No abstract

It remains a challenge for platinum-based oxygen reduction reaction catalysts to simultaneously possess high mass activity and high durability in proton-exchange-membrane fuel cells. Herein, we report ultrathin holey nanotube (UHT)-structured Pt–M (M = Ni, Co) alloy catalysts that achieve unprecedented comprehensive performance. The nanotubes have ultrathin walls of 2–3 nm and construct self-supporting network-like catalyst layers with thicknesses of less than 1 μm, which have efficient mass transfer and 100% surface exposure, thus enabling high utilization of Pt atoms. Combined with the high intrinsic activity produced by the alloying effect, the catalysts achieve high mass activity. Moreover, the nanotube structure not only avoids the agglomeration problem of nanoparticles, but the low curvature of the tube wall also gives UHT a low surface energy (less than 1/3 of that of the same size nanoparticle), so UHT is more resistant to the Ostwald ripening and is stable. For the first time, the U.S. DOE mass activity target and dual durability targets for load and start–stop cycles are achieved on one catalyst. This study provides an effective structural strategy for the preparation of electrocatalysts with high atomic efficiency and excellent durability.

An advanced transient state model was developed based on the dynamic behavior of the porous air electrode of non-aqueous Li-air battery, which was determined by a numerical solution of the combined continuity, transport, and kinetics equations. The effects of linear porosity in air electrode on the detail performance such as the distribution of the oxygen concentration, Li2O2 volume fraction, porosity, and oxygen diffusion coefficient of non-aqueous Li-air battery during the discharge were investigated. The results revealed that the employing linear porosity air electrode leaded to the higher specific capacity, the uniform porosity and the preferable oxygen diffusion coefficient of Li-air battery caused by the high-efficiency utilization of porous air electrode and sufficient oxygen transfer. The discharge current density had significant effects on the property of Li-air battery based on linear porosity air electrode due to the great increasing of ohm polarization and serious air electrode passivation. The porosity became uniformly with the reaction, which indicated utilization rate of air electrode near membrane side was significantly improved due to the large initial oxygen concentration difference. The detailed results provided a deeper understanding of producing more efficient Li-air batteries as potential power sources to expand the range of electric vehicles.