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Non‐noble metal‐based metal–organic framework (MOF)‐derived electrocatalysts have recently attracted great interest in the oxygen evolution reaction (OER). Here we report a facile synthesis of nickel‐based bimetallic electrocatalysts derived from 2D nanosheet‐assembled nanoflower‐like MOFs. The optimized morphologies and large Brunauer–Emmett–Teller (BET) surface area endow FeNi@CNF with efficient OER performance, where the aligned nanosheets can expose abundant active sites and benefit electron transfer. The complex nanoflower morphologies together with the synergistic effects between two metals attributed to the OER activity of the Ni‐based bimetallic catalysts. The optimized FeNi@CNF afforded an overpotential of 356 mV at a current density of 10 mA cm−2 with a Tafel slope of 62.6 mV dec−1, and also exhibited superior durability with only slightly degradation after 24 hours of continuous operation. The results may inspire the use of complex nanosheet‐assembled nanostructures to explore highly active catalysts for various applications. [ABSTRACT FROM AUTHOR]

Hydrogen production is one of the most effective methods for combating the global energy crisis. However, improving the electrochemical performance of oxygen‐evolution catalysts is a significant challenge. In this paper, exceptionally active electrocatalysts for oxygen‐evolution reactions (OERs) were successfully developed and characterized by using SEM, TEM, XRD, BET, and X‐ray photoelectron spectroscopy. The nitrogen‐doped hollow‐carbon‐encapsulated bimetallic nanoparticles (MM′‐NHCNPs) were prepared by using folic acid coordination polymerization. The hollow structure and the synergistic effect of bimetallic doping exhibited remarkable catalytic performance and outstanding stability for the OER in a 1.0 m KOH alkaline electrolyte. For the OER, the overpotential of the best catalyst was only 350 mV at a current density of 10 mA cm−2 with a small Tafel slope of 58 mV dec−1. High durability was also demonstrated by the MM′‐NHCNPs. Such an MM′‐NHCNP catalyst with excellent electrochemical properties provides a promising material for OERs. It′s a wrap! Bimetallic nitrogen‐doped hollow‐carbon‐wrapped nanoparticles (MM′‐NHCNPs) were prepared by using folic acid coordination polymerization. Such an MM′‐NHCNP catalyst with excellent electrochemical properties provides a promising material for oxygen‐evolution reactions (see figure). [ABSTRACT FROM AUTHOR]

Abstract: Metal–organic frameworks (MOFs) and MOF‐derived nanomaterials have recently attracted great interest as highly efficient, non‐noble‐metal catalysts. In particular, two‐dimensional MOF nanosheet materials possess the advantages of both 2D layered nanomaterials and MOFs and are considered to be promising nanomaterials. Herein, we report a facile and scalable in situ hydrothermal synthesis of Co–hypoxanthine (HPA) MOF nanosheets, which were then directly carbonized to prepare uniform Co@N‐Carbon nanosheets for efficient bifunctional electrocatalytic hydrogen‐evolution reactions (HERs) and oxygen‐evolution reactions (OERs). The Co embedded in N‐doped carbon shows excellent and stable catalytic performance for bifunctional electrocatalytic OERs and HERs. For OERs, the overpotential of Co@N‐Carbon at 10 mA cm−2 was 400 mV (vs. reversible hydrogen electrode, RHE). The current density of Co@N‐Carbon reached 100 mA cm−2 at an overpotential of 560 mV, which showed much better performance than RuO2; the largest current density of RuO2 that could be reached was only 44 mA cm−2. The Tafel slope of Co@N‐Carbon was 61 mV dec−1, which is comparable to that of commercial RuO2 (58 mV dec−1). The excellent electrocatalytic properties can be attributed to the nanosheet structure and well‐dispersed carbon‐encapsulated Co, CoN nanoparticles, and N‐dopant sites, which provided high conductivity and a large number of accessible active sites. The results highlight the great potential of utilizing MOF nanosheet materials as promising templates for the preparation of 2D Co@N‐Carbon materials for electrocatalysis and will pave the way to the development of more efficient 2D nanomaterials for various catalytic applications. [ABSTRACT FROM AUTHOR]

In this work, internal damage condition of concrete subjected to freeze-thaw (F-T) cycles was investigated by means of electrochemical impedance spectroscopy (EIS) technique. The equivalent circuit model was adopted to explain the EIS results according to the establishment of physical model simulating the internal micro structure of concrete. As a result, continuous decrease of resistance of continuous path was found out in the process of F-T cycle because of the expansion and propagation of internal cracking of concrete. This was also demonstrated by microscopic analysis obtained from environmental scanning electron microscope (ESEM) observation. Besides, damage degree calculated based on the decrease of resistance was introduced to evaluate the internal degradation condition of concrete suffering from F-T cycles. [ABSTRACT FROM AUTHOR]