Authors acknowledge financial support from U.S. Department of Energy (US DOE) under the federal grant DE-FE-0023385. Technical discussion with Drs. Rin Burke and Shailesh Vora (National Energy Technology Laboratory) is gratefully acknowledged. Drs. Amit Pandey (LG Fuel Cells, Canton OH), Jeff Stevenson and Matt Chou (Pacific Northwest National Laboratory, Richland WA) are acknowledged for their help with long term test validation of the performance of the getters. Authors acknowledge the University of Connecticut for providing laboratory support. Dr. Lichun Zhang and Ms. Chiying Liang is acknowledged for technical discussion and help with the experiments.

1. Synthesis of chromium getter
<ol>
	<li>Synthesize precursor powder using alkaline earth and transition metal oxide salts via conventional coprecipitation synthesis route as depicted in Figure 116.
	<ol>
		<li>Prepare a stock solution using 50.33 g of strontium nitrate Sr(NO3)2 and 43.97 g of nickel nitrate hexahydrate Ni(NO3)2.6H2O in order to prepare 2.4 M solutions in 100 mL of de-ionized water.&#160;</li>
		<li>Use 9 mL of 2.4 M Sr(NO3)2 and add with 7 mL of 2.4 M solution of Ni(NO3)2.6H2O, followed by stirring the mixed solution and heating up to 80 &#176;C.</li>
		<li>Add 30 mL of 5 M NH4OH to increase the pH to 8.5 for precipitation, then, dry the solution in a dry oven and ensure that all the water evaporates until a blue waxy compound is observed. Rinse&#160;the powder in DI water to ensure that residual ammonium nitrate is removed by filtration. Finally, dry the powder at 120 &#176;C for 2 h.&#160; 
		Note: This will produce&#160;precursor powder for strontium nickel oxide (SNO) getter.&#160;</li>
	</ol>
	</li>
	<li>Dissolve the powder in water to prepare a slurry.&#160;</li>
	<li>Immerse the cordierite substrate in the slurry for dip-coating, followed by drying in air at ~120 &#176;C for at least 2 h with a ramp rate of 5 &#176;C.</li>
	<li>Calcine the substrate in air at the temperature of 650 &#176;C for 12 h with a ramp rate of 5 &#176;C to produce SNO getter.&#160;</li>
</ol>
2. Screening of chromium getter using Cr transpiration test
<ol>
	<li>Set up experiment following the illustration of Figure 2a&#160;for the validation of Cr getters.
	<ol>
		<li>Place 2 gram of sintered chromium oxide pellet (1,200 &#176;C, 2 h) as a chromium source in a quartz tube.&#160; 
		Note: the quartz tube is specifically designed with a diffuser inside (shown in Figure 2) to prevent any back diffusion of chromium vapor during operation. The dimensions of the fabricated getter cartridge match the inside diameter of the quartz tube. Getter cartridge is placed between the chromium source and the outlet elbow (shown in Figure 2).&#160;</li>
		<li>Flow the compressed air at a flow rate of 300 sccm through a mass flow controller (MFC). Bubble the air at room temperature water to ensure that the humidity is 3% H2O. This humidified air passes through the chromia pellets, evaporate chromium vapor and flow through the getter.&#160; 
		Note: The chiller and condenser are placed at the outlet of the transpiration setup to enable condensation of chromium-containing vapor which deposits at the outlet elbow (at the low temperature zone).</li>
		<li>Place additional wash bottles before venting the gas at the outlet to ensure that the evaporated chromium is captured.&#160;</li>
		<li>Having completed the setup, purge the tube with air for at least 1 h to ensure that there is no leaks or contaminants.&#160;</li>
		<li>Start the furnace to heat up to the desired temperature (for example, 850 &#176;C in this case) and hold it there for 500 h.&#160;</li>
		<li>Monitor the color change of outlet elbow and record for any discoloration due to deposited chromium compounds.&#160;</li>
		<li>Lower the furnace temperature back to room temperature (RT) after the completion of the test. Turn off the air flow until the furnace temperature reaches RT.&#160;</li>
		<li>Remove the getter sample for post-test analyses and characterization.&#160;</li>
	</ol>
	</li>
	<li>Quantitative analysis of chromium species by inductively coupled plasma mass spectroscopy (ICP-MS)&#160; 
	Note: ICP-MS sample preparation of post Cr transpiration test17.
	<ol>
		<li>Wash the deposited chromium from glass elbow, condenser, wash bottles and quartz tubes using 20% nitric acid to extract the chromium after conducting transpiration test for 500 h.&#160;</li>
		<li>Extract the deposited chromium by dissolving it in 20% nitric acid (HNO3) for 12 h.&#160;</li>
		<li>Further remove any undissolved chromium species from the glass wall by dissolution in alkaline potassium permanganate solution upon heating at 80 &#176;C. 
		Note: Convert any partial unreacted Cr3+ species to Cr6+ species in this step.&#160;</li>
		<li>Analyze the DI water and nitric acid blank sample by ICP-MS.</li>
		<li>Divide each sample into three parts for ICP-MS analysis and report the average value.</li>
	</ol>
	</li>
</ol>
3. Electrochemical validation of chromium getter using SOFC cells with and without getter&#160;
<ol>
	<li>Cell fabrication and in-operando electrochemical testing of Cr getters18,19
	<ol>
		<li>Fabricate SOFCs by screen printing LSM paste on the surface of YSZ electrolyte (Figure 3a).&#160;</li>
		<li>Sinter the applied LSM ink at 1,200 &#176;C for 2 h, heated with a ramp rate of 3 &#176;C/min.&#160;</li>
		<li>Use Pt electrode as the anode. Attach a Pt on the YSZ disc (anode side) as a reference electrode, and attach Pt gauze and Pt wires to YSZ electrolyte disc using Pt ink and then cure the SOFC at 850 &#176;C for 2 h at a ramp rate of 3 &#176;C/min.&#160;</li>
		<li>Conduct three distinct experiments using three identical SOFCs (namely Cell a, b, and c) to validate the efficacy of getters and demonstrate chromium poisoning without a getter.&#160; 
		Note: make sure to use the identical test conditions to simulate nominal SOFC operating conditions of 850 &#176;C and maintain the anode air (dry) for all the tests at 150 sccm.&#160;</li>
		<li>Assembly the Cell-a in the tube reactor in the absence of chromium source using paste for sealing. Heat the furnace with a ramp rate of 5 &#176;C/min up to a designed temperature (for example: 850 &#176;C in this study). Then, flow the 3% H2O/air (for example 300-500 sccm) to the LSM cathode.</li>
		<li>Measure the electrochemical performance of the SOFC using a multi-channel potentiostat9.&#160;</li>
		<li>Record the cell current every minute with a bias of 0.5 V applied between the cathode and the reference electrode.&#160;</li>
		<li>Conduct electrochemical impedance spectroscopy (EIS) analyses between cathode and reference electrode using three electrode mode in the frequency range of 0.5 Hz to 200 KHz with 10 mV sinus amplitude at an interval of 1 h. After a 100-hour test, cool down the furnace to room temperature and take the Cell-a for characterization.</li>
		<li>Place 2 gram chromium oxide (Cr2O3) pellets (source of chromium vapor) in a porous container at the constant heating zone of the alumina tube. Assembly the Cell-b in the tube reactor using paste for sealing.&#160; Heat the furnace with a ramp rate of 5 &#176;C/min up to 850 &#176;C. Then, flow the humidified air (for example 300-500 sccm) through the chromia pellets and ensure a constant generation of the chromium vapor species9.&#160;</li>
		<li>Repeat Steps 3.1.6 &#8211; 3.1.8. After a 100-hour test, cool down the furnace to room temperature and take the Cell-b for characterization.</li>
		<li>Place 2 gram chromium oxide (Cr2O3) pellets (source of chromium vapor) in a porous container at the constant heating zone of the alumina tube. Place a chromium getter above the chromium source. Assembly the Cell-c on the top of the tube reactor using paste for sealing. Heat the furnace with a ramp rate of 5 &#176;C/min up to a designed temperature (for example: 850&#176;C in this study). Then, flow the 3% H2O/air (for example 300-500 sccm) to the LSM cathode.</li>
		<li>Repeat Steps 3.1.6 &#8211; 3.1.8. After a 100-hour test, cool down the furnace to room temperature and take the Cell-c for characterization.</li>
	</ol>
	</li>
	<li>Posttest getter morphological and chemical characterization 
	Note: Posttest characterization is conducted using scanning electron microscopy coupled with energy dispersive spectroscopy and scanning transmission electron microscopy (STEM) coupled with EDS analyses. Focused electron and ion-beam technologies (FIB) have utilized for the preparation of nanoscale samples.&#160;
	<ol>
		<li>Analyze the microstructures of the cell component by fracturing after the electrochemical test.&#160; Use SEM instrument for morphological analysis. Ensure that both the morphologies and chemical compositions of LSM cathode surface and LSM/YSZ interface are analyzed13,14
		<ol>
			<li>Prior to conducting SEM analysis, prepare samples by sputter coating of gold (Au) films to make sure the sample surface is conductive (avoiding of charge on the sample surface). The coating chamber was under a vacuum (&#60; 50 mm Torr). The applied current was at 40 mA and the coating time was 1 min.&#160;&#160;</li>
			<li>Conduct quantitative elemental distribution using energy dispersive X-ray spectroscopy (EDS) technique. The distance between the specimen and the lower pole piece in SEM system was set at 10 mm. A voltage of 20 KV was applied for the SEM and EDS analysis.&#160;</li>
		</ol>
		</li>
		<li>Conduct the chemical, structural and morphological analyses of the chromium getter using the SEM-EDS technique to obtain the chromium capture profile across the getter channels.&#160;
		<ol>
			<li>Prepare the posttest getter sample by dissecting the getter sample into half using a knife.&#160;</li>
			<li>Repeat Step 3.1.1.1 to coat conductive gold films on the getter surface.</li>
			<li>Repeat Step 3.2.1.2. Ensure that detailed EDS analyses were conducted from the inlet of the getter towards the outlet along the central channel as shown in Figure 2b. Use weight (wt.) % of total chromium measured against the channel length to plot the chromium profile.</li>
		</ol>
		</li>
		<li>Conduct in-depth chemical, structural and morphological analyses of the chromium getter using the FIB-STEM-EDS technique17,20.
		<ol>
			<li>Repeat Step 3.1.1.1 to coat conductive gold films on the getter surface.</li>
			<li>Load the sample in the FIB-STEM instrument, select the region of interest (ROI) for sample extraction, deposit four layers of Pt to mark and protect the sample (a typical area of 30 &#181;m length &#215; 15 &#181;m width).</li>
			<li>Mill the channels around the above ROI using the FIB beam until a &#8220;bridge-like&#8221; strip is left. Then, make wedges at both sides of the strip to make sure the depth is enough for your analysis (a typical depth is 10-20 &#181;m).</li>
			<li>Mount to the micromanipulator needle and cut the FIB sample by milling using an ion beam with 15 nA current. Then lift the FIB sample from the bulk getter sample to the FIB-STEM grid holder, which is perpendicular to the electron beam. After the specimen touch the grid at right position, Pt is deposited using an ion beam current of 0.5 nA to connect the specimen to the grid.&#160; &#160;&#160;</li>
			<li>Make the specimen thinner using a FIB current of about 20 pA at 2 kV to obtain a 50-60 nm sample thickness. Final clean-up of the specimen is also performed using argon-milling at an extra low current (0.5 pA at 1 kV).&#160;</li>
			<li>Conduct STEM-EDS mapping of the above getter specimen. The scanning transmission electron microscope was operated at 200 kV. A High Angle Annular Dark Field (HAADF) image of the selected area on the getter specimen was obtained and elemental maps of relevant elements (such as Cr and Sr) were taken.&#160;&#160;</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>

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Authors do not have anything to disclose.

The experimental results clearly demonstrate the effectiveness of chromium getters during long-term chromium transpiration tests and electrochemical tests. Presence of getters successfully mitigates the contamination of the electrode which otherwise would lead to rapid increase in polarization resistance and electrochemical performance degradation.
The formation of gas phase chromium species from chromia is favored and enhanced with an increase of water vapor concentration (humidity level)16. The water content in the cathodic air is maintained at 3% representing room temperature humidification and saturation. A high temperature cell exposure condition of 850 &#176;C has been selected to demonstrate the effectiveness of the prepared chromium getters in this study.
For the rational design of Cr getters, the first step is to identify various chromium species present in the humid air environment. Thermodynamic calculations indicated significantly different equilibrium partial pressures of chromium vapor species in dry and humidified air. CrO3 was found as predominant gaseous species at elevated temperatures in dry air whereas hydrated oxides such as CrO2(OH) and CrO2(OH)2 were identified as prevalent species in humid air at elevated temperatures15. Amongst all the chromium vapor species, the partial pressure of CrO2(OH)2 remained relatively high throughout the entire temperature range (Figure 4a). It is noted that lowering of the temperature did not significantly lower the chromium vapor pressure. Presence of alkaline oxide (SrO for example) containing getter, however, has indicated significant reduction in the equilibrium chromium vapor pressure due to the formation of thermodynamically stable compound (SrCrO4)14. In this study, our observations indicate that the cordierite supported SNO getter reacts with chromium vapors to form crystalline SrCrO4 and that also lowers the partial pressure of Cr vapors considering the reaction (Eq. 1):
SrO (s) + CrO2(OH)2 (g)&#8594; SrCrO4 (s) + H2O (g)&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;(1)
During the long-term capture test using the transpiration method, discoloration of the outlet elbow was not observed, indicating absence of gaseous chromium vapor in the exiting air stream and hence the formation of yellowish deposit at lower temperatures on the exposed outlet elbow area. Most Cr vapor was captured within 5 mm of inlet getter (Figure 2b). In contrast, the outlet elbow shows significant discoloration after 500 h chromium transpiration test due to deposition of chromium species in the absence of getter. The discoloration on the outlet quartz tube is a visual indication of the presence of Cr vapor species in the gas phase. More precisely, the Cr capture efficiency has been evaluated by the ICP-MS analysis method. After conducting transpiration test for 100-500 h, the deposited chromium from glass elbow, condenser, wash bottles and quartz tubes were washed to extract the chromium by a fixed volume of 20% HNO3 acid (for example, 1 L). The total moles of Cr species released per hour, measured by ICP-MS in different transpiration experiments, are compared for getter optimization. In our experiments, sintered Cr2O3 pellets were utilized as a stable chromium source of chromium vapor to minimize the carryover of fine Cr2O3 particles.
During baseline electrochemical experiment performed in the presence of chromium without a getter, gaseous chromium species flow through the porous LSM cathode are further reduced to form a Cr2O3 layer (Figure 4a) at the gas/LSM cathode/YSZ triple phase boundaries and cathode/electrolyte interface under a bias as shown in Eq.2.
2CrO2(OH)2 (g) + 6e- = Cr2O3 (s) + 3O2- (ion)+ 2H2O (g) &#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;(2)
Stoichiometric LSM remains largely unreacted under the entire SOFC operation range of chromium vapor species9. Our observations indicate that smaller amounts of Cr2O3 deposits at the LSM cathode surface (Figure 4c1) whereas majority of the Cr2O3 deposits at the triple phase boundaries (TPB) blocking the active sites for further oxygen reduction, increase in the polarization resistance (Figure 4b) and poor electrochemical performance of the cell16.
The three-electrode electrochemical cell design and test setup, utilized in our previous studies of LSM cathode stability in CO2 and humidified air18,19, has proven to be a powerful test vehicle and configuration for electrochemical impedance measurements. A reference electrode is added at the anode side near the periphery of the YSZ electrolyte using platinum paste and wire. This Pt electrode acts as a reference for measuring and controlling the working electrode potential, without current flow (ideal case). The stable Pt electrode remains free of Cr deposition on the anode site.
During the electrochemical experiments in the presence of chromium with a getter, sintered and pure Cr2O3 pellets are utilized as the stable Cr source. Due to the utilization of pure Cr2O3 pellets in our getter validation tests, the resulting concentration of Cr vapor species is expected to be much higher than those found in conventional fuel cell stacks and systems, in which protected coatings are added to reduce Cr evaporation. Our electrochemical experiments, hence, can be considered as accelerated tests. Pure LSM cathode are utilized as the cathode, which is very sensitive to chromium poisoning to validate the cathode poisoning and getter mechanisms. With an increase of air flow rates from 50 sccm to 500 sccm, which is similar to the real application conditions, the LSM&#449;YSZ&#449;Pt SOFCs maintain stable electrochemical performance as shown in Figure 3c, indicating the Cr getter still effectively capture Cr vapors at relatively high flow rates. In our ongoing and future work, high surface area getters and computational fluid dynamics (CFD) method are being developed for more active and longer lasting getters.

Solid oxide fuel cell (SOFC) power system, a high temperature direct electrochemical energy conversion device, offers an environmentally friendly pathway to generate electricity from a wide variety of fossil and renewable fuels. SOFC technology finds its applications in centralized as well as distributed power generation areas1. This technology relies on electrochemical conversion of chemical energy stored in the fuels into electricity. Numerous advantages are offered by SOFCs in terms of high energy efficiency, high quality heat, ease of modularity, and no or negligible carbon footprints2. Several individual SOFC cells are connected in series or parallel fashion (namely SOFC stacks) to obtain desired output voltage. SOFC stacks consist of components such as dense electrolyte, porous electrodes, interconnection (IC) and seals3,4. Anode and cathode of adjacent cells are connected using IC, which not only serves as a separator to prevent any mixing of oxidant with fuel but also provides electrical connection between the adjacent anode and cathode5.
Improvements over decades of research and development in materials engineering have led to reduction in operating temperature for SOFCs, enabling replacements of ceramics materials with inexpensive stainless-steel alloys for the fabrication of electrochemically active cell and stack components and balance-of-plant (BOP) sub-systems. Commercially available ferritic and austenitic stainless steels are utilized for the fabrication of system components due to their low cost, matched coefficient of thermal expansion (CTE) and resistance to oxidation and corrosion at high operating temperatures6. Formation of Cr2O3 type passivating oxide scale on the alloy surface acts as a barrier layer against inward diffusion of oxygen from air or outward diffusion of cations from bulk alloy7.
In the presence of humidified air, Cr2O3 undergoes significant chemical transformation leading to hydrated chromium vapor species formation at SOFC operating temperatures. The gaseous chromium vapor is subsequently carried through the air stream into the cathode leading to surface and interface reactions with the cathode materials. Such cathode experiences both ohmic and non-ohmic increases in the polarization and electrical performance degradation. Details of the cathode degradation mechanisms have been illustrated elsewhere8,9,10.
The state-of-the-art methods to reduce or eliminate the above cathode degradation processes commonly consist of modifications of the alloy chemistry, application of surface coating and the use of chromium tolerant cathodes11,12. Although these techniques have demonstrated reduction of the cathode degradation due to Cr vapor interactions (namely Cr poisoning) for short-term, long-term efficacy for performance stability remains a concern, mainly due to cracking and spallation within the coating and interdiffusion of cations.
We have demonstrated a novel method to mitigate the problem of chromium poisoning by capturing the incoming chromium vapor before it reacts with the cathode materials13. The getters have been synthesized from low-cost alkaline earth and transition metal oxides using conventional ceramic processing techniques. The cost advantage of this approach is use of non-noble and non-strategic materials as well as conventional processing methods to fabricate getters for the mitigation of cathode degradation arising from airborne contaminants. The placement of the getter can be tailored to capture chromium vapor arising from BOP components or it can also be tailored to be placed within the electrochemically active stack components14,15. Here, we present methods to validate the chromium getters using transpiration and electrochemical tests. Experimental setup and characterization results will also be demonstrated to show the getter effectiveness and the mechanisms of Cr capture on the getter under typical SOFC operating conditions.

<table>
	<tbody>
		<tr>
			<td>Sr(NO3)2</td>
			<td>Sigma-Aldrich</td>
			<td>243426</td>
			<td>Getter precursor material</td>
		</tr>
		<tr>
			<td>Ni(NO3)2-6H2O</td>
			<td>Alfa Aesar</td>
			<td>A15540</td>
			<td>Getter precursor material</td>
		</tr>
		<tr>
			<td>NH4OH</td>
			<td>Alfa Aesar</td>
			<td>L13168</td>
			<td>Getter precursor material</td>
		</tr>
		<tr>
			<td>Pt ink</td>
			<td>ESL ElectroScience</td>
			<td>5051</td>
			<td>Current collector paste</td>
		</tr>
		<tr>
			<td>Pt wire</td>
			<td>Alfa Aesar</td>
			<td>10288</td>
			<td>Current collector wire</td>
		</tr>
		<tr>
			<td>Pt gause</td>
			<td>Alfa Aesar</td>
			<td>40935</td>
			<td>Current collector</td>
		</tr>
		<tr>
			<td>Cr2O3 powder</td>
			<td>Alfa Aesar</td>
			<td>12286</td>
			<td>Chromium source</td>
		</tr>
		<tr>
			<td>Nitric acid (HNO3)</td>
			<td>Sigma-Aldrich</td>
			<td>438073</td>
			<td>Chromium extraction</td>
		</tr>
		<tr>
			<td>Potassium permanganate (KMnO4)</td>
			<td>Alfa Aesar</td>
			<td>A12170</td>
			<td>Chromium extraction</td>
		</tr>
		<tr>
			<td>LSM paste</td>
			<td>Fuelcellmaterials</td>
			<td>18007</td>
			<td>Cathode</td>
		</tr>
		<tr>
			<td>YSZ electrolyte</td>
			<td>Fuelcellmaterials</td>
			<td>211102</td>
			<td>Electrolyte</td>
		</tr>
		<tr>
			<td>Alumina fiber board</td>
			<td>Zircar</td>
			<td>GJ0014</td>
			<td>Getter substrate</td>
		</tr>
		<tr>
			<td>Ceramabond paste</td>
			<td>AREMCO</td>
			<td>552-VFG</td>
			<td>For cell sealing</td>
		</tr>
		<tr>
			<td>ICP-MS (7700s)</td>
			<td>Agilent</td>
			<td>NA</td>
			<td>For Cr analysis</td>
		</tr>
		<tr>
			<td>Potentiostat (VMP3)</td>
			<td>Biologic</td>
			<td>NA</td>
			<td>For EIS/I-t measurement</td>
		</tr>
		<tr>
			<td>FIB (Helios Nanolab 460F1)</td>
			<td>FEI</td>
			<td>NA</td>
			<td>For Nano-sample preparation</td>
		</tr>
		<tr>
			<td>TEM (Talos F200X S/TEM)</td>
			<td>FEI</td>
			<td>NA</td>
			<td>For composition analysis</td>
		</tr>
	</tbody>
</table>

development and validation of chromium getters for solid oxide fuel cell power systems

Degradation of cathode in solid oxide fuel cells (SOFC) remains a major concern for the long-term performance stability and operational reliability. The presence of gas phase chromium species in air has demonstrated significant cathode performance degradation during long-term exposure due to unwanted compound formation at the cathode and electrolyte interface which retards the oxygen reduction reaction (ORR). We have demonstrated a novel method to mitigate the cathode degradation using chromium getters which capture the gas phase chromium species before it is ingested in the cathode chamber. Low-cost getter materials, synthesized from alkaline earth and transition metal oxides, are coated on the cordierite honeycomb substrate for application in the SOFC power systems. As-fabricated getters have been screened by chromium transpiration tests for 500 h in humidified air atmosphere in presence of chromium vapor. Selected getters have been further validated utilizing electrochemical tests. Typically, electrochemical performance of SOFCs (lanthanum strontium manganite (LSM) &#449; yttria stabilized zirconia (YSZ) &#449; Pt) was measured at 850 &#176;C in the presence and absence of Cr getter. For the 100 h cell tests containing getters, stable electrochemical performance was maintained, whereas the cell performance in the absence of Cr getters rapidly decreased in 10 h. Analyses of Nyquist plots indicated significant increase in the polarization resistance within the first 10 h of the cell operation. Characterization results from posttest SOFCs and getters have demonstrated the high efficiency of chromium capture for the mitigation of cell degradation.

A Cr transpiration experiment is a screening test for the selection of Cr getters. Cr transpiration setup was utilized to validate the performance of chromium getter under the SOFC operating conditions. Experiments were conducted in the presence of a chromium getter operated at 850 &#176;C in humidified (3% H2O) air for 500 h. Visual observations during Cr transpiration tests indicated significant discoloration of the outlet elbow during 500 h in the absence of getter. However, placing a getter next to the chromium source demonstrated no discoloration of the outlet elbow. This indicated that the getter can effectively capture all the incoming chromium vapor species under nominal SOFC operating conditions. To validate the chromium capture and understand the gettering mechanism, the posttest getter was dissected and observed under the SEM. Detailed EDS analyses were also conducted to measure the elemental distribution of chromium (wt.%) along the central channel of the getter (shown in Figure 2b). EDS elemental distribution of chromium shows that majority of Cr (wt.%) is captured within first 4000 &#181;m of distance from the getter inlet. SEM-EDS data further shows that the middle and the outlet of the getter contains no or negligible chromium during transpiration test.
Proven Cr getters have been utilized for electrochemical validation tests. The electrochemical performance comparisons of the three LSM&#449;YSZ&#449;Pt SOFCs under different experimental test conditions are shown in Figure 3b. The LSM cathodes of the three SOFCs were exposed to humidified air (3% H2O/air) to control the Cr vapor exposure to the cathodes. The cathode from cell a was exposed to 3% H2O/air with no getter and no Cr vapor for 100 h. The results show stable I-t curve with a presence of cathodic activation period (0-20 h). The cell b, exposed to 3% H2O/air with Cr vapor and no getter, shows a rapid drop in the current within the first few hours of the test. This indicated chromium poisoning of the cell. For the cell c in presence of a chromium getter and 3% H2O/air at the cathode side with chromium vapor, the electrochemical performance of the cell c demonstrated a significant improvement, which was very close to that of the cell a (not shown in figures).
Effect of chromium vapor on cathode degradation, also known as chromium poisoning, has been studied as shown in Figure 4. A representative Nyquist plot is provided for cell b (Figure 4b), which was exposed to chromium vapor but without the getter. The electrochemical impedance of the cathode was measured independent of changes that may occur at the anode electrode using a three-electrode mode. When the cathode of the cell b was exposed in chromium vapor, the semi-circles of the Nyquist spectra of the cathode stretched with time, indicating an increase of polarization resistance with increase in exposure time. During the 100-h tests, the polarization resistance of the cathode in cell b exhibited a rapid increase during first 20 h, followed by slower change during the next 40 h, and significantly no change after 60 h. The non-polarization resistance (Rnp) of cathode showed only negligible changes. Above experiments indicate that chromium vapor mainly resulted in a rapid change of Rp which led to the cathode degradation. The increase in the polarization resistance of the cathode occurs mainly due to retardation of oxygen reduction reaction (ORR) at the electrode/electrolyte interface. To demonstrate this, morphological characterization of the fractured SOFC was conducted and compared with the morphology at the cathode surface. Figure 4 (c1 and c2) shows the SEM micrographs of the LSM surfaces and LSM/YSZ interfaces from cell b, respectively. The SEM-EDS analysis shows ~2.5 wt.% chromium on the cathode surface while 11.2 wt.% of chromium was observed at the electrode/electrolyte interface layer (Table 1). Significant deposition of chromium vapor takes place at the cathode-electrolyte interface, which inhibits the ORR and degrades the cathode performance with time.
After electrochemical tests, the chromium getter was prepared for microstructural analysis. The morphology of the deposited chromium on fiber supported getters was examined by SEM-EDS (Figure 5a). At localized areas near the air inlet, large particles rich in Cr (44.8 atom%) and Sr (54.3 atom%) were formed on the getter fibers. The getter fiber support from the mid-section and outlet remains free of chromium (not shown here).
To further investigate the reaction processes for the capture of chromium, a posttest getter fiber was milled using FIB technique (Figure 5b). Figure 5c shows the HAADF image of the cross-section of the posttest getter fiber by STEM. From the elemental mapping, a surface layer containing Sr and Cr has been observed as shown in Figure 5d,e, indicating a stable reaction product (SrCrO4) formation on the surface of the alumina fiber. Near the surface of the SrNiOx coated alumina fiber, the outward diffusion of Sr from the SrNiOx coated getter material.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/59623/59623fig1.jpg" /> 
Figure 1. Procedures for getter synthesis and fabrication. Schematic illustration of getter power synthesis and coating method using conventional ceramic processing route. <a href="https://www.jove.com/files/ftp_upload/59623/59623fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/59623/59623fig2.jpg" /> 
Figure 2. Illustration of Cr transpiration test setup and testing results. (a) Experimental setup to conduct transpiration test under nominal SOFC conditions. (b) Distribution of chromium (wt.%) profile along the getter length from inlet to outlet. This figure has been modified from reference [14] with a permission. <a href="https://www.jove.com/files/ftp_upload/59623/59623fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/59623/59623fig3.jpg" /> 
Figure 3. Electrochemical validation of getter and testing results. (a) Schematic of LSM&#449;YSZ&#449;Pt SOFC, (b) I-t plots in presence and absence of getter, and (c) I-t plots in various cathode air flow rates. <a href="https://www.jove.com/files/ftp_upload/59623/59623fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/59623/59623fig4.jpg" /> 
Figure 4. Effect of chromium poisoning on LSM cathode surface and LSM/YSZ interface. (a) Illustration of chromium evaporation processing in presence of O2 and H2O. (b) Nyquist plot of the SOFC exposed to Cr vapor in 3% H2O air. (c) 1. Surface morphology of the LSM cathode exposed to Cr vapor, and 2. deposition of Cr2O3 along the interface of LSM and YSZ indicating electrode poisoning. <a href="https://www.jove.com/files/ftp_upload/59623/59623fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/59623/59623fig5.jpg" /> 
Figure 5. Characterization results of posttest getter by EDS and FIB-TEM. (a) Morphology of deposited Cr vapor on the surface of getter fiber long with respective elemental distribution. (b) Cross-section of a getter sample with deposited Cr using focused ion beam (FIB) technique. (c) High-angle annular dark-field imaging (HAADF) of the getter sample prepared by the FIB technique (d, e) Elemental maps of the FIB sample showing presence of Cr and Sr on the getter surface. <a href="https://www.jove.com/files/ftp_upload/59623/59623fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Development and Validation of Chromium Getters for Solid Oxide Fuel Cell Power Systems at JoVE.com

Development and Validation of Chromium Getters for Solid Oxide Fuel Cell Power Systems

Cathode poisoning from airborne contaminants in trace levels remains a major concern for long-term stability of high-temperature electrochemical systems. We provide a novel method to mitigate the cathode degradations using getters, which capture airborne contaminants at high temperature before entering electrochemically active stack area.

Degradation of cathode in solid oxide fuel cells (SOFC) remains a major concern for the long-term performance stability and operational reliability. The ...

development-validation-chromium-getters-for-solid-oxide-fuel-cell

Nanyang Technological University

Research

JoVE Journal

Chemistry

7.1K Views.  University of Connecticut. Cathode poisoning from airborne contaminants in trace levels remains a major concern for long-term stability of high-temperature electrochemical systems. We provide a novel method to mitigate the cathode degradations using getters, which capture airborne contaminants at high temperature before entering electrochemically active stack area.

Video: Development and Validation of Chromium Getters for Solid Oxide Fuel Cell Power Systems

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high surface area microporous materials, such as metal-organic frameworks (MOFs), unique challenges present themselves for PECVD treatments. Herein the protocol for development of a MOF that was previously unstable to humid conditions is presented. The protocol describes the synthesis of Cu-BTC (also known as HKUST-1), the treatment of Cu-BTC with PECVD of perfluoroalkanes, the aging of materials under humid conditions, and the subsequent ammonia microbreakthrough experiments on milligram quantities of microporous materials. Cu-BTC has an extremely high surface area (~1,800 m2/g) when compared to most materials or surfaces that have been previously treated by PECVD methods. Parameters such as chamber pressure and treatment time are extremely important to ensure the perfluoroalkane plasma penetrates to and reacts with the inner MOF surfaces. Furthermore, the protocol for ammonia microbreakthrough experiments set forth here can be utilized for a variety of test gases and microporous materials.

Herein the procedures for plasma enhanced chemical vapor deposition of perfluoroalkanes on microporous materials such as metal-organic frameworks to enhance their stability and hydrophobicity are described. Furthermore, breakthrough testing of milligram quantities of samples is described in detail.

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high ...

Activating Molecules, Ions, and Solid Particles with Acoustic Cavitation

The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species and to the emission of light, named sonoluminescence. In this manuscript, we describe the techniques allowing study of extreme intrabubble conditions and chemical reactivity of acoustic cavitation in solutions. The analysis of sonoluminescence spectra of water sparged with noble gases provides evidence for nonequilibrium plasma formation. The photons and the "hot" particles generated by cavitation bubbles enable to excite the non-volatile species in solutions increasing their chemical reactivity. For example the mechanism of ultrabright sonoluminescence of uranyl ions in acidic solutions varies with uranium concentration: sonophotoluminescence dominates in diluted solutions, and collisional excitation contributes at higher uranium concentration. Secondary sonochemical products may arise from chemically active species that are formed inside the bubble, but then diffuse into the liquid phase and react with solution precursors to form a variety of products. For instance, the sonochemical reduction of Pt(IV) in pure water provides an innovative synthetic route for monodispersed nanoparticles of metallic platinum without any templates or capping agents. Many studies reveal the advantages of ultrasound to activate the divided solids. In general, the mechanical effects of ultrasound strongly contribute in heterogeneous systems in addition to chemical effects. In particular, the sonolysis of PuO2 powder in pure water yields stable colloids of plutonium due to both effects.

Acoustic cavitation in liquids submitted to power ultrasound creates transient extreme conditions inside the collapsing bubbles, which are the origin of unusual chemical reactivity and light emission, known as sonoluminescence. In the presence of noble gases, nonequilibrium plasma is formed. The "hot" particles and the photons generated by collapsing bubbles are able to excite species in solution.

The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic ...

High-pressure Sapphire Cell for Phase Equilibria Measurements of CO2/Organic/Water Systems

The high pressure sapphire cell apparatus was constructed to visually determine the composition of multiphase systems without physical sampling. Specifically, the sapphire cell enables visual data collection from multiple loadings to solve a set of material balances to precisely determine phase composition. Ternary phase diagrams can then be established to determine the proportion of each component in each phase at a given condition. In principle, any ternary system can be studied although ternary systems (gas-liquid-liquid) are the specific examples discussed herein. For instance, the ternary THF-Water-CO2 system was studied at 25 and 40&#160;&#176;C and is described herein. Of key importance, this technique does not require sampling. Circumventing the possible disturbance of the system equilibrium upon sampling, inherent measurement errors, and technical difficulties of physically sampling under pressure is a significant benefit of this technique. Perhaps as important, the sapphire cell also enables the direct visual observation of the phase behavior. In fact, as the CO2 pressure is increased, the homogeneous THF-Water solution phase splits at about 2 MPa. With this technique, it was possible to easily and clearly observe the cloud point and determine the composition of the newly formed phases as a function of pressure.
The data acquired with the sapphire cell technique can be used for many applications. In our case, we measured swelling and composition for tunable solvents, like gas-expanded liquids, gas-expanded ionic liquids and Organic Aqueous Tunable Systems (OATS)1-4. For the latest system, OATS, the high-pressure sapphire cell enabled the study of (1) phase behavior as a function of pressure and temperature, (2) composition of each phase (gas-liquid-liquid) as a function of pressure and temperature and (3) catalyst partitioning in the two liquid phases as a function of pressure and composition. Finally, the sapphire cell is an especially effective tool to gather accurate and reproducible measurements in a timely fashion.

High-pressure Sapphire Cell for Phase Equilibria Measurements of CO2/Organic/Water Systems

The high pressure sapphire cell apparatus is a unique tool to study, without sampling, phase behavior under a wide range of pressures. Using a cathetometer, very precise volume measurements can be recorded to measure liquid expansion and phase composition. Thus, this synthetic method enables the study of (1) phase equilibria of multi-component mixtures and (2) the partition behavior of catalyst or model compounds as a function of pressure.

The high pressure sapphire cell apparatus was constructed to visually determine the composition of multiphase systems without physical sampling. ...

Quantitative Detection of Trace Explosive Vapors by Programmed Temperature Desorption Gas Chromatography-Electron Capture Detector

The direct liquid deposition of solution standards onto sorbent-filled thermal desorption tubes is used for the quantitative analysis of trace explosive vapor samples. The direct liquid deposition method yields a higher fidelity between the analysis of vapor samples and the analysis of solution standards than using separate injection methods for vapors and solutions, i.e., samples collected on vapor collection tubes and standards prepared in solution vials. Additionally, the method can account for instrumentation losses, which makes it ideal for minimizing variability and quantitative trace chemical detection. Gas chromatography with an electron capture detector is an instrumentation configuration sensitive to nitro-energetics, such as TNT and RDX, due to their relatively high electron affinity. However, vapor quantitation of these compounds is difficult without viable vapor standards. Thus, we eliminate the requirement for vapor standards by combining the sensitivity of the instrumentation with a direct liquid deposition protocol to analyze trace explosive vapor samples.

Trace explosive vapors of TNT and RDX collected on sorbent-filled thermal desorption tubes were analyzed using a programmed temperature desorption system coupled to GC with an electron capture detector. The instrumental analysis is combined with direct liquid deposition method to reduce sample variability and account for instrumentation drift and losses.

The direct liquid deposition of solution standards onto sorbent-filled thermal desorption tubes is used for the quantitative analysis of trace explosive ...

Synthetic Methodology for Asymmetric Ferrocene Derived Bio-conjugate Systems via Solid Phase Resin-based Methodology

Early detection is a key to successful treatment of most diseases, and is particularly imperative for the diagnosis and treatment of many types of cancer. The most common techniques utilized are imaging modalities such as Magnetic Resonance Imaging (MRI), Positron Emission Topography (PET), and Computed Topography (CT) and are optimal for understanding the physical structure of the disease but can only be performed once every four to six weeks due to the use of imaging agents and overall cost. With this in mind, the development of &#8220;point of care&#8221; techniques, such as biosensors, which evaluate the stage of disease and/or efficacy of treatment in the clinician&#8217;s office and do so in a timely manner, would revolutionize treatment protocols.1 As a means to exploring ferrocene based biosensors for the detection of biologically relevant molecules2, methods were developed to produce ferrocene-biotin bio-conjugates described herein. This report will focus on a biotin-ferrocene-cysteine system that can be immobilized on a gold surface.

The synthesis of asymmetric species of ferrocene is challenging using solution techniques. This report focuses on the methods carried out to produce a ferrocene-biotin bioconjugate using facile and clean reactions accomplished via solid-phase synthesis. Incorporation of a thiolate moiety is shown to impart the ability for immobilization on gold surfaces.

Early detection is a key to successful treatment of most diseases, and is particularly imperative for the diagnosis and treatment of many types of cancer. ...

Development of a Backbone Cyclic Peptide Library as Potential Antiparasitic Therapeutics Using Microwave Irradiation

Protein-protein interactions (PPIs) are intimately involved in almost all biological processes and are linked to many human diseases. Therefore, there is a major effort to target PPIs in basic research and in the pharmaceutical industry. Protein-protein interfaces are usually large, flat, and often lack pockets, complicating the discovery of small molecules that target such sites. Alternative targeting approaches using antibodies have limitations due to poor oral bioavailability, low cell-permeability, and production inefficiency.
Using peptides to target PPI interfaces has several advantages. Peptides have higher conformational flexibility, increased selectivity, and are generally inexpensive. However, peptides have their own limitations including poor stability and inefficiency crossing cell membranes. To overcome such limitations, peptide cyclization can be performed. Cyclization has been demonstrated to improve peptide selectivity, metabolic stability, and bioavailability. However, predicting the bioactive conformation of a cyclic peptide is not trivial. To overcome this challenge, one attractive approach it to screen a focused library to screen in which all backbone cyclic peptides have the same primary sequence, but differ in parameters that influence their conformation, such as ring size and position.
We describe a detailed protocol for synthesizing a library of backbone cyclic peptides targeting specific parasite PPIs. Using a rational design approach, we developed peptides derived from the scaffold protein Leishmania receptor for activated C-kinase (LACK). We hypothesized that sequences in LACK that are conserved in parasites, but not in the mammalian host homolog, may represent interaction sites for proteins that are critical for the parasites&#39; viability. The cyclic peptides were synthesized using microwave irradiation to reduce reaction times and increase efficiency. Developing a library of backbone cyclic peptides with different ring sizes facilitates a systematic screen for the most biological active conformation. This method provides a general, fast, and facile way to synthesize cyclic peptides.

A simple and general method for the synthesis of cyclic peptides using microwave irradiation is outlined. This procedure enables the synthesis of backbone cyclic peptides with a collection of different conformations while retaining the side chains and the pharmacophoric moieties., and therefore, allows to screen for the bioactive conformation.

Protein-protein interactions (PPIs) are intimately involved in almost all biological processes and are linked to many human diseases. Therefore, there is ...

X-ray Powder Diffraction in Conservation Science: Towards Routine Crystal Structure Determination of Corrosion Products on Heritage Art Objects

The crystal structure determination and refinement process of corrosion products on historic art objects using laboratory high-resolution X-ray powder diffraction (XRPD) is presented in detail via two case studies.
The first material under investigation was sodium copper formate hydroxide oxide hydrate, Cu4Na4O(HCOO)8(OH)2&#8729;4H2O (sample 1) which forms on soda glass/copper alloy composite historic objects (e.g., enamels) in museum collections, exposed to formaldehyde and formic acid emitted from wooden storage cabinets, adhesives, etc. This degradation phenomenon has recently been characterized as &#34;glass induced metal corrosion&#34;.
For the second case study, thecotrichite, Ca3(CH3COO)3Cl(NO3)2&#8729;6H2O (sample 2), was chosen, which is an efflorescent salt forming needlelike crystallites on tiles and limestone objects which are stored in wooden cabinets and display cases. In this case, the wood acts as source for acetic acid which reacts with soluble chloride and nitrate salts from the artifact or its environment.
The knowledge of the geometrical structure helps conservation science to better understand production and decay reactions and to allow for full quantitative analysis in the frequent case of mixtures.

Modern high resolution X-ray powder diffraction (XRPD) in the laboratory is used as an efficient tool to determine crystal structures of long-known corrosion products on historic objects.

The crystal structure determination and refinement process of corrosion products on historic art objects using laboratory high-resolution X-ray powder ...

Original Experimental Approach for Assessing Transport Fuel Stability

The study of fuel oxidation stability is an important issue for the development of future fuels. Diesel and kerosene fuel systems have undergone several technological changes to fulfill environmental and economic requirements. These developments have resulted in increasingly severe operating conditions whose suitability for conventional and alternative fuels needs to be addressed. For example, fatty acid methyl esters (FAMEs) introduced as biodiesel are more prone to oxidation and may lead to deposit formation. Although several methods exist to evaluate fuel stability (induction period, peroxides, acids, and insolubles), no technique allows one to monitor the real-time oxidation mechanism and to measure the formation of oxidation intermediates that may lead to deposit formation. In this article, we developed an advanced oxidation procedure (AOP) based on two existing reactors. This procedure allows the simulation of different oxidation conditions and the monitoring of the oxidation progress by the means of macroscopic parameters, such as total acid number (TAN) and advanced analytical methods like gas chromatography coupled to mass spectrometry (GC-MS) and Fourier Transform Infrared - Attenuated Total Reflection (FTIR-ATR). We successfully applied AOP to gain an in-depth understanding of the oxidation kinetics of a model molecule (methyl oleate) and commercial diesel and biodiesel fuels. These developments represent a key strategy for fuel quality monitoring during logistics and on-board utilization.

Oxidation stability of transport fuels has become a concern for future fuel development. This work presents an original methodology developed by IFP Energies Nouvelles for assessing fuel stability using two different reactors. This methodology was successfully applied to gain an in-depth understanding of the oxidation kinetics and pathways of model molecules and commercial fuels.

The study of fuel oxidation stability is an important issue for the development of future fuels. Diesel and kerosene fuel systems have undergone several ...

Measurement of Particle Size Distribution in Turbid Solutions by Dynamic Light Scattering Microscopy

A protocol for measuring polydispersity of concentrated polymer solutions using dynamic light scattering is described. Dynamic light scattering is a technique used to measure the size distribution of polymer solutions or colloidal particles. Although this technique is widely used for the assessment of polymer solutions, it is difficult to measure the particle size in concentrated solutions due to the multiple scattering effect or strong light absorption. Therefore, the concentrated solutions should be diluted before measurement. Implementation of the confocal optical component in a dynamic light scattering microscope1 helps to overcome this barrier. Using such a microscopic system, both transparent and turbid systems can be analyzed under the same experimental setup without a dilution. As a representative example, a size distribution measurement of a temperature-responsive polymer solution was performed. The sizes of the polymer chains in an aqueous solution were several tens of nanometers at a temperature below the lower critical solution temperature (LCST). In contrast, the sizes increased to more than 1.0 &#181;m when above the LCST. This result is consistent with the observation that the solution turned turbid above the LCST.

A protocol for the direct measurement of particle size distribution in concentrated solutions using dynamic light scattering microscopy is presented.

A protocol for measuring polydispersity of concentrated polymer solutions using dynamic light scattering is described. Dynamic light scattering is a ...

In Situ Detection and Single Cell Quantification of Metal Oxide Nanoparticles Using Nuclear Microprobe Analysis

Micro-analytical techniques based on chemical element imaging enable the localization and quantification of chemical composition at the cellular level. They offer new possibilities for the characterization of living systems and are particularly appropriate for detecting, localizing and quantifying the presence of metal oxide nanoparticles both in biological specimens and the environment. Indeed, these techniques all meet relevant requirements in terms of (i) sensitivity (from 1 up to 10 &#181;g.g-1 of dry mass), (ii) micrometer range spatial resolution, and (iii) multi-element detection. Given these characteristics, microbeam chemical element imaging can powerfully complement routine imaging techniques such as optical and fluorescence microscopy. This protocol describes how to perform a nuclear microprobe analysis on cultured cells (U2OS) exposed to titanium dioxide nanoparticles. Cells must grow on and be exposed directly in a specially designed sample holder used on the optical microscope and in the nuclear microprobe analysis stages. Plunge-freeze cryogenic fixation of the samples preserves both the cellular organization and the chemical element distribution. Simultaneous nuclear microprobe analysis (scanning transmission ion microscopy, Rutherford backscattering spectrometry and particle induced X-ray emission) performed on the sample provides information about the cellular density, the local distribution of the chemical elements, as well as the cellular content of nanoparticles. There is a growing need for such analytical tools within biology, especially in the emerging context of Nanotoxicology and Nanomedicine for which our comprehension of the interactions between nanoparticles and biological samples must be deepened. In particular, as nuclear microprobe analysis does not require nanoparticles to be labelled, nanoparticle abundances are quantifiable down to the individual cell level in a cell population, independently of their surface state.

In Situ Detection and Single Cell Quantification of Metal Oxide Nanoparticles Using Nuclear Microprobe Analysis

We describe a procedure for the detection of chemical elements present in situ in human cells as well as their in vitro quantification. The method is well-suited to any cell type and is particularly useful for quantitative chemical analyses in single cells following in vitro metal oxide nanoparticles exposure.

Micro-analytical techniques based on chemical element imaging enable the localization and quantification of chemical composition at the cellular level. ...