Gas sensors are fundamental for continuous online monitoring of volatile organic compounds. Gas sensors based on semiconductor materials have demonstrated to be highly competitive, but are generally ...made of expensive materials and operate at high temperatures, which are drawbacks of these technologies. Herein is described a novel ethanol sensor for room temperature (25 °C) measurements based on hematite (α‑Fe
O
)/silver nanoparticles. The AgNPs were shown to increase the oxide semiconductor charge carrier density, but especially to enhance the ethanol adsorption rate boosting the selectivity and sensitivity, thus allowing quantification of ethanol vapor in 2-35 mg L
range with an excellent linear relationship. In addition, the α-Fe
O
/Ag 3.0 wt% nanocomposite is cheap, and easy to make and process, imparting high perspectives for real applications in breath analyzers and/or sensors in food and beverage industries. This work contributes to the advance of gas sensing at ambient temperature as a competitive alternative for quantification of conventional volatile organic compounds.
Efficient dispersion of M-N-C molecular macrocycles on carbon nanomaterials support is an attractive strategy to develop a highly efficient and noble metal-free Oxygen Reduction Reaction (ORR) ...electrocatalyst for fuel cell devices. Herein, Cobalt Phthalocyanine (CoPc)/reduced graphene oxide (rGO) nanocomposite has been synthesized through non-covalent functionalization of CoPc and GO followed by electrochemical reduction of the resulting hybrid. A comprehensive structural, topographic and morphologic study on the nanocomposite confirmed the GO and CoPc assembly based on π-π interaction and electrochemical reduction leads to enhanced dispersion of CoPc aggregates by breaking its microparticles into nanoclusters. A chemical mapping of the catalysts surface by Confocal Raman Imaging further proved that CoPc and GO phase is homogeneously distributed and impregnated into each other as a result of the electrochemical reduction. The ORR activity of the CoPc/rGO was evaluated through voltammetry and amperometry techniques, which revealed a synergic ORR catalysis at the composite surface highlighted by larger current densities, 300 mV positive shift of the onset potential, and negligible generation of H2O2 as compared to CoPc and GO. In addition, the composite material revealed better stability and resistance to methanol poisoning than a commercial Pt/C catalyst, and such features make it ideal for application in methanol fuel cells.
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•Bimetallic molecular catalysts supported on graphene is synthesized.•Electrochemical activation promotes dispersion of the catalytic sites.•The composite exhibited high ORR efficiency & stability in ...neutral medium.•DFT calculations predict a sandwich configuration with correlated electron density.•O2 interaction on a metal site depends on the other neighboring metal in the sandwich.
Noble-metal-free macrocycles dispersed on a carbonaceous support are a promising alternative to expensive Pt-based electrocatalysts to revolutionize the market outreach of low-cost clean energies technologies like fuel cells. Herein, a new composite material made of two transition metal phthalocyanines (MPc; M: Co, Fe) immobilized on a graphene support is presented as efficient and stable electrocatalyst for the oxygen reduction reaction (ORR). Electrochemical activation breaks the microparticles of MPcs into nanoclusters, facilitating their homogeneous dispersion on the support. The catalytic performance of the composite examined in oxygen-saturated KNO3 revealed tetra-electronic behavior and superior ORR activity compared to the similar loading of Pt/C catalyst. Moreover, high stability and negligible interference from methanol on the ORR response of the composite make it an ideal catalyst for direct methanol fuel cell. Density Functional Theory (DFT) calculations provide insights into the composite structure, revealing preferred arrangements in which two MPc sandwich graphene, and into the ORR mechanism in such configurations. The simulations revealed intricate interplay of interaction strengths between the composite's metal ions and ORR intermediates and O2, demonstrating that mixture of MPc facilitates higher ORR efficiency. Such enhancement is attributed to charge redistribution in sandwiched configurations, causing localization of dipoles on MPc.
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The energy requirement of modern society increases every day. The depletion of the reserves of fossil fuel combined with the deleterious effects of CO2 in the atmosphere is forcing all the world to ...search for alternative ways of generation and storing energy. Many scientists around the world are pursuing different forms to produce and store energy. Solar and wind sources are a reality for production of electricity, but are not continuous and require storage devices. The development of batteries and hybrid supercapacitors of high energy and power density is of great importance to complement this requirement of energy storage. Rechargeable metal–air batteries which utilize oxygen electrocatalysis seem to be an ideal choice, once the source of energy is not intermittent as solar and wind energy and is based on oxygen bifunctional electrocatalysis of both oxygen reduction and O2 evolution reactions. In addition, water splitting allows the conversion and storage of solar/wind energy into chemical energy, generating fuels with high energy content. From this perspective, spinel MnCo2O4-based materials are promising structures for energy storage and conversion of energy. In this review, the use of low cost and abundant multifunctional materials for the development of supercapacitor devices and batteries was summarized. Completely, the design of electrocatalysts for water splitting and their capability to proportionate the tetra-electronic process of the oxygen reduction reaction are reviewed, including the main strategies in the preparation of these materials and considering their key multifunctional role in the way to a more sustainable society.
The frenetic global development is improving the average quality of life in an unprecedented way, but at the expense of increasing pressure on natural resources, environmental pollution and energy ...demand, which are being exacerbated by population growth and industrialization in developing countries. The energy demand probably is the one contributing the most to such a situation, thus urging the development of clean and renewable alternative energy sources in order to avoid an imminent energy crisis in the near future. A possible solution is a society in which most energy needs are fulfilled by photoinduced or electrochemical water-splitting, storing solar energy as hydrogen and dioxygen gas, and releasing the chemical energy in fuel cells while regenerating water. However, the oxygen evolution reaction (OER) and the oxygen reduction reaction taking place respectively in water-splitting and fuel cells are quite sluggish because of their multielectronic and multiprotonic nature. Catalysts such as IrO
2
and RuO
2
are being successfully used as state-of-the-art OER electrocatalysts but such noble metal-based materials are severely limited by their scarcity and high cost. Thus, noble metal free electro/photocatalysts are being eagerly pursued to provide more sustainable alternatives. In this context, vanadium-based and vanadium-containing electro and photocatalysts based on hydroxides/oxyhydroxides/oxides, vanadates, chalcogenides and nitrides stand out among the most promising alternatives, and recent advances have demonstrated their key role in enhancing the catalytic activity by strong synergic electronic and structural effects. In fact, such high-performance materials have potential in the fabrication of fuel cells and photosynthetic devices competitive enough in converting chemical energy into electricity and solar energy into solar fuel, enabling large-scale production, storage and usage of the infinite energy of the sun in a more convenient and safe manner. Perspectives are also provided on the preparation, evaluation of synergic effects in OER electro/photocatalytic activity, and their correlation with the electronic and crystalline structure of the materials, as well as on the electrode material design.
This review summarizes the recent progress in vanadium-containing catalysts, including the synthesis strategies and performance in electrocatalytic and photocatalytic oxygen evolution.
Environmentally friendly energy sources such as solar and wind power as alternatives to fossil fuels are strategic for meeting the energy needs of an increasingly demanding population, but they are ...periodic or intermittent in nature, making energy storage devices fundamental for the realization of a sustainable society. Thus, the quest for much higher power and energy dense devices, especially hybrid supercapacitors, as alternatives to lithium-ion batteries, has been scaling up since the combining of the outstanding power density of supercapacitive materials with the high energy density of battery-type materials into a single device. Despite their high resistance, transition metal oxides are promising electrode materials for use in devices, since their rich electrochemistry can be activated by three main strategies to boost the specific charge capacity, charge-discharge and ion diffusion kinetics, and cyclability of devices
via
: (a) the incorporation of hetero-atoms that generate trimetallic oxides, (b) nanostructuration
via
hierarchical core@shell furry and mesoporous systems, and (c) combination with other materials to generate nanocomposites. These strategies, especially those leading to highly porous 3D core@shell architecture nanomaterials, are very successful, where trimetallic oxides, and ternary
T
LDHs and multicomponent systems, realized
via
the combination of mono- and/or bimetallic oxides and hydroxides, have demonstrated exceptionally good performances as electrode materials, presenting bright new perspectives for the future of hybrid energy storage devices.
The main strategies to impart synergistic catalytic effects to trimetallic oxide/layered double hydroxide materials are discussed: (a) heteroatom incorporation, (b) the formation of nanocomposites, and (c) hierarchical core@shell nanostructuration.
Understanding the structure and origin of catalytic sites at the nanometer/subnanometer scale in porous nanomaterials is essential for an efficient and durable catalyst design. Herein, chemically ...pure nanoporous gold (NPG) having a hierarchically porous network is electrochemically synthesized, and its microstructure is investigated by electron microscopies, electrochemical methods, and ab initio simulations to unravel the identification of catalytic sites for ascorbic acid (AA) electrochemical oxidation. Experimental characterizations reveal a highly porous NPG film containing polycrystalline and interconnected dendrite fractals. The film growth follows a unique pattern such that at the beginning of the film growth, Au grains are smaller, which at the later growth stage become larger and expose low-index facets and structural defects such as dislocation of Au atoms, atomic steps, and kinks. Such structural defects and facet evolutions in the NPG film cause a remarkable electrocatalytic effect toward the electrochemical oxidation of AA, which is interpreted based on density function theory (DFT) simulation. The simulation predicts stronger binding of AA on the low-indexed Au facets and grain boundaries, leading to a larger electronic charge transfer from AA to the Au atoms. In particular, grain boundary regions provide vacancy-like sites, in which part of AA locks itself, forming a stronger bond with a Au atom of partial covalent character. The low catalytic activity of the thermodynamically stable (111) facet is assigned to its flat topography, over which AA interacts through mainly van der Waals forces, causing weaker binding.
Herein, the promising world of nanoporous gold (NPG) as an electrode material for energy storage and conversion is reviewed. NPG has excellent conductivity and a porous structure, providing a huge ...active surface area for deposition of transition metal atoms and electrochemically active materials. Moreover, NPG materials display high intrinsic activity because of their crystallographic structural defects to catalyze hosts of electrochemical reactions, considered pertinent in clean energy technologies. Therefore, taking into account their superior specific and mass activity, they provide a versatile platform for developing high‐performance catalysts for oxidation and reduction reactions, supercapacitors, and battery‐type electrode materials for the assembly of high density electric energy storage devices. Initially, a full overview of the strategies used to build NPG structures and incorporate other metallic elements in the pore walls is presented. Afterward, the water‐splitting parameters and performance of NPG catalysts for hydrogen generation are reviewed. Next, the possibility of using such porous materials as fuel cell electrodes is discussed. In short, the most recent advancements in the field paving the way for the preparation of advanced electrode materials meeting the most stringent requirements are reviewed, demonstrating the bright perspectives for innovation in the key area of energy conversion and storage.
The promising world of nanoporous gold (NPG) as an electrode material for energy storage and conversion is reviewed. In short, the most recent advancements in the field paving the way for the preparation of advanced electrode materials meeting the most stringent requirements are reviewed, demonstrating the bright perspectives for innovation in the area.
This work presents new insights on the electrocatalytic reduction of 2,4,6-trinitrotoluene (TNT) on carbon nanotubes (CNTs)-modified electrodes (multi-walled carbon nanotubes and double-walled carbon ...nanotubes). Cyclic voltammetry showed at least 5-fold current increase in the electrochemical reduction of TNT on GCE modified with pristine (“as received”) CNTs. The improved performance was also verified after 60 s of accumulation and scanning using adsorptive stripping voltammetry, with slope values 20-fold higher. Acid functionalization removed residual metals from CNTs and reduced their surface area. Hence, the improved electrochemical response of TNT on pristine CNTs seems to be not only due to surface roughness (electroactive area) but mainly originating from residual metallic catalysts on CNTs. The modified electrode with pristine CNTs was applied for the determination of TNT residues on different surfaces contaminated with the explosive, showing its applicability for forensic investigations.
The high demand for energy by our society, and consequent large consumption of fossil fuel, is leading not only to its depletion but also to increasing environmental pollution, thus urging the ...development of clean and renewable energy sources such as based in solar energy and water in a cyclic way, by photoinduced water-splitting and regeneration in fuel cells. This means being in command of the tetra-protonic and tetra-electronic reaction mechanism of the oxygen evolution reaction, a formidable challenge that is starting to be overcome using catalysts based on more abundant and inexpensive elements. Interestingly, the most promising ones in this context are low-cost materials based on NiFe, NiCo and NiV-LDH precursors, highly flexible and tunable materials that would enable large-scale production, storage and utilization in a more convenient and safe manner. In fact, the vast majority of high performance electrocatalysts based on ternary LDHs are being produced by doping of that matrix with Co
2+/3+
and V
2+/3+/4+
ions to modulate the electronic and structural properties of NiFe-LDH metal sites, thus reducing the OER overpotentials while activating and increasing the concentration of active sites and improving the OER rate. On the other hand, the V ion coordination geometry can be distorted from octahedral to tetrahedral and used to induce very strong electronic effects to the neighboring transition metal ions to adjust the metal-oxygen bond energy in the transition state to the expected optimal value, and optimize the O
2
release in the OER process. Finally, nanostructuration and deposition on suitable conducting materials generating nanocomposites can be used as additional strategies to enhance further the conductivity as well as the concentration and number of available active sites, while facilitating the electrolyte diffusion, thus improving their electrocatalytic performances. In short, catalysts for oxygen evolution reaction based on ternary LDHs were reviewed considering their key role in the way to a more sustainable society.
The recent advances in ternary layered double hydroxide electrocatalysts, including the strategies used for the design, synthesis, and evaluation of their performance for oxygen evolution reaction are reviewed in this account.
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