Financial support was provided by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy under contract number DE-AC36-08GO28308 to NREL.

1. Synthesis of Pt-Ni Nanowires
<ol>
	<li>To begin the displacement process, suspend the nickel nanowire template in water and heat it to 90 &#176;C.
	<ol>
		<li>Add 40 mg of commercially available, nickel nanowires to 20 mL of deionized water in a 50 mL centrifuge tube. Sonicate it for 5 min. 
		&#8203;NOTE: The nanowires are approximately 150-250 nm in diameter and 100-200 &#181;m in length.</li>
		<li>Transfer the suspended nanowires to a 250 mL glass round bottom flask and add 60 mL of deionized water. Heat the flask to 90 &#176;C in a mineral oil bath. Stir the reaction mixture at 500 rpm with a polytetrafluoroethylene paddle connected to a glass shaft and electric stirrer.</li>
	</ol>
	</li>
	<li>Form the Pt-Ni nanowires by spontaneous galvanic displacement.
	<ol>
		<li>Add 8.1 mg of potassium tetrachloroplatinate to 15 mL of deionized water. Add the solution to a 20 mL syringe with approximately 8 cm of 0.318 cm polyurethane-based tubing attached to the tip. Place the syringe in an automated syringe pump and set the rate to 1 mL/min.</li>
		<li>Start the syringe pump and allow the pump to add the solution to the round bottom flask over 15 min. Heat the flask at 90 &#176;C for 2 h.</li>
		<li>Centrifuge the solution at 2,500 x g for 15 min, and pour the supernatant into a waste stream. Resuspend the solidswith bath sonication (approximately 10 s) using fresh solution (water or 2-propanol, as specified). Centrifuge the solution again and remove the supernatant. Repeat the washing process three times with deionized water and then once with 2-propanol.</li>
		<li>Dry the Pt-Ni nanowires at 40 &#176;C in a vacuum oven overnight (approximately 16 h).</li>
	</ol>
	</li>
</ol>
2. Check Composition with Inductively Coupled Plasma-Mass Spectrometry (ICP-MS).
Note: Catalyst composition should be 7.3 &#177; 0.3 wt. % Pt.
<ol>
	<li>Digest 1 mg of sample in 10 mL of aqua regia at room temperature overnight.</li>
	<li>Dilute to concentrations of 200, 20, and 2 ppb, with a matrix matching of the dilutions to 1.5% hydrochloric and 0.5% nitric acid.
	<ol>
		<li>Add 20 &#181;L of digestate into 9.98 mL of stock solution (1.5% hydrochloric and 0.5% nitric acid) for 200 ppb; 2 &#181;L of digestate into 10.00 mL of stock solution (1.5% hydrochloric and 0.5% nitric acid) for 20 ppb; and 0.2 &#181;L of digestate into 10.00 mL of stock solution (1.5% hydrochloric and 0.5% nitric acid) for 2 ppb. Filter the dilutions using a 0.4 &#181;m polytetrafluoroethylene-based filter.</li>
	</ol>
	</li>
</ol>
3. Post-synthesis Process of the Pt-Ni Nanowires by Annealing and Acid Leaching.
<ol>
	<li>Hydrogen anneal the synthesized Pt-Ni nanowires.</li>
	<li>Add the entire nanowire sample to a tubular furnace. Apply vacuum to the tube overnight. 
	&#8203;NOTE: Since gas flow (hydrogen, oxygen) was used at elevated temperature in the tubular furnace, safety considerations were required. The tube-gas connections were built to ensure that the apparatus could handle vacuum and 500 Torr of back pressure during operation. The tube outlet was vented to exhaust, and the entire furnace was placed in an enclosure vented to an exhaust line.
	<ol>
		<li>Feed a low flow rate of hydrogen into the tube with 500 Torr of back pressure.</li>
		<li>Heat the sample to 250 &#176;C for 2 h, using a 10 &#176;C/min ramp rate.</li>
		<li>Allow for the sample to cool to room temperature naturally.</li>
	</ol>
	</li>
	<li>Acid leach the hydrogen annealed Pt-Ni nanowires.
	<ol>
		<li>Add 25 mg of the nanowires to 20 mL of deionized water and bath sonicate it. Transfer the suspended nanowires to a 100 mL round bottom flask.</li>
		<li>Add room temperature diluted nitric acid to the flask (25 mL of 0.2 M nitric acid to 25 mL of water/nanowire suspension), to bring the flask contents to 50 mL of 0.1 M nitric acid, and shake the flask to ensure a uniform concentration. Add the nitric acid all at once.</li>
		<li>Connect the flask to a Schlenk line. Turn on the vacuum for 10 min and then close off the vacuum. Slowly add nitrogen gas into the line and allow the flask to proceed at room temperature for 2 h. Remove the flask from the Schlenk line and wash the products as described in step 1.2.3.</li>
		<li>Check the composition with ICP-MS, which should be 15.2 &#177; 0.3 wt. % Pt.</li>
	</ol>
	</li>
	<li>Oxygen anneal the acid leached Pt-Ni nanowires.
	<ol>
		<li>Add the nanowires to a commercially available tubular furnace. Apply vacuum to the tube overnight.</li>
		<li>Feed a low flow rate of oxygen into the tube with 500 Torr of back pressure.</li>
		<li>Heat the sample to 175 &#176;C for 2 h, using a 10 &#176;C/min ramp rate.</li>
		<li>Allow for the sample to cool to room temperature naturally.</li>
	</ol>
	</li>
</ol>
4. Electrochemically Characterize the Nanowires in Rotating Disk Electrode (RDE) Half-Cells8
<ol>
	<li>Coat the glassy carbon working electrodes.
	<ol>
		<li>Add catalyst, which contains 73 &#181;g of Pt, to 7.6 mL of deionized water in a 20 mL scintillation vial, and then add 2.4 mL of 2-propanol. The vial contents are subsequently referred to as the ink. Ice the ink for 5 min and then add 10 &#181;L of a commercially available ionomer. 
		NOTE: For the as-synthesized and hydrogen annealed catalyst, 1 mg (7.3 wt. % Pt) should be used. For the acid leached and oxygen annealed catalyst, 480 &#181;g (15.2 wt. % Pt) should be used.</li>
		<li>Sonicate the ink in ice, 30 s by horn followed by 20 min by bath and 30 s by horn. Add 7.5 mL of the ink to 0.5 mg of graphitized carbon nanofibers.</li>
		<li>Sonicate the ink in ice, 30 s by horn followed by 20 min by bath and 30 s by horn. Pipette 10 &#181;L of ink onto a glassy carbon working electrode (5 mm outer diameter), with the inverted electrode rotating at 100 rpm. After pipetting the ink, increase the rotation to 700 rpm.</li>
		<li>Sonicate the ink again (30 s horn, 20 min bath, 30 s horn) while the electrode dries and pipette an additional ink (10 &#181;L) onto the electrode. Continue the coating process to increase the loading to 1.9 &#181;g cmelec-2, five 10 &#181;L drops of ink.</li>
	</ol>
	</li>
	<li>Assemble the RDE test station.
	<ol>
		<li>Soak the glassware overnight in concentrated sulfuric acid. Then, soak the glassware overnight in a commercially available substitute for chromic acid. Boil eight times in deionized water. Assemble the glassware, by connecting the working, counter, and reference electrodes to the main testing cell. 
		NOTE: The RDE half-cells use a three-electrode configuration. The working and counter electrodes were glassy carbon and Pt mesh, respectively. The reference electrode was a reversible hydrogen electrode (RHE), a Pt wire contained in a glass bubbler with 0.1 M perchloric acid electrolyte.</li>
		<li>Fill the RDE half-cell with 0.1 M perchloric acid. Connect the working electrode to a commercially available modulated speed controller, and submerge the working electrode tip.</li>
		<li>Take electrochemical measurements with a commercially available potentiostat. Purge the electrolyte with nitrogen for 7 min.</li>
	</ol>
	</li>
	<li>Take electrochemical surface areas.
	<ol>
		<li>Input parameters into an automated cyclic voltammetry file supplied by the potentiostat manufacturer. Set the cycle number to 50, the scan rate to 100 mV s-1, the lower potential to 0.025 V, and the upper potential to 1.4 V. Run the cyclic voltammetry file and discard the electrolyte. Refill with 0.1 M perchloric acid and purge with carbon monoxide.</li>
		<li>Input parameters into an automated potential hold file supplied by the potentiostat manufacturer. Set the potential 0.1 V and the time to 20 min, and start rotating the working electrode at 2,500 rpm. Run the potential hold file: for the first 10 min of the program, purge carbon monoxide; for the second 10 min of the program, purge nitrogen. During the last 30 s of the hold, turn off the rotation and set the bubbler to blanket the electrolyte.</li>
		<li>Input parameters into an automated cyclic voltammetry file supplied by the potentiostat manufacturer. Set the cycle number to 3, the scan rate to 20 mV s-1, the start potential to 0.1 V, the lower potential to 0.025 V, and the upper potential to 1.2 V. Run the cyclic voltammetry file.</li>
	</ol>
	</li>
	<li>Take oxygen reduction polarization curves.
	<ol>
		<li>Purge the electrolyte with oxygen for at least 7 min with the working electrode rotating at 2,500 rpm.</li>
		<li>Set the oxygen purge to blanket the electrolyte and slow the working electrode rotation to 1,600 rpm.</li>
		<li>Input parameters into an automated linear sweep voltammetry file supplied by the potentiostat manufacturer. Set the cycle number to 10, the scan rate to 20 mV s-1, the start potential to -0.1 V, and the end potential to 1.05 V. Run the linear sweep voltammetry file. Discard the electrolyte.</li>
		<li>Refill with 0.1 M perchloric acid and purge with oxygen for at least 7 min. Rerun the linear sweep voltammetry file used in step 4.4.3.</li>
	</ol>
	</li>
	<li>Run durability tests.
	<ol>
		<li>Purge the electrolyte with nitrogen while rotating the working electrode at 2,500 rpm. Set the nitrogen purge to blanket the electrolyte and stop the working electrode rotation.</li>
		<li>Input parameters into an automated cyclic voltammetry file supplied by the potentiostat manufacturer. Set the cycle number to 30,000, the scan rate to 500 mV s-1, the lower potential to 0.6 V, and the upper potential to 1.0 V. Run the cyclic voltammetry file.</li>
		<li>After durability, take electrochemical surface areas and oxygen reduction polarization curves using the protocols supplied in steps 4.3 and 4.4.</li>
	</ol>
	</li>
</ol>

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	<li>Bregoli, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+Platinum+Crystallite+Size+on+Electrochemical+Reduction+of+Oxygen+in+Phosphoric-Acid.">Influence of Platinum Crystallite Size on Electrochemical Reduction of Oxygen in Phosphoric-Acid.</a> Electrochim. Acta. 23 (6), 489-492 (1978).</li><li>Debe, M. K., Parsonage, E. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanostructured+electrode+membranes.">Nanostructured electrode membranes.</a> US patent. , (1994).</li><li>Papandrew, A. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oxygen+Reduction+Activity+of+Vapor-Grown+Platinum+Nanotubes.">Oxygen Reduction Activity of Vapor-Grown Platinum Nanotubes.</a> ECS Trans. 50 (2), 1397-1403 (2013).</li><li>Alia, S. M., Yan, Y. S., Pivovar, B. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Galvanic+displacement+as+a+route+to+highly+active+and+durable+extended+surface+electrocatalysts.">Galvanic displacement as a route to highly active and durable extended surface electrocatalysts.</a> Cat. Sci. Tech. 4 (10), 3589-3600 (2014).</li><li>Alia, S. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Platinum-Coated+Nickel+Nanowires+as+Oxygen-Reducing+Electrocatalysts.">Platinum-Coated Nickel Nanowires as Oxygen-Reducing Electrocatalysts.</a> ACS Cat. 4 (4), 1114-1119 (2014).</li><li>Alia, S. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exceptional+Oxygen+Reduction+Reaction+Activity+and+Durability+of+Platinum-Nickel+Nanowires+through+Synthesis+and+Post-Treatment+Optimization.">Exceptional Oxygen Reduction Reaction Activity and Durability of Platinum-Nickel Nanowires through Synthesis and Post-Treatment Optimization.</a> ACS Omega. 2 (4), 1408-1418 (2017).</li><li>Norskov, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Origin+of+the+Overpotential+for+Oxygen+Reduction+at+a+Fuel-Cell+Cathode.">Origin of the Overpotential for Oxygen Reduction at a Fuel-Cell Cathode.</a> J. Phys. Chem. B. 108 (46), 17886-17892 (2004).</li><li>Sha, Y., Yu, T. H., Merinov, B. V., Shirvanian, P., Goddard, W. 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Chem. 118 (18), 2963-2967 (2006).</li><li>Cui, C., Gan, L., Heggen, M., Rudi, S., Strasser, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Compositional+segregation+in+shaped+Pt+alloy+nanoparticles+and+their+structural+behaviour+during+electrocatalysis.">Compositional segregation in shaped Pt alloy nanoparticles and their structural behaviour during electrocatalysis.</a> Nat Mater. 12 (8), 765-771 (2013).</li><li>Chen, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+Crystalline+Multimetallic+Nanoframes+with+Three-Dimensional+Electrocatalytic+Surfaces.">Highly Crystalline Multimetallic Nanoframes with Three-Dimensional Electrocatalytic Surfaces.</a> Science. 343 (6177), 1339-1343 (2014).</li><li>Alia, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Porous+Platinum+Nanotubes+for+Oxygen+Reduction+and+Methanol+Oxidation+Reactions.">Porous Platinum Nanotubes for Oxygen Reduction and Methanol Oxidation Reactions.</a> Adv. Funct. Mater. 20 (21), 3742-3746 (2010).</li><li>Alia, S. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Platinum+Coated+Copper+Nanowires+and+Platinum+Nanotubes+as+Oxygen+Reduction+Electrocatalysts.">Platinum Coated Copper Nanowires and Platinum Nanotubes as Oxygen Reduction Electrocatalysts.</a> ACS Cat. 3 (3), 358-362 (2013).</li><li>Alia, S. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Platinum-Coated+Cobalt+Nanowires+as+Oxygen+Reduction+Reaction+Electrocatalysts.">Platinum-Coated Cobalt Nanowires as Oxygen Reduction Reaction Electrocatalysts.</a> ACS Cat. 4 (8), 2680-2686 (2014).</li><li>Alia, S. M., Duong, K., Liu, T., Jensen, K., Yan, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Palladium+and+Gold+Nanotubes+as+Oxygen+Reduction+Reaction+and+Alcohol+Oxidation+Reaction+Catalysts+in+Base.">Palladium and Gold Nanotubes as Oxygen Reduction Reaction and Alcohol Oxidation Reaction Catalysts in Base.</a> ChemSusChem. , (2014).</li><li>Alia, S. M., Pylypenko, S., Neyerlin, K. C., Kocha, S. S., Pivovar, B. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Platinum+Nickel+Nanowires+as+Methanol+Oxidation+Electrocatalysts.">Platinum Nickel Nanowires as Methanol Oxidation Electrocatalysts.</a> J. Electrochem. Soc. 162 (12), 1299-1304 (2015).</li><li>Alia, S. 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The authors have nothing to disclose.

These protocols have been used to produce extended surface electrocatalysts with both high surface areas and specific activities in the oxygen reduction reaction8. By depositing Pt onto nanostructured templates, the nanowires avoided low coordinated sites and minimize particle size effects, producing specific activities more than 12 times greater than carbon-supported Pt nanoparticles. Using galvanic displacement as the synthesis approach also produced an approximate coating on the Ni template<sup...

Proton exchange membrane fuel cells are partially limited by the amount and cost of platinum required in the catalyst layer, which can account for half of fuel cell costs1. In fuel cells, nanomaterials are typically developed as oxygen reduction catalysts, since the reaction is kinetically slower than hydrogen oxidation. Carbon-supported Pt nanoparticles are often used as oxygen reduction electrocatalysts due to their high surface area; however, they have specific selective activity and are prone to durability losses.
Extended thin films offer potential benefits to nanoparticles by addressing these limitations. Extended Pt surfaces typically produce specific activities an order of magnitude greater than nanoparticles, by limiting less active facets and particle size effects, and have been shown to be durable under potential cycling2,3,4. While high mass activities have been achieved in extended surface electrocatalysts, improvements have been made primarily through increases in specific activity, and the catalyst type has been limited to Pt with a low surface area (10 m2 gPt-1)3,4,5.
Spontaneous galvanic displacement combines the aspects of corrosion and electrodeposition6. The process is generally governed by the standard redox potentials of the two metals, and the deposition typically occurs when the metal cation is more reactive than the template. The displacement tends to produce nanostructures that match the template morphology. By applying this technique to extended nanostructures, Pt-based catalysts can be formed that take advantage of the high specific oxygen reduction activity of extended thin films. Through partial displacement, small amounts of Pt have been deposited, and have produced materials with high surface areas (&#62; 90 m2 gPt-1)7,8.
These protocols involve hydrogen annealing to mix Pt and Ni zones and improve oxygen reduction activity. A number of studies have theoretically established the mechanism and experimentally confirmed an alloying effect in Pt oxygen reduction. Modeling and correlating Pt-OH and Pt-O binding to oxygen reduction activity suggest that Pt improvements can be made through lattice compression9,10. Alloying Pt with smaller transition metals has confirmed this benefit, and Pt-Ni has been investigated in a number of forms, including polycrystalline, faceted electrodes, nanoparticles, and nanostructures11,12,13,14.
Galvanic displacement has been used in Pt-oxygen reduction catalyst development with a variety of other templates, including silver, copper, and cobalt nanostructures15,16,17. The synthesis technique has also been used in the deposition of other metals and has produced electrocatalysts for fuel cells, electrolyzers, and the electrochemical oxidation of alcohols18,19,20,21. Similar protocols can also be adapted for the synthesis of nanomaterials with a wider range of electrochemical applications.

<table><tbody><tr><td>Nickel nanowires</td><td>Plasmachem GmbH</td><td></td><td></td></tr><tr><td>250 mL round bottom flask</td><td>Ace Glass</td><td></td><td></td></tr><tr><td>Hot plate</td><td>VWR International</td><td></td><td></td></tr><tr><td>Mineral oil</td><td>VWR International</td><td></td><td></td></tr><tr><td>Potassium tetrachloroplatinate</td><td>Sigma Aldrich</td><td></td><td></td></tr><tr><td>Syringe pump</td><td>New Era Pump Systems</td><td></td><td></td></tr><tr><td>Rotator</td><td>Arrow Engineering</td><td></td><td></td></tr><tr><td>Teflon paddle</td><td>Ace Glass</td><td></td><td></td></tr><tr><td>Glass shaft</td><td>Ace Glass</td><td></td><td></td></tr><tr><td>Split hinge tubular furnace</td><td>Lindberg</td><td></td><td>Customized in-house</td></tr><tr><td>Schlenk line</td><td>Ace Glass</td><td></td><td></td></tr><tr><td>Condensers</td><td>VWR International</td><td></td><td></td></tr><tr><td>Nitric acid</td><td>Fisher Scientific</td><td></td><td></td></tr><tr><td>2-propanol</td><td>Fisher Scientific</td><td></td><td></td></tr><tr><td>Nafion ionomer (5 wt. %)</td><td>Sigma Aldrich</td><td></td><td></td></tr><tr><td>Glassy carbon working electrode</td><td>Pine Instrument Company</td><td></td><td></td></tr><tr><td>RDE glassware</td><td>Precision Glassblowing</td><td></td><td>Customized in-house</td></tr><tr><td>Platinum wire</td><td>Alfa Aesar</td><td></td><td>Customized in-house</td></tr><tr><td>Platinum mesh</td><td>Alfa Aesar</td><td></td><td>Customized in-house</td></tr><tr><td>MSR Rotator</td><td>Pine Instrument Company</td><td></td><td></td></tr><tr><td>Potentiostat</td><td>Metrohm Autolab</td><td></td><td></td></tr></tbody></table>

synthesis of platinum-nickel nanowires and optimization for oxygen reduction performance

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen reduction reaction. Spontaneous galvanic displacement was used to deposit Pt layers onto Ni nanowire substrates. The synthesis approach produced catalysts with high specific activities and high Pt surface areas. Hydrogen annealing improved Pt and Ni mixing and specific activity. Acid leaching was used to preferentially remove Ni near the nanowire surface, and oxygen annealing was used to stabilize near-surface Ni, improving durability and minimizing Ni dissolution. These protocols detail the optimization of each post-synthesis processing step, including hydrogen annealing to 250 &#176;C, exposure to 0.1 M nitric acid, and oxygen annealing to 175 &#176;C. Through these steps, Pt-Ni nanowires produced increased activities more than an order of magnitude than Pt nanoparticles, while offering significant durability improvements. The presented protocols are based on Pt-Ni systems in the development of fuel cell catalysts. These techniques have also been used for a variety of metal combinations, and can be applied to develop catalysts for a number of electrochemical processes.

Spontaneous galvanic displacement of Ni nanowires with Pt, using the specified amount, produced Pt-Ni nanowires that were 7.3 wt. % Pt (Figure 1 and Figure 2A). Some modification to the amount of Pt precursor may be required to reach the optimum Pt loading. Pt displacement is sensitive to the thickness of the surface Ni oxide layer, which can vary based on template age (air exposure) and upstream variability<sup ...

Watch this Scientific Journal Video about Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance at JoVE.com

Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance

&#160; The protocol describes the synthesis and electrochemical testing of platinum-nickel nanowires. Nanowires were synthesized by the galvanic displacement of a nickel nanowire template. Post-synthesis processing, including hydrogen annealing, acid leaching, and oxygen annealing were used to optimize nanowire performance and durability in the oxygen reduction reaction.

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen ...

synthesis-platinum-nickel-nanowires-optimization-for-oxygen-reduction

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7.7K Views.  National Renewable Energy Laboratory.   The protocol describes the synthesis and electrochemical testing of platinum-nickel nanowires. Nanowires were synthesized by the galvanic displacement of a nickel nanowire template. Post-synthesis processing, including hydrogen annealing, acid leaching, and oxygen annealing were used to optimize nanowire performance and durability in the oxygen reduction reaction.

Video: Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance

Preparation and Use of Photocatalytically Active Segmented Ag|ZnO and Coaxial TiO2-Ag Nanowires Made by Templated Electrodeposition

Photocatalytically active nanostructures require a large specific surface area with the presence of many catalytically active sites for the oxidation and reduction half reactions, and fast electron (hole) diffusion and charge separation. Nanowires present suitable architectures to meet these requirements. Axially segmented Ag|ZnO and radially segmented (coaxial) TiO2-Ag nanowires with a diameter of 200 nm and a length of 6-20 &#181;m were made by templated electrodeposition within the pores of polycarbonate track-etched (PCTE) or anodized aluminum oxide (AAO) membranes, respectively. In the photocatalytic experiments, the ZnO and TiO2 phases acted as photoanodes, and Ag as cathode. No external circuit is needed to connect both electrodes, which is a key advantage over conventional photo-electrochemical cells. For making segmented Ag|ZnO nanowires, the Ag salt electrolyte was replaced after formation of the Ag segment to form a ZnO segment attached to the Ag segment. For making coaxial TiO2-Ag nanowires, a TiO2 gel was first formed by the electrochemically induced sol-gel method. Drying and thermal annealing of the as-formed TiO2 gel resulted in the formation of crystalline TiO2 nanotubes. A subsequent Ag electrodeposition step inside the TiO2 nanotubes resulted in formation of coaxial TiO2-Ag nanowires. Due to the combination of an n-type semiconductor (ZnO or TiO2) and a metal (Ag) within the same nanowire, a Schottky barrier was created at the interface between the phases. To demonstrate the photocatalytic activity of these nanowires, the Ag|ZnO nanowires were used in a photocatalytic experiment in which H2 gas was detected upon UV illumination of the nanowires dispersed in a methanol/water mixture. After 17 min&#160;of illumination, approximately 0.2 vol% H2 gas was detected from a suspension of ~0.1 g of Ag|ZnO nanowires in a 50 ml 80 vol% aqueous methanol solution.

Preparation and Use of Photocatalytically Active Segmented Ag|ZnO and Coaxial TiO2-Ag Nanowires Made by Templated Electrodeposition

Procedures are outlined to prepare segmented and coaxial nanowires via templated electrodeposition in nanopores. As examples, segmented nanowires consisting of Ag and ZnO segments, and coaxial nanowires consisting of a TiO2 shell and a Ag core were made. The nanowires were used in photocatalytic hydrogen formation experiments.

Photocatalytically active nanostructures require a large specific surface area with the presence of many catalytically active sites for the oxidation and ...

Engineering

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The silica-encapsulated metal oxide nanoparticles are then carburized in a methane/hydrogen atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal carbide nanoparticles. During the carburization process, the silica shells prevent the sintering of adjacent carbide nanoparticles while also preventing the deposition of excess surface carbon. Alternatively, the silica-encapsulated metal oxide nanoparticles can be nitridized in an ammonia atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal nitride nanoparticles. By adjusting the reverse microemulsion parameters, the thickness of the silica shells, and the carburization/nitridation conditions, the transition metal carbide or nitride nanoparticles can be tuned to various sizes, compositions, and crystal phases. After carburization or nitridation, the silica shells are then removed using either a room-temperature aqueous ammonium bifluoride solution or a 0.1 to 0.5 M NaOH solution at 40-60 &#176;C. While the silica shells are dissolving, a high surface area support, such as carbon black, can be added to these solutions to obtain supported early transition metal carbide or nitride nanoparticles. If no high surface area support is added, then the nanoparticles can be stored as a nanodispersion or centrifuged to obtain a nanopowder.

A &#8220;removable ceramic coating method&#8221; is presented in visual format for the synthesis of non-sintered and metal-terminated monometallic and bimetallic early transition metal carbide and nitride nanoparticles with tunable sizes and crystal structures.

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The ...

Synthesis and Testing of Supported Pt-Cu Solid Solution Nanoparticle Catalysts for Propane Dehydrogenation

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are demonstrated here. The catalyst forms a substitutional solid solution structure, with a small and uniform particle size around 2 nm. This is realized by careful control over the impregnation, calcination, and reduction steps during catalyst preparation and is identified by advanced in situ synchrotron techniques. The catalyst propane dehydrogenation performance continuously improves with increasing Cu:Pt atomic ratio.

A convenient method for the synthesis of 2 nm supported bimetallic nanoparticle Pt-Cu catalysts for propane dehydrogenation is reported here. In situ synchrotron X-ray techniques allow for the determination of the catalyst structure, which is typically unobtainable using laboratory instruments.

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are ...

Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of NixNb1-xO nanoparticles with different atomic compositions (x = 0.03, 0.08, 0.15, and 0.20) have been prepared by chemical precipitation. These NixNb1-xO catalysts are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The study revealed the sponge-like and fold-like appearance of Ni0.97Nb0.03O and Ni0.92Nb0.08O on the NiO surface, and the larger surface area of these NixNb1-xO catalysts, compared with the bulk NiO. Maximum surface area of 173 m2/g can be obtained for Ni0.92Nb0.08O catalysts. In addition, the catalytic hydroconversion of lignin-derived compounds using the synthesized Ni0.92Nb0.08O catalysts have been investigated.

Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

A protocol for the synthesis of sponge-like and fold-like Ni1-xNbxO nanoparticles by chemical precipitation is presented.

We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of ...

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity in aqueous CO2 reduction. Different from traditional metal nanocrystals, the synthesis of metal single atoms involves a matrix material that can confine those single atoms and prevent them from aggregation. We report an electrospinning and thermal annealing method to prepare Ni single atoms dispersed and coordinated in a graphene shell, as active centers for CO2 reduction to CO. During the synthesis, N dopants play a critical role in generating graphene vacancies to trap Ni atoms. Aberration-corrected scanning transmission electron microscopy and three-dimensional atom probe tomography were employed to identify the single Ni atomic sites in graphene vacancies. Detailed setup of electrochemical CO2 reduction apparatus coupled with an on-line gas chromatography is also demonstrated. Compared to metallic Ni, Ni single atom catalyst exhibit dramatically improved CO2 reduction and suppressed H2 evolution side reaction.

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

Here, we present a protocol for the synthesis and electrochemical testing of transition metal single atoms coordinated in graphene vacancies as active centers for selective carbon dioxide reduction to carbon monoxide in aqueous solutions.

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity ...

Synthesis of Substrate-Bound Au Nanowires Via an Active Surface Growth Mechanism

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a challenge, as it requires asymmetric growth of symmetric crystals. Here, we report a distinctive synthesis of substrate-bound Au nanowires. This template-free synthesis employs thiolated ligands and substrate adsorption to achieve the continuous asymmetric deposition of Au in solution at ambient conditions. The thiolated ligand prevented the Au deposition on the exposed surface of the seeds, so the Au deposition only occurs at the interface between the Au seeds and the substrate. The side of the newly deposited Au nanowires is immediately covered with the thiolated ligand, while the bottom facing the substrate remains ligand-free and active for the next round of Au deposition. We further demonstrate that this Au nanowire growth can be induced on various substrates, and different thiolated ligands can be used to regulate the surface chemistry of the nanowires. The diameter of the nanowires can also be controlled with mixed ligands, in which another &#34;bad&#34; ligand could turn on the lateral growth. With the understanding of the mechanism, Au nanowire-based nanostructures can be designed and synthesized.

We report a solution-based method to synthesize substrate-bound Au nanowires. By tuning the molecular ligands used during the synthesis, the Au nanowires can be grown from various substrates with different surface properties. Au nanowire-based nanostructures can also be synthesized by adjusting the reaction parameters.

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a ...

A Continuous-flow Photocatalytic Reactor for the Precisely Controlled Deposition of Metallic Nanoparticles

In this work, a novel photocatalytic reactor for the pulsed and controlled excitation of the photocatalyst and the precise deposition of metallic nanoparticles is developed. Guidelines for the replication of the reactor and its operation are provided in detail. Three different composite systems (Pt/graphene, Pt/TiO2, and Au/TiO2) with monodisperse and uniformly distributed particles are produced by this reactor, and the photodeposition mechanism, as well as the synthesis optimization strategy, are discussed. The synthesis methods and their technical aspects are described comprehensively. The role of the ultraviolet (UV) dose (in each excitation pulse) on the photodeposition process is investigated and the optimum values for each composite system are provided.

For a continuous and scalable synthesis of noble-metal-based nanocomposites, a novel photocatalytic reactor is developed and its structure, operation principles, and product quality optimization strategies are described.

In this work, a novel photocatalytic reactor for the pulsed and controlled excitation of the photocatalyst and the precise deposition of metallic ...

Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid nanosheets, a series of Pt/xHMNO6/CNTs with different solid acid compositions (x = 5, 20 wt%; M = Nb, Ta; N = Mo, W) have been prepared by carbon nanotube pretreatment, protonic exchange, solid acid exfoliation, aggregation and finally Pt particles impregnation. The Pt/xHMNO6/CNTs are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and NH3-temperature programmed desorption. The study revealed that HNbWO6 nanosheets were attached on CNTs, with some edges of the nanosheets being bent in shape. The acid strength of the supported Pt catalysts increases in the following order: Pt/CNTs &#60; Pt/5HNbWO6/CNTs &#60; Pt/20HNbMoO6/CNTs &#60; Pt/20HNbWO6/CNTs &#60; Pt/20HTaWO6/CNTs. In addition, the catalytic hydroconversion of lignin-derived model compound: diphenyl ether using the synthesized Pt/20HNbWO6 catalyst has been investigated.

A protocol for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs is presented.

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid ...

A Salt-Templated Synthesis Method for Porous Platinum-based Macrobeams and Macrotubes

The synthesis of high surface area porous noble metal nanomaterials generally relies on time consuming coalescence of pre-formed nanoparticles, followed by rinsing and supercritical drying steps, often resulting in mechanically fragile materials. Here, a method to synthesize nanostructured porous platinum-based macrotubes and macrobeams with a square cross section from insoluble salt needle templates is presented. The combination of oppositely charged platinum, palladium, and copper square planar ions results in the rapid formation of insoluble salt needles. Depending on the stoichiometric ratio of metal ions present in the salt-template and the choice of chemical reducing agent, either macrotubes or macrobeams form with a porous nanostructure comprised of either fused nanoparticles or nanofibrils. Elemental composition of the macrotubes and macrobeams, determined with x-ray diffractometry and x-ray photoelectron spectroscopy, is controlled by the stoichiometric ratio of metal ions present in the salt-template. Macrotubes and macrobeams may be pressed into free standing films, and the electrochemically active surface area is determined with electrochemical impedance spectroscopy and cyclic voltammetry. This synthesis method demonstrates a simple, relatively fast approach to achieve high-surface area platinum-based macrotubes and macrobeams with tunable nanostructure and elemental composition that may be pressed into free-standing films with no required binding materials.

A synthesis method to obtain porous platinum-based macrotubes and macrobeams with a square cross section through chemical reduction of insoluble salt-needle templates is presented.

The synthesis of high surface area porous noble metal nanomaterials generally relies on time consuming coalescence of pre-formed nanoparticles, followed ...

Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production

A method for facile synthesis of nanostructured catalysts supported on carbon nanotubes with atomically dispersed cobalt and nitrogen dopant is presented herein. The novel strategy is based on a facile one-pot pyrolysis treatment of cobalt (II) acetylacetonate and nitrogen-rich organic precursors under Ar atmosphere at 800 &#176;C, resulting in the formation of Co- and N- co-doped carbon nanotube with earthworm-like morphology. The obtained catalyst was found to have a high density of defect sites, as confirmed by Raman spectroscopy. Here, cobalt (II) nanoparticles were stabilized on the atomically dispersed cobalt- and nitrogen-doped carbon nanotubes. The catalyst was confirmed to be effective in the catalytic hydrolysis of ammonia borane, in which the turnover frequency was 5.87 mol H2&#183;molCo-1&#183;min-1, and the specific hydrogen generation rate was determined to be 2447 mL H2&#183;gCo-1&#183;min-1. A synergistic function between the Co nanoparticle and the doped carbon nanotubes was proposed for the first time in the catalytic hydrolysis of ammonia borane reaction under a mild condition. The resulting hydrogen production with its high energy density and minimal refueling time could be suitable for future development as energy sources for mobile and stationary applications such as road trucks and forklifts in transport and logistics.

Here, we present a protocol to synthesize Co nanoparticles supported on carbon nanotubes with Co- and N- dopants for hydrogen productions.

A method for facile synthesis of nanostructured catalysts supported on carbon nanotubes with atomically dispersed cobalt and nitrogen dopant is presented ...

Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance

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Preparation and Use of Photocatalytically Active Segmented Ag|ZnO and Coaxial TiO₂-Ag Nanowires Made by Templated Electrodeposition