Anion exchange membranes containing no β-hydrogen atoms on ammonium groups: synthesis,properties, and alkaline stability

Novel anion conductive polymer membranes have been designed and synthesized to investigate whether the absence of β-hydrogen atoms of ammonium groups affects the membranes'' properties and chemical stability. The hydrophilic monomer, 2,2-bis(4-chlorobenzyl)-2-phenyl-ethylamine (3), was obtained via a two-step reaction with an overall yield of 98% under mild reaction conditions. Ni(0)-promoted copolymerization of 3 with 2,2-bis(4-chlorophenyl)hexafluoropropane (1) afforded high molecular weight copolymers (M_n = 12.8–19.6 kDa, M_w = 82.1–224.6 kDa). After quaternization with iodomethane, QBAF-BS polymers formed bendable, robust membranes from solution casting. The ion exchange capacity (IEC) of the membranes ranged from 1.50 to 2.44 mequiv. g⁻¹. The membranes exhibited high hydroxide ion conductivity in water (up to 191 mS cm⁻¹ at 80 °C for IEC = 2.25 mequiv. g⁻¹), suggesting that the newly designed hydrophilic structure was effective in improving the ion conductivity. Based on small-angle X-ray scattering (SAXS) analyses and transmission electron microscopy (TEM) images, all membranes featured nano-phase separated morphology with a large dependence on the copolymer composition. The strain properties were improved on increasing the content of the hydrophilic component up to IEC = 2.25 mequiv. g⁻¹, above which the strain became smaller due to the larger water absorption. The membranes were not stable under harsh alkaline conditions (in 8 M KOH at 80 °C) gradually losing the hydroxide ion conductivity. Compared to our previous AEMs which contained typical aliphatic ammonium groups, the lack of β-hydrogen atoms did not practically improve the alkaline stability of AEMs possibly due to the main chain degradation but contributed to higher ion conductivity.

A novel hydrophilic structure with no β-hydrogen atoms on the quaternary ammonium functionality has been developed for anion exchange membranes. The membranes featured high hydroxide conductivity and alkaline stability under harsh conditions.     

Comb-shaped cardo poly(arylene ether nitrile sulfone) anion exchange membranes: significant impact of nitrile group content on morphology and properties

A series of comb-shaped cardo poly(arylene ether nitrile sulfone) (CCPENS-x) materials were synthesized by varying the content of nitrile groups as anion exchange membranes (AEMs). The well-designed architecture of cardo-based main chains and comb-shaped C10 long alkyl side chains bearing imidazolium groups was responsible for the clear microphase-separated morphologies, as confirmed by atomic force microscopy. The ion exchange capacity (IEC) of the AEMs ranged from 1.56 to 1.65 meq. g⁻¹. With strong dipole interchain interactions, the effects of nitrile groups on the membrane morphology and properties were investigated. With the nitrile group content increasing from CCPENS-0.2 to CCPENS-0.8, CCPENS-x revealed larger and more interconnected ionic domains to form more efficient ion-transport channels, thus increasing the corresponding ionic conductivity from 25.8 to 39.5 mS cm⁻¹ at 30 °C and 58.6 to 83 mS cm⁻¹ at 80 °C. Furthermore, CCPENS-x with a higher content of nitrile groups also exhibited lower water uptake (WU) and swelling ratio (SR), and better mechanical properties and thermal stability. This work presents a promising strategy for enhancing the performance of AEMs.

A series of comb-shaped cardo poly(arylene ether nitrile sulfone) (CCPENS-x) materials were synthesized by varying the content of nitrile groups as anion exchange membranes (AEMs).     

Gd3+ and Bi3+ co-substituted cubic zirconia; (Zr1−x−yGdxBiyO2−δ): a novel high κ relaxor dielectric and superior oxide-ion conductor

Solid oxide fuel cells (SOFCs) offer several advantages over lower temperature polymeric membrane fuels cells (PMFCs) due to their multiple fuel flexibility and requirement of low purity hydrogen. In order to decrease the operating temperature of SOFCs and to overcome the high operating cost and materials degradation challenges, the Cubic phase of ZrO₂ was stabilized with simultaneous substitution of Bi and Gd and the effect of co-doping on the oxide-ion conductivity of Zr_1−x−yBi_xGd_yO_2−δ was studied to develop a superior electrolyte separator for SOFCs. Up to 30% Gd and 20% Bi were simultaneously substituted in the cubic ZrO₂ lattice (Zr_1−x−yGd_xBi_yO_2−δ, x + y ≤ 0.4, x ≤ 0.3 and y ≤ 0.2) by employing a solution combustion method followed by multiple calcinations at 900 °C. Phase purity and composition of the material is confirmed by powder XRD and EDX measurements. The formation of an oxygen vacant Gd/Bi co-doped cubic zirconia lattice was also confirmed by Raman spectroscopy study. With the incorporation of Bi³⁺ and Gd³⁺ ions, the cubic Zr_1−x−yBi_xGd_yO_2−δ phase showed relaxor type high κ dielectric behaviour (ε′ = 9725 at 600 °C at applied frequency 20 kHz for Zr_0.6Bi_0.2Gd_0.2O_1.8) with T_m approaching 600 °C. The high polarizability of the Bi³⁺ ion coupled with synergistic interaction of Bi and Gd in the host ZrO₂ lattice seems to create the more labile oxide ion vacancies that enable superior oxide-ion transport resulting in high oxide ion conductivity (σ_o > 10⁻² S cm⁻¹, T > 500 °C for Zr_0.6Bi_0.2Gd_0.2O_1.8) at relatively lower temperatures.

The high polarizability of the Bi³⁺ ion coupled with synergistic interaction of Bi and Gd in the host ZrO₂ lattice seems to create the more labile oxide ion vacancies that enable high oxide ion conductivity at lower temperatures.     

A simple synthesis of transparent and highly conducting p-type CuxAl1−xSy nanocomposite thin films as the hole transporting layer for organic solar cells

Inorganic p-type films with high mobility are very important for opto-electronic applications. It is very difficult to synthesize p-type films with a wider, tunable band gap energy and suitable band energy levels. In this research, p-type copper aluminum sulfide (Cu_xAl_1−xS_y) films with tunable optical band gap, carrier density, hole mobility and conductivity were first synthesized using a simple, low cost and low temperature chemical bath deposition method. These in situ fabricated Cu_xAl_1−xS_y films were deposited at 60 °C using an aqueous solution of copper(ii) chloride dihydrate (CuCl₂·2H₂O), aluminium nitrate nonohydrate [Al(NO₃)₃·9H₂O], thiourea [(NH₂)₂CS], and ammonium hydroxide, with citric acid as the complexing agent. Upon varying the ratio of the precursor, the band gap of the Cu_xAl_1−xS_y films can be tuned from 2.63 eV to 4.01 eV. The highest hole mobility obtained was 1.52 cm² V⁻¹ s⁻¹ and the best conductivity obtained was 546 S cm⁻¹. The Cu_xAl_1−xS_y films were used as a hole transporting layer (HTL) in organic solar cells (OSCs), and a good performance of the OSCs was demonstrated using the Cu_xAl_1−xS_y films as the HTL. These results demonstrate the remarkable potential of Cu_xAl_1−xS_y as hole transport material for opto-electronic devices.

Inorganic p-type films with high mobility are very important for opto-electronic applications.     

Structure and transport properties of triple-conducting BaxSr1−xTi1−yFeyO3−δ oxides

In this work, Ba_xSr_1−xTi_1−yFe_yO_3−δ perovskite-based mixed conducting ceramics (for x = 0, 0.2, 0.5 and y = 0.1, 0.8) were synthesized and studied. The structural analysis based on the X-ray diffraction results showed significant changes in the unit cell volume and Fe(Ti)–O distance as a function of Ba content. The morphology of the synthesized samples studied by means of scanning electron microscopy has shown different microstructures for different contents of barium and iron. Electrochemical impedance spectroscopy studies of transport properties in a wide temperature range in the dry- and wet air confirmed the influence of barium cations on charge transport in the studied samples. The total conductivity values were in the range of 10⁻³ to 10⁰ S cm⁻¹ at 600 °C. Depending on the barium and iron content, the observed change of conductivity either increases or decreases in humidified air. Thermogravimetric measurements have shown the existence of proton defects in some of the analysed materials. The highest observed molar proton concentration, equal to 5.0 × 10⁻² mol mol⁻¹ at 300 °C, was obtained for Ba_0.2Sr_0.8Ti_0.9Fe_0.1O_2.95. The relations between the structure, morphology and electrical conductivity were discussed.

Ba_xSr_1−xTi_1−yFe_yO_3−δ-based perovskite materials with different barium and iron contents are reported as triple conducting oxides (TCOs), which may conduct three charge carriers: oxygen ions, protons and electrons/holes.     

Influence of defect on the electrical and optical properties of A-site non-stoichiometry Ca0.67La0.22□0.11Ti(1−x)CrxO3−δ perovskite

An investigation of the dielectric dispersion, electrical properties, scaling behavior and optical defects of Ca_0.67La_0.22□_0.11Ti_(1−x)Cr_xO_3−δ (CLT_(1−x)Cr_x) with x = 0 and x = 0.1 compositions is presented. The square in the formula is attributed to a vacancy in A-site. Relaxation phenomena were studied with dielectric and modulus formalism, while, the conductivity mechanism was investigated using electrical conductivity. A high permittivity of around 10⁴, low dielectric loss and low electrical conductivity of around 10⁻³ S cm⁻¹ for Ca_0.67La_0.22TiO₃ (CLT) was observed. These values make this composition interesting for microelectric applications. A comparison between the Z′′ and M′′ indicated that the short-range carrier motion dominates at low temperature and becomes less localized at high temperature. The optical defects of CLT and Ca_0.67La_0.22Ti_0.9Cr_0.1O₃ (CLT_0.9Cr_0.1) were studied by electron paramagnetic resonance (EPR) spectroscopy. The results suggest the formation of a [TiO₆]⁹⁻ center, a (Ti³⁺–V_O) center, and dipole defect for CLT compound and Cr³⁺–V_O center defect for CLT_0.9Cr_0.1 compound. These defects are the source of the in-gap electron traps, which improve the optical properties of CLT_(1−x)Cr_x and hence make it an interesting optical material for different applications.

An investigation of the real part of permittivity for the compositions (a) x = 0 and (b) x = 0.1 solid solution Ca_0.67La_0.22□_0.11Ti_(1−x)Cr_xO_3−δ ceramics.     

Solution combustion synthesis of Ni-based hybrid metal oxides for oxygen evolution reaction in alkaline medium

Oxygen evolution reaction (OER) has arisen as an outstanding technology for energy generation, conversion, and storage. Herein, we investigated the synthesis of nickel-based hybrid metal oxides (Ni_xM_1−xO_y) and their catalytic performance towards OER. Ni_xM_1−xO_y catalysts were synthesized by solution combustion synthesis (SCS) using the metal nitrates as oxidizer and glycine as fuel. Scanning electron microscope (SEM) micrographs display a porous morphology for the hybrid binary Ni_xM_1−xO_y, the common feature of combusted materials. X-ray diffraction (XRD) of Ni_xM_1−xO_y depicted well-defined diffraction peaks, which confirms the crystalline nature of synthesized catalysts. The particle size of as-synthesized materials ranges between 20 and 30 nm with a mesoporous nature as revealed by N₂-physisorption. The electrocatalytic performance of the as-prepared materials was evaluated towards OER in alkaline medium. Among them, Ni_xCo_1−xO_y showed the best catalytic performance. For instance, it exhibited the lowest overpotential at a current density of 10 mA cm⁻² (404 mV), onset potential (1.605 V), and Tafel slope (52.7 mV dec⁻¹). The enhanced electrocatalytic performance of Ni_xCo_1−xO_y was attributed to the synergism between cobalt and nickel and the alteration of the electronic structure of nickel. Also, Ni_xCo_1−xO_y afforded the highest Ni³⁺/Ni²⁺ when compared to other electrocatalysts. This leads to higher oxidation states of Ni species, which promote and improve the electrocatalytic activity.

Ni-based mixed transition metal oxides (MTMO) (Ni_xM_1−xO_y) were synthesized using the solution combustion synthesis (SCS), and investigated as electrocatalysts towards oxygen evolution reaction (OER) in alkaline medium.     

Bayesian optimisation with transfer learning for NASICON-type solid electrolytes for all-solid-state Li-metal batteries

NASICON-type LiZr₂(PO₄)₃ (LZP) has attracted significant attention as a solid oxide electrolyte for all-solid-state Li-ion or Li-metal batteries owing to its high Li-ion conductivity, usability in all-solid-state batteries, and electrochemical stability against Li metal. In this study, we aim to improve the Li-ion conductivity of Li-rich NASICON-type LZPs doped with CaO and SiO₂, i.e., Li_1+x+2yCa_yZr_2−ySi_xP_3−xO₁₂(0 ≤ x ≤ 0.3, 0 ≤ y ≤ 0.3) (LCZSP). Herein, a total of 49 compositions were synthesised, and their crystal structures, relative densities, and Li-ion conductivities were characterised experimentally. We confirmed the improvement in Li-ion conductivity by simultaneous replacement of Zr and P sites with Ca and Si ions, respectively. However, the intuition-derived determination of the composition exhibiting the highest Li-ion conductivity is technically difficult because the compositional dependence of the relative density and the crystalline phase of the sample is very complex. Bayesian optimisation (BO) was performed to efficiently discover the optimal composition that exhibited the highest Li-ion conductivity among the samples evaluated experimentally. We also optimised the composition of the LCZSP using multi-task Gaussian process regression after transferring prior knowledge of 47 compositions of Li_1+x+2yY_xCa_yZr_2−x−yP₃O₁₂ (0 ≤ x ≤ 0.376, 0 ≤ y ≤ 0.376) (LYCZP), i.e., BO with transfer learning. The present study successfully demonstrated that BO with transfer learning can search for optimal compositions two times as rapid as the conventional BO approach. This approach can be widely applicable for the optimisation of various functional materials as well as ionic conductors.

Demonstrate BO approaches to search for optimal composition with high ionic conductivity efficiently.     

Arrangement of water molecules and high proton conductivity of tunnel structure phosphates,KMg1−xH2x(PO3)3·yH2O

A fast proton conductor was investigated in a mixed-valence system of phosphates with a combination of large cations (K⁺) and small cations (Mg²⁺), which resulted in a new phase with a tunnel structure suitable for proton conduction. KMg_1−xH_2x(PO₃)₃·yH₂O was synthesized by a coprecipitation method. A solid solution formed in the range of x = 0–0.18 in KMg_1−xH_2x(PO₃)₃·yH₂O. The structure of the new proton conductor was determined using neutron and X-ray diffraction measurements. KMg_1−xH_2x(PO₃)₃·yH₂O has a tunnel framework composed of face-shared (KO₆) and (MgO₆) chains, and PO₄ tetrahedral chains along the c-direction by corner-sharing. Two oxygen sites of water molecules were detected in the one-dimensional tunnel, one of which exists as a coordination water of K⁺ sites. Multi-step dehydration was observed at 30 °C and 150 °C from thermogravimetric/differential thermal analysis measurements, which reflects the different coordination environments of the water of crystallization. Water molecules are connected to PO₄ tetrahedra by hydrogen bonds and form a chain along the c-axis in the tunnel, which would provide an environment for fast proton conduction associated with water molecules. The KMg_1−xH_2x(PO₃)₃·yH₂O sample with x = 0.18 exhibited high proton conductivity of 4.5 × 10⁻³ S cm⁻¹ at 150 °C and 7.0 × 10⁻³ S cm⁻¹ at 200 °C in a dry Ar gas flow and maintained the total conductivity above 10⁻³ S cm⁻¹ for 60 h at 150 °C under N₂ gas atmosphere.

A fast proton conductor exhibiting high proton conductivity of 7.0 × 10⁻³ S cm⁻¹ at 200 °C in a dry Ar gas flow was developed by designing water chains in a rigid tunnel framework.     

Highly enhanced electrical properties of lanthanum-silicate-oxide-based SOFC electrolytes with co-doped tin and bismuth in La9.33−xBixSi6−ySnyO26

Solid oxide fuel cells (SOFCs) are one of the most promising clean energy sources to be developed. However, the operating temperature of SOFCs is currently still very high, ranging between 1073 and 1273 K. Reducing the operating temperature of SOFCs to intermediate temperatures in between 773 and 1073 K without decreasing the conductivity value is a challenging research topic and has received much attention from researchers. The electrolyte is one of the components in SOFCs which has an important role in reducing the operating temperature of the SOFC compared to the other two fuel cell components, namely the anode and cathode. Therefore, an electrolyte that has high conductivity at moderate operating temperature is needed to obtain SOFC with medium operating temperature as well. La_9.33Si₆O₂₆ (LSO) is a potential electrolyte that has high conductivity at moderate operating temperatures when this material is modified by doping with metal ions. Here, we report a modification of the structure of the LSO by partial substitution of La with Bi³⁺ ions and Si with Sn⁴⁺, which forms La_9.33−xBi_xSi_6−ySn_yO₂₆ with x = 0.5, 1.0, 1.5, and y = 0.1, 0.3, 0.5, in order to obtain an electrolyte of LSO with high conductivity at moderate operating temperatures. The addition of Bi and Sn as dopants has increased the conductivity of the LSO. Our work indicated highly enhanced electrical properties of La_7.83Bi_1.5Si_5.7Sn_0.3O₂₆ at 873 K (1.84 × 10⁻² S cm⁻¹) with considerably low activation energy (E_a) of 0.80 eV comparing to pristine La_9.33Si₆O₂₆ (0.08 × 10⁻² S cm⁻¹).

Structure modification of La_9.33Si₆O₂₆ (LSO) as SOFC electrolyte via a bi-doping mechanism provides enhanced electrical properties of La_7.83Bi_1.5Si_5.7Sn_0.3O₂₆ at 873 K (1.84 × 10⁻² S cm⁻¹) with low activation energy of 0.80 eV compared to pristine LSO (0.08 × 10⁻² S cm⁻¹).     

Hydroxypropyl-β-cyclodextrin-incorporated Pebax composite membrane for improved permselectivity in organic solvent nanofiltration

Thanks to the characteristic hollow cavity structure and sustainable and nontoxic macrocycle molecule feature, cyclodextrins have been used as building block to fabricate organic solvent nanofiltration (OSN) membranes with enhanced permeability and selectivity. Herein, hydroxypropyl-β-cyclodextrin (HP-β-CD) was incorporated into a poly(ether-block-amide) (Pebax) layer on a polysulfone support, followed by crosslinking with toluene 2,4-diisocyanate to prepare a crosslinked HP-β-CD/Pebax (CHP) membrane. By adjusting the initial HP-β-CD concentration (x) and crosslinking reaction time (y), the microporous structure and surface morphology of CHP_x–y (x = 0, 0.25, 0.5, 0.75; y = 5, 10, 15) membranes could be manipulated. The OSN performances of the CHP_x–y membranes were evaluated by the removal of dyes in methanol solution. The results revealed that the optimal CHP_0.5–10 membrane exhibited a high methanol permeance of 8.7 L m⁻² h⁻¹ bar⁻¹, high dye rejection (>96%), and high running stability (at least 336 h), due to the intrinsically microporous structure and surface morphology. This work would inspire the further development of cyclodextrins and other macrocyclic molecules in the preparation of OSN membranes and provide a promising strategy to fabricate state-of-the-art membranes for the efficient separation of organic solvent reclamation and removal of organic pollutants.

The OSN membrane was prepared via crosslinking HP-β-CD in Pebax layer with TDI. The as-prepared membrane exhibited high methanol permeability and good dye rejections, as well as longer running stability.     

Unexpected bowing band evolution in an all-inorganic CsSn1−xPbxBr3 perovskite

We theoretically investigated the structural and electronic properties of the all-inorganic perovskite CsSn_1−xPb_xBr₃, compared with the mixed perovskite compound MA_yCs_1−ySn_1−xPb_xBr₃, based on first-principle calculations. It has been demonstrated that Pb and Sn atoms are inclined to occupy the lattice sites uniformly in the all-inorganic perovskite, and this is distinguished from the most stable configurations observed in the mixed Cs-MA system. It is interesting that small Sn atoms prefer to stay close to the large MA⁺ cations, leading to smaller local structural distortion. Through spin-orbital coupling calculations, we found non-linear bowing band evolution in the all-inorganic mixed Sn–Pb system with a small bowing parameter (b = 0.35), while the band gap of MA_yCs_1−ySn_1−xPb_xBr₃ was clearly reduced as the ratio of MA was around 0.5 (y ≥ 0.25). We determined the bowing band evolution in the mixed cation perovskites and the intrinsic electronic deficiency of the all-inorganic perovskite to obtain the optimal band gap.

We theoretically investigated the structural and electronic properties of the all-inorganic perovskite CsSn_1−xPb_xBr₃, compared with the mixed perovskite compound MA_yCs_1−ySn_1−xPb_xBr₃, based on first-principle calculations.     

The effects of microstructure,Nb content and secondary Ruddlesden–Popper phase on thermoelectric properties in perovskite CaMn1−xNbxO3 (x = 0–0.10) thin films

CaMn_1−xNb_xO₃ (x = 0, 0.5, 0.6, 0.7 and 0.10) thin films have been grown by a two-step sputtering/annealing method. First, rock-salt-structured (Ca,Mn_1−x,Nb_x)O thin films were deposited on 1$\bar{1}$00 sapphire using reactive RF magnetron co-sputtering from elemental targets of Ca, Mn and Nb. The CaMn_1−xNb_xO₃ films were then obtained by thermally induced phase transformation from rock-salt-structured (Ca,Mn_1−xNb_x)O to orthorhombic during post-deposition annealing at 700 °C for 3 h in oxygen flow. The X-ray diffraction patterns of pure CaMnO₃ showed mixed orientation, while Nb-containing films were epitaxially grown in [101] out of-plane-direction. Scanning transmission electron microscopy showed a Ruddlesden–Popper (R–P) secondary phase in the films, which results in reduction of the electrical and thermal conductivity of CaMn_1−xNb_xO₃. The electrical resistivity and Seebeck coefficient of the pure CaMnO₃ film were measured to 2.7 Ω cm and −270 μV K⁻¹ at room temperature, respectively. The electrical resistivity and Seebeck coefficient were reduced by alloying with Nb and was measured to 0.09 Ω cm and −145 μV K⁻¹ for x = 0.05. Yielding a power factor of 21.5 μW K⁻² m⁻¹ near room temperature, nearly eight times higher than for pure CaMnO₃ (2.8 μW K⁻² m⁻¹). The power factors for alloyed samples are low compared to other studies on phase-pure material. This is due to high electrical resistivity originating from the secondary R–P phase. The thermal conductivity of the CaMn_1−xNb_xO₃ films is low for all samples and is the lowest for x = 0.07 and 0.10, determined to 1.6 W m⁻¹ K⁻¹. The low thermal conductivity is attributed to grain boundary scattering and the secondary R–P phase.

Reduction of thermal conductivity of sputtered CaMn_1−xNb_xO₃ thin films by secondary Ruddlesden–Popper phase and grain size optimization.     

Ionic self-assembled organogel polyelectrolytes for energy storage applications

High performance organogel polyelectrolytes were synthesized by super acid catalyst step-growth polycondensation of isatin and the non-activated multiring aromatic p-terphenyl. Subsequently, a chemical modification reaction was carried out to obtained quaternary ammonium functionalized polyelectrolytes through a nucleophilic substitution reaction with (3-bromopropyl)trimethylammonium bromide and potassium carbonate at room temperature. Different functionalization degrees were obtained by controlling the molar ratio of the polymer and the modification agent. The organogel polyelectrolytes were formed due to the high phase segregation and self-assembling observed owing to the amphiphilic character of the material (hydrophobic backbone and hydrophilic fragment grafted). The organogel polyelectrolytes were used to fabricate supercapacitors using two commercial graphite electrodes. These polyelectrolytes displayed good ionic conductivity without the use of another doping agent such as salts, acids or ionic liquids. In this work, a strong correlation of functionalization degree and ionic conductivity of the polyelectrolytes and capacitance of the supercapacitors was observed. The ionic conductivity of the polyelectrolytes reached 0.46 mS cm⁻¹ for the 100% functionalization degree, meanwhile the polyelectrolyte with the 10% functionalization degree shows 0.036 mS cm⁻¹. Li-doped polyelectrolytes showed higher ionic conductivity due the presence of extra ionic charges (2.26 and 0.2 mS cm⁻¹ for the polyelectrolytes with the 100% and 10% of functionalization degree, respectively). The principal novelty of this work lies in the possibility of modulating the ionic conductivity of organogels and the capacitance of supercapacitors by chemical modifications. The capacitance of the supercapacitors was 1.17 mF cm⁻² for the 100% functionalized polyelectrolyte and is higher in comparison with the polyelectrolyte with 10% functionalization degree (0.68 mF cm⁻²) measured at a discharge current of 52 μA cm⁻² by galvanostatic charge discharge technique. Additionally, when lithium salt (lithium triflate) was added, the polyelectrolytes retained a gel consistency, increasing the ionic conductivity and capacitance. For the doped polyelectrolytes, the areal capacitance reaches 1.37 mF cm⁻² for the 100% functionalization degree polyelectrolyte with lithium triflate. These organogel polyelectrolytes open the possibility to design flexible and all solid-state supercapacitors without the risk of leakage.

High performance organogel polyelectrolytes were synthesized by super acid catalyst step-growth polycondensation of isatin and the non-activated multiring aromatic p-terphenyl.     

The improvement in hole-transporting and electroluminescent properties of diketopyrrolopyrrole pigment by grafting with carbazole dendrons

Diketopyrrolopyrrole (DPP) pigments are essential and have been intensively exploited as building-blocks for the synthesis of organic semiconducting polymers and small molecules; however, DPP derivatives as emissive materials for electroluminescent (EL) devices have rarely been explored. In this work, a series of new DPP derivatives grafted with carbazole dendrons in a non-conjugated fashion using an amide linkage was designed to improve the performance of DPP in EL devices. Three DPP derivatives (G0DPP, G1DPP and G2DPP) bearing di(p-chlorophenyl)-DPP (Pigment Red 254) as the core substituted with a hexyl chain, N-hexyl carbazole and N-hexyl-N′-9,3′:6′,N′′-tercarbazole, respectively, were synthesized to afford improved hole-transporting properties without affecting the photophysical and electronic properties of the DPP core. The synthesized DPP derivatives displayed an intense yellow fluorescence emission peaked at 536 nm with an absolute photoluminescence quantum yield close to unity in solution. The hole-transporting capability of molecules was improved when carbazole dendrons were incorporated, which increased with an increase in the generation of substituent carbazole dendrons in the order of G0DPP < G1DPP < G2DPP. Significantly, the use of G2DPP, showing the highest hole mobility, in an EL device yielded a strong and stable yellow emission peaked at 556 nm (CIE x, y color coordinates of (0.45, 0.53)) with a brightness of 3060 cd m⁻², maximum luminous efficiency of 9.24 cd A⁻¹ and a maximum EQE of 3.11%.

Diketopyrrolopyrrole pigments grafted with carbazole dendrons in OLEDs exhibit strong and stable yellow emissions with brightness of 3060 cd m⁻², luminous efficiency of 9.24 cd A⁻¹ and EQE of 3.11%.     

Synthesis of a MnS/NixSy composite with nanoparticles coated on hexagonal sheet structures as an advanced electrode material for asymmetric supercapacitors

Herein, a facile hydrothermal method was designed to synthesize a novel structure of micro-flowers decorated with nanoparticles. The micro-flower structure consists of enormous cross-linked flat hexagonal nanosheets with sufficient internal space, providing fluent ionic channels and enduring volume change in the electrochemical storage process. As expected, the MnS/Ni_xS_y (NMS) electrode exhibits a relatively high specific capacitance of 1073.81 F g⁻¹ (at 1 A g⁻¹) and a good cycling stability with 82.14% retention after 2500 cycles (at 10 A g⁻¹). Furthermore, the assembled asymmetric supercapacitor achieves a high energy density of 46.04 W h kg⁻¹ (at a power density of 850 W kg⁻¹) and exhibits excellent cycling stability with 89.47% retention after 10 000 cycles. The remarkable electrochemical behavior corroborates that NMS can serve as an advanced electrode material.

A MnS/Ni_xS_y composite with nanoparticles coated on hexagonal sheets was successfully synthesized and exhibited enhanced performance.     

Thermochemistry of cation disordered Li ion battery cathode materials, (M′ = Nb and Ta,M′′ = Mn and Fe)

High temperature oxide melt solution calorimetry studies on (M′ = Nb⁵⁺, M′′ = Mn³⁺ and Fe³⁺ and x = 0.20, 0.30 and 0.40) oxides and a new family of Ta containing Li excess disordered cathode materials, (M′ = Ta⁵⁺, M′′ = Fe³⁺ and x = 0.20, 0.30 and 0.40), synthesized by a rapid quenching method, are reported in this study. The enthalpies of formation determined from high temperature calorimetry studies reveal that the stability of compounds increases with the increasing Li content per formula unit. The reaction between more basic Li₂O and acidic transition metal oxides results in the more negative enthalpies of formation for these compounds. The work reveals that the formation enthalpy term plays a more important role in the stabilization of such disordered Li ion materials at room temperature whereas configurational entropy along with lattice entropy (vibrational and magnetic) contributes to the stabilization at high temperature from which the samples are quenched.

Enthalpies of formation from oxides (ΔH_f,ox) of novel disordered Li_1+xTa_xFe_1−2xO₂ and reported (M′′ = Mn³⁺ and Fe³⁺).     

Probing the ionic structure of FLiNaK–ZrF4 salt mixtures by solid-state NMR

In this study, by applying ¹⁹F, ²³Na and ⁷Li high-resolution NMR methods, the evolution of the [Zr_xF_y]^4x−y local ionic structures in FLiNaK–ZrF₄ salt mixtures were elucidated. K₃ZrF₇, Na₃ZrF₇ and Na₇Zr₆F₃₁ crystal phases were identified when the melt salts were being solidified. The distribution of these [Zr_xF_y]^4x−y species was dependent on the content of ZrF₄ in FLiNaK eutectic salts. Moreover, K₃ZrF₇ phase transition from an orthorhombic lattice into a disordered cubic lattice was clarified, thereby causing dynamics of the coordinated F⁻ ions to be reduced and the well-ordered crystal lattices to be destroyed. These mentioned results provide a further insight into the Zr–F based ionic structure and the formation of the disordered Zr–F structure in ZrF₄-based eutectic salts.

The evolution of the [Zr_xF_y]^4x−y ionic structures in FLiNaK–ZrF₄ salt mixtures was elucidated through solid-state NMR techniques when the melt salts were being solidified.     

Water management in anion-exchange membrane water electrolyzers under dry cathode operation

Dry cathode operation is a desired operation mode in anion-exchange membrane water electrolyzers to minimize contamination of the generated hydrogen. However, water management under such operation conditions makes it challenging to maintain reliable performance and durability. Here, we utilize high-resolution in situ neutron imaging (∼6 μm effective resolution) to analyze the water content inside the membrane-electrode-assembly of an anion-exchange membrane water electrolyzer. The ion-exchange capacity (IEC) and thus hydrophilicity of the polymer binder in the cathode catalyst layer is varied to study the influence on water content in the anode (mid IEC, 1.8–2.2 meq. g⁻¹ and high IEC, 2.3–2.6 meq. g⁻¹). The neutron radiographies show that a higher ion-exchange capacity binder allows improved water retention, which reduces the drying-out of the cathode at high current densities. Electrochemical measurements confirm a generally better efficiency for a high IEC cell above 600 mA cm⁻². At 1.5 A cm⁻² the high IEC has a 100 mV lower overpotential (2.1 V vs. 2.2 V) and a lower high frequency resistance (210 mΩ cm⁻²vs. 255 mΩ cm⁻²), which is believed to be linked to the improved cathode water retention and membrane humidification. As a consequence, the performance stability of the high IEC cell at 1 A cm⁻² is also significantly better than that of the mid IEC cell (45 mV h⁻¹vs. 75 mV h⁻¹).

Dry cathode operation is a desired operation mode in anion-exchange membrane water electrolyzers, but water management is crucial. This is visualized using high-resolution neutron radiography and the ion-exchange capacity of the cathode ionomer is varied.     

Partially fluorinated copolymers containing pendant piperidinium head groups as anion exchange membranes for alkaline fuel cells

A new series of partially fluorinated copolymers with varying alkyl side chain length (C3, C6 and C9) and piperidinium head groups have been synthesized and characterized in detail in an effort to improve membrane properties for alkaline fuel cell applications. The copolymers (QPAF4-Cx-pip) provided thin and bendable membranes by solution casting, and achieved high hydroxide ion conductivity up to 97 mS cm⁻¹ in water at 80 °C. Membrane properties such as water absorbability, conductivity, and mechanical properties were tunable with the side chain length. The copolymer main chain and the piperidinium groups were both alkaline stable and the membranes retained high conductivity in 4 M KOH at 80 °C for as long as 1000 h, however, conductivity was lost in 8 M KOH due to Hofmann degradation of the side chain. QPAF4-C3-pip copolymer with the best-balanced properties as anion exchange membrane functioned well in a hydrogen/oxygen alkaline fuel cell to achieve 226 mW cm⁻² peak power density at 502 mA cm⁻² current density under fully humidified conditions with no back pressure.

Piperidinium functionalized partially fluorinated copolymers with varying alkyl spacer length were synthesized and evaluated as anion exchange membranes to achieve improved performance in alkaline fuel cells.