N-Doped Carbon Confined NiCo Alloy Hollow Spheres as an Efficient and Durable Oxygen Electrocatalyst for Zinc-Air Batteries.

Exploring cost-efficient/durability bifunctional electrocatalysts are of upmost importance for the practical application of metal-air batteries. However, preparing bifunctional electrocatalysts with the above three advantages remains conceptually challenging. This work reports the preparation of N-doped carbon confined NiCo alloy hollow spheres (NiCo@N-C HS) as bifunctional oxygen electrocatalyst for Zn-air battery with a higher energy density (788.7 mWh gZn -1 ) and outstanding cycling stability (over 200 h), which are more durable than the commercialized Pt/C+RuO2 -based device. Electrochemical results and theoretical calculation demonstrate that the synergy in the NiCo@N-C accelerates the electronic transmission for improving activation of O2 * and OH* intermediates and optimizing reacted free energy pathways, while the hollow structures exposure more active sites for improving the reaction kinetics and enhancing the activity of ORR/OER reaction. This work provides crucial understanding for constructing low-cost transition metal-based catalyst to overcome the efficiency and durability barriers of metal-air batteries for widespread applications.

Electrocatalytic Overall Water Splitting Induced by Surface Reconstruction of an Iron-Modified Ni2P/Ni5P4 Heterojunction Array Encapsulated into a N-Doped Carbon Layer.

Reasonable development of high-efficiency and robust electrocatalysts for efficient electrocatalytic water splitting at high current density is hopeful for renewable energy, but the real challenge is substituting the precious metal catalysts. Herein, ultrathin Fe-modified Ni2P/Ni5P4 nanosheet arrays hybridized with N-doped carbon grown on Ni foam (Fe-Ni2P/Ni5P4@N-C) were synthesized via a solvothermal-pyrolysis strategy. Theoretical calculations and in situ Raman characterizations confirm that the Fe sites can facilitate the surface reconstruction of highly active NiOOH species and significantly lower the energy barrier for the formation of the *OOH intermediate owing to the electron coupling effect between Fe and the Ni2P/Ni5P4 heterostructure. On account of the structural advantages and compositional synergy, the optimized Fe-Ni2P/Ni5P4@N-C exhibits superior hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities with an overpotential of 105 and 280 mV to reach 10 and 50 mA cm-2, respectively, and can work stably for 60 h at 100 mA cm-2. Impressively, the electrolyzer with Fe-Ni2P/Ni5P4@N-C only needs 1.56 V to achieve 10 mA cm-2 current density for water splitting. This protocol not only provides inspiration for designing transitional metal electrocatalysts for water splitting but also puts forward a pathway for practical application.

Immobilization of AgCl/Pd Heterojunctions on Nitrogen-Doped Carbon Nanotubes: Interfacial Design-Induced Electronic Regulation Enhances Photocatalytic Activity.

Rationally designing interface structure to modulate the electronic structure of a photocatalyst is an efficient strategy to facilitate the separation and migration of photogenerated charge carriers and improve photocatalytic activity. In this work, a AgCl/Pd heterostructure encapsulated by N-doped carbon nanotubes (AgCl/Pd@N-C) with a fan-like morphology assembled hollow tubes was synthesized by pyrolysis of a AgCl/Pd@Bim precursor. The unique interface structure not only increases the number of photogenerated charge carriers, but also provides an effective channel for the separation of electrons and holes, which have been proved by density functional theory (DFT) calculations. As expected, the obtained AgCl/Pd-3@N-C exhibited greatly enhanced conversion efficiency and recyclability toward the photocatalytic oxidative coupling of amine under blue-light irradiation.

Regulating the Electronic Structure and Active Sites in Ni Nanoparticles by Coating N-Doped C Layer and Porous Structure for an Efficient Overall Water Splitting.

Developing efficient and robust bifunctional electrocatalysts are in high demand for the production of hydrogen by water splitting. Engineering an electrocatalyst with a regulated electronic structure and abundant active sites is an effective way to enhance the electrocatalytic activity. Herein, N-doped C-encapsulated Ni nanoparticles (Ni@N-C) are synthesized through a traditional hydrothermal reaction, followed by pyrolyzing under an Ar/H2 atmosphere. The electrochemical measurements and density functional theory (DFT) calculations reveal that the electron transfer between the Ni core and the N-C shell induces the electron density redistribution on Ni@N-C, which directly promotes the adsorption and desorption of H* on the N-doped carbon (N-C) layer and thus dramatically enhances hydrogen production. Taking advantage of the porous spherical structure and the synergistic effects between Ni and N-doped carbon (N-C) layer, we obtain a Ni@N-C electrocatalyst that exhibits remarkable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity with low overpotentials of 117 and 325 mV, respectively. Impressively, the assembled cell using Ni@N-C as both anode and cathode exhibits excellent activity as well as stable cyclability for over 12 h.

A Self-Repairing Cathode Material for Lithium-Selenium Batteries: Se-C Chemically Bonded Selenium-Graphene Composite.

Lithium-selenium batteries, employing selenium as a cathode material, exhibit some notable advantages, such as high discharge rates and good cycling performance, due to their high electrical conductivity, high output voltages, and high volumetric capacity density. However, an important problem, termed the "shuttle effect", can lead to capacity decay in Li-Se cells (and in Li-S cells), which arises from aggregation and the loss of Se or S from the cathode into the electrolyte. In this work, in order to solve this problem, a new self-repairing system has been devised, in which some Se atoms are chemically bonded to the carbon atoms of graphene and act as reclaiming points for dissociated Se atoms through the establishment of -Se-Se-Se- chains. Se-decorated graphene (Se-GE) was first constructed through a facile high-energy ball-milling process. Its formation was confirmed by XRD, SEM, HRTEM, XPS, and Raman analyses. As we anticipated, in examining cell properties, the as-prepared Se-GE composite underwent an initial capacity decay in the first 20 cycles (from 1050 mAh g-1 to 750 mAh g-1 , ca. 29 % loss), but the capacity then reverted to 970 mAh g-1 (ca. 92 % of the initial value). Other measurements were also consistent with the recapture of dissociated Se atoms.

Spatial separation of electrons and holes for enhancing the gas-sensing property of a semiconductor: ZnO/ZnSnO3 nanorod arrays prepared by a hetero-epitaxial growth.

The construction of semiconductor composites is known as a powerful method used to realize the spatial separation of electrons and the holes in them, which can result in more electrons or holes and increase the dispersion of oxygen ions ([Formula: see text] and O - ) (one of the most critical factors for their gas-sensing properties) on the surface of the semiconductor gas sensor. In this work, using 1D ZnO/ZnSnO3 nanoarrays as an example, which are prepared through a hetero-epitaxial growing process to construct a chemically bonded interface, the above strategy to attain a better semiconductor gas-sensing property has been realized. Compared with single ZnSnO3 nanotubes and no-matching ZnO/ZnSnO3 nanoarrays gas sensors, it has been proven by x-ray photoelectron spectroscopy and photoluminescence spectrum examination that the as-obtained ZnO/ZnSnO3 sensor showed a greatly increased quantity of active surface electrons with exceptional responses to trace target gases and much lower optimum working temperatures (less than about 170 °C). For example, the as-obtained ZnO/ZnSnO3 sensor exhibited an obvious response and short response/recovery time (less than 10 s) towards trace H2S gas (a detection limit down to 700 ppb). The high responses and dynamic repeatability observed in these sensors reveal that the strategy based on the as-presented electron and hole separation is reliable for improving the gas-sensing properties of semiconductors.

Self-supported Ni2P/NiMoP2 bimetallic phosphide with strong electronic interaction for efficient overall water splitting.

Electronic regulation via interface engineering is recognized as an attractive strategy for boosting electrocatalytic activity. In this work, a self-supported heterostructure electrocatalyst is explored by a feasible hydrothermal-pyrolysis strategy, in which Ni2P nanoparticles are anchored on NiMoP2 nanosheet arrays grown on carbon cloth (Ni2P/NiMoP2/CC). Benefitting from the nanosheet array architecture and the synergy effect between the Ni2P and NiMoP2, the as-prepared Ni2P/NiMoP2/CC manifests highly efficient activity and stability toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Density functional theory calculations further indicates that the heterointerface in Ni2P/NiMoP2/CC enable optimized interface electron structure and reduce the activation barriers for intermediates, improving the intrinsic electrocatalytic activity. Remarkably, the Ni2P/NiMoP2/CC||Ni2P/NiMoP2/CC electrolyzer affords 10 mA cm-2 at a low voltage of 1.59 V, outperforming its monometallic phosphides counterparts and most of transition metal-based bifunctional electrocatalysts. The electrolyser was powered by a solar cell to produce H2 and O2 simultaneously, indicating its potential application in solar-to-hydrogen conversion.

Chemical Ni-C Bonding in Ni-Carbon Nanotube Composite by a Microwave Welding Method and Its Induced High-Frequency Radar Frequency Electromagnetic Wave Absorption.

In this work, a microwave welding method has been used for the construction of chemical Ni-C bonding at the interface between carbon nanotubes (CNTs) and metal Ni to provide a different surface electron distribution, which determined the electromagnetic (EM) wave absorption properties based on a surface plasmon resonance mechanism. Through a serial of detailed examinations, such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectrum, the as-expected chemical Ni-C bonding between CNTs and metal Ni has been confirmed. And the Brunauer-Emmett-Teller and surface zeta potential measurements uncovered the great evolution of structure and electronic density compared with CNTs, metal Ni, and Ni-CNT composite without Ni-C bonding. Correspondingly, except the EM absorption due to CNTs and metal Ni in the composite, another wide and strong EM absorption band ranging from 10 to 18 GHz was found, which was induced by the Ni-C bonded interface. With a thinner thickness and more exposed Ni-C interfaces, the Ni-CNT composite displayed less reflection loss.