Numerical modelling of a bromide–polysulphide redox flow battery: Part 1: Modelling approach and validation for a pilot-scale system

Numerical modelling of redox flow battery (RFB) systems for energy storage applications allows the technical performance of different designs to be predicted without costly lab, pilot and full-scale testing. A one-dimensional numerical model has been developed for RFB systems with bipolar flow-by electrodes, soluble redox couples, and recirculating batch operation. Overpotential losses were estimated from the Butler-Volmer equation, accounting for mass transfer. The effects of cross-membrane solvent transport and self-discharge were also considered. The model predicted the variation in concentration and current along the electrode and determined the charge–discharge efficiency, energy density and power density. The model was validated using data obtained from a pilot-scale bromide–polysulphide (PSB) system commercialised by Regenesys Technologies (UK) Ltd. Electrochemical rate constants were obtained by fitting the model results to the experimental data, and values of 4 × 10⁻⁷ and 3 × 10⁻⁸ m s⁻¹ were found for the bromide and sulphide electrolytes on the activated carbon electrodes. The model was able to predict cell performance, species concentration, current distribution and electrolyte deterioration for the Regenesys system.     

Energy use, cost and CO2 emissions of electric cars

We examine efficiency, costs and greenhouse gas emissions of current and future electric cars (EV), including the impact from charging EV on electricity demand and infrastructure for generation and distribution.Uncoordinated charging would increase national peak load by 7% at 30% penetration rate of EV and household peak load by 54%, which may exceed the capacity of existing electricity distribution infrastructure. At 30% penetration of EV, off-peak charging would result in a 20% higher, more stable base load and no additional peak load at the national level and up to 7% higher peak load at the household level. Therefore, if off-peak charging is successfully introduced, electric driving need not require additional generation capacity, even in case of 100% switch to electric vehicles.GHG emissions from electric driving depend most on the fuel type (coal or natural gas) used in the generation of electricity for charging, and range between 0 g km⁻¹ (using renewables) and 155 g km⁻¹ (using electricity from an old coal-based plant). Based on the generation capacity projected for the Netherlands in 2015, electricity for EV charging would largely be generated using natural gas, emitting 35-77 g CO_2 eq km⁻¹.We find that total cost of ownership (TCO) of current EV are uncompetitive with regular cars and series hybrid cars by more than 800 € year⁻¹. TCO of future wheel motor PHEV may become competitive when batteries cost 400 € kWh⁻¹, even without tax incentives, as long as one battery pack can last for the lifespan of the vehicle. However, TCO of future battery powered cars is at least 25% higher than of series hybrid or regular cars. This cost gap remains unless cost of batteries drops to 150 € kWh⁻¹ in the future. Variations in driving cost from charging patterns have negligible influence on TCO.GHG abatement costs using plug-in hybrid cars are currently 400-1400 € tonne⁻¹ CO_2 eq and may come down to −100 to 300 € tonne⁻¹. Abatement cost using battery powered cars are currently above 1900 € tonne⁻¹ and are not projected to drop below 300-800 € tonne⁻¹.     

Non-aqueous manganese acetylacetonate electrolyte for redox flow batteries

A single-metal redox flow battery employing manganese(III) acetylacetonate in tetraethylammonium tetrafluoroborate and acetonitrile has been investigated. Cyclic voltammetry was used to evaluate electrode kinetics and reaction thermodynamics. The Mn^II/Mn^III and Mn^III/Mn^IV redox couples appeared to be quasi-reversible. A cell potential of 1.1 V was measured for the one-electron disproportionation of the neutral Mn^III complex. The diffusion coefficient for manganese acetylacetonate in the supporting electrolyte solution was estimated to be in the range of 3-5 × 10⁻⁶ cm² s⁻¹ at room temperature. The charge-discharge characteristics of this system were evaluated in an H-type glass cell. Coulombic efficiencies increased with cycling suggesting an irreversible side reaction. Energy efficiencies for this unoptimized system were ∼21%, likely due to the high cell-component overpotentials.     

Methoxyethoxyethoxyphosphazenes as ionic conductive fire retardant additives for lithium battery systems

The current highly flammable configurations for rechargeable lithium batteries generate safety concerns. Although commercial fire retardant additives have been investigated, they tend to decrease the overall efficiency of the battery. We report here ionically conductive, non-halogenated lithium battery additives based on a methoxyethoxyethoxyphosphazene oligomer and the corresponding high polymer, which can increase the fire resistance of a battery while retaining a high energy efficiency. Conductivities in the range of 10⁻⁴ S cm⁻¹ have been obtained for self-extinguishing, ion-conductive methoxyethoxyethoxyphosphazene oligomers. The addition of 25 wt% high polymeric poly[bis(methoxyethoxyethoxy)phosphazene] to propylene carbonate electrolytes lowers the flammability by 90% while maintaining a good ionic conductivity of 2.5 × 10⁻³ S cm⁻¹.     

Development of the all‐vanadium redox flow battery for energy storage: a review of technological,financial and policy aspects

The commercial development and current economic incentives associated with energy storage using redox flow batteries (RFBs) are summarised. The analysis is focused on the all‐vanadium system, which is the most studied and widely commercialised RFB. The recent expiry of key patents relating to the electrochemistry of this battery has contributed to significant levels of commercialisation in, for example, Austria, China and Thailand, as well as pilot‐scale developments in many countries. The potential benefits of increasing battery‐based energy storage for electricity grid load levelling and MW‐scale wind/solar photovoltaic‐based power generation are now being realised at an increasing level. Commercial systems are being applied to distributed systems utilising kW‐scale renewable energy flows. Factors limiting the uptake of all‐vanadium (and other) redox flow batteries include a comparatively high overall internal costs of $217 kW^?1 h^?1 and the high cost of stored electricity of ≈ The commercial development and current economic incentives associated with energy storage using redox flow batteries (RFBs) are summarised. The analysis is focused on the all‐vanadium system, which is the most studied and widely commercialised RFB. The recent expiry of key patents relating to the electrochemistry of this battery has contributed to significant levels of commercialisation in, for example, Austria, China and Thailand, as well as pilot‐scale developments in many countries. The potential benefits of increasing battery‐based energy storage for electricity grid load levelling and MW‐scale wind/solar photovoltaic‐based power generation are now being realised at an increasing level. Commercial systems are being applied to distributed systems utilising kW‐scale renewable energy flows. Factors limiting the uptake of all‐vanadium (and other) redox flow batteries include a comparatively high overall internal costs of $217 kW^?1 h^?1 and the high cost of stored electricity of ≈ $0.10 kW^?1 h^?1. There is also a low‐level utility scale acceptance of energy storage solutions and a general lack of battery‐specific policy‐led incentives, even though the environmental impact of RFBs coupled to renewable energy sources is favourable, especially in comparison to natural gas‐ and diesel‐fuelled spinning reserves. Together with the technological and policy aspects associated with flow batteries, recent attempts to model redox flow batteries are considered. The issues that have been addressed using modelling together with the current and future requirements of modelling are outlined. Copyright © 2011 John Wiley & Sons, Ltd.     

Feasibility study and techno-economic analysis of an SOFC/battery hybrid system for vehicle applications

A feasibility study and techno-economic analysis for a hybrid power system intended for vehicular traction applications has been performed. The hybrid consists of an intermediate temperature solid oxide fuel cell (IT-SOFC) operating at 500–800 °C and a sodium–nickel chloride (ZEBRA) battery operating at 300 °C. Such a hybrid system has the benefits of extended range and fuel flexibility (due to the IT-SOFC), high power output and rapid response time (due to the battery). The above hybrid has been compared to a fuel cell-only, a battery-only and an ICE vehicle. It is shown that the capital cost associated with a fuel cell-only vehicle is still much higher than that of any other power source option and that a battery-only option would potentially encounter weight and volume limitations, particularly for long drive times. It is concluded that increasing drive time per day decreases substantially the payback time in relation to an ICE vehicle running on gasoline and thus that the hybrid vehicle is an economically attractive option for commercial vehicles with long drive times. In the case where the battery has reached volume production prices at £70 kWh⁻¹ and current fuel duty values remain unchanged then a payback time <2 years is obtained. For a light delivery van operating with 6 h drive time per day, a fuel cell system model predicted a gasoline equivalent fuel economy of 25.1 km L⁻¹, almost twice that of a gasoline fuelled ICE vehicle of the same size, and CO₂ emissions of 71.6 g km⁻¹, well below any new technology target set so far. It is therefore recommended that a SOFC/ZEBRA demonstration be built to further explore its viability.     

Mechanistic understanding of monosaccharide-air flow battery electrochemistry

Recently, an inexpensive monosaccharide-air flow battery configuration has been demonstrated to utilize a strong base and a mediator redox dye to harness electrical power from the partial oxidation of glucose. Here the mechanistic understanding of glucose oxidation in this unique glucose-air power source is further explored by acid-base titration experiments, ¹³C NMR, and comparison of results from chemically different redox mediators (indigo carmine vs. methyl viologen) and sugars (fructose vs. glucose) via studies using electrochemical techniques. Titration results indicate that gluconic acid is the main product of the cell reaction, as supported by evidence in the ¹³C NMR spectra. Using indigo carmine as the mediator dye and fructose as the energy source, an abiotic cell configuration generates a power density of 1.66 mW cm⁻², which is greater than that produced from glucose under similar conditions (ca. 1.28 mW cm⁻²). A faster transition from fructose into the ene-diol intermediate than from glucose likely contributed to this difference in power density.     

Carbon-supported manganese oxide nanocatalysts for rechargeable lithium-air batteries

Manganese oxide based catalysts were synthesised in the form of nano-particles using a redox reaction of MnSO₄ and KMnO₄, housed into the pores of a carbon matrix and followed by a thermal treatment. Particle sizes of the manganese oxide nanocatalysts were around 50 nm, based on the tunnelling electron microscope measurement. They were uniformly distributed in the carbon matrix, which contributed to an improved electrical connection among the catalyst and current collectors. The charge/discharge tests using this material as the cathode material in a rechargeable lithium-air battery showed high discharge capacities up to 4750 mAh (g carbon)⁻¹. The cycle ability of the composite electrode was superior to those of the commercial electrolytic manganese dioxide electrodes.     

Oxygen-selective immobilized liquid membranes for operation of lithium-air batteries in ambient air

In this work, nonaqueous electrolyte-based Li-air batteries with an O₂-selective membrane have been developed for operation in ambient air of 20-30% relative humidity (RH). The O₂ gas is continuously supplied through a membrane barrier layer at the interface of the cathode and ambient air. The membrane allows O₂ to permeate through while blocking moisture. Such membranes can be prepared by loading O₂-selective silicone oils into porous supports such as porous metal sheets and Teflon (PTFE) films. It was found that the silicone oil of high viscosity shows better performance. The immobilized silicone oil membrane in the porous PTFE film enabled the Li-air batteries with carbon black air electrodes to operate in ambient air (at 20% RH) for 16.3 days with a specific capacity of 789 mAh g⁻¹ carbon and a specific energy of 2182 Wh kg⁻¹ carbon. Its performance is much better than a reference battery assembled with a commercial, porous PTFE diffusion membranes as the moisture barrier layer on the cathode, which only had a discharge time of 5.5 days corresponding to a specific capacity of 267 mAh g⁻¹ carbon and a specific energy of 704 Wh kg⁻¹ carbon. The Li-air battery with the present selective membrane barrier layer even showed better performance in ambient air operation (20% RH) than the reference battery tested in the dry air box (<1% RH).     

The economics of using plug-in hybrid electric vehicle battery packs for grid storage

We examine the potential economic implications of using vehicle batteries to store grid electricity generated at off-peak hours for off-vehicle use during peak hours. Ancillary services such as frequency regulation are not considered here because only a small number of vehicles will saturate that market. Hourly electricity prices in three U.S. cities were used to arrive at daily profit values, while the economic losses associated with battery degradation were calculated based on data collected from A123 Systems LiFePO₄/Graphite cells tested under combined driving and off-vehicle electricity utilization. For a 16 kWh (57.6 MJ) vehicle battery pack, the maximum annual profit with perfect market information and no battery degradation cost ranged from ∼US$140 to $250 in the three cities. If the measured battery degradation is applied, however, the maximum annual profit (if battery pack replacement costs fall to $5000 for a 16 kWh battery) decreases to ∼$10-120. It appears unlikely that these profits alone will provide sufficient incentive to the vehicle owner to use the battery pack for electricity storage and later off-vehicle use. We also estimate grid net social welfare benefits from avoiding the construction and use of peaking generators that may accrue to the owner, finding that these are similar in magnitude to the energy arbitrage profit.     

Nafion/SiO2 hybrid membrane for vanadium redox flow battery

Sol–gel derived Nafion/SiO₂ hybrid membrane is prepared and employed as the separator for vanadium redox flow battery (VRB) to evaluate the vanadium ions permeability and cell performance. Nafion/SiO₂ hybrid membrane shows nearly the same ion exchange capacity (IEC) and proton conductivity as pristine Nafion 117 membrane. ICP-AES analysis reveals that Nafion/SiO₂ hybrid membrane exhibits dramatically lower vanadium ions permeability compared with Nafion membrane. The VRB with Nafion/SiO₂ hybrid membrane presents a higher coulombic and energy efficiencies over the entire range of current densities (10–80 mA cm⁻²), especially at relative lower current densities (<30 mA cm⁻²), and a lower self-discharge rate compared with the Nafion system. The performance of VRB with Nafion/SiO₂ hybrid membrane can be maintained after more than 100 cycles at a charge–discharge current density of 60 mA cm⁻². The experimental results suggest that the Nafion/SiO₂ hybrid membrane approach is a promising strategy to overcome the vanadium ions crossover in VRB.     

A GIS-based analysis on the relationship between the annual available amount and the procurement cost of forest biomass in a mountainous region in Japan

The feasibility of utilization of forest biomass for energy in a mountainous region in Japan is discussed based on analyses with a geographic information system (GIS). In this study, ‘forest biomass’ denotes logging residues, thinned trees, and trees from broad-leaved forests. First, using the GIS, the distribution map of biomass resources was completed, and the topographical information of each sub-compartment was prepared. Second, harvesting and transportation systems were classified into six types by fraction of tree for energy (two types) and by topographical conditions (three types). Equations for cost calculation were developed and included the variables slope, skidding/yarding distance, and transportation distance. Finally, the relationship between the mass and the procurement cost of forest biomass in the region was analyzed. The results show that logging residues (the available amount was 4.035 Gg y⁻¹ on a dry-mass basis) were the least costly followed by broad-leaved forests (20.317 Gg y⁻¹) while thinned trees (27.854 Gg y⁻¹) were the most costly. The analysis may support operational planning, especially the decision of selecting sub-compartments to be felled. For instance, the amount of biomass needed to supply a power-plant covering 24.8% of the regional household need was calculated to 30.106 Gg y⁻¹. This amount of forest biomass could optimally be harvested from sub-compartments whose procurement costs were lower than 108.6 US$ Mg⁻¹.     

Potential improvement to a citric wastewater treatment plant using bio-hydrogen and a hybrid energy system

Treatment of highly concentrated organic wastewater is characterized as cost-consuming. The conventional technology uses the anaerobic-anoxic-oxic process (A²/O), which does not produce hydrogen. There is potential for energy saving using hydrogen utilization associated with wastewater treatment because hydrogen can be produced from organic wastewater using anaerobic fermentation. A 50 m³ pilot bio-reactor for hydrogen production was constructed in Shandong Province, China in 2006 but to date the hydrogen produced has not been utilized. In this work, a technical-economic model based on hydrogen utilization is presented and analyzed to estimate the potential improvement to a citric wastewater plant. The model assesses the size, capital cost, annual cost, system efficiency and electricity cost under different configurations. In a stand-alone situation, the power production from hydrogen is not sufficient for the required load, thus a photovoltaic array (PV) is employed as the power supply. The simulated results show that the combination of solar and bio-hydrogen has a much higher cost compared with the A²/O process. When the grid is connected, the system cost achieved is 0.238 US$ t⁻¹ wastewater, which is lower than 0.257 US$ t⁻¹ by the A²/O process. The results reveal that a simulated improvement by using bio-hydrogen and a FC system is effective and feasible for the citric wastewater plant, even when compared to the current cost of the A²/O process. In addition, lead acid and vanadium flow batteries were compared for energy storage service. The results show that a vanadium battery has lower cost and higher efficiency due to its long lifespan and energy efficiency. Additionally, the cost distribution of components shows that the PV dominates the cost in the stand-alone situation, while the bio-reactor is the main cost component in the parallel grid.     

Fuel cells for automotive powertrains—A techno-economic assessment

With the objective of identifying the hurdles currently preventing a widespread application of fuel cell technology in passenger cars an assessment of technical and economic parameters is carried out. Patent and publication analysis is used to assess current status of fuel cell technology regarding its position on technology life cycle. S-curve methodology leads to the conclusion that further scientific activity is to be expected but for today's low-temperature PEM fuel cell technology might level by 2015. Technical analysis identifies power density and platinum loading as parameters for which further improvements are necessary in order to satisfy future customer needs. A detailed cost evaluation suggests that in future for high production volumes (approx. 1 million vehicles cumulative) significantly lower costs for fuel cell stacks (12–40$ kW⁻¹) and systems (35–83$ kW⁻¹) will be viable. Reducing costs to such a level will have to be the main focus for upcoming research activities in order to make fuel cell driven road vehicles a competitive alternative.     

Modelling airflow,heat transfer and moisture transport around a standing human body by computational fluid dynamics

In this study a combined computational model of a room with virtual thermal manikin with real dimensions and physiological shape was used to determine heat and mass transfer between human body and environment. Three dimensional fluid flow, temperature and moisture distribution, heat transfer (sensible and latent) between human body and ambient, radiation and convection heat transfer rates on human body surfaces, local and average convection coefficients and skin temperatures were calculated. The radiative heat transfer coefficient predicted for the whole-body was 4.6 W m^− 2 K^− 1, closely matching the generally accepted whole-body value of 4.7 W m^− 2 K^− 1. Similarly, the whole-body natural convection coefficient for the manikin fell within the mid-range of previously published values at 3.8 W m^− 2 K^− 1. Results of calculations were in agreement with available experimental and theoretical data in literature.     

Recent advances in NiMH battery technology

Nickel-metal hydride (NiMH) is a commercially important rechargeable battery technology for both consumer and industrial applications due to design flexibility, excellent energy and power, environmental acceptability and cost. [1] From the initial product introduction in 1991 of cylindrical cells having an energy of 54 Wh kg⁻¹, today's small consumer cells have a specific energy over 100 Wh kg⁻¹. Numerous licensed manufacturers produce a myriad of NiMH products ranging from 30 mAh button cells to a wide variety of consumer cylindrical products, prismatic cells up to 250 Ah for electric buses and 6 Ah multicell modules for hybrid electric vehicles. Power has increased from under 200 to 1200 W kg⁻¹ commercially and up to 2000 W kg⁻¹ at a development level [2].     

The air quality and human health effects of integrating utility-scale batteries into the New York State electricity grid

In a restructured electricity market, utility-scale energy storage technologies such as advanced batteries can generate revenue by charging at low electricity prices and discharging at high prices. This strategy changes the magnitude and distribution of air quality emissions and the total carbon dioxide (CO₂) emissions. We evaluate the social costs associated with these changes using a case study of 500 MW sodium-sulfur battery installations with 80% round-trip efficiency. The batteries displace peaking generators in New York City and charge using off-peak generation in the New York Independent System Operator (NYISO) electricity grid during the summer. We identify and map charging and displaced plant types to generators in the NYISO. We then convert the emissions into ambient concentrations with a chemical transport model, the Particulate Matter Comprehensive Air Quality Model with extensions (PMCAM_x). Finally, we transform the concentrations into their equivalent human health effects and social benefits and costs. Reductions in premature mortality from fine particulate matter (PM_2.5) result in a benefit of 4.5 ¢ kWh⁻¹ and 17 ¢ kWh⁻¹ from displacing a natural gas and distillate fuel oil fueled peaking plant, respectively, in New York City. Ozone (O₃) concentrations increase due to decreases in nitrogen oxide (NO_x) emissions, although the magnitude of the social cost is less certain. Adding the costs from charging, displacing a distillate fuel oil plant yields a net social benefit, while displacing the natural gas plant has a net social cost. With the existing base-load capacity, the upstate population experiences an increase in adverse health effects. If wind generation is charging the battery, both the upstate charging location and New York City benefit. At $20 per tonne of CO₂, the costs from CO₂ are small compared to those from air quality. We conclude that storage could be added to existing electricity grids as part of an integrated strategy from a human health standpoint.     

A novel electrode-bipolar plate assembly for vanadium redox flow battery applications

A novel electrode-bipolar plate assembly has been developed and evaluated for application in the vanadium redox flow battery (VRB). It is composed of three parts: a graphite felt (electrode), an adhesive conducting layer (ACL) and a flexible graphite plate (bipolar plate). The ACL connects the electrode with the bipolar plate to an assembly. By the evaluations of cost, resistivity, surface morphology, electrolyte permeation and single cell performance, this novel assembly demonstrates its applicability in VRB as evident in the following outcomes: (1) lowers the cost and area resistivity to about 10% and 40% of the conventional setups, respectively; (2) improves electrical conductivity to 4.97 mΩ cm as compared to over 100 mΩ cm of the carbon-plastic composite bipolar plate; (3) attains zero electrolyte permeation; and (4) achieves a higher energy efficiency of 81% at a charge/discharge current density of 40 mA cm⁻² when employed in a VRB single cell, which is 73% for the conventional setup. All these indicate that the novel electrode-bipolar plate assembly is a promising candidate for VRB applications.     

Highly stable graphene oxide composite proton exchange membrane for electro-chemical energy application

Proton exchange membrane is a basic element for any redox flow battery. Nafion is the only commercial available proton exchange membrane used in different electro-chemical energy systems. High cost restrict it's used for energy generation devices. In present work, we synthesised styrene divinylbenzene based composite proton exchange membranes (PEMs) with varying sulfonated graphene oxide (sGO) content for redox flow battery (RFB). Synthesized copolymer PEMs were analyzed in terms of their chemical structure with the help of FT-IR spectroscopy to confirm desired functional groups at appropriate position. Electrochemical characterization was performed in terms proton-exchange capacity, protonic conductivity and water uptake. Membrane shows adequate proton exchange capacity with good proton conductivity. Vanadium ion permeability was also tested for the prepared membrane to assess capability for vanadium redox flow battery (VRFB) in contrast with commercially available Nafion 117 PEM. Higher VO⁺² ion cross-over resistance was found for CEM-4 with 7.17 × 10⁻⁷ cm² min⁻¹ permeability, which is about half of the CEM-1. Further CEM-4 was also evaluated for charging-discharging phenomenon for single cell VRFB. The values of columbic, voltage and energy efficiency for VRFB confirms prepared membrane as a good candidate for redox flow battery. Composite PEM also shows better mechanical and thermal stability. Results indicates that synthesized composite membrane can be used in vanadium redox flow battery.     

Polypyrrole/carbon black composite as a novel oxygen reduction catalyst for microbial fuel cells

A polypyrrole/carbon black (Ppy/C) composite has been employed as an electrocatalyst for the oxygen reduction reaction (ORR) in an air-cathode microbial fuel cell (MFC). The electrocatalytic activity of the Ppy/C is evaluated toward the oxygen reduction using cyclic voltammogram and linear sweep voltammogram methods. In comparison with that at the carbon black electrode, the peak potential of the ORR at the Pp/C electrode shifts by approximate 260 mV towards positive potential, demonstrating the electrocatalytic activity of Ppy toward ORR. Additionally, the results of the MFC experiments show that the Ppy/C is well suitable to fully substitute the traditional cathode materials in MFCs. The maximum power density of 401.8 mW m⁻² obtained from the MFC with a Ppy/C cathode is higher than that of 90.9 mW m⁻² with a carbon black cathode and 336.6 mW m⁻² with a non-pyrolysed FePc cathode. Although the power output with a Ppy/C cathode is lower than that with a commercial Pt cathode, the power per cost of a Ppy/C cathode is 15 times greater than that of a Pt cathode. Thus, the Ppy/C can be a good alternative to Pt in MFCs due to the economic advantage.