Conversion Of Chemical Energy Research Articles

Identification of the Translocation Step of a Replicative DNA Polymerase

Replicative DNA polymerases are molecular motors that catalyze template-directed DNA replication. In each catalytic cycle, these enzymes incorporate the correct nucleotide into the primer or growing strand releasing pyrophosphate as a product. As a result of this reaction replicative polymerases translocate along their DNA substrates in steps of one nucleotide at a time (0.34 nm). Although accurate translocation is essential for genome integrity little is known about the kinetics, energetics and integration of this process in the nucleotide addition cycle during processive DNA replication. To address these subjects we have used optical tweezers to manipulate individual Phi29 DNA polymerase-DNA complexes and measure the effect of mechanical force aiding and opposing translocation on the polymerase activity at varying nucleotide (dNTPs) concentrations. Application of controlled forces on a single polymerase biases the rates of chemical reactions involving translocation and provided quantitative information about the ‘real time’ kinetics of elongation and the conversion of chemical energy to motion (mechano-chemistry) during protein activity. Fits to the replication velocity dependencies on force and dNTP concentration were inconsistent with a model for movement incorporating a power stroke tightly coupled to pyrophosphate release. Instead, our data is consistent with a Brownian ratchet model in which the polymerase oscillates between the pre- and post-translocation states separated by ∼0.34 nm. The post-translocation state is energetically favored only by 0.7 KBT but it is further stabilized by the binding of the correct dNTP.

Microbial Fuel Cells for Energy Recovery from Waste

Microbial fuel cells (MFCs) are bioelectrochemical systems which enable the conversion of chemical energy directly into electrical energy with microorganism. Studies focused on using organic materials of waste to increase power production performance. In this study, two different MFC reactors were investigated to produce electricity using domestic wastewater. The highest current and power density were 1385 mA/m 2 and 16 mW/m 2 at Ti-TiO2/Nafion combination with 78% COD removal. Ti-TiO2/CMI7000 assemblies generated 750 mA/m2 of current densities and 5 mW/m2 of power density and HRT of 1 day was found favorable for MFC system.

The Effect of Substrates at Cathodes in Low‐temperature Fuel Cells

AbstractThe direct electrochemical conversion of chemical energy in low‐temperature fuel cells is underpinned by the activity of the catalytic center. The latter, in nanodivided form (either precious or non‐precious), is also influenced by the effect of the support, which serves as electron conductor. Herein, we discuss the relevant physicochemical driving force that leads to a “strong interaction” with substrates of carbon and oxide nature. Due to the interest in the activity and stability, special attention is given to the cathodic process, that is, to the oxygen reduction reaction (ORR).

How Reactive are Metal Surfaces in Solution? A Comparison of the Electrochemical Adsorption of Organic Molecules on Pt At Low Potentials

IntroductionTransition metal surfaces are widely employed as catalysts ofchemical reactions, both at the metal/gas [1] and at the metal/solution [2] interfaces. Well-known examples are ceramic-supportedcatalystsusedingasexhaustsofvehiclestooxidizepartially burnt fuels [3] and metal-based catalysts used in fuelcell devices to promote electrochemical oxidation of organicmolecules for direct conversion of chemical energy into elec-trical energy with high efficiency [4].In this context, the electrochemical oxidation of alcoholshasbeenextensivelystudiedinthelastdecades[5]duetotheirpotentialfor practical applicationsinfuelcells.Directalcoholfuelcell(DAFC),especiallydirectethanolfuelcell(DEFC),isbecominga veryattractivealternative energysourcefor fossilfuel combustion engines due to several advantages, includingits high theoretical efficiency, high energy density of alcohols(comparable to gasoline) [6], and the possibility of energyproduction from renewable sources [7]. However, for theDEFC to become commercially attractive, a few issues mustbeovercome.Oneofthedifficultiesisthatthecurrentstate-of-the-art anodes are not capable of fully oxidizing ethanol toCO

Combination of a photosystem 1-based photocathode and a photosystem 2-based photoanode to a Z-scheme mimic for biophotovoltaic applications.

Combination of a photosystem 1-based photocathode and a photosystem 2-based photoanode to a Z-scheme mimic for biophotovoltaic applications.

Acceleration of Fe2O3 Reduction Kinetics by Wet Methane with Calcium Titanate as Support

Abstract To develop new chemical-energy conversion and storage systems using metal oxides, the kinetics of iron oxide (Fe2O3) reduction by humidified methane using an oxide ion conductor, CaTi1−xFexO3−δ (CTFO), as a support was analyzed. Significant improvements in Fe2O3 reduction rate and lattice oxygen utilization were observed using CTFO, which may be induced by rapid ion transport at the interface between Fe2O3 and CTFO.

CO2 gasification of coal under concentrated thermal radiation: A numerical study

Solar coal gasification is a promising technology to convert coal into gaseous fuel. In this study, a steady-state one-dimensional (1D) two-phase model was developed to simulate CO2 gasification of coal in a quartz fluidized bed reactor directly exposed to concentrated thermal radiation as the heating source. Coupled with chemical kinetics, the present model encompasses energy equations for the gas phase, the solid phase, and the quartz reactor. The discretized energy equations were solved using the Levenberg–Marquardt algorithm. The initial carbon particle size was 140μm and the peak radiative heating flux was as high as 1270kWm−2. The CO2 flow velocity for fluidization was in the range of 0.10 to 4.0mmin-1 under standard conditions (25°C, 1bar). Simulated gas and coal particle temperature distributions, CO production rates, product gas compositions, and coal conversion rates were in good agreement with the experimental data reported in the literature. Furthermore, the present simulation provided insightful explanation on the optimum fluidization velocity for maximum CO production rate or maximum solar to chemical energy conversion. The present simulation also provided an energy balance analysis of the solar CO2 gasification process, which is challenging to conduct in experimental studies.

Oxide semiconductors for solar to chemical energy conversion: nanotechnology approach

The present work considers the application of oxide semiconductors in the conversion of solar energy into the chemical energy required for water purification (removal of microbial cells and toxic organic compounds from water) and the generation of solar hydrogen fuel by photoelectrochemical water splitting. The first part of this work considers the concept of solar energy conversion by oxide semiconductors and the key performance-related properties, including electronic structure, charge transport, flat band potential and surface properties, which are responsible to the reactivity and photoreactivity of oxides with water. The performance of oxide systems for solar energy conversion is briefly considered in terms of an electronic factor. The progress of research in the formation of systems with high performance is considered in terms of specific aspects of nanotechnology, leading to the formation of systems with high performance. The nanotechnology approach in the development of high-performance photocatalysts is considered in terms of the effect of surface energy associated with the formation of nanostructured system on the formation of surface structures that exhibit outstanding properties. The unresolved problems that should be tackled in better understanding of the effect of nanostructures on properties and performance of oxide semiconductors in solar energy conversion are discussed. This part is summarised by a list of unresolved problems of crucial importance in the formation of systems with enhanced performance. This work also formulates the questions that must be addressed in order to overcome the hurdles in the formation of oxide semiconductors with high performance in water purification and the generation of solar fuel. The research strategy in the development of oxide systems with high performance, including photocatalysts for solar water purification and photoelectrodes for photoelectrochemical water splitting, is considered. The considerations are focused on the systems based on titanium dioxide of different defect disorder as well as its solid solutions and composites.

A composite efficiency metrics for evaluation of resource and energy utilization

Polygeneration systems are commonly found in chemical and energy industry. These systems often involve chemical conversions and energy conversions. Studies of these systems are interdisciplinary, mainly involving fields of chemical engineering, energy engineering, environmental science, and economics. Each of these fields has developed an isolated index system different from the others. Analyses of polygeneration systems are therefore very likely to provide bias results with only the indexes from one field. This paper is motivated from this problem to develop a new composite efficiency metrics for polygeneration systems. This new metrics is based on the second law of thermodynamics, exergy theory. We introduce exergy cost for waste treatment as the energy penalty into conventional exergy efficiency. Using this new metrics could avoid the situation of spending too much energy for increasing production or paying production capacity for saving energy consumption. The composite metrics is studied on a simplified co-production process, syngas to methanol and electricity. The advantage of the new efficiency metrics is manifested by comparison with carbon element efficiency, energy efficiency, and exergy efficiency. Results show that the new metrics could give more rational analysis than the other indexes.

Combinatorial approaches for efficient screening of multicomponent photocatalysts and fuel cell catalysts

Environmental issues and fossil fuel demands have propelled renewable energy research and development. Photocatalytic systems are inspired by artificial photosynthesis, which is capable of converting solar energy into chemical energy. Fuel cells, on the other hand, hold great potential for direct conversion of chemical energy into electricity. A rational combination of photocatalytic systems and fuel cells can effectively convert, store and utilize solar energy as compared with hybrid solar cell–battery systems. The critical issues for both the systems are to discover suitable and low-cost catalysts for chemical conversion with high efficiency. In general, catalysts involved with several synergistic components and an optimal recipe for each constituent should be derived. Traditional methods were based on pure empirical and trial-error testing, which are time consuming and labor intensive. Alternative method that can screen catalysts rapidly could be of great importance. In this mini review, preparation of sample arrays with various compositions and libraries suitable for combinatorial characterization is discussed. Next, the focus is on discussing several methods including scanning mass spectrometry, pH imaging and scanning electrochemical microscopy for efficient screening in serial. Successful implementation of these approaches has a potential to open up opportunities for identification and commercialization of efficient solar energy–harvesting catalysts.

Fuel Cells for Autonomous Underwater Vehicles

A long-distance performance is a significant parameter for mobile platforms. A key condition is a highly efficient source of energy. Fuel cells, i.e. electrochemical devices, capable of direct conversion of chemical energy accumulated in fuel into electrical energy, occurred to be relevant. In this paper there were presented the results of the analysis pertaining to the volumetric requirements of the system exploiting the fuel cell that is capable of ensuring the running time comparable with that of conventionally used rechargeable batteries.

High speed imaging of particle flow fields in CFB risers

Particle flows of high particle concentration are important in many fields, including chemical processing, pharmaceutical processing, energy conversion and powder transport. Circulating fluidized beds (CFB) are widely employed in industry because they enhance reaction rates and heat transfer through rapid mixing of particles at high particle concentrations and high particle flow rates. However, despite decades of research and industrial application, the real time behavior of particle flow fields in CFB's is still not well understood. One of the reasons is that experimental data is difficult to acquire in such harsh, opaque environments. In this study, a new high speed particle imaging velocimetry (high speed PIV) technology, developed by the USDOE National Energy Technology Laboratory (NETL), is applied to observe and measure the real time behavior of individual particle motion inside the risers of CFB's. High speed PIV data acquired in three pilot scale CFB units at two laboratories: two CFB's with 0.305 m diameter risers and one CFB with a 0.2 m diameter riser. The high speed PIV system records high speed videos of particle motion with excellent spatial and temporal clarity. The high speed videos are analyzed to measure the concentration and the two-dimensional motion (velocity and trajectory) of individual particles. Data sample rates for velocity vectors are in the range of 0.1 to 3 million vectors per second thereby providing full resolution of the temporal domain of particle velocity. To see and measure particle motion inside the CFB risers at high particle concentrations, a custom borescope was inserted into the risers. The CFB risers were operated over a wide range of industrially relevant conditions: superficial gas velocities from 6.5 to 18.3 m/s with solid fluxes from 20 to 400 kg/m2/s. The particles used in the CFBs included fluid cracking catalyst (FCC) with a mean diameter of 70 μm, high density polyethylene (HDPE) with a mean diameter of 750 μm, and glass beads with mean diameters of 170 and 650 μm. High speed videos and high speed PIV data enabled careful study of the real time behavior of gas-particle flow fields in CFB risers. In all of the CFBs of this study, one or more “jets” of high speed gas were observed at any time in the CFB risers. The jets move around the riser and appear to wander from one location against the riser wall to another. The jets have width range of 1/10 to 1/2 of the riser diameter. When a jet moves away from an area, the void is immediately filled with large clusters of particles. The clusters have sizes up to several riser diameters and contain significant percentages of the total particle flow. Clusters reduce mixing and interaction of particles with the transport gas, and therefore may inhibit reaction rates. Shearing of the clusters by high speed jets gives rise to cluster shapes that are either undulating or in the form of long, thin vertical strands which are often called streamers. The well known core-annulus concentration profile does not exist in real time, but rather is a long time averaged phenomenon. The data and insight from this work should be valuable for design and operation of risers, and for development of computational fluid dynamic (CFD) models of riser flow fields.

Multiphysics Design and Development of Heterogeneous Functional Materials for Renewable Energy Devices: The HeteroFoaM Story

The electrochemical science that makes many energy conversion and storage technologies work rests on our knowledge and understanding of heterogeneous materials and material systems. The function and functionality of those systems share many common features across a wide range of technologies including fuel cells, batteries, capacitors, and membranes. The science that controls that functionality for these complex material systems is typically summoned in fragments to design a specific device. The present paper discusses an attempt to create a codified multiphysics approach to that general subject, across multiple scales in space and time, for heterogeneous functional materials, or “HeteroFoaM” as we call it. The scope of the paper will be necessarily limited to a general definition of the problem focused on a few specific examples of the progress made for directions that support technologies such as conversion of chemical energy to electricity, membranes for selective transport, and charge storage devices. The principal motivation for this approach is to establish the science that controls emergent properties in heterogeneous functional materials as a foundation for design of functional material systems with performance not bounded by constituent properties.

Review of Glucose-Driven Decompression Device for a Chemical Controlled Artificial Pancreas

Glucose-driven decompression device which utilizes conversion of chemical energy (glucose) to mechanical energy (actual pressure) has been developed and applied for a novel chemical controlled artificial pancreas system. The artificial system does not need to require any other power source such as electrical or mechanical energy. Integrated intermittent drug release actions and pressure changes were observed in record with CCD camera. The system was then evaluated in closed loop system setting for feedback control of the glucose concentration. The data revealed that drug release interval was extended causing stabilized constant glucose concentration on feedback effect. Accordingly, glucose concentration can be controlled autonomously similar with natural pattern of interdependent relationship between pancreas insulin secretion and glucose level. Potential applications of the organic engine include intelligent actuators, DDS (drug delivery system) and artificial muscles using biological energies (sugar, acid, lipid, etc.) with a neglibly-small heat loss.

The assembly of kinesin-based nanotransport systems

At the nano-scale many proteins act as biological actuators for rotation or translation. Among these proteins, the building blocks of self-assembled, highly efficient natural motors, kinesin is considered a promising tool in the development of synthetic nanorobots. Conversion of chemical energy into mechanical work, harnessed by the hydrolysis of adenosine triphosphate, propels kinesin along a cytoplasmic system of fibers, known as a microtubule. Even though recent efforts were made to engineer tailor-made artificial nanotransport systems using kinesin, no systematic study investigated how these systems can be organized from the bottom up using the surface plasmon resonance technique. Here, we show that it is possible to quantitatively evaluate how each component of such nanoscopic machines is sequentially assembled by monitoring the individual association of its components, focusing specifically on the kinesin association to microtubules as well as the cargo-kinesin association. Furthermore, the kinetic parameters reported here for the microtubules and recombinant biotinylated kinesin binding process properties are of utmost importance due to the current widespread use of biotinylated kinesin in the construction of synthetic nano-machines.

Decreasing contact resistance in proton-exchange membrane fuel cells with metal bipolar plates

Ohmic, or I2R, losses occur in electrochemical devices, such as proton -exchange membrane fuel cells (PEMFCs) due to the resistance of materials and the contact resistance between the electrochemical active area, the gas diffusion and current collector materials. Such losses must be lessened to maximize the conversion of chemical energy to electricity rather than heat. We probe how to decrease the contact resistance in PEMFCs with metal bipolar plates with state-of-the-art membrane electrode assemblies, specifically Au/TiO2-coated titanium bipolar plates (BPPs), gas diffusion layers with microporous layers (GDLs with MPLs), and catalyst-coated membranes (CCMs) comprising a 15-μm-thick proton-exchange membranes. Through in situ tests of a model system, we find that the system resistance decreases after a compression break-in cycle and then remains low subsequently by keeping the stack assembly compressed at >1 MPa. Ex situ tests show that the surface roughness of the BPPs also affects contact resistance with the GDLs. After accounting for the bulk resistance of the cell constituents (BPPs, GDLs, MPLs and CCMs), we conclude that in a state-of-the-art PEMFC, the contact resistances between the materials contribute 55% of the total I2R losses, and thus dominate the ohmic loss contributions.

An Exergy Analysis of Biological Energy Conversion

Great portions of the world's exergy requirements come from solar energy. In addition, green plants can be viewed as biological energy conversion processes in which exergy from solar energy is converted into chemical energy by chlorophyll using water and carbon dioxide. In this article, exergy analysis of biological energy conversion and a comparative study of four photosynthetic pathways are presented. This comparison is made by using the thermal efficiency of light to chemical energy conversion and derived simple thermal efficiency. Non sulfur purple bacteria and non sulfur green bacteria from the others have the best thermodynamic performance. The rate of lost work consists of photochemical reaction, respiration, and thermal absorption of radiation. According to calculated lost work components or, equivalently, the available work or exergy lost, the photochemical process accounting for the work lost has the highest rate. Apparently, chemical reactions taking place inside the system are higher entropy producers than material or energy transport between the leaf and its environment.

Intrinsic microtubule GTP-cap dynamics in semi-confined systems: kinetochore–microtubule interface

In order to quantify the intrinsic dynamics associated with the tip of a GTP-cap under semi-confined conditions, such as those within a neuronal cone and at a kinetochore-microtubule interface, we propose a novel quantitative concept of critical nano local GTP-tubulin concentration (CNLC). A simulation of a rate constant of GTP-tubulin hydrolysis, under varying conditions based on this concept, generates results in the range of 0-420s(-1). These results are in agreement with published experimental data, validating our model. The major outcome of this model is the prediction of 11 random and distinct outbursts of GTP hydrolysis per single layer of a GTP-cap. GTP hydrolysis is accompanied by an energy release and the formation of discrete expanding zones, built by less-stable, skewed GDP-tubulin subunits. We suggest that the front of these expanding zones within the walls of the microtubule represent soliton-like movements of local deformation triggered by energy released from an outburst of hydrolysis. We propose that these solitons might be helpful in addressing a long-standing question relating to the mechanism underlying how GTP-tubulin hydrolysis controls dynamic instability. This result strongly supports the prediction that large conformational movements in tubulin subunits, termed dynamic transitions, occur as a result of the conversion of chemical energy that is triggered by GTP hydrolysis (Satarić et al., Electromagn Biol Med 24:255-264, 2005). Although simple, the concept of CNLC enables the formulation of a rationale to explain the intrinsic nature of the "push-and-pull" mechanism associated with a kinetochore-microtubule complex. In addition, the capacity of the microtubule wall to produce and mediate localized spatio-temporal excitations, i.e., soliton-like bursts of energy coupled with an abundance of microtubules in dendritic spines supports the hypothesis that microtubule dynamics may underlie neural information processing including neurocomputation (Hameroff, J Biol Phys 36:71-93, 2010; Hameroff, Cognit Sci 31:1035-1045, 2007; Hameroff and Watt, J Theor Biol 98:549-561, 1982).

Proposed combined-cycle power system based on oxygen-blown coal partial gasification

A combined-cycle power system based on oxygen-blown coal partial gasification is proposed to promote the performance and reduce the investment of conventional integrated gasification combined cycle (IGCC) power system. The proposed power system combines the characteristics of IGCC and pressurized fluidized-bed cycle power systems, and its performance is analyzed. The thermal efficiency of the proposed power system is about 3% higher than that of the reference system. Exergy analysis is also performed to reveal the internal phenomenon of the energy conversion. It is found that the main character of the proposed power system is the reduction of exergy destruction during chemical energy conversion processes, i.e., the gasification process and the syngas combustion process. Such a result implies the proposed power system can realize better utilization of the coal chemical energy. Some other configurations of the proposed power system are also considered for varying the work conditions or for further adaptation to state-of-the-art technology. The primary investment cost of the proposed power system is also reduced due to the decrease in the gasification temperature and the carbon conversion ratio.

ChemInform Abstract: Modern Methods of Thermochemical Biomass Conversion into Gas, Liquid and Solid Fuels

AbstractReview: 23 refs.