Conversion Of Chemical Energy Research Articles

Investigation of the Influence of Selected Operating Modes on the Long-Term Stability of Electrocatalysts in the PEM Fuel Cell

The membrane electrode assembly (MEA) is the core component of the fuel cell stack. In it, the conversion of chemical energy into electrical energy takes place at the catalyst layers. The functional capability of the MEA is an indispensable prerequisite for the operation of the fuel cell stack and thus plays a decisive role in defining its stability. In addition to the selection of suitable materials, the mode of operation plays a major role in the durability of the MEA. It is known from the literature that electrochemical degradation reactions generally depend on operating parameters such as temperature, potential and dynamics. [1] Therefore, in order to derive a durability promoting mode of operation for the PEM Fuel Cell as well as to make lifetime predictions, it is necessary to identify and understand the processes occurring during the aging of the MEA.This work deals with the investigation of the influence of the operating parameters in the drive cycle as an important operating mode on the aging of the cathode catalyst layer in the MEA. According to the state of the art, nanoparticulate platinum supported on carbon (Pt/C) is usually used as the cathode catalyst. The degradation of Pt/C has been intensively studied in recent years. Platinum dissolution and Pt agglomeration are discussed as the main causes of Pt/C degradation during PEMFC operation. [2, 3]Studies have shown that the dissolution rate generally increases with potential and can accelerate under potentiodynamic conditions. [1] Dissolution of Pt from the catalyst, transport of Pt ions through the electrode, and precipitation of Pt in the membrane, possibly due to reduction of Pt ions by the H2 crossover from the anode can be associated with the loss of cathode electrochemical surface area (ECSA) and thus irreversible performance loss. [4]The primary objective of this work is to investigate the influence of different operating parameters such as temperature and potential range on the degradation rate of the cathode using an accelerated stress test (AST) which was developed to simulate an analogous to real drive cycle operation of a PEM fuel cell in a vehicle.A secondary objective is to evaluate the AST itself in order to determinate its capability of fuel cell lifetime prediction. For that the transferability of the observed degradation rates are to be evaluated on different integration levels such as single-cell PEM test bench and short-stack multi-cell test bench. As a measure to evaluate the transferability of the accelerated stress tests, the loss of electrochemical active surface area (ECSA) serves as an indirect measure of catalyst degradation and the resulting Pt particle size distribution which is determined by TEM serves as a direct measure. The derivation of acceleration factors for the lifetime tests of the different integration levels would allow an early estimation of the lifetime, this way test time and cost could be significantly saved in the evaluation of new materials.

Layered Double Hydroxides for Photo(electro)catalytic Applications: A Mini Review.

Chemical energy conversion strategies by photocatalysis and electrocatalysis are promising approaches to alleviating our energy shortages and environmental issues. Due to the 2D layer structure, adjustable composition, unique thermal decomposition and memory properties, abundant surface hydroxyl, and low cost, layered double hydroxides (LDHs) have attracted extensive attention in electrocatalysis, photocatalysis, and photoelectrocatalysis. This review summarizes the main structural characteristics of LDHs, including tunable composition, thermal decomposition and memory properties, delaminated layer, and surface hydroxyl. Next, the influences of the structural characteristics on the photo(electro)catalytic process are briefly introduced to understand the structure–performance correlations of LDHs materials. Recent progress and advances of LDHs in photocatalysis and photoelectrocatalysis applications are summarized. Finally, the challenges and future development of LDHs are prospected from the aspect of structural design and exploring structure-activity relationships in the photo(electro)catalysis applications.

Electrochemical Responses and Microbial Community Shift of Electroactive Biofilm to Acidity Stress in Microbial Fuel Cells

Microbial community changes in response to acid stress in microbial fuel cells (MFCs) were studied. Acid mine drainage (AMD) wastewater is usually difficult to treat because of the high concentration of sulfate and heavy metals. MFCs, which have multiple functions based on the principle of synergistically treating organic and heavy metal wastewater while generating electrical energy, represent a promising direction for the development of new heavy metal wastewater treatment technologies. Maintaining a neutral or slightly alkaline wastewater pH in MFCs facilitates the growth of electricity-producing microorganisms in the anode chamber. Studies on the response of anode electroactive biofilms to acidic pH stress and its correlation with changes in AMD treatment capacity have not been reported. Results showed that the anolyte pH of 4.0 and 5.0 affected the electron output capacity of the electrogenic microbial community in the MFCs. In contrast, MFCs working at an anolyte pH of 6.0 exhibited a high efficiency of chemical energy conversion to electrical energy. The microbial abundance and microbial diversity of the electroactive biofilm were significantly affected by the H+ concentration in the medium when the ambient acidity was continuously reduced. The classic exoelectrogen Geobacter decreased gradually with the increase of H+ concentration in the medium. In addition, Cu2+ was recovered from the simulated AMD in the MFCs cathodic chambers at low anode pH, but the removal rate of Cu2+ decreased as the pH of the anode environment decreased. At 48 h, 86.2% of Cu2+ was removed from the MFCs cathode solution at pH 5.0, while the removal rate of Cu2+ from the MFCs cathode solution at pH 4.0 was 84.2%. Trace amounts of Cu2O and Cu3(OH)2[CO3]2 were present on the cathode, which reduced the amount of Cu2+ that precipitated on the cathode carbon cloth. Conversely, the concentration of Cu2+ in the catholyte of MFCs with electroactive biofilm at pH 6.0 decreased rapidly, and by 36 h, no detectable Cu2+ was present in the cathodic solution. This study will provide researchers with valuable information regarding the optimal pH for resource recovery with MFCs.

Phosphorus based hybrid materials for green fuel generation

AbstractPhosphorene, also referred to as phosphorus‐based elemental material (black and red), display unusual electronic‐structure characteristics, which can significantly enrich the fields of energy application and possesses huge potential in photocatalysis owing to its bandgap tunability, high optical absorption, large surface area, high charge carrier mobilities, and efficient solar to chemical energy conversion. However, due to chemical instability and the poor visible‐light utilization efficiency, individual phosphorus materials cannot promote charge transfer and separation. For designing active photocatalysts, phosphorus‐based hybrid materials with effective charge carriers separation at the heterojunction interface has played significant role. In this respect, considerable attempts have been made to fabricate black–red phosphorus heterostructure for photocatalytic applications and solar fuel generation, such as photocatalytic and electrocatalysis water splitting, CO2 reduction, carbohydrates synthesis, etc. This review article highlights the strategies for the synthesis of black–red phosphorus heterostructure materials for catalysis with a special focus on their potential for solar fuel generation applications. Recently developed black–red phosphorus heterostructure will be discussed, which can improve the most challenging drawback of phosphorus materials. Finally, the major challenges along with future trends of black–red phosphorus heterostructure in catalytic applications are outlined.This article is categorized under: Sustainable Energy > Solar Energy Emerging Technologies > Materials Emerging Technologies > Hydrogen and Fuel Cells

ZrP2O7 as a Cathodic Material in Single-Chamber MFC for Bioenergy Production.

The present work is the first investigation of the electrocatalytic performances of ZrP2O7 as a cathode in a single-chamber Microbial Fuel Cell (MFC) for the conversion of chemical energy from wastewater to bioelectricity. This catalyst was prepared by a coprecipitation method, then characterized by X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), ultraviolet–visible–near-infrared spectrophotometry (UV–Vis–NIR), and cyclic voltammetry analyses. The acid–basic characteristics of the surface were probed by using 2-butanol decomposition. The conversion of 2-butanol occurs essentially through the dehydrating reaction, indicating the predominantly acidic character of the solid. The electrochemical test shows that the studied cathode material is electroactive. In addition, the ZrP2O7 in the MFC configuration exhibited high performance in terms of bioelectricity generation, giving a maximum output power density of around 449 mW m−2; moreover, it was active for wastewater treatment, reducing the chemical oxygen demand (COD) charge to 50% after three days of reaction.

Compressive-Strain-Facilitated Fast Oxygen Migration with Reversible Topotactic Transformation in La0.5Sr0.5CoOx via All-Solid-State Electrolyte Gating

Modifying the crystal structure and corresponding functional properties of complex oxides by regulating their oxygen content has promising applications in energy conversion and chemical looping, where controlling oxygen migration plays an important role. Therefore, finding an efficacious and feasible method to facilitate oxygen migration has become a critical requirement for practical applications. Here, we report a compressive-strain-facilitated oxygen migration with reversible topotactic phase transformation (RTPT) in La0.5Sr0.5CoOx films based on all-solid-state electrolyte gating modulation. With the lattice strain changing from tensile to compressive strain, significant reductions in modulation duration (∼72%) and threshold voltage (∼70%) for the RTPT were observed, indicating great promotion of RTPT by compressive strain. Density functional theory calculations verify that such compressive-strain-facilitated efficient RTPT comes from significant reduction of the oxygen migration barrier in compressive-strained films. Further, ac-STEM, EELS, and sXAS investigations reveal that varying strain from tensile to compressive enhances the Co 3d band filling, thereby suppressing the Co-O hybrid bond in oxygen vacancy channels, elucidating the micro-origin of such compressive-strain-facilitated oxygen migration. Our work suggests that controlling electronic orbital occupation of Co ions in oxygen vacancy channels may help facilitate oxygen migration, providing valuable insights and practical guidance for achieving highly efficient oxygen-migration-related chemical looping and energy conversion with complex oxides.

Compact and fast-response 150 kW hydrogen-oxygen steam generator

Burning of hydrogen produces high-grade heat, which can be used for zero-carbon power generation and/or heating and in heat-intensive industries. In combination with water electrolysis, hydrogen combustion provides efficient energy storage method for variable renewables. Hydrogen combustion systems are compact, powerful and highly maneuverable in comparison with fuel cells. We present experimental results of fire tests of a water-cooled hydrogen-oxygen steam generator (HOSG). This fast-response device has start-up time less than 15 s to thermal capacity of 147 kW. Temperature of generated steam is within 1173–1273 K, parameters of steam and energy conversion efficiency can be adjusted the water-to-hydrogen ratio. The maximum efficiency of conversion of chemical energy of hydrogen into enthalpy of steam is 98.7%.

Improving the performance of steam power cycle through thermo-photovoltaic device: A novel combined system and thermodynamic analysis

In this study, a new system consisting of a thermophotovoltaic device and steam Rankine cycle system is proposed to prevent the mismatch between the combustion temperature and the steam maximum temperature to achieve photo-thermal energy cascade utilization and improve the fuel conversion efficiency. The energy balance model of the proposed system is established, and the influence of parameters such as emitter area and heat exchange coefficients on the system’s performance is investigated. Exergy analysis of the system is performed based on the second law of thermodynamics. The results show that the proposed system has 11–13% higher efficiency than the steam Rankine cycle system. The addition of a thermophotovoltaic device mainly reduces the exergy loss of the boiler due to the temperature difference between the combustion flue gas and the steam. Increasing the emitter area improves the system efficiency, and a system with Si cells is more efficient than a system with GaSb cells. Increasing the heat transfer coefficient of the air heat exchanger and the outlet flue gas temperature to generate a higher flame temperature is crucial to improving the performance of the combined system. The addition of a thermophotovoltaic device does not reduce the exergy loss during combustion. Thus, further energy cascade utilization should consider the efficient conversion of high-order chemical energy of a fuel. This study contributes to the theory of photo-thermal energy cascade conversion and provides new insights into improving the performance of the steam Rankine cycle.

Analytical study of fluid flow and thermal characteristics of flow in micro channel heat sinks with working fluid as water and alumina & water nanofluid

The electronic industry is looking at microchannel based MEMS technology to resolve the issue of increasing heat dissipation from electronic circuits. Micro-channels play an important role in development of small scale fluid flow devices. The internal flow configuration represents a convenient geometry for heat transfer between fluids used in chemical processing, environmental control, and energy conversion technologies. In order to fabricate such micro devices effectively, it is extremely important to understand the fundamental mechanisms involved in fluid flow and heat transfer characteristics in microchannels. This paper presents an analytical study of flow mechanism in microchannels, with a focus on effect of geometric dimensions and flow rate on the various flow parameters of a Rectangular microchannel. An attempt is also made to determine optimum microchannel dimensions based on the analysis. Basic flow equations are used for modelling the flow and determining various parameters. Further, the study analyses the effect of using Alumina & Water nanofluid on flow and thermal characteristics as compared to using water alone. The results observed show a deeper and wider microchannel would keep the pressure drop across the microchannel lower. Also using nanofluid as working fluid would result in lower pressure drop.

Solar Architecture in Energy Engineering

Solar Architecture represents the confluence of the two disciplines of energy engineering and architecture. The concept of Solar Architecture defines a decision-making process to select, design, deploy, and operate solar energy-enabled solutions for environments where solar energy resources are part of the energy mix. The principles of Solar Architecture include maximizing solar energy harvesting from solution’s surfaces with a positive balance of energy, carbon, and cost provided by the solution. Solar Architecture application selection is built on two major cornerstones, features and groups, defining the best options in energy engineering of a solar solution. Solar surfaces are key to solar architecture. They are the “heart”, and balance-of-system components are the “muscles” of solar solutions. Addressing energy losses in photovoltaic, solar to thermal, and solar to chemical energy conversion allows for increasing energy harvesting yield. Life Cycle Assessment and solar energy harvesting methodologies based on solar surface characteristics define Solar Architecture Balance. This balance allows for defining energy, carbon, and cost return on investment for solar solutions and selecting the best solution for related assets/environment.

Thermal behaviors and energy conversion efficiency for all-vanadium flow battery based on thermodynamics entropy analysis

• Thermodynamics entropy analysis is coupled with transient electrochemical model. • System efficiency suits the battery evaluation with different electrode porosities. • The entropy generation rates under different operating conditions are proposed. • The power consumption and Joule heating loss are both explored and quantified. All-vanadium flow battery mainly relies on the conversion of chemical and electric energy to realize power storage and utilization, but there will inevitably be heat loss coming from the power consumption and resistance heat in the process of energy conversion. Herein, from the perspective of the thermodynamics, the impacts of entropy generation rates on the efficiencies of the battery under different porosities, electrolyte flow rates, current densities and electrolyte concentrations are analyzed, in the cases that the larger average rate of entropy generation will lead to lower voltage efficiency and energy efficiency. The power consumption in the negative electrode is higher than that in the positive electrode in discharge, and the Joule heating in the positive electrode is higher than that in the negative electrode. The entropy generation rate affected by the activation overpotential and transfer current density drops with the increase in electrolyte flow rate, ionic concentration and the decrease in current density. In the mode with the electrodes of different electrode porosities, system efficiency can be used to evaluate the energy conversion efficiency of the battery more accurately as the pump work is included, and the maximum system efficiency of 86.01 % can be obtained in the battery with the electrode porosity of ε = 0.8 .

Improved Durability of High-Performance Intermediate-Temperature Solid Oxide Fuel Cells with a Ba-Doped La0.6Sr0.4Co0.2Fe0.8O3-δ Cathode.

As a device for direct conversion of chemical energy into electrical energy, the solid oxide fuel cell (SOFC) contributes positively to the sustainable development strategy. However, the commercialization of fuel cells is still impeded by severe cathode degradation caused by its limited stability at operating temperatures and being prone to Cr-poisoning from Cr-containing alloy interconnectors commonly used in these cells. This paper reports the development of a high-durability Ba-doped LSCF(La0.6Sr0.4Co0.2Fe0.8O3-δ) cathode material under realistic fuel cell operating conditions in the presence of the Cr alloy. In particular, when tested in a symmetrical cell constructed of Ba-doped LSCF, the polarization resistance of the cell remains very low at 0.06 Ω cm2 after being tested at 800 °C for 120 h exposed to Cr in 3% humidified air. In contrast, for the undoped LSCF under the same testing conditions, the polarization resistance of the cell increases ∼10 times from 0.22 Ω cm2 of the pristine cell to 2.18 Ω cm2 after Cr-exposure testing. Furthermore, when tested in an anode-supported complete cell as a cathode under typical SOFC operation conditions at 750 °C, the cell with the Ba-doped LSCF cathode displays significantly low degradation rates of 0.00056% h-1 (without Cr) and 0.00310% h-1 (with Cr); both are much lower than that of the cell using the undoped LSCF cathode (0.00124% h-1 without Cr and 0.01082% h-1 with Cr). This enhanced durability and Cr-tolerance exhibited by the Ba-doped LSCF cathode stem from its higher crystal structure stability and improved chemical resistance compared to undoped LSCF.

Dual-network polyacrylamide/carboxymethyl chitosan-grafted-polyaniline conductive hydrogels for wearable strain sensors

Conductive, wearable, and flexible hydrogel-based sensors are considered as promising applications in human motion detection and physiological signal monitoring. However, it is still a problem to integrate multiple functions into one material for the next-generation smart devices. Herein, we fabricated an ionic/electronic dual conductive hydrogel by combining the chemically crosslinked polyacrylamide (PAM) and the physically crosslinked carboxymethyl chitosan-grafted-polyaniline (CMCS-g-PANI)/Ag+ network. The double-network hydrogel displays a high stretchability, repeatable adhesiveness, antibacterial activities, and biocompatibility. It also has high sensitivity and stable electrical performance for wearable strain sensors. Furthermore, we assembled a self-powered strain sensor based on the conversion of chemical energy to electrical energy. It can be used for human motion detection even without external power supply. This work provides an avenue for the development of multifunctional hydrogels with outstanding mechanical and electronic performances for application in wearable electronic devices.

Novel Trends in Proton Exchange Membrane Fuel Cells

Fuel cells (FCs) have received huge attention for development from lab and pilot scales to full commercial scale. This is mainly due to their inherent advantage of direct conversion of chemical energy to electrical energy as a high-quality energy supply and, hence, higher conversion efficiency. Additionally, FCs have been produced at a wide range of capacities with high flexibility due to modularity characteristics. Using the right materials and efficient manufacturing processes is directly proportional to the total production cost. This work explored the different components of proton exchange membrane fuel cells (PEMFCs) and their manufacturing processes. The challenges associated with these manufacturing processes were critically analyzed, and possible mitigation strategies were proposed. The PEMFC is a relatively new and developing technology so there is a need for a thorough analysis to comprehend the current state of fuel cell operational characteristics and discover new areas for development. It is hoped that the view discussed in this paper will be a means for improved fuel cell development.

High-temperature transport properties of BaSn1−xScxO3−δ ceramic materials as promising electrolytes for protonic ceramic fuel cells

Protonic ceramic fuel cells (PCFCs) offer a convenient means for electrochemical conversion of chemical energy into electricity at intermediate temperatures with very high efficiency. Although BaCeO3- and BaZrO3-based complex oxides have been positioned as the most promising PCFC electrolytes, the design of new protonic conductors with improved properties is of paramount importance. Within the present work, we studied transport properties of scandium-doped barium stannate (Sc-doped BaSnO3). Our analysis included the fabrication of porous and dense BaSn1−xScxO3−δ ceramic materials (0 ⩽ x ⩽ 0.37), as well as a comprehensive analysis of their total, ionic, and electronic conductivities across all the experimental conditions realized under the PCFC operation: both air and hydrogen atmospheres with various water vapor partial pressures (p(H2O)), and a temperature range of 500–900 °C. This work reports on electrolyte domain boundaries of the undoped and doped BaSnO3 for the first time, revealing that pure BaSnO3 exhibits mixed ionic-electronic conduction behavior under both oxidizing and reducing conditions, while the Sc-doping results in the gradual improvement of ionic (including protonic) conductivity, extending the electrolyte domain boundaries towards reduced atmospheres. This latter property makes the heavily-doped BaSnO3 representatives attractive for PCFC applications.

Electron Injection in Metal Assisted Chemical Etching as a Fundamental Mechanism for Electroless Electricity Generation.

Metal-assisted chemical etching (MACE) is a widely applied process for fabricating Si nanostructures. As an electroless process, it does not require a counter electrode, and it is usually considered that only holes in the Si valence band contribute to the process. In this work, a charge carrier collecting p–n junction structure coated with silver nanoparticles is used to demonstrate that also electrons in the conduction band play a fundamental role in MACE, and enable an electroless chemical energy conversion process that was not previously reported. The studied structures generate electricity at a power density of 0.43 mW/cm2 during MACE. This necessitates reformulating the microscopic electrochemical description of the Si-metal-oxidant nanosystems to separately account for electron and hole injections into the conduction and valence band of Si. Our work provides new insight into the fundamentals of MACE and demonstrates a radically new route to chemical energy conversion by solar cell-inspired devices.

Non-Equilibrium Protein Folding and Activation by ATP-Driven Chaperones.

Recent experimental studies suggest that ATP-driven molecular chaperones can stabilize protein substrates in their native structures out of thermal equilibrium. The mechanism of such non-equilibrium protein folding is an open question. Based on available structural and biochemical evidence, I propose here a unifying principle that underlies the conversion of chemical energy from ATP hydrolysis to the conformational free energy associated with protein folding and activation. I demonstrate that non-equilibrium folding requires the chaperones to break at least one of four symmetry conditions. The Hsp70 and Hsp90 chaperones each break a different subset of these symmetries and thus they use different mechanisms for non-equilibrium protein folding. I derive an upper bound on the non-equilibrium elevation of the native concentration, which implies that non-equilibrium folding only occurs in slow-folding proteins that adopt an unstable intermediate conformation in binding to ATP-driven chaperones. Contrary to the long-held view of Anfinsen’s hypothesis that proteins fold to their conformational free energy minima, my results predict that some proteins may fold into thermodynamically unstable native structures with the assistance of ATP-driven chaperones, and that the native structures of some chaperone-dependent proteins may be shaped by their chaperone-mediated folding pathways.

MOF-Derived Porous Ternary Nickel Iron Nitride Nanocube as a Functional Catalyst toward Water Splitting Hydrogen Evolution for Solar to Chemical Energy Conversion

MOF-Derived Porous Ternary Nickel Iron Nitride Nanocube as a Functional Catalyst toward Water Splitting Hydrogen Evolution for Solar to Chemical Energy Conversion

Production Process of Steam Power Plant and Calculation of Thermal Efficiency: Case Study of Teluk Sirih Steam Power Plant

The performance of a power plant can be known from the calculation of efficiency in the generating sector. Steam power plants utilize a series of energy conversion processes including: conversion of chemical energy into thermal energy when extracting heat from coal as fuel to heat boilers, conversion of thermal energy into mechanical energy in turbines and conversion of mechanical energy into electrical energy in generators. Like other steam power plants, the Teluk Sirih PLTU located in Bungus Teluk Kabung, West Sumatra has the same energy production process. it's just that the source of the water is taken from the sea so it requires special treatment to turn the water into water suitable for producing steam used in this power plant. The electricity production process will be explained in this study and an efficiency calculation process with a simple Rankine cycle is carried out to determine the efficiency of this power plant. From the calculation results, the thermal efficiency of PLTU Teluk Sirih is 29%. Based on the results of these calculations, it is known that the Telusk Sirih PLTU can be classified as a power plant with good efficiency.

Effect of Turbocharger Compression Ratio on Performance of the Spark-Ignition Internal Combustion Engine

Internal Combustion Engines (ICE) are one of the most important engineering applications that operate based on the conversion of chemical energy from fuel into thermal energy as a result of direct combustion. The obtained thermal energy is then turned into kinetic energy to derive various means of transportation, such as marine, air, and land vehicles. The efficiency of ICE today is considered in the range of the intermediate level, and various improvements are being made to enhance its efficiency. The turbocharger can support the ICE, which works by increasing the pressure in the engine to enhance its efficiency. In this investigation, the effect of the turbocharger pressure on ICE performance was studied in the range of 2 to 10 bar. It was found that the increase in turbocharger pressure enhanced the pressure inside the engine, positively affecting engine efficiency indicators. Therefore, the increase in turbocharger pressure is directly proportional to the ICE efficiency. Doi: 10.28991/ESJ-2022-06-03-04 Full Text: PDF