Pt 3 Co catalyst nanoparticles of 4.9 nm size present on the cathode side of a PEMFC membrane-ele... more Pt 3 Co catalyst nanoparticles of 4.9 nm size present on the cathode side of a PEMFC membrane-electrode assembly (MEA) were analyzed by transmission electron microscopy after 10K voltage cycles under dierent operating conditions. The operating conditions include baseline (0.4-0.95 V, 80 • C, 100% Relative Humidity (RH)), high potential (0.4-1.05 V, 80 • C, 100% RH), high temperature (0.4-0.95 V, 90 • C, 100% RH), and low humidity (0.4-0.95 V, 80 • C, 30% RH). Particle growth and particle loss to the membrane is more severe in the high potential sample than in the high temperature and baseline MEAs, while no signicant particle growth and particle precipitation in the membrane can be observed in the low humidity sample. Particles with dierent morphologies were seen in the cathode including: 1-Spherical individual particles resulting from modied electro-chemical Ostwald ripening and 2-aggregated and coalesced particles resulting from either necking of two or more particles or preferential deposition of Pt between particles with consequent bridging. The dierence in the composition of these morphologies results in composition variations through the cathode from cathode/diusion media (DM) to the cathode/membrane interface.
... fully charged. 2. Experimental. LiMn 2 O 4 was obtained by mixing stoichiometric amounts of L... more ... fully charged. 2. Experimental. LiMn 2 O 4 was obtained by mixing stoichiometric amounts of Li 2 CO 3 and MnO 2 , subsequent firing in air in a furnace at 1123 K for 24 h, and cooling down under ambient atmosphere. The spinel ...
... fully charged. 2. Experimental. LiMn 2 O 4 was obtained by mixing stoichiometric amounts of L... more ... fully charged. 2. Experimental. LiMn 2 O 4 was obtained by mixing stoichiometric amounts of Li 2 CO 3 and MnO 2 , subsequent firing in air in a furnace at 1123 K for 24 h, and cooling down under ambient atmosphere. The spinel ...
Subcontractors • Johnson Matthey Fuel Cells, Sonning Common, United Kingdom Jonathan Sharman, Ale... more Subcontractors • Johnson Matthey Fuel Cells, Sonning Common, United Kingdom Jonathan Sharman, Alex Martinez, Dash Fongalland, Stephen Thorpe, Brian Theobald, L. Smith, D. Ozkaya, M. Gutierrez, Eleanor Dann, Graham Hards, and Willie Hall • United Technologies Research Center (UTRC), East Hartford, CT Zhiwei Yang and Michael Perry • University of Texas at Austin, Austin, TX Paulo Ferreira, Kang Yu, Somaye Rasouli, and Andres Godoy • Indiana University Purdue University Indianapolis (IUPUI), Indianapolis, IN Jian Xie, Chuankun Jia, Zhefei Li, Yun Zhou, and Fan Yang
Replacing scarce and expensive platinum (Pt) with metal-nitrogen-carbon (M-N-C) catalysts for the... more Replacing scarce and expensive platinum (Pt) with metal-nitrogen-carbon (M-N-C) catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) has largely been impeded by the low activity of M-N-C, in turn limited by low site density and low site utilization. Herein, we overcome these limits by implementing chemical vapor deposition (CVD) to synthesize Fe-N-C, an approach fundamentally different from previous routes. The Fe-N-C catalyst, prepared by flowing iron chloride vapor above a N-C substrate at 750 ℃, has a record Fe-N4 site density of 2×1020 sites·gram-1 with 100% site utilization. A combination of characterizations shows that the Fe-N4 sites formed via CVD are located exclusively on the outer-surface, accessible by air, and electrochemically active. This catalyst delivers an unprecedented current density of 33 mA·cm-2 at 0.90 ViR-free (iR-corrected) in an H2-O2 PEMFC at 1.0 bar and 80 ℃.
ABSTRACT The influence of the electrode metal on the kinetics of outer-sphere redox reactions is ... more ABSTRACT The influence of the electrode metal on the kinetics of outer-sphere redox reactions is still an unsettled question with contradictory results being re indicate the complete absence of an effect, while there is also experimental evidence that underpotential deposited (UPD) metal layers can influence th suggested that some of the reported catalytic effect may be experimental artifacts caused by anion adsorption on the electrodes. We have carried out a UPD-metal layers on the rate of the Fe2+/Fe3+ redox reaction on polycrystalline gold and platinum electrodes in perchloric acid solutions rigor with copper, silver, and bismuth UPD layers. Our experimental results indicate clearly that the catalytic effect of UPD-metal layers on outer-sphere re since the phenomenon persisted in rigorously purified solutions. We also suggest a possible theoretical explanation of this phenomenon. In a recent stu at a gold surface to be non-adiabatic, i.e. electronic coupling contributed significantly to the rate. In the work reported here we have investigated, effect observed for this reaction at a gold electrode with a UPD-copper monolayer may be due to changes in electronic coupling. We have found that, whi UPD-copper layer, the observed catalytic effect may still be due to a larger electronic coupling because the hydrated ion approaches closer to the UPD- electronic coupling and the rate of the reaction.
Non-Precious Metal Nano-Composite Oxygen Reduction Electrocatalysts: In situ X-ray Absorption Spe... more Non-Precious Metal Nano-Composite Oxygen Reduction Electrocatalysts: In situ X-ray Absorption Spectroscopy Studies. [ECS Meeting Abstracts 801, 343 (2008)]. Matt Smith, Jeremy Kropf, Deborah Myers, Jerzy Chlistunoff, Christina Johnston, Steven Conradson, Piotr Zelenay.
Pyrolysis is indispensable for synthesizing highly active Fe-N-C catalysts for the oxygen reducti... more Pyrolysis is indispensable for synthesizing highly active Fe-N-C catalysts for the oxygen reduction reaction (ORR) in acid, but how Fe, N, and C precursors transform to ORR-active sites during pyrolysis remains unclear. This knowledge gap ob- scures the connections between the input precursors and output products, clouding the pathway toward Fe-N-C catalyst improve- ment. Herein, we unravel the evolution pathway of precursors to ORR-active catalyst comprised exclusively of single atom Fe1(II)- N4 sites via in-temperature X-ray absorption spectroscopy. The Fe precursor transforms to Fe oxides below 300 °C, and then to tetrahedral Fe1(II)-O4 via a crystal-to-melt-like transformation below 600 °C. The Fe1(II)-O4 releases a single Fe atom that flows into the N-doped carbon defect forming Fe1(II)-N4 above 600 °C. This vapor phase single Fe atom transport mechanism is verified by synthesizing Fe1(II)-N4 sites via “non-contact pyrolysis” wherein the Fe precursor is not in physical contact ...
Journal of Electroanalytical Chemistry and Interfacial Electrochemistry
Linear scan voltammetry of carbon monoxide on platinum was conducted with the electrode surface m... more Linear scan voltammetry of carbon monoxide on platinum was conducted with the electrode surface modified by coadsorbed organic and inorganic compounds (surface lateral modifiers). The current-potential peak of carbon monoxide electrooxidation moved in the positive direction in all cases studied. Two mechanistic components are proposed to account for our observation. The structural effects are related to the nucleation-growth mechanism of the oxidation which assigns the reaction zone to the perimeter of the growing islands of a surface oxidant. Electrooxidation of an ideally uniform and coherent CO adlattice should be unaffected by a modifier present outside of such islands. On the contrary, many small islands of CO, diluted by the two dimensional network of the surface modifiers, create a favorable situation for the lateral modification. The modifier's induced transitions between small and large islands are reflected in the shift of the CO oxidation peak potential. The second component relates to the redistribution of the modifier's electronic charge between the surface and the chemisorbed CO. A part of the charge is locahred on the So(CO)-Sd(Pt) bond and increases the stability of surface attached CO. The electronic charge shifted towards the metal, can also screen the reacting CO/H,0 system against the growing electric field during the potential scan. Both effects are interpreted to increase the overpotential of the electrooxidation of CO and contribute to the gross effect observed experimentally.
Journal of Electroanalytical Chemistry and Interfacial Electrochemistry
A new method of single crystal preparation for electrochemical application is described in this r... more A new method of single crystal preparation for electrochemical application is described in this report. This method does not require the annealing-quenching procedure or ultra-high vacuum methodology. The crystal is armealed and cooled in iodine vapor, then transferred to an electrochemical cell where the chemisorbed iodine is replaced by carbon monoxide present in the electrolyte. The carbon monoxide is subsequently electrooxidized from the surface, leaving the clean, ordered surface exposed to the electrolyte. Thus, the crystal is obtained in situ. The ordered crystal is not subject to the strains imposed by quenching and at no time is the unprotected surface exposed to the atmosphere. The voltammetric evidence presented shows that this procedure is successful in the characterization of a clean and adsorbate-covered Pt (111) surface.
The submitted manuscript has been created by the University of Chicago as Operator of Argonne Nat... more The submitted manuscript has been created by the University of Chicago as Operator of Argonne National Laboratory ("Argonne") under Contract No. W-31-109-ENG-38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid-up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.
The oxygen evolution reaction (OER) plays a critical role in multiple energy conversion and stora... more The oxygen evolution reaction (OER) plays a critical role in multiple energy conversion and storage applications. However, its sluggish kinetics usually results in large voltage polarization and unnecessary energy loss. Therefore, designing efficient catalysts that could facilitate this process has become an emerging topic. Here, we present a unique Pt-Cu core-shell nanostructure for catalyzing the nonaqueous OER. The catalysts were systematically investigated with comprehensive spectroscopic techniques, and applied in nonaqueous Li-O2 electrochemical cells, which exhibited dramatically reduced charging overpotential (<0.2 V). The superior performance is explained by the robust Cu(I) surface sites stabilized by the Pt core in the nanostructure. The insights into the catalytic mechanism of the unique Pt-Cu core-shell nanostructure gained in this work are expected to serve as a guide for future design of other nanostructured bimetallic OER catalysts.
Pt 3 Co catalyst nanoparticles of 4.9 nm size present on the cathode side of a PEMFC membrane-ele... more Pt 3 Co catalyst nanoparticles of 4.9 nm size present on the cathode side of a PEMFC membrane-electrode assembly (MEA) were analyzed by transmission electron microscopy after 10K voltage cycles under dierent operating conditions. The operating conditions include baseline (0.4-0.95 V, 80 • C, 100% Relative Humidity (RH)), high potential (0.4-1.05 V, 80 • C, 100% RH), high temperature (0.4-0.95 V, 90 • C, 100% RH), and low humidity (0.4-0.95 V, 80 • C, 30% RH). Particle growth and particle loss to the membrane is more severe in the high potential sample than in the high temperature and baseline MEAs, while no signicant particle growth and particle precipitation in the membrane can be observed in the low humidity sample. Particles with dierent morphologies were seen in the cathode including: 1-Spherical individual particles resulting from modied electro-chemical Ostwald ripening and 2-aggregated and coalesced particles resulting from either necking of two or more particles or preferential deposition of Pt between particles with consequent bridging. The dierence in the composition of these morphologies results in composition variations through the cathode from cathode/diusion media (DM) to the cathode/membrane interface.
... fully charged. 2. Experimental. LiMn 2 O 4 was obtained by mixing stoichiometric amounts of L... more ... fully charged. 2. Experimental. LiMn 2 O 4 was obtained by mixing stoichiometric amounts of Li 2 CO 3 and MnO 2 , subsequent firing in air in a furnace at 1123 K for 24 h, and cooling down under ambient atmosphere. The spinel ...
... fully charged. 2. Experimental. LiMn 2 O 4 was obtained by mixing stoichiometric amounts of L... more ... fully charged. 2. Experimental. LiMn 2 O 4 was obtained by mixing stoichiometric amounts of Li 2 CO 3 and MnO 2 , subsequent firing in air in a furnace at 1123 K for 24 h, and cooling down under ambient atmosphere. The spinel ...
Subcontractors • Johnson Matthey Fuel Cells, Sonning Common, United Kingdom Jonathan Sharman, Ale... more Subcontractors • Johnson Matthey Fuel Cells, Sonning Common, United Kingdom Jonathan Sharman, Alex Martinez, Dash Fongalland, Stephen Thorpe, Brian Theobald, L. Smith, D. Ozkaya, M. Gutierrez, Eleanor Dann, Graham Hards, and Willie Hall • United Technologies Research Center (UTRC), East Hartford, CT Zhiwei Yang and Michael Perry • University of Texas at Austin, Austin, TX Paulo Ferreira, Kang Yu, Somaye Rasouli, and Andres Godoy • Indiana University Purdue University Indianapolis (IUPUI), Indianapolis, IN Jian Xie, Chuankun Jia, Zhefei Li, Yun Zhou, and Fan Yang
Replacing scarce and expensive platinum (Pt) with metal-nitrogen-carbon (M-N-C) catalysts for the... more Replacing scarce and expensive platinum (Pt) with metal-nitrogen-carbon (M-N-C) catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) has largely been impeded by the low activity of M-N-C, in turn limited by low site density and low site utilization. Herein, we overcome these limits by implementing chemical vapor deposition (CVD) to synthesize Fe-N-C, an approach fundamentally different from previous routes. The Fe-N-C catalyst, prepared by flowing iron chloride vapor above a N-C substrate at 750 ℃, has a record Fe-N4 site density of 2×1020 sites·gram-1 with 100% site utilization. A combination of characterizations shows that the Fe-N4 sites formed via CVD are located exclusively on the outer-surface, accessible by air, and electrochemically active. This catalyst delivers an unprecedented current density of 33 mA·cm-2 at 0.90 ViR-free (iR-corrected) in an H2-O2 PEMFC at 1.0 bar and 80 ℃.
ABSTRACT The influence of the electrode metal on the kinetics of outer-sphere redox reactions is ... more ABSTRACT The influence of the electrode metal on the kinetics of outer-sphere redox reactions is still an unsettled question with contradictory results being re indicate the complete absence of an effect, while there is also experimental evidence that underpotential deposited (UPD) metal layers can influence th suggested that some of the reported catalytic effect may be experimental artifacts caused by anion adsorption on the electrodes. We have carried out a UPD-metal layers on the rate of the Fe2+/Fe3+ redox reaction on polycrystalline gold and platinum electrodes in perchloric acid solutions rigor with copper, silver, and bismuth UPD layers. Our experimental results indicate clearly that the catalytic effect of UPD-metal layers on outer-sphere re since the phenomenon persisted in rigorously purified solutions. We also suggest a possible theoretical explanation of this phenomenon. In a recent stu at a gold surface to be non-adiabatic, i.e. electronic coupling contributed significantly to the rate. In the work reported here we have investigated, effect observed for this reaction at a gold electrode with a UPD-copper monolayer may be due to changes in electronic coupling. We have found that, whi UPD-copper layer, the observed catalytic effect may still be due to a larger electronic coupling because the hydrated ion approaches closer to the UPD- electronic coupling and the rate of the reaction.
Non-Precious Metal Nano-Composite Oxygen Reduction Electrocatalysts: In situ X-ray Absorption Spe... more Non-Precious Metal Nano-Composite Oxygen Reduction Electrocatalysts: In situ X-ray Absorption Spectroscopy Studies. [ECS Meeting Abstracts 801, 343 (2008)]. Matt Smith, Jeremy Kropf, Deborah Myers, Jerzy Chlistunoff, Christina Johnston, Steven Conradson, Piotr Zelenay.
Pyrolysis is indispensable for synthesizing highly active Fe-N-C catalysts for the oxygen reducti... more Pyrolysis is indispensable for synthesizing highly active Fe-N-C catalysts for the oxygen reduction reaction (ORR) in acid, but how Fe, N, and C precursors transform to ORR-active sites during pyrolysis remains unclear. This knowledge gap ob- scures the connections between the input precursors and output products, clouding the pathway toward Fe-N-C catalyst improve- ment. Herein, we unravel the evolution pathway of precursors to ORR-active catalyst comprised exclusively of single atom Fe1(II)- N4 sites via in-temperature X-ray absorption spectroscopy. The Fe precursor transforms to Fe oxides below 300 °C, and then to tetrahedral Fe1(II)-O4 via a crystal-to-melt-like transformation below 600 °C. The Fe1(II)-O4 releases a single Fe atom that flows into the N-doped carbon defect forming Fe1(II)-N4 above 600 °C. This vapor phase single Fe atom transport mechanism is verified by synthesizing Fe1(II)-N4 sites via “non-contact pyrolysis” wherein the Fe precursor is not in physical contact ...
Journal of Electroanalytical Chemistry and Interfacial Electrochemistry
Linear scan voltammetry of carbon monoxide on platinum was conducted with the electrode surface m... more Linear scan voltammetry of carbon monoxide on platinum was conducted with the electrode surface modified by coadsorbed organic and inorganic compounds (surface lateral modifiers). The current-potential peak of carbon monoxide electrooxidation moved in the positive direction in all cases studied. Two mechanistic components are proposed to account for our observation. The structural effects are related to the nucleation-growth mechanism of the oxidation which assigns the reaction zone to the perimeter of the growing islands of a surface oxidant. Electrooxidation of an ideally uniform and coherent CO adlattice should be unaffected by a modifier present outside of such islands. On the contrary, many small islands of CO, diluted by the two dimensional network of the surface modifiers, create a favorable situation for the lateral modification. The modifier's induced transitions between small and large islands are reflected in the shift of the CO oxidation peak potential. The second component relates to the redistribution of the modifier's electronic charge between the surface and the chemisorbed CO. A part of the charge is locahred on the So(CO)-Sd(Pt) bond and increases the stability of surface attached CO. The electronic charge shifted towards the metal, can also screen the reacting CO/H,0 system against the growing electric field during the potential scan. Both effects are interpreted to increase the overpotential of the electrooxidation of CO and contribute to the gross effect observed experimentally.
Journal of Electroanalytical Chemistry and Interfacial Electrochemistry
A new method of single crystal preparation for electrochemical application is described in this r... more A new method of single crystal preparation for electrochemical application is described in this report. This method does not require the annealing-quenching procedure or ultra-high vacuum methodology. The crystal is armealed and cooled in iodine vapor, then transferred to an electrochemical cell where the chemisorbed iodine is replaced by carbon monoxide present in the electrolyte. The carbon monoxide is subsequently electrooxidized from the surface, leaving the clean, ordered surface exposed to the electrolyte. Thus, the crystal is obtained in situ. The ordered crystal is not subject to the strains imposed by quenching and at no time is the unprotected surface exposed to the atmosphere. The voltammetric evidence presented shows that this procedure is successful in the characterization of a clean and adsorbate-covered Pt (111) surface.
The submitted manuscript has been created by the University of Chicago as Operator of Argonne Nat... more The submitted manuscript has been created by the University of Chicago as Operator of Argonne National Laboratory ("Argonne") under Contract No. W-31-109-ENG-38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid-up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.
The oxygen evolution reaction (OER) plays a critical role in multiple energy conversion and stora... more The oxygen evolution reaction (OER) plays a critical role in multiple energy conversion and storage applications. However, its sluggish kinetics usually results in large voltage polarization and unnecessary energy loss. Therefore, designing efficient catalysts that could facilitate this process has become an emerging topic. Here, we present a unique Pt-Cu core-shell nanostructure for catalyzing the nonaqueous OER. The catalysts were systematically investigated with comprehensive spectroscopic techniques, and applied in nonaqueous Li-O2 electrochemical cells, which exhibited dramatically reduced charging overpotential (<0.2 V). The superior performance is explained by the robust Cu(I) surface sites stabilized by the Pt core in the nanostructure. The insights into the catalytic mechanism of the unique Pt-Cu core-shell nanostructure gained in this work are expected to serve as a guide for future design of other nanostructured bimetallic OER catalysts.
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Papers by Deborah Myers