A review of Pt-based electrocatalysts for oxygen reduction reaction

Development of active and durable electro- catalyst for oxygen reduction reaction （ORR） remains one challenge for the polymer electrolyte membrane fuel cell （PEMFC） technology. Pt-based nanomaterials show the greatest promise as electrocatalyst for this reaction among all current catalytic structures. This review focuses on Pt- based ORR catalyst material development and covers the past achievements, current research status and perspectives in this research field. In particular, several important categories of Pt-based catalytic structures and the research advances are summarized. Key factors affecting the catalyst activity and durability are discussed. An outlook of future research direction of ORR catalyst research is provided.

Optimizing magnetic/dielectric matching in permalloy/carbonized cotton fiber composites by strain-tunable ferromagnetic resonance and defect-induced dielectric polarization

Electromagnetic losses in composites could be synergistically controlled by permeability and permittivity,associated with multiple ferromagnetic resonances and dielectric polarization.However,it is still challenging for simultaneous tunability for both the terms in a magnetic/dielectric composite system.Here,we demonstrate the tunable ferromagnetic resonances and the enhanced dielectric losses at gigahertz frequencies in permalloy/carbonized cotton fiber composites with different annealing temperatures.It is theoretically confirmed that the stress field acting on the magnetic permalloy layer increases with increasing temperature because of the shrinkage of the dielectric carbonized cotton fibers,resulting in multiple ferromagnetic resonances,in which there is a linear relationship(f=1.52×σ+9.38)between the resonance frequency(f)and the stress(σ).The present work provides a fundamental insight into understanding the micromagnetic dynamics of the magnetic/dielectric composite system.