Surface Area For Electron Transfer Research Articles

Advanced Two-Dimensional Materials for Green Hydrogen Generation: Strategies toward Corrosion Resistance Seawater Electrolysis─Review and Future Perspectives

Excessive usage of nonrenewable resources to meet global energy requirements has become a serious concern from the energy and environmental perspective. The continuous emission of CO2 in the environment from fossil fuels has become a major cause of global warming. Green hydrogen generation through seawater electrolysis has been an emergent technology that can play a prominent role in replacing conventional energy sources. Electrolysis of seawater using renewable sources such as solar, wind, and geothermal generates green hydrogen which has almost negligible harmful byproducts. Different ions present in seawater such as chlorides and sulfates impose serious corrosion problems during the electrolysis process as chloride ions penetrate the metal electrode surface and oxidize it and also liberate chlorine gas at the anode. For the electrolysis processes, catalysis plays a challenging task to reduce the kinetic barrier for the conversion of water molecules to hydrogen and oxygen products. Photoelectrocatalysts are another kind of semiconductor-based catalyst in which band gap, exchange charge carrier, and surface area play key roles in the water-splitting process. Two-dimensional nanomaterials offer many advantages like high specific surface area for electron transfer, high tunable functionalities, and flexible structural properties that make them suitable for different applications. Layered double hydroxide (LDH) as a highly efficient catalyst has the potential to perform the hydrogen production process as per the industrial application. LDH has many advantages in an effective water-splitting mechanism that includes easy synthesis methods, flexible morphology, long-term stability, and adaptability to different applications. Another major advantage is the corrosion inhibition property of LDH by different mechanisms like adsorption of corrosion-responsible ions, self-healing technique, and protective film formation which are discussed briefly in this review. This review provides a state-of-the-art analysis about the various important strategies to be adopted for effective seawater electrolysis. Finally, we examine the new challenges and the novel approaches to suppress corrosion processes during seawater electrolysis.

Spherical montmorillonite-supported molybdenum disulfide nanosheets as a self-sedimentary catalyst for organic pollutants removal

Water containing organic and carcinogenic pollutants has become a serious environmental problem, threatening the life of the aquatic ecosystem and human beings. Molybdenum disulfide (MoS2), especially monolayered MoS2 sheets, has been proven as an effective catalyst for degradation of organic contaminants due to its more exposed edges and active sites for electron transfer. However, monolayered MoS2 nanosheets easily aggregate due to their high surface energy and strong π-π electron interaction, heavily affecting the catalytic performances. In addition, monolayered MoS2 nanosheets with small tiny size are difficult to recover from the mixture, restricting the capacity of recyclability and further mass application. Herein, we solved these issues via supporting the small tiny MoS2 nanosheets on spherical montmorillonite (SMt). The SMt can not only provide large pore volume and specific surface area for supporting abundant MoS2 but also reduce the fouling and enhance the transport during the mass production process. The prepared microspheres exhibited a high catalytic activity towards organic pollutants including methylene blue (MB) and 4-nitrophenol (4-NP) in the presence of NaBH4 due to the strong adsorption capacity of SMt and the large catalytic surface area for electron transfer. Furthermore, the micro-sized granular catalyst can be facile recovered and reused without any devices involved due to the excellent self-sedimentary capacity and large size. Moreover, the catalytic performance and the morphology were almost unaltered after recycling 20 times. Our straightforward strategy to solve the issues through porous micro-sized self-sedimentary SMt supporting tiny monolayered MoS2 nanosheet with high catalytic activity facilitates the practical application of these kinds of catalyst towards the reduction of organic and carcinogenic pollutants.

Carbon nanohorns/nanotubes: An effective binary conductive additive in the cathode of high energy-density zinc-ion rechargeable batteries

Manganese oxide (MnO2) is proven to be an efficient cathode material in zinc-ion batteries (ZIBs). However, its poor electronic conductivity strongly limits the performance of Zn–MnO2 batteries. In order to improve performance beyond typical graphitic carbon additives, a binary conductive additive, a combination of carbon nanohorns (CNHs) and carbon nanotubes (CNTs), is added into the MnO2 electrode to establish high-speed electron-channels in the CNTs/CNHs network with an efficient “line-to-surface-to-point” microstructure. In this electrode, the high aspect-ratio CNTs create a conducting highway for the collected charges, while the CNHs provide extra surface area for electron transfer. Moreover, the specific surface area of the electrode increases due to the introduction of CNHs, which increases the Zn2+ diffusion coefficient. As a result, the corresponding battery reaches a high specific capacity (343 mAh g−1 at 0.3 A g−1), excellent rate performance (191.3 mAh g−1 at 3 A g−1) and long-life cycle. Moreover, it achieves an admirable specific energy density of 466 W h kg−1, together with a peak power density of 9.4 kW kg−1 (normalized to the weight of MnO2), the performance of which is among the best reported ZIBs. This work reveals new pathways to improve the performance of MnO2 cathodes for ZIBs.

Photocatalytic Evaluation of the ZrO2:Zn5(OH)6(CO3)2 Composite for the H2 Production via Water Splitting

The present work studies the effect of zirconium dioxide addition in hydrozincite (Zn5(OH6)(CO3)2). The composites samples shows an efficient photocatalytic activity for H2 production under UV light irradiation and employing methanol as a sacrificial reagent. The composites were synthesized in one-pot method, dried to 100 °C and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), elemental mapping by SEM and transmission electron microscopy (TEM). The most active composite with 3 mol% of ZrO2 exhibited a H2 production of 1908 μmol g−1 h−1 and an apparent quantum yield (AQY) of 41%. The photoactivity is attributed to the formation of heterojunctions, it is confirmed by the characterization techniques. The heterojunctions result in a synergic effect, the hydrozincite provides a wide surface area for electron transfer while the zirconium dioxide inhibits the recombination through the photogenerated holes attraction.

Incorporating electrospun nanofibers of TEMPO-grafted PVDF-HFP polymer matrix in viologen-based electrochromic devices

A novel polymer, denoted as TP-X, is synthesized by grafting 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) onto the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) backbone. TP-X was electrospun into a nanofibrous polymer matrix and introduced into viologen-based electrochromic devices (ECDs). Heptyl viologen (HV) was chosen as the electrochromic material and TEMPO was added as the stable redox couple in the ECDs in this study. The results show that the addition of TP-X nanofibers (TP-X NF) effectively reduced the aggregation of HV and the grafted TEMPO moieties provide the extended surface area for electron transfer. The reduction in viologen aggregation led to outstanding stability and the extended electron transfer surface area resulted in fast write-erase response for ECDs with TP-X NF polymer matrix. The optimized ECD containing the TP-10 NF showed fast write-erase response times of 2.3 and 1.5 s for bleaching and coloring at 605 nm, respectively. More importantly, the incorporation of TP-10 NF gave improved stability of the ECDs, which retained more than 83% of its initial transmittance change at 605 nm after 10,000 operation cycles, as compared to the conventional solution-type ECD (27.3%). This study provides a potential polymer matrix to be utilized in various electrochemical applications for pursuing decent performance and reliable stability.

A novel carbon tipped single micro-optrode for combined optogenetics and electrophysiology.

Optical microelectrodes (optrodes) are used in neuroscience to transmit light into the brain of a genetically modified animal to evoke and record electrical activity from light-sensitive neurons. Our novel micro-optrode solution integrates a light-transmitting 125 micrometer optical fiber and a 9 micrometer carbon monofilament to form an electrical lead element, which is contained in a borosilicate glass sheathing coaxial arrangement ending with a micrometer-sized carbon tip. This novel unit design is stiff and slender enough to be used for targeting deep brain areas, and may cause less tissue damage compared with previous models. The center-positioned carbon fiber is less prone to light-induced artifacts than side-lit metal microelectrodes previously presented. The carbon tip is capable of not only recording electrical signals of neuronal origin but can also provide valuable surface area for electron transfer, which is essential in electrochemical (voltammetry, amperometry) or microbiosensor applications. We present details of design and manufacture as well as operational examples of the newly developed single micro-optrode, which includes assessments of 1) carbon tip length–impedance relationship, 2) light transmission capabilities, 3) photoelectric artifacts in carbon fibers, 4) responses to dopamine using fast-scan cyclic voltammetry in vivo, and 5) optogenetic stimulation and spike or local field potential recording from the rat brain transfected with channelrhodopsin-2. With this work, we demonstrate that our novel carbon tipped single micro-optrode may open up new avenues for use in optogenetic stimulation when needing to be combined with extracellular recording, electrochemical, or microbiosensor measurements performed on a millisecond basis.

Gold particles growth on carbon felt for efficient micropower generation in a hybrid biofuel cell

In this study, homogeneously dispersed gold particles growth onto carbon felt were fabricated by electrodeposition method followed by a thermal treatment at 1000°C under nitrogen. The thermal treatment induced the dewetting of gold and the formation of well-crystallized gold particles that exhibited large surface area. The structural properties of the resulted Au@CF material were evaluated by SEM, XRD and TGA. We studied the electrocatalytic properties of this new gold material through the abiotic glucose oxidation in alkaline medium and the enzymatic dioxygen electroreduction by the enzyme bilirubin oxidase. Finally, we showed the potentiality of the resulting Au@CF material to build a 3-dimensional glucose hybrid biofuel cell by assemblying an abiotic anode with an enzymatic cathode. The system exhibited high electrochemical performance with an open circuit voltage of 0.71V and a maximum power density of 310μWcm−2 at 352mV (by taking into account the projected surface area), in spite of a low gold loading (0.2wt%). The advance presented in this work is the efficiency of the synthesis technique to get a new free-standing material for electrocatalysis based on gold particles with high reactive surface area for electron transfer and macropores for diffusion transport.

Chemical oxidation polymerization and characterization of poly ortho-anisidine nanoparticles

Poly o-anisidine (POA) is a conductive polymer that can conduct electrons by a π-conjugated system. POA is a derivative of polyaniline, however, it still exhibits low electrical conductivity. This work is focused on the improvement of electrical conductivity of POA by synthesizing POA in nanoparticle forms using an anion as a dopant. POA nanoparticles were obtained from chemical oxidation polymerization using an ammonium persulfate as an oxidant and a sodium dodecyl sulfate (SDS) as a surfactant for controlling POA size and shape. The properties of the POA nanoparticles were characterized by FT-IR, UV-Vis spectroscopy, TGA, and SEM. POA nanoparticles shapes were nano-fibers with a diameter varying from 63 to 129 nm depending on the polymerization temperature, polymerization time, and SDS concentration. The electrical conductive obtained varied from 0.022 to 168 S/cm, a variation of 4 orders of magnitude, depending on the POA nanoparticle size and SDS concentration. The smallest POA nanoparticle size provided the highest electrical conductivity because of the larger surface area for electron transfer. Thus, this work demonstrated the extremely high electrical conductivity of the synthesized nano-fiber shape POA which have not previously been reported elsewhere.

Fabrication of Conductive Microparticles as Anodal Electrode in Microfluidic Microbial Fuel Cell

Microbial fuel cell (MFC) is developed as a renewable energy source, which can simultaneously carries out wastewater treatment. The ability of microorganism in generating extractable electricity highly affects the performance of a MFC; therefore, it is critical to construct a high throughput analysis platform for microorganism screening. Microfluidic MFCs are recently developed for the rapid analysis; however, several challenges remained to be overcome to construct straightforward techniques. This study presents an innovative anode composed of conductive microparticles for encapsulating electricity-generating microbes in microfluidic MFCs. The conductive polymer microparticles (Diallyldimethylammonium chloride, DADMAC) encapsulating microorganisms were generated by a T-junction microchannel. The surface area per volume of the pDADMAC micro-particle was 2.17x106 cm-1 and it can provide extensive surface area for electron transfer. We first examined the electricity generated from these particles using a batch-type operation. Microparticles containing microbes generated open circuit voltage (OCV) of 8mV in the first hour and the OCV gradually decreased to 0mV in 6hours, indicating the depletion of substrate. Particles without microbes had relatively stable OCV around 1mV throughout the operation except for the first 10min. The conductive microparticles were also applied in an air-cathode batch-type MFC and they increased the OCV from ∼0V to ∼20mV compared with freely suspended microorganisms. These results show the great potential of utilizing the conductive microparticles as anodal electrode in microfluidic microbial fuel cells.