.neapolitana strain is carried out in double-chamber electrochemical systems. The aim is to explore the interaction of these bacteria with the anode and the cathode, stressing their capability to survive in presence of a polarized electrode which can drastically change the pH of the media. A culture enriched of 5 g/L of glucose, under CO2 pressure (80 °C) was used to fill both the anodic and cathodic compartments of the electrochemical system, applying a voltage of 1.5 V between the anode and the cathode. The test lasted ten days. Results clearly indicate that bacteria colonize both electrodes, but the glucose metabolism is completely inhibited in the anodic compartments. On the contrary, metabolism is stimulated in the cathodic compartment. Bacteria are alive on the electrodes in the pH interval of 3 - 9.

MICROBIAL ENRICHMENT PROCESS IN THE ANODE OF MICROBIAL FUEL CELL SYSTEM USING TOFU WASTEWATER (TWW) ANAEROBIC SLUDGE

Microbial fuel cell consisting two main components which are anode and cathode materials. In the microbial fuel cell, both anode and cathode compartments are separated with a separator. Anode generates the protons and electrons while cathode converts protons into water with the presence electrons and oxygen. During the Microbial fuel cell operation, the performance of anode is very crucial due to it provides the protons and electrons. Hence, the high efficiency microbial fuel cell is very related with the high anode performance. This work addressed to the enrichment process of electroactive bacteria (EAB) in anode of microbial fuel cell. In this work, some parameters such as current generations, , and pH changes were used to assess the enrichment process of EAB was reached. In addition, the presence of EAB on the anode surface was identified based on the morphology of anode surface. The removal of COD and the pH value were determined by using the American public health analysis method and pH tester, respectively. The morphology of anode surface was analysed by using a scanning electron microscope. Whereas, current generation was tested by using a mustimeter. The removal of COD and final pH were obtained 71.4 % and 5.7, respectively. The optimum current generation was observed 0.19 mA. The surface morphology of anode before enriched with microbes was clear surface, while after enriched with microbes was attached by microbes. The removal of COD, pH changes, current generation and morphology of anode surface could be used to assess the EAB in the anode compartment. 
 Keywords: Microbial fuel cell; anode; cathode; electroactive bacteria; pH changes.

On the behaviour of Atrazine removal from water using fabrics as anodes and cathodes

This study examines the degradation of atrazine (ATZ) with Pt-modified textile electrodes using an electrochemical method that is comparatively studied in two electrochemical cell configurations: cells with separated anodic and cathodic compartments (divided configuration); and without any separation (undivided configuration). The influence of the presence of chloride ions was studied. The best results were obtained when an undivided cell was used. The morphology and composition of the dispersed Pt coatings were analyzed using field emission scanning electron microscopy (FESEM) and Energy Dispersive X-Ray Analysis. The FESEM analyses confirmed that the textile surface was effectively modified by the electrocatalytic material. High performance liquid chromatography, gas chromatography mass spectrometry, and spectroscopic methods were used to follow the evolution of major oxidation products. Total organic carbon, chemical oxygen demand, and total nitrogen were used to evaluate the degradation efficiency of treated aqueous solutions. The experimental results obtained indicate that the efficiency of the electrochemical treatment was high with a low energy consumption when using electrodes based on textile materials, such as anodes or as cathodes (in particular, in electrolysis without compartment separation). All these can be produced at very competitive prices.

Effects of ammonium concentration in the catholyte on electricity and algal biomass generation in a photosynthetic microbial fuel cell treating wastewater

In this study, algal cathodic compartments were integrated to generate oxygen in microbial fuel cells. Chlorella vulgaris and Scenedesmus quadricauda were grown under three NH4+–N concentrations (50, 300, and 900 mg L−1) in the catholyte. With 50 mg L−1 of NH4+–N, the highest maximum power densities of 16.72 and 5.96 mW m−2 were obtained with Chlorella vulgaris and Scenedesmus quadricauda, respectively. Under this condition, dissolved oxygen reached 19.27 and 9.87 mg L−1 for Chlorella vulgaris and Scenedesmus quadricauda respectively, along with 100% removal of NH4+–N within 210 h. Both cultures showed inhibition under higher concentrations of NH4+–N, resulting in decreased photoautotrophic growth that generates oxygen for the cathodic reaction. Under all concentrations, Chlorella vulgaris displayed better tolerance to ammonium. From the results, it can be summarized that 50 mg L−1 of NH4+–N in wastewater is suitable as a microalgal cultivation medium in a cathodic compartment.

Electrochemical Hydrogen Compression and Its Optimization through Computational Modeling

Climate change resulting from the heavy use of fossil fuels poses a serious threat to our environment. It is critically important to find alternatives to combustion-based energy technologies and promote renewable energy production. Hydrogen is a leading candidate for the transportation sector as a carbon-free fuel with high energy density. Hydrogen can be produced in a carbon-neutral manner via water electrolysis and other means. However, the establishment of the hydrogen infrastructure still faces serious challenges such as storage. Due to its lightweight nature, hydrogen is very difficult to store either as a compressed gas or as a liquid. Typically, hydrogen is compressed using mechanical compressors which contain moving parts that require frequent maintenance adding to their cost and complexity. Electrochemical compression (ECC) is a promising alternative to mechanical compressors. ECC is an electrochemical device that uses a proton exchange membrane (PEM) to compress the gas. When a voltage is applied across the PEM, low-pressure hydrogen supplied to the anode is oxidized to generate protons and electrons. The electrons are driven through the external circuit by the power source, whereas the protons travel through the PEM towards the cathode. The protons and electrons recombine via the cathodic reduction to obtain hydrogen at elevated pressure. The currently available knowledge base regarding electrochemical compressors has mainly resulted from experimental studies and less attention has been paid to modeling. The current work presents a comprehensive three-dimensional model of a single cell ECC that incorporates the relevant electrochemical phenomena as well as physical processes including water transport. It also takes into account the important phenomenon of back diffusion due to the pressure difference between the cathode and anode that limits the achievable pressure in the cathode compartment. Simulations were conducted for the pressurized cathode case . It was observed that back diffusion limits the compression ratio to a value well below that predicted by Nernst equation. Additionally, the effects of membrane thickness, temperature, and applied voltage on ECC performance are analyzed. The results show that there is a tradeoff between different objectives that must be addressed to optimize the ECC process. For example, thinner membranes permit faster compression rates but at the cost of increased back diffusion. Similarly, higher temperatures improve the pressure efficiency and the compression rate but at a higher operational cost. The results also show that ECC is more efficient at lower voltages because the associated compression ratio is smaller which consequently reduces back diffusion; however, such small voltages do not allow higher pressures. As a result of these tradeoffs, all design parameters need to be optimized simultaneously. This study offers valuable insights on the effect of different parameters on ECC performance. The results suggest that ECC is a viable alternative to conventional technologies for hydrogen compression. Back diffusion significantly reduces ECC efficiency; therefore, ECCs would benefit from membranes with low hydrogen diffusivity. The results provide a foundation for the modeling, analysis, and optimization of a full scale ECC system. Keywords—Hydrogen; Computational Model; Back Diffusion; Electrochemical Compression; Optimization;

Control of Transport Water in Direct Toluene Electro-Hydrogenation Electrolyzer

Introduction Recently, to decrease carbon dioxide emissions, utilization of renewable energy has been expected. Therefore, the large-scale storage and transportation of hydrogen as secondary energy is needed for effective utilization of fluctuated and unevenly distributed renewable energy. Toluene (TL) / methylcyclohexane (MCH) organic hydride system is one of the best candidates of hydrogen energy carrier because TL and MCH are liquid at ambient temperature and pressure, and it would be able to use oil infrastructure. To improve the energy conversion efficiency for TL hydrogenation using renewable electricity, we have studied direct electro-hydrogenation of TL with water decomposition using proton exchange membrane (PEM). The rate-determining step at the cathode for the hydrogenation of TL is the mass transfer of TL to the cathode catalyst layer [1]. One of the major factors that inhibit the supply of TL to the reaction field is transport water from the anode through the membrane. The accumulation of the water in the catalyst layer inhibits the supply of TL and reduces the current efficiency, but its behavior has not been clarified. In this study, the influence of current density, sulfuric acid concentration supplied to the anode and cell temperature on the amount of the transport water were evaluated in order to control the water in direct TL electro-hydrogenation electrolyzer. Experimental A DSE® (De Nora Permelec, Ltd.) for the oxygen evolution and Nafion 117® (Du Pont) were used as the anode and PEM, respectively. Carbon paper (10BC, SGL carbon ltd.) loaded with 0.5 mg cm-2 of PtRu/C (TEC61E54, Tanaka Kikinzoku Kogyo) was also used as the cathode. The cathode was hot-pressed on the PEM at 120 oC and 15 MPa for 3 min to fabricate a membrane cathode assembly. The anode and cathode compartments were circulated 0-1.5 M (= mol dm-3) H2SO4 and 10% TL/MCH, respectively. Operation temperature of the electrolyzer conducted at 50-80 oC. As the electrochemical measurement, chronopotentiometry at 0.1-0.4 A cm-2 was conducted for 20 min, and the amount of water was evaluated by measuring the weight of it in the reservoir after electrolysis. The concentration of sulfuric acid of the water was determined by measuring the pH. Results and discussion The water permeates the PEM by electro-osmosis and diffusion, and the water flux is given by eq. 1 in the images [2]. The linear region of Fig. 1 would mean water flux had linear relation to current density with constant apparent electro-osmotic coefficient with constant back diffusion flux from eq. 1. The constant back diffusion would mean that the aqueous phase is formed in the cathode catalyst layer, and its activity would be constant.Figure 1 shows dependence of cell voltage and water flux at 60 oC with various sulfuric acid concentrations on current density. There was no significant difference in cell voltages except for 0 M. Relationships between the water flux and the current density were linear except 0.1 A cm-2 at 1.5 M. The water flux decreased as the sulfuric acid concentration increases except 0 M. The absolute value of the intercept by extrapolating the linear region increased with sulfuric acid concentration. The slope of the straight line also decreased as the sulfuric acid concentration increased. In addition, the water detected on the cathode side was sulfuric acid whose concentration was about one-tenth that of the anode. The sulfuric acid concentration in the membrane would also change with the anodic sulfuric acid concentration. The electro-osmotic coefficient obtained from the slope of Fig.1 would decrease with the increase of the sulfuric acid concentration in the membrane.Figure 2 shows the diffusion flux and the concentration difference between the anolyte and cathode side sulfuric acid, which transported from anode side, as functions of the anolyte concentration. They increased linearly with anolyte concentration. Correspondingly, the back diffusion flux, which is affected by the sulfuric acid concentration difference, would have increased linearly with increasing anolyte concentration. Acknowledgements This work was supported by the Toyota Mobility Foundation. Anode was supplied by De Nora Permelec Ltd. We appreciate the person concerned them. Reference [1] K. Nagasawa, Y. Sawaguchi, A. Kato, Y. Nishiki, S. Mitsushima, Electrocatalysis, 8, 164, (2017).[2] T. E. Springer, T. A. Zawodzinski, S. Gottesfeld, J. Electrochemical Society, 138, 2334, (1991). Figure 1

Visualization Guided Mitigation of Mechanical Membrane Degradation in Fuel Cells

Dynamic operational power demands from a fuel cell, especially in transportation applications, are known to causefluctuations in its relative humidity (RH) and temperature [1]. This leads to repetitive in-plane compressive and tensile stress build-up in the confined perfluorosulfonic acid (PFSA) ionomer membranes due to constraining of their cyclic swelling and shrinkage under hydrated and dehydrated states, respectively. The ionomer’s dynamic water sorption characteristics during these hygrothermal variations lead to catalyst coated membrane (CCM) deformation and cyclic mechanical stresses resulting in structural fatigue and micro-crack development at high stress accumulation sites [2]. Lately, laboratory-based X-ray computed tomography (XCT) was used for non-destructive four-dimensional (4D) visualization and microstructural analysis of fuel cell parts showing novel insights on their failure processes [3,4]. The objective of the present work is to leverage 4D XCT visualization to design and demonstrate novel mitigation strategies for mechanical membrane degradation in fuel cells. A custom designed X-ray transparent fixture housing a small-scale single cell fuel cell was subjected to 2 min. each of wet and dry cycles with N2 gas at anode and cathode compartments, thereby causing fatigue-based membrane damage [5]. 3D tomographic data sets of same membrane electrode assembly (MEA) locations were acquired as a function of degradation time, which facilitated to study the damage development and growth. As a baseline for this work, a non-bonded MEA with high surface roughness gas diffusion layers (GDLs) demonstrated that the primary membrane failure mode was CCM buckling into GDL voids/pores [6]. To overcome this failure mode, two separate mitigation approaches are explored in the present work: (i) a commercial GDL with low surface roughness; and (ii) bonding of MEA to arrest buckling. Furthermore, a multi-physics finite element method (FEM) model is developed to simulate the contact interaction at the catalyst layer | GDL interface and non-uniformity in the GDL microstructure. The XCT findings are correlated with the numerical model to perceive the specific impact of GDL surface features on the development and distribution of membrane failures.Similar to the baseline MEA, membrane crack development was observed to be the key failure mode for both mitigation approaches. When the two mitigation designs are compared at similar cycling stages with the baseline (Fig. 1), however, the size and density of membrane cracks is drastically reduced. Since both mitigation strategies are tested using the same accelerated stress test protocol as the baseline, it is hereby established that each approach provides substantial mitigation against fatigue driven mechanical membrane degradation, predominantly due to reduced severity of CCM buckling deformation, resulting in a doubling of the membrane lifetime in each case. Complementary finite element simulations corroborate the experimental findings and further estimate the critical GDL void sizes to prevent CCM buckling and the required interfacial MEA adhesion quality to stabilize the MEA for overall membrane durability. Acknowledgements Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, and Ballard Power Systems through an Automotive Partnership Canada grant. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program.

Electrochemical Aperture Optimization for Rapid Activation of Lithium-Ion Reserve Batteries

Reserve batteries fulfill a unique role among energy storage technologies in which long-term shelf life (years, decades) is required while ensuring optimal performance upon activation. This is typically achieved through isolation of the electroactive components until battery operation is desired. Commonly, the electrolyte is isolated from one or both electrodes, and thus, limiting premature degradation and parasitic side-reactions until battery activation is desired. During the reserve battery activation process, electrolyte is delivered to the electrode(s), which enable ionic conduction between the anode and cathode, and thus permitting normal operations analogous to a non-reserve design.The feasible activation mechanisms are largely determined by battery chemistries and material properties, which give rise to several classifications including: thermal, spin-activated, and gas-activated reserve type batteries. Reserve battery activation under these various classifications require ancillary components and/or specific conditions which contribute excess complexity, weight, and/or volume towards the overall battery design and thus, significant penalties in reliability, specific and/or volumetric densities are incurred. Improvements in reserve battery technology must include strategies for limiting these penalties through innovated electrolyte delivery designs tailored for modern, high-energy, high-power density lithium-based batteries.Herein, we report a novel electrolyte delivery mechanism facilitated by an electrochemical aperture. The electrochemical aperture exists as a physical barrier, isolating the liquid, lithium-containing electrolyte. Reserve battery activation proceeds via lithium transport to/from the electrochemical aperture, thus inducing physical transformations which permit liquid electrolyte permeation and delivery through the aperture and into the appropriate compartment, thus establishing ionic conduction between the anode and cathode. The accompanying figure highlights two embodiments of the lithium electrochemical aperture (LiECA) concept, specifically Li-containing Aperture and Li-host Aperture. During the inactive period, liquid electrolyte is isolated by the LiECA and stored within the cathode compartment. Electrochemical transport of lithium between the LiECA and cathode induce aperture openings, injecting electrolyte into the anode compartment, and ultimately resulting in battery activation and enabling battery operation.Acknowledgements: Faraday Technology acknowledges the technical assistance of Dr. Joseph P. Fellner at the Air Force Research Laboratory, Wright-Patterson AFB (Dayton, OH) under Air Force Contract No. FA8650-19-P2024 (Phase I SBIR program). Figure 1

Tungsten Trioxide Photoanode-Palladium Cathode Cell for Solar Seawater Splitting

N-type semiconductor-tungsten trioxide (WO3) finds application in a large variety of fields including photocatalysis, gas sensors, smart windows or as a substrate for heterogeneous catalysts. This presentation will focus on recent improvements in optoelectronic and photoelectrochemical (PEC) properties of WO3 thin films achieved in our laboratory. The semitransparent WO3 films are formed on F-doped tin oxide (FTO) conductive glass substrates, using a sol-gel method, by depositing the precursor layer-by-layer and annealing sequentially in the flow of oxygen. Use of appropriate mixtures of tungstic acid and organic structure-directing agents that form the WO3 film precursor, combined with a two-step annealing, allows the formation of highly crystalline nanostructured (NS) electrodes with controlled, large porosity. This renders possible the permeation of the whole mesoporous film by the electrolyte. Annealing of the as-deposited samples in oxygen above 500°C ensures structural ordering with formation of monoclinic WO3. Since none among photostable (metallic oxide) semiconductors exhibits band-edge energy levels that match those of hydrogen and oxygen evolution reactions to allow unassisted water splitting, the present efforts focus on minimizing the bias voltage required to perform visible light-driven photooxidation of water. In fact, a bias voltage of the order of 1 V may be provided by several single-junction PV cells likely to operate in a tandem device with the PEC cell. Despite visible-light absorption range of the WO3 films restricted to 500 nm, under standard conditions, i.e. at 1.23 V vs RHE and under simulated AM 1.5G solar light (100 mW/cm2), stable anodic water splitting photocurrents exceeding 4.5 mA/cm2 are regularly attained.This presentation will principally focus on photoelectrolysis experiments employing synthetic seawater electrolyte, in a two compartment (separated by a sintered glass diaphragm) cell, that showed dominant (with 60-70% Faradaic efficiency) formation of chlorine at the WO3 photoanode with remarkably stable photocurrents reaching 4.7 mA/cm2. In fact, as demonstrated in an earlier work from our laboratory1, the WO3 photoelectrodes exhibit preferentially oxidation of anions (including Cl-) of the acidic aqueous electrolytes. However, in contrast with the Cl- ions, the photooxidation of oxy-anions of acidic electrolytes leads generally to the "passivation" of the WO3 electrodes due to the formation of the surface layers of peroxo species.1 The only identified exception is the methane-sulfonic acid that allows oxygen generation at the WO3 photoanode with large stable photocurrents.2 In the case of seawater photoelectrolysis, the operating potential point at which the photocurrent approaches saturation occurs at ca 0.4 V below E(Cl-/Cl2)=1.36 V vs SHE. Consistently, the incident photon conversion efficiencies (IPCEs) reach a maximum of 85% over 390-410 nm range of wavelengths.3 Good mechanical and chemical stability of the WO3 electrodes in the presence of chlorine evolved from seawater was confirmed by monitoring the photocurrents over a 20 hours-long continuous photoelectrolysis runs.A schematic diagram of the seawater splitting PEC cell, including a NS WO3 film photoanode and a Pd sheet cathode, used in our experiments is shown below.Fig. 1 Schematic diagram of the seawater splitting PEC cell.The current of CO2 gas passing through the seawater represents a possible option for maintaining slightly acidic pH in the cathodic cell compartment. The important advantage of the adopted PEC cell configuration is to circumvent the problem of gas separation, i.e. chlorine/oxygen formed at the photoanode and hydrogen generated at the Pd cathode that is stored in the form of a Pd-H hydride. The storage of hydrogen generated in a PEC water splitting device in the form of a hydride, opens the possibility of its subsequent use as an anode in a hydride-oxygen battery.Such sunlight-driven PEC seawater splitting device can be implemented in remote places to provide on-site relatively small amounts of chlorine for disinfecting purposes including purification of drinking water.More generally, the prospect of using seawater electrolyte for a larger scale PEC hydrogen generation would release the strain on vital fresh water resources. Considering relatively low concentration of Cl- ions in seawater, roughly equivalent to 0.5 M NaCl, the photoelectrolysis delivering photocurrents in the range of mA/cm2 appears well suited for such applications.

Advanced Rechargeable Zinc-Air Batteries with Precious Metal Free Catalysts

Rechargeable zinc-air batteries (ZABs) could be promising energy storage devices with high energy and power density, enabling safe and cost-effective operation. ZABs have higher practical specific energy compared to traditional aqueous and lithium-ion batteries [1]. The schematic of rechargeable of ZAB is shown in Figure 1a. The main challenge of the electrically rechargeable ZABs in alkaline electrolytes is the limitation during recharging [2, 3]. The performance of ZAB largely depends on oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Figure 1a shows that the cell rechargeability is realized by the OER and design of the Zn electrode. Hence, advances of the air electrode enabled by bifunctional catalysts as well as the development of the Zn electrode are important.In this presentation, we will discuss rechargeable ZAB with novel NiCo and NiFe catalysts, as well as an advanced Zn electrode that is created with a hybrid method using electrodeposition and powder coating. These catalysts were pre-scanned by using rotating disk electrode (RDE) in the alkaline solution, as shown in Figure 1b. NiCo and NiFe exhibited high catalytic activity towards OER but not towards ORR. These catalysts were applied and tested in the in-house designed ZAB cell. The Zn electrode was made by coating the Zn power on the CuZn mesh that was prepared by electrodeposition. The ZAB in a two-electrode configuration exhibited a discharge cell voltage of ~0.8 V at 20 mA/cm2 (3 hours cycle time), as shown in Figure 1c. To determine which electrode is limiting the efficiency, an additional Zn reference electrode was introduced into the cell to setup a four-electrode configuration. The additional reference is inserted into the cathode compartment enable measurement of the overpotential in solution and for the oxygen electrode. Test results, for different types of catalyst and Zn electrodes will be shown and discussed.

Towards the Electrochemical Retention of CO2: Is it Worth it?

AbstractThis work focuses on the use of NaOH produced cathodically by reduction of water to retain gaseous CO2 in a combined electrolyzer‐absorber device. The process deals with two relevant environmental concerns: desalination and carbon sequestering, using only electricity and heat, which can be provided using green sources. Results demonstrate that technology is feasible, and the composition of the final product depends on the operation conditions applied. Removal rates of 130 mmol CO2/h were obtained at 7.5 A with coulombic efficiency in the removal of CO2 of 47.63 %. Efficiency in the production of chlorine, hydrogen and NaOH decreases at large current densities because of the promotion in the oxidation of water and the promoted transport of protons from the anodic to the cathodic compartment of the cell. Low current densities should be used to promote the formation of NaHCO3 and avoid scaling problems (formation of deposits of Na2CO3) in the spray column. The use of heated air to evaporate the product of the absorption column produces evaporated water with higher quality (in terms of lower conductivity) from the product of the absorption column.

Integration of ultraviolet irradiation with electrochemical chlorine and hydrogen peroxide production for micropollutant abatement

This research evaluated integrating ultraviolet (UV) irradiation with electrochemical chlorine (Cl2) and/or hydrogen peroxide (H2O2) production for micropollutant abatement in water treatment. Combining UV with anodic Cl2 production (E-UV/Cl2) effectively abated gemfibrozil and naproxen, but ineffectively abated ibuprofen due to its low reactivity with chlorine radicals (e.g., ClO• and Cl2-•). In comparison, combining UV with cathodic H2O2 production (E-UV/H2O2) more effectively abated ibuprofen, but less efficiently abated gemfibrozil and naproxen due to the significant scavenging of •OH by the water matrix. Moreover, simultaneously producing Cl2 and H2O2 during UV irradiation (E-UV/Cl2/H2O2) in an undivided reactor did not further enhance micropollutant abatement compared to the E-UV/H2O2 process because of the mutual consumption of anodically generated Cl2 and cathodic generated H2O2. In contrast, by separating the anodic and cathodic compartments with an anion exchange membrane and operating the E-UV/Cl2/H2O2 process in an anode-to-cathode configuration, all test micropollutants could be adequately abated through the sequential oxidation with the selective chlorine radicals and non-selective •OH in the anodic and cathodic compartments. In general, the concentrations of micropollutants could be abated by 84–100% with a short hydraulic residence time (HRT) of 9.4 min and feasible energy demand (EEO ≤ 3.15 kWh/m3-log) in the selected groundwater and secondary wastewater during the E-UV/Cl2/H2O2 process in the divided reactor. The results indicate that different synergistic effects can be obtained for micropollutant abatement by combining UV and electrochemical processes in varying configurations, and the divided E-UV/Cl2/H2O2 process is a more robust and energy-efficient method for micropollutant abatement during decentralized water treatment.