bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regenerative Fuel Cells for Energy Storage Application: Performance Limitation Studies
Authors: Yufit Vladimir , Hewa Dewage Harini , Brandon Nigel P. 
Published: February 2020

Redox flow batteries are a potentially versatile and attractive solution to store and deliver energy over the kW/kWh to MW/MWh range. A variety of redox flow chemistries exist, with all-vanadium battery being the most mature and developed. Nonetheless, all-vanadium systems suffer from a relatively low power density, specific energy and high cost, associated with the use of vanadium based electrolytes. These issues can be circumvented by replacing the vanadium anolyte or catholyte with a cheaper alternative. Particularly, novel regenerative fuel cells have been developed that utilise a combination of a liquid and a gaseous redox reactions; either hydrogen oxidation reaction on the anode side or oxygen reduction reaction on the cathode side. Previous work by the authors has demonstrated a regenerative fuel cell based on hydrogen/vanadium redox reactions whichachieved a specific power of 200 mW/cm2. Further optimisation of this system has increased the power density to more than 400 mW/cm2. This paper will present a study of the performance limiting factors in the Regenerative Hydrogen Vanadium Fuel Cell, showing how this information can be generally implemented in other energy storage systems utilising hydrogen and metal redox couples.
Modelling and Validation of Water Hydration of PEM Fuel Cell Membrane in Dynamic Operations
Authors: Liso Vincenzo , Nielsen Mads Pagh 
Published: February 2020

Fuel cells convert chemical energy of hydrogen and oxygen directly in to electricity. High efficiency and zero emission have made them a prime candidate for powering the next generation of electric vehicles. PEM fuel cells require good hydration in order to deliver high performance and ensure long life operation. Water is essential for membrane proton conductivity which increases by nearly six orders of magnitude from dry to fully hydrated. Adequate water management in PEM fuel cell is crucial in order to avoid an imbalance between water production and water removal from the fuel cell.
In the present study, a novel mathematical zero-dimensional model has been formulated for the water mass balance and hydration of a polymer electrolyte membrane. This model incorporates all the essential fundamental physical and electrochemical processes occurring in the membrane electrolyte and considers the water adsorption/desorption phenomena in the membrane. The effect of diffusivity model, surface roughness and water content driving force is considered. The model is validated against experimental data.
In the results it is shown that the fuel cell water balance calculated by this model display better fit with experimental data-points compared with model where only water transport equilibrium were considered. We conclude that this discrepancy is due a different rate of water transport when membrane absorption/ desorption is considered in the model.
Many studies have erroneously considered fuel cell membrane in equilibrium condition disrigarding non-ficknian behavior of the cell membrane. For this reason the model presented in this study becomes useful when studying PEM fuel cell system in dynamic conditions.
Active Non-Platinum Cathode Catalysts for Direct-Methanol Alkaline Fuel Cells
Authors: Kruusenberg Ivar , Ratso Sander , Vikkisk Merilin , Kanninen Petri , Kallio Tanja , Kannan Arunachala Mada , Tammeveski Kaido 
Published: February 2020

The development of novel catalyst materials for oxygen reduction reaction (ORR) is one of the key topics in fuel cell research. In order to replace expensive noble-metal based catalysts that have been primarily employed as cathode catalysts in low-temperature fuel cells, different carbon-based materials that possess lower price, better availability and improved chemical stability have been investigated. An attractive approach is to employ nitrogen-containing carbon nanomaterials for this purpose 1-3.

In this work the electrochemical reduction of oxygen has been studied on nitrogen-doped carbon nanomaterials modified glassy carbon (GC) electrodes. N-doped carbon nanotubes (N-CNT) and N-doped few-layer graphene/carbon nanotube (N-FLG/CNT) composite materials were investigated as catalyst materials. Dicyandiamide (DCDA) was used as nitrogen precursor for nitrogen doping of carbon nanomaterials. The doping was achieved by pyrolysing nanocarbon materials in the presence of DCDA at 800 °C. The CNT or FLG/CNT-to-nitrogen precursor mass ratio was 1:20. Electrochemical experiments were carried out in 0.1 M KOH using the rotating disk electrode (RDE) method. GC electrodes were modified using carbon nanomaterial suspension in isopropanol in the presence of Fuma-Tech FAA3 ionomer. The fuel cell performance of N-doped carbon materials was investigated by fabricating membrane-electrode assemblies (MEAs) using Fuma-Tech FAA3 membrane and for comparison purposes a commercial Pt/C catalyst was used as cathode material.
The RDE experiments showed extraordinary electrocatalytic activity of N-doped carbon nanomaterials toward the ORR in alkaline media. A comparative study of direct methanol alkaline fuel cell performance was also performed. The power density curves are presented in Fig. 1. The MEAs with N-CNT, N-FLG/CNT and commercial 60% Pt/C cathode catalysts had power densities of 0.92, 0.72 and 0.72 mW cm−2 respectively, using methanol as fuel on anode side and pure O2 gas on cathode side. The results obtained in this work show that N-FLG/CNT and N-CNT catalysts possess excellent ORR activity in alkaline media and could be used as alternative cathode catalysts in alkaline anion-exchange membrane fuel cells.

References

1. I. Kruusenberg, S. Ratso, M. Vikkisk, P. Kanninen, T. Kallio, A.M. Kannan, K. Tammeveski, J. Power Sources, 281, 94, 2015.
2. M. Vikkisk, I. Kruusenberg, U. Joost, E. Shulga, I. Kink, and K. Tammeveski, Appl. Catal. B: Environ.,
147, 369, 2014.
3. S. Ratso, I. Kruusenberg, M. Vikkisk, U. Joost, E. Shulga, I. Kink, T. Kallio, and K. Tammeveski, Carbon, 73, 361, 2014.

Figure 1
Design of Low pH Stable and Highly Active (Ti, Zn) Doped RuO2 Electrocatalysts for Electrochemical Water Oxidation
Authors: Kishor Koshal , Saha Sulay , Gupta Manish Kumar , Bajpai Anshuman , Chatterjee Moitrayee , Sivakumar Sri , Pala Raj Ganesh 
Published: February 2020

High overpotential, low stability and cost of the electrocatalysts represent significant challenges for oxygen evolution reaction (OER) operating in the acidic medium. In this regard, blending active (usually unstable) and passive (usually not active) components is one of the methods to tackle this challenge. Here, active Zn and passive Ti are blended in Ru-based oxides through co-electrodeposition method. The composition of the electrodes has been optimized by controlling the electrodeposition bath concentration. The surface roughness of the resultant electrode is increased due to introduction of ‘chemical inhomogeneity’ by Ti and ‘structural inhomogeneity’ through Zn. It has been found that incorporation of Zn and Ti additives increase both activity and stability of electrodes. The maximum catalytic activity is found in the composition of Ru0.259Ti0.736Zn0.006Ox with a current density of 63mA/cm2 at an operating voltage of 1.35V (vs Ag/AgCl). The activity of this electrode is four times higher than electrodeposited RuO2 and also higher than other possible binary combinations in Ru-electrodes (RuTi, RuZn). The stability of the electrodes among the co-electrodeposited electrodes are found to be in order of co-electrodeposited RuZn<co-electrodeposited RuTi<co-electrodeposited RuTiZn.The increase in catalytic activity of the co-electrodeposited electrodes can be attributed to the combination of lowering of activation energy thereby increasing site activity and increase of available active sites due to promotion of roughness in surface by the Zn and Ti. The increased stability may be attributed to intermixing of additives leading to formation of porous stable surface layer as suggested by impedance spectroscopy.
Focused Ion Beam Reduced Graphene Oxide Micro-Supercapacitors with Unprecedented Energy and Power Densitites
Authors: Chakraborty Banerjee Parama , Lobo Derrek Lobo , Easton Christopher , Majumder Mainak 
Published: February 2020

Miniaturization of energy storage devices with high energy and power densities can reduce the footprint of micro-devices being used in our daily life. Micro-supercapacitors with planar geometries offer several advantages, such as, the ability to control and reduce the distances ions travel between two electrodes, easy integration to micro devices as the separator and the electrodes are in the same plane, and offer the potential of being extended into 3D without compromising the inter-electrode separation distances. In this study, we have used focused ion beam technology (which is capable of producing reduced graphene oxide patterns and complex shapes in insulating films of graphene oxide with a possible spatial resolution down to ~20 nm in a mask-less and direct write approach) to directly write miniaturized planar electrodes of reduced graphene oxide on films of graphene oxide (GO). We have optimised the ion-beam irradiation and have investigated the influence of ion beam irradiation on the resultant microstructure and the electrochemical properties of the resultant reduced graphene oxide films. Subsequently, using the optimized ion-beam irradiation, interdigitated electrode designs (40 μm long and 3.5 μm wide fingers with ultra-small inter-electrode spacing of 1 μm) have been generated, which have demonstrated a large capacitance (102 mF/cm2), ultra-small time response (0.03 ms), low equivalent series resistance (0.35 mΩ cm2), and have retained 95 % of the specific capacitance after 1000 cycles at an ultrahigh current density of 45 mA/cm2. These performance metrics show unprecedented improvements on several aspects of supercapacitor performance over existing reports due to the miniaturized electrode dimensions and minimal damage to the graphene sheets. We believe our results can provide opportunities for large-scale fabrication of arrayed, planar, high performance micro-supercapacitors with a small environmental footprint.
In Situ Study of Strain-Dependent Ion Conductivity of Stretchable Polyethylene Oxide Electrolyte
Authors: Kelly Taylor , Moradi Ghadi Bahar , Berg Sean , Ardebili Haleh 
Published: February 2020

There is a strong need in developing stretchable batteries that can accommodate stretchable or irregularly shaped applications including medical implants, wearable devices and stretchable electronics. There has been a fair amount of work exploring the development and performance of stretchable electrodes, but very little for stretchable electrolytes. Solid polymer electrolytes are ideal candidates for creating fully stretchable lithium ion batteries because of their mechanical and electrochemical stability, thin-film manufacturability and enhanced safety. However, the characteristics of ion conductivity of polymer electrolytes during tensile deformation are not well understood.
We have investigated the effects of tensile strain on the ion conductivity of thin-film polyethylene oxide (PEO) through an in situ study. The results of this investigation demonstrate that both in-plane and through-plane ion conductivities of PEO undergo steady and linear growth with respect to the tensile strain. This increasing trend in conductivity infers that the structural changes induced in the polymer electrolyte results in altered and improved ion conduction. The coefficients of strain-dependent ion conductivity enhancement (CSDICE) for in-plane and through-plane conduction were found to be 28.5 and 27.2, respectively.
We hypothesize that the stretching and aligning of the amorphous polymer chains decreases the degree of tortuosity in the polymer, allowing for faster, and less obstructed ion transport. Semi-crystalline PEO consists of a crystalline phase and an amorphous phase. The amorphous phase is generally present along the edges of the crystallites where the polymer chains are disordered, twisted and entangled and tie one crystallite to another. The semi-crystalline conformation of PEO can be seen using polarization light microscopy, which confirms the growth and extension of the amorphous regions as the chains stretch and disentangle due to tensile strain.
In conclusion, the present work confirms the feasibility of using solid polymer PEO as a stretchable electrolyte for next generation stretchable batteries.
Influence of Porous Separators on the Ionic Conductivity of Nonflammable Liquid Perfluoropolyether Electrolytes
Authors: Devaux Didier , Chang Yu Hao , Villaluenga Irune , Chen Xi chelsea , Chintapalli Mahati , Balsara Nitash P. 
Published: February 2020

Conventional Lithium-ion coin cell batteries contain a volatile flammable liquid electrolyte, impregnated in a porous separator. This leads to a serious safety issue with, for example, the possibility of flammable reaction products and internal short-circuits.[1] Commercial microporous polyolefin membranes, made of semi-crystalline polymers as polyethylene (PE) and polypropylene (PP), have been widely used as battery separators. [2] The main functions of the separator are to act as a physical barrier to prevent short-cut between the two electrodes and to allow ionic transport. Ionic transport within the separator depends on several factors such as the separator geometry, porosity and tortuosity, the electrolyte resistance and wettability.[3] Thus, the presence of the separator leads to an effective ionic conductivity lower than the bulk electrolyte conductivity, and an increase of the Li battery internal resistance.
The recent development of non-flammable liquid electrolytes based on functionalized perfluoropolyethers (PFPEs) opened the path of safe Li-ion batteries.[4, 5] PFPE is chemically resistant, non-crystalline, and nonflammable exhibit low glass transition temperature and low toxicity. It was demonstrated that a methyl carbonate-terminated perfluoropolyether (see Figure 1) is suitable for lithium battery operation, but optimization is necessary to improve the performance. So far little is known on the transport properties of this new class of non-flammable liquid electrolytes within the separator. As for any conventional liquid electrolyte, investigating the nature of the separator and its effect on the effective ionic conductivity is required to achieve an optimal battery design.
We investigated the physico-chemical and electrochemical properties of three commercial separators: a PP monolayer, a trilayer PP-PE-PP and a polytetrafluoroethylene (PTFE). The ionic conductivities of low molecular weight PFPEs, with dimethyl carbonate or ethoxylated alcohol end-groups, doped with the lithium salt LiTFSI was measured as a function of the temperature either in the bulk or in the presence of the separators. For comparison, a conventional liquid electrolyte made of 1M LiPF6 in a mixture of ethylene carbonate and dimethyl carbonate was also studied. In addition, the effective ionic conductivity of each electrolyte impregnated in the separator is modeled based on the bulk electrolyte conductivity and a separator morphological form factor.

References

[1] J.-M. Tarascon, M. Armand, Nature, 414 (2001) 359-367.
[2] S. S. Zhang, Journal of Power Sources, 164 (2007) 351-364.
[3] K. M. Abraham, Electrochimica Acta, (1993) 1233-1248.
[4] D.H.C. Wong et al., PNAS, 111 (2014) 3327-3331.
[5] D.H.C. Wong et al., Chemistry of Materials, 27 (2015) 597-603.

Figure 1

Figure 1
Electrochemical Capacitor of MnFe2O4 with Organic Li-Ion Electrolyte
Authors: Chien Jen-Hao , Wu Nae-Lih 
Published: February 2020

Compared with batteries, electrochemical capacitors have the potential for providing higher power density and good cyclability. Pseudocapacitance results from either superficial or multi electron-transfer faradaic reactions with fast charge/discharge properties. An increasing number of metal oxides exhibiting pseudocapacitive behaviors have been discovered in recent years. We have previously discovered a new nanocrystalline oxide material having the formula of MnFe2O4that have so far been the only oxide electrode showing pseudocapacitance in both aqueous and organic Li-ion electrolytes. The discovery of this material has opened up the possibility of setting up a high voltage asymmetric supercapacitors of substantially enhanced energy density over the state-of-the-art EDLC organic supercapacitors.
In this study, MnFe2O4 spinel oxide electrodes was synthesized and characterized for supercapacitor applications using organic Li-ion electrolyte. The change in structure, valence state and local atomic arrangement upon charging/discharging are investigated with in operando X-ray analyses. The operation voltage window is carefully determined in view of leakage current for the upper voltage limit. The lower voltage window is selected to maximize the energy density of the spinel oxide electrode. For the purpose of increasing the energy density of cell up for the demand of electronic devices, asymmetric capacitor is assembled using the spinel oxide as positive electrode and pre-lithiated silicon coated graphite (SGF) as negative electrode. It is shown that the asymmetric capacitor has greatly increased the energy density by asymmetric mass matching between anode and cathode and by extending the overall operation voltage window.

Figure 1
Development of All-Solid-State Structural Supercapacitor Using an Epoxy Based Adhesive Polymer Electrolyte
Authors: Wang Yuchen , Qiao Xiaoyao , Zhang Chen , Karkkainen Ryan L , Zhou Xiangyang 
Published: February 2020

While major efforts are paid to increase the specific energy and power of energy storage devices to meet the demand of transport systems, an alternative approach is to turn the structural components of the systems into energy storage devices. For example, an all electric airplane powered by structural supercapacitors or batteries with a relatively low specific energy would fly the same range as one powered by a conventional storage device with a very high specific energy.
Structural supercapacitors were fabricated according to the schematic shown in Fig. 1. The graphite reinforcement (fiber) is attached with carbon nanofiber and mediators (redox molecules). The matrix is an ionic conducting polymer or adhesive polymer electrolyte. One of the main issues for structural supercapacitor is the low ionic conductivity of adhesive polymer electrolyte as separator and as matrix in reinforcement/electrode. The presence of mediators can increases the ionic conductivity in the electrode area up to 10-2 S/cm. A new method for preparing epoxy adhesive based dual functional polymer electrolyte was adopted. The ionic conductivity of PVDF/LiTFS/epoxy electrolyte can reach to 3x10-3 S/cm. All-solid-state structural supercapacitors with PVDF/LiTFS /epoxy electrolyte and the conventional supercapacitors with a high conductivity liquid electrolyte (0.1 S/cm) are fabricated and tested. They have similar size and weight. The cyclic voltammetry (CV) curves show that the all-solid-state structural supercapcitors with two electrolytes have a similar specific charge capacity of ~4 mAh/g (Fig. 2 and Fig. 3). Also, the in-plane elastic constant is 1-2 GPa and the in-plane ultimate strength of the all-solid-state structural supercapacitor with PVDF/LiTFS /epoxy electrolyte is 20 MPa. The electrochemical properties and the strength of the structural supercapacitor as functions of the composition of the adhesive electrolyte and the composition of the electrode material are evaluated experimentally.

Figure 1
Dimensionally Stable and Fast Charging Graphite-Silicon Planar Composite Anode for Li-Ion Batteries
Authors: Wu Nae-Lih , Yang Nai-Hsuan , Wu Yu-Shiang , Chou Jackey 
Published: February 2020

Advanced Li-ion batteries (LIBs) have been developed to have high capacity density, long cycle life, and high-rate performance for portable electronics, electric vehicles (EVs), and renewable energy storage. Graphite is currently the predominant anode material for commercial LIBs because it has a low cost, low charge/discharge plateau potential, satisfactory specific capacity (372 mAh g-1), and substantially high dimensional stability; its essential role in high-energy LIBs is expected to continue. Si is a potential Li-insertion anode material that has a substantially higher capacity than graphite but is susceptible to large (>300% when fully lithiated) volume expansion. The cyclic dimensional variations during charge/discharge cycles result in pulverization and electrical disconnection from the conductive paths of the Si active materials, leading to rapid capacity reduction during the cycles. In spite of a large amount of literature devoted to solving this issue in the past years, long-lasting Si anode up to now remains as a formidable challenge. On the other hand, composite anodes comprising graphite and limited amount of Si or Si oxide may be attractive transient products for advanced high-energy LIBs before viable Si-dominant anodes are realized. Moreover, improvement in the rate capability of Si-based anodes is needed for meeting the power requirements of various applications.
In this presentation, a planar graphite-silicon composite Li-ion battery anode showing substantially higher capacities than graphite, fast-charging capability, and exceptional cycle stability will be described. The Si oxide-coated graphite flake (SGF) composite anode for Li-ion batteries (LIBs) synthesized by a unique microwave-heating process of graphite flakes (GFs) in a solution made of liquid polysiloxanes as the Si-containing precursor. Microwave-heating of the GFs induces the deposition of a conformal Si-containing conformal layer on the GF surfaces, which is subsequently turned into oxide-graphite-oxide sandwiched planar composite structure. The resulting SGF exhibits a reversible specific capacity of nearly 480 mAh g-1, 97% capacity retention at the current density of 2.5 A g-1 (~5C-rate), and 94% capacity retention after 500 cycles with an average Coulombic efficiency > 99.9%. Coating the composite with a thin layer of conducting polymer further enhance the overall specific capacity greater than 520 mAh g-1. The work suggest a new strategy for both designing and synthesizing high-performance anode materials for LIB applications.

Figure 1