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The rise of heterocycle cations, a new class of stable cations, has fueled faster growth of research interest in heterocycle cation‐attached anion exchange membranes (AEMs). However, once cations are grafted onto backbones, the effect of backbones on properties of AEMs must also be taken into account. In order to comprehensively study the influence of cations effect and backbones effect on AEMs performance, a series of AEMs were prepared by grafting spacer cations, heterocycles cations, and aromatic cations onto brominated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (BPPO) or poly(vinylbenzyl chloride) (PVB) backbones, respectively. Spacer cation [trimethylamine (TMA), N,N‐dimethylethylamine (DMEA)]‐attached AEMs showed general ion transportation and stability behaviors, but exhibited high cationic reaction efficiency. Heterocycle cation [1‐methylpyrrolidine (MPY), 1‐methylpiperidine (MPrD)]‐attached AEMs showed excellent chemical stability, but their ion conduction properties were unimpressive. Aromatic cation [1‐methylimidazole (MeIm), N,N‐dimethylaniline (DMAni)]‐attached AEMs exhibited superior ionic conductivity, while their poor cations stabilities hindered the application of the membranes. Besides, it was found that PVB‐based AEMs had excellent backbone stability, but BPPO‐based AEMs exhibited higher OH− conductivity and cation stability than those of the same cations grafted PVB‐based AEMs due to their higher water uptake (WU). For example, the ionic conductivities (ICs) of BPPO‐TMA and PVB‐TMA at 80 °C were 53.1 and 38.3 mS cm−1, and their WU was 152.3 and 95.1 %, respectively. After the stability test, the IC losses of BPPO‐TMA and PVB‐TMA were 21.4 and 32.2 %, respectively. The result demonstrated that the conductivity and stability properties of the AEMs could be enhanced by increasing the WU of the membranes. These findings allowed the matching of cations to the appropriate backbones and reasonable modification of the AEM structure. In addition, these results helped to fundamentally understand the influence of cation effect and backbone effect on AEM performance. [ABSTRACT FROM AUTHOR]

Highlights from the article: Cover Feature: Fabrication of Efficient and Stable Perovskite Solar Cells in High-Humidity Environment through Trace-Doping of Large-Sized Cations (ChemSusChem 11/2019) B The Cover Feature b shows the efficient and stable CH SB 3 sb NH SB 3 sb PbI SB 3 sb (MAPbI SB 3 sb ) perovskite solar cell prepared under high humidity atmosphere. Humid conditions, MAPbI3, organic cations, perovskite solar cells, X-ray diffraction.

Sodium tantalate (NaTaO3) is the first semiconductor photocatalyst that produces hydrogen–oxygen mixed bubbles in the overall water splitting reaction, when appropriately doped with metal cations. A series of studies are reviewed herein to answer the question of why doping with metal cations raised the quantum efficiency of the reaction. Infrared absorption of band‐gap‐excited photocatalysts demonstrated that cation doping reduced the electron–hole recombination rate and the steady‐state population of charge carriers accordingly increased. In‐depth studies are focused on Sr cations incorporated through solid‐state, flux, and hydrothermal reactions. The recombination rate was reduced when Ta cations were exchanged with Sr cations. Sodium cations were simultaneously exchanged to balance the cationic and anionic charges with no need for creating oxygen anion vacancies. NaTaO3Sr(Sr1/3Ta2/3)O3 solid solution was formed as a result of the simultaneous doping. In addition to doping at the appropriate sites, the intraparticle distribution of Sr cations played an essential role to reduce the recombination rate. Strontium cations segregated to produce graded composition from the Sr‐rich surface to the Sr‐poor core. The bottom of the conduction band was raised at the Sr‐rich surface and the excited electrons were driven to the Sr‐poor core, leaving holes at the surface. However, the graded composition had a dual purpose; the excited electron population increased and its fractional contribution to the surface reaction decreased. [ABSTRACT FROM AUTHOR]

It is essential to minimize the interfacial trap states and improve the carrier collection for high efficiency perovskite solar cells (PSCs). Herein, we present a facile method to construct a p-type graded heterojunction (GHJ) in normal PSCs by deploying a gradient distribution of hole-transporting materials (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], PTAA, in this case) in the shallow perovskite layer. The formation of the GHJ structure facilitates charge transfer and collection, and passivates interfacial trap states, thus delivering a power conversion efficiency (PCE) of 20.05% along with steady output efficiency of 19.3 %, which is among the highest efficiencies for cesium formamidinium (Cs-FA) lead halide PSCs. Moreover, the unencapsulated devices based on these (Cs-FA) lead halide perovskites show excellent long-term stability; more than 95% of their initial PCE can be retained after 1440 h storage under ambient conditions. This study may provide an effective strategy to fabricate high-efficiency PSCs with great stability. [ABSTRACT FROM AUTHOR]

Abstract: Alkaline anion‐exchange membrane fuel cells (AEMFCs) are attracting much attention because of their potential use of nonprecious electrocatalysts. The anion‐exchange membrane (AEM) is one of the key components of AEMFCs. An ideal AEM should possess high hydroxide conductivity and sufficient long‐term durability at elevated temperatures in high‐pH solutions. Herein, recent progress in research into the alkaline stability behavior of cations (including quaternary ammonium, imidazolium, guanidinium, pyridinium, tertiary sulfonium, phosphonium, benzimidazolium, and pyrrolidinium) and their analogous AEMs, which have been investigated by both experimental studies and theoretical calculations, is reviewed. Effects, including conjugation, steric hindrance e, σ–π hyperconjugation, and electrons, on the alkaline stability of cations and their analogous AEMs have been discussed. The aim of this article is to provide an overview of some key factors for the future design of novel cations and their analogous AEMs with high alkaline stability. [ABSTRACT FROM AUTHOR]

Metal-air batteries are intensively studied because of their high theoretical energy-storage capability. However, the fundamental science of electrodes, electrolytes, and reaction products still needs to be better understood. In this work, the ionic liquid N-butyl- N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) was chosen to study the influence of a wide range of metal cations (M n+) on the electrochemical behavior of oxygen. The relevance of the theory of Lewis hard and soft acids and bases to predict satisfactorily the reduction potential of oxygen in electrolytes containing metal cations is demonstrated. Systems with soft and intermediate M n+ acidity are shown to facilitate oxygen reduction and metal oxide formation, whereas oxygen reduction is hampered by hard acid cations such as sodium and lithium. Furthermore, DFT calculations on the energy of formation of the resulting metal oxides rationalize the effect of M n+ on oxygen reduction. A case study on the Na-O2 system is described in detail. Among other things, the Na+ concentration of the electrolyte is shown to control the electrochemical pathway (solution precipitation vs. surface deposition) by which the discharge product grows. All in all, fundamental insights for the design of advanced electrolytes for metal-air batteries, and Na-air batteries in particular, are provided. [ABSTRACT FROM AUTHOR]

Branching at the alkyl side chain of the imidazolium cation in ionic liquids (ILs) was evaluated towards its effect on carbon dioxide (CO2) solubilization at 10 and 80 bar (1 bar=1×105 Pa). By combining high-pressure NMR spectroscopy measurements with molecular dynamics simulations, a full description of the molecular interactions that take place in the IL-CO2 mixtures can be obtained. The introduction of a methyl group has a significant effect on CO2 solubility in comparison with linear or fluorinated analogues. The differences in CO2 solubility arise from differences in liquid organization caused by structural changes in the cation. ILs with branched cations have similar short-range cation-anion orientations as those in ILs with linear side chains, but present differences in the long-range order. The introduction of CO2 does not cause perturbations in the former and benefits from the differences in the latter. Branching at the cation results in sponge-like ILs with enhanced capabilities for CO2 capture. [ABSTRACT FROM AUTHOR]

The alkaline stability of 26 different quaternary ammonium groups (QA) is investigated for temperatures up to 160 °C and NaOH concentrations up to 10 mol L−1 with the aim to provide a basis for the selection of functional groups for hydroxide exchange membranes in alkaline fuel cells and of ionic-liquid cations stable in basic conditions. Most QAs exhibit unexpectedly high alkaline stability with the exception of aromatic cations. β-Protons are found to be far less susceptible to nucleophilic attack than previously suggested, whereas the presence of benzyl groups, nearby hetero-atoms, or other electron-withdrawing species promote degradation reactions significantly. Cyclic QAs proved to be exceptionally stable, with the piperidine-based 6-azonia-spiro[5.5]undecane featuring the highest half-life at the chosen conditions. Absolute and relative stabilities presented herein stand in contrast to literature data, the differences being ascribed to solvent effects on degradation. [ABSTRACT FROM AUTHOR]

Graphene sheet (GS)-ionic liquid (IL) supercapacitors are receiving intense interest because their specific energy density far exceeds that of GS-aqueous electrolytes supercapacitors. The electrochemical properties of ILs mainly depend on their diverse ions, especially anions. Therefore, identifying suitable IL electrolytes for GSs is currently one of the most important tasks. The electrochemical behavior of GSs in a series of ILs composed of 1-ethyl-3-methylimidazolium cation (EMIM+) with different anions is systematically studied. Combined with the formula derivation and building models, it is shown that the viscosity, ion size, and molecular weight of ILs affect the electrical conductivity of ILs, and thus, determine the electrochemical performances of GSs. Because the EMIM-dicyanamide IL has the lowest viscosity, ion size, and molecular weight, GSs in it exhibit the highest specific capacitance, smallest resistance, and best rate capability. In addition, because the tetrafluoroborate anion (BF4−) has the best electrochemical stability, the GS-[EMIM][BF4] supercapacitor has the widest potential window, and thus, displays the largest energy density. These results may provide valuable information for selecting appropriate ILs and designing high-performance GS-IL supercapacitors to meet different needs. [ABSTRACT FROM AUTHOR]