Dye-sensitized solar cells (DSSCs) are regarded as prospective solar cells for the next generation of photovoltaic technologies and have become research hotspots in the PV field. The counter electrode, as a crucial component of DSSCs, collects electrons from the external circuit and catalyzes the redox reduction in the electrolyte, which has a significant influence on the photovoltaic performance, long-term stability and cost of the devices. Solar cells, dye-sensitized solar cells, as well as the structure, principle, preparation and characterization of counter electrodes are mentioned in the introduction section. The next six sections discuss the counter electrodes based on transparency and flexibility, metals and alloys, carbon materials, conductive polymers, transition metal compounds, and hybrids, respectively. The special features and performance, advantages and disadvantages, preparation, characterization, mechanisms, important events and development histories of various counter electrodes are presented. In the eighth section, the development of counter electrodes is summarized with an outlook. This article panoramically reviews the counter electrodes in DSSCs, which is of great significance for enhancing the development levels of DSSCs and other photoelectrochemical devices.

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Counter electrodes in dye-sensitized solar cells

Room-temperature (RT) gas sensing is desirable for battery-powered or self-powered instrumentation that can monitor emissions associated with pollution and industrial processes. This review (with 171 references) discusses recent advances in three types of porous nanostructures that have shown remarkable potential for RT gas sensing. The first group comprises hierarchical oxide nanostructures (mainly oxides of Sn, Ni, Zn, W, In, La, Fe, Co). The second group comprises graphene and its derivatives (graphene, graphene oxides, reduced graphene oxides, and their composites with metal oxides and noble metals). The third group comprises 2D transition metal dichalcogenides (mainly sulfides of Mo, W, Sn, Ni, also in combination with metal oxides). They all have been found to enable RT sensing of gases such as NOx, NH3, H2, SO2, CO, and of vapors such as of acetone, formaldehyde or methanol. Attractive features also include high selectivity and sensitivity, long-term stability and affordable costs. Strengths and limitations of these materials are highlighted, and prospects with respect to the development of new materials to overcome existing limitations are discussed.

A review on chemiresistive room temperature gas sensors based on metal oxide nanostructures, graphene and 2D transition metal dichalcogenides

Gas barrier performance of graphene/polymer nanocomposites

Due to its exceptionally outstanding electrical, mechanical and thermal properties, graphene is being explored for a wide array of applications and has attracted enormous academic and industrial interest. Graphene and its derivatives have also been considered as promising nanoscale fillers in gas barrier application of polymer nanocomposites (PNCs). In this review, recent research and development of the utilization of graphene and its derivatives in the fabrication of nanocomposites with different polymer matrices for barrier application are explored. Most synthesis methods of graphene-based PNCs are covered, including solution and melt mixing, in situ polymerization and layer-by-layer process. Graphene layers in polymer matrix are able to produce a tortuous path which works as a barrier structure for gases. A high tortuosity leads to higher barrier properties and lower permeability of PNCs. The influence of the intrinsic properties of these fillers (graphene and its derivatives) and their state of dispersion in polymer matrix on the gas barrier properties of graphene/PNCs are discussed. Analytical modeling aspects of barrier performance of graphene/PNCs are also reviewed in detail. We also discuss and address some of the work on mixed matrix membranes for gas separation.

Gas Barrier Performance of Graphene/Polymer Nanocomposites

This review focuses on some recent advances made in the field of gas sensors based on polyaniline [PANI], a conducting polymer with excellent electronic conductivity and electrochemical properties. Conducting polymers represent an important class of organic materials with an enhanced resistivity towards external stimuli. Among them, PANI polymers have attracted wide interest because of the versatility in their use, combined with the easy of synthesis, high yield and good environmental stability, together with a favorable response to guest molecules at room temperature. Moreover, PANI can be shaped into various structures with different morphologies and the possibility of obtaining nanofibers, in addition to thin films, has opened a rapid development of ultrasensitive chemical sensors, with improved processability and functionality. This review provides a brief description of the current status of gas chemiresistive sensors based on polyaniline and highlights the properties and applications of these devices in diverse range of applications.

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Chemiresistive polyaniline-based gas sensors: A mini review

High-level gentamicin resistance and vancomycin resistance in enterococci, a family of important opportunistic pathogens, have emerged as a significant clinical problem over recent years. The present study was conducted to determine the high-level gentamicin and vancomycin resistance among the clinical isolates of enterococci. A total of 110 phenotypically identified enterococcal isolates were subjected to determination of high-level gentamicin resistance (by disk diffusion and agar dilution methods) and vancomycin resistance (by agar screening and agar dilution methods). About 36% of the isolates were found to have high-level gentamicin resistance, which indicates that gentamicin no longer remains an appropriate choice for inclusion in combination therapy with cell wall-active agents. Ten percent isolates exhibited resisance to vancomycin during screening. However, agar dilution confirmed that the isolates did not have resistance to vancomycin but had reduced susceptibility to it, which indicates their impending emergence of resistance to vancomycin.

High-level gentamicin resistance and vancomycin resistance in clinical isolates of enterococci in a tertiary care hospital in eastern Nepal.

Incorporation of non-conjugated polymer chain in conjugated polymer matrix: A new single step strategy for free standing non-volatile polymer memory

Memory and ferroelectric photovoltaic effects arising from quasi-reversible oxidation and reduction in porphyrin entrapped aminopropyl-silicate films

The effect of different milling time on thermoelectric properties of bismuth telluride (Bi2Te3) was investigated. The nanomaterial was prepared by varying the ball milling time and followed by hot press sintering. The crystal structure and phase formation were verified by X-ray diffraction and Raman Spectroscopy. The experimental results show that electrical conductivity increases whereas thermal conductivity decreases with increasing milling time. The negative sign of seebeck coefficient indicate the n-type nature with majority charge carriers of electrons. A maximum figure of merit about 0.55 is achieved for l5hr ball milled Bi2Te3 sample. The present study demonstrates the simple and cost-effective method for synthesis of Bi2Te3 thermoelectric material at large scale thermoelectric applications.

Effect of ball milling time on thermoelectric properties of bismuth telluride nanomaterials

Bismuth Telluride (Bi2Te3) nanocrystalline material was synthesized using high energy planetary ball-mill at 600 RPM. The Reitveld refined X-ray diffraction pattern of the powder samples confirms the formation of pure Bi2Te3 phase with the particle size of∼58nm. The effect of sintering temperature on the thermoelectric property of the ball-mill sample was studied by sintering the material at 450°C and 550°C. The thermoelectric properties of the sintered pellets were measured in the temperature range of 30-350°C using various characterization techniques. The samples exhibit maximum power factor value of 3mW/m-K and 2.4mW/m-K for the sintering temperature of 450°C and 550°C, respectively. We achieved maximum figure-of-merit (ZT) of 0.8 at 350°C in case of sample sintered at 450°C which is attributed to the better power factor value in this sample.

P. Jha

Papers

High-level gentamicin resistance and vancomycin resistance in clinical isolates of enterococci in a tertiary care hospital in eastern Nepal.

Incorporation of non-conjugated polymer chain in conjugated polymer matrix: A new single step strategy for free standing non-volatile polymer memory

Memory and ferroelectric photovoltaic effects arising from quasi-reversible oxidation and reduction in porphyrin entrapped aminopropyl-silicate films

Effect of ball milling time on thermoelectric properties of bismuth telluride nanomaterials

Tailoring of thermoelectric properties in Bi2Te3 by varying the sintering temperature