Doping-engineered bifunctional oxygen electrocatalyst with Se/Fe-doped Co3O4/N-doped carbon nanosheets as highly efficient rechargeable zinc-air batteries.

Highly efficient oxygen reduction and oxygen evolution reactions have the critical role in the practical application of zinc-air batteries. Herein, doping engineering strategy has been adopted by construction of Se/Fe-doped in Co3O4/N-doped carbon nanosheets (denoted as Se/Fe-Co3O4/N-CNs) catalyst for boosting oxygen electrocatalytic activity. The achieved Se/Fe-Co3O4/N-CNs catalyst presents high-performances electrocatalytic characteristics, which exhibits a small overpotential gap (0.79 V), excellent oxygen evolution reaction activity with a small overpotential of 361 mV and a low Tafel slope of 57.3 mV dec-1 at 10 mA cm-2 as well as excellent oxygen reduction reaction activity with a large half-wave potential of 0.8 V, also surpassing the majority of reported Co3O4-based electrocatalysts. The outstanding catalytic performances are benefiting from the contributions between Se/Fe doping engineering and N-doped carbon nanosheets optimizing the electronic structure of Co species, endowing more active sites, enhancing the intrinsic catalytic activity and accelerating charge transfer rate for oxygen electrocatalytic process. Particularly, the as-fabricated zinc-air batteries with Se/Fe-Co3O4/N-CNs as air cathode presents a high open circuit potential of 1.41 V, a prominent highly efficient peak power density of 141.3 mW cm-2, a high specific capacity of 765.6 mAh g-1 and energy density 861.3 Wh kg-1 at current density of 10 mA cm-2 as well as an excellent cycling stability, which are exceeding the commercial Pt/C-RuO2 based zinc-air batteries. This work lays a foundation for design and development of high-performance bifunctional cobalt-based electrocatalysts for rechargeable metal-air batteries application.

Effect of Gd-Doping on Structural, Optical, and Magnetic Properties of NiFe2O4 As-prepared Thin Films via Facile Sol-Gel Approach.

In the present research work, gadolinium-doped nickel ferrite (NiFe2-x Gd x O4, x = 0-0.1) thin films have been synthesized by a facile sol-gel approach. The structural, optical, and magnetic performances of Gd-doping on nickel ferrite films have been investigated. The X-ray diffraction pattern indicated a cubic spinel ferrite structure and that the lattice parameter increased, while the crystalline size decreased with increasing the Gd concentration. Scanning electron microscopy analysis indicated that Gd-doped thin films were dense and smooth. The optical band gap value of the as-prepared thin films increased with increasing the Gd concentration. It showed that Gd-doping endowed nickel ferrite thin films with much better saturation magnetization (278.53 emu/cc) and remnant magnetization (67.83 emu/cc) at an appropriate 0.05 Gd-doping concentration. In addition, our results also revealed that the saturation magnetization remarkably increased, then sharply decreased with increasing of Gd doping content, which is attributed to effects of Gd-doping, exchange interaction, and redistribution of cations. Moreover, X-ray photoelectron spectroscopy analysis exhibited the effect of Gd-doping substitution on exchange interaction and redistribution of cations at the octahedral site and tetrahedral site.