Chemical State of Adsorbed Sulfur on Pt Nanoparticles

An Efficient H2S-Tolerant Hydrogen Oxidation Electrocatalyst Enabled by a Lewis Acid Modifier for Fuel Cells

Industrial hydrogen fuel typically comprises about 5 ppm of hydrogen sulfide (H2S), incurring irreversible poisoning of platinum on carbon (Pt/C) catalyst in fuel cells. For realistic use, H2S should be removed to below 4 ppb; this process, however, is challenging and costly. We describe an exceptional H2S-tolerant yet high-performing hydrogen oxidation reaction (HOR) catalyst prepared by chemical grafting of chromic oxide (Cr2O3) onto a molybdenum-nickel (MoNi4) alloy. Cr2O3 as a Lewis acid enhances the specific adsorption of hydroxyl ions, which in turn prevents from S2- diffusing to the catalyst surface via electrostatic repulsion. Meanwhile, the adsorbed hydroxyl species boost HOR kinetics through improving the hydrogen-bond networks in electrical double layers. The composite catalyst achieved HOR performance comparable to that of commercial Pt/C in an alkaline electrolyte. Moreover, a fuel cell using this catalyst as anode can survive 5 ppm of H2S without deactivation, compared with rapid degradation observed over the Pt/C counterpart.

The characteristics of Raman spectroscopy of isomer CBD- and THC-Au nanoparticles using the density functional theory

The isomers cannabidiol (CBD) and Δ9-tetrahydrocannabinol (THC) can both be extracted from cannabis. We use density functional theory to study the Raman activity spectra, frontier molecular orbitals, and molecular electrostatic potentials of CBD, THC, and their respective gold complexes. A "selectivity enhancement" phenomenon for the spectral peaks at frequencies of 1144 cm^-1 and 1553 cm^-1 in the Raman spectrum of the CBD-Au_n complex, and at frequencies of 865 cm^-1, 1335 cm^-1, and 1553 cm^-1 in the Raman spectrum of the THC-Au_n complex, was observed and explained. The frontier molecular orbital energy gaps of CBD and THC are 5.4085 eV and 5.4461 eV, respectively, indicating that CBD is more likely to react than THC. The CBD/THC-Au complexes had the strongest chemical activities and greater charge transfer effects with an Au₃ cluster. The most electronegative sites of CBD and THC were found from molecular electrostatic potential (MEP) mapping. It is assumed that these sites are the adsorption sites of the CBD/THC molecules and gold surface. The MEP of the CBD/THC complexes also demonstrates the charge transfer effect between CBD/THC and Au. Both the "selectivity" phenomenon in the Raman activity spectra of the complex and the above assumption are explained by a surface selection rule. The conformation of the CBD/THC molecules on the gold surface are determined, showing that CBD is adsorbed vertically through the resorcinol structure while THC is adsorbed vertically through the tetrahydropyran and benzene ring.