Name: combustion characterization and model fuel development for micro-tubular flame-assisted fuel cells
Uploaded: 2016-10-02T15:00:00.000+00:00
Duration: 8 min 16 s
Description: Watch this Scientific Journal Video about Combustion Characterization and Model Fuel Development for Micro-tubular Flame-assisted Fuel Cells at JoVE.com

This work is supported by an agreement with Syracuse University awarded by the Syracuse Center of Excellence in Energy and Environmental Systems with funding under prime award number DE-EE0006031 from the US Department of Energy and matching funding under award number 53367 from the New York State Energy Research and Development Authority (NYSERDA), contract 61736 from NYSERDA, and an award from Empire State Development's Division of Science, Technology and Innovation (NYSTAR) through the Syracuse Center of Excellence, under award number #C120183. This work is supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. 1247399.

1. Combustion Calculations
<ol>
	<li>Select fuel for analysis. Here, choose methane as the reference fuel, but the principles are transferable to other hydrocarbon fuels.</li>
	<li>With 1 mole of methane as the fuel, balance equation (1) for stoichiometric combustion to get equation (2). 
	<img alt="Equation 1" src="/files/ftp_upload/54638/54638eq1.jpg" /> 
	<img alt="Equation 2" src="/files/ftp_upload/54638/54638eq2.jpg" /></li>
	<li>Calculate the fuel-air ratio for stoichiometric (F/Astoich.) as in equation 3 for methane combustion by dividing the mass of methane by the mass of air. To calculate, the numerator is the number of moles of methane times the molar mass of methane (16 g&#183;mol-1) and denominator is the number of moles of oxygen times the molar mass of oxygen (32 g&#183;mol-1) plus the number of moles of nitrogen times the molar mass of nitrogen (28 g&#183;mol-1). 
	<img alt="Equation 3" src="/files/ftp_upload/54638/54638eq3.jpg" /></li>
	<li>In order to vary the equivalence ratio (equation 4), vary either the air flow rate, the fuel flow rate or both simultaneously. Typically, fix one of the quantities and vary the other. Determine whether to fix either the fuel or air flow rate for the burner. For this experiment, fix the fuel flow rate at 10 L/min and allow the air flow rate to vary in this setup. 
	<img alt="Equation 4" src="/files/ftp_upload/54638/54638eq4.jpg" /></li>
	<li>With the fuel flow rate, f, fixed (10 L/min), F/Astoic. calculated (0.0583), and given the definition of the equivalence ratio, calculate the air flow rate, a, for each equivalence ratio to be tested. Equation (5) provides a direct way of calculating the air flow rate in L/min for each equivalence ratio and the results are shown for an equivalence ratio of 1 for stoichiometry. 
	<img alt="Equation 5" src="/files/ftp_upload/54638/54638eq5.jpg" /> 
	NOTE: The upper flammability limit (or upper explosion limit) is the richest equivalence ratio that can be burned without quenching the flame in the absence of a catalyst. Higher equivalence ratios can be obtained with the use of a catalyst, but only non-catalytic combustion is described in this paper. Consult the literature to assess the upper flammability limit for the fuel chosen.</li>
</ol>
2. Combustion Characterization Experimental Setup
<ol>
	<li>Select mass flow controllers (MFCs) for methane and air based on the flow rates obtained in Step 1.5. Use caution when selecting a MFC size to ensure that the MFC will not be operating at the low end of its range (&#60; 10% of full scale value) during testing. For this specific case, use 40 L/min and 200 L/min MFCs for methane and air, respectively.</li>
	<li>Connect the MFCs to the methane and air tanks via copper tubing.</li>
	<li>Set the regulators on the methane and air tanks to the appropriate pressure for the MFC as specified by the manufacturer. In this case, set the pressure to 138 kPa (20 psi).</li>
	<li>Calibrate the MFCs to ensure accurate flow rates.</li>
	<li>Construct the combustion chamber. For this experiment, develop a combustion chamber 914 mm long with a 168 mm exit diameter.
	<ol>
		<li>Drill ports for combustion exhaust analysis and for thermocouple placement along the length of the combustion chamber. The exact number and spacing needed depends on the size of the flame and the purposes of the experiment. For this setup, space the first 5 thermocouples placed closest to the combustion region 7 mm apart. Space the final 6 thermocouples 14 mm apart. Use the same spacing for the exhaust ports.</li>
		<li>Insert the K-type thermocouples into the combustion chamber via the port holes. Align the thermocouple tip at the center of the combustion chamber. Size the port holes to fit the thermocouple and seal with high temperature metal ferrules and nuts to prevent leakage.</li>
	</ol>
	</li>
	<li>Connect the K-type thermocouples directly to the data acquisition module.</li>
	<li>Connect the data acquisition module to the computer via the USB drive.</li>
	<li>Attach a one-way valve in the copper tubing path immediately after the fuel MFC and just before the burner. Orient the valve so that flow can only move away from the MFC. The one-way valves are an important safety feature to prevent flash back.</li>
	<li>Check the copper tubing before and after the MFC setup for leaks. Use soapy water applied with a brush to the tubing to detect leaks as leaks would create bubbles.</li>
	<li>Connect the combustion chamber and burner to the mass flow controllers via copper tubing.</li>
	<li>After completing the combustion chamber setup, select one of the exhaust ports for testing. Connect this port to copper tubing that extends to the GC analysis port.</li>
	<li>Select a syringe to pull the exhaust from the combustion chamber and then push it into the GC for analysis. For this experiment, use a 25 ml syringe.</li>
	<li>Place a three-way valve in line with the copper tubing connecting the exhaust port to the GC. Connect one end of the two-way valve to the GC, the second to the exhaust port and the third to the 25 ml syringe. Connect the copper tubing to the 3-way valve. Use the syringe to suck combustion exhaust from the chamber and then push it into the GC for analysis.</li>
	<li>Connect the 3-way valve to the GC and syringe. Actuate the syringe plunger to ensure successful operation. 
	NOTE: A simplified schematic of the setup is shown in Figure 1.</li>
</ol>
<img alt="Figure 1" src="/files/ftp_upload/54638/54638fig1.jpg" /> 
Figure 1. Combustion characterization experimental setup schematic. Combustion characterization experimental setup schematic showing fuel, air and exhaust flows (black arrows) and data flows (red arrows). One-way valves are used to prevent flash back. <a href="https://www.jove.com/files/ftp_upload/54638/54638fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
3. Combustion Characterization Experiment
<ol>
	<li>Before testing, push the syringe plunger in fully and open the three-way valve on the exhaust port side.</li>
	<li>Turn the air MFC on first to a flow rate of 86.5 L/min.</li>
	<li>Turn methane MFC on to a flow rate of 10 L/min. This creates a premixed equivalence ratio of 1.10, a slightly rich mixture, which is easier to ignite.</li>
	<li>Turn thermocouples on via the computer module to begin recording data.</li>
	<li>Ignite the mixture at the end of the combustion chamber using a butane lighter. After ignition, the flame should stabilize at the burner front.</li>
	<li>Adjust the equivalence ratio by adjusting the flow rate of air slowly from the initial value of 86.5 L/min to the desired value. Take care to not move too quickly or go outside of the flammability limits which would cause flame quenching.</li>
	<li>Record the temperature reading in a data file after the thermocouples temperatures stabilize.</li>
	<li>Once again, pull the syringe plunger to extract combustion exhaust from the exhaust port.</li>
	<li>After extracting the combustion exhaust, open the three-way valve to the GC side and close the exhaust port side.</li>
	<li>Push the syringe plunger till it closes completely and all of the exhaust has been sent to the GC.</li>
	<li>Repeat steps 3.8-3.10 until all of the residual gases in the copper tubing connecting the port to the GC is removed. A simple analysis of the internal volume of the copper tubing compared to the volume of the syringe will indicate how many times steps 3.8-3.10 need to be repeated.</li>
	<li>After removing all residual gases in the tubing extract a final exhaust sample for analysis. Push the exhaust gas into the GC and turn the GC to analysis mode7,17.</li>
	<li>Record the GC data by saving the GC analysis data.</li>
	<li>Repeat steps 3.1-3.13 until all desired equivalence ratios are tested.</li>
</ol>
4. Development of the Model Combustion Exhaust
<ol>
	<li>Plot the combustion exhaust species volume percentage to observe the trends.</li>
	<li>Determine the cut off concentration value for the model combustion exhaust. In developing a model combustion exhaust fuel for initial mT-FFC analysis, only the components appearing in significant proportions (&#62;1%) are included in the model fuel.</li>
	<li>For the model fuel select only those equivalence ratios that generate significant hydrogen and carbon monoxide (&#62;1% for each component) in the exhaust.</li>
	<li>Record the volume percentage for each of the exhaust gas components meeting the criteria of 4.3.</li>
</ol>
5. Fuel Cell Testing Setup
<ol>
	<li>Determine the flow rate ranges for each gas. Multiply the volume percentage obtained from the GC analysis results by the total flow rate of the model combustion exhaust desired within each fuel cell.</li>
	<li>Assess the range of flow rates for each combustion exhaust species to determine the maximum and minimum flow for each species.</li>
	<li>Select flow meters according to the same principles described in step 2.1.</li>
	<li>Build the testing apparatus by attaching the flow meters to the gas tanks via copper tubing.</li>
	<li>Set the gas pressure regulators to the prescribed value for the flow meters.</li>
	<li>Place one-way valves in the copper tubing path downstream of each flow meter using a combustible gas.</li>
	<li>Connect all flow meter exit ports together via copper tubing and a manifold.</li>
	<li>Set the micro-tubular SOFC on the inside of steel tubing having an internal diameter just larger than the fuel cell&#39;s external diameter. Seal the fuel cell to the steel tubing using ceramic adhesive.</li>
	<li>Connect the steel tubing with micro-tubular SOFC to a piece of ceramic refractory material to hold the fuel cell in the furnace.</li>
	<li>Utilize the 4 probe technique10,11 with current collection and voltage sense wires connected to the micro-tubular SOFC with 2 wires on the anode and 2 wires on the cathode. Ensure that the wires do not cross each other creating shorts.</li>
	<li>Connect the four wires to the four probes of the potentiostat10,11.</li>
	<li>Connect the potentiostat to the computer10,11.</li>
	<li>Place a thermocouple in the furnace with the tip touching the exterior of the micro-tubular SOFC electrolyte10,11.</li>
	<li>Attach thermocouple wires to the data acquisition module.</li>
	<li>Connect the data acquisition module to the computer via the USB port. 
	NOTE: Figure 2 is a simplified schematic showing the mT-FFC testing setup. With the model fuel developed and the setup established for controlling the model fuel flow to the fuel cell, testing can proceed according to conventional fuel cell testing methods. These methods are well established in the literature and will not be repeated here.</li>
</ol>
<img alt="Figure 2" src="/files/ftp_upload/54638/54638fig2.jpg" /> 
Figure 2. Micro-tubular flame-assisted fuel cell testing setup schematic. Flows of H2, CO, CO2, N2 (black arrows) are regulated with a MFC and a one-way valve to prevent flash back. Electrons flow (green line) from the SOFC in the furnace to the potentiostat and back to the SOFC. Flow of thermocouple data and electrochemical data is represented by red arrows. <a href="https://www.jove.com/files/ftp_upload/54638/54638fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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The authors have nothing to disclose.

The protocol discussed here is an important bridge between previous combustion characterization research and fuel cell testing. The use of combustion for fuel reforming and fuel cell testing has been applied for several years in DFFC setups10-15. However, the characterization of the combustion process in DFFCs is primarily concerned with in-situ characterization of the flame composition16 and uses a MS8. As the DFFC is open to the ambient, the exhaust composition consists mostly ...

Solid oxide fuel cell (SOFC) innovations have been reported in recent years as the technology continues to develop. Among the many advantages, SOFCs have become known for high fuel efficiency, low emissions and moderate fuel flexibility compared to other combustion based power generation techniques1. Furthermore, SOFCs are scalable allowing for high fuel efficiency even at small scales. Unfortunately, limitations in current hydrogen infrastructure have created a need for fuel reforming systems that are often inefficient. A recent development is the micro-tubular flame-assisted fuel cell (mT-FFC) reported in the author&#39;s previous work2. The mT-FFC is the first example of a flame-assisted fuel cell (FFC) that builds on the benefits of the original direct flame fuel cell (DFFC), which provides heat generation and fuel reforming via combustion3. The DFFC setup places a SOFC in direct contact with a flame open to the ambient environment. The flame partially oxidizes heavier hydrocarbon fuels to create H2 and CO, which can be used directly in the SOFC with less potential for carbon coking compared to pure methane or other heavier hydrocarbons. In addition, the flame provides the thermal energy needed to bring the SOFC to its operating temperature. A recent change to the original DFFC occurred by moving the SOFC out of the flame region and channeling the combustion exhaust to the SOFC to create the FFC2. Unlike the DFFC, the combustion occurs in a partially enclosed chamber (instead of the ambient) so that the fuel to air ratio can be controlled and the exhaust can be directly fed to the fuel cell without complete combustion occurring. FFCs have additional advantages including high fuel utilization and high electrical efficiency compared to DFFCs2.
As an emerging area of research, experimental techniques are needed that can assess the potential of mT-FFCs for future power generation applications. These techniques require analysis of partial oxidation, or fuel-rich combustion, and the exhaust which has been identified as a way of generating H2 and CO, also known as syngas, along with CO2 and H2O. The syngas can be used directly in the fuel cells for power generation. The analysis of fuel-rich combustion exhaust has been well established in recent years and has been carried out theoretically4, computationally5,6 and experimentally7 for many different purposes. Many of the theoretical and computational studies have relied on chemical equilibrium analysis (CEA) to assess the combustion product species that are energetically favorable, and chemical kinetic models for reaction mechanisms. While these methods have been very useful, many emerging technologies have relied upon experimental techniques during research and development. Experimental techniques typically rely on analysis of the combustion exhaust using either a gas chromatograph (GC)7 or a mass spectrometer (MS)8. Either the GC line/syringe or the MS probe is inserted into the combustion exhaust and measurements are taken to assess the species concentration. Application of the experimental techniques has been common in the area of small scale power generation. Some examples include micro combustors that have been developed to operate with single chamber SOFCs7,9 and DFFCs10-15. The analysis of the combustion exhaust occurs under a wide range of operating conditions including different temperatures, flow rates and equivalence ratios.
In the area of DFFC research, fuel and oxidant can be partially premixed or non-premixed, with the burner open to the ambient which ensures complete combustion. With a need to analyze the flame composition, a MS has been used in many instances for DFFC research and combustion analysis16. The more recent development of the FFC differs by relying on premixed combustion with the burner in a partially enclosed environment to prevent complete oxidation of the fuel. As a result, analysis of the combustion exhaust in a controlled environment free from air leakage is needed. Experimental techniques developed for this purpose rely on the earlier techniques used for micro combustor research with GC analysis of the combustion exhaust at varying equivalence ratios. The GC analysis leads to characterization of the combustion exhaust composition (i.e., the volume percent of each exhaust constituent including CO2, H2O, N2, etc.) This analysis allows for mixing of separate gases according to the ratios measured by the GC to create a model fuel-rich combustion exhaust for future FFC research.
The protocols for analyzing fuel-rich combustion exhaust, developing a model fuel-rich combustion exhaust and applying the exhaust for SOFC testing are established in this paper. Common challenges and limitations are discussed for these techniques.

<table><tbody><tr><td>Gas chromotograph</td><td>SRI Instruments, Inc.</td><td>SRI 8610C</td><td></td></tr><tr><td>K type thermocouples</td><td>Omega</td><td>KQXL-116G-6</td><td>Custom length</td></tr><tr><td>K type thermocouple extension wire</td><td>Omega</td><td>EXTT-K-20-SLE-100</td><td></td></tr><tr><td>Mass flow controller</td><td>Omega</td><td>FMA5427</td><td>0-40 L/min (N&lt;sub&gt;2&lt;/sub&gt;)&lt;br/&gt; Used for methane</td></tr><tr><td>Mass flow controller</td><td>Omega</td><td>FMA5443</td><td>0-200 L/min (N&lt;sub&gt;2&lt;/sub&gt;)&lt;br/&gt; Used for air</td></tr><tr><td>Mass flow controller</td><td>Omega</td><td>FMA5402A</td><td>0-10 ml/min (N&lt;sub&gt;2&lt;/sub&gt;)&lt;br/&gt; Used for CO</td></tr><tr><td>Mass flow controller</td><td>Brooks Instrument</td><td>SLA5850</td><td>200 SCCM (Propane)&lt;br/&gt; Used for CO&lt;sub&gt;2&lt;/sub&gt;</td></tr><tr><td>Mass flow controller</td><td>Brooks Instrument</td><td>SLA5850</td><td>5 L/min (Air)&lt;br/&gt; Used for N&lt;sub&gt;2&lt;/sub&gt;</td></tr><tr><td>Mass flow controller</td><td>Brooks Instrument</td><td>SLA5850</td><td>500 SCCM (N&lt;sub&gt;2&lt;/sub&gt;)&lt;br/&gt; Used for H&lt;sub&gt;2&lt;/sub&gt;</td></tr><tr><td>Regulator</td><td>Harris Products Group</td><td>HP721-125-350-F</td><td>Methane tank</td></tr><tr><td>Regulator</td><td>Harris Products Group</td><td>HP702-050-590-E</td><td>Air tank</td></tr><tr><td>Regulator</td><td>Airgas</td><td>Y11-SR145B</td><td>CO tank</td></tr><tr><td>Regulator</td><td>Harris Products Group</td><td>HP702-050-320-E</td><td>CO&lt;sub&gt;2&lt;/sub&gt; tank</td></tr><tr><td>Regulator</td><td>Airgas</td><td>Y12-215B</td><td>N&lt;sub&gt;2&lt;/sub&gt; tank</td></tr><tr><td>Regulator</td><td>Harris Products Group</td><td>HP702-015-350-D</td><td>H&lt;sub&gt;2&lt;/sub&gt; tank</td></tr><tr><td>Methane, Compressed,&lt;br/&gt;Ultra high purity</td><td>Airgas</td><td>UN1971</td><td>Extremely Flammable</td></tr><tr><td>Air, Compressed,&lt;br/&gt;Ultra pure</td><td>Airgas</td><td>UN1002</td><td>Not classified as hazardous to health.</td></tr><tr><td>CO, Compressed,&lt;br/&gt;Ultra high purity</td><td>Airgas</td><td>UN1016</td><td>Toxic by inhalation, Extremely flammable</td></tr><tr><td>CO&lt;sub&gt;2&lt;/sub&gt;, Compressed,&lt;br/&gt;Research grade</td><td>Airgas</td><td>UN1013</td><td>Asphyxiant in high concentrations</td></tr><tr><td>N&lt;sub&gt;2&lt;/sub&gt;, Compressed,&lt;br/&gt; Ultra high purity</td><td>Airgas</td><td>UN1066</td><td>Not classified as hazardous to health.</td></tr><tr><td>H&lt;sub&gt;2&lt;/sub&gt;, Compressed,&lt;br/&gt; Ultra high purity</td><td>Airgas</td><td>UN1049</td><td>Extremely flammable, burns with invisible flame</td></tr><tr><td>Source meter</td><td>Tektronix, Inc.</td><td>Keithley 2420</td><td>Connects to computer via USB</td></tr><tr><td>Horizontal split tube furnace</td><td>MTI Corportation</td><td>OTF-1200X</td><td></td></tr><tr><td>Data acquisition</td><td>National Instruments</td><td>NI cDAQ-9172</td><td>Connects to computer via USB</td></tr><tr><td>Thermocouple input</td><td>National Instruments</td><td>NI 9211</td><td>Connects to cDAQ-9172</td></tr><tr><td>Computer control for Mass Flow Controllers</td><td>National Instruments</td><td>NI 9263</td><td>Connects to cDAQ-9172&lt;br/&gt; Computer control for Mass Flow Controllers</td></tr><tr><td>Testing software</td><td>National Instruments</td><td>LabVIEW 8.6</td><td></td></tr><tr><td>Ceramabond</td><td>Aremco</td><td>552-VFG</td><td>1 Pint</td></tr></tbody></table>

combustion characterization and model fuel development for micro-tubular flame-assisted fuel cells

Combustion based power generation has been accomplished for many years through a number of heat engine systems. Recently, a move towards small scale power generation and micro combustion as well as development in fuel cell research has created new means of power generation that combine solid oxide fuel cells with open flames and combustion exhaust. Instead of relying upon the heat of combustion, these solid oxide fuel cell systems rely on reforming of the fuel via combustion to generate syngas for electrochemical power generation. Procedures were developed to assess the combustion by-products under a wide range of conditions. While theoretical and computational procedures have been developed for assessing fuel-rich combustion exhaust in these applications, experimental techniques have also emerged. The experimental procedures often rely upon a gas chromatograph or mass spectrometer analysis of the flame and exhaust to assess the combustion process as a fuel reformer and means of heat generation. The experimental techniques developed in these areas have been applied anew for the development of the micro-tubular flame-assisted fuel cell. The protocol discussed in this work builds on past techniques to specify a procedure for characterizing fuel-rich combustion exhaust and developing a model fuel-rich combustion exhaust for use in flame-assisted fuel cell testing. The development of the procedure and its applications and limitations are discussed.

The combustion characterization chamber should be checked prior to testing at the desired equivalence ratios for back-flow of air into the chamber or other air leakage during testing. Combustion processes in open chambers are known to be nearly isobaric. As a result, pressure within the combustion chamber may not be enough to ensure that no air from the external environment is back-flowing into the combustion chamber from the chamber exhaust port or other leakage points. There are several...

Watch this Scientific Journal Video about Combustion Characterization and Model Fuel Development for Micro-tubular Flame-assisted Fuel Cells at JoVE.com

Combustion Characterization and Model Fuel Development for Micro-tubular Flame-assisted Fuel Cells

A protocol for creating a model fuel-rich combustion exhaust is developed through combustion characterization and is applied for micro-tubular flame-assisted fuel cell testing and research.

Combustion based power generation has been accomplished for many years through a number of heat engine systems. Recently, a move towards small scale power ...

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9.5K Views.  Syracuse University. A protocol for creating a model fuel-rich combustion exhaust is developed through combustion characterization and is applied for micro-tubular flame-assisted fuel cell testing and research.

Video: Combustion Characterization and Model Fuel Development for Micro-tubular Flame-assisted Fuel Cells

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen 1-7. The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion2. Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation8-12. It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition8, 10, 13, 14 ("coking") and sulfur poisoning11, 15 and the manner in which surface modifications stave off this degradation16. The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated17-22. In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode.

We present a unique platform for characterizing electrode surfaces in solid oxide fuel cells (SOFCs) that allows simultaneous performance of multiple characterization techniques (e.g. in situ Raman spectroscopy and scanning probe microscopy alongside electrochemical measurements). Complementary information from these analyses may help to advance toward a more profound understanding of electrode reaction and degradation mechanisms, providing insights into rational design of better materials for SOFCs.

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen ...

Flame Experiments at the Advanced Light Source: New Insights into Soot Formation Processes

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics Beamline of the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory1-4. This video demonstrates how the complex chemical structures of laboratory-based model flames are analyzed using flame-sampling mass spectrometry with tunable synchrotron-generated vacuum-ultraviolet (VUV) radiation. This experimental approach combines isomer-resolving capabilities with high sensitivity and a large dynamic range5,6. The first part of the video describes experiments involving burner-stabilized, reduced-pressure (20-80 mbar) laminar premixed flames. A small hydrocarbon fuel was used for the selected flame to demonstrate the general experimental approach. It is shown how species&#8217; profiles are acquired as a function of distance from the burner surface and how the tunability of the VUV photon energy is used advantageously to identify many combustion intermediates based on their ionization energies. For example, this technique has been used to study gas-phase aspects of the soot-formation processes, and the video shows how the resonance-stabilized radicals, such as C3H3, C3H5, and i-C4H5, are identified as important intermediates7. The work has been focused on soot formation processes, and, from the chemical point of view, this process is very intriguing because chemical structures containing millions of carbon atoms are assembled from a fuel molecule possessing only a few carbon atoms in just milliseconds. The second part of the video highlights a new experiment, in which an opposed-flow diffusion flame and synchrotron-based aerosol mass spectrometry are used to study the chemical composition of the combustion-generated soot particles4. The experimental results indicate that the widely accepted H-abstraction-C2H2-addition (HACA) mechanism is not the sole molecular growth process responsible for the formation of the observed large polycyclic aromatic hydrocarbons (PAHs).

Gas sampling from laboratory-scale flames with online analysis of all species by mass spectrometry is a powerful method to investigate the complex mixture of chemical compounds occurring during combustion processes. Coupled with tunable soft ionization via synchrotron-generated vacuum-ultraviolet radiation, this technique provides isomer-resolved information and potentially fragment-free mass spectra.

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics ...

Preparation and Evaluation of Hybrid Composites of Chemical Fuel and Multi-walled Carbon Nanotubes in the Study of Thermopower Waves

When a chemical fuel at a certain position in a hybrid composite of the fuel and a micro/nanostructured material is ignited, chemical combustion occurs along the interface between the fuel and core materials. Simultaneously, dynamic changes in thermal and chemical potentials across the micro/nanostructured materials result in concomitant electrical energy generation induced by charge transfer in the form of a high-output voltage pulse. We demonstrate the entire procedure of a thermopower wave experiment, from synthesis to evaluation. Thermal chemical vapor deposition and the wet impregnation process are respectively employed for the synthesis of a multi-walled carbon nanotube array and a hybrid composite of picric acid/sodium azide/multi-walled carbon nanotubes. The prepared hybrid composites are used to fabricate a thermopower wave generator with connecting electrodes. The combustion of the hybrid composite is initiated by laser heating or Joule-heating, and the corresponding combustion propagation, direct electrical energy generation, and real-time temperature changes are measured using a high-speed microscopy system, an oscilloscope, and an optical pyrometer, respectively. Furthermore, the crucial strategies to be adopted in the synthesis of hybrid composite and initiation of their combustion that enhance the overall thermopower wave energy transfer are proposed.

A protocol for conducting thermopower wave experiments is presented. The synthesis of hybrid composites of a chemical fuel and micro/nanostructured material, manufacturing of a thermopower wave generator, and methods for measuring the corresponding physical phenomena are described.

When a chemical fuel at a certain position in a hybrid composite of the fuel and a micro/nanostructured material is ignited, chemical combustion occurs ...

Characterization of Nanocrystal Size Distribution using Raman Spectroscopy with a Multi-particle Phonon Confinement Model

Analysis of the size distribution of nanocrystals is a critical requirement for the processing and optimization of their size-dependent properties. The common techniques used for the size analysis are transmission electron microscopy (TEM), X-ray diffraction (XRD) and photoluminescence spectroscopy (PL). These techniques, however, are not suitable for analyzing the nanocrystal size distribution in a fast, non-destructive and a reliable manner at the same time. Our aim in this work is to demonstrate that size distribution of semiconductor nanocrystals that are subject to size-dependent phonon confinement effects, can be quantitatively estimated in a non-destructive, fast and reliable manner using Raman spectroscopy. Moreover, mixed size distributions can be separately probed, and their respective volumetric ratios can be estimated using this technique. In order to analyze the size distribution, we have formulized an analytical expression of one-particle PCM and projected it onto a generic distribution function that will represent the size distribution of analyzed nanocrystal. As a model experiment, we have analyzed the size distribution of free-standing silicon nanocrystals (Si-NCs) with multi-modal size distributions. The estimated size distributions are in excellent agreement with TEM and PL results, revealing the reliability of our model.

We demonstrate how to determine the size distribution of semiconductor nanocrystals in a quantitative manner using Raman spectroscopy employing an analytically defined multi-particle phonon confinement model. Results obtained are in excellent agreement with the other size analysis techniques like transmission electron microscopy and photoluminescence spectroscopy.

Analysis of the size distribution of nanocrystals is a critical requirement for the processing and optimization of their size-dependent properties. The ...

Compact Lens-less Digital Holographic Microscope for MEMS Inspection and Characterization

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and automotive. However, effective inspection and characterization metrology systems are needed to ensure the functional reliability of MEMS. This study presents a system based on digital holography as a tool for MEMS metrology. Digital holography has gained increasing attention in the past 20 years. With the fast development and decreasing cost of sensor arrays, resolution of such systems has increased broadening potential applications. Thus, it has attracted attention from both research and industry sides as a potential reliable tool for industrial metrology. Indeed, by recording the interference pattern between an object beam (which contains sample height information) and a reference beam on a CCD camera, one can retrieve the quantitative phase information of an object. However, most of digital holographic systems are bulky and thus not easy to implement on industry production lines. The novelty of the system presented is that it is lens-less and thus very compact. In this study, it is shown that the Compact Digital Holographic Microscope (CDHM) can be used to evaluate several characteristics typically consider as criteria in MEMS inspections. The surface profiles of MEMS in both static and dynamic conditions are presented. Comparison with AFM is investigated to validate the accuracy of the CDHM.

We present a compact reflection digital holographic system (CDHM) for inspection and characterization of MEMS devices. A lens-less design using a diverging input wave providing natural geometrical magnification is demonstrated. Both static and dynamic studies are presented.

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and ...

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices have used devices prepared by spin coating, a process that is not amenable to large-scale fabrication. This mismatch in device fabrication makes it difficult to translate quantitative results obtained in the laboratory to the commercial level, making optimization difficult. Using a mini-slot die coater, this mismatch can be resolved by translating the commercial process to the laboratory and characterizing the structure formation in the active layer of the device in real time and in situ as films are coated onto a substrate. The evolution of the morphology was characterized under different conditions, allowing us to propose a mechanism by which the structures form and grow. This mini-slot die coater offers a simple, convenient, material efficient route by which the morphology in the active layer can be optimized under industrially relevant conditions. The goal of this protocol is to show experimental details of how a solar cell device is fabricated using a mini-slot die coater and technical details of running in situ structure characterization using the mini-slot die coater.

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Here, we present a protocol to fabricate organic thin film solar cells using a mini-slot die coater and related in-line structure characterizations using synchrotron scattering techniques.

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices ...

Experimental Methodology for Estimation of Local Heat Fluxes and Burning Rates in Steady Laminar Boundary Layer Diffusion Flames

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex interactions occurring at the interface between gas-phase flames and condensed-phase fuels. The current research provides a technique to explore the dynamic relationship between a combustible condensed fuel surface and gas-phase flames in laminar boundary layers. Experiments have previously been conducted in both forced and free convective environments over both solid and liquid fuels. A unique methodology, based on the Reynolds Analogy, was used to estimate local mass burning rates and flame heat fluxes for these laminar boundary layer diffusion flames utilizing local temperature gradients at the fuel surface. Local mass burning rates and convective and radiative heat feedback from the flames were measured in both the pyrolysis and plume regions by using temperature gradients mapped near the wall by a two-axis traverse system. These experiments are time-consuming and can be challenging to design as the condensed fuel surface burns steadily for only a limited period of time following ignition. The temperature profiles near the fuel surface need to be mapped during steady burning of a condensed fuel surface at a very high spatial resolution in order to capture reasonable estimates of local temperature gradients. Careful corrections for radiative heat losses from the thermocouples are also essential for accurate measurements. For these reasons, the whole experimental setup needs to be automated with a computer-controlled traverse mechanism, eliminating most errors due to positioning of a micro-thermocouple. An outline of steps to reproducibly capture near-wall temperature gradients and use them to assess local burning rates and heat fluxes is provided.

We describe the use of micro-thermocouples to estimate local temperature gradients in steady laminar boundary layer diffusion flames. By extension of the Reynolds Analogy, local temperature gradients can be further used to estimate the local mass burning rates and heat fluxes in such flames with high accuracy.

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex ...

A Guide to Concentration Alternating Frequency Response Analysis of Fuel Cells

An experimental setup capable of generating a periodic concentration input perturbation of oxygen was used to perform concentration-alternating frequency response analysis (cFRA) on proton-exchange membrane (PEM) fuel cells. During cFRA experiments, the modulated concentration feed was sent to the cathode of the cell at different frequencies. The electric response, which can be cell potential or current depending on the control applied on the cell, was registered in order to formulate a frequency response transfer function. Unlike traditional electrochemical impedance spectroscopy (EIS), the novel cFRA methodology makes it possible to separate the contribution of different mass transport phenomena from the kinetic charge transfer processes in the frequency response spectra of the cell. Moreover, cFRA is able to differentiate between varying humidification states of the cathode. In this protocol, the focus is on the detailed description of the procedure to perform cFRA experiments. The most critical steps of the measurements and future improvements to the technique are discussed.

We present a protocol for concentration alternating frequency response analysis of fuel cells, a promising new method of studying fuel cell dynamics.

An experimental setup capable of generating a periodic concentration input perturbation of oxygen was used to perform concentration-alternating frequency ...

Environment

Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectrometer

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This flexible tool offers a detailed observation of chemical gas-phase kinetics in reacting flows under well-controlled conditions. The vast range of operating conditions available in a laminar flow reactor enables access to extraordinary combustion applications that are typically not achievable by flame experiments. These include rich conditions at high temperatures relevant for gasification processes, the peroxy chemistry governing the low temperature oxidation regime or investigations of complex technical fuels. The presented setup allows measurements of quantitative speciation data for reaction model validation of combustion, gasification and pyrolysis processes, while enabling a systematic general understanding of the reaction chemistry. Validation of kinetic reaction models is generally performed by investigating combustion processes of pure compounds. The flow reactor has been enhanced to be suitable for technical fuels (e.g. multi-component mixtures like Jet A-1) to allow for phenomenological analysis of occurring combustion intermediates like soot precursors or pollutants. The controlled and comparable boundary conditions provided by the experimental design allow for predictions of pollutant formation tendencies. Cold reactants are fed premixed into the reactor that are highly diluted (in around 99 vol% in Ar) in order to suppress self-sustaining combustion reactions. The laminar flowing reactant mixture passes through a known temperature field, while the gas composition is determined at the reactors exhaust as a function of the oven temperature. The flow reactor is operated at atmospheric pressures with temperatures up to 1,800 K. The measurements themselves are performed by decreasing the temperature monotonically at a rate of -200 K/h. With the sensitive MBMS technique, detailed speciation data is acquired and quantified for almost all chemical species in the reactive process, including radical species.

An investigation of the oxidative combustion chemistry of novel biofuels, fuel components, or jet fuels by comparison of quantitative speciation data is presented. The data can be used for kinetic model validation and enables fuel assessment strategies.This manuscript describes the atmospheric high-temperature flow reactor and demonstrates its capabilities.

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This ...

Chemistry

Improving the Combustion Performance of a Hybrid Rocket Engine using a Novel Fuel Grain with a Nested Helical Structure

A technique to improve the combustion performance of a hybrid rocket engine using a novel fuel grain structure is presented. This technique utilizes the different regression rates of acrylonitrile butadiene styrene and paraffin-based fuels, which increase the exchanges of both matter and energy by swirl flow and recirculation zones formed at the grooves between the adjacent vanes. The centrifugal casting technique is used to cast the paraffin-based fuel into an acrylonitrile butadiene styrene substrate made by three-dimensional printing. Using oxygen as the oxidizer, a series of tests were conducted to investigate the combustion performance of the novel fuel grain. In comparison to paraffin-based fuel grains, the fuel grain with a nested helical structure, which can be maintained throughout the combustion process, showed significant improvement in the regression rate and great potential in improvement of combustion efficiency.

A technique utilizing a solid fuel grain with a novel nested helical structure to improve the combustion performance of a hybrid rocket engine is presented.

A technique to improve the combustion performance of a hybrid rocket engine using a novel fuel grain structure is presented. This technique utilizes the ...

Combustion Characterization and Model Fuel Development for Micro-tubular Flame-assisted Fuel Cells

Summary

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Chapters in this video

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

Flame Experiments at the Advanced Light Source: New Insights into Soot Formation Processes

Preparation and Evaluation of Hybrid Composites of Chemical Fuel and Multi-walled Carbon Nanotubes in the Study of Thermopower Waves

Characterization of Nanocrystal Size Distribution using Raman Spectroscopy with a Multi-particle Phonon Confinement Model

Compact Lens-less Digital Holographic Microscope for MEMS Inspection and Characterization

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Experimental Methodology for Estimation of Local Heat Fluxes and Burning Rates in Steady Laminar Boundary Layer Diffusion Flames

A Guide to Concentration Alternating Frequency Response Analysis of Fuel Cells

Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectrometer

Improving the Combustion Performance of a Hybrid Rocket Engine using a Novel Fuel Grain with a Nested Helical Structure