Titanium Carbide and Titanium Nitride-Based Nanocomposites as Efficient Catalysts for the Co²⁺/Co³⁺ Redox Couple in Dye-Sensitized Solar Cells

Two different kinds of nanocomposites were developed by electrochemical deposition of poly­(3,4-ethylenedioxythiophene) (PEDOT) into porous hard template films of TiC or TiN nanoparticles, in order to evaluate their use as alternative catalysts in dye-sensitized solar cells (DSSC) utilizing a Co²⁺/Co³⁺ polypyridyl redox mediator. Cyclic voltammograms indicate that both types of nanocomposite show comparable catalytic activity to platinum-coated electrodes. However, electrochemical impedance spectroscopy (EIS) reveals that electron transfer resistances are significantly reduced with the porous nanocomposite electrodes (<1 Ω), to about an order of magnitude lower than those observed for the Pt coated electrode. As a result, DSSCs with the composite counter electrodes achieved equivalent or higher photovoltaic conversion efficiencies compared to cells with pristine PEDOT or Pt coated electrodes. In particular, the highest efficiency (8.26%) was achieved with a DSSC using a TiN-PEDOT counter electrode

Redox-Active Quasi-Solid-State Electrolytes for Thermal Energy Harvesting

Thermoelectrochemical cells (TECs) are a promising and cost-effective approach to harvesting waste thermal energy. For the widespread uptake of this new technology and the development of flexible, leak-free devices, solidification of the redox electrolyte is key. Thus, here we report the first quasi-solid-state electrolyte incorporating the ferri/ferrocyanide redox couple within a cellulose matrix. The electrolyte with 5 wt % cellulose achieved an optimum balance of mechanical properties, Seebeck coefficients, and diffusion coefficients and supported power outputs comparable to those of the liquid electrolyte systems

Highly Selective and Tunable CO₂/N₂ Separation Performance in Ammonium-Based Organic Ionic Plastic Crystal Composite Membranes with Self-Healing Properties

An advancement in light gas separation performance is realized by using organic ionic plastic crystal (OIPC)-based composites. In this work, a composite membrane is synthesized from tetraethylammonium bis­(fluoro­sulfonyl)­imide ([N2222]­[FSI]) and poly­(vinylidene fluoride-co-hexafluoro­propylene) (PVDF-HFP) for the first time and tested under different thermal conditions to investigate the performance in different solid phases. The composite demonstrates tunable performance within a small range of temperatures and enhanced CO2 solubility upon annealing, reaching a CO2 permeability of ∼130 barrer with a remarkable CO2/N2 selectivity of α ≈ 70 at 55 °C. The thermophysical properties of the composite reveal a strong dependency between the structure and the overall gas separation performance. Higher homogeneity in the [N2222]­[FSI]:PVDF-HFP mixture is concluded to hinder OIPC crystallinity and enhance interfacial disorder, boosting CO2 solubility and ionic conductivity and concomitantly providing good mechanical support. Additionally, self-healing behavior is observed in the composite, which makes it more attractive for practical applications. These results provide valuable insights into the advanced design of more selective and durable OIPC-based composite membranes for light gas separation

Solution−Surface Electropolymerization: A Route to Morphologically Novel Poly(pyrrole) Using an Ionic Liquid

Solution−Surface Electropolymerization:  A Route to Morphologically Novel Poly(pyrrole) Using an Ionic Liqui

Highly Selective and Tunable CO₂/N₂ Separation Performance in Ammonium-Based Organic Ionic Plastic Crystal Composite Membranes with Self-Healing Properties

An advancement in light gas separation performance is realized by using organic ionic plastic crystal (OIPC)-based composites. In this work, a composite membrane is synthesized from tetraethylammonium bis­(fluoro­sulfonyl)­imide ([N2222]­[FSI]) and poly­(vinylidene fluoride-co-hexafluoro­propylene) (PVDF-HFP) for the first time and tested under different thermal conditions to investigate the performance in different solid phases. The composite demonstrates tunable performance within a small range of temperatures and enhanced CO2 solubility upon annealing, reaching a CO2 permeability of ∼130 barrer with a remarkable CO2/N2 selectivity of α ≈ 70 at 55 °C. The thermophysical properties of the composite reveal a strong dependency between the structure and the overall gas separation performance. Higher homogeneity in the [N2222]­[FSI]:PVDF-HFP mixture is concluded to hinder OIPC crystallinity and enhance interfacial disorder, boosting CO2 solubility and ionic conductivity and concomitantly providing good mechanical support. Additionally, self-healing behavior is observed in the composite, which makes it more attractive for practical applications. These results provide valuable insights into the advanced design of more selective and durable OIPC-based composite membranes for light gas separation

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

Investigation of the Physicochemical Properties of Pyrrolidinium-Based Mixed Plastic Crystal Electrolytes

Organic ionic plastic crystals (OIPCs) are promising candidates for solid-state electrolyte materials for energy storage applications. Mixing of two OIPCs to produce new solid-state electrolyte materials is proposed to be a route to increasing defects/disorder in the materials, which may in turn promote ion transport. In this work, the thermal phase behavior and transport properties of two different pyrrolidinium-based binary OIPC mixtures were investigated. The most promising was the mixture of N,N-diethylpyrrolidinium bis(fluorosulfonyl)imide ([C2epyr][FSI]) and N-isopropyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ([C(i3)mpyr][FSI]), studied across the entire composition range, where the 10 mol % [C(i3)mpyr][FSI] mixture showed the highest ionic conductivity of 2 × 10–5 S cm–1 at 30 °C, consistent with the increased ion dynamics indicated by solid-state NMR analysis. Synchrotron XRD analysis revealed that the addition of 10 mol % [C(i3)mpyr][FSI] to [C2epyr][FSI] contributed to lattice expansion, hinting at increased defect volume and/or rotational disorder that assists with improved transport properties. Additionally, 10 mol % LiFSI was added to the chosen binary OIPC mixtures to investigate their potential use as electrolytes. The 10 mol % binary mixture with 10 mol % LiFSI showed the highest ionic conductivity (1.8 × 10–3 S cm–1 at 30 °C), while PFG analysis showed that the [FSI]− anions in the 10 mol % mixture with Li-salt have the highest diffusivity compared to other binary mixtures with Li-salt. Analysis of the structure-dynamics of mixed pyrrolidinium-based binary OIPCs provides insights into this scarcely explored strategy for improving the physicochemical properties of plastic crystal systems and toward the development of improved solid-state electrolytes for battery applications

The Madelung Constant of Organic Salts

The Madelung constant is a key feature determining the lattice energy of a crystal structure and hence its stability. However, the complexity of the calculation has meant that it has previously not been readily available for complex structures, for example for organic salts. We propose a new robust method for calculating Madelung constants of such structures based on a generalized numerical direct summation approach. The method is applied to various organic salts from the ionic liquid and pharmaceutical fields. The values calculated are seen to be a unique feature of the crystal structure, reflecting the positioning of the ions in the unit cell and being sensitive to ion pairing. The difference in Madelung constants between different polymorphs of a compound is also shown

Anisotropic MRI Contrast Reveals Enhanced Ionic Transport in Plastic Crystals

Organic ionic plastic crystals (OIPCs) are attractive as solid-state electrolytes for electrochemical devices such as lithium-ion batteries and solar and fuel cells. OIPCs offer high ionic conductivity, nonflammability, and versatility of molecular design. Nevertheless, intrinsic ion transport behavior of OIPCs is not fully understood, and their measured properties depend heavily on thermal history. Solid-state magnetic resonance imaging experiments reveal a striking image contrast anisotropy sensitive to the orientation of grain boundaries in polycrystalline OIPCs. Probing triethyl­(methyl)­phosphonium bis­(fluorosulfonyl)­imide (P1222FSI) samples with different thermal history demonstrates vast variations in microcrystallite alignment. Upon slow cooling from the melt, microcrystallites exhibit a preferred orientation throughout the entire sample, leading to an order of magnitude increase in conductivity as probed using impedance spectroscopy. This investigation describes both a new conceptual window and a new characterization method for understanding polycrystalline domain structure and transport in plastic crystals and other solid-state conductors