Performance Of Energy Conversion Devices Research Articles

Mn-Doped Zn Metal-Organic Framework-Derived Porous N-Doped Carbon Composite as a High-Performance Nonprecious Electrocatalyst for Oxygen Reduction and Aqueous/Flexible Zinc-Air Batteries.

Developing low-cost, efficient, and stable oxygen reduction reaction (ORR) electrocatalysts is crucial for the commercialization of energy conversion devices such as metal-air batteries. In this study, we report a Mn-doped Zn metal-organic framework-derived porous N-doped carbon composite (30-ZnMn-NC) as a high-performance ORR catalyst. 30-ZnMn-NC exhibits excellent electrocatalytic activity, demonstrating a kinetic current density of 9.58 mA cm-2 (0.8 V) and a half-wave potential of 0.83 V, surpassing the benchmark Pt/C and most of the recently reported non-noble metal-based catalysts. Moreover, the assembled zinc-air battery with 30-ZnMn-NC demonstrates high peak power densities of 207 and 66.3 mW cm-2 in liquid and flexible batteries, respectively, highlighting its potential for practical applications. The excellent electrocatalytic activity of 30-ZnMn-NC is attributed to its unique porous structure, the strong electronic interaction between metal Zn/Mn and adjacent N-doped carbon, as well as the bimetallic Mn/Zn-N active sites, which synergistically promote faster reaction kinetics. This work offers a controllable design strategy for efficient electrocatalysts with porous structures and bimetallic active sites, which can significantly enhance the performance of energy conversion devices.

Electron Probe Bridging Solid-State Chemistry and Surface Chemistry: Example of the TiO2-O2 System

This work reports the capacity of a high-temperature electron probe to bridge solid-state chemistry and surface chemistry. This goal could be accomplished by performing the characterization of the surface layer in equilibrium with both the gas phase and bulk phase, thus dealing with a system governed by thermodynamic laws, which is free of unknown kinetic terms. In this work, we contemplate the use of the electron probe in surface defect engineering of the next generation of energy materials, that are expected to enhance the production of clean energy. The concept of this kind of engineering is considered for the TiO2-O2 model system. Such example demonstrates the role of surface segregation in the formation of a quasi-isolated surface structure, that has a profound impact on the reactivity of solids and their performance in energy conversion devices. Consequently, it is essential that studies of the effect of surface defect structure on the reactivity of solids are conducted in situ and in operando, under conditions of real application. This is expected to aid directly the rational design of surface properties in the processing of high-performance energy materials for fuel cells, solar cells, batteries, catalysts and photo-catalysts, as well as sensors.

Nano/micro-structural engineering of Nafion membranes for advanced electrochemical applications

Nafion membranes are actively electrochemical devices such as fuel cells, conventional two compartments electrochemical cells, and photoassisted electrolyzer cells. It provides good selectivity of penetrating ions from one electrode compartment to another and accelerates the separation of the products. Though the conventional Nafion membrane has been widely applied, there are still some crucial challenges, such as the flow of ions transferred by fouling, charge gradient resistance, and mechanical instabilities in long-term applications. In particular, the charge transfer resistance of the membrane is a key characteristic to realize the efficient transfer of charges across the electrodes within the electrolyte. The researchers have tried cost-effective nano/micro-structural engineering strategies to produce high-quality Nafion membranes for improved electrochemical applications. The proper surface patterning and selective functionalization or hybrid formation of Nafion with specialized materials could improve the overall mechanical strength, charge sustaining and flow rate potentials of the parent Nafion. This manuscript provides a brief overview of Nafion based nano and microstructured membrane and their modification strategies for energy conversion devices. Two strategies are shortly overviewed with respective examples: (1) physical modification via nano/micropatterning and (2) nanocomposite formation with selective materials. The modified Nafion membranes by various structural engineering strategies propose new and effective pathways to enhance the performance of energy conversion devices, which are keys for solving current environmental issues.

Structural engineering of Ti-Mn bimetallic phosphide nanotubes for efficient photoelectrochemical water splitting

Designing next-generation advanced electrode materials by engineering their structural and compositional features can provide a feasible strategy to enhance the electrochemical performance of energy conversion devices. In this study, the rational pathway to design and fabricate nanotube arrays of titanium manganese phosphide via etching of titanium-manganese alloy followed by plasma phosphidation in PH3 environment is presented and discussed. The structural and elemental analyses of the air-annealed electrodes before plasma treatment confirmed the presence of different binary oxides; TiO2, MnO, and Mn2O3. However, the XPS fitting showed the presence of Ti3+ and higher ratio of MnO when annealed in hydrogen atmosphere. The presence of composite oxides resulted in a band gap reduction, which increased the light harvesting capability of the material. This synergetic effect resulted also in a shift in the open-circuit voltage (VOC) and almost 10-fold increase in the photocurrent density compared to the performance of the nanotubes annealed in air. Mott-Schottky analysis showed a four-orders of magnitude enhancement in the carrier density for the electrodes annealed in Hydrogen and treated in PH3-plasma compared to those annealed in O2 or air, ascribed to the creation of Ti3+ defects and phosphidation. Our study thus paves the way to a new approach for creating high-performance hybrid electrodes for PEC water splitting.

Impacts of catalyst nanolayers on water permeation and swelling of polymer electrolyte membranes

Polymer electrolyte membranes with catalyst layers are the most crucial components of proton exchange membrane (PEM) electrolyzer cells and fuel cells. Their water permeation and swelling behavior significantly impact the proton transport and performance in energy conversion devices. In this study, water permeations and swelling properties of Nafion membranes with different platinum (Pt) nanolayers under different conditions are investigated. Visualization results demonstrate the entire swelling process of Pt-coated Nafion membranes and reveal water transport in Nafion membranes and breakage of the Pt nanolayer. The water permeation of Nafion membranes with a 17 nm Pt nanolayer coating reduces from 40 to less than 20 μmol min−1 cm−2 at 80 °C and 70 kPa differential pressure. The water permeation of Nafion membranes with a 36 nm Pt coating is slightly lower than one with a 17 nm Pt coating due to higher transport resistance through the thicker Pt nanolayer and smaller cracks on the Pt nanolayer. Nevertheless, the water permeation of Nafion membranes with Pt nanolayers is still in a good range for proton transport applications, demonstrating the feasibility of Pt or other metal coating on Nafion membranes as catalysts or substrates in PEM-based energy devices.

Semiconductor nanowires improve the performance of energy conversion devices

Controlling the growth and composition of nanowires is key to building photovoltaics, thermoelectrics and betavoltaics with optimal performance.

Interpretation of Complex Capacitance Using Equivalent Circuit Involving Constant Phase Element

An electrochemical impedance spectroscopy (EIS) is powerful tool to evaluate the electrochemical parameters of inside the energy conversion devices. The electric-double layer capacitance C dl can be estimated by the curve fitting of the impedance spectrum generally. It is important to obtain the C dl of the electrode because it is related to the surface area and structure of electrode/electrolyte interface. The performance of energy conversion devices can be investigated by the capacitance plots calculated from the impedance. (1-5) Our group (6) previously reported the calculations of the electrochemical impedance and complex capacitance corresponding to typical equivalent circuits involving a transmission line model (TLM) in order to determine the precise value of the C dl of electrochemical capacitor. In the present work, theory of complex capacitance were summarized by calculations using equivalent circuits. The complex capacitance calculated by equivalent circuit involving the constant phase element (CPE) was also discussed theoretically.

Enhancing Charge Transfer Kinetics by Nanoscale Catalytic Cermet Interlayer

Enhancing the density of catalytic sites is crucial for improving the performance of energy conversion devices. This work demonstrates the kinetic role of 2 nm thin YSZ/Pt cermet layers on enhancing the oxygen reduction kinetics for low temperature solid oxide fuel cells. Cermet layers were deposited between the porous Pt cathode and the dense YSZ electrolyte wafer using atomic layer deposition (ALD). Not only the catalytic role of the cermet layer itself but the mixing effect in the cermet was explored. For cells with unmixed and fully mixed cermet interlayers, the maximum power density was enhanced by a factor of 1.5 and 1.8 at 400 °C, and by 2.3 and 2.7 at 450 °C, respectively, when compared to control cells with no cermet interlayer. The observed enhancement in cell performance is believed to be due to the increased triple phase boundary (TPB) density in the cermet interlayer. We also believe that the sustained kinetics for the fully mixed cermet layer sample stems from better thermal stability of Pt islands separated by the ALD YSZ matrix, which helped to maintain the high-density TPBs even at elevated temperature.

Engineering Performance in TCO Films for Energy Applications

Thin film materials that exhibit both good electrical conductivity and high transparency owe this duality to careful control of the chemical state of the constituents and the attendant structure. Through manipulation of deposition conditions n- or p-type semi-conducting oxide films readily can be prepared. Such films enable the performance of energy conversion devices and promote development of architectural elements including smart energy efficient windows. This paper summarizes current TCO research trends, reviews processing approaches, and offers guidelines for engineering high performance TCO films. Also provided is a glimpse of optical engineering approaches where impedance matching and quantum mechanical tunneling offer alternative avenues to further improvement of film properties.

Review of near-field thermal radiation and its application to energy conversion

Understanding energy transfer via near-field thermal radiation is critical for the future advances of nanotechnology. Evanescent waves and photon tunneling are responsible for the near-field energy transfer being several orders of magnitude greater than that between two blackbodies. The enhanced energy transfer may be used for improving the performance of energy conversion devices, developing novel nanofabrication techniques, and imaging nanostructures with higher spatial resolution. Near-field heat transfer can be analyzed using fluctuational electrodynamics. This article reviews the fundamentals of near-field radiation and outlines the recent advances in this field. Important results are presented for near-field energy transfer between parallel plates and between multilayered structures. Application of near-field thermal radiation in near-field thermophotovoltaic devices is also discussed. Copyright © 2009 John Wiley & Sons, Ltd.

Application of exergy to design

The design of an energy-intensive system for lower cost and higher efficiency is one of the essential approaches to sustainable development. A principle is presented whereby exergy is elevated from a tool that reveals opportunities of higher efficiency to a tool that reveals opportunities of both lower cost and higher efficiency. The principle states that minimizing the individual costs of the energy conversion devices of a system with respect to their efficiency decision variables leads to a minimized cost of the system and an optimal overall system efficiency. The cost of a device is the sum of its fixed charges and its running expenses. The cost of exergy destruction of a device is its major running expense. The premises on which the principle is established are explained. Second-law analysis and design models of energy conversion devices play a central role in establishing these premises. Three useful design model manipulations seeking equations for the costing and for the performance of energy conversion devices are presented. Applications to the optimal design of systems and extensions to their optimal operation are given elsewhere.

POTENTIAL NAVAL SHIPBOARD APPLICATION OF NONAZEOTROPIC ENERGY CONVERSION

ABSTRACTThe thermodynamic performance of an energy conversion device may be improved potentially by using a nonazeotropic mixture in a vapor cycle. A nonazeotropic mixture has a temperature distribution parallel to that of the surrounding fluid with which heat transfer takes place during the evaporation and condensation processes. Interest has increased in recent years in the use of nonazeotropic refrigerant mixtures to improve the performance of energy conversion devices. This report surveys developments in nonazeotropic energy conversion, describes the theory of a nonazeotropic energy conversion cycle, predicts energy savings possible from use of nonazeotropic energy conversion devices, and discusses potential naval shipboard application of such an energy conversion cycle.