Replacement
of Pt-based oxygen reduction reaction (ORR) catalysts
with non-precious metal catalysts (NPMCs) such as Fe/N/C is one of
the most important issues in the commercialization of proton exchange
membrane fuel cells (PEMFCs). Despite numerous studies on Fe/N/C catalysts,
a fundamental study on the development of a versatile strategy is
still required for tuning the kinetic activity of a single Fe-N4 site. Herein, we report a new and intuitive design strategy
for tuning and enhancing the kinetic activity of a single Fe-N4 site by controlling electron-withdrawing/donating properties
of a carbon plane with the incorporation of sulfur functionalities.
The effect of electron-withdrawing/donating functionalities was elucidated
by experimentation and theoretical calculations. Finally, the introduction
of an oxidized sulfur functionality decreases the d-band center of
iron by withdrawing electrons, thereby facilitating ORR at the Fe-N4 site by lowering the intermediate adsorption energy. Furthermore,
this strategy can enhance ORR activity without a decrease in the stability
of the catalyst. This simple and straightforward approach can be a
cornerstone to develop optimum NPMCs for application in the cathodes
of PEMFCs.
Ankle sprains are the most common injuries sustained during sports activities. Most ankle sprains recover fully with non-operative treatment but 20-30% develop chronic ankle instability. Predicting which patients who sustain an ankle sprain will develop instability is difficult. This paper summarises a consensus on identifying which patients may require surgery, the optimal surgical intervention along with treatment of concomitant pathology given the evidence available today. It also discusses the role of arthroscopic treatment and the anatomical basis for individual procedures.
Medison.Sang Bong Ahn has received grants from Hanwha, Samjin, Ildong, and Hanmi.Dae Won Jun has served as an advisory committee member of Sysmax, J2H, and Future medicine. He is a speaker for Gilead Sciences,
Organic light-emitting diodes (OLEDs) are among the most promising organic semiconductor devices. The recently reported external quantum efficiencies (EQEs) of 29-30% for green and blue phosphorescent OLEDs are considered to be near the limit for isotropically oriented iridium complexes. The preferred orientation of transition dipole moments has not been thoroughly considered for phosphorescent OLEDs because of the lack of an apparent driving force for a molecular arrangement in all but a few cases, even though horizontally oriented transition dipoles can result in efficiencies of over 30%. Here we use quantum chemical calculations to show that the preferred orientation of the transition dipole moments of heteroleptic iridium complexes (HICs) in OLEDs originates from the preferred direction of the HIC triplet transition dipole moments and the strong supramolecular arrangement within the co-host environment. We also demonstrate an unprecedentedly high EQE of 35.6% when using HICs with phosphorescent transition dipole moments oriented in the horizontal direction.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.