Boron Nitride Nanosheets Strengthened PVA/Borax Hydrogels with Highly Efficient Self-Healing and Rapid pH-Driven Shape Memory Effect

Self-healing hydrogels often possess poor mechanical properties which largely limits their applications in many fields. In this work, boron nitride nanosheets are introduced into a network of the poly(vinyl alcohol)/borax (PVA/borax) hydrogels to enhance the mechanical properties of the hydrogel without compromising the self-healing abilities. The obtained hydrogels exhibit excellent mechanical properties with a tensile strength of 0.410 ± 0.007 MPa, an elongation at break of 1712%, a Young's Modulus of 0.860 ± 0.023 MPa, and a toughness of 3.860 ± 0.075 MJ m⁻³. In addition, the self-healing efficiency of the hydrogels is higher than 90% within 10 min at room temperature. Benefiting from the excellent self-healing properties, the shapeability of the hydrogel fragments is observed using different molds. In addition, the hydrogels display rapid pH-driven shape memory effects and can recover to their original shape within 260 s. Overall, this work provides a new approach to hydrogels with integrated excellent mechanical properties, self-healing abilities, and rapid pH-driven shape memory effects.     

Viscosity effect of ionic liquid-assisted controlled growth of CH3NH3PbI3 nanoparticle-based planar perovskite solar cells

A precise control of the morphology and crystallization of perovskite thin-films is well-correlated to higher perovskite solar cells performances. Ionic liquids (ILs) can retard perovskite crystallization to aid the formation of films with uniform morphology to realize highly efficient perovskite solar cells. Herein, we attempt to control the nanostructural growth of CH₃NH₃PbI₃ thin films by adding ILs to the perovskite spin-coating solution and investigate the effect of IL viscosity on the resulting CH₃NH₃PbI₃ nanoparticle (NP) thin films. NPs with desirable morphology were obtained using ILs with a low viscosity that completely dissolved in the CH₃NH₃PbI₃ solution. In particular, the IL tetrabutylammonium chloride yielded NPs with a diameter of 500 nm and controllable morphology, crystallinity, and absorption behavior, which led to improved photovoltaic performance compared with that of solar cells containing NPs produced using other ILs. Our findings revealed a pathway to obtain uniformly distributed CH₃NH₃PbI₃ NP thin films for use in perovskite solar cells. The developed method is well suited for large-scale production of perovskite thin films on flexible substrates.     

Ⅱ型滑移开裂行为下竹胶板单搭接结构力学特性

为研究竹胶板的剪切滑移力学行为与失效机理,建立竹胶板单搭接结构Ⅱ型滑移开裂数值模型,考虑非线性接触,利用无厚度cohesive黏聚力行为模拟黏接层损伤失效,从极限失效载荷、剥离应力及剪切应力角度分析单搭接结构在位移载荷作用下发生剪切滑移失效的演化规律,探究了竹胶板厚度、黏接长度、位移载荷量对搭接结构失效机制影响规律。结果表明,竹胶板厚度越小,搭接面沿长度两侧剥离失效越剧烈,一定范围内的竹板厚度增加可提高单搭接结构胶合能力;随着搭接长度增加,极限失效载荷增长率下降,搭接面上出现更多胶层界面黏合破坏区域,混合破坏模式更加明显,而自由边长度对搭接效果无显著影响;搭接面剥离失效占比随位移载荷增加而增加。研究结果可为竹材的胶合结构设计提供理论依据。     

Novel electrode substrates for rechargeable lithium/polypyrrole batteries

A lightweight and inexpensive stainless steel mesh has been investigated as an electrode substrate material for Li/polypyrrole rechargeable battery. The effects of substrate materials on surface morphology of films, charge–discharge capacity and coulombic efficiency are discussed in detail. The results show that the capacity of the cell with stainless steel mesh is about 10% lower than the cell using platinum mesh, but it is much lighter and cheaper than that of platinum mesh, therefore, it is a promising substrate material for Li/polymer batteries.     

Hydrogen sorption studies of palladium decorated graphene nanoplatelets and carbon samples

With the increasing population of the world, the need for energy resources is increasing rapidly due to the development of the industry. 88% of the world's energy needs are met from fossil fuels. Since there is a decrease in fossil fuel reserves and the fact that these fuels cause environmental pollution, there is an increase in the number of studies aimed to develop alternative energy sources nowadays. Hydrogen is considered to be a very important alternative energy source due to its some specific properties such as being abundant in nature, high calorific value and producing only water as waste when burned. An important problem with the use of hydrogen as an energy source is its safe storage. Therefore, method development is extremely important for efficient and safe storage of hydrogen. Surface area, surface characteristics and pore size distribution are important parameters in determining the adsorption capacity, and it is needed to develop new adsorbents with optimum parameters providing high hydrogen adsorption capacity. Until recently, several porous adsorbents have been investigated extensively for hydrogen storage. In this study, it was aimed to develop and compare novel Pd/carbon, Pd/multiwalled carbon nanotube, and Pd/graphene composites for hydrogen sorption. All the palladium/carbon composites were characterized by t-plot, BJH desorption pore size distributions, N₂ adsorption/desorption isotherms, and SEM techniques. The maximum hydrogen storage of 2.25 wt.% at −196 °C was achieved for Pd/KAC composite sample. It has been observed that the spillover effect of palladium increases the hydrogen sorption capacity.     

Multistep kinetic study of Fe2O3 reduction by H2 based on isothermal thermogravimetric analysis data deconvolution

The multistep kinetics of Fe₂O₃ reduction by H₂ is investigated by data deconvolution in this study. The reduction process was conducted in a TGA apparatus isothermally in the temperature range of 750–950 °C. The stepwise reduction of Fe₂O₃, i.e. Fe₂O₃–Fe₃O₄, Fe₃O₄–FeO, and FeO–Fe, was successfully decoupled from each other without controlling the reduction gas atmosphere. The overlapping, as well as the reaction rate, of each reduction step can be described by the deconvoluted data with R² > 0.995 for all the tested temperatures. Based on the deconvolution, relatively stable activation energy with increasing the conversion was obtained for each step with the model-free iso-conversion method, indicating the rationality of the decoupled multistep profiles. Master plot was then applied to evaluate the suitability of kinetic models reported in the open literature. The JMA model (Avrami-Erofe'ev equation), corresponding to the nucleation and growth mechanism, was found to be most suitable for describing each reduction step. The activation energies obtained by the JMA model fitting for Fe₂O₃–Fe₃O₄, Fe₃O₄–FeO, and FeO–Fe were 10.3, 26.7, and 24.8 kJ/mol, respectively, which also agree well with the E_a obtained by the model-free method.     

Effects of H2/O2 and H2/O3 gases on PtMo/C cathode PEMFCs performance operating at different temperatures

This study reported the activity of catalysts synthesized from platinum and molybdenum alloys in different atomic ratios and used as cathode electrocatalysts in the PEMFC. The structural properties of PtMo/C and Pt/C catalysts were analyzed by XRD analysis. The composition and distribution of these alloys in Vulcan XC-72R Carbon were determined by SEM and EDX techniques. CV studies assessed electrochemical properties such as ORR and ECSA activity. The performance of PEMFC cathodes that supplied pure hydrogen and oxygen was examined using polarization curves at different temperatures. Another way to improve the cathodic reaction is to use ozone as a potent oxidizing agent. It was measured that the OCV of the H₂/O₃ PEM fuel cell was 1.60 V, much greater than the open circuit voltage of the traditional H₂/O₂ PEM fuel cell. The PtMo/C catalyst achieved its highest power density of 137 mWcm⁻² at 70 °C, 128 mWcm⁻² at 60 °C, 101 mWcm⁻² at 50 °C, and 85 mWcm⁻² at 40 °C when exposed to H₂/O₂. As the temperature of the cell was raised, it was seen that the catalyst's catalytic activity increased.The maximum power density was detected to be inversely related to the rise in temperature when ozone was used. At low current densities, however, ozone was observed to greatly boost activation polarization.     

Generation of green hydrogen using self-sustained regenerative fuel cells: Opportunities and challenges

The ever-increasing energy demand, depleting fossil fuel reserves, and rising temperatures due to greenhouse gas emissions have necessitated the transition towards the generation of green and clean energy through renewable energy sources. Solar energy is one such renewable energy source that has received significant attention owing to its abundance and inexhaustibility. However, solar energy alone cannot replace fossil fuels in the energy portfolio. There exists a need to develop another clean energy source that can potentially act as an alternative to conventional fuels. Hydrogen proves to be an ideal candidate in this domain and can be sustainably generated by water electrolysis by powering the electrolyzer using solar energy. The hydrogen thus synthesized has net zero carbon emissions and is a suitable asset for decarbonizing the environment. This review encompasses the generation of hydrogen using PV-Electrolyzer systems and addresses the challenges associated with the same. Overcoming these drawbacks can ensure a strong position for hydrogen as an alternative fuel in the energy infrastructure. By employing electrolyzers that are fueled by renewable energy and then using that hydrogen to feed a fuel cell, this study aims to clarify the potential and constraints of producing green hydrogen. Since this area of research has not yet been fully investigated, a review article that enables and encourages academics to develop original solutions is urgently needed.     

Gel-type polymer electrolytes with different types of ceramic fillers and lithium salts for lithium-ion polymer batteries

Gel-type polymer electrolytes are prepared using PVdF/PEGDA/PMMA, LiPF₆/LiCF₃SO₃ mixed lithium salts and ceramic fillers such as Al₂O₃, BaTiO₃ and TiO₂. The electrochemical properties of these electrolytes, such as electrochemical stability, ionic conductivity and compatibility with electrodes are investigated in addition to the physical properties. The charge–discharge performances of lithium-ion polymer batteries using these get-type polymer electrolytes are investigated. The gel-type polymer electrolytes containing a mixed lithium salt of LiPF₆/LiCF₃SO₃ (10/1, wt.%) exhibit more stable ionic conductivity and lower interfacial resistance than those containing only LiPF₆. In addition, an Al₂O₃ filler improves interfacial stability between the electrode and the polymer electrolyte. Stacking cells (MCMB 1028/LiCoO₂, 8 cm × 13 cm × 7 ea) composed of gel-type polymer electrolytes based on PVdF/PEGDA/PMMA, LiPF₆/LiCF₃SO₃ (10/1, wt.%) and Al₂O₃ filler maintain 95% of initial capacity after 100 cycles at a C/2 rate.