Flexible zinc–air batteries (ZAB) are a promising battery candidate for emerging flexible electronic devices, but the catalysis‐based working principle and unique semi‐opened structure pose a severe challenge to their overall performance at cold temperature. Herein, we report the first flexible rechargeable ZAB with excellent low‐temperature adaptability, based on the innovation of an efficient electrocatalyst to offset the electrochemical performance shrinkage caused by decreased temperature and a highly conductive hydrogel with a polarized terminal group to render the anti‐freezing property. The fabricated ZABs show excellent electrochemical performances that outperform those of many aqueous ZABs at room temperature. They also deliver a high capacity of 691 mAh g−1 and an energy density of 798 Wh kg−1 at −20 °C (92.7 % and 87.2 % retention of the room temperature counterparts, respectively), together with excellent flexibility and reverting capability.

Hydrogen production from direct water electrolysis has long been pursued as a key that may revolutionize the hydrogen economy. With the rapid availability of electricity generated using renewable energy resources,...

Metal–nitrogen–carbon (M–N–C) single-atom catalysts (SACs) show high catalytic activity for many important chemical reactions. However, an understanding of their intrinsic catalytic activity remains ambiguous because of the lack of well-defined atomic structure control in current M–N–C SACs. Here, we use covalent organic framework SACs with an identical metal coordination environment as model catalysts to elucidate the intrinsic catalytic activity of various metal centers in M–N–C SACs. A pH-universal activity trend is discovered among six 3d transition metals for hydrogen peroxide (H2O2) synthesis, with Co having the highest catalytic activity. Using density functional calculations to access a total of 18 metal species, we demonstrate that the difference in the binding energy of O2* and HOOH* intermediates (E O2* – E HOOH*) on single metal centers is a reliable thermodynamic descriptor to predict the catalytic activity of the metal centers. The predicted high activity of Ir centers from the descriptor is further validated experimentally. This work suggests a class of structurally defined model catalysts and clear mechanistic principles for metal centers of M–N–C SACs in H2O2 synthesis, which may be further extendable to other reactions.

Na+diffuses and re-dissolves into matrix grains, resulting in carrier concentration modulation and thereby superior high temperature TE performances.

Preparation of carbon nanotube (CNT)/alumina composites by a simple colloidal processing method has been reported in this paper. The surface modification process of carbon nanotubes was characterized by means of zeta potential measurements and TEM microscopy. The addition of only 0.1 wt % carbon nanotubes in the alumina composite increases the fracture toughness from 3.7 to 4.9 MPa·m1/2. Microstructure characterization, performed by SEM, showed that the bridging effect on cracks, the tight bonding between CNTs and alumina matrix, and the pullout of CNTs from matrix are possible mechanisms leading to the improvement of the fracture toughness.

Synthesis of structurally controlled graphene materials is critical for realizing their practical applications. The electrochemical exfoliation of graphite has emerged as a simple method to produce graphene materials. This review examines research progress in the last 5 years, from 2015 to 2019. Graphene material synthesis methods generally have a trade‐off between increasing production yield and achieving better material property control. The synthesis conditions for synthesizing pristine graphene, graphene oxide (GO), and graphene composites are significantly different. Thus, in this review, we first discuss synthesis methods for graphene materials with high C/O ratios from four aspects: graphite electrodes, equipment engineering, electrolytes, and additional reduction methods. Next, we survey synthesis methods for GO and examine how the pretreatment of the graphite electrodes, electrolytes, and operation parameters, such as applied voltages, electrolyte temperatures, and mechanical forces, affect the quality of GO. Further, we summarize electrochemical exfoliation methods used to dope graphene materials, introduce covalent functional groups, incorporate various nanoparticles, and assembly of graphene architectures. For all synthesis methods, we compare the properties of resulting graphene materials such as C/O ratios, lateral size, layer numbers, and quality characterized by Raman spectroscopy. Lastly, we propose our perspectives on further research. We hope this review stimulates more studies to realize the on‐demand production of graphene materials with desired properties using electrochemical exfoliation methods.

Ammonia (NH3) synthesis is an important industrial chemical process. Recently, electrochemically converting the earth-abundant dinitrogen (N2) in the aqueous phase to NH3 at ambient conditions has been proposed as an alternative to the well-established Haber–Bosch process. Catalysts for the electrochemical N2 reduction to NH3 play crucial roles in realizing this NH3 synthesis route. Electrochemical N2 reduction has been studied for decades, and many studies have emerged in the past few years. Herein, we provide a comprehensive review to summarize various catalysts used for achieving electrochemical N2 reduction to NH3, including homogeneous, heterogeneous and biological catalysts, as well as relevant computational studies to understand their reaction mechanisms. We compare the advantages and shortcomings of these catalytic systems. Future research directions for realizing catalysts with low overpotentials, high energy efficiency, good scalability, and stability modularity are also proposed. This review provides an overview of this fast-growing research field and encourages more studies toward the rational design of catalysts for electrochemical N2 reduction to NH3 under ambient conditions.

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