Conducting Polymers

Conducting Polymer

Evaluation of electrochemical methods for determination of the seebeck coefficient of redox electrolytes

Recent advances in thermoelectrochemical cells, which are being developed for harvesting low grade waste heat, have shown the promise of cobalt bipyridyl salts as the active redox couple. The Seebeck coefficient, Se, of a redox couple determines the open circuit voltage achievable, for a given temperature gradient, across the thermoelectrochemical cell. Thus, the accurate determination of this thermodynamic parameter is key to the development and study of new redox electrolytes. Further, techniques for accurate determination of Se using only one half of the redox couple reduces the synthetic requirements. Here, we compare three different experimental techniques for measuring Se of a cobalt tris(bipyridyl) redox couple in ionic liquid electrolytes. The use of temperature dependent cyclic voltammetry (CV) in isothermal and non-isothermal cells was investigated in depth, and the Se values compared to those from thermo-electromotive force measurements. Within experimental error, the Se values derived from CV methods were found to be in accordance with those obtained from electromotive force (emf) measurements. The applicability of cyclic voltammetry techniques for determining Se when employing only one part of the redox couple was demonstrated

Operando magnetic resonance imaging for mapping of temperature and redox species in thermo-electrochemical cells

AbstractLow-grade waste heat is an abundant and underutilised energy source. In this context, thermo-electrochemical cells (i.e., systems able to harvest heat to generate electricity) are being intensively studied to deliver the promises of efficient and cost-effective energy harvesting and electricity generation. However, despite the advances in performance disclosed in recent years, understanding the internal processes occurring within these devices is challenging. In order to shed light on these mechanisms, here we report an operando magnetic resonance imaging approach that can provide quantitative spatial maps of the electrolyte temperature and redox ion concentrations in functioning thermo-electrochemical cells. Time-resolved images are obtained from liquid and gel electrolytes, allowing the observation of the effects of redox reactions and competing mass transfer processes such as thermophoresis and diffusion. We also correlate the physicochemical properties of the system with the device performance via simultaneous electrochemical measurements

Titanium carbide and titanium nitride-based nanocomposites as efficient catalysts for the Co2+/Co3+ redox couple in dye-sensitized solar cells

Titanium carbide and titanium nitride-based nanocomposites as efficient catalysts for the Co2+/Co3+ redox couple in dye-sensitized solar cell

Zwitterionic versus organic ionic plastic crystal electrolytes with mixed anions: probing the unique physicochemical and electrolyte properties

The feasibility of achieving high performance Li metal batteries, with the associated benefits of high energy density, relies on the development of safe and stable electrolytes suitable for use with the highly reactive Li metal. The use of solid electrolytes can improve safety, decrease the evolution of Li dendrites, and increase the cycle life of a battery. Zwitterions (ZIs) are a unique class of material in which the cationic and anionic moieties are covalently bound, and these have previously been used as additives in electrolytes to improve ion transport. We recently reported a novel class of material, zwitterionic plastic crystals, that have intrinsic molecular disorder and offer a promising alternative to traditional organic ionic plastic crystal (OIPC)-based electrolytes. Here we report an investigation into the use of zwitterionic plastic crystals as matrix electrolytes by the incorporation of different types and concentrations of Li salts, namely lithium bis(fluorosulfonyl)imide (LiFSI) or lithium tetrafluoroborate (LiBF4), and the influence of lithium salt species and concentration on the thermal behaviour and ion dynamics. To understand the effect of ion tethering on the physicochemical properties of the ZI electrolytes we compared their thermal behaviour and ionic conductivity with the analogous OIPC electrolytes, namely [C2mpyr][BF4]. The low and high salt concentrations of ZI/LiBF4 and ZI/LiFSI mixtures form solid-state electrolytes, and the middle concentrations (30-80 mol%) yield liquids at room temperature. The ion dynamics and diffusion were studied by NMR spectroscopy and pulsed-field gradient NMR. The ZI/LiFSI mixtures exhibited lower glass transition temperatures and higher ionic conductivity and higher Li ion mobility than the ZI/LiBF4 mixtures. Finally, electrochemical analysis of the high LiFSI content ZI electrolyte demonstrated a high Li transference number and stable stripping/plating of Li in Li symmetrical and full cells. The combination of high ionic conductivity, high Li ion transference number and stable lithium cycling make zwitterion-based electrolytes promising candidates for lithium metal battery applications

Improved efficiency and stability of flexible dye sensitized solar cells on ITO/PEN substrates using an ionic liquid electrolyte

Flexible dye-sensitized solar cells (DSSCs) built on plastic substrates have attracted great interest as they are lightweight and can be roll-to-roll printed to accelerate production and reduce cost. However, plastic substrates such as PEN and PET are permeable to water, oxygen and volatile electrolyte solvents, which is detrimental to the cell stability. Therefore, to address this problem, in this work, an ionic liquid (IL) electrolyte is used to replace the volatile solvent electrolyte. The initial IL-based devices only achieved around 50% of the photovoltaic conversion efficiency of the cells using the solvent electrolyte. Current-voltage and electrochemical impedance spectroscopy (EIS) analysis of the cells in the dark indicated that this lower efficiency mainly originated from (i) a lack of blocking layer to reduce recombination, and (ii) a lower charge collection efficiency. To combat these problems, cells were developed using a 12 nm thick blocking layer, produced by atomic layer deposition, and 1 μm thick P25 TiO2 film sensitized with the hydrophobic MK-2 dye. These flexible DSSCs utilizing an IL electrolyte exhibit significantly improved efficiencies and a <10% drop in performance after 1000 h aging at 60°C under continuous light illumination

1-Methyl-1-propylpyrrolidinium chloride

1-Methyl-1-propylpyrrolidinium chlorid

Titanium carbide and titanium nitride-based nanocomposites as efficient catalysts for the Co2+/Co3+ redox couple in dye-sensitized solar cells

Titanium carbide and titanium nitride-based nanocomposites as efficient catalysts for the Co2+/Co3+ redox couple in dye-sensitized solar cell

Exploring the electrochemical properties of mixed ligand Fe(II) complexes as redox couples

Exploring the electrochemical properties of mixed ligand Fe(II) complexes as redox couple

Phase Change Materials for Renewable Energy Storage at Intermediate Temperatures

Thermal energy storage technologies utilizing phase change materials (PCMs) that melt in the intermediate temperature range, between 100 and 220 °C, have the potential to mitigate the intermittency issues of wind and solar energy. This technology can take thermal or electrical energy from renewable sources and store it in the form of heat. This is of particular utility when the end use of the energy is also as heat. For this purpose, the material should have a phase change between 100 and 220 °C with a high latent heat of fusion. Although a range of PCMs are known for this temperature range, many of these materials are not practically viable for stability and safety reasons, a perspective not often clear in the primary literature. This review examines the recent development of thermal energy storage materials for application with renewables, the different material classes, their physicochemical properties, and the chemical structural origins of their advantageous thermal properties. Perspectives on further research directions needed to reach the goal of large scale, highly efficient, inexpensive, and reliable intermediate temperature thermal energy storage technologies are also presented