Xiuchen Zhao

Synthesis of hierarchical sword-like cobalt particles and their microwave absorption properties

In this paper, we reported synthesis of the cobalt particles with a hierarchical sword-like structure through a liquid reduction method. We have investigated the electromagnetic properties of the cobalt particles in the microwave frequency range of 2–18 GHz. The cobalt particles presented multiple dielectric and magnetic resonance peaks, which are related to their unique structure. We have predicted the microwave absorption properties of the cobalt particles according to the transmit line theory. The maximum reflection loss (RL) of the cobalt particles reaches −60.13 dB, and the effective absorption bandwidth (RL ≤ −10 dB) is 5.42 GHz corresponding to a thickness of 1.4 mm, revealing better microwave absorption than previously reported materials. The superior microwave absorption properties indicate that the as-prepared cobalt particles have potential application as candidates for microwave absorption.

Vertically porous nickel thin film supported Mn3O4 for enhanced energy storage performance.

Three-dimensionally porous metal materials are often used as the current collectors and support for the active materials of supercapacitors. However, the applications of vertically porous metal materials in supercapacitors are rarely reported, and the effect of vertically porous metal materials on the energy storage performance of supported metal oxides is not explored. To this end, the Mn3O4-vertically porous nickel (VPN) electrodes are fabricated via a template-free method. The Mn3O4-VPN electrode shows much higher volumetric specific capacitances than that of flat nickel film supported Mn3O4 with the same loading under the same measurement conditions. The volumetric specific capacitance of the vertically porous nickel supported Mn3O4 electrode can reach 533Fcm(-3) at the scan rate of 2mVs(-1). The fabricated flexible all-solid microsupercapacitor based on the interdigital Mn3O4-VPN electrode has a volumetric specific capacitance of 110Fcm(-3) at the current density of 20μAcm(-2). The capacitance retention rate of this microsupercapacitor reaches 95% after 5000 cycles under the current density of 20μAcm(-2). The vertical pores in the nickel electrode not only fit the micro/nanofabrication process of the Mn3O4-VPN electrode, but also play an important role in enhancing the capacitive performances of supported Mn3O4 particles.

Vertically aligned carbon nanotube@MnO2 nanosheet arrays grown on carbon cloth for high performance flexible electrodes of supercapacitors

Vertical alligned carbon nanotube@MnO2 (VACNT@MnO2) arrays grown on carbon cloth were prepared as high performance flexible electrodes for supercapacitors. VACNTs first grew on carbon cloth with the method of plasma enhanced chemical vapor deposition (PECVD) to obtain firm connection between CNTs and carbon cloth, and δ-MnO2 nanosheets were deposited on the surface of VACNTs to form a VACNT@MnO2 core–shell structure. The VACNT@MnO2 on carbon cloth (VACNT@MnO2/CC) exhibited a remarkable specific capacitance (235 F g−1 at the scan rate of 2 mV s−1 based on the total mass of VACNTs and MnO2), an excellent rate performance with a specific capacitance of 188 F g−1 at 100 mV s−1 and a stable cycling ability (nearly 100% retention after 5000 charge/discharge cycles at 5 A g−1). The fabricated symmetric supercapacitor from the self-supported VACNT@MnO2/CC without any additive reagents had the same electrochemical energy storage performance when this supercapacitor was bent 180°, revealing the excellent flexibility of our prepared flexible electrodes. The excellent performances in electrochemical properties and flexibility mainly originated from a strong mechanical coupling between CNTs and CC as well as sufficient contact between the electrolyte and the surface of MnO2 nanosheets in such an arrayed structure.