MOF-mediated synthesis of novel PtFeCoNiMn high-entropy nanoalloy as bifunctional oxygen electrocatalysts for zinc-air battery

High-entropy alloy(HEA)-based materials are expected to be promising oxygen electrocatalysts due to their exceptional properties.The electronic structure regulation of HEAs plays a pivotal role in enhancing their elctrocatalytic ability.Herein,PtFeCoNiMn nanoparticles(NPs)with subtle lattice distortions are constructed on metal-organic framework-derived nitrogen-doped carbon by an ultra-rapid Joule heating process.Thanks to the modulated electronic structure and the inherent cocktail effect of HEAs,the as-synthesized PtFeCoNiMn/NC exhibits superior bifunctional electrocatalytic performance with a positive half-wave potential of 0.863 V vs.reversible hydrogen electrode(RHE)for oxygen reduction reaction and a low overpotential of 357 mV at 10 mA·cm^(-2)for oxygen evolution reaction.The assembled quasi-solid-state zinc-air battery using PtFeCoNiMn/NC as air electrode shows a high peak power density of 192.16 mW·cm^(-2),low charge−discharge voltage gap,and excellent durability over 500 cycles at 5 mA·cm^(-2).This work demonstrates an effective route for rational design of bifunctional nanostructured HEA electrocatalysts with favorable electronic structures,and opens up a fascinating directions for energy storage and conversion,and beyond.

Atomic-level correlation between the electrochemical performance of an oxygen-evolving catalyst and the effects of CeO_(2) functionalization

Herein,we prepared a bimetallic layered double hydroxide(FeCo LDH)featuring a dandelion-like structure.Anchoring of CeO_(2)onto FeCo LDH produced interfaces between the functionalizing CeO_(2)and the parent LDH.Comparative electrochemical studies were carried out.Onset potential,overpotential,and Tafel slope point to the superior oxygen-evolving performance of CeO_(2)-FeCo LDH with respect to FeCo LDH,therefore,demonstrating the merits of CeO_(2)functionalization.The electronic structures of Fe,Co,and Ce were analyzed by X-ray photoelectron spectroscopy(XPS)and electron energy loss spectroscopy(EELS)from which the increase of Co^(3+)and the concurrent lowering of Ce^(4+)were established.With the use of CeO_(2)-FeCo LDH,accelerated formation at a sizably reduced potential of Co-OOH,one of the key intermediates preceding the release of O_(2)was observed by in situ Raman spectroscopy.We now have the atomic-level and location-specific evidence,the increase of the active Co^(3+)across the interface to correlate the enhanced catalytic performance with CeO_(2)functionalization.

中空核壳型锑碳材料的钠化过程观测与高效率储钠

锑因其高容量、低电压等优点成为备受关注的钠离子电池负极材料,但钠化过程中巨大的体积膨胀使其难以实现稳定的循环.本文提出了一个氧化-包覆-还原的策略,将不适合直接用作负极的商业化锑粉加工成中空核壳型棒状锑碳复合材料.氧化锑受热升华还原的过程中,在碳层上形成了密集分布的锑单原子.利用原位环境电镜,将该材料构建成微观纳米电池,实现了钠化过程的实时观测.发现锑在钠化过程中发生不规则膨胀,碳层可随锑膨胀产生相应变形.碳层内部的原有空间以及碳层向外扩张的能力,均有利于维持碳层对锑在钠化膨胀过程中的包覆效果.在电池测试中,该材料在0.1 C下的可逆比容量超过620 mA h g^(−1),首圈的库伦效率高达84.9%(显著高于文献报道的水平),以及在1 V vs.Na^(+)/Na的电位以下可完成95%的充电容量.该材料优异的电池性能说明中空核壳型结构设计可用于开发实用型锑基钠电负极材料.

La_(0.7)Ca_(0.3)MnO_(3-δ):Ag nanocomposite thin films with large temperature coefficient of resistance(TCR)

In this work, oxygen vacancy-regulated La_(0.7)Ca_(0.3)MnO_(3-δ):Ag (LCMO:A) nanocomposite thin films onLaAlO_(3) (001) substrates were investigated to obtain films with large temperature coefficient of resistance(TCR) values. LCMO:A nanocomposite thin films were synthesized using pulsed laser deposition, andoxygen pressures during film deposition and annealing steps were optimized. As oxygen pressuresincreased, lattice parameter increased from 70 Pa to 100 Pa, Tp increased monotonically from 168 K to282 K, and average Mn^(4+) concentration in the film increased as indicated by X-ray photoemissionspectroscopy data. Record high TCR value of ~37% K^(-1) was achieved in LCMO:A nanocomposite thin filmprepared with optimal oxygen pressures, making this film promising candidate for applications inbolometers.