Band Structure Asymmetry of Bilayer Graphene Revealed by Infrared Spectroscopy

We report on infrared spectroscopy of bilayer graphene integrated in gated structures. We observe a significant asymmetry in the optical conductivity upon electrostatic doping of electrons and holes. We show that this finding arises from a marked asymmetry between the valence and conduction bands, which is mainly due to the inequivalence of the two sublattices within the graphene layer and the next-nearest-neighbor interlayer coupling. From the conductivity data, the energy difference of the two sublattices and the interlayer coupling energy are directly determined

ZIF-Mg(OH)2 Dual Template Assisted Self-Confinement of Small PtCo NPs as Promising Oxygen Reduction Reaction in PEM Fuel Cell

Traditional calcination usually causes sintering of Pt, which diminishes Pt exposure in proton exchange membrane fuel cell (PEMFC) electrodes. In the present work, a facile self-confined method for synthesizing highly dispersed PtCo-alloy on Co, N co-doped mesoporous carbon (PCN-MC) is developed via a dual-template strategy. Owing to the co-confined effect of Zn in the bimetallic zeolite-based imidazolate framework (ZIF) and Mg(OH)2 template, ultra-fine 2.7 nm PtCo-alloy with 2–3 atomic-layer Pt-skin nanoparticles are obtained. By adjusting the Co/Zn feeding-ratio in the bimetallic ZIF at 8/7, the alloying degree and nanoparticle size are optimized to achieve an outstanding oxygen reduction reaction activity with a high mass activity (MA) of 0.956 A mgPt−1 in 0.1 m HClO4, about 7.5-fold of that of commercial Pt/C. Furthermore, notable durability is also achieved with 81% retention of the initial MA after 30k cycles conducted between 0.6–1.0 V (versus reversible hydrogen electrode). These features are also verified by a H2–Air fuel cell test with an excellent combination of mass activity, power density, and durability. This strategy provides a feasible route for the large-scale synthesis of highly-dispersed PtCo-alloy catalysts. © 2022 Wiley-VCH GmbH