A proton exchange membrane fuel cell is an energy device in which chemical energy is directly converted into electric energy through the oxygen reduction reaction (ORR). In this work, we have performed first-principles density functional theory calculations for the ORR of FeN4 center embeded in graphene (Gr) and carbon nanotube (CNT) to investigate reaction dynamics. At the beginning of reaction, an O2 molecule is adsorbed on the center with the end-on bent geometry and an electron of the Fe atom is transferred to the O2 molecule (Fe(3dz2)−O2(1πga)). The successive adsorption of two hydrogen atoms generates a water molecule which immediately dissociates from the surface. The remaining oxygen atom on the Fe atom also adsorbs hydrogen atoms and generates the second water molecule. We found that the in-plane Fe atom embedded in Gr becomes out-of-plane with the height of 0.344 Å and this height is reduced in the CNT case due to the mechanical surface tension. After the ORR, the FeN4 centers on Gr and CNT recover their initial electronic and geometrical structures, enabling the subsequent ORR. These results demonstrates the feasibility of the ORR of FeN4 center in carbon systems.

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We study spin-valley and lattice-pseudo spin currents in a dual ferromagnetic-gated silicene-based junction. Silicene has buckled atomic structure which allows us to take sublattice-dependent ferromagnetism into account in the investigation. One of the study results show that transmission at the junctions exhibits anisotropic property only in antiparallel cases. Interestingly, the studied junctions can be switched from a pure spin-polarizer to a pure valley-polarizer by reversing directions of exchange fields in the parallel junctions.The perfect control of spin-valley currents can be done only in the parallel cases and its resolution can be enhanced by increasing gate potential between the ferromagnetic barriers.The asymmetric barriers of anti-parallel junction is found to destroy both spin and valley filtering effects and yield a novel result, pure sub-lattice pseudo-spin polarization. The current in the anti-parallel junctions can be controlled to flow solely in either A or B sub-lattice, saying that the controllable lattice current in silicene is created in double ferromagnetic-gated junction. Our work reveals the potential of dual ferromagnetic-gated silicene junction which may be possible for applications in spin-valleytronics and lattice-pseudospintronics.