Search

The development of highly active and stable iron–nitrogen (Fe–Nx) based oxygen reduction reaction (ORR) catalysts with pH versatility is one of the future directions of electrochemical energy. However, the task of designing and controlling the three-dimensional local structure of Fe species to obtain high ORR activity and stability remains a challenge. In this study, we prepared hierarchical porous FeN–hcC (iron–nitrogen–highly curved carbon) catalysts derived from ZIF-L by a soft template method. The highly curved carbon surface possibly results in a compressive strain effect on the supported Fe–Nx active site, which can not only enhance the high exposure of the active site to improve the electrocatalytic activity, but also facilitate the stability of the Fe–Nx site during the ORR catalytic process. FeN–hcC-1 exhibited a high half-wave potential of 0.89, 0.77 and 0.82 V vs. RHE in alkaline, acidic, and neutral media, respectively. In addition, after cyclic durability tests in different electrolyte environments, good stability is still maintained, which is significantly better than the planar Fe–Nx site and Pt/C catalyst. This work provides a new synthetic strategy for the construction of highly curved surfaces of carbon materials, while inspiring a method to improve the ORR performance of ZIF-derived materials. [ABSTRACT FROM AUTHOR]

0.7CaTi1-x(Mg1/3Nb2/3)xO3–0.3SmAlO3 (0 ≤ x ≤ 0.04) ceramics were prepared by solid-state reaction method. The effects of (Mg1/3Nb2/3)4+ substitution on crystal structure, microstructure, and microwave dielectric properties of the ceramics were investigated. The orthorhombic perovskite structure remains unchanged, but the dielectric properties are affected significantly by replacing Ti4+ with (Mg1/3Nb2/3)4+. The dielectric constant (εr) exhibits a slight decrease from 44.9 to 43.9, and the temperature coefficient of resonance frequency (τf) exhibits a transition from + 4.1 to ‒1.4 ppm/°C with the increase of x. An appropriate amount of (Mg1/3Nb2/3)4+ substitution can promote sintering and, thus, reduce dielectric loss. The ceramic with x = 0.02 sintered at 1390 °C shows excellent microwave dielectric properties: εr = 44.1, Q × f = 45 600 GHz, and τf = + 0.8 ppm/°C. [ABSTRACT FROM AUTHOR]

Developing highly effective and stable non‐precious bifunctional oxygen electrocatalysts is crucial and challenging. Herein, we report nano‐mediated straight bamboo‐shaped nitrogen‐doped carbon nanotubes modified with encapsulated NiCo2S4‐based nanoparticles (E‐NiCo2S4/SBS‐NCNTs) by electrodeposition and procedural calcination strategy, in which nitrogen‐doped carbon nanotubes with straight bamboo shape (SBS‐NCNTs) show more average diameter and encapsulated NiCo2S4‐based nanoparticles (E‐NiCo2S4) are coated by carbon, and what makes us even more excited is that they are evenly dispersed on SBS‐NCNTs surface, not just at the tip or inside. When applied for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), E‐NiCo2S4/SBS‐NCNTs show excellent catalytic activity, and onset potential (Eonset) in OER and ORR is only 1.52 V and 0.95 V (vs. RHE) in 0.1 M KOH, respectively. More importantly, the hybrids exhibit good methanol tolerance, with almost unchanged for ORR performance after adding 0.5 M methanol, and it has highly stability, the current density dropped by 22% after 7 h of reaction. The interaction of NiCo2S4 with the external carbon layer can greatly enhance the electrocatalytic activity toward the OER and it has a complete 4e– reaction process toward the ORR. The excellent electrocatalytic activity is mainly due to synergistic enhancement effect, in which SBS‐NCNTs with highly catalytic activity provide good conductivity, expose more active sites and promotes fast mass transfer; Carbon‐coated NiCo2S4‐based nanoparticles can improve the local work function of SBS‐NCNT through synergistic electronic interaction, promoting O2 adsorption, ensure rapid electron transport, and enable SBS‐NCNT to improve its electrocatalytic activity. Because of the weakness of Ostwald effect and synergistic enhancement, the stability and catalytic activity of NiCo2S4‐based nanoparticles can be greatly improved. All these advantages can synergistically improve the electrocatalytic efficiency and make it become one of the most promising bifunctional oxygen electrocatalysts. [ABSTRACT FROM AUTHOR]

In this study, the effect of Ti and Zr elements with equal mass ratio on microstructure and corrosion resistance of Zn‐11Al‐3Mg alloy was investigated. The microstructure was significantly refined and Al‐rich phase transformed from dendrite to petal‐like with the addition of Zr and Ti elements, due to the Al3(TixZr1 − x) phase as the nucleation substrate. The corrosion resistance of Zn‐11Al‐3Mg‐x(Ti,Zr) alloy was effectively improved. Moreover, the corrosion products of Zn‐Al‐Mg alloy were not changed by the addition of Ti and Zr, which are mainly composed of Zn5(OH)8Cl2·H2O and Zn6Al2(OH)16CO3·4H2O. [ABSTRACT FROM AUTHOR]