2020 roadmap on two-dimensional materials for energy storage and conversion

Energy storage and conversion have attained significant interest owing to its important applications that reduce CO₂ emission through employing green energy. Some promising technologies are included metal-air batteries, metal-sulfur batteries, metal-ion batteries, electrochemical capacitors, etc. Here, metal elements are involved with lithium, sodium, and magnesium. For these devices, electrode materials are of importance to obtain high performance. Two-dimensional (2D) materials are a large kind of layered structured materials with promising future as energy storage materials, which include graphene, black phosporus, MXenes, covalent organic frameworks (COFs), 2D oxides, 2D chalcogenides, and others. Great progress has been achieved to go ahead for 2D materials in energy storage and conversion. More researchers will join in this research field. Under the background, it has motivated us to contribute with a roadmap on ‘two-dimensional materials for energy storage and conversion.     

Challenges in the assignment of relative and absolute configurations of complex molecules: computation can resolve conflicts between theory and experiment

The configuration of (−)-brevianamides was assigned as (2S,13S) based on X-ray structure analysis and hydrolysis experiments. However, our theoretical investigation of its chiroptical properties strongly implied that the correct configuration should be (2R,13R). The reasons for the incorrect earlier assignment are analyzed by calculations of conversion energy barriers among different intermediates, starting materials and final products. This study demonstrates that conflicting theoretical and, experimental results suggest that it is premature to assign the configuration of a natural product.     

History-dependent ion transport through conical nanopipettes and the implications in energy conversion dynamics at nanoscale interfaces

The dynamics of ion transport at nanostructured substrate–solution interfaces play vital roles in high-density energy conversion, stochastic chemical sensing and biosensing, membrane separation, nanofluidics and fundamental nanoelectrochemistry. Further advancements in these applications require a fundamental understanding of ion transport at nanoscale interfaces. The understanding of the dynamic or transient transport, and the key physical process involved, is limited, which contrasts sharply with widely studied steady-state ion transport features at atomic and nanometer scale interfaces. Here we report striking time-dependent ion transport characteristics at nanoscale interfaces in current–potential (I–V) measurements and theoretical analyses. First, a unique non-zero I–V cross-point and pinched I–V curves are established as signatures to characterize the dynamics of ion transport through individual conical nanopipettes. Second, ion transport against a concentration gradient is regulated by applied and surface electrical fields. The concept of ion pumping or separation is demonstrated via the selective ion transport against concentration gradients through individual nanopipettes. Third, this dynamic ion transport process under a predefined salinity gradient is discussed in the context of nanoscale energy conversion in supercapacitor type charging–discharging, as well as chemical and electrical energy conversion. The analysis of the emerging current–potential features establishes the urgently needed physical foundation for energy conversion employing ordered nanostructures. The elucidated mechanism and established methodology can be generalized into broadly-defined nanoporous materials and devices for improved energy, separation and sensing applications.     

Noble metal doped graphene nanocomposites and its study of photocatalytic hydrogen evolution

This work reports the deposition of platinum (Pt) nanoparticles on the surface of graphene nanosheet by a simple approach, using a microwave-assisted method. The photocatalytic activity has been investigated for hydrogen evolution. The hydrogen evolutions were attributed to graphene, due to its high photoelectron transport properties, and the Pt nanoparticles attached on the surface of graphene sheet, which act as reaction centers for H₂ evolution. The “as-prepared” composites were characterized by Brunauer Emmett Teller (BET) surface area measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectra (DRS). This work highlights the potential application of graphene-based materials in the field of energy conversion.     

Wide bandgap OPV polymers based on pyridinonedithiophene unit with efficiency >5%

We report the properties of a new series of wide band gap photovoltaic polymers based on the N-alkyl 2-pyridone dithiophene (PDT) unit. These polymers are effective bulk heterojunction solar cell materials when blended with phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM). They achieve power conversion efficiencies (up to 5.33%) high for polymers having such large bandgaps, ca. 2.0 eV (optical) and 2.5 eV (electrochemical). Grazing incidence wide-angle X-ray scattering (GIWAXS) reveals strong correlations between π–π stacking distance and regularity, polymer backbone planarity, optical absorption maximum energy, and photovoltaic efficiency.     

A critical review-promises and barriers of conversion electrodes for Li-ion batteries

Conversion-type electrode materials are discussed in this critical review. Most of the conversion materials are significantly less expensive than modern intercalation-type materials, and the materials involved are appreciably abundant in the nature. However, up to now, no practically viable battery with conversion material-based electrodes was reported, as there are several major barriers to a practical employment of these materials. First, material utilization and cell energy performance are seriously compromised by a low conductivity of the most conversion materials and by a substantial electrolyte involvement in the electrochemical process. Second, the conversion reactions usually demonstrate a severe volume effect, and also conversion electrodes interact with electrolyte developing thick and resistant solid electrolyte interphase films; both of these features result in impractically low electrode cyclability. Third, a large lithiation/de-lithiation voltage hysteresis results in impractically low charge/discharge energy efficiency and suggests a severe battery heating in the course of the battery operation. All these problems present serious challenges for the researchers in the field; the approaches for handling these issues are discussed in the review. For the foreseeable future, there are grounds to expect progress in tackling some of these issues. The issue of high voltage hysteresis is a bottleneck, though, and it actually precludes conversion materials from any practical application.     

Bridging X-ray computed tomography and computational modeling for electrochemical energy-conversion and –storage

X-ray imaging techniques are powerful tools for understanding morphology, transport and even reactions within the electrochemical energy systems. Transmission X-ray microscopy (TXM) and X-ray computed tomography (CT) have been widely used in ex-situ studies to probe morphology of electrochemical energy materials. Emerging operando studies highlight the possibility of imaging energy materials and devices under realistic operating conditions. We present an overview of recent advances in the X-ray CT methods with application to fuel cells, batteries and other energy technologies, and describe how the information obtained with multimodal imaging is used within the multi-scale computational models. Overall, the progress in imaging outran the modeling progress, and current models are limited in their utility to incorporate vast amount of multimodal image data.     

Effect of thermo-lime and hot-water pretreatment on the thermal-decomposition characteristics and structure of Spartina alterniflora

The thermal-decomposition characteristics and kinetics of Spartina alterniflora (smooth cordgrass; SC) pretreated with thermo-lime and hot water were investigated by thermogravimetric analysis. Results showed that pretreatment changed the thermal-decomposition behavior of pretreated biomass, as shown in the change of the volatile-matter yield, the thermal-decomposition temperature for a given conversion and the mass-loss rate, because of the breakage of lignocellulosic structure. The activation energy of SC ranged from 40.8 to 55.8 kJ mol^?1 for conversion ratios between 0.15 and 0.8. Pretreatment increased the activation energy of thermal-decomposition reaction, indicating the increment of the thermal stability of biomass. Compared with thermo-lime pretreatment, hot-water pretreatment increased the volatile-matter yield, activation energy, and mass-loss rate of the sample. Structure changes were further investigated by X-ray and Fourier-transform infrared (FTIR) spectroscopy analysis to determine the effect of pretreatment on thermal decomposition. FTIR analyses revealed the depolymerization of lignocellulosic structure and the disruption of carboxyl carbons attached to the lignin side chain. X-ray and FTIR results also showed that thermo-lime and hot-water pretreatment broke the crystalline structure of cellulose by disrupting hydrogen bonding and removing amorphous matter. Compared with hot water, thermo-lime pretreatment resulted in many modifications of lignocellulosic structure and composition. Furthermore, structure breakage and composition removal changed thermal-decomposition characteristics of pretreated samples.     

In situ X-ray absorption spectroscopic investigation of the electrochemical conversion reactions of CuF2-MoO3 nanocomposite

We have used X-ray absorption spectroscopy at the Cu K-edge to investigate the electrochemical conversion reaction of 20 nm size 85 wt% CuF₂−15 wt% MoO₃ nanocomposite under in situ conditions. The nanocomposite was prepared by high energy milling. Upon discharge, the lithiation reaction with the nanocomposite resulted in the formation of nanophase metallic Cu, which is consistent with the conversion of CuF₂ into Cu and LiF. Based on XANES and Fourier transforms of EXAFS spectra, we show that the discharge process proceeded via the formation of highly dispersed Cu particles. Based on the coordination number of the first shell of Cu, the average size of the Cu particles was estimated to be in the 1-3 nm range in the fully discharged state.     

Internal conversion in energy dispersive X-ray analysis of actinide-containing materials.

The use of X-ray elemental analysis tools like energy dispersive X-ray (EDS) is described in the context of the investigation of nuclear materials. These materials contain radioactive elements, particularly alpha-decaying actinides that affect the quantitative EDS measurement by producing interferences in the X-ray spectra. These interferences originating from X-ray emission are the result of internal conversion by the daughter atoms from the alpha-decaying actinides. The strong interferences affect primarily the L X-ray lines from the actinides (in the typical energy range used for EDS analysis) and would require the use of the M lines. However, it is typically at the energy of the actinide's M lines that the interferences are dominant. The artifacts produced in the X-ray analysis are described and illustrated by some typical examples of analysis of actinide-bearing material.     

Advances in Hybrid Composites for Photocatalytic Applications: A Review

Heterogeneous photocatalysts have garnered extensive attention as a sustainable way for environmental remediation and energy storage process. Water splitting, solar energy conversion, and pollutant degradation are examples of nowadays applications where semiconductor-based photocatalysts represent a potentially disruptive technology. The exploitation of solar radiation for photocatalysis could generate a strong impact by decreasing the energy demand and simultaneously mitigating the impact of anthropogenic pollutants. However, most of the actual photocatalysts work only on energy radiation in the Near-UV region (<400 nm), and the studies and development of new photocatalysts with high efficiency in the visible range of the spectrum are required. In this regard, hybrid organic/inorganic photocatalysts have emerged as highly potential materials to drastically improve visible photocatalytic efficiency. In this review, we will analyze the state-of-art and the developments of hybrid photocatalysts for energy storage and energy conversion process as well as their application in pollutant degradation and water treatments.     

Method for the degradation of dibutyl phthalate in water by gamma-ray irradiation

The degradation and mineralization of dibutyl phthalate (DBP), one of endocrine disruptors, by g-ray irradiation were demonstrated. The degradation was enhanced by the effective energy conversion of g-rays to low-energy electrons and photons with the assistance of the interactions between g-rays and metals, which is especially in the case of high Z materials effective. Numerical simulations using EGS code supported the experimental results. Improvements of the energy conversion process are also suggested by controlling the shape of the metal and its spatial configuration in the DBP solution.     

石墨烯/聚吡咯纳米纤维超级电容器电极材料的制备及其电化学性能

超级电容器因其具有较高的循环稳定性和较好的能量密度而成为储能器件中的研究热点,其电极材料及制备方法是决定超级电容器电化学性能的关键因素。 本文以聚环氧乙烷-聚环氧丙烷-聚环氧乙烷三嵌段共聚物(P123)为软模板,通过一步原位聚合法成功地制备了石墨烯/聚吡咯纳米纤维(GR/PPy NF)复合超级电容器电极材料。 通过X射线衍射(XRD),X射线光电子能谱(XPS)、透射电子显微镜(TEM)和傅里叶变换红外光谱仪(FT-IR)等对复合材料的结构和形态进行了系统的表征。 利用电化学方法对GR/PPy NF复合电极材料的电化学性能进行了系统的分析。 结果表明,在电流密度0.5 A/g下,纳米复合材料的比电容量高达969.5 F/g,在充放电600圈之后,仍可保留初始比电容的88%,展示了良好的电容性能及循环稳定性。 GR/PPy NF制备简单,性能优异,是一种很有前途的能量转换/存储材料。     

Characterization and electrochemical applications of a carbon with high density of surface functional groups produced from beer yeast

Carbon materials enriched with nitrogen and oxygen surface functional groups were obtained by pyrolyzing strained beer yeast at 750 °C under an inert atmosphere. Physical and surface properties of the carbon obtained were characterized by X-ray powder diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, Raman spectrometry, and X-ray photoelectron spectroscopy. Results show that the carbon possesses an amorphous structure, a spherical morphology, and a high density of surface functional groups. Electrochemical properties were evaluated by cyclic voltammetry, a galvanostatic charge–discharge technique, and electrochemical impedance spectroscopy. The carbon has 989.65 mAh·g⁻¹ of initial discharge capacity and a stable cycle performance for a Li–C cell. A specific capacitance of 120 F·g⁻¹ was obtained for a single carbon electrode and good cycle performance was achieved for a symmetrical supercapacitor fabricated using this carbon. These carbons derived from strained beer yeast have promising applications in energy storage and conversion systems.     

Integrating Perovskite Solar Cells into a Flexible Fiber

Perovskite solar cells have triggered a rapid development of new photovoltaic devices because of high energy conversion efficiencies and their all‐solid‐state structures. To this end, they are particularly useful for various wearable and portable electronic devices. Perovskite solar cells with a flexible fiber structure were now prepared for the first time by continuously winding an aligned multiwalled carbon nanotube sheet electrode onto a fiber electrode; photoactive perovskite materials were incorporated in between them through a solution process. The fiber‐shaped perovskite solar cell exhibits an energy conversion efficiency of 3.3 %, which remained stable on bending. The perovskite solar cell fibers may be woven into electronic textiles for large‐scale application by well‐developed textile technologies.     

Synthesis of Nickel Lysine Salen Complex and Its Catalytic Performance for Styrene Epoxidation

Nickel lysine salen complex was successfully synthesized via a stepwise procedure and applied as a heterogeneous catalyst for styrene epoxidation. For comparison, several other transition metal (Mn, Fe, Co, and Cu) lysine salen complexes were also synthesized. The prepared catalysts were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX). Data obtained by FT-IR and Raman spectroscopy indicated the formation of C=N bonds and the complexation of these bonds with metal ions. SEM analysis revealed that the complexation of metal ions with the C=N involves the change in surface morphology of samples. In addition, atomic percent composition of samples was obtained from EDX spectra, which was the complementary evidence for the formation of complexes. Results of catalytic measurements showed that a high conversion of styrene (91.51%) and selectivity to styrene oxide (91.99%) could be achieved over the nickel lysine salen complex with tert-butyl hydroperoxide as the oxidant. When the catalyst was reused the conversion of styrene decreased but the selectivity to styrene oxide still remained high.     

Composite electrolytes based on poly(ethylene oxide) and binary ionic liquids for dye-sensitized solar cells

The sunlight is the largest single available source of clean and renewable energy to ensure human society’s sustainable development. Owing to their low production cost and high energy conversion efficiency, dye-sensitized solar cells (DSSCs) have been regarded as good alternatives to conventional photovoltaic devices. Herein, a series of composite electrolytes based on poly(ethylene oxide) (PEO) and the binary ionic liquids 1-propyl-3-methy-imidazolium iodide ([PMIm]I) and 1-ethyl-3-methylimidazolium thiocyanate ([EMIm][SCN]) were prepared and then applied to fabricate six DSSCs. The composite electrolytes were characterized by fourier transform infrared spectroscopy (FTIS), X-ray diffraction (XRD), and electrochemical impedance spectra (EIS). It was shown that the addition of binary ionic liquids would reduce the degree of crystallinity of PEO, thus improving the ionic conductivities of the electrolytes by about 2 orders of magnitude. Investigation on the photovoltaic performances of these DSSCs showed that the fill factor (FF) could reach up to 0.67 and energy conversion efficiency (η) could reach up to 4.04% under AM 1.5 full sunlight (100 mW/cm2).     

Trigonal pyramidal CuInSe2 nanocryastals derived by a new method for photovoltaic applications

Copper indium selenide (CuInSe₂) nanocrystals with trigonal pyramidal shape are synthesized by a two-step process for photovoltaic applications. Structural, morphological and optical properties of the as-synthesized CuInSe₂ nanocrystals are characterized by using powder X-ray diffraction analysis, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-Vis absorption spectroscopy. Results indicate that the monodispersed nanocrystals show a single phase polycrystalline and the size of the trigonal pyramid is in the range of 10-12 nm, and the average composition ratio of the Cu/In/Se is measured to be 1.0:1.2:2.0. It is also investigated that the size and morphology of the CuInSe₂ nanocrystals can be tuned through a manipulation of the reaction time. Under an illumination of the simulated AM 1.5, the as-fabricated hybrid solar cell based on the P3HT/CuInSe₂ nanocrystals blends exhibits a promising open circuit voltage (V_oc) of 0.42 V and its energy conversion efficiency is as 3 times as that of the solar cell fabricated by only the naked P3HT polymer.     

Glass fibre sizing effect on dynamic mechanical properties of cyanate ester composites I. Single frequency investigations

In order to investigate sizing effect in composite materials, we studied three types of composites, with different sizings. Dynamic mechanical analysis appeared to be a good way to characterize the α relaxation process of composites and their interphases. Results showed that α relaxation temperature shifted to higher temperatures for composites without sizing. Study of sizing extract/resin blend showed too that interphase was a mixture of polyvinyl acetate and cyanate resin. The results allow us to deduce that a plastification effect of resin by sizing could occur, with modification of crosslink density. Moreover, we can think that all resin is affected by sizing and the conversion rate in interphase is not total.     

High capacity SnxSbyCuz composite anodes for lithium ion batteries

To increase the volumetric discharge capacity of negative electrode for rechargeable lithium batteries, a composite anode Sn_xSb_yCu_z has been synthesized by using high energy mechanical ball milling method. The synthesized composite anode materials have been characterized by X-ray diffraction and SEM analysis. The charge/discharge characteristics of the fabricated coin cells have been evaluated galvanostatically in the potential range 0.01–2 V using 1 M LiPF₆ in 1:1 EC/DEC as electrolyte. Results indicate that the composition with 90 wt% Sn, 8 wt% Sb and 2 wt% Cu delivers an average discharge capacity of 740 mAh g⁻¹ over the investigated 50 cycles which is a potential candidate for use as an anode material for lithium rechargeable cells.