Panakkattu K. Babu

Bio: Panakkattu K. Babu is an academic researcher from Western Illinois University. The author has contributed to research in topics: Nuclear magnetic resonance spectroscopy & Surface diffusion. The author has an hindex of 16, co-authored 34 publications receiving 1448 citations. Previous affiliations of Panakkattu K. Babu include Urbana University & Tata Institute of Fundamental Research.

An NMR investigation of CO tolerance in a Pt/Ru fuel cell catalyst.

Abstract: We report the first combined application of solid-state electrochemical NMR (EC NMR), cyclic voltammetry (CV), and potentiostatic current generation to investigate the topic of the ruthenium promotion of MeOH electro-oxidation over nanoscale platinum catalysts. The CV and EC NMR results give evidence for two types of CO: CO on essentially pure Pt and CO on Pt/Ru islands. There is no NMR evidence for rapid exchange between the two CO populations. CO molecules on the primarily Pt domains behave much like CO on pure Pt, with there being little effect of Ru on the Knight shift or on Korringa relaxation. In sharp contrast, COs on Pt/Ru have highly shifted 13C NMR resonances, much weaker Korringa relaxation, and, at higher temperatures, they undergo thermally activated surface diffusion. For CO on Pt, the correlation observed between the 2π* Fermi level local density of states and the steady-state current suggests a role for Ru in weakening the Pt−CO bond, thereby increasing the CO oxidation rate (current). Th...

UHV, Electrochemical NMR, and Electrochemical Studies of Platinum/Ruthenium Fuel Cell Catalysts

Abstract: It is well-known that platinum/ruthenium fuel cell catalysts show enhanced CO tolerance compared to pure platinum electrodes, but the reasons are still being debated. We have combined cyclic voltammetry (CV), temperature programmed desorption (TPD), electrochemical nuclear magnetic resonance, and radio active labeling to probe the origin of the ruthenium enhancement in Pt electrodes modified through Ru deposition. The results prove that the addition of ruthenium not only modifies the electronic structure of all the platinum atoms but also leads to the creation of a new form of adsorbed CO. This new form of CO may be ascribed to CO chemisorbed onto the “Ru” region of the electrode surface. TPD and CV results show that the binding of hydrogen is substantially modified due to the presence of Ru. Surprisingly though, TPD indicates that the binding energy of CO on platinum is only weakly affected. Therefore, the changes in the bond energy of CO due to the ligand effect only play a small role in enhancing CO to...

Particle-size effect of nanoscale platinum catalysts in oxygen reduction reaction: an electrochemical and 195Pt EC-NMR study

Abstract: Oxygen reduction reaction (ORR) measurements and 195Pt electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy were combined to study a series of carbon-supported platinum nanoparticle electrocatalysts (Pt/CB) with average diameters in the range of roughly 1–5 nm. ORR rate constants and H2O2 yields evaluated from hydrodynamic voltammograms did not show any particle size dependency. The apparent activation energy of 37 kJ mol−1, obtained for the ORR rate constant, was identical to that obtained for bulk platinum electrodes. Pt/CB catalysts on Nafion produced only 0.7–1% of H2O2, confirming that the direct four-electron reduction of O2 to H2O is the predominant reaction. NMR spectral features showed characteristic size dependence, and the line shapes were reproduced by using the layer-deconvolution model. Namely, the variations in the NMR spectra with particle size can be explained as due to the combined effect of the layer-by-layer variation of the s-type and d-type local density of states. However, the surface peak position of 195Pt NMR spectra and the spin–lattice relaxation time of surface platinum atoms showed practically no change with the particle size variation. We conclude that there is a negligible difference in the surface electronic properties of these Pt/CB catalysts due to size variations and therefore, the ORR activities are not affected by the differences in the particle size.

Electronic Alterations Caused by Ruthenium in Pt−Ru Alloy Nanoparticles as Revealed by Electrochemical NMR

Abstract: We have carried out a series of 195Pt and 13C NMR spectroscopic and electrochemical experiments on commercial Pt−Ru alloy nanoparticles and compared the results with those on Pt-black samples having similar particle sizes. The Pt NMR spectrum of the alloy nanoparticles consists of a single Gaussian peak, completely different from the broad “multi-Gaussian” NMR spectra, which are generally observed for carbon-supported Pt catalysts. Spin−echo decay measurements show that the intrinsic spin−spin relaxation time (T2) is much larger in the alloy compared to Pt-black. A “slow-beat” is observed in the spin−echo decay curve of the alloy, implying that the NMR frequencies of spin−spin coupled Pt nuclei in the alloy nanoparticles are quite similar, unlike the situation found with Pt-black. These 195Pt NMR results strongly suggest that there is a surface enrichment of Pt atoms in the Pt−Ru alloy nanoparticles. The CO-stripping cyclic voltammogram (CV) of the Pt−Ru alloy nanoparticles is broader than that observed w...

Selenium becomes metallic in Ru-Se fuel cell catalysts: an EC-NMR and XPS investigation.

Abstract: We report the results of an investigation of the interaction between Se and Ru in Ru−Se electrocatalysts showing high activity and methanol tolerance in the oxygen reduction reaction (ORR). The res...

Nanoalloys: From Theory to Applications of Alloy Clusters and Nanoparticles

Abstract: 5.1. Nanoalloys of Group 11 (Cu, Ag, Au) 865 5.1.1. Cu−Ag 866 5.1.2. Cu−Au 867 5.1.3. Ag−Au 870 5.1.4. Cu−Ag−Au 872 5.2. Nanoalloys of Group 10 (Ni, Pd, Pt) 872 5.2.1. Ni−Pd 872 * To whom correspondence should be addressed. Phone: +39010 3536214. Fax:+39010 311066. E-mail: ferrando@fisica.unige.it. † Universita di Genova. ‡ Argonne National Laboratory. § University of Birmingham. | As of October 1, 2007, Chemical Sciences and Engineering Division. Volume 108, Number 3

Recent Advances in Electrocatalysts for Oxygen Reduction Reaction

Abstract: The recent advances in electrocatalysis for oxygen reduction reaction (ORR) for proton exchange membrane fuel cells (PEMFCs) are thoroughly reviewed. This comprehensive Review focuses on the low- and non-platinum electrocatalysts including advanced platinum alloys, core–shell structures, palladium-based catalysts, metal oxides and chalcogenides, carbon-based non-noble metal catalysts, and metal-free catalysts. The recent development of ORR electrocatalysts with novel structures and compositions is highlighted. The understandings of the correlation between the activity and the shape, size, composition, and synthesis method are summarized. For the carbon-based materials, their performance and stability in fuel cells and comparisons with those of platinum are documented. The research directions as well as perspectives on the further development of more active and less expensive electrocatalysts are provided.

Oxygen electrochemistry as a cornerstone for sustainable energy conversion

Abstract: Electrochemistry will play a vital role in creating sustainable energy solutions in the future, particularly for the conversion and storage of electrical into chemical energy in electrolysis cells, and the reverse conversion and utilization of the stored energy in galvanic cells. The common challenge in both processes is the development of-preferably abundant-nanostructured materials that can catalyze the electrochemical reactions of interest with a high rate over a sufficiently long period of time. An overall understanding of the related processes and mechanisms occurring under the operation conditions is a necessity for the rational design of materials that meet these requirements. A promising strategy to develop such an understanding is the investigation of the impact of material properties on reaction activity/selectivity and on catalyst stability under the conditions of operation, as well as the application of complementary in situ techniques for the investigation of catalyst structure and composition.

Ru-Pt core-shell nanoparticles for preferential oxidation of carbon monoxide in hydrogen.

Abstract: Most of the world’s hydrogen supply is currently obtained by reforming hydrocarbons. ‘Reformate’ hydrogen contains significant quantities of CO that poison current hydrogen fuel-cell devices. Catalysts are needed to remove CO from hydrogen through selective oxidation. Here, we report first-principles-guided synthesis of a nanoparticle catalyst comprising a Ru core covered with an approximately 1–2-monolayer-thick shell of Pt atoms. The distinct catalytic properties of these well-characterized core–shell nanoparticles were demonstrated for preferential CO oxidation in hydrogen feeds and subsequent hydrogen light-off. For H2 streams containing 1,000 p.p.m. CO, H2 light-off is complete by 30 ∘C, which is significantly better than for traditional PtRu nano-alloys (85 ∘C), monometallic mixtures of nanoparticles (93 ∘C) and pure Pt particles (170 ∘C). Density functional theory studies suggest that the enhanced catalytic activity for the core–shell nanoparticle originates from a combination of an increased availability of CO-free Pt surface sites on the Ru@Pt nanoparticles and a hydrogen-mediated low-temperature CO oxidation process that is clearly distinct from the traditional bifunctional CO oxidation mechanism. To produce hydrogen by reforming hydrocarbons, efficient catalysts capable of removing carbon monoxide are needed. This can now be achieved via a preferential oxidation mechanism using nanoparticle catalysts consisting of a ruthenium core covered with platinum.