Search

Abstract: A high temperature polymer electrolyte membrane water electrolyser (PEMWE) was investigated at temperatures between 80 and 130°C and pressures between 0.5 and 4bar. Nanometer size Ru0.7Ir0.3O2 and Pt/C were employed as anode and cathode catalysts respectively. The catalyst coated on membrane (CCM) method was used to fabricate the membrane electrode assemblies. The membrane, oxygen evolution catalysts and MEAs were characterized with SEM, XRD and TEM. The influence of high temperature and pressure was investigated using in situ electrochemical measurements. Increasing temperature and pressure produced higher current densities for oxygen evolution, and smaller terminal voltages. The high temperature PEMWE achieved a voltage of 1.51V at a current density of 1Acm−2, at 130°C and 4bar pressure. [Copyright &y& Elsevier]

Oligoether branched-and-spaced “acid-in-chain” polymers, with variable length side chains attached to the acidic borons have been prepared by a simple two-step reaction sequence. These may be used as anion-retarding hosts for “salt-in-polymer” electrolytes or, alternatively, may be converted to polyanionic electrolytes by reacting with strong Lewis base anions. High ionic conductivities, reaching 7.6×10−5 S cm−1 at 25 °C have been obtained for the former case, using LiTFSI:B proportions of 1:1, and optimized side chain and spacer lengths. The electrochemical windows are wide enough (>4.5 V) for most applications. [Copyright &y& Elsevier]

Lithium polyMOB has been investigated as the polymer in a polymer-in-salt type electrolyte incorporating the salts lithium perchlorate (LiClO4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium tetrafluoroborate (LiBF4). While all salts give rubbery solids at high salt contents, only LiClO4 provides high conductivity because only in the case of LiClO4 is the lithium cation motion highly decoupled from the structural relaxation. The crystallization of the salt at high salt contents prevents a favorable combination of mechanical and electrical properties, but the system provides an excellent example of the principle of the polymer-in-salt ionic rubber electrolyte and the factors determining its performance. [Copyright &y& Elsevier]

Plasticized and crosslinked versions of poly(lithium oligoetherato mono-oxalato borate), called lithium polyMOBs, have been studied. In heavily plasticized forms of both polyMOB, and a LiBH4-crosslinked polyMOB, the ionic conductivity reaches 10−3 S cm−1 at room temperature while single ion conductivity is automatically retained. The electrochemical stability window is up to 5 V, for both stainless steel (SS) electrodes. The plasticized forms are fluid, not a gel, due to the low molecular weight of the polyanions. Freestanding gel electrolytes with high single ionic conductivity of 10−4 S cm−1 at ambient can be obtained by incorporation of high molecular weight poly(methyl methacrylate) (PMMA) into the solution. Electrochemical cells using these electrolytes will not suffer from concentration polarization. [Copyright &y& Elsevier]

We describe the synthesis of new chain polymers that contain weakly basic anionic mono-oxalato orthoborate (MOB) moieties in a polyether backbone at controllable anionic separations. The conductivities of these lithium-conducting polymers are found to be high relative to those of most conventional dry salt-in-polymer electrolytes. An ambient conductivity of about 10−5 S cm−1 has been obtained for a solid polymer with 14 ethyleneoxy repeating units. The electrochemical window for these materials is in excess of 4.5 V. These inexpensive benign materials should be very suitable as electrolytes for rechargeable lithium batteries. [Copyright &y& Elsevier]

Poly[lithium-N(4-sulfophenyl) maleimide -co- methoxy oligo-(oxyethylene) methacrylates] [P(LiSMOEn)s] with three different oligoether side chains and different salt concentrations were synthesized. The copolyelectrolytes are essentially random in structure, with blocks of methoxy oligo(oxyethylene) meth-acrylate (MOEnM) recurring sporadically in between the salt units of N(4-sulfophenyl) maleimide. They all show two glass transitions in the temperature range of -100 to 100°C. The first one below -30°C is assigned to the oligo(oxyethylene) side chain (Tg1), while the second one located between 20 and 50°C is attributed to the main chain of the polymer host (Tg2). The maximum ionic conductivity of the copolymer electrolytes, 1.6 × 10-7 S cm-1 at 25°C, occurs at lithium salt concentration [Li+]/[EO] = 2.2 mol%. The ionic conductive behavior of the copolyelectrolytes follows the Vogel-Tammann-Fulcher (VTF) equation. Moreover, a special VTF behavior exists in the copolymers with shorter oligoether side chain and higher salt concentration. Sweep voltammetric results indicate that these copolyelectrolytes have a good electrochemical stability window. [ABSTRACT FROM AUTHOR]

Recharging battery‐powered electric vehicles (EVs) in a similar timeframe as those used for refueling gas‐powered internal combustion vehicles is highly desirable for rapid penetration of the EV market. It is well known that the electrolyte in a battery plays a critical role in fast‐charging capability of the battery because it determines the rate of ion transport together with its derived electrode/electrolyte interphases on both cathode and anode of the battery. In this study, the effects of contents of salt, coordinating solvent, and noncoordinating diluent on salt dissociation degree and electrolyte ionic conductivity are investigated, and a controlled solvation structure electrolyte is developed to improve the lithium ion mobility and conductivity in the electrolyte and to enhance the kinetics and stability of the electrode/electrolyte interphases in the battery. This electrolyte enables fast‐charging capability of high energy density lithium‐ion batteries (LIBs) at up to 5 C rate (12‐min charging), which significantly outperforms the state‐of‐the‐art electrolyte. The controlled solvation structure sheds light on the future electrolyte design for fast‐charging LIBs. [ABSTRACT FROM AUTHOR]

The adsorption process of a geminized amphiphilic polyelectrolyte, comprising double elementary charges and double hydrophobic tails in each repeat unit (denoted as PAGC8), was investigated and characterized by means of quartz crystal microbalance with dissipation (QCM-D), ellipsometry, and atomic force microscopy (AFM). By comparison, the self-assembly behaviors of a traditional polyelectrolyte without hydrophobic chains (denoted as PASC1) and an amphiphilic polyelectrolyte with a single hydrophilic headgroup and hydrophobic tail in each repeat unit (denoted as PASC8) at the solid/liquid interface were also investigated in parallel. A two-regime buildup was found in both amphiphilic systems of PASC8 and PAGC8, where the first regime was dependent on electrostatic interactions between polyelectrolytes and oppositely charged substrates, and the rearrangements of the preadsorbed chains and their aggregation behaviors on surface dominated the second regime. Furthermore, it was found that the adsorbed amount and conformation changed as a function of the charge density and bulk concentrations of the polyelectrolytes. The comparison of the adsorbed mass obtained from QCM-D and ellipsometry allowed calculating the coupling water content which reached high values and indicated a flexible aggregate conformation in the presence of PAGC8, resulting in controlling the suspension stability even at an extremely low concentration. In order to provide an insight into the mechanism of the suspension stability of colloidal dispersions, we gave a further explanation with respect to the interactions between surfaces in the presence of the geminized polyelectrolyte. [ABSTRACT FROM AUTHOR]

Off-lattice computer simulations of polyelectrolyte brushes are carried out using the Debye approximation with explicit counterions but implicit salt. The results are compared with explicit salt ion simulations and self-consistent field theory. We demonstrate that the data generated with these different techniques are in excellent agreement, thereby confirming the validity of the Debye approximation in the context of polyelectrolyte brushes. The efficiency of the Debye approximation is verified through benchmark computations. Further on, we develop an improved Flory-type mean-field model, based on the original argument by Pincus, but taking into account both the excluded volume and finite extensibility of chains. On the basis of this model, we demonstrate how the interplay of counterion pressure and excluded volume repulsion explains the observed effect of salt on the swelling of the brush under good solvent conditions. The brush height as a function of grafting density is investigated, and it is argued that the resulting power law scaling of −1/3 is incapable of distinguishing between excluded volume and electrostatic effects. [ABSTRACT FROM AUTHOR]

Off-lattice molecular dynamics simulations are carried out to study fully charged polyelectrolyte brushes with salt, and a comparison with an off-lattice self-consistent field (SCF) theory including finite stretching and volume effects [Biesheuvel et al. Macromolecules2008, 41, 6254] is presented. The SCF approach is able to reproduce the brush heights at different grafting densities, salt concentrations, and chain lengths on a semiquantitative level. At high grafting densities, the density profiles obtained with both techniques exhibit a particularly close agreement, while at low densities systematic deviations between their shapes are observed. The approximation of local electroneutrality, which the SCF approach is based on, is studied, and its implications are discussed. In this context, the strengths and limitations of the SCF model are analyzed in detail. [ABSTRACT FROM AUTHOR]

Due to the limited oxidation stability (<4 V) of ether oxygen in its polymer structure, polyethylene oxide (PEO)‐based polymer electrolytes are not compatible with high‐voltage (>4 V) cathodes, thus hinder further increases in the energy density of lithium (Li) metal batteries (LMBs). Here, a new type of polymer‐in‐"quasi‐ionic liquid" electrolyte is designed, which reduces the electron density on ethereal oxygens in PEO and ether solvent molecules, induces the formation of stable interfacial layers on both surfaces of the LiNi1/3Mn1/3Co1/3O2 (NMC) cathode and the Li metal anode in Li||NMC batteries, and results in a capacity retention of 88.4%, 86.7%, and 79.2% after 300 cycles with a charge cutoff voltage of 4.2, 4.3, and 4.4 V for the LMBs, respectively. Therefore, the use of "quasi‐ionic liquids" is a promising approach to design new polymer electrolytes for high‐voltage and high‐specific‐energy LMBs. [ABSTRACT FROM AUTHOR]