Water Stable Ionic Liquid Research Articles

Ionic liquid–electrode interface: Classification of ions, saturation of layers, and structure-determined potentials

Progress in electrochemical applications of ionic liquids builds on an understanding of electrical double layer. This computational study focuses on structure-determined quantities – maximum packing density, potentials, and capacitances – evaluated using a one-electrode electrical double layer model. Interfaces of the 40 studied ions are grouped into four distinct classes according to their characteristic packing at the model surface. The simulations suggest that the exact screening by a monolayer of counter-ions (preceding the crowding of ions) is unlikely for ions in known air- and water-stable ionic liquids within their electrochemical stability window. This work discusses how the assessed structure-determined quantities can guide the experimental tuning of (electro/mechano)chemical properties and characterize the structure of ionic liquid–electrode interfaces.

Enhanced Water Purification Performance of Ionic Liquid Impregnated Metal-Organic Framework: Dye Removal by [BMIM][PF6]/MIL-53(Al) Composite.

We incorporated a water-stable ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6], into a water-stable metal–organic framework (MOF), MIL-53(Al), to generate the [BMIM][PF6]/MIL-53(Al) composite. This composite was examined for water purification by studying its capacity for methylene blue (MB) and methyl orange (MO) removal from aqueous solutions having either single dye or a mixture of both. Data illustrated that the removal efficiency and the maximum adsorption capacity of MIL-53(Al) were increased several times upon [BMIM][PF6] incorporation. For instance, within 1 min, 10 mg of pristine MIL-53(Al) adsorbed 23.3% MB from 10 mg/L of MB solution, while [BMIM][PF6]/MIL-53(Al) composite was adsorbed 82.3% MB in an identical solution. In the case of MO, 10 mg of pristine MIL-53(Al) achieved 27.8 and 53.6% MO removal from 10 mg/L of MO solution, while [BMIM][PF6]/MIL-53(Al) composite removed 61.4 and 99.2% within 5 min and 3 h, respectively. Moreover, upon [BMIM][PF6] incorporation, the maximum MB and MO adsorption capacities of the pristine MOF were increased from 84.5 to 44 mg/g to 204.9 to 60 mg/g, respectively. The adsorption of dyes in pristine MIL-53(Al) and [BMIM][PF6]/MIL-53(Al) followed a pseudo-second-order kinetic model and a Langmuir isotherm model. In a mixture of both dyes, the IL/MOF composite showed a doubled MB selectivity after the IL incorporation. The composite was successfully regenerated at least two times after its use in water purification to remove MB, MO, and their mixtures. Infrared (IR) spectra indicated that the MB/MO adsorption occurs on [BMIM][PF6]/MIL-53(Al) by electrostatic interactions, hydrogen bonding, and π-π interactions. These results showed that [BMIM][PF6]/MIL-53(Al) composite is a highly promising material for efficient water purification.

Template-assisted electrodeposition of freestanding Sn, In and Sn-In nanowire arrays in an ionic liquid

In this paper we report on the template assisted electrochemical synthesis of Sn, In, and Sn-In nanowire arrays in the air and water stable ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate ([EMIm]TfO). Polycarbonate membrane was employed as a template for the synthesis of nanowires. The electrochemical synthesis of nanowire arrays occurred in two steps; the electrodeposition inside the pores of the membrane and the chemical dissolution of the membrane. The results show that high quality, freestanding nanowire arrays of Sn, In and Sn-In, can be made in the employed ionic liquid electrolytes via a template-assisted electrodeposition regime. The reported synthesis process is quite facile and assures the formation of mechanically stable, freestanding nanowire arrays.

High-Voltage and Noncorrosive Ionic Liquid Electrolyte Used in Rechargeable Aluminum Battery.

As a promising post-lithium battery, rechargeable aluminum battery has the potential to achieve a three-electron reaction with fully use of metal aluminum. Alternative electrolytes are strongly needed for further development of rechargeable aluminum batteries, because typical AlCl3-contained imidazole-based ionic liquids are moisture sensitive, corrosive, and with low oxidation voltage. In this letter, a kind of noncorrosive and water-stable ionic liquid obtained by mixing 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM]OTF) with the corresponding aluminum salt (Al(OTF)3) is studied. This ionic liquid electrolyte has a high oxidation voltage (3.25 V vs Al3+/Al) and high ionic conductivity, and a good electrochemical performance is also achieved. A new strategy, which first used corrosive AlCl3-based electrolyte to construct a suitable passageway on the Al anode for Al3+, and then use noncorrosive Al(OTF)3-based electrolyte to get stable Al/electrolyte interface, is put forward.

Aluminium electrodeposition from a novel hydrophobic ionic liquid tetramethyl guanidinium-perfluoro-3-oxa-4,5 dichloro-pentan-sulphonate

Aluminium electrodeposition is demonstrated from a novel ionic liquid (IL), tetramethyl guanidinium-perfluoro-3-oxa-4,5 dichloro-pentan-sulphonate [C5H14N3+][CF2ClCFClOCF2CF2SO3−]. This air and water stable ionic liquid owns a strong hydrophobic nature that was conceived to allow aluminium deposition in ambient conditions. This work presents the studies performed on the electrodeposition processes and reports images regarding the surface morphology of aluminium electrodeposited on vitreous carbon from solutions having a wide range of AlCl3:IL molar ratios. The electrochemical window of this liquid is temperature dependent and sufficiently wide to allow aluminium deposition. The conductivity of solutions is highly influenced by the AlCl3 content. Solutions that allow aluminium electrodeposition are characterized by an AlCl3:IL molar ratio that ranges between 0.9 and 1.3. This compositional range probably represents the best compromise between Al(III) concentration and conductivity values that allow sufficient mobility of the electroactive species. Nucleation and three dimensional growth was evidenced from both voltammetric and potentiostatic experiments. Cyclic voltammograms show a significant loop and j-t transients the characteristic maximum, conventionally attributed to nucleation. Electrochemical evidences are confirmed by SEM images of the deposits, in which rounded or faceted crystals were observed depending on the electrodeposition conditions.

Influence of Fluid Dynamics on the Electrochemical Deposition of Tantalum

In the past decade there were many attempts for developing a method for the electrodeposition of refractory metals (Ti, Ta, Nb and W) at rather moderate temperatures employing ionic liquids [1]. Such tantalum thin coatings would exhibit advanced properties like excellent chemical and corrosion resistance and therefore have a large application potential e.g. in chemical process industry. This is why this metal has attracted the attention of many researchers aiming to develop new and cost-effective methods for its synthesis [2-5]. A special interest lies in developing an electrodeposition method with a quite simple procedure and high deposition rate, but with the ability to control precisely the layer thickness and quality. The deposition from ionic liquids proved more challenging than originally anticipated, e.g. when using halide precursors often sub-halides are formed instead of the metal [1-4]. Nevertheless, it has been shown recently that thin Ta metal layers can be deposited from ionic liquids [5, 6]. However, thicker coatings in the micrometer range and the accurate control of the crystallographic parameters remain challenging. The focus of this study is to investigate the influence of fluid dynamics (e.g. rotation, ultrasound) on the deposition of pure Ta metal. Furthermore, the in-situ microgravimetry is applied for investigating the influence of different electrochemical parameters on the Ta deposition rate. The deposited layers are characterized by Scanning Electron Microscopy and ex-situ scanning probe microscopy techniques. [1] A. Ispas, A. Bund, F. Endres, Application of the Electrochemical Quartz Crystal Microbalance for the Investigation of Metal Depositions from Ionic Liquids, ECS Transactions, 16 (2009) 411-420. [2] S. Zein El Abedin, H.K. Farag, E.M. Moustafa, U. Welz-Biermann, F. Endres, Electroreduction of tantalum fluoride in a room temperature ionic liquid at variable temperatures, Physical Chemistry Chemical Physics, 7 (2005) 2333-2339. [3] N. Borisenko, A. Ispas, E. Zschippang, Q. Liu, S. Zein El Abedin, A. Bund, F. Endres, In situ STM and EQCM studies of tantalum electrodeposition from TaF5 in the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, Electrochimica Acta, 54 (2009) 1519-1528 [4] A. Ispas, B. Adolphi, A. Bund, F. Endres, On the electrodeposition of tantalum from three different ionic liquids with the bis(trifluoromethyl sulfonyl) amide anion, Physical Chemistry Chemical Physics, 12 (2010) 1793-1803. [5] A. Ispas, A. Bund, Pulse plating of tantalum from 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)amide ionic liquids, Transactions of the Institute of Metal Finishing, 90 (2012) 298-304 [6] T. Carstens, A. Ispas, N. Borisenko, R. Atkin, A. Bund, F. Endres, In situ scanning tunneling microscopy (STM), atomic force microscopy (AFM) and quartz crystal microbalance (EQCM) studies of the electrochemical deposition of tantalum in two different ionic liquids with the 1-butyl-1-methylpyrrolidinium cation, Electrochimica Acta 197(2016)374–387

Electrodeposition in Ionic Liquids.

Due to their attractive physico-chemical properties, ionic liquids (ILs) are increasingly used as deposition electrolytes. This review summarizes recent advances in electrodeposition in ILs and focuses on its similarities and differences with that in aqueous solutions. The electrodeposition in ILs is divided into direct and template-assisted deposition. We detail the direct deposition of metals, alloys and semiconductors in five types of ILs, including halometallate ILs, air- and water-stable ILs, deep eutectic solvents (DESs), ILs with metal-containing cations, and protic ILs. Template-assisted deposition of nanostructures and macroporous structures in ILs is also presented. The effects of modulating factors such as deposition conditions (current density, current density mode, deposition time, temperature) and electrolyte components (cation, anion, metal salts, additives, water content) on the morphology, compositions, microstructures and properties of the prepared materials are highlighted.

Palladium electrodeposition in 1-butyl-1-methylpyrrolidinium dicyanamide ionic liquid

In aqueous solutions, Pd electrodeposition is complicated by hydrogen embrittlement. As an alternative, ionic liquids have been suggested. However, the physical and chemical properties of each ionic liquid are unique. In this work, Pd electrodeposition was investigated on Ni at room temperature in one of the promising air- and water-stable ionic liquids, 1-butyl-1-methylpyrrolidinium dicyanamide ([Bmpyrr][DCA]). The goal of this study was to elucidate kinetics of the Pd electro-reduction in [Bmpyrr][DCA] on Ni using current-time transient method (CTT) and its effect on the structure of the Pd deposits using chronoamperometry. The kinetics of the electrodeposition process was found to be limited by mass transfer. The nucleation and growth mechanism on Ni, extracted from the CTTs and analyzed using Scharifker and Hills model, showed potential dependence; at lower overpotential, the nucleation and growth was progressive that transitioned to instantaneous as the overpotential increased. Pd films obtained after potential holds for 30min were crack-free and had a surface morphology that was less granular when overpotential increased showing clear potential-dependent nucleation and growth. Evidence of [Bmpyrr][DCA] on the surface of the Pd films was observed using X-ray photoelectron spectroscopy. The Pd films had well-defined crystallinity only after heat treatment at 600°C.

Potential-Dependent Adlayer Structure and Dynamics at the Ionic Liquid/Au(111) Interface: A Molecular-Scale In Situ Video-STM Study.

Room-temperature ionic liquids are of great current interest for electrochemical applications in material and energy science. Essential for understanding the electrochemical reactivity of these systems are detailed data on the structure and dynamics of the interfaces between these compounds and metal electrodes, which distinctly differ from those in traditional electrolytes. In situ studies are presented of Au(111) electrodes in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][TFSA]) by high-speed scanning tunneling microscopy (video-STM). [BMP][TFSA] is one of the best-understood air and water stable ionic liquids. The measurements provide direct insights into the potential-dependent molecular arrangement and surface dynamics of adsorbed [BMP](+) cations in the innermost layer on the negatively charged Au electrode surface. In particular, two distinct subsequent transitions in the adlayer structure and lateral mobility are observed with decreasing potential.

Electroplating Dysprosium from IL-Based Solutions: A Promising Electrochemical Step to Produce Stronger High Performance Nd(Dy)-Fe-B Sintered Magnets

An electrodeposition replacement to the commonly used physical vapor deposition methods used in enhancing the coercivity of Nd-Fe-B sintered magnets has been proposed. Dysprosium was galvanostatically electroplated on Nd-Fe-B sintered magnets that were previously electrochemically coated with copper. Electroplated dysprosium films were characterized by X-ray photoelectron spectroscopy, depth profiling, scanning electron micrographs, and energy dispersive X-ray spectroscopy. XPS analysis after argon ion sputtering indicates that minor impurities are only superficial as their atomic fractions in the sample nearly disappear with increasing etching time. The electrochemistry of synthesized dysprosium bis(trifluromethylsulfonyl)imide dissolved in the air- and water-stable ionic liquid 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsuflonyl)imide was studied by cyclic voltammetry. Electroplating of metallic dysprosium was followed by a heat-treatment above the melting temperature of the Nd-rich phases of the sintered magnet base body whose magnetic characterization was performed in a hysteresis loop tracer for hard magnetic materials.

Surface Modification and Electrochemical Metallization of Advanced Polymers for Energy Application

For some demanding applications the peculiar properties of polymers, as lightweight, flexibility and chemical resistance, need to be enriched with additional characteristics that are traditionally associated with metals, such as thermal and electrical conductivity, barrier to fluids, high hardness, tribological resistance and reflectivity. Applications, requiring this coupling of different properties, include flexible electronics, barrier layers and alternative energy1–3. In these applications a thin layer of metal, on top of the polymeric substrate, is sufficient to assure the required properties. The main issue of these composites is the adhesion between the two materials and is related to the low surface energy of polymers4. To overcome adhesion issues between the polymeric and metallic layer, several dry and wet processes have been proposed5–7 that imply the utilization of expensive tools or aggressive chemicals. We propose an alternative method to perform metallization of partially fluorinated polymers based on a two-step process: a) chemical functionalization of the substrate surface, for increased adhesion and b) activation and electroless metallization with Cu or Ni-P. After this process we have a continuous, adherent and conductive metallic layer that allows for surface finishing by electrodeposition. We produced continuous metallic thin layers of Cu and Ni-P on different partially fluorinated polymers achieving a 5B adhesion in the ASTM D3359 cross cut test. Considering the application of metallized polymeric films for solar thermodynamic, the electrodeposition of Al from air and water stable ionic liquids is being investigated.

Electrodeposition of Palladium in 1-Butyl-3-Methylimidazolium Chloride Ionic Liquid

Ionic liquids (ILs) have superior electrochemical properties that make them ideal for electrodeposition (1, 2). These properties include higher conductivity than non-aqueous solvents, wide electrochemical window and high solubility of metal salts. Moreover, complications due to air or water reaction at a metal/IL interface could be readily managed in air and water stable ILs (2).Electrodeposition of a metal is strongly affected by IL properties such as viscosity and conductivity which are depended upon its cations and anions (3). Cations also adsorb on the electrode surface and influence double layer structure at reduction potentials, while anions control the metal speciation (2). In addition, concentration of the dissolved metal ion affect the electrodeposition by changing the properties of ionic liquid and affecting the interactions at the metal/IL interface (2). Study of these phenomena on electrodeposition is limited (2). In this work, electrodeposition of Pd ions in 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) and 1-butyl-3-methylimidazolium dicyanamide ([Bmim][DCA]) was investigated for fission palladium recovery application. Deposition properties are strongly depended upon the IL selected. For example, Figure 1a shows a Ni flag electrode immediately after Pd electrodeposition in [Bmim][DCA] at -0.9 V vs Fc/Fc+ for 2 h at room temperature. On the Ni substrate, black deposits of Pd particles were found which was washed away upon insertion into methanol (Figure 1b) suggesting that the Pd particles formed were loosely attached onto the Ni surface. More studies on the effect of the ILs and substrate on the electrodeposition of Pd will be presented. Figure 1 (a) Black Pd particles on Ni flag electrode (0.25 cm2) after potential hold at -0.9 V vs Fc/Fc+ in 1-butyl-3-methylimidazolium dicyanamide at room temperature for 2 h. Pt wire served as the counter electrode. (b) Detachment of the Pd particles from the Ni electrode in methanol.

In situ STM study of zinc electrodeposition on Au(111) from the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate

The electrodeposition of Zn on Au(111) was investigated with cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM) in the air and water stable ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate ([EMIm]TfO) with a Zn(TfO)2 concentration of 0.2 M. It has been found that the structure [EMIm]TfO/Au(111) is very complex. Furthermore, the addition of Zn(TfO)2 changes the interfacial structure significantly. The first STM-probed Zn islands appear at +0.3 V, and their growth leads to the formation of a thin zinc layer. A bulk deposition of Zn is obtained with in situ STM at −0.1 V. Furthermore, in situ STM reveals that the deposition of Zn is accompanied by the formation of Au-Zn surface alloys.

Synthesis of Silicon and Germanium Nanowire Assemblies by Template-Assisted Electrodeposition from an Ionic Liquid

We report on the template-assisted synthesis of silicon and germanium nanowires from the air- and water-stable ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4] TFSA). The synthesis was done by electrochemical deposition in the pores of a commercial track-etched polycarbonate membrane. After chemical dissolution of the polycarbonate membrane in dichloromethane, nanowire assemblies with a regular arrangement were obtained. Different lengths of nanowires can be obtained by varying the applied potential and the time of deposition. The nanowire assemblies were characterised by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDX). Our results show that the template-assisted electrochemical deposition approach in ionic liquids has the potential to easily synthesise germanium and silicon nanowire assemblies.

Cathodic Electrodeposition of Amorphous Elemental Selenium from an Air- and Water-Stable Ionic Liquid

Electrodeposition of selenium from 1-propyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide is reported. In situ UV-vis spectroelectrochemistry was used to investigate the reduction of diethyl selenite to form elemental selenium thin films from an ionic liquid-acetonitrile medium. Three reduction peaks of diethyl selenite were observed via cyclic voltammetry and are attributed to the stepwise reduction of the selenium precursor adsorbed on the electrode. The electrodeposition mechanism is influenced by both potential and time. Electrodeposition at -1.7 V vs Pt QRE resulted in the deposition of elemental selenium nanoparticles that with time coalesced to form a continuous film. At reduction potentials more negative than -1.7 V the morphology of the deposit changed significantly due to the reduction of elemental Se to Se(2-). In addition, p-type photoconductivity of the films was observed during the spectroelectrochemical measurements. X-ray diffraction and Raman spectroscopy confirmed that the deposited selenium films were amorphous. X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy confirm the films consisted of pure selenium with minor residual contamination from the precursor and ionic liquid.

Aluminium oxidation at high anodic potentials in an AlCl3-containing air- and water-stable ionic liquid solution

The observation of a multi-step stripping process at high positive potentials is reported for aluminium electrodeposition from a solution of AlCl3 in the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide. Cyclic voltammograms recorded on an aluminium-coated boron-doped diamond electrode revealed complex oxidative behaviour, suggesting that a passive layer forms on the freshly deposited aluminium that hinders electro-oxidation. High positive potentials are required to induce chloride attack of the passive film, composed of Al-NTf2 compounds, and facilitate the rapid oxidation of the underlying aluminium metal. These results have important implications in bipolar-pulse electroplating and electrorefining applications where electrodissolution of aluminium is required.

The influence of thermal degradation on the electrodeposition of aluminium from an air- and water-stable ionic liquid

Aluminium electrodeposition is demonstrated from a thermally degraded ionic liquid solution. NMR and voltammetric analyses established that Al(3+) reduction was remarkably similar to that in non-degraded IL solutions suggesting that the electroactive metal-containing species was unaffected by heat treatment. Electron microscopy revealed a significant grain refinement of the deposited metal.

Electrodeposition of zinc films from ionic liquids and ionic liquid/water mixtures

The electrodeposition of zinc films from zinc triflate (Zn(TfO)2) in two air and water stable ionic liquids namely, 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate, [Py1,4]TfO, and 1-ethyl-3-methylimidazolium trifluoromethylsulfonate, [EMIm]TfO, was studied. The influence of water on the deposition process was also investigated. The morphology of the obtained deposit is different in the two liquids. Dense and uniform silvery zinc deposits with good adherence were obtained from [EMIm]TfO while less adhering and dark gray zinc deposits were obtained from [Py1,4]TfO. The SEM results of the deposit obtained from [EMIm]TfO revealed a hexagonal zinc structure while a flower-like structure was observed for the deposits obtained from [Py1,4]TfO under the same conditions. Water added to the electrolyte has a distinct effect on the deposits obtained in [EMIm]TfO and [Py1,4]TfO, respectively. The difference in the structure might be attributed to the different interaction of the ions with the substrate. Furthermore, the addition of water to the solution decreases the electrochemical window of both ionic liquids and shifts the reduction of zinc(II) to less negative values. The XRD phase analysis showed that not only Zn was deposited in the dried ionic liquids also Zn-Au alloys were obtained. However, in ionic liquid/water mixtures only Zn was obtained, surprisingly. Furthermore, Zn deposits obtained at 50°C showed a preferential orientation compared with those ones obtained at room temperature. Both the water concentration and the temperature affect the deposition process.

UV-Assisted Electrodeposition of Germanium from an Air- and Water-Stable Ionic Liquid

The effect of UV light during electrodeposition of germanium on Au and on indium tin oxide (ITO) from the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4]Tf2N) has been investigated. From cyclic voltammetric analysis, two reduction peaks were observed and were assigned to the reduction of Ge(IV) to Ge(II) species, and Ge(II) to Ge(0) species. On using 254 nm UV light during electrodeposition, a decrease of 140 mV occurred on the ITO substrate for the reduction of Ge(IV) to Ge(II) compared with that observed without UV, and a decrease of 204 mV was observed in the reduction of Ge(II) to Ge. The shift in the reduction peak seems to be related to the photoabsorption of UV by the electrolyte, possibly altering the ionic liquid/electrode interface. By characterizing the Ge deposit using scanning electron microscopy, it was observed that the presence of UV irradiation significantly decreased the Ge particle size. A green luminescence was also observed from the electrolyte du...

Electrochemical synthesis of PEDOT and PPP macroporous films and nanowire architectures from ionic liquids

We report on the electrochemical synthesis of macroporous films and on nanowire architectures of conducting polymers from ionic liquids. The electrodeposition of poly(3,4-ethylenedioxythiophene) (PEDOT) and of poly(para-phenylene) (PPP) from the air and water stable ionic liquids 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMIm]TFSA) and from 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIm]FAP) within the voids of a polystyrene opal structure on gold and on platinum substrates yield macroporous films. For this purpose, polystyrene spheres with an average diameter of about 600 nm were applied onto the employed electrodes by a simple dipping process resulting in a layer thickness of about 10 μm. The macroporous films turn into yellow, orange, blue, and green colors owing to the Bragg reflection of the incident artificial white light. PPP and PEDOT nanowires were electrochemically prepared in a track-etched polycarbonate (PC) membrane with an average pore diameter of 90 nm. One side of the membrane was sputtered with a thin gold film to serve as a working electrode. Electrodeposition occurs along the pores of the template. Nanowires with an average diameter of 90 nm and a length of up to 17 μm can be easily synthesized by this electrochemical template-assisted method. Such materials are of interest as catalyst in metal/air batteries and as cathode material in, e.g., microbatteries.