Single-Shot 3D Topography of Transmissive and Reflective Samples with a Dual-Mode Telecentric-Based Digital Holographic Microscope

Common path DHM systems are the most robust DHM systems as they are based on self-interference and are thus less prone to external fluctuations. A common issue amongst these DHM systems is that the two replicas of the sample’s information overlay due to self-interference, making them only suitable for imaging sparse samples. This overlay has restricted the use of common-path DHM systems in material science. The overlay can be overcome by limiting the sample’s field of view to occupy only half of the imaging field of view or by using an optical spatial filter. In this work, we have implemented optical spatial filtering in a common-path DHM system using a Fresnel biprism. We have analyzed the optimal pinhole size by evaluating the frequency content of the reconstructed phase images of a star target. We have also measured the accuracy of the system and the sensitivity to noise for different pinhole sizes. Finally, we have proposed the first dual-mode common-path DHM system using a Fresnel biprism. The performance of the dual-model DHM system has been evaluated experimentally using transmissive and reflective microscopic samples

Deposition of EDOT-Decorated Hollow Nanocapsules into PEDOT Films for Optical and Electrochemical Sensing

Hollow nanocapsules (NCs) with 1 nm thin porous walls offer unique possibilities for chemical and biosensor design. When used as containers for reagents for optical or electrochemical sensors, e.g., a catalyst, an indicator dye, or a redox mediator, their nanometer-thin porous wall holds and protects the valuable cargo but, at the same time, warrants unhindered bidirectional transport for analyte, substrate, and reaction product molecules. However, the practical utility of such NCs requires an immobilization method that retains the inherent advantages of the reagent loaded NCs. Here, we report an immobilization possibility, namely, the covalent attachment of the reagent loaded NCs to a conductive polymer (PEDOT) film, that overcomes the disadvantages of the incorporation of the NCs in a gel-like supporting matrix which is the most common immobilization method. It required the decoration of the NC surfaces with EDOT moieties that could be copolymerized with free EDOT molecules electrochemically onto electrode surfaces. The EDOT-substituted nanocapsules used in this work were loaded with the indicator dye Nile Blue or an in situ synthesized iron(II) tris(2,2′-bipyridine) complex (Fe(bpy)3) prior to their immobilization. The presence and distribution of the nanocapsules in electrochemically deposited PEDOT films were demonstrated by digital microscopy, SEM, and XPS depth profiling

Differences in Electrochemically Deposited PEDOT(PSS) Films on Au and Pt Substrate Electrodes: A Quartz Crystal Microbalance Study

Studying the responses of potassium ion-selective electrodes with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), PEDOT(PSS), as solid contact (SC) revealed significant differences in the equilibration times and standard potentials of the electrodes fabricated on Au or Pt as substrate electrodes. To trace the source of these differences, PEDOT(PSS) films were deposited under the same conditions onto Au and Pt electrodes on the surface of 10 MHz quartz crystals. During the galvanostatic polymerization, the frequency decrease of the quartz crystal was monitored by an electrochemical quartz crystal microbalance (EQCM). In the initial 15 seconds of the electrochemical deposition, the rate of PEDOT(PSS) polymer growth was significantly faster on Au compared to Pt although the current density used for the deposition was the same. Consequently, the total frequency change after a given electrolysis time was always larger on Au compared to Pt, indicating a larger deposited mass or PEDOT(PSS) layer thickness. The differences in the thicknesses of the PEDOT(PSS) films on Au and Pt could be quantitatively confirmed by X-ray photoelectron spectroscopy (XPS) etching studies. Scanning electron microscopy (SEM) analysis of PEDOT(PSS) films on Au and Pt also showed characteristic differences

A facile preparation of sulfur doped nickel–iron nanostructures with improved HER and supercapacitor performance

Since the use of diverse synthesis approaches can induce the variation in the density of active sites, which impacts electrocatalytic performance, the strategy utilized to fabricate the electrode materials for energy devices is just as important as the materials themselves. Herein, porous NiFe-oxide nanoflowers (NiFe-NFs) and macroparticles (NiFe-MPs) and corresponding S-doped NiFe-oxide nanoflowers (NiFeS-NFs) and macroparticles (NiFeS-MPs) were fabricated using facile co-precipitation and hydrothermal-sulfurization strategies, respectively. The prepared NiFe-NFs, NiFeS-NFs, NiFe-MPs, and NiFeS-MPs materials were investigated for their electrocatalytic HER in 1 M KOH electrolyte. The results indicated that NiFe-NFs displayed an overpotential of 177 mV @ 10 mA/cm2 for HER, whereas the NiFe-MPs, having similar composition, exhibited a high HER overpotential of 187 mV @ 10 mA/cm2. The enhanced HER catalytic performance of NiFe-NFs was attributed to the extensive exposure of active sites at the edges and vertices of nanocubes in the NFs-architecture. Moreover, after sulfurization, NiFeS-NFs and NiFeS-MPs demonstrated a considerable enhancement in their HER activity (54 mV and 152 mV @ 10 mA/cm2, respectively) as compared to un-sulfurized materials, which can be attributed to the enhanced conductivity of materials after S-doping, as supported by theoretical studies. Further, the capacitance experiments showed a significant increment in specific capacitances of NFs and MPs after sulfurization, from 69 to 604 F/g and from 185 to 514 F/g, respectively. This work shows that morphological and compositional changes in metal oxide-based materials may considerably enhance their catalytic activity and capacitance

Pyridine catalyzed acylation of electrospun chitosan membranes by C6-C12 acyl chlorides: Effect of reaction time and chain length

Chitosan nanofiber membranes manufactured via electrospinning are attractive for drug delivery applications due to their increased surface area. The as-spun fibers contain trifluoroacetate (TFA)-salts that cause swelling and loss of nanofiber structure in physiological solutions and are cytotoxic. Here, a post-electrospinning treatment has been reported using fatty acyl chlorides and pyridine to O-acylate the membranes with different acyl chain-length (C6, C8, C10, and C12). The O-acylation reactions were carried out with acyl chlorides in a basic environment for 2 hr, 3 hr, 4 hr and, 5 hr. The effects of the acyl chain length and the reaction time were assessed using various physio-chemical characterization techniques including FTIR, NMR, Contact Angle, XPS, and SEM. The acylated nanofibers displayed hydrophobic properties and allowed the removal of the cytotoxic TFA salts without compromising the nanofibrous structure. The fiber diameter increased with the increasing length of the substituted acyl chain. The degree of substitution of the acyl chains did not change significantly when reacted for a longer period indicating the completion of the reaction within 2 hr. This could allow the faster modification of the membranes for potential application in the delivery of hydrophobic drugs

Tuning the electrochemical properties of nanostructured CoMoO4 and NiMoO4 via a facile sulfurization process for overall water splitting and supercapacitors

In contemporary society, there are many different ways that energy is used in daily life. From applications that require a high energy density to long-term storage in a stable manner, the requirements for energy usage are diverse. Therefore, the greater the number of uses a designed material exhibits, the more practical it may be for wide-scale manufacture. Two areas of particular interest for energy applications are fuel cells (to generate energy) and supercapacitors (to store energy). To provide cheaper and more durable alternatives for energy storage, electrodes containing CoMoO4, NiMoO4, CoMoS4, and NiMoS4 were synthesized. The electrodes were synthesized through a hydrothermal method using Ni-foam as the substrate then tested as electrocatalysts for water splitting and electrodes for supercapacitor. As an electrocatalyst for hydrogen evolution reaction, NiMoS4 displayed the lowest overpotential of 148 mV with a Tafel slope of 159 mV/dec. On the other hand, CoMoS4 showed the lowest overpotential of 189 mV with a Tafel slope of 78 mV/dec among all four samples for oxygen evolution reactions. In terms of energy storage, the CoMoO4 had the highest specific capacitance of 2652 F/g at a current density of 0.5 A/g with an averaged charge retention of 91% and a Coulombic efficiency of 99% after 10,000 cycles

Pomegranate: An eco-friendly source for energy storage devices

With an increasing demand for energy and concerns about the environment, scientists are trying to find a better way to generate green energy and store the generated energy efficiently. Biowaste could be an attractive source for the preparation of active materials for energy storing devices. In this project, a shell of pomegranate was used to prepare high surface area carbon for supercapacitor applications. The dry powder of pomegranate was chemically activated using various ratios of pomegranate and activating agent to produce carbon with a range of properties. The unactivated pomegranate-based carbon\u27s surface area was 40 m2/g, which improved to 1459, 1737, and 2189 m2/g upon chemical activation using 1:1, 1:2, and 1:3 ratios of pomegranate: activating agent, respectively. The energy storage capacity was calculated using galvanostatic charge-discharge measurements, and the highest specific capacitance of 190 F/g at 1 A/g was observed for PG-2 (1:2 ratio of pomegranate: activating agent) carbon. Using the electrode, the symmetric supercapacitor devices were fabricated utilizing various electrolytes (aqueous, organic, and ionic liquid electrolytes). The highest energy density of 8.8, 39, and 68 Wh/kg were obtained for aqueous, organic, and ionic liquid electrolytes, respectively. On the other hand, the highest power density of 3950, 8943, and 11,316 W/kg have been achieved for the pomegranate-based carbon in aqueous, organic, and ionic liquid electrolytes, respectively. Our research suggests that pomegranate-based carbon could be an attractive material for the fabrication of energy storage devices

Polystyrene activated linear tube carbon nanofiber for durable and high-performance supercapacitors

With increasing demand for sustainable energy, it is essential to develop low cost, high performance, and environment-friendly materials for energy storage application. Metal oxides and sulfides are mostly being used as electrode materials for energy storage devices. However, their wide applications are precluded due to their higher cost, low stability, and adverse effect on the environment. Therefore, development of environment-friendly supercapacitors with low cost, high performance, and stable performance is a big challenge. Here, we report surface engineered carbon nanofibers for durable and high-performance supercapacitor. Surface engineered carbon nanofibers showed the highest specific capacitance of 277 F/g (at 1 mV/s), along with superior flexibility and cyclic stability. Moreover, they showed high energy and power density of 30.5 Wh/kg and 8.3 kW/kg, respectively. The cyclic stability showed almost 100% retention in charge storage capacity up to 5000 cycles. Electrochemical properties of a fabricated symmetrical supercapacitor device using these carbon nanofibers showed improved charge storage capacity at elevated temperatures. The charge storage capacity improved by over 150% by increasing temperature from 10 to 60 °C. Our results suggest that surface engineered carbon nanofibers could be a potential candidate for higher performance and durable supercapacitors