Nitrogen-doped carbon-based catalysts are attracting increased interest as potential Pt-free electrode catalysts for polymer electrolyte fuel cells. In this computational study, we inspect possible oxygen adsorption and reduction processes on various models for the exposed edges of these catalysts. The dynamics of an O 2 molecule solvated in water, which mimicks the cathode environment, shows that O 2 adsorption depends on the morphology and the atomic structure of the system. We show that carbon alloys with N dopants at specific sites can exhibit metal-free catalytic activity.

The quark number susceptibility near the QCD critical end-point (CEP), the tricritical point (TCP) and the O(4) critical line at finite temperature and quark chemical potential is investigated. Based on the universality argument and numerical model calculations we propose a possibility that the hidden tricritical point strongly affects the critical phenomena around the critical endpoint. We made a semi-quantitative study of the quark number susceptibility near CEP/TCP for several quark masses on the basis of the Cornwall-Jackiw-Tomboulis (CJT) potential for QCD in the improved-ladder approximation. The results show that the susceptibility is enhanced in a wide region around CEP inside which the critical exponent gradually changes from that of CEP to that of TCP, indicating a crossover of different universality classes.