Voltage Efficiency Research Articles

Efficient Ni-NC Gas Diffusion Electrodes for CO2 Electrolyzer with High Utilization Efficiencies and Single Pass Conversions Towards CO

The electrochemical CO2 reduction in membrane electrolyzer devices can become a key technology to close the anthropologic carbon cycle. For industrialisation of CO2 electrolyzers, however, performance shortcomings of today’s state-of-art electrolyzer designs and cathodes have to be addressed. Alkaline Membrane CO2 electrolyzers suffer from low utilization efficiency of CO2 due to an acid-base CO2 loss to carbonates, which limits the CO2 utilization efficiency and single pass conversion to 50% in AEM CO2-to-CO electrolyzer. Bipolar Membrane CO2 electrolyzers suffer from high cell voltage and lower Faradic efficiencies due to the acidic environment. All thoses designs suffer from layer flooding or salting events which limit the durability of the cells. New cell designs and new diagnostic tools are needed to predict, diagnose, and eliminate detrimental operating regimes of CO2 electrolyzers.In this work, we report on NiNC catalyst-based cathode GDEs for CO2 reduction to CO in a zero-gap membrane electrolyzer cell. We compare AEM and BPM cell designs. We propose the carbon crossover coefficient, CCC, as a new diagnostic analysis tool to monitor and understand through- or in-plane mass transport limitations in AEM and BPM cells. We also demonstrate how N2 bleeds can be used as diagnostic tools to recognize salting inside the electrolyzer cell.In our AEM studies, we show that sufficient CO2 access to the catalyst surface sites is important to achieve a high performance. Under near neutral conditions on the anode we report 85% FE towards CO at 300 mA cm-2 at 3.6 V with single pass conversion of 40% which is very close to the theoretical maximum. In addition, we can report high energy efficiency but only a utilization efficiency of around 50%.In our BPM studies, we show that NiNC GDEs are active and stable cathodes in zero-gap membrane electrolyzer. Protons raise the utilization efficiency as the carbonate will decompose into CO2 and water. To handle the changed electro osmotic water drag we replaced the ionomer with PTFE and could achieve 82% FE and 69% single pass conversion at 500 mA cm-2 with close to 100% CO2 utilization efficiency towards CO.We show that using a either an AEM or BPM electrolyzer design we can reach over 100h stable performance at 100 mA cm-2.Figure caption: CO2 singel pass conversion and lambda comparison of AEM and BPM CO2 reduction electrolyzer cells. Figure 1

(Invited) Towards the Next Generation of High Performance, Durable Water Electrolyzer Membranes

Proton exchange membrane water electrolysis (PEMWE) has emerged as one of the most promising methods to produce clean hydrogen at industrial scale. Incumbent membranes (such as Nafion™ N115) have proven to enable high durability in the PEMWE application. However, it is well understood that novel PEMWE stack designs require higher voltage efficiency and low effective gas crossover, which implies thin, low resistance membranes containing gas recombination catalysts (GRCs). Compared to Nafion™ N115, thin membranes are at enhanced risk of failure from both mechanical and (electro)chemical mechanisms. While promising examples of these membranes have been recently disclosed,1 a systematic demonstration of their durability has not yet been performed.In PEM fuel cells, decades of research have resulted in accelerated stress test (AST) protocols that are effective to mimic real failures while shortening the time to observe them. These ASTs have not yet been proven/implemented for PEMWE membranes. Progress toward engineering high performance, durable thin membranes will be presented, along with a perspective on how best to engineer ASTs for PEMWE. Park, A., Performance and Durability Investigation of Thin, Low Crossover Proton Exchange Membranes for Water Electrolyzers. DOE Annual Merit Review. 2020.

Nanocone-Modified Surface Facilitates Gas Bubble Detachment for High-Rate Alkaline Water Splitting

Alkaline water splitting (AWS) is one of the most attractive technologies for green hydrogen production. In comparison to the acidic proton exchange membrane (PEM), AWS offers greater flexibility in using non-platinum group metal catalysts and could generate higher-purity hydrogen. However, commercial AWS systems are normally operated at a lower current density (~400 mA cm-2) than PEM electrolyzers. To rapidly generate hydrogen at an industrial scale, it is critical to boost the operating current density of AWS to a level of ~1000 mA cm-2. Nevertheless, the significant amount of gas bubbles generated during high-rate AWS could be detrimental to the process. Bubbles can block the catalysts’ active site, hinder electrolyte diffusion, and increase Ohmic resistance, thus deteriorating the reaction rate and restricting the cell voltage efficiency. The detachment of gas bubbles may also damage the catalyst layer. In this study, we demonstrate a general strategy for facilitating bubble detachment by modifying the nickel electrode surface with nickel nanocone nanostructures, which turns the surface into underwater superaerophobic. The simulation and experimental data show that bubbles take a considerably shorter time to detach from the nanocone-modified nickel foil than the unmodified foil. As a result, these bubbles also have a smaller detachment size and less chance for bubble coalescence. The nanocone-modified electrodes, including nickel foil, nickel foam, and 3D-printed nickel lattice, all show substantially reduced overpotentials at 1000 mA cm-2 compared to their pristine counterpart. The electrolyzer assembled with two nanocone-modified nickel lattice electrodes retains >95% of the performance after testing at ~900 mA cm-2 for 100 hours and the surface NC structure is also well preserved, demonstrating its excellent electrochemical and mechanical stability at high current density. Our findings offer an exciting and simple strategy for enhancing the bubble detachment and, thus, the electrode activity for high-rate AWS.

Effective Non-Precious Metal Oxide Supported Carbon as a High Performance Bifunctional Electrocatalyst for All Vanadium Redox Flow Batteries

As one of the most promising electrochemical energy storage systems, vanadium redox flow batteries (VRFBs) have received increasing attention owing to their attractive features for large-scale storage applications. However, their high production cost and relatively low energy efficiency still limit their feasibility. One of the critical components of VRFBs that can significantly influence the effectiveness and final cost is the electrode. Therefore, the development of an ideal electrocatalyst with low cost, large active surface area, good chemical stability, and excellent electrochemical activity toward the VO2+/VO2 + and V2+/V3+ redox reactions is essential for the design of VRFBs. Hence, we prepared a stable, high catalytic activity and uniformly distributed non-precious metal oxide nanoparticles on the surface graphene sheets via two step routes, hydrothermal followed by annealing at optimum temperature for VRFB applications. Among the samples, the prepared electrocatalyst shows the best electrochemical activity with lowest peak potential separation and highest peak current density toward VO2 +/VO2+ and V2+/V3+ redox reactions. This observation is due to the synergistic effects related to the presence of excess oxygen vacancies on the metal oxide, the high content of oxygen functional groups, and the high electrical conductivity of the graphene sheets. Hence, the prepared electrocatalyst grown on the surface of graphite felt (GF) support demonstrates the optimal electrochemical activity with the energy and voltage efficiencies of 76.8% and 80.9%, respectively, which are much greater than those of the 59.8% and 63.2% attained from pristine GF at 100 mA cm–2. Moreover, the electrode presented good stability and durability in acidic electrolyte during long-term operations for 100 cycles at a higher current density of 100 mA cm–2.

Amorphous Cobalt Tin Oxide/Reduced Graphene Oxide Decorated on Graphite Felt as Positive Electrode for Vanadium Redox Flow Battery

The Vanadium Redox Flow Battery (VRFB) stands out as one of the most promising large-scale energy storage systems. Nevertheless, the graphite electrode materials commonly used in VRFBs often exhibit drawbacks such as limited electrochemical activity and insufficient conductivity, ultimately resulting in suboptimal performance for the VRFB. In this study, we utilized highly conductive reduced graphene oxide (rGO) as a carrier for cobalt tin oxide (CoSnO3), aiming to enhance their catalytic capability towards vanadium ions. CoSnO3/rGO composite was confirmed using XRD and TEM, revealing nanoboxes morphology and amorphous structure. XPS and EPR analysis showed an increase in oxygen vacancies after composite formation. In order to further prove the effect of CoSnO3/rGO composite catalyst modified graphite felt, the modified graphite felt electrode was applied to the positive electrodes of VRFB, and the charge and discharge tests at different current densities were carried out. At a current density of 160 mA/cm², the composite demonstrated a voltage efficiency of 74.22%, surpassing the heat treated graphite felt by 2.69%. Noteworthy enhancements in capacitance were also evident at this specific current density. Furthermore, stability testing over 50 cycles revealed no significant degradation, underscoring the superior performance and outstanding durability of the CoSnO3-rGO modified graphite felt throughout charge and discharge cycling. The result of this study highlight the promising potential of CoSnO3-rGO composites as efficient catalysts for vanadium redox flow batteries, providing improvements in electrochemical performance and long-term stability.

Resilient and Reversible Phosphotungstic Acid Passivated Zinc Anode.

Aqueous zinc ion batteries (ZIBs) present a compelling solution for grid-scale energy storage, which is crucial for integrating renewable energy resources into the electric infrastructure. The cycling stability of ZIBs hinges on the electrochemical reversibility of the zinc anode, which is often compromised by corrosion and dendritic zinc deposition. Here, we present a straightforward surface passivation strategy that significantly enhances the cycling stability of zinc anodes. By immersing zinc in a solution of phosphotungstic acid, we promoted the dominance of the 002 plane of zinc's hexagonal structure. This process facilitates the creation of a uniform nucleation and protective layer on the native zinc surface, resulting in a more uniform plating-stripping process and increased corrosion resistance. In symmetric cells, the passivated zinc exhibits a capacity retention of 68.7% after 1000 cycles at a current density of 1.0 Ag1-, whereas untreated zinc anodes retain only 7.4% of capacity under identical conditions. In full cell zinc iodine batteries employing the passivated zinc anode, over 1000 stable charge-discharge cycles were achieved at a current density of 20 mA cm-2, with approximately 96% Coulombic efficiency (CE), 86% voltage efficiency (VE), and 82% energy efficiency (EE). This study demonstrates a promising pathway for the construction and upscaling of flow batteries with high capacity and low cost.

Comparative examination of both spectral properties and hybrid solar cell application of 2,4,6-trimethoxyphenoxy substituted phthalocyanine dyes

In this study, novel octa 2,4,6-trimethoxyphenoxy substituted phthalocyanines, and tetra chloro and tetra 2,4,6-trimethoxyphenoxy substituted phthalocyanines were synthesized, characterized, examined their spectral properties comparatively and investigated of hybrid solar cell application of them. The spectral characterizations can be performed for all phthalocyanine compounds, solar cell application was only possible for tetra chloro tetra 2,4,6-trimethoxyphenoxy substituted phthalocyanines, the others phthalocyanines not due to their low yield.Solar cell properties of the tetra chloro tetra 2,4,6-trimethoxyphenoxy substituted phthalocyanines were studied using the ITO/ZnO/C60/ P3HT /LiF/Al structure. In order to improve and compare performance parameters of the poly(3-hexylthiophene) (P3HT) based solar cells, the tetra chloro tetra 2,4,6-trimethoxyphenoxy substituted H2Pc (2), Co(II)Pc (3) and Ni(II)Pc (4) compounds were incorporated individually into the solar cell structure between ZnO and C60 layers in which amorphous ZnO nanoparticles serves as electron transfer layer. Solar cell performance parameters such as short circuit current density (JSC), open circuit voltage (VOC), fill factor (FF) and power conversion efficiency (η) were studied as comparison parameters. Incorporation of Ni(II)Pc (4) into the reference structure between ZnO and C60 caused an increase 23.4 % in Jsc and 4.4 % in η whereas incorporation of Co(II)Pc (3) layer into the reference structure caused an increase 135.0 % in Jsc and 107.0 % in η under an illumination of 100 mW/cm2 with an AM 1.5G solar simulator. The best JSC and η (%) values were obtained for P3HT based solar cells with Co(II)Pc (3) interlayer.

Coordinated Control of Constant Output Voltage and Maximum Efficiency in Wireless Power Transfer Systems

This article presents a coordinated control method used for wireless power transfer (WPT) systems. This method can improve WPT system transmission efficiency while maintaining the constant output voltage. First, the topology of the DC–DC converter is selected and the equivalent circuit model of the WPT system is established. Then, the WPT system characteristics are discussed and the mutual inductance estimation process is presented. Furthermore, the coordinated control method is proposed, where the constant voltage output is achieved by connecting the Buck–Boost converter after the diode rectifier. Meanwhile, the optimal phase shift angle is calculated and sent to the controller to achieve maximum transmission efficiency tracking control, according to the measured load voltage and current. Finally, simulations and experiments are adopted to verify the proposed coordinated control method. The experimental results indicate that the average system transmission efficiency is increased by 1.80% and the efficiency fluctuation is decreased by 2.67% when the system load resistance varies, while the average system transmission efficiency is increased by 1.80%, and the efficiency fluctuation is decreased by 3.14% when the mutual inductance changes. This means the proposed coordinated control method is effective under the conditions of the WPT load and mutual inductance variations.

Elevating Discharge Voltage of Li2CO3-Routine Li-CO2 Battery over 2.9 V at an Ultra-Wide Temperature Window.

The Li-CO2 batteries utilizing greenhouse gas CO2 possess advantages of high energy density and environmental friendliness. However, these batteries following Li2CO3-product route typically exhibit low work voltage (<2.5 V) and energy efficiency. Herein, we have demonstrated for the first time that cobalt phthalocyanine (CoPc) as homogeneous catalyst can elevate the work plateau towards 2.98 V, which is higher than its theoretical discharge voltage without changing the Li2CO3-product route. This unprecedented discharge voltage is illustrated by mass spectrum and electrochemical analyses that CoPc has powerful adsorption capability with CO2 (-7.484 kJ mol-1) and forms discharge intermediate of C33H16CoN8O2. Besides high discharge capacity of 18724 mAh g-1 and robust cyclability over 1600 hours (1000 mAh g-1 cut-off) at a current density of 100 mA g-1, the batteries show high temperature adaptability (-30-80 °C). Our work is paving a promising avenue for the progress of high-efficiency Li-CO2 batteries.

Effect of Supporting Carbon Fiber Anode by Activated Coconut Carbon in the Microbial Fuel Cell Fed by Molasses Decoction from Yeast Production

A microbial fuel cell (MFC) is a bioelectrochemical system that generates electrical energy using electroactive micro-organisms. These micro-organisms convert chemical energy found in substances like wastewater into electrical energy while simultaneously treating the wastewater. Thus, MFCs serve a dual purpose, generating energy and enhancing wastewater treatment processes. Due to the high construction costs of MFCs, there is an ongoing search for alternative solutions to improve their efficiency and reduce production costs. This study aimed to improvement of MFC operation and minimize MFC costs by using anode material derived from by-products. Therefore, the proton exchange membrane (PEM) was abandoned, and a stainless steel cathode and a carbon anode were used. To improve the cell’s efficiency, a carbon fiber anode supplemented with activated coconut carbon (ACCcfA) was utilized. Micro-organisms were provided with molasses decoction (a by-product of yeast production) to supply the necessary nutrients for optimal functioning. For comparison, an anode made solely of carbon fibers (CFA) and an anode composed of activated carbon grains without carbon fibers (ACCgA) were also tested. The results indicated that the ACCcfA system achieved the highest cell voltage, power density, and COD reduction efficiency (compared to the CFA and ACCgA electrodes). Additionally, the study demonstrated that incorporating activated coconut carbon significantly enhances the performance of the MFC when powered by a by-product of yeast production.

Enhancing the performance of photovoltaic using exhausted air from thermal comfort spaces

This paper presents an experimental investigation using the exhaust air from the central air conditioning system as cooling air for the PV modules. Experimental tests were conducted under harsh outdoor weather conditions in Baghdad, Iraq, during the summer session, where the recorded ambient temperature was around 33 to 47 °C. In this study, the exhaust air was flowing in the back side of the PV module to reduce the operating temperature of the PV module and thus improve its performance and electrical efficiency. The results show that the temperature of the PV module decreased from 62.42 to 47.42 °C, the output voltage increased from 14.28 to 16.17 V, the generated electrical power increased from 80.39 to 87.89 W, and the electrical efficiency increased from 13.88% to 15.18%. Overall, the enhancement percentage of the PV temperature, voltage, power, and electrical efficiency is 23.7%, 13%, 9.33%, and 9.33%, respectively, compared to the PV module without cooling.

Elevating Discharge Voltage of Li2CO3‐Routine Li−CO2 Battery over 2.9 V at an Ultra‐Wide Temperature Window

AbstractThe Li−CO2 batteries utilizing greenhouse gas CO2 possess advantages of high energy density and environmental friendliness. However, these batteries following Li2CO3‐product route typically exhibit low work voltage (&lt;2.5 V) and energy efficiency. Herein, we have demonstrated for the first time that cobalt phthalocyanine (CoPc) as homogeneous catalyst can elevate the work plateau towards 2.98 V, which is higher than its theoretical discharge voltage without changing the Li2CO3‐product route. This unprecedented discharge voltage is illustrated by mass spectrum and electrochemical analyses that CoPc has powerful adsorption capability with CO2 (−7.484 kJ mol−1) and forms discharge intermediate of C33H16CoN8O2. Besides high discharge capacity of 18724 mAh g−1 and robust cyclability over 1600 hours (1000 mAh g−1 cut‐off) at a current density of 100 mA g−1, the batteries show high temperature adaptability (−30–80 °C). Our work is paving a promising avenue for the progress of high‐efficiency Li−CO2 batteries.

2-Acrylamido-2-methylpropane sulfonic acid (AMPS) grafted poly(vinylidene fluoride) (PVDF) membrane for improved vanadium redox flow battery (VRFB) performance

Polymer modification techniques are crucial for customizing material properties to suit specific applications, particularly in energy storage systems. This study investigates the modification of poly(vinylidene fluoride) (PVDF) membranes via atom transfer radical polymerization (ATRP) to graft 2-acrylamido-2-methylpropane sulfonic acid (AMPS) onto the fluorinated backbone. The successful grafting was confirmed via nuclear magnetic resonance (NMR) spectroscopy, while the membrane structure was evaluated using infrared (IR) and X-ray photoelectron spectroscopies (XPS). Thermogravimetric analysis (TGA) and universal testing machine (UTM) tests verified the thermal and mechanical stability of the membranes. Electrochemical analysis showed sustained performance over 300 cycles. The FluorCat-25 membrane demonstrated high coulombic efficiency (>98 %), voltage efficiency (83 %), and energy efficiency (81 %) at a current density of 100 mA cm−2. Notably, FluorCat-25 achieved a peak power density of 353 mW cm⁻², surpassing that of Nafion-117 (304 mW cm⁻²), with >85 % capacity retention, indicating its superior performance and suitability for VRFB applications. These findings position FluorCat-25 as a promising candidate for efficient and durable energy storage solutions in VRFB technology.

Numerical Modeling of Hybrid Solar/Thermal Conversion Efficiency Enhanced by Metamaterial Light Scattering for Ultrathin PbS QDs-STPV Cell

Ultrathin cells are gaining popularity due to their lower weight, reduced cost, and enhanced flexibility. However, compared to bulk cells, light absorption in ultrathin cells is generally much lower. This study presents a numerical simulation of a metamaterial light management structure made of ultrathin lead sulfide colloidal quantum dots (PbS CQDs) sandwiched between a top ITO grating and a tungsten backing to develop an efficient hybrid solar/thermophotovoltaic cell (HSTPVC). The optical properties were computed using both the finite integration technique (FIT) and the finite element method (FEM). The absorptance enhancement was attributed to the excitations of magnetic polaritons (MP), surface plasmon polaritons (SPP), and lossy mode resonance (LMR). The HSTPVC with the metamaterial optical light management structure was assessed for short-circuit current density, open-circuit voltage, and conversion efficiency. The results show a conversion efficiency of 18.02% under AM 1.5 solar illumination and a maximum thermophotovoltaic conversion efficiency of 12.96% at TB = 1600 K. The HSTPVC can operate in a hybrid solar/thermal conversion state when the ITO grating is included by combining the advantages of QDs and metamaterials. This work highlights the potential for developing a new generation of hybrid STPV cells through theoretical modeling and numerical simulations.

Comprehensive investigation of material properties and operational parameters for enhancing performance and stability of FASnI3-based perovskite solar cells

Recent advancements in the efficiency of lead-based halide perovskite solar cells (PSCs), exceeding 25%, have raised concerns about their toxicity and suitability for mass commercialization. As a result, tin-based PSCs have emerged as attractive alternatives. Among diverse types of tin-based PSCs, organic–inorganic metal halide materials, particularly FASnI3 stands out for high efficiency, remarkable stability, low-cost, and straightforward solution-based fabrication process. In this work, we modelled the performance of FASnI3 PSCs with four different hole transporting materials (Spiro-OMeTAD, Cu2O, CuI, and CuSCN) using SCAPS-1D program. Compared to the initial structure of Ag/Spiro-OMeTAD/FASnI3/TiO2/FTO, analysis on current–voltage and quantum efficiency characteristics identified Cu2O as an ideal hole transport material. Optimizing device output involved exploring the thickness of the FASnI3 layer, defect density states, light reflection/transmission at the back and front metal contacts, effects of metal work function, and operational temperature. Maximum performance and high stability have been achieved, where an open-circuit voltage of 1.16 V, and a high short-circuit current density of 31.70 mA/cm2 were obtained. Further study on charge carriers capture cross-section demonstrated a PCE of 32.47% and FF of 88.53% at a selected capture cross-section of electrons and holes of 1022 cm2. This work aims to guide researchers for building and manufacturing perovskite solar cells that are more stable with moderate thickness, more effective, and economically feasible.

Machine-learning assisted analysis on coupled fluid-dynamics and electrochemical processes in interdigitated channel for iron-chromium flow batteries

This study explores the impact of interdigitated flow channel spacing on electrolyte distribution and flow velocity in porous electrodes, thereby affecting pump consumption and system efficiency. Utilizing a 3D electrochemical flow-coupled model, the research investigates the electrochemical performance and energy efficiency across various channel spacings, specific flow rates, and current densities. It elucidates the mechanisms by which interdigitated channel spacing influences battery performance. Through controlled trial-and-error, the optimal spacing for flow channels in Iron-Chromium Redox Flow Batteries (ICRFBs) was determined to be 4 mm. At a current density of 140 mA/cm2, the voltage efficiency reached 86.3 %, and the pump-based voltage efficiency achieved 85.9 %. To quickly and efficiently explore the impact of each individual parameter on battery efficiency and identify the optimal operating conditions, this study further developed a multi-task machine learning (ML) model. Initially trained on simulation data, the model achieved high predictive accuracy (R2 > 0.88) and effectively linked the interdigitated flow field design of ICRFBs with current density, specific flow rate, and channel spacing. The ML model was then validated through further investigation to ensure its accuracy and to achieve optimum performance efficiency as recommended by the model. This integrated approach offers a comprehensive understanding of RFBs performance under varying conditions, driving advancements in RFBs technology.

Determination of light-independent shunt resistance in CIGS photovoltaic cells using a collection function-based model

Shunt resistance Rsh is a critical parameter for photovoltaic cells designed for low light indoor applications because it negatively affects the open circuit voltage, fill factor, and conversion efficiency. Standard CIGS cells are known to have low Rsh and are, therefore, unpromising candidates for indoor energy sources. In this paper, we extend the original work of Virtuani et al. by determining the electrical specifications of many CIGS cells with copper contents [Cu]/([Ga]+[In]) as low as 0.33 and gallium contents between 0.28 and 0.81. First, IV data are fitted by a standard single-diode electrical circuit model for each illumination, resulting in light-dependent parameters. Then, we use a procedure based on a single dataset of electrical variables, i.e., independent of light, corrected by the experimental collection function, which captures light-dependent physical mechanisms. In this way, we are able to correctly reproduce the illuminance dependence of the electrical response of the PV cell over three orders of magnitude, in particular with a fixed value of the shunt resistance. The highest Rsh is obtained with a low copper composition of 0.5, regardless of the gallium composition.

PEDOT: PSS/PC71BM with various Rubrene doping levels for the production of Organic/Inorganic hybrid silicon solar cells with enhanced yield efficiency

Polymer-based solar cells (PSCs) have garnered considerable interest due to their potential advantages over traditional organic/inorganic hybrid silicon solar cells, including reduced material and production costs, compact substrates, and lightweight finished photovoltaic cells. To explore this further, we examined the impact of Rubrene in the PEDOT: PC71BM hole transport layer within the bulk Heterojunction framework of solution-processable polymer photovoltaic cells. Cells were created by combining PEDOT: PSS and PC71BM, incorporating Rubrene at 6, 9, 12, and 15 wt% ratios. The device structure comprised Si/PEDOT: PSS/PC71BM: Rubrene: DMSO/Ag, with Ag serving as a cathode fabricated in a low-pressure chamber. Notably, employing a 6 wt% Rubrene solution yielded improved short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF), and power conversion efficiency (PCE) of 13.97 mA.cm−2, 514.80 mV, 40.97, and 2.948 %, respectively. These results demonstrate enhanced PCE with the addition of Rubrene compared to prior studies utilizing an active Rubrene surface.

Investigation of the impact of the flow mode in all-vanadium-redox-flow battery using macroporous and mesoporous carbon electrodes

Energy storage in vanadium redox flow batteries (VRFBs) is significantly impacted by both the cell design and the kinetics of electron transfer at the electrode/electrolyte interfaces. In this work, a novel VRFB flow field was designed and evaluated, allowing a portion of the flow to go through the porous electrodes in the direction of current flow. It was found that, when using standard carbon paper electrodes with moderate hydrophilicity, as compared to flow-by or only flow-through, concurrent 50 % flow-through and 50 % flow-by mode decreased the voltage loss by 46 % and increased the voltage efficiency from 74 % to 80 % compared to flow-by only (flow rate of 60 ml s−1). The voltage efficiency and energy efficiency were also enhanced to 82 % and 68 %, respectively, in the flow-through mode. This was likely due to enhanced mass transfer and increased utilization of the internal electrode surface area, in turn lowering the overpotential during both charging and discharging. To further determine the benefits of flow-through conditions, the effect of a binder-free, hydrophilic, and mesoporous carbon scaffold electrode (NCS85) was also investigated under flow-through mode and compared with the standard carbon paper electrodes with moderate hydrophilicity. NCS 85 has monodisperse, 3-D interconnected 85 nm pore diameters and thus a much higher surface area, resulting in a further increase in voltage and energy efficiency to 86 and 65 %, respectively. Heat treatment of the NCS85 to graphitize it and thus lower its resistance showed further improvements when using the flow-through mode, giving a voltage efficiency of 94 % and energy efficiency of 72 %. These improvements show the benefits that can be realized by optimizing both flow mode and carbon electrode porosity and permeability on VRFB performance.

Zwitterionic channels within covalent organic frameworks facilitate proton-selective transport for flow battery membrane

Flow batteries demand for ion conductive membranes (ICMs) with high ion selectivity to achieve efficient energy conversion. Herein, we engineered a cysteine-modified covalent organic framework (Cys-COF) by a Thiol-ene click reaction. As a promising proton carrier, the incorporation of the Cys-COF with sulfonated poly(ether ketone) (SPEEK) yields advanced ICMs for vanadium flow batteries (VFBs). The zwitterionic cysteine groups anchored on the nanochannel walls simultaneously narrowed the pore size and ameliorated the protophilicity of Cys-COF, resulting in improved vanadium permeating resistance and proton conductivity. As a result, the optimal membrane demonstrated synchronized improvements in coulombic efficiency (95.01 %–98.84 %), voltage efficiency (95.15 %–77.84 %) and energy efficiency (90.41 %–76.94 %) with the current densities ranging from 40 to 200 mA cm−2. Regarding stability test, it achieved exceptional energy efficiency (∼84.3 %) over 1100 cycles and 550 h at the constant current density of 120 mA cm−2, outperforming pure polymer membrane and Nafion 212.