Spontaneous parity and charge-conjugation violations at real isospin and imaginary baryon chemical potentials

The phase structure of two-flavor QCD is investigated at real isospin and imaginary quark chemical potentials by using the Polyakov-loop extended Nambu--Jona-Lasinio model. In the region, parity symmetry is spontaneously broken by the pion superfluidity phase transition, whereas charge-conjugation symmetry is spontaneously violated by the Roberge-Weiss transition. The chiral (deconfinement) crossover at zero isospin and quark chemical potentials is a remnant of the parity (charge-conjugation) violation. The interplay between the parity and charge-conjugation violations are analyzed, and it is investigated how the interplay is related to the correlation between the chiral and deconfinement crossovers at zero isospin and quark chemical potentials.Comment: 12 pages, 18 figures. Typos were revised. Symbols /P and /C were added in Figures 8a and 8b. Colors of the figures were changed. Some sentences were added and revise

Challenging the Durability of Intermetallic Mo-Ni Compounds in the Hydrogen Evolution Reaction

Molybdenum-nickel materials are catalysts of industrial interest for the hydrogen evolution reaction (HER). Well-characterized surfaces of the single-phase intermetallic compounds Ni7Mo7, Ni3Mo, and Ni4Mo were subjected to accelerated durability tests (ADTs) and thorough characterization to unravel whether crystallographic ordering affects the activity. Their intrinsic instability leads to molybdenum leaching, resulting in higher specific surface areas and nickel-enriched surfaces. These are more prone to form Ni(OH)2 layers, which leads to deactivation of the Mo-Ni materials. The crystal structure of the intermetallic compounds has, due to the intrinsic instability of the materials in alkaline media, no effect on the activity. Ni7Mo7, identified earlier as durable, proves to be highly unstable in the applied ADTs. The results show that the enhanced activity of unsupported bulk Mo-Ni electrodes can solely be ascribed to increased specific surface areas. © 2021 The Authors. Published by American Chemical Society

Disentangling Electronic and Geometric Effects in Electrocatalysis through Substitution in Isostructural Intermetallic Compounds

Efficient development of catalytic materials requires knowledge of the decisive parameters defining the catalytic properties. In multicomponent metallic catalysts, these are categorized as electronic and geometric effects, yet they are strongly interrelated. A systematic disentanglement can be achieved by fixing one parameter while altering the other, which becomes possible through the substitution in isostructural intermetallic compounds. This approach enables the evaluation of electronic or geometric contributions both individually and combined. Herein, this is achieved by substitution of indium (three valence electrons) with tin (four valence electrons) in the series In(1-x)SnxPd(2), which allows for a systematic variation of the total number of electrons per unit cell with only a minor variation of the unit cell parameters and thus the evaluation of the electronic effect. Geometric effects were evaluated by substitution of indium with gallium in the Ga(1-x)InxPd(2) series, which allows for a systematic variation of the interatomic distances while maintaining the same number of valence electrons per unit cell and close atomic coordinates. By substituting gallium with tin in the Ga(1-x)SnxPd(2) series, both effects are combined and addressed simultaneously. The activity enhancement of the methanol oxidation reaction on the Ga(1-x)SnxPd(2) series is attributed to the synergy of the combined effects