We predict a new two-dimensional allotrope of phosphorus, which we call red phosphorene, by restructuring the segments of the previously proposed blue and black phosphorenes. Its atomic and electronic structures as well as the thermodynamic and dynamic stabilities are systematically studied by first-principles calculations. The results indicate that the red phosphorene is dynamically stable and possesses remarkably thermodynamical stability comparable to that of the black one. Because of the sp(3)-hybridization and the formation of a localized lone pair, red phosphorene is a semiconductor with an indirect band gap of about 1.96 eV, which can be effectively modulated by in-plane strains due to its wave-like configuration. We find that the red, black and blue phosphorenes show evident distinction in their layer thicknesses, surface work functions, and possible colors, based on which one can distinguish them in future experiments.
A perfluorosulfonic
acid (PFSA) ionomer, used as the proton conductor
in the catalyst layer, influences significantly the performance of
proton exchange membrane fuel cell catalyst-coated membrane (CCM).
In this paper, SSC-CCM is prepared by the SSC-PFSA (Aquivion, EW 720)
ionomer, and the comparative sample (LSC-CCM) is based on the LSC-PFSA
ionomer (Nafion, EW 1100). Compared with LSC-CCM, SSC-CCM shows higher
porosity, larger electrochemical surface area (ECSA), and smaller
high-frequency resistance. Polarization curves of SSC-CCM tested by
the short stack show better performance than those of LSC-CCM, especially
under the lower relative humidity operations. Moreover, the SSC-CCM
outputs higher voltage and is more stable in the dynamic process with
temperature continuously increasing under lower relative humidity
operation. Such excellent performance of SSC-CCM is confirmed from
the higher proton conductivity of SSC-PFSA under low relative humidity.
These results indicate that the SSC-PFSA ionomer could be employed
for the CCM catalyst layer under the operation conditions of low relative
humidity and dynamic running for automotive applications.
The non-precious metal graphene catalyst doped with Fe-Px are recently proposed as a promising candidate in substituting Pt for catalyzing oxygen reduction reaction (ORR) in fuel cells. Systematic DFT calculations are performed to investigate the catalytic activity and the ORR mechanism on the Fe-Px (x = 1-4) system in acid medium in this work. Our results indicated that the configuration with one Fe and two P atoms codoped at zigzag edge site (Fe-P2-zig-G) is the most stable, in excellent agreement with the experimental observation that the ratio of Fe and P is nearly 1 : 2. The four-electron reduction mechanism for ORR on the Fe-P2-zig-G is via the competing OOH hydrogenation pathways (to form either OH + OH or O + H2O). The rate determining step is the O2 hydrogenation with an energy barrier of 0.43 eV, much smaller that of calculated 0.80 eV for pure Pt. In addition, the highest energy barrier of the studied ORR mechanism is the O2 dissociation with an energy barrier of 0.70 eV, a value also smaller than that of pure Pt. This demonstrated that the zigzag edge site of the Fe-P2 codoped graphene should be active for the ORR.
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