Conversion Of Chemical Energy Research Articles

(Invited) Electrocatalysis and Photoelectrochemistry Based on Modified Titanium Dioxide Nanomaterials

With an ever-increasing population, the importance of industrial processes to ensuring enough food and energy are produced to meet increasing demand cannot be understated. Unfortunately, these processes often produce byproducts that become waste and cause ecological damage. A large concern arises when these waste products enter the water system, resulting in serious consequences for the environment. Various methods have been explored towards the removal of these pollutants. Catalysis plays a key role in chemical production, energy conversion and storage, air purification, water treatment, food processing, and the life sciences. In this presentation, we report on the preparation and modification of TiO2 nanostructured materials as advanced electrocatalysts and photocatalysts for environmental applications and water disinfection. TiO2 nanopores and nanotubes were directly grown on a titanium substrate using anodization processes. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction were employed to characterize the formed TiO2 nanostructures. The electrocatalytic and photocatalytic activities of the nanoporous and nanotubular TiO2 were investigated by the degradation of phenolic pollutants and lignin, a byproduct of the pulp and paper industry, as the model pollutants. The formed TiO2 nanostructures were further treated using electrochemical methods in enhance their catalytic activities. The effectiveness of electrochemical and photoelectrochemical degradation of phenolic species and lignin was determined by UV-Visible spectroscopy and total organic carbon analyzer. The effect of the growth time, the morphology, and the electrochemical treatment on the performance of the formed nanoporous and nanotubular TiO2 is discussed. In addition, the increasing lack of drinking water around the globe is of great concern. The synergistic effect of the integration of photocatalysis and electrocatalysis on bacterial disinfection is highlighted.

Operando Insights into Nanoparticle Transformations during Catalysis

Nanostructured materials play an important role in today’s chemical industry, acting as catalysts in heterogeneous thermal and electrocatalytic processes for chemical energy conversion and the prod...

Coherent Bragg imaging of 60 nm Au nanoparticles under electrochemical control at the NanoMAX beamline.

Nanoparticles are essential electrocatalysts in chemical production, water treatment and energy conversion, but engineering efficient and specific catalysts requires understanding complex structure-reactivity relations. Recent experiments have shown that Bragg coherent diffraction imaging might be a powerful tool in this regard. The technique provides three-dimensional lattice strain fields from which surface reactivity maps can be inferred. However, all experiments published so far have investigated particles an order of magnitude larger than those used in practical applications. Studying smaller particles quickly becomes demanding as the diffracted intensity falls. Here, in situ nanodiffraction data from 60 nm Au nanoparticles under electrochemical control collected at the hard X-ray nanoprobe beamline of MAX IV, NanoMAX, are presented. Two-dimensional image reconstructions of these particles are produced, and it is estimated that NanoMAX, which is now open for general users, has the requisites for three-dimensional imaging of particles of a size relevant for catalytic applications. This represents the first demonstration of coherent X-ray diffraction experiments performed at a diffraction-limited storage ring, and illustrates the importance of these new sources for experiments where coherence properties become crucial.

Novel g-C3N4/g-C3N4 S-scheme isotype heterojunction for improved photocatalytic hydrogen generation

Rationally designing heterostructure is a promising way to promote the charge carrier separation of intrinsic photocatalysts, thus contributes the improvement of solar to chemical energy conversion. Herein, a novel isotype heterojunction consisted of MCN and UCN, respectively derived from hydrothermally-treated melamine and urea, was synthesized. Owing to the well compatibility and matched band structure, an S-scheme charge transfer mechanism is confirmed for working on MCN/UCN isotype heterojunction, thus endowing strong redox ability, efficient charge carrier separation efficiency and prolonged lifetime. As a result, MCN/UCN exhibits improved photocatalytic water splitting activity under visible light irradiation, which displays approximately 5.5 and 1.8-fold enhancement as compared to the pure MCN and UCN, respectively. The rationally synthesized S-scheme isotype heterojunction will pave the way for developing highly efficient g-C3N4-based photocatalysts.

Noble‐Metal‐Free Colloidal‐Copper Based Low Overpotential Water Oxidation Electrocatalyst

AbstractWater oxidation catalysis is gaining more attention in recent times owing to its potential for solar and chemical energy conversion and for green fuel generation. The overwhelming hurdle in this quest is to develop a noble‐metal‐free, efficient, low overpotential water oxidation electrocatalyst exhibiting tremendous stability and to be obtained from earth‐abundant materials. We show here unique copper‐based water oxidation electrocatalyst derived from thin film Cu‐colloidal nanoparticles and is highly efficient, robust for water oxidation. The catalyst advantageously exhibits nanobeads and nanorods type mixed morphological features with narrow size distribution. The onset for oxygen evolution reaction occurs at a small potential of 1.45 VRHE (η=220 mV) which is the lowest observed relative to other copper‐based materials. The catalyst also maintains remarkable stability during long‐term water electrolysis experiments. Moreover, the catalyst shown to exhibit a high electroactive area with a Tafel slope of 52 mV dec1−, high TOF of 0.81 s1− and mass activity of 87 mA mg−1. Copper is an interesting material because it can also serve as CO2 reduction catalysts at the cathode side. The straightforwardly prepared, handy, and inexpensive Cu‐based electrocatalytic system is a flexible catalyst for electrooxidation of water and for chemical energy conversion and is an attractive alternative to Pt, Ir, and Ru based electrocatalysts obtained from expensive resources and tedious methods.

Review of the principal mechanisms, prospects, and challenges of bioelectrochemical systems

AbstractBioelectrochemical systems (BES) are commonly utilized to generate green electricity, chemicals, and materials through bioelectrocatalytic processes. Over the years, the growing interests in low carbon energy, wastes valorization and the sustainable bioremediation of environmental pollutants have generated interests in BES such as microbial fuel cells (MFC) and bioelectrochemical fuel cells (BFC). The MFCs are the most advanced BES that can ensure the microbial conversion of chemical energy into electrical energy. Therefore, this article seeks to review and present valuable literature on the fundamental operational principles, mechanisms and understanding of BES such as MFCs. It seeks to highlight the schematics of these systems along with the processes and mechanisms such as the oxidation of organic substrates ranging from acetate compounds to complex mixtures. Furthermore, the prospects, challenges, and future applications of BES technologies are presented. The findings indicate that BFCs and MFCs are hampered by low efficiencies, energy output, mass transfer, porosity, and proton conductivity of the electrode and membrane materials along with mechanical strength, scalability, biocompatibility, and chemical stability. However, BES could potentially impact on clean energy production, greenhouse gases mitigation, wastewater treatment, bioanalysis, biosensors, and environmental remediation in the future.

On the Conversion Efficiency of CO2 Electroreduction on Gold

Benjamin A. Zhang is a PhD student at Harvard University. His research focus is on the control of mass transport and concentration gradients in electrochemical reactions, in particular CO2 reduction, through nano- and mesostructuring of electrodes. Cyrille Costentin is Professor at Universite Paris Diderot. He received his undergraduate education at Ecole Normale Superieure de Cachan and his PhD at Universite Paris Diderot. He is currently a Visiting Scientist in the group of D.G. Nocera at Harvard University. His interests include mechanisms and reactivity in electron transfer chemistry with particular emphasis on proton-coupled electron transfer and catalysis of electrochemical reactions. Daniel G. Nocera is the Patterson Rockwood Professor of Energy at Harvard University. His group studies mechanisms of biological and chemical energy conversion.

Построение туннельных осесимметричных сверхзвуковых воздухозаборников

Актуальность работы. Эффективность преобразования химической энергии топлива в механическое движение сверхзвукового летательного аппарата определяется потерями механической энергии на сопротивление летательного аппарата и потерями полного давления при торможении потока в воздухозаборнике воздушно-реактивного двигателя. Поэтому при прочих равных условиях более энергоэффективным будет тот летательный аппарат, у которого эти потери меньше. Существенное повышение энергоэффективности ожидается от применения осесимметричных изоэнтропических туннельных воздухозаборников. В рамках модели невязкого течения предлагается численная методика построения указанных воздухозаборников с профилированным центральным телом и цилиндрической обечайкой. Цель работы. В настоящее время отсутствуют способы профилирования осесимметричных изоэнтропических туннельных воздухозаборников, не имеющих элементов, выступающих за цилиндрический корпус летательного аппарата. Поэтому целью исследования является разработка методики построения таких воздухозаборников. Методы исследования. Используется численная реализация метода характеристик при условии изоэнтропичности течения. Предлагаемая методика состоит из двух задач. В первой задаче от угловой точки строится контур центрального тела с заданной ординатой точки фокусировки характеристик. Во второй задаче производится построение оставшейся части контура до другой угловой точки, при этом используется обращенное течение в кольцевом сопле с цилиндрической обечайкой. Одновременно с решением второй задачи определяется положение обечайки. Центральное тело может содержать на краях по угловой точке. При использовании промежуточной линии тока центральное тело будет гладким. Результаты. Создана методика для расчета семейства контуров осесимметричных туннельных сверхзвуковых воздухозаборников, геометрические характеристики которых однозначно описываются исходными данными.

Direct Ammonia-Fueled Solid Oxide Fuel Cells

Ammonia, as a hydrogen carrier, has a much higher volumetric energy density than hydrogen and can be safely handled and distributed in a liquid form at an ambient temperature with a pressure greater than 1MPa. Similar to hydrogen, a clean-burning ammonia potentially can be used for power generation with zero greenhouse gas emissions. A Solid Oxide Fuel Cell (SOFC), typically operating at a temperature of 700ºC – 900ºC, has been widely acknowledged by the R&D society for a direct conversion of chemical energy of fuels (e.g. hydrocarbon fuels, ammonia, etc.) into electricity at a proven efficiency as high as 60%. Lowering the SOFC operating temperature to 700°C or below potentially enables considerable cost reduction with opportunities of using inexpensive materials for constructing SOFC systems that otherwise could not be considered. However, the corresponding SOFC inevitably faces challenges of higher electrode polarization losses and electrolyte ohmic losses, as well as reduced electrode catalytic activities. Chemtronergy is actively pursuing the development of the anode-supported SOFC technology capable of operating directly on the ammonia fuel at a temperature below 650ºC for reliable power generation. This talk will cover discussions of cell materials design and ammonia catalyst consideration for the mitigation of the increased polarization losses and ammonia reaction with the nickel-based anode, respectively, caused by lowering operating temperatures. Materials implementation and validation on both button cells (2 cm2) and single cells (100 cm2) over time will also be presented.

Solar to chemical energy conversion using titania nanorod photoanodes augmented by size distribution of plasmonic Au-nanoparticle

Amid a substantial development of plasmonic noble metal sensitized TiO2 nanostructure based photoanodes used in solar to chemical energy conversions, two key considerations to further enhance the broad spectrum photocurrent are the reduction in the recombination of photogenerated charge carriers at the interface and an amplification of local electric field near the interface to promote the surface plasmon resonance mediated hot electron injection. We present in this article the enhanced photo-activity of sputtered Au nanoparticles (Au-NPs) of different size distribution attached to the hydrothermally grown TiO2 nanorod (TiO2-NRs) arrays which well addresses the above two considerations. A six fold increase in the device photocurrent is complemented by a homogeneous distribution of Au-NP centered at 15 nm led hot electron transfer into the titania conduction band. The present combination of the TiO2-NRs and size distributed Au-NP exhibits a charge transfer resistance as low as 1.5 kΩ as compared to 5kΩ in unsensitised electrode which results in a reduced exciton recombination and local field enhancement as confirmed by finite difference time domain based simulation. The enhanced solar water splitting capability is also demonstrated.

A comprehensive review on thermochemical, biological, biochemical and hybrid conversion methods of bio-derived lignocellulosic molecules into renewable fuels

In this review, the conversion (thermochemical, biological and hybrid) of chemical energy chiefly enclosed in biomass structures i.e. as 30–50% cellulose, 15–35% hemicellulose and 10–20% lignin into various forms of fuels/energy products is comparatively analyzed. Cellulose and hemicelluloses formulate almost ∼70% of the biomass and are definitely linked to the lignin structural units all the way through covalent and hydrogenic bonds; thereby, the structure formulated is tremendously rigid and resistive against processing. Hence, the vital confront towards the conversion of lignocellulosic biomass into important bio-yields via biorefining is to overcome this obstacle. This article gives an outlook over the major conversion technologies to produce biofuels from lignocellulosic biomass feedstock, by focusing on their typical performances. The core points outlined and argued will be the currently positioned pathways, utilizing the lignocellulosic materials to produce (bio) fuels, prospect on biomass supplies, and discussion on the impact of sustainability criteria, main influencing factors and uncertainties.

Enhanced photocatalytic performance of poly(3,4-ethylenedioxythiophene)-coated TiO2 nanotube electrodes

This study presents the design of a mixed organic–inorganic system to be utilized in solar-light chemical energy conversion applications, where the visible-light absorption properties of the conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), are combined with the enhanced charge transport properties of TiO2 nanotubes, thus creating an efficient photoelectrode. A dispersion of PEDOT doped with p-toluenesulfonate (tosylate) ions was synthesized using a simple solution-casting polymerization process, which was then spin-coated onto an ordered array of anodically fabricated TiO2 nanotubes to be used for solar energy conversion. Electron microscopy observation confirmed the presence of PEDOT in the hybrid (PEDOT–TiO2) and Fourier transform infrared spectroscopy verified the vibrational modes of the polymerized PEDOT. The ultraviolet-visible diffuse reflectance data indicated a change in the absorption edge of the pure TiO2 nanotubes to longer wavelengths after PEDOT coating. The developed photo-electrodes exhibited a significant increase in photocurrent response and lower charge transfer resistance with respect to the pure TiO2 nanotubes, as verified by electrochemical impedance spectroscopy.

Metal Nanoclusters: New Paradigm in Catalysis for Water Splitting, Solar and Chemical Energy Conversion.

A sustainable future demands innovative breakthroughs in science and technology today, especially in the energy sector. Earth-abundant resources can be explored and used to develop renewable and sustainable resources of energy to meet the ever-increasing global energy demand. Efficient solar-powered conversion systems exploiting inexpensive and robust catalytic materials for the photo- and photo-electro-catalytic water splitting, photovoltaic cells, fuel cells, and usage of waste products (such as CO2 ) as chemical fuels are appealing solutions. Many electrocatalysts and nanomaterials have been extensively studied in this regard. Low overpotentials, catalytic stability, and accessibility remain major challenges. Metal nanoclusters (NCs, ≤3 nm) with dimensions between molecule and nanoparticles (NPs) are innovative materials in catalysis. They behave like a "superatom" with exciting size- and facet-dependent properties and dynamic intrinsic characteristics. Being an emerging field in recent scientific endeavors, metal NCs are believed to replace the natural photosystem II for the generation of green electrons in a viable way to facilitate the challenging catalytic processes in energy-conversion schemes. This Review aims to discuss metal NCs in terms of their unique physicochemical properties, possible synthetic approaches by wet chemistry, and various applications (mostly recent advances in the electrochemical and photo-electrochemical water splitting cycle and the oxygen reduction reaction in fuel cells). Moreover, the significant role that MNCs play in dye-sensitized solar cells and nanoarrays as a light-harvesting antenna, the electrochemical reduction of CO2 into fuels, and concluding remarks about the present and future perspectives of MNCs in the frontiers of surface science are also critically reviewed.

Boosting CO2 photoreduction activity by large Fresnel lens concentrated solar light

CO2 photoreduction to hydrocarbons is an important process for solar energy. Herein, the reaction rate is massively pushed up by large Fresnel lens (diameter = 1 m) concentrating solar light technology. The maximum CH4 yield rate reached 3157.2 μmol·g−1·h−1, C2H4 rate to 511.6 μmol·g−1·h−1, C2H6 to 1346.0 μmol·g−1·h−1, and the CO2 conversion reached 3.94%. The total solar to chemical energy conversion efficiency got 0.15%. The results are considered from the intensification of reaction conditions such as light intensity, reaction temperature, and pressure of H2O and CO2. The findings will be beneficial for the further discussion of CO2 photoreduction basing upon the existed catalysts system, and decrease the research threshold in CO2 photoreduction.

Visible-light-driven reduction of nitrostyrene utilizing plasmonic silver nanoparticle catalysts immobilized on oxide supports

Abstract The localized surface plasmon resonance (LSPR) mediated enhanced chemical activity can be entitled as a promising strategy for efficient solar to chemical energy conversion. To tune the selectivity of a desired product in a chemical reaction is of paramount importance yet a great challenge. In this paper, a new strategy to effectively enhance the selectivity of the product formation under visible light irradiation is reported. A series of Ag catalysts deposited on metal oxide support materials (TiO2, ZrO2, Al2O3 and CeO2) along with their preparative techniques, optimum metal content ratio and effect of different wavelength of light is explored for the chemoselective reduction of p-nitrostyrene to p-aminostyrene under visible light irradiation. The prepared catalysts were characterized by a range of physicochemical techniques including UV–vis, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The reduction reaction was carried out in ethanolic suspension at room temperature and pressure utilizing ammonia borane (AB) as an in-situ source of H2. The reaction results displayed 100% conversion with a maximum chemoselectivity of 81% shown by Ag/TiO2 under light irradiation conditions. The high chemoselectivity could be attributed to the preferential alignment of polar nitro group on the surface of plasmonic silver under light irradiation conditions.

Rational Design of Holey 2D Nonlayered Transition Metal Carbide/Nitride Heterostructure Nanosheets for Highly Efficient Water Oxidation

AbstractDue to integrated advantages in electrochemical functionalities for energy conversion, 2D nonlayered heterostructure nanosheets offer new and fascinating opportunities for electrocatalysis but their fabrication is challenging when compared with the widely studied 2D layered heterostructure. Herein, a bottom‐up approach is established for facile synthesis of holey 2D transition metal carbide/nitride heterostructure nanosheets (h‐TMCN) with regulated hole sizes by controlled thermal annealing of the Mo/Zn bimetallic imidazolate frameworks (Mo/Zn BIFs). Ex situ phase and structural identifications disclose that the Mo/Zn BIFs precursor experiences interconnected three steps of transformation to produce h‐TMCN. Especially, the slow successive solid‐state diffusion of nitrogen and carbon into immediate noncrystalline molybdenum oxides allows the intergrowth of Mo2C and Mo2N into the 2D nonlayered heterostructure. X‐ray fine structure analysis coupled with high resolution X‐ray photoelectron spectroscopy demonstrate that Mo2C and Mo2N in the microdomains can chemically bond with each other, producing the abundant active N–Mo–C interfaces toward water splitting. Consequently, h‐TMCN affords low overpotentials, high turnover frequencies, rapid charge transfer, and superior long‐term stability toward electrocatalytic water oxidation. The present work demonstrates the feasibility of developing a broad range of 2D nonlayered heterostructures for high efficiency chemical energy conversion.

Analysis of the current state and development of direct carbon fuel cells with an alkaline electrolyte

Among the numerous modern, high-efficiency energy technologies allowing for the conversion of chemical energy of coal into electricity and heat, the Direct Carbon Fuel Cells (DCFC) deserve special attention. These are devices that allow, as the only one among all types of fuel cells, to directly convert the chemical energy contained in solid fuel (coal) into electricity. In addition, they are characterized by high efficiency and low emission of pollutants. The paper reviews and discusses previous research and development works, both around the world and in Poland, into the technology of direct carbon fuel cells with an alkaline (hydroxide) electrolyte.

The Telomerization of 1,3‐Dienes – A Reaction Grows Up

AbstractThe front cover artwork for Issue 04/2019 is provided by researchers from the group for Molecular Catalysis at the Max‐Planck‐Institute for Chemical Energy Conversion (Germany). The image shows an assembly line that symbolizes the versatility and potential selectivity of the telomerization reaction. See the Minireview itself at https://doi.org/10.1002/cctc.201801821.

An internal combustion alternator with both free piston and cylinder

The free-piston generator has more merits than the traditional reciprocating engines, and has been under extensive investigation. This study focuses on the development two novel perspective ideas unlike already advanced the linear free piston generator. These are: (1) to make both piston and cylinder free that provides ideally balancing of the system; (2) to turn from the linear scheme of a generator to rotary design because of simplicity and compactness. The mathematical simulation of operation of the linear two-stroke cycle alternator with both free piston and cylinder was conducted with using the model of zero-dimensional dynamics. Combustion of methane-air mixture with excess air ratio of 1.2 was considered. Both heat and friction losses were taken into account. Operation particularities of such system were analyzed. It was found that oscillation amplitude of moving parts did not exceed of 70 mm at frequency of ∼50 Hz for alternator with following basic parameters: cylinder bore of 80 mm, length of 400 mm, piston length of 120 mm. Mass of both piston and cylinder was chosen identical and equal of 3 kg. It was shown that the efficiency of the chemical energy conversion reached of 46%, and specific power was high as 40 kW/l at compression ratio of 40. The lab scale pneumatic alternator in rotor variant with both free rotor and cylindrical body was assembled for experimental demonstration of rotary design capability. The alternator was fed with compressed air of low pressure below of 6 atm. The electrical power in the load reached of 10 W at input power with intake compressed air about 100 W. The results indicate that alternators with both free piston and cylinder in linear and rotary designs have the potential to achieve high efficiency and provide the vibration – free operation.

Hydrothermal synthesis of Fe[sbnd]Mn bimetallic nanocatalysts as high-efficiency cathode catalysts for microbial fuel cells

High-efficiency cathode catalysts are essential for microbial fuel cell development since they are one of the key components in chemical energy conversion in organic compounds into electricity. Here, novel FeMn bimetallic nanocatalysts are designed and hydrothermally synthesized for microbial fuel cells. Fe:Mn (atom%) = 1:4, 1:2, 1:1, and α-MnO2 are applied in air-cathodes with Pt/C and activated carbon catalysts as benchmarks, and FeMn catalysts can enhance the performance. When Fe:Mn = 1:2, the FeMn2 achieves a maximum power density of 1940 ± 31 mW m−2 in microbial fuel cells and a current density of 19.4 A m−2 at −0.056 V in abiotic electrochemical tests, 24% and 37% higher than Pt/C respectively. Material characteristics are systematically analyzed since they are directly related to the catalytic performance. The high catalytic activity of FeMn2 proves to result from a combination of the weak MnO bonds, large quantity of defects, large specific surface area and high Mn(III):Mn(IV) ratio, according to the proposed possible mechanisms of FeMn catalysts to enhance the output. This work not only puts forwards an easy-to-accomplish method to design and prepare bimetallic nanocatalysts, but also provides a potential alternative to Pt/C in microbial fuel cells for sustainable energy generation.