High Energy Density Power Sources Research Articles

Ultrathin-Walled Bi2 S3 Nanoroll/MXene Composite toward High Capacity and Fast Lithium Storage.

It is extremely important to develop a high energy density power source with rapid charge-discharge rate to meet people's growing needs. Hence, the development of advanced electrode materials is the top priority. Herein, a simple yet elaborate vacuum-assisted room-temperature phase transfer method is reported to transform MXene nanosheets from water into organic solution. Subsequently, an in-situ growth strategy is employed to deposit ultrathin-walled bismuth sulfide (Bi2 S3 ) nanorolls on MXene surface to prepare Bi2 S3 /MXene composite as an efficient and high-performance anode material for lithium-ion batteries. Attributed to the unique nanoroll-like structure and the strong synergistic effect, the Bi2 S3 /MXene-10 composite can deliver the high discharge capacities of 849 and 541 mAh g-1 at 0.1 and 5 A g-1 , respectively. The Bi2 S3 /MXene-10 electrode can deliver a high specific capacity of 541 mAh g-1 even after 600 cycles at a large current density of 1 A g-1 , proving the superb cycling stability of the Bi2 S3 /MXene-10 composite. Additionally, the simple vacuum-assisted room-temperature phase transfer strategy can enlighten researchers to expand the potential application of MXene. Furthermore, the formation mechanism of Bi2 S3 nanorolls is also proposed, which may open a new avenue to design and fabricate other nanoroll-like structures.

Exploring the Ion Solvation Environments in Solid-State Polymer Electrolytes through Free-Energy Sampling

Lithium-ion batteries are high energy density power sources that find uses in the automobile industry for electric cars and various portable devices like smartphones, laptops etc. There are strong motivations for developing solid-state electrolytes due to safety concerns associated with the combination of flammable liquid electrolytes and cell shorting due to lithium dendrite growth in current technology. A major issue with solid electrolytes is their low conductivity, which limits the power density (rate of charge/discharge), and possible loss of electrical contact due to anode shrinking. Lithium salts dissolved in poly(ether-acetals) are prime candidates for such electrolytes but the major challenge in improving the performance of these batteries is that the exact mechanism of the motion of the Li+ ions in such systems is not yet well understood. Our goal is to understand the underlying structural differences in the lithium coordination environments in these different systems and how this would affect the movement of the lithium ion from one coordination cage to another. This insight will allow us to suggest new compositions for electrolytes with improved performance for battery applications.Molecular dynamics simulations using newly developed, accurate interaction potentials have helped elucidate possible mechanisms for various transport properties in these systems. The presence of a second coordination shell around the Li ion, observed in some of these systems, seems to distort the first coordination shell, creating a more open cage structure that may help facilitate transport in these polymers. Furthermore, this distorted coordination may also assist in the formation of a lower coordination transition state while the Li ions jump from one cage to another during diffusion. This may be similar to the pathways followed in solid-state transport - either during topotactic intercalation, as ions move from interstitial to interstitial site; or within materials with solid-solid phase transitions related to thermally induced rotations of complex anions. Free energy calculations further elucidate the relative stability of these different Li-ether coordination environments and the possible pathways to move between them (See figure 1 for example). Furthermore, to understand the associated correlations of glass transition temperature in these systems with microscopic chemical details like the polymer backbone chemistry, ion clustering and coordination, we study the trends in these different systems with extensive statistics from long time molecular dynamics simulations at different temperatures and compositions. Figure 1

Identification of the Active Chemical Species in the Sulfone Based Electrolyte for Rechargeable Aluminum Batteries

Introduction The Li-ion battery is the most dominant as practical rechargeable batteries because of its high energy density, high power density, and high cyclability. However, the energy density of the Li-ion battery is not sufficient for the electric vehicle (EV), which can realize the practical driving range as long as classical gasoline and the internal combustion engine system. Multivalent cation batteries are considered as one of the most promising next-generation power sources for mobile electric devices and EVs. The Al electrode has the highest volumetric energy density (8042 mAh cm-3), which is 4-fold higher than the Li metal electrode (2060 mAh cm-3). Therefore, the rechargeable Al battery has the possibility for the high energy density power sources for EVs. Moreover, Al metal is safer than Li metal because of its high melting point and has higher reserves on the earth than Li. Even though there are several advantages of the rechargeable Al battery, such as high energy density, high safety, and low cost, however, it is difficult to realize rechargeable Al battery because of two factors. The first one is the positive electrode material that can store the Al trivalent cation which strongly adsorb to the positive electrode materials reducing the cyclability of the battery. The second one is the electrolyte solution, which can reversibly deposit/strip Al metal. There are several amounts of researches about rechargeable Al battery, however, almost all of those researches used the solution of AlCl3 in the ionic liquid, 1-ethyl-3-methylimidazolium chloride, as an electrolyte solution. The ionic liquid show excellent reversibility for the Al metal deposit/strip reaction and the active species in the electrolyte solution was already identified as Al2Cl7. We have used the solution of AlCl3 in dipropylsulfone (DPSO2) as the electrolyte solution of the rechargeable Al battery. Here, we tried to identify the active chemical species of the solution of AlCl3 in DPSO2 to understand the difference between our electrolyte solution for rechargeable Al battery and conventional ionic liquid-based electrolyte.Experimental All electrochemical experiments were measured with a glass cell. Mo plates (1.3 × 1.3 cm2) were used as working electrode and current collector. An Al plate (10 mm in diameter) and wire were used as the counter and reference electrodes for three-electrode configuration. A glass fiber filter was used as separator.Results & discussion Figure 1(a) shows the 27Al NMR results of the electrolyte containing different ratios of AlCl3 and DPSO2. Four different Al chemical species (AlCl4 -, Al2Cl7 -, AlCl3-DPSO2, and Al(DPSO2)3) were detected, and we analyzed the ratio of each chemical species in the electrolyte containing different ratios of AlCl3 and DPSO2 (Fig. 1b). AlCl4 - is known as inactive for the electrochemical reaction; therefore, we investigated the remaining three species. Figure 1c shows the CV results of each electrolyte solution. We analyzed the CV result from three different points of view; over voltage for Al deposition, over voltage for Al stripping, and the electrochemical window. The electrolyte with the ratio of AlCl3: DPSO2: toluene = 1: 10 (2): 5, which was mainly consisted of Al(DPSO2)3, show small over voltage for deposition/stripping of Al and wide electrochemical window. The electrolyte with the ratio of AlCl3: DPSO2: toluene = 1: 1.1 (1): 5, which mainly consisted of AlCl3-DPSO2, show large over voltage for deposition/stripping of Al and narrow electrochemical window. The electrolyte with the ratio of AlCl3: DPSO2: toluene = 1: 0.9: 5, which mainly consisted of Al2Cl7 -, which is the same as the ionic liquid-based electrolyte solution, show small over-voltage for deposition of Al, large over voltage for the Al stripping, and narrow electrochemical potential window. These results suggested the superiority of the chemical species of Al(DPSO2)3 and our electrolyte solution of AlCl3: DPSO2: toluene = 1: 10: 5, compared with the ionic liquid-based electrolyte solution, which containing Al2Cl7 - as active species. Figure 1

Semihollow Core-Shell Nanoparticles with Porous SiO2 Shells Encapsulating Elemental Sulfur for Lithium-Sulfur Batteries.

Lithium-sulfur batteries have shown great promise as next-generation high energy density power sources, but their commercial applications are hindered by short battery cycle life arising from the dissolution and shuttling of polysulfides. To address this shortcoming, we prepared two types of semihollow core-shell nanoparticles in which (1) elemental sulfur is encapsulated within a porous silica shell (S@SiO2) and (2) elemental sulfur is encapsulated within a porous silica shell where the inner surface of the shell is decorated with small Au nanoparticles (S@Au@SiO2). These core-shell nanoparticles, both ∼300 nm in diameter, were generated from analogous zinc sulfide-based core-shell nanoparticles (ZnS@SiO2 and ZnS@Au@SiO2, respectively) by converting the ZnS cores to elemental sulfur upon treatment with Fe(NO3)3. With a high surface area and strong host-polysulfide interaction, the SiO2 shells effectively trap the polysulfides; moreover, the internal void space of these nanostructures accommodates the volume expansion of the sulfur core upon lithiation. By decorating ∼5-7 nm Au nanoparticles evenly on the inner surface of the porous SiO2 shells (i.e., S@Au@SiO2), electron transport is enhanced, with consequently enhanced sulfur conversion kinetics at high current rates. Studies of battery performance showed that the S@SiO2 cathode can deliver an initial capacity of 1153 mA h g-1 under 0.2 C and retain 816 mA h g-1 after 100 cycles. More importantly, the Au-decorated S@Au@SiO2 cathode can deliver a high capacity of 500 mA h g-1 under 5 C.

Extremely flexible and mechanically durable planar supercapacitors: High energy density and low-cost power source for E-skin electronics

The development of multifunctional devices on highly flexible and biocompatible substrates has received great attention in the field of wearable and healthcare technologies. To realize such a unique technology typically on a single platform, it is very crucial to adopt highly-flexible and embeddable energy storage devices with adequate efficiencies as power sources. In this direction, we introduce a versatile and scalable approach to fabricate planar and symmetric micro-supercapacitors, which can be mounted on any complicated surface. The micro-supercapacitors developed on highly flexible and ultrathin substrates by the angular spray of graphene-ink showed excellent performance with a maximum areal capacitance of ~8.38 mF/cm 2 and operating flexibility for a bending radius of 1.8 mm. The devices also displayed outstanding mechanical stability for 10,000 bending cycles with a high specific capacitance (~22 F/g) and power density (~1.13 kW/kg) typically at a scan rate of 100 mV/s. Further, the demonstrations on skin-mountable and wrappable characteristics of mSCs emphasized their adaptability as embeddable power sources for various epidermal and wearable devices. • Micro-supercapacitors fabricated using cost-effective spray method. • Device exhibits high energy density and excellent sustainability. • Extremely flexible micro-supercapacitor showed high mechanical durability and stability. • Our device developed on epidermal substrate showed integrability with human skin. • This micro-supercapacitors can greatly support for e-skin device as a power source.

Latest Advances in Flexible Symmetric Supercapacitors: From Material Engineering to Wearable Applications.

Flexible symmetric supercapacitors (FSSs) have received enormous attention in energy storage and conversion areas by virtue of their superior flexibility, high power density, and good cycling stability. FSS devices are typically composed of one solid electrolyte layer laminated by two electrode layers, which can realize energy storage, response to electrical stimulus, and even detect external stress or strain change based on various working mechanisms. The as-mentioned multifunctions of FSS devices are expected to play many critical roles in practical applications of wearable power supply and in artificial intelligence. This realization strongly associates with the rapid development of materials science and engineering, especially nanomaterials and smart structure design, and the multifunctions are results of rational designs of critical materials, optimization of device dimensions, and selectivity of active ion species.This Account showcases the latest advances in FSS devices concerning several critical aspects from fundamental material engineering to practical wearable applications. We first describe advanced functional materials utilized in flexible solid electrolytes and electrodes of FSS systems. Several highly ion-conductive hydrogel and ionogel electrolytes with excellent mechanical properties have been designed for the fast and stable ionic migration kinetics in devices. Some high-performance electrode materials with high charge storage capacity, efficient electromechanical conversion, and sensitive ionic response are presented for realizing multifunctions of FSS devices. After that, analysis of interfaces in devices on their performances is provided, and the construction strategies of robust interface are displayed as well. We then summarize flexible and wearable applications of FSS devices, including high-energy density power sources, flexible and electroactive actuators, and wearable and sensitive sensors. These multifunctions are realized by optimization of device dimensions, control of ion migration kinetics, and development of advanced materials, and the corresponding working mechanisms of the devices are presented in detail. The long-term development and future research directions of FSS devices are also envisioned.At present, the rise of nanomaterials and nanoscience is providing great opportunity to further improve performances of FSS devices and finally realize their wearable applications. These wearable FSS devices with smart multifunctions will significantly promote the development of next-generation flexible electronics for artificial intelligence. It is expected that this Account can promote tremendous efforts toward fundamental clarification of FSS devices, and the design mentality will accelerate the development of other flexible and wearable electrochemical energy devices.

Single Lithium-Ion Conducting Covalent Organic Frameworks

The demands for high-energy density power sources are growing from the beginning on the advent of portable devices. Since the beginning, liquid electrolyte was adopted owing to their high ionic conductivity, excellent wetting to electrode components. However, liquid electrolyte contains risks since it exhibits highly flammable and sometimes explosive characteristics. To resolve safety issue for demanded high-energy density batteries, all-solid-state battery, which utilizes solid electrolyte instead of liquid electrolyte, hold particular promise as solid-state electrolytes feature low flammability and highly compaction nature for high-energy density battery performance.So far, all-solid-state batteries have generally been powered using inorganic sulfides/oxides or polymer-based electrolyte. In addition to these conventional approaches, solid-state Li-ion conductors based on porous crystalline materials (i. e. covalent organic frameworks (COFs) and metal–organic frameworks (MOFs)) have garnered attention due to their directional ion conduction pathways through the ordered pores and versatile structural design. Porous crystalline materials, however, additionally incorporate lithium salts and/or solvents inside the pores of frameworks so that these COFs or MOFs act as conducting medium, not solid-state ion conductors in specific. Herein, we demonstrate a lithium sulfonated covalent organic framework (denoted as TpPa-SO3Li) as a solvent-free, single lithium-ion conductors. Benefiting from the well-designed directional ion channels, high number density of lithium-ions, and covalently tethered anion groups, TpPa-SO3Li exhibits an ionic conductivity of 2.7 × 10–5 S cm–1 with a lithium-ion transference number of 0.9 at room temperature, and an activation energy of 0.18 eV. Moreover, unusual ion transport phenomena of TpPa-SO3Li allow reversible and stable lithium plating/stripping on lithium metal electrodes. These features show promising results to be adopted in next-generation all-solid-state batteries and also demonstrate potential usage for lithium metal batteries.

On the Relation between Ionic Transport Properties and Viscoelastic Response of Solid Polymer Electrolytes

The need for high energy density and micro-scaled power sources is pushing researchers and industries towards the development of three-dimensional architecture micro-batteries and structural batteries. In this perspective, solid polymer electrolytes (SPEs) represents an appealing alternative to conventional (liquid) electrolyte. Due to their intrinsic multifunctionality, SPEs can serve as the structural matrix of fiber-reinforced composites and as the electrolyte of a battery. In addition, the improved safety features, excellent flexibility and processability, allow to cast SPEs into complex three-dimensional geometries without leakage. Experimental studies indicate that mechanical and electrochemical responses of SPEs are related. In particular, the segmental motion of the polymer molecules is crucial for both the viscoelastic properties and the ionic conductivity of the material. A limited polymer segmental motion generally results in a stiffer mechanical response and a reduced ionic conductivity, while the opposite applies when the polymer segmental motion is enhanced. This results in a trade-off between mechanical and electrical performance from a material design point of view [1] and a deformation-dependent ionic transport mechanism in the polymer during service [2]. In this work we present a coupled electrochemo-mechanical model for SPEs. The polymer is modeled as a solid through which the transport of multiple charged species takes place and is described in terms of molar concentration of ions, electric potential and displacement field. Since the molar concentration of ions in the SPE is notably non-uniform during battery service [3,4], the model explicitly accounts for concentration-dependent diffusion coefficients and viscoelastic properties. Results of a finite element method formulation are presented, and the impact of the viscoelastic mechanical behavior on the overall battery response is discussed.

Interface effects on self-forming rechargeable Li/I2-based solid state batteries

Abstract

Microstructures and Reaction Properties of Ti/Ni, Ti/Al and Ni/Al Multilayer Films

Reactive multilayer thin films are well-defined heterogeneous nanostructured energetic materials which can release chemical energy through a self-sustainable reaction. They have attracted intense interests due to potential applications in diverse fields such as joining, igniters, and high energy density power sources. In this paper, Ti/Ni, Ti/Al and Ni/Al multilayer films were prepared by magnetron sputtering. The reaction kinetics, microstructure and phase variation of these free-standing films are comparatively investigated. During slow heat reaction, the reaction products of reactive multilayer Ti/Ni nanofoils change from B2-TiNi austenite phase into TiNi3, illustrating an evolution of the phase transformation during reaction. These intermediate phases are also identified by slow heating and quenching. The fast speed imaging exhibits that the front speed is 0.47m/s, 0.8m/s and 3m/s respectively for as-deposited Ti/Ni, Ti/Al, and Ni/Al films. Differential thermal analysis yields that the corresponding releasing heat is 551.44 J/g, 434.18 J/g, and 562.5 J/g for these three composites. The theoretical minimum multilayer thickness for melting a tin solder layer has been calculated on the base of these characterizations, which proved the application potential of joining using the as-deposited film.

Uniformly Thin and Large Surface Modification of Lithium Anode for Improving Cycling Performance of Lithium Metal Batteries

Rechargeable lithium batteries using lithium metal as a negative electrode are attractive candidates for high energy density power sources, because the lithium metal offers a high specific capacity and possesses a low electrochemical potential.1,2 However, the development of rechargeable lithium metal batteries has been hindered for several decades by the high reactivity of lithium metal toward liquid electrolytes and the occurrence of dendrite growth during charge and discharge cycles. The formation and growth of lithium dendrites result in safety and cycle life problems. Additionally, continuous generation of the new solid electrolyte interphase (SEI) layer on lithium metal causes uncontrolled reductive decomposition of the organic electrolyte and gradual loss in capacity and cycling efficiency with repeated cycling. Therefore, protection of lithium metal and the formation of a stable SEI layer on the lithium electrode are very important for developing lithium metal batteries with good capacity retention and enhanced safety. In this work, a prospective approach for protecting a lithium metal is presented by spray coating with a conductive poly(3,4-ethylenedioxythiohene)-co-poly(ethylene glycol) (PEDOT-co-PEG) and inorganic particles (AlF3), which allows for lithium ion diffusion and restricts the access of the reactive solvents to the lithium surface. The protective composite layer played a positive role in reducing the reductive decomposition of the electrolyte and suppressing the dendrite growth of lithium during cycling. As a result, the surface modification of lithium electrode with PEDOT-co-PEG and AlF3 significantly improved the cycling stability of the lithium metal batteries.

Metal Free Hybrid Capacitor Using Intercalation of 1-Butyl-3-Methylimidazolium Cation to Acetylene Black, Ketjen Black and Graphite

1. Introduction Lithium ion capacitor (LIC) is one of the most promising hybrid capacitors (HCs) with the negative electrode for lithium ion battery (LIB) and activated carbon (AC) positive electrode. Recent progress of LIC realized its high energy density over 80 Wh kg-1 and LIC is already commercially available for several applications like backup power supply, load leveling for natural power sources, energy regeneration etc. 1 Moreover, LIC has better cyclic performance and power density than LIB so high performance LIC is considered as next generation power sources for mobile electric devices and electric vehicles. However, the charging mechanism of the carbon negative electrode is insertion of Li+ ion and its potential is 0.01 V vs. Li/Li+ which is quite similar to the Li metal precipitating potential (0V vs. Li/Li+). It is well known that the precipitation of Li metal causes internal short circuiting and deadly explosion. To avoid such risk, Li free HC is one of the most promising idea. In this work, we realized the Li+ free HC with ionic liquid for safe and high energy density power sources. Recent study suggested the large cation like 1-Butyl-3-methylimidazolium (BMI+) can be inserted/deserted into carbon electrode. So we used the ionic liquid (1-Butyl-3-methylimidazolium tetrafluoroborate (BMIBF4)) as electrolyte and insertion/desertion of BMI+ into carbon electrode was used as negative electrode reaction. AC was used as positive electrode. Three different carbon materials (acetylene black (AB), ketjen black (KB) and graphite) were investigated as negative electrode materials. 2. Experimental Mo sheet was used as current collector. AB, KB and graphite powder was dispersed into N-methyl-2-pyrrolidon with polyvinylidene difluoride which is used as binder. The slurry was sonicated for 15 min and casted onto Mo current collector. AC was mixed with polytetrafluoroethylene in mortar and cold pressed with 30 MPa for 5 min, which was used as positive electrode. BMIBF4 was dried under vacuum for 24 h at 85 °C. The homemade glass cell was used for HC. Ag wire was used as pseudo reference electrode. 3. Results and discussion Fig. 1 shows the charge/discharge curves of HCs with the KB, AB and graphite negative electrodes. HCs with AB and graphite negative electrode was charged to 3.7 V but the cell voltage was limited below 3.2 V in the case of the HC with KB negative electrode because decomposition of the electrolyte was started below 3.5 V. Excepting the charge voltage, three HCs showed almost the same features. Fig. 2 shows the changes in the potential of KB, AB and graphite negative electrode and AC positive electrode. Each negative electrode showed plateaus during charge/discharge process around -2 V vs Ag and -1 V vs Ag, respectively. On the other hand, AC positive electrode showed triangular charge/discharge curves which is typical for the electrochemical double layer capacitor. These phenomena suggests the charge/discharge process of negative electrode in HCs is insertion/desertion of BMI+ and the positive electrode worked as electrochemical double layer capacitor. Fig. 3 shows the change in discharge capacitance with cycle number for the HCs. The discharge capacitance of HC with AB and graphite negative electrode rapidly decreased. However, the HC with KB electrode showed long life cycle durability over 1500 cycles. This might be due to the property of KB, which has shell like carbon layers and it prevented collapse of the negative electrode materials. References 1) K. Naoi et. al. Energy Environ. Sci., 5, 9363 (2012) Figure 1

Cost Effective Fabrication and Characterization of in-Membrane Micro-Fuel Cell

Micro fuel cells (μFCs) have been attracting much attention as a leading candidate for prospective portable power sources and battery replacements [1-3]. Their ability to create an efficient and clean source of energy combined with the ease of portability makes μFCs available to meet the needs of various portable electronic applications in the future [3, 4]. To this purpose, making more efficient devices with cost effective processes and materials is crucial. Many efforts on fuel cell miniaturization are focused on silicon-based techniques as silicon is the most common substrate in MEMS technology [5, 6]. However, combining silicon devices with polymeric fuel cells at mm or sub-mm scale presents many challenges, none of which have been solved in a completely satisfactory manner [7]. Distinct from previous attempts at fabricating in-plane μFCs by other studies, in this work we present a novel IMμFC (In-Membrane Micro Fuel Cell) design where the micro-flow channels for fuel and oxidant input and the MEA are fabricated using a Nafion membrane as the starting substrate. The fabrication procedure of IMμFCs has been illustrated in Fig. 1. In preparation for the microfabrication process, 100 μm thick SU-8 photoresist was spin coated, baked and developed to produce a micro stamp. The developed SU-8 on Si wafer was hard baked at 200°C for an hour to enhance the rigidity of the stamps. Fabricated stamps were cut and pressed onto Nafion 1110 membrane at 140°C and 300 psi by a NX2000- Nanoimprinter (Nanonex Corp., NJ, USA). Catalyst loading of conventional Pt/C dispersion on a selected area of microchannels was made by screen printing. Silver wire connections were secured in the designed electrical channels by Kapton tape and carbon black paste. In the sealing step, a laser patterned acrylic sheet was pressed onto the Nafion substrate by the nanoimprinter machine. The fabrication process was completed by mounting the gas inlet tubes on the acrylic sheet side of IMμFCs. The micro device performance was characterized by I-V polarization curves and impedance spectroscopy under dry and humidified conditions. Comparing to other studies on μFCs, the presented fabrication approach consists of cost effective processes with a great potential for scale-up production. This new architecture may lead to the deployment of an ultra-low weight, high energy density power source for flat-board-oriented electronic structures. Refrences: 1. Sundarrajan, S., Allakhverdiev, S. I., & Ramakrishna, S. (2012). Progress and perspectives in micro direct methanol fuel cell. International Journal of Hydrogen Energy, 37(10), 8765-8786. 2. Taylor, A. D., Lucas, B. D., Guo, L. J., & Thompson, L. T. (2007). Nanoimprinted electrodes for micro-fuel cell applications. Journal of Power Sources, 171(1), 218-223. 3. Kamarudin, S. K., Daud, W. R. W., Ho, S. L., & Hasran, U. A. (2007). Overview on the challenges and developments of micro-direct methanol fuel cells (DMFC).Journal of Power Sources, 163(2), 743-754. 4. Cao, J., Xu, J., Chen, Z., Wang, W., Huang, Q., & Zou, Z. (2013). A silicon‐based micro direct methanol fuel cell stack with a serial flow path design.International Journal of Energy Research, 37(4), 370-376. 5. Shah, K., Shin, W. C., & Besser, R. S. (2004). A PDMS micro proton exchange membrane fuel cell by conventional and non-conventional microfabrication techniques. Sensors and Actuators B: Chemical, 97(2), 157-167. 6. Lu, G. Q., Wang, C. Y., Yen, T. J., & Zhang, X. (2004). Development and characterization of a silicon-based micro direct methanol fuel cell.Electrochimica Acta, 49(5), 821-828. 7. Omosebi, A., & Besser, R. S. (2013). Fabrication and performance evaluation of an in membrane micro-fuel cell. Journal of Power Sources, 242, 672-676. Figure1. (a) Top-view illustration of μFC design imprinted on Nafion and (b) schematic fabrication steps of the μFC production Figure 1

Review—Development of Advanced Rechargeable Batteries: A Continuous Challenge in the Choice of Suitable Electrolyte Solutions

Non-aqueous, rechargeable battery development is one of the most important challenges of modern electrochemistry. Li ion batteries are a commercial reality for portable electronics with intensive efforts underway to apply this technology to electro-mobility. Extensive investigations of high energy density Li-sulfur and Li-oxygen systems have also been carried-out. Efforts to promote high energy density power sources for electric vehicles have been accompanied by intensive work on the development of rechargeable sodium and magnesium batteries for load-leveling applications. The electrolyte solution is a key consideration in all batteries determining cell stability, cycle life, and safety. This review discusses the importance of solution selection for advanced, high-voltage, Li ion batteries, sodium ion batteries, as well as Li-sulfur, Li-oxygen and magnesium batteries. Li ion battery standard solutions are discussed and their further optimization is outlined. Limitations of Li metal electrodes are explained. Unique problems in the use of conventional non-aqueous solutions for Li-oxygen batteries, related to intrinsic stability, are delineated. Finally, electrolyte solutions for Mg batteries are briefly reviewed, concluding that only the relatively inert ethereal solutions are suitable for future consideration. Several systems exhibit wide electrochemical windows and reversible behavior with Mg anodes, however compatibility with high-voltage/high-capacity cathodes remains a major challenge.

Enhancing Role of Nickel in the Nickel–Palladium Bilayer for Electrocatalytic Oxidation of Ethanol in Alkaline Media

Direct ethanol fuel cells (DEFCs) have been widely studied because of their potential as a high-energy density and low-toxicity power source of the future. Suitable catalysts for the anode reaction, however, are necessary to fully utilize the advantages of DEFCs. In this paper, we fabricated nickel (Ni)–palladium (Pd) bimetallic catalysts with a bilayer structure, using sputtering deposition on a titanium (Ti) foil substrate, and investigated the activity and stability of the catalysts toward ethanol electro-oxidation in alkaline media. Our results suggest that while Pd is the active component and Ni has negligible activity toward ethanol oxidation, Ni-modified Pd (NiPd/Ti) provides the best activity in comparison to PdNi/Ti and the monometallic catalysts. In fact, optimizing the Ni amount could lead to a highly active and stable bimetallic electrocatalyst because of Ni’s ability to increase the active surface area of the Pd layer, provide hydroxyl species to replenish the active sites, and act as a prote...

Discharge behaviour and interfacial properties of a magnesium battery incorporating trihexyl(tetradecyl)phosphonium based ionic liquid electrolytes

Magnesium-air batteries are a promising high-energy density power source that utilises an active magnesium electrode and oxygen. Herein, the magnesium surface formed during 0.2mA/cm2 galvanostatic discharge in trihexy(tetradecyl)phosphonium chloride ionic liquid electrolyte was characterised using FTIR, XPS and mass spectroscopy and the complex nature of the interfacial film formed is described. This film has a conductive gel-like structure and consists of hydrated organophosphonium–magnesium(hydroxyl)chlorides. A laboratory synthesised form of the gel showed comparable discharge behaviour and was able to support a discharge current of 0.05mA/cm2. The ionic liquid is shown to support oxygen reduction currents of greater than 0.8mA/cm2, suggesting that this electrolyte is a suitable candidate for magnesium-air battery applications.

The potential for ionic liquid electrolytes to stabilise the magnesium interface for magnesium/air batteries

Magnesium/air batteries are a possible high-energy density power source that, to date, have not received strong commercial interest due to issues with the corrosion of the magnesium and evaporation of the electrolyte. In this work we report on the use of ionic liquid based electrolytes to stabilise the metal/electrolyte interface and their impact on the electrochemical performance. Galvanostatic measurements indicate that the water content of the ionic liquid electrolyte plays an important role in the cell discharge characteristics. Surface characterisation using EIS, ATR-FTIR and powder diffraction examined the unique properties of the surface film formed on the magnesium anode.

Millimeter-Scale Fuel Cell With Onboard Fuel and Passive Control System

We report microfabrication of a millimeter-scale fuel cell with onboard fuel and a passive control mechanism. This unique power source has a total volume of 9 muL (3times3times1 mm3), which makes it the smallest fully integrated fuel cell reported in the literature. The first generation of this device delivered an energy density of 254 Wmiddoth/L. The device uses a reaction between a metal hydride, LiAlH4, and water vapor to generate hydrogen in a reactor. The generated hydrogen exits the reactor through a nanoporous silicon wall to reach a hybrid silicon/Nafion membrane electrode assembly. A passive micro- fluidic control system regulates hydrogen generation through controlled delivery of water vapor to the metal hydride based on the reactor pressure. The development of this unique power source greatly benefits the portable electronics industry and enables future technologies that require significantly high energy density power sources such as cognitive arthropods (thinking insect- sized robots). This paper provides details of the device micro- fabrication processes, component integration, and performance analysis. [2008-0168].

Liquid fuel microcombustor using microfabricated multiplexed electrospray sources

The use of hydrocarbons is very appealing for the realization of high energy density power sources, so long as the fuel can be stored in the liquid phase. As a result, except for the most volatile hydrocarbons, a miniaturized combustor must rely on a good design of the fuel atomizer, which should yield small, rapidly evaporating droplets to generate the fuel vapor promptly, mix it with the oxidizer and subsequently burn it with the attending heat release. To achieve this goal, we relied on the use of multiplexed electrosprays and a catalytic reactor for fuel conversion consisting of a pack of catalyst impregnated meshes (Microliths ®). Fuel dispersion was achieved by microfabricating the fuel distributor in Si using deep reactive ion etching. Tests were performed using JP-8 as the liquid fuel. Preliminary experiments in a 0.8 cm 3 optically accessible combustor, enabling the measurements of droplet size and velocity, revealed that the spreading of the electrospray by Coulombic repulsion is the phenomenon controlling the volume of the mixing/evaporation chamber. Droplet evaporation occurs in the thin (Peclet number dependent) thermal layer preceding the catalytic section of the combustor. Subsequent system optimization in a fully ceramic combustor yielded a volumetric heat release rate as large as 270 MW/m 3, a value that is of the same order as that of conventional gas turbines. The small overall combustor volume, at only 0.22 cm 3, suggests that the large volumetric energy density was achieved despite the device large surface-to-volume ratio and attending heat losses. The fuel was fully oxidized, with CO/CO 2 ratios well under 1% over a range of equivalence ratios. Inspection of the combustor inner walls after operating continuously for 10 h, revealed no traces of deposits. The design has the potential of being scaled either up or down, depending on power needs.

Microfabrication and characterization of a silicon-based millimeter scale, PEM fuel cell operating with hydrogen, methanol, or formic acid

A silicon-based microfabricated fuel cell has been developed to provide a high energy and power density power source on the millimeter size scale. An integrated silicon microscale membrane electrode assembly (Si-μMEA) consisting of a Nafion 112™ membrane bonded between two electrodes on microstructured silicon substrates forms the core element of this polymer electrolyte membrane fuel cell. The use of silicon meshes that serve the purpose of catalyst support, current collector, and structural element provides a promising alternative to the traditional gas diffusion layer-based MEAs for the development of robust, high-performance microfuel cells. The cell performance was characterized using hydrogen, methanol, and concentrated formic acid–water fuels at the anode, and oxygen at the cathode. The catalyst used for each fuel was Pt black. Preliminary results show that the microfabricated fuel cell running on formic acid may be a promising alternative for fuel cell applications running at ambient temperature and pressure, provided additional work on catalyst improvement, assembly, and packaging is performed so that the power density achieves that of traditional forced fed PEM fuel cell design.