Prashant V. Kamat

Bio: Prashant V. Kamat is an academic researcher from University of Notre Dame. The author has contributed to research in topics: Racism & Excited state. The author has an hindex of 140, co-authored 725 publications receiving 79259 citations. Previous affiliations of Prashant V. Kamat include Indian Institute of Technology Kanpur & Council of Scientific and Industrial Research.

Gas Diffusion Electrodes for CO2 and N2 Reduction: A Virtual Issue

Abstract: Electrocatalytic reduction reactions of CO2 (CO2RR) and N2 (N2RR) to produce value-added products have received wide attention across the globe. Despite the development of new catalyst materials, product selectivity, poor efficiency, and low rates of CO2RR and N2RR remain major hurdles in designing practical devices. The development of gas diffusion electrodes (GDEs) offers opportunities to drive these electrocatalytic reactions in continuous-flow reactors. Among the polymer membranes separating the electrode compartments, bipolar membranes (BPMs) are a popular choice for GDEs. A BPM consists of two fused layers of cation-exchange (CEL) and anion-exchange (AEL) polymers, which allows the separation of reactants in the reduction and oxidation chambers and suppresses crossover of reactants and products. The water molecules within the BPM exist in the dissociated form (H in CEL and OH− in the AEL parts of the BPM). By applying a reverse electrochemical bias (cathodefacing CEL), one can drive the H ions to induce reduction. On the other hand, a forward bias (cathode-facing AEL) drives H and OH− ions toward the interface to produce water (Figure 1). The reduction of H (hydrogen evolution reaction) can compete with CO2 or N2 reduction and needs to be mitigated with a moderate pH and electrochemical management. Major developments in the design of GDEs for selective reduction of CO2 and N2 and other developments are presented in this Virtual Issue. Electrode Design and Protocols. Electrocatalytic reactors employing GDEs are based on traditional fuel cell architecture. The electrocatalysts are either directly deposited on the polymer membrane or attached to a substrate (thin metal foil or carbon paper) containing electrocatalysts. The reactant gas and electrolyte are passed through the cathode and anode compartments of the cell. Gas diffusion electrode assemblies are now commercially available, and they can be tailored to suit the experimental needs. Figure 2 shows an example of a GDE assembled with a BPM to reduce CO2 to formate. The choice of membrane, its ion-exchange property, and the conductivity become important when buffered electrolytes of different cations are employed. It is also important to properly place reference electrodes to control the potential of the working electrode in a three-electrode assembly while evaluating the performance of an electrocatalyst. Interlab comparisons of GDE performance in the oxygen reduction reaction showed that careful consideration of iR corrections and the deposition of homogeneous catalysts layers are keys to comparing performances. CO2 Reduction. Two types of designs, “hybrid” and “membrane” flow cell reactors, are being considered for the CO2RR. In the hybrid-type design, a catholyte separates the electrode and the gas diffusion membrane. In the membrane design, the polymer membrane separates the two electrodes. Zero-gap electrolyzers have been demonstrated where a membrane separates the two electrodes and the catholyte is removed to allow direct feeding of humidified CO2 to the catalyst layer through the GDE. Whereas both designs can deliver high currents, it is important to consider voltage losses occurring throughout the cell. Such voltage losses need to be managed to maintain high-efficiency CO2 reduction. 10,11 Depending on the reactor design and the reactant flow/ pressure, one can tune selectivity to produce formate or CO as part of the CO2RR. 12 For example, the reduction of CO2 into CO is more effective on Ni-N/C than on Ag in dilute CO2 feeds, highlighting the importance of operating conditions on reactivity. The wetting characteristics of carbon-based GDEs are affected by the highly negative potentials required to drive the CO2RR. 13,14 A moderate hydrophobicity of the catalyst layer is required to balance the local concentrations of gaseous CO2 and the liquid electrolyte. For example, analyses of nanoporous Au catalyst layers suggested that only half of the catalyst was in contact with the electrolyte, while the other half remained dry. The complex mechanism of electrocatalytic CO2RR has been analyzed by modeling three CO2 masstransport regimes within a liquid-filled catalyst layer. These include the CO2 penetration depth, CO2 conversion along the solid−electrolyte double-phase boundaries, and CO2 conversion concentrated around the gas−solid−electrolyte triplephase boundaries. The critical role of water in GDEs is also related the source of the H incorporated into products. Using selective deuteration of the water in humidified CO2 fed to a GDE in a zero-gap system, or deuteration of the anolyte, it was observed that most H incorporated into ethylene derived from CO2RR comes from the anolyte (Figure 3). 17

Electron transfer reactions. Reaction of furanones and bifurandiones with potassium and oxygen

Abstract: Treatment of furanones (1a – c, 25, 34) and bifurandiones (23, 37) with potassium in THF gave rise to radical anion intermediates, which reacted with oxygen to give superoxide and ultimately products derived through the reaction of superoxide with the starting furanones and bifurandiones. Thus, the reaction of 1a with potassium gave a mixture of 4-oxo-2,2,4-triphenylbutanoic acid (7a), 1,3,3-triphenyl-2-propen-1-one (11a), and benzoic acid (12). The reaction of 11a itself, under similar conditions, gave a mixture of benzophenone (18a) and 12. Similar reactions have been observed in the case of 1b and c. The bifurandione 23, on treatment with potassium, gave a mixture of the 2(5H)-furanone 25, 2,3-diphenylpropenoic acid (31), and 12. The reaction of 25 itself with potassium under similar conditions gave the same mixture of 31 and 12. Treatment of 3-phenyl-2(3H)-benzofuranone (34) with potassium, however, did not give any isolable product; only the starting material could be recovered. Under similar conditions, the bifurandione 37 gave the fragmentation product 34. Cyclic voltammetric studies have been employed to measure the reduction potentials, leading to radical anions, and these intermediates have been characterized through their electronic spectra. Elektronen-Ubertragungs-Reaktionen. Reaktion von Furanonen und Bifurandionen mit Kalium und Sauerstoff Bei der Behandlung von Furanonen (1a – c, 25, 34) und Bifurandionen (23, 37) mit Kalium in THF entstehen Radikalanion-Zwischenstufen, die mit Sauerstoff zu Superoxid reagieren, das seinerseits mit den Ausgangsfuranonen und -bifuranonen weiterreagiert. So ergab die Reaktion von 1a mit Kalium eine Mischung von 4-Oxo-2,2,4-triphenylbutansaure (7a), 1,3,3-Triphenyl-2-propen-1-on (11a) und Benzoesaure (12). Unter ahnlichen Bedingungen reagierte 11a selbst zu einer Mischung von Benzophenon (18a) und 12. Ahnliche Ergebnisse wurden im Falle von 1b und c erhalten. Das Bifurandion 23 ergab mit Kalium eine Mischung von 2(5H)-Furanon 25, 2,3-Diphenylpropensaure (31) und 12. 25 selbst reagierte mit Kalium unter ahnlichen Bedingungen zur selben Mischung von 31 und 12. 3-Phenyl-2(3H)-benzofuranon (34) fuhrte mit Kalium jedoch zu keinem isolierbaren Produkt; nur Ausgangsmaterial wurde zuruckgewonnen. Unter vergleichbaren Bedingungen lieferte das Bifurandion 37 das Fragmentierungsprodukt 34. Mit Hilfe der cyclischen Voltammetrie wurden die zu den Radikalanionen fuhrenden Reduktionspotentiale gemessen. Die Radikalanion-Zwischenstufen wurden durch ihre Elektronenspektren charakterisiert.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells

Abstract: Two organolead halide perovskite nanocrystals, CH3NH3PbBr3 and CH3NH3PbI3, were found to efficiently sensitize TiO2 for visible-light conversion in photoelectrochemical cells. When self-assembled on mesoporous TiO2 films, the nanocrystalline perovskites exhibit strong band-gap absorptions as semiconductors. The CH3NH3PbI3-based photocell with spectral sensitivity of up to 800 nm yielded a solar energy conversion efficiency of 3.8%. The CH3NH3PbBr3-based cell showed a high photovoltage of 0.96 V with an external quantum conversion efficiency of 65%.

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

Abstract: Single-layer metal dichalcogenides are two-dimensional semiconductors that present strong potential for electronic and sensing applications complementary to that of graphene.

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

Abstract: Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346

Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides

Abstract: To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Films and powders of TiO 2- x N x have revealed an improvement over titanium dioxide (TiO 2 ) under visible light (wavelength 2 has proven to be indispensable for band-gap narrowing and photocatalytic activity, as assessed by first-principles calculations and x-ray photoemission spectroscopy.