Many reactions involve metals, especially noble metals or metal oxides as catalysts. Although metal-based catalysts have been playing a major role in various industrial processes, they still suffer from multiple competitive disadvantages, including their high cost, susceptibility to gas poisoning, and detrimental effects on the environment. Owing to their wide availability, environmental acceptability, corrosion resistance, and unique surface properties, certain carbon nanomaterials have recently been demonstrated to be promising metal-free alternatives for low-cost catalytic processes. This perspective highlights recent progresses in the development of carbon-based metal-free catalysts. Scheme 1. ODH of (1) Ethylbenzene and (2) Alkanes (a) and ORR in Alkaline (b) and Acidic (c) Media

Abstract

As an atomically thin sheet of carbon atoms packed in a twodimensional (2D) honeycomb lattice with excellent electronic, thermal, and mechanical properties, graphene has shown great potential for a wide range of applications. Examples include the use of graphene and its derivatives as transparent conductive electrodes or active materials in solar cells, counter electrodes in dye-sensitized solar cells, electrocatalysts for oxygen reduction in fuel cells, high-performance electrodes in supercapacitors, batteries, actuators, and sensors. [1, 2] Of particular interest, Guo et al. [2f] reported a significant advancement in the development of layered graphene/quantum dots for highly efficient solar cells. Stoller et al.[1j] produced graphene-based supercapacitors free from any conducting filler with a specific capacitance of 135 F g À1 in aqueous electrolytes. We also demonstrated that N-doped graphene could act as a metal-free electrode with a much better electrocatalytic activity, long-term operational stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells.[2b] By using graphene as a superior dimensionally compatible and electrically conductive component, Guo et al. [2g,h] further constructed a smart graphene-based multifunctional biointerface for cell growth as well as in situ selective and quantitative molecular detection. There is now a pressing need to integrate graphene sheets into multidimensional and multifunctional systems with spatially well-defined configurations, and hence integrated systems with a controllable structure and predictable performance. This requires controlled functionalization of graphene sheets at the molecular level, which is still a big challenge.The recent availability of solution-processable graphene by exfoliation of graphite into graphene oxides (GOs), followed by solution reduction, [3] has allowed the functionalization of graphene sheets through various solution reactions.[4] As far as we are aware, however, there is still no report on the asymmetric functionalization of graphene sheets by attaching different chemical moieties to their two opposite surfaces. The asymmetric functionalization, if realized, should significantly advance the self-assembling of graphene sheets into many new multidimensional and multifunctional systems with molecular-level control. Herein, we report for the first time a simple but effective asymmetric modification method for functionalizing the two opposite surfaces of individual graphene sheets with different nanoparticles (NPs) in either a patterned or nonpatterned fashion. The resultant asymmetrically modified graphene sheets with ZnO and Au NPs on their two opposite surfaces were demonstrated to show a strong photodependent diode rectifying behavior.We have previously developed a polymer masking technique for asymmetric functionalization of carbon-nanotube sidewalls by sequentially masking vertically aligned carbon nanotubes twice, with only half of the nanotube length being modified each time. [5,6]...

Nobel metal composite aerogel fibers made from flexible and porous biopolymers offer a wide range of applications, such as in catalysis and sensing, by functionalizing the nanostructure. However, producing these composite aerogels in a defined shape is challenging for many protein-based biopolymers, especially ones that are not fibrous proteins. Here, we present the synthesis of silk fibroin composite aerogel fibers up to 2 cm in length and a diameter of ~300 μm decorated with noble metal nanoparticles. Lyophilized silk fibroin dissolved in hexafluoro-2-propanol (HFIP) was cast in silicon tubes and physically crosslinked with ethanol to produce porous silk gels. Composite silk aerogel fibers with noble metals were created by equilibrating the gels in noble metal salt solutions reduced with sodium borohydride, followed by supercritical drying. These porous aerogel fibers provide a platform for incorporating noble metals into silk fibroin materials, while also providing a new method to produce porous silk fibers. Noble metal silk aerogel fibers can be used for biological sensing and energy storage applications.

Principles of sealed iron flow batteries are introduced and a semi-empirical model that incorporates the hydrogen evolution reaction and electrolyte rebalancing is developed. Hydrogen generation rates are measured using pressure measurements in sealed vessels. Electrolyte dynamics with and without electrolyte rebalancing are simulated and discussed, and a good agreement is found between measured and simulated pressure responses. The sealed battery system with in-tank rebalancing demonstrates stable operation at low hydrogen partial pressure during 10 days and 100 cycles at ± 100 mA cm −2 at room temperature.

In this paper, an electrochemical impedance spectroscopy (EIS) model for flowing electrosorptive slurry electrodes is developed. The model takes into account the current that is induced by the convection of surface charge carried by particles in the slurry. The use of this model facilitates the in situ characterization of critical slurry electrode properties including the conductivity, the electronic diffusivity, and the contact resistance. When applied to experimental results from an electrochemical flow capacitor (EFC), the model allowed for the discernment of a decrease in the slurry's electronic conductivity with increasing flow rate, an increase in contact resistance, and a rise in the electronic diffusivity. The in situ determination of these properties is essential for the selection of optimal slurry compositions and operating conditions for any electrochemical cell that uses flowing slurry electrodes. Slurry electrodes have become increasingly important in modern electrochemical systems. Examples of systems enhanced and enabled by slurry electrodes include flow batteries, 1-5 flow capacitive deionization (FCDI) systems, 6-8 and electrochemical flow capacitors (EFCs).9-10 Much as is the case in conventional porous electrodes, the physical properties of the slurry (e.g. specific capacitance and electronic conductivity) determine the ultimate performance of these systems. The in situ determination of these slurry properties in actual electrochemical cells is therefore essential for optimization of slurry compositions.In order to quantify these properties, EIS has long been applied to a wide variety of fluidized bed and slurry electrodes.11-15 None of the papers, however, took into account the effect that the convection of the surface charge has on the resulting impedance.10,17 The work of Gabrielli, et al., 11 for example, looked exclusively at fluidized bed electrodes, where velocities are small and, hence, the convective effect is negligible. Similarly, Youssry, et, al. 13 examined slurry electrodes in a membrane-less cell with no inlets or outlets, thereby eliminating any effects of the convective current mechanism. Petek, et al.14 considered flowing electrosorptive slurries and pointed out that convective current does have an effect on the EIS spectra, but no attempt was made to quantitatively address the effect. Instead, the EIS spectra were analyzed at high frequencies only, where convection is irrelevant and the slurry acts as a quasi-steady porous electrode.To truly characterize a slurry for use in an EFC or other slurry electrode application, the current induced by convection is of paramount importance as it controls the low frequency behavior, and, hence, the steady-state performance. Any proper EIS model of a flowing slurry electrode system must therefore take this effect into account. This paper develops the mathematical models that are necessary to fully characterize slurry electrode performance and introduces an equivalent circuit element that can be used to quantify slurry electrode propert...

Hierarchically structured platinum macrotubes with square cross‐section and porous sidewalls composed of fibril textured nanoparticles are synthesized from high aspect ratio insoluble Mangus’ salt needles in a single reduction step. Macrotubes 10’s to 100’s of micrometers long pressed into free‐standing films exhibit a specific capacitance of 18.5 Fg−1 and a solvent accessible specific surface area of 61.7 m2g−1. Insoluble salt templates offer a synthesis route to achieve a range of porous metal structures.

Per- and polyfluoroalkyl substances (PFAS) are a class of chemicals used in various commercial industries to include food packaging, non-stick repellent, and waterproof products. International environmental protection agencies are currently looking for ways to detect and safely remediate both solid and aqueous PFAS waste due to their harmful effects. Incineration is a technique that disposes of chemicals by breaking down the chemicals at high temperatures, upwards of 1400 °C. Incineration has been used on other related compounds, but PFAS presents a challenge during thermal degradation due to the molecular stability and reactivity of fluorine. Research on the efficacy of this method is currently limited, as the degradation byproducts of PFAS are not fully characterized. Current research is mostly focused on the development of benchtop methods for the safe remediation of solid PFAS waste. Aqueous fire fighting foams (AFFFs) have garnered significant attention due to extensive use since development in the 1960s. Numerous communities that are closely located near airports have been shown to have higher than average PFAS contamination from the repeated use. Detection and remediation of surface, subsurface, and wastewater have become a primary concern for environmental agencies. Use of electrochemical techniques to remove the PFAS contaminants has shown recent promise to help address this issue. Critical to the remediation efforts is development of standardized detection techniques and the implementation of local and international regulations to control the production and use of fluorinated products. No single solution has yet been developed, but much progress has been made in recent years in governmental regulation, detection, and remediation techniques.