Poly(acrylic acid)-Based Composite Gel Polymer Electrolytes with High Mechanical Strength and Ionic Conductivity toward Flexible Zinc-Air Batteries with Long Cycling Lifetime.

The rapid development of portable, flexible, and wearable devices motivates the requirement for flexible zinc-air batteries (FZABs) not only to provide high energy density but also to have sufficient deformability for wearer comfort. The gel polymer electrolyte (GPE) serves as the core part of the FZABs, playing a key function in the battery's practical output performance such as discharge voltage, energy density, and cycling life. Unfortunately, ascribed to its high water absorption, the GPE regularly shows comparatively poor mechanical strength, which is difficult to offer sufficient physical support between electrodes. Herein, we report an optimized poly(acrylic acid) (PAA)-based composite GPE with the aluminum oxide (Al2O3) filler and apply it for FZAB. The mechanical strength, electrolyte absorption capacity, electrolyte retention ability, and ionic conductivity of the PAA-Al2O3 gel polymers and corresponding GPEs were investigated. The results indicate that the above performances of polymers and corresponding GPEs depend to a considerable extent on the content of the addition of Al2O3 particles. When 20 wt.% Al2O3 is added to the PAA polymer, the obtained PAA-20 wt.% Al2O3 gel polymer exhibits improved mechanical strength. The corresponding PAA-20 wt.% Al2O3 GPE shows a high ionic conductivity of 186 mS cm-1 and pleasurable electrolyte retention capability. This optimized GPE enables the assembled FZAB to display a long cycling lifetime of 384 h, a large power density of 77.7 mW cm-2, and excellent discharge performance. Moreover, the integrated FZAB can power various electronic devices, demonstrating its outstanding practicability and extensibility as a flexible power source.

A Rechargeable Zn-Air Battery with High Energy Efficiency and Long Life Enabled by a Highly Water-Retentive Gel Electrolyte with Reaction Modifier.

Tremendous effort have recently been made in optimizing the air catalysts of flexible zinc-air batteries (ZABs). Unfortunately, the bottleneck factors in electrolytes that largely limit the working life and energy efficiency of ZABs have long been relatively neglected. Herein, an alkaline gel polymer electrolyte (GPE) is fabricated through multiple crosslinking reactions among poly(vinyl alcohol) (PVA), poly(acrylic acid), and graphene oxide followed by intense uptake of an alkali and the KI reaction modifier. The prepared GPE exhibits essentially improved properties compared to traditional PVA gel electrolyte in terms of mechanical strength, ionic conductivity, and water retention capability. In addition, the introduced reaction modifier I- in the GPE changes the path of the conventional oxygen evolution reaction, leading to a more thermodynamically favorable path. The optimized GPE enables flexible ZABs exhibiting an exceptionally low charge potential of 1.69 V, a long cycling time of 200 h, a high energy efficiency of 73%, and rugged reliability under different extreme working conditions. Moreover, the successful integration of ZABs in a variety of real wearable electronic devices demonstrates their excellent practicability as flexible power sources.

Electrochemical Oxidation of Chlorine-Doped Co(OH)2 Nanosheet Arrays on Carbon Cloth as a Bifunctional Oxygen Electrode.

The primary challenge of developing clean energy conversion/storage systems is to exploit an efficient bifunctional electrocatalyst both for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with low cost and good durability. Here, we synthesized chlorine-doped Co(OH)2 in situ grown on carbon cloth (Cl-doped Co(OH)2) as an integrated electrode by a facial electrodeposition method. The anodic potential was then applied to the Cl-doped Co(OH)2 in an alkaline solution to remove chlorine atoms (electro-oxidation (EO)/Cl-doped Co(OH)2), which can further enhance the electrocatalytic activity without any thermal treatment. EO/Cl-doped Co(OH)2 exhibits a better performance both for ORR and OER in terms of activity and durability because of the formation of a defective structure with a larger electrochemically active surface area after the electrochemical oxidation. This approach provides a new idea for introducing defects and developing active electrocatalyst.

Synthesis of Cubic-Shaped Pt Particles with (100) Preferential Orientation by a Quick, One-Step and Clean Electrochemical Method.

A new approach has been developed for in situ preparing cubic-shaped Pt particles with (100) preferential orientation on the surface of the conductive support by using a quick, one-step, and clean electrochemical method with periodic square-wave potential. The whole electrochemical deposition process is very quick (only 6 min is required to produce cubic Pt particles), without the use of particular capping agents. The shape and the surface structure of deposited Pt particles can be controlled by the lower and upper potential limits of the square-wave potential. For a frequency of 5 Hz and an upper potential limit of 1.0 V (vs saturated calomel electrode), as the lower potential limit decreases to the H adsorption potential region, the Pt deposits are changed from nearly spherical particles to cubic-shaped (100)-oriented Pt particles. High-resolution transmission electron microscopy and selected-area electron diffraction reveal that the formed cubic Pt particles are single-crystalline and enclosed by (100) facets. Cubic Pt particles exhibit characteristic H adsorption/desorption peaks corresponding to the (100) preferential orientation. Ge irreversible adsorption indicates that the fraction of wide Pt(100) surface domains is 47.8%. The electrocatalytic activities of different Pt particles are investigated by ammonia electro-oxidation, which is particularly sensitive to the amount of Pt(100) sites, especially larger (100) domains. The specific activity of cubic Pt particles is 3.6 times as high as that of polycrystalline spherical Pt particles, again confirming the (100) preferential orientation of Pt cubes. The formation of cubic-shaped Pt particles is related with the preferential electrochemical deposition and dissolution processes of Pt, which are coupled with the periodic desorption and adsorption processes of O-containing species and H adatoms.

Clarifying the Controversial Catalytic Performance of Co(OH)2 and Co3O4 for Oxygen Reduction/Evolution Reactions toward Efficient Zn-Air Batteries.

Cobalt-based nanomaterials have been widely studied as catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) due to their remarkable bifunctional catalytic activity, low cost, and easy availability. However, controversial results concerning OER/ORR performance exist between different types of cobalt-based catalysts, especially for Co(OH)2 and Co3O4. To address this issue, we develop a facile electrochemical deposition method to grow Co(OH)2 directly on the skeleton of carbon cloth, and further Co3O4 was obtained by post thermal treatment. The entire synthesis strategy removes the use of any binders and also avoids the additional preparation process (e.g., transfer and slurry coating) of final electrodes. This leads to a true comparison of the ORR/OER catalytic performance between Co(OH)2 and Co3O4, eliminating uncertainties arising from the electrode preparation procedures. The surface morphologies, microstructures, and electrochemical behaviors of prepared Co(OH)2 and Co3O4 catalysts were systemically investigated by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and electrochemical characterization methods. The results revealed that the electrochemically deposited Co(OH)2 was in the form of vertically aligned nanosheets with average thickness of about 4.5 nm. After the thermal treatment in an air atmosphere, Co(OH)2 nanosheets were converted into mesoporous Co3O4 nanosheets with remarkably increased electrochemical active surface area (ECSA). Although the ORR/OER activity normalized by the geometric surface area of mesoporous Co3O4 nanosheets is higher than that of Co(OH)2 nanosheets, the performance normalized by the ECSA of the former is lower than that of the latter. Considering the superior apparent overall activity and durability, the Co3O4 catalyst has been further evaluated by integrating it into a Zn-air battery prototype. The Co3O4 nanosheets in situ supported on carbon cloth cathode enable the assembled Zn-air cells with large peak power density of 106.6 mW cm-2, low charge and discharge overpotentials (0.67 V), high discharge rate capability (1.18 V at 20 mA cm-2), and long cycling stability (400 cycles), which are comparable or even superior to the mixture of state-of-the-art Pt/C and RuO2 cathode.

Association between the rs11614913 variant of miRNA-196a-2 and the risk of epithelial ovarian cancer.

Polymorphisms in microRNA (miR) genes and their target sites are a distinct classification of variation in the human genome, which are rapidly being identified and investigated in human cancer. A polymorphism in the miR-196a-2 locus has demonstrated significant associations with various types of cancer, including lung, breast, esophageal and gastric tumors. However, miR-196a-2 has not been fully explored in ovarian cancer, which shares similar biological characteristics with other types of cancer. Therefore, the present study aimed to elucidate the association between a single nucleotide polymorphism (SNP) in the mature sequence of miR-196a-2 (rs11614913, T/C) and the clinical features of 479 Chinese patients with epithelial ovarian cancer (EOC). In addition, the biological significance of this polymorphism was investigated in the OVCAR3 ovarian cancer cell line. Risk association was evaluated in 479 cases of EOC patients and 431 controls. SNPs were analyzed by using polymerase chain reaction based restriction fragment length polymorphism assay. miR-196a expression was evaluated with reverse transcription polymerase chain reaction. The influence of miR-196a-2 rs11614913 T/C on EOC cell migration and invasion ability was further investigated in vitro. The results revealed significant differences in the homozygous CC genotype distribution in patients with EOC (n=479), compared with that of the control subjects (n=431; P=0.026). Analysis of the association between genotype and the risk of EOC revealed that individuals who carried the homozygous CC genotype were 1.34-fold more susceptible to EOC, compared with those carrying the wild-type TT and heterozygous CT genotypes [odds ratio, 1.34; 95% confidence interval, 1.04-2.17; P=0.023]. In addition, the role of this polymorphism in the production of mature miR-196a was investigated. Significantly enhanced production of mature miR-196a was revealed in the C-allelic compared with that of the T-allelic miR-196a-2 precursor (P<0.05). Further examination indicated that miR-196a significantly promoted cell migration and invasion ability in the human OVCAR3 ovarian cell line (P<0.05). In conclusion, the results indicated that the miR-196a-2 rs11614913 CC genotype may increase the risks of ovarian cancer by affecting the expression of mature miR-196a and enhancing cell migration/invasion. The current results provided evidence that the T>C polymorphism in the miR-196a-2 precursor may influence tumorigenesis and metastasis in EOC, and suggested that the functional SNP rs11614913 in the promoter region of pri-miR-196a-2 may be a potential indicator of EOC susceptibility in the population analyzed.