Publications:

 

 

  1. Investigation of competitive and site-specific nature of anion adsorption on Pt using in situ x-ray absorption spectroscopy

http://pubs.acs.org/doi/pdf/10.1021/jp8067359
T. Arruda, S. Badri, J. M. Ziegelbauer, S. Mukerjee and D. E. Ramaker
J. Phys. Chem. C, 112, 18087 (2008)

 

Abstract
In situ X-ray absorption spectroscopy along with electrochemical measurements (CV and RDE) and previously published EQCN data provide further understanding of the nature of chloride poisoning on different faces/sites of carbon supported platinum clusters (1−2 nm) in acidic medium (HClO4). Chloride is shown to adsorb in 3-fold sites on the Pt(111) faces at the investigated Cl− concentrations (10−3 and 10−2 M). Atop chloride was found to be present within a narrow potential range (0.4−0.7 V RHE) when compressed adlayers of Cl− are formed on the Pt(111) faces forcing some Cl− to exist in atop/bridged sites. The interplay of anionic (Cl−, Br−, OH−, and HSO4−) adsorption on the different surfaces of Pt are also considered. For example O/OH can easily displace atop chloride on the edges/corners but not the Cl− at the Pt(111) sites, and therefore Cl− dramatically raises the overpotential for water activation at the Pt(111) sites. Chloride also drastically alters the ORR causing an increase of the overpotential by 85 mV for every 10-fold increase in chloride concentration with a total 150−200 mV increase in the overpotential at large concentrations at the Pt(111) sites. Finally Cl− ions cannot displace the bisulfate overlayer on the Pt(111) faces after it is formed at lower potentials; however, once the bisulfate adsorption is disturbed at higher potentials, the bisulfate cannot displace the Cl− adsorption. These relative anion adsorption preferences can help to explain the different dependencies of the important ORR on anion adsorption, and suggests that the effect of Cl− poisoning might be quite dependent on the Pt particle size.

 

  1. Functionalizing of FeCo alloy nanoparticles with highly dielectric amorphous oxide coatings

Q. Nguyen, C. N. Chinnasamy, S. D. Yoon, S. Sivasubramanian, T. Sakai, A. Baraskar, S. Mukerjee, C. Vittoria and V. G. Harris
J. App. Phys. 103, 07D532/1 (2008)

 

Abstract
FeCo alloy nanoparticles have been prepared by using a two step modified polyol process using Fe(II) chloride and Co acetate tetrahydrate as Fe and Co metal precursors. Tetraethyl silicate, aluminum isopropoxide, and zirconium(IV) acetyl acetonate were used to make amorphous SiO2, Al2O3, and ZrO2 coatings, respectively. X-ray diffraction studies showed that there are no crystalline peaks corresponding to SiO2, Al2O3, and ZrO2 because the oxide coatings of the FeCo core are amorphous in nature. The scanning electron micrograph analysis depicted the cubic nature of the particles with mean particle size of about 45 nm. The maximum saturation magnetization of 205 emu/g was achieved at 300 and 4 K. FeCo nanocomposites were screen printed as films and aligned by using an external magnetic field of 10 kOe. The microwave properties measured by in-plane ferromagnetic resonance at various frequencies indicate a minimum linewidth of [approximate]3700 Oe.

 

  1. Voltammetric characterization of Pt single crystal electrodes with basal orientations in trifluoromethanesulfonic acid

Berna, A. Feliu, L. Gancs and S. Mukerjee
Electrochem. Comm., 10, 1695 (2008)

 

Abstract
The behaviour of platinum single crystal electrodes in 0.1 M trifluoromethanesulphonic acid (TFMSA) is reported. The electrode–solution interface depicts the characteristics observed in absence of specific adsorption. At Pt(1 1 0) a small increase of the potential of zero total charge is envisaged. Water splitting region is slightly different than that at perchloric acid solutions thus precluding differences in water adsorption that are reported to be important in electrocatalysis.

 

  1. Direct Spectroscopic Observation of the Structural Origin of Peroxide Generation from Co-based Pyrolyzed Porphyrins for ORR Applications

http://pubs.acs.org/doi/pdf/10.1021/jp8001564
J. Ziegelbauer, T. Olson, S. Plylypenko, F. Alamgir, C. Jaye, P. Atanassov, and S. Mukerjee
J. Phys. Chem. C, 112, 8839 (2008)

 

Abstract
Pyrolyzed transition metal based porphyrins present an attractive alternative to state of the art Pt-based electrocatalysts for fuel cell applications based on their comparatively low cost. Unfortunately, the large array of precursors and synthetic strategies has led to considerable ambiguity regarding the specific structure/property relationships that give rise to their activity for oxygen reduction. Specifically, considerable debate exists in actual chemical structure of the pyrolyzed reaction centers, and their relationship to membrane-damaging peroxide yield. In this manuscript a comprehensive electrochemical and spectroscopic study of pyrolyzed CoTMPP produced via a self-templating process is presented. The resulting electrocatalysts are not carbon-supported, but are highly porous self-supported pyropolymers. Rotating ring disk electrode measurements showed that the materials pyrolyzed at 700 °C exhibited the highest performance, whereas pyrolysis at 800 °C resulted in a significant increase in the peroxide yield. X-ray photoelectron spectroscopy and Co L and K edge extended X-ray absorption fine structure (EXAFS) studies confirm that the majority of the Co−N4 active site has broken down to Co−N2 at 800 °C. Application of Δμ analysis (an X-ray absorption near-edge structure difference technique) to the in situ Co K edge EXAFS data allowed for direct spectroscopic observation of the geometry of Oads on the pyropolymer active sites. The specific geometrical adsorption of molecular oxygen with respect to the plane of the Co−Nx moieties highly influences the oxygen reduction reaction pathway. The application of the Δμ technique to other transition metal based macrocycle electrocatalyst systems is expected to provide similarly detailed information.

 

  1. Electrode Kinetics and X-Ray Absorption Spectroscopy Investigation of Select Chalcogenide Electrocatalysts for Oxygen Reduction Reaction Application

J. M. Ziegelbauer, V. S. Murthi, C. Olaoire, A. F. Gulla and S. Mukerjee
Electrochim Acta, 53, 5587 (2008)

 

Abstract
Transition metal-based chalcogenide electrocatalysts exhibit a promising level of performance for oxygen reduction reaction applications while offering significant economic benefits over the state of the art Pt/C systems. The most active materials are based on RuxSey clusters, but the toxicity of selenium will most likely limit their embrace by the marketplace. Sulfur-based analogues do not suffer from toxicity issues, but suffer from substantially less activity and stability than their selenium brethren. The structure/property relationships that result in these properties are not understood due to ambiguities regarding the specific morphologies of RuxSy-based chalcogenides. To clarify these properties, an electrochemical kinetics study was interpreted in light of extensive X-ray diffraction, scanning electron microscopy, and in situ X-ray absorption spectroscopy evaluations. The performance characteristics of ternary MxRuySz/C (M = Mo, Rh, or Re) chalcogenide electrocatalysts synthesized by the now-standard low-temperature nonaqueous (NA) route are compared to commercially available (De Nora) Rh- and Ru-based systems. Interpretation of performance differences is made in regards to bulk and surface properties of these systems. In particular, the overall trends of the measured activation energies in respect to increasing overpotential and the gross energy values can be explained in regards to these differences.

 

  1. Degradation Mechanism Study of Perfluorinated Proton Exchange Membranes Under Actual Fuel Cell Operating Conditions

N. Ramasewamy, N. Hakim, and S. Mukerjee
Electrochim Acta, 53, 3279 (2008)

 

Abstract
Perfluorinated sulfonic acid proton exchange membranes are in the forefront as solid electrolytes for fuel cell applications. Although expensive, its potential utilization in commercial fuel cells can be validated provided it can be established that it is highly durable. In this context, peroxide radical-initiated attack of the membrane electrode interface is one of the key issues requiring further systematic investigation under fuel cell operating conditions, to better determine the fundamental degradation mechanism. In this study, we attempt to analyze the durability of the membrane electrode assembly (MEA) made with different commercial electrodes from the perspective of peroxide radical-initiated chemical attack on the electrode/electrolyte interface and find the pathway of membrane degradation as well. A novel segmented fuel cell is employed for durability characterization, and use of this cell and pre and post analysis of the membrane are presented. Correlation of membrane degradation data with the peroxide yield determined by RRDE experiments is obtained. This method is able to separate the membrane evaluation process into cathode and anode aspects. Fenton type mechanism of peroxide radical generation from H2O2 formed due to two-electron pathway of ORR is found to be the dominant membrane degrading factor.

 

  1. Size Dependent Magnetic Properties and Cation Inversion on Chemically Synthesized MnFe2O4 Nanoparticles

http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=JAPIAU00010100000909M509000001&idtype=cvips
C.N. Chinaswamy, A. Yang, S. D. Doon, K. Hsu, M. D. Shultz, E. E. Carpenter, S. Mukerjee, C. Vittoria and V. G. Harris
J. Appl. Phys., 101, 09M509 (2007)

 

Abstract
MnFe2O4 nanoparticles with diameters ranging from about 4  to  50  nm were synthesized using a modified coprecipitation method. X-ray diffractograms revealed a pure phase spinel ferrite structure for all samples. Transmission electron microscopy showed that the particles consist of a mixture of both spherical (smaller) and cubic (larger) particles dictated by the reaction kinetics. The Néel temperatures (TN) of MnFe2O4 for various particle sizes were determined by using high temperature magnetometry. The ~4  nm MnFe2O4 particles showed a TN of about 320  °C whereas the ~50  nm particles had a TN of about 400  °C. The high Néel temperature, compared with the bulk MnFe2O4 TN of 300  °C, is due to a change in cation distribution between the tetrahedral and octahedral sites of the spinel lattice. Results of extended x-ray absorption fine structure measurements indicate a systematic change in the cation distribution dependent on processing conditions.

 

  1. PtM/C Catalyst Prepared Using Reverse Micelle Method for Oxygen Reduction Reaction in PEM Fuel Cells

http://pubs.acs.org/doi/pdf/10.1021/jp074929i
Y. Qian, W. Wen, P. Adcock, N. Hakim, M. Saha and S. Mukerjee
J. Phys. Chem. C 112, 1146 (2008)

 

Abstract
Synthesis of carbon-supported PtM/C catalysts (M = Co, Cr, or Fe) using a new preparation technique, a reverse micelle method, is reported. The catalysts were characterized by different surface techniques:  X-ray diffraction, scanning electron microscope, transmission electron microscope, and energy dispersive X-ray microanalysis. Surface characterization showed that Pt/M nanoparticles on catalysts were synthesized using the reverse micelle method. Pt/M nanoparticles were observed to be uniform spherical objects. The performance of the PtM/C catalysts was tested by the rotating disk electrode technique. A trend of catalytic activity for oxygen reduction reaction (ORR) was obtained:  PtCo/C(T, 500) PtCo/C(S) > PtCr/C(S) > PtFe/C(S) Pt/C > PtFe/C(T, 500) PtCr/C(T, 500), showing that PtCo/C-type catalysts had a higher catalytic activity for ORR.