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Transition metal/nitrogen/carbon (M-N/C) catalysts are considered as one of the most promising candidates to replace Pt/C catalysts for oxygen reduction reactions (ORRs). Here, we have designed novel reduced graphene oxide (rGO)-supported Fe-N-doped carbon (Fe-N-C/rGO) catalysts via simple pyrolysis of polypyrrole (Ppy)-FeO-GO composites. The as-prepared catalysts induced an onset potential of 0.94 V and a half-wave potential of 0.81 V in alkaline solutions, which is much better than those of the counterpart N-C and N-C/rGO catalysts and comparable to that of Pt/C catalysts. Moreover, the Fe-N-C/rGO catalysts showed improved durability and higher tolerance against methanol crossover than Pt/C in alkaline solutions. This superior ORR performance can be ascribed to the combined catalytic effect of both Fe-based nanoparticles (FeO, FeC) and Fe-N sites, as well as fast mass transfer and accessible active sites benefiting from the mesoporous structure and high specific surface area. This work provides new insight for synthesis of a more promising nonplatinum electrocatalyst for metal-air batteries and fuel-cell applications.

Epitaxial films of the B20-structure compound Fe 1−y Co y Ge were grown by molecular beam epitaxy on Si (111) substrates. The magnetization varied smoothly from the bulklike values of one Bohr magneton per Fe atom for FeGe to zero for nonmagnetic CoGe. The chiral lattice structure leads to a Dzyaloshinskii-Moriya interaction (DMI), and the films' helical magnetic ground state was confirmed using polarized neutron reflectometry measurements. The pitch of the spin helix, measured by this method, varies with Co content y and diverges at y ∼ 0.45. This indicates a zero crossing of the DMI, which we reproduced in calculations using first-principles methods. We also measured the longitudinal and Hall resistivity of our films as a function of magnetic field, temperature, and Co content y. The Hall resistivity is expected to contain contributions from the ordinary, anomalous, and topological Hall effects. Both the anomalous and topological Hall resistivities show peaks around y ∼ 0.5. Our first-principles calculations show a peak in the topological Hall constant at this value of y, related to the strong spin polarization predicted for intermediate values of y. Our calculations predict half-metallicity for y = 0.6, consistent with the experimentally observed linear magnetoresistance at this composition, and potentially related to the other unusual transport properties for intermediate value of y. While it is possible to reconcile theory with experiment for the various Hall effects for FeGe, the large topological Hall resistivities for y ∼ 0.5 are much larger than expected when the very small emergent fields associated with the divergence in the DMI are taken into account.

Monodisperse, size-controlled Ni-P nanoparticles were synthesised in a single step process using triphenyl-phosphane (TPP), oleylamine (OA), and Ni(II)acetyl-acetonate. The nanoparticles were amorphous, contained ~30 at% P and their size was controlled between 7-21 nm simply by varying the amount of TPP. They are catalytically active for tailored carbon nanotube growth.