Published papers

[1] Rechargeable Lithium/TEGDME-LiPF₆/O₂ Battery [pdf]

Cormac Ó Laoire,^a Sanjeev Mukerjee,^a,* Edward J. Plichta,^b

^aDepartment of Chemistry and Chemical Biology, Northeastern University, Boston, Massachusetts 02115, USA
^bUS Army CERDEC, Army Power Division, Ft. Monmouth, New Jersey 07703, USA

Journal of The Electrochemical Society, 158
(3) A302-A308 (2011)

Abstract
A rechargeable Li–air cell utilizing an electrolyte composed of a solution of LiPF₆ in tetraethylene glycol dimethyl ether, CH₃O(CH₂CH₂O)₄CH₃ (TEGDME), and an uncatalyzed porous carbon electrode, investigated to elucidate the baseline Li–air battery chemistry, is reported. From the x-ray diffraction patterns of the discharged carbon electrodes, the discharge product of the cell was identified to be Li₂O₂ during normal discharge to 1.5 V. Discharging the cell to 1.0 V or below produces Li₂O as well. The cell can be recharged without a catalyst in the carbon cathode, albeit at low depths of discharge. The high resistance of the discharged carbon cathode is a major impediment to recharging cells displaying a high specific capacity. The cell capacity decreases with continued cycling, which was found to be due to the poor cycling efficiency of the Li anode and the high resistance of the discharge products, which slowly accumulate in the porous electrode.

[2] Zn-Doped RuO₂ electrocatalyts for Selective Oxygen Evolution: Relationship between Local Structure and Electrocatalytic Behavior in Chloride Containing Media [pdf]

Valery Petrykin,^*,† Katerina Macounova, Jiri Franc, Oleg Shlyakhtin,^‡ Mariana Klementova,^§ Sanjeev Mukerjee,^⊥ and Petr Krtil^*,†

^†J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i, Dolejskova 3, 18223 Prague, Czech Republic,
^‡Department of Chemistry, Moscow State University, 117899 Moscow, Russia,
^§Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic, vvi Rez, 25263 Prague, Czech Republic, and
^⊥Depratment of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts, United States

Chem. Mater., Vol. 23, No. 2, 2011

Abstract
Nanocrystalline electrocatalytically active materials of chemical composition Ru_1-xZn_xO₂ (0 ‹ x ‹ 0.3) were synthesized by freeze-drying technique. The diffraction patterns of the prepared samples corresponded to single-phase rutile type oxides.Local structure of theRu_1-x Zn_xO₂ based on refinement of Ru K and Zn K edge EXAFS functions shows clustering of the Zn ions in the blocks with ilmenite structure intergrowing with Ru-rich rutile blocks. Ru_1-xZn_xO₂ oxides are selective catalysts for anodic oxygen evolution. The selectivity toward oxygen evolution in the presence of chlorides is affected by the actual Zn content and can be ascribed to structural hindrance of the formation of the surface peroxo group based active sites for chlorine evolution. The selectivity toward oxygen evolution in presence of chlorides is accompanied by the drop of the total activity, which gets more pronounced with increasing Zn content.

[3] Analysis of Double Layer and Adsorption Effects at the Alkaline Polymer Electrolyte Interface

M. Unlu, D. Abbott, N. Ramaswamy, X. Ren, S. Mukerjee and P. A. Kohl

J. Electrochem. Soc., (In Press)

Abstract
In this study, the performance of the anionic electrodes in polymer-based alkaline fuel cells is analyzed. Direct alcohol, alkaline fuel cells suffer from a rapid decrease in cell potential at low discharge currents. Several effects are described to account for this drop in cell potential. Quaternary ammonium ions can specifically adsorb on the catalyst surface decreasing the active surface area and lowering the rate of methanol oxidation. In addition, the tethering of the quaternary ammonium cations on the polymer electrolyte inhibits the cation mobility causing a diffuse double layer to be formed. The diffuse double layer electrostatically inhibits the migration of hydroxide to the surface of the electrode which is needed for alcohol oxidation.

[4] Electrochemical Kinetics and X-ray Absorption Spectroscopic Investigation of Oxygen Reduction on Chalcogen-Modified Ru Catalysts in Alkaline Medium

N. Ramaswamy, R. J. Allen and S. Mukerjee

J. Phys. Chem. C., (In Press).

Abstract
Oxygen Reduction Reaction (ORR) in alkaline medium has been investigated on chalcogen modified ruthenium nanoparticles (Ru/C, Se/Ru/C, Se/RuMo/C, S/Ru/C, S/RuMo/C) synthesized in-house via aqueous routes. In acidic medium it is well known that modification by chalcogen prevents the oxidation of the underlying transition metal (Ru) surface thereby promoting direct molecular O₂ adsorption on the Ru metal. However on an unmodified Ru catalyst in alkaline medium, the surface oxides on Ru mediate the 2e¯ reduction of molecular O₂ to stable peroxide anion (HO₂¯) intermediate via an outer-sphere electron transfer mechanism. This increases the activity of HO₂¯ near the electrode surface and decreases the overpotential for ORR by effectively carrying out the reduction of HO₂¯ to OH¯ at the oxide free ruthenium metal site. Increase in ORR activity of Ru is observed by modification with chalcogen however the increase is not as significant as observed in acidic medium. Ternary additives such as Mo was found to significantly improve the stability of the chalcogen modified catalysts. Detailed investigations of the ORR activity of these class of catalyst have been carried out in alkaline medium along with comparisons to acidic medium whereever neccessary. A combination of electrochemical and Xray absorption spectroscopic (EXAFS, XANES, Delta Mu) studies have been performed in order to understand the structure/property relationships of these catalysts within the context of ORR in alkaline electrolytes.

[5] Oxygen Electrode Rechargeability in an Ionic Liquid for the Li-Air Battery

Chris J. Allen,^† Sanjeev Mukerjee,^† Edward J. Plichta,^‡ Mary A. Hendrickson,^‡ and K. M. Abraham^*,†

^†Department of Chemistry and Chemical Biology, NUCRET, Northeastern University, Boston, MA 02115, US
^‡U.S. Army CERDEC, Army Power Division, Fort Monmouth, New Jersey 07703, United States

J. Phys. Chem. C., 2011 (In Press)

Abstract
Oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) on glassy carbon (GC) and gold electrodes were investigated in a neat and Li⁺-containing room-temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium bis(triflouromethanesulfonyl) imide (EMITFSI). The presence of Li⁺ significantly changes the ORR mechanism. While similar one-electron O₂/O₂ ^•- reversible couples result on both electrodes in neat EMITFSI, in the presence of added LiTFSI, the initially formed LiO₂ decomposes to Li₂O₂. In addition, the ORR andOER in the Li⁺-doped solution exhibit strong distinctions between the Au and GC electrodes. The voltammetric data on the Au electrode revealed a highly rechargeable ORR, yielding LiO₂ and Li₂O₂, which underwent multiple cycles without electrode passivation.

[6] A Novel Non Noble CuFe/C Catalyst for Electroreduction of Oxygen in Alkaline Media

Q. He, X. Yang, X. Ren, B. E. Koel, N. Ramaswamy, S. Mukerjee and R. Kostecki

J. Power Sources (In Press)

Abstract
The primary objective of this work was to evaluate a novel commercial CuFe/C ORR catalyst for the oxygen reduction reaction (ORR) in alkaline fuel cells, which was synthesized from a mixture of iron and copper phthalocyanine-based complexes. This composite catalyst exhibits electrochemical performance for ORR in 0.1M KOH similar to a commercial Pt/C catalyst at 6 fold lower metal loading. High resolution X-ray photoelectron spectroscopy of the CuFe/C composite catalyst indicate presence of strong NxFe(III) and mixed Cu(I)/Cu(II) valence compounds in the CuFe/C catalyst. The postulated operation mechanism involves NxFe(III) as the active site for ORR and the Cu(II)/Cu(I) redox mediator as the electron shuttle from the electrode to the catalyst-oxygen (NxFe-O2) adduct. The results of this study may offer a new approach to development of efficient catalysts for oxygen reduction in alkaline media.

[7] Influence of Inner and Outer Sphere Electron Transfer Mechanisms during Electrocatalysis of Oxygen in Alkaline Medium

N. Ramaswamy and S. Mukerjee

J. Phys. Chem. C., (In Press)

Abstract
Oxygen reduction reaction (ORR) is generally considered to be more facile in alkaline media compared to its acidic counterparts. The fundamental reasoning for this statement has been quite elusive and not understood very well. A pertinent review of the literature in alkaline media on noble and non-noble metal electrocatalysts is presented here along with experimental results to investigate the rationale behind the so-called kinetic facility in alkaline media. Increasing the pH from 0 to 14 has several effects on the electrode
electrolyte interface in terms of the working electrode potential range, the strength of adsorption of the reaction intermediates, and spectator species. Besides these, the reasons for kinetic facility are investigated from the perspective of the changes in the double layer structure and electrochemical reaction mechanisms in transitioning from acidic to alkaline environment. In this context, specifically adsorbed hydroxyl species are found to promote an outer-sphere electron transfer ORR mechanism in alkaline media. A surface independent outer-sphere electron transfer component is proposed to be the reason for the so-called facile kinetics of ORR in alkaline media on a wide range of non-noble metal surfaces. However, this outer-sphere process predominantly leads only to a 2e¯ peroxide intermediate as the final product. The importance of promoting the electrocatalytic inner-sphere electron transfer mechanism by facilitation of direct adsorption of molecular oxygen and the stabilization of the peroxide intermediate on the active site are emphasized with the usage of chalcogen modified transition metals and pyrolyzed biomimetic metal porphyrins as electrocatalysts.

[8] Protein Hotspots at Bio-Nano Interface [pdf]

G. F. Audette^a,*, S. Lombardo^a, J. Dudzik^a, T. M. Arruda^b, M. Kolinski^c, S. Filipek^d, S. Mukerjee^b, A. M. Kannan^e, V. Thavasi^f, S. Ramakrishna^f, M. Chin^g, P. Somasundaram^g, S. Viswanathan^h,*, R. S. Kelesⁱ and V. Renugopalakrishnan^b,j,*

^a Department of Chemistry, York University, Toronto, ON, M3J1P3, Canada
^b Center for Renewable Energy Technologies, Department of Chemistry and Chemical Biology, Northeastern University, Boston, MA 02115, USA
^c International Institute of Molecular and Cell Biology, 02-109 Warsaw, Poland
^d Faculty of Chemistry, University of Warsaw, ul. Pasteura 1, 02-093 Warsaw, Poland
^e Electronic Systems Department, Arizona State University, Mesa, AZ 85212, USA
^f NUS Nanoscience and Nanotechnology Initiative, National University of Singapore, Singapore 117576, Singapore
^g Department of Earth & Environmental Engineering, Langmuir Center for Colloids and Interfaces, Columbia University, New York, NY 10027, USA
^h Newton-Wellesley Hospital/ Partners Healthcare System, Newton, MA 02462, USA
ⁱ Department of Physics & Astronomy, Hunter College, The City University of New York, New York, NY 10021, USA
^j Children’s Hospital, Harvard Medical School, Boston, MA 02115, USA
^* E-Mail: audette@yorku.ca (G. F. Audette); sviswanathan1@partners.org (S. Viswanathan); v.renugopalakrishnan@neu.edu (V. Renugopalakrishnan)

Materials Today, 14, 360 (2011)

Abstract
Nanotechnology has influenced the direction of research across the sciences, medicine, and engineering. Carbon nanotubes (CNTs) and, more recently, protein nanotubes (PNTs) and protein-inorganic nanocomposites have received considerable attention due to their unique nanostructures that can be utilized as a scaffold to house proteins or create nanowires. A shift towards protein-inorganic interactions has numerous applications from biosensors to biofuel cells and bio-based nanodevices. We examine several systems where protein hot spots, the active domains on proteins and the interactive dynamics in them, play a critical role in the interactions at the interface of these unique systems.

[9] Exceptional Rechargeability of a Catalyst Free Li-Air Cell

Matthew J Trahan ^a, Sanjeev Mukerjee ^a, Edward J. Plichta ^b and Mary A. Hendrickson ^b and K. M. Abraham ^a,*

^a Department of Chemistry and Chemical Biology, Northeastern UniVersity, 360 Huntington AVenue, Boston, Massachusetts 02115
^b U.S. Army CERDEC, Army Power DiVision, Ft. Monmouth, New Jersey 07703

J. Phys. Chem. C., (In Press)

Abstract
A detailed study of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) processes in dimethyl Sulfoxide (DMSO)-LiPF₆ has revealed for the first time that the oxygen electrode can be repeatedly cycled with a capacity utilization of up to 4 electrons per O₂. A catalyst-free Li-air cell has demonstrated remarkable ability for recharge with relatively small, 0.9 Volts, separation between discharge and charge curves.

[10] The Beneficial Role of Co-Metals Pd and Au in Carbon Supported PtPdAu Catalyst Towards Promoting Ethanol Oxidation Kinetics in Alkaline Fuel Cells: Temperature Effect and Mechanism [pdf]

J. Datta,^*,† A. Dutta^† and S. Mukerjee^‡

^†Electrochemistry & Fuel Cell Laboratory, Department of Chemistry, Bengal Engineering and Science University, Shibpur, Howrah
711 103, West Bengal, India
^‡Department of Chemistry and Chemical Biology, 317 Egan Center, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts 02115, United States

J. Phys. Chem. C., 115, 15324 (2011) qq

Abstract
Electrochemical investigations have been carried out to study the oxidation kinetics of ethanol in alkaline solution on carbon-supported ternary alloy catalysts Pt
Pd
Au within the temperature range of 20
80C. To derive a better understanding of the contribution of each of the metallic components toward the catalytic oxidation of ethanol, some of the investigations were extended to the individual noble metals for comparison, however, at a single temperature (20C). The individual metals could barely show their catalytic efficiency toward ethanol oxidations when compared to the alloyed catalyst. The ternary catalyst exhibited much lower values and a larger temperature dependence of onset potential for ethanol oxidation. With the rise of potential, the apparent activation energy (E_a(app)) for ethanol oxidation on the Pt/C electrode increased, whereas a decreasing trend was observed with the Pt₃₀Pd₃₈Au₃₂/C electrode. It was suggested that the Pt₃₀Pd₃₈Au₃₂/C electrode bears an excellent tolerance toward ethanolic residues, for the temperature range studied. In correlation with the results obtained from the above study, attempts were made to elucidate the oxidation reaction mechanism, and this further evoked interest in extending the work to the estimation of products formed during oxidation of ethanol within the same temperature range through ion chromatographic analysis. The pronounced increase in the quantity of oxidation products, such as acetate and carbonate, obtained over the ternary catalyst as compared to single Pt, substantiates the kinetic enhancement of ethanol oxidation, attributable to the cometal partnership between Pd and Au when incorporated in the Pt matrix. In summary, the multimetallic nanocrystallites can not only show their capability of extracting the best possible number of electrons from the alcohol fuel in alkaline solutions, harnessing more energy, but also, at the same time, bring down the cost of the catalyst material by reducing the Pt content to a considerable extent.

[11] Unveiling N-protonation and Anion Binding Effects on Fe/N/C Catalysts for Oxygen Reduction in PEM Fuel Cells

Juan Herranz,_† Fr
ed
eric Jaouen,_*,† Michel Lefevre,_† Ulrike I. Kramm,_†,‡ Eric Proietti,_† Jean-Pol Dodelet,_† Peter Bogdanoff,_‡ Sebastian Fiechter,_‡ Irmgard Abs-Wurmbach,_§ Patrick Bertrand,_|| Thomas M. Arruda,_⊥ and Sanjeev Mukerjee_⊥

^†Institut National de la Recherche Scientifique,
Energie, Mat
eriaux et T
el
ecommunications, Varennes, Qu
ebec, J3X 1S2, Canada
^‡Helmholtz-Zentrum Berlin f€ur Materialien und Energie Lise-Meitner-Campus, Institute for Solar Fuels and Energy Storage (E-I-6),
Hahn-Meitner-Platz 1, D-14109, Berlin, Germany
^§Technical University Berlin, Faculty VI, Ackerstrasse 76, D-13355, Berlin, Germany
^||Universite Catholique de Louvain, Institut de la Matiere Condens
ee et des Nanosciences, Croix-du-sud 1,
1348 Louvain-la-neuve, Belgium ^⊥Department of Chemistry and Chemical Biology, Northeastern University, Boston, Massachusetts 02115, United States

J. Phys. Chem. C., (In Press)

Abstract
The high cost of proton-exchange-membrane fuel cells would be considerably reduced if platinum-based catalysts were replaced by ironbased substitutes, which have recently demonstrated comparable activity for oxygen reduction but whose cause of activity decay in acidic medium has been elusive.Here, we reveal that the activity of Fe/N/C catalysts prepared through a pyrolysis in NH3 is mostly imparted by acid-resistant FeN4 sites whose turnover frequency for the O₂ reduction can be regulated by fine chemical changes of the catalyst surface. We show that surface N-groups protonate at pH 1 and subsequently bind anions. This results in decreased activity for the O₂ reduction. The anions can be removed chemically or thermally, which restores the activity of acid-resistant FeN₄ sites. These results are interpreted as an increased turnover frequency of FeN₄ sites when specific surface N-groups protonate. These unprecedented findings provide a new perspective for stabilizing the most active Fe/N/C catalysts known to date.