Facile in Situ Preparation of Graphitic-C₃N₄@carbon Paper As an Efficient Metal-Free Cathode for Nonaqueous Li-O₂ Battery

Constructing Bimetallic ZIF-Derived Zn,Co-Containing N-Doped Porous Carbon Nanocube as the Lithiophilic Host to Stabilize Li Metal Anodes in Li-O2 Batteries

Li metal, because of its ultrahigh theoretical capacity, has attracted extensive attention. However, uncontrollable dendritic Li formation and infinite electrode dimensional variation hinder application of Li anodes. Herein, Zn,Co bimetallic zeolitic imidazolate frameworks (ZIFs) were synthesized and further pyrolyzed to obtain Zn,Co-containing N-doped porous carbon nanocube (Zn/Co-N@PCN), which was further applied as lithiophilic host to construct the lithiated Zn/Co-N@PCN (Li-Zn/Co-N@PCN). Zn vapor produced many pores on the carbon framework during calcination process that could store enough Li and thus inhibit the huge electrode volume change. Additionally, there were abundant lithiophilic groups in Zn/Co-N@PCN, such as N- or Co/Zn-based species, which were beneficial to uniform Li deposition. Moreover, the stable and conductive carbon-based matrix could ensure superior and reproducible Li plating/stripping behavior in Zn/Co-N@PCN over cycling. As a result, the Li-Zn/Co-N@PCN anode showed a steady and high columbic efficiency of around 99.0 % for 600 cycles at 0.5 mA cm^-2 . The Li-Zn/Co-N@PCN-based Li-O₂ battery could continuously work beyond 200 cycles, superior to a cell with a Li-Cu anode. These results in this work provide a novel way for construction of the advanced Li-based anodes and the corresponding high-performance Li-O₂ batteries.

Polyaniline/reduced graphene oxide foams as metal-free cathodes for stable lithium-oxygen batteries

Lithium-oxygen batteries (LOBs) are considered as next-generation energy storage devices owing to their high-energy densities, yet they generally suffer from low actual specific capacity and poor cycle performance. To solve these issues, a range of electrocatalysts have been introduced in the cathode to reduce the overpotential during charge/discharge cycles and minimize unwanted side reactions. Due to relative high costs and limited reserves of noble metals and their compounds, it is important to develop low-cost and efficient metal-free electrocatalysts. Here, we report a simple method to prepare three-dimensional porous polyaniline (PANI)/reduced graphene oxide foams (PPGFs) with different PANI contents via a two-step self-assembly process. When these foams are tested as the cathode in LOBs, the device using the PPGF with 50% PANI content exhibits a discharge capacity up to 36 010 mAh g^-1 and an excellent cycling stability (260 cycles at 1000 mAh g^-1 and 500 cycles at 500 mAh g^-1), provid ing new insights into the design of next-generation metal-free cathodes for LOBs.

Recent Progress of In Situ Transmission Electron Microscopy for Energy Materials

In situ transmission electron microscopy (TEM) is one of the most powerful approaches for revealing physical and chemical process dynamics at atomic resolutions. The most recent developments for in situ TEM techniques are summarized; in particular, how they enable visualization of various events, measure properties, and solve problems in the field of energy by revealing detailed mechanisms at the nanoscale. Related applications include rechargeable batteries such as Li-ion, Na-ion, Li-O₂ , Na-O₂ , Li-S, etc., fuel cells, thermoelectrics, photovoltaics, and photocatalysis. To promote various applications, the methods of introducing the in situ stimuli of heating, cooling, electrical biasing, light illumination, and liquid and gas environments are discussed. The progress of recent in situ TEM in energy applications should inspire future research on new energy materials in diverse energy-related areas.

One step synthesis of efficient photocatalysts by TCAP doped g-C3N4 for enhanced visible-light photocatalytic activity

CN/TCAP with enhanced visible light absorption, large surface area and defect structure allow efficient separation of charge carriers.

Single-atom Pt supported on holey ultrathin g-C3N4 nanosheets as efficient catalyst for Li-O2 batteries

As for electrocatalysis, single-atom metal catalysts have been proved to lower the cost and utilize precious metals more efficiently. Herein, single-atom Pt catalyst supported on holey ultrathin g-C₃N₄ nanosheets (Pt-CNHS) was synthesized via a facile liquid-phase reaction of g-C₃N₄ and H₂PtCl₆. The single-atom Pt can achieve high dispersibility and stability, which can promote the utilization efficiency as well as enhance the electrochemical activity. When employed as Li-O₂ batteries' cathode catalyst, Pt-CNHS exhibits excellent electrocatalytic activity. Li-O₂ batteries utilizing Pt-CNHS show much higher discharge specific capacities than those with pure CNHS. Li-O₂ batteries with Pt-CNHS cathode can be cycled stably for 100 times under the discharge capacity of 600 mAh g^-1. Based on experimental results and density functional theory calculations, the superior electrocatalytic activity of Pt-CNHS can be ascribed to the large surface area, the enhanced electrical conductivity and the efficient interfacial mass transfer through Pt atoms and porous structure of CNHS.

Electrolytes for Rechargeable Lithium-Air Batteries

Lithium-air batteries are promising devices for electrochemical energy storage because of their ultrahigh energy density. However, it is still challenging to achieve practical Li-air batteries because of their severe capacity fading and poor rate capability. Electrolytes are the prime suspects for cell failure. In this Review, we focus on the opportunities and challenges of electrolytes for rechargeable Li-air batteries. A detailed summary of the reaction mechanisms, internal compositions, instability factors, selection criteria, and design ideas of the considered electrolytes is provided to obtain appropriate strategies to meet the battery requirements. In particular, ionic liquid (IL) electrolytes and solid-state electrolytes show exciting opportunities to control both the high energy density and safety.

Freestanding Hierarchical Carbon Nitride/Carbon-Paper Electrode as a Photoelectrocatalyst for Water Splitting and Dye Degradation

Freestanding electrodes composed of 2D materials are highly attractive for many applications such as batteries, membranes, actuators, optical devices, and other energy-related devices owing to their low price, unique structure, high specific surface area, and excellent mechanical and electrical properties. Here, we report the facile large-scale fabrication of freestanding hierarchical carbon nitride/carbon electrodes (CN/C) by the in situ crystallization of CN precursors on conductive carbon paper, followed by thermal annealing. The resulting CN exhibits a vertically aligned morphology with a homogeneous layer distribution, improved crystallinity, and excellent contact with the carbon paper. The freestanding electrodes exhibit high electrical conductivity and good photoelectrochemical activity as anodes in water splitting photoelectrochemical cells. Furthermore, we show here as a proof-of-concept that the freestanding CN/C electrodes can be used as photoelectrocatalysts for the oxidative degradation of organic compounds in water, with enhanced activity compared to photocatalytic and electrocatalytic degradation, while the extracted electrons can be used for the simultaneous production of hydrogen at the cathode.

Enhancement of Rhodamine B Degradation by Ag Nanoclusters-Loaded g-C₃N₄ Nanosheets

In this paper, silver (Ag) nanoclusters-loaded graphitic carbon nitride (g-C₃N₄) nanosheets are synthesized and their physical properties as well as photocatalytic activities are systematically investigated by different techniques. The existence of Ag atoms in the form of nanoclusters (NCs) rather than well-crystallized nanoparticles are evidenced by X-ray diffraction patterns, SEM images, and XPS spectra. The deposition of Ag nanoclusters on the surface of g-C₃N₄ nanosheets affect the crystal structure and slightly reduce the band gap energy of g-C₃N₄. The sharp decrease of photoluminescence intensity indicates that g-C₃N₄/Ag heterojunctions successfully prevent the recombination of photo-generated electrons and holes. The photocatalytic activities of as-synthesized photocatalysts are demonstrated through the degradation of rhodamine B (RhB) solutions under Xenon lamp irradiation. It is demonstrated that the photocatalytic activity depends strongly on the molar concentration of Ag⁺ in the starting solution. The g-C₃N₄/Ag heterojunctions prepared from 0.01 M of Ag⁺ starting solution exhibit the highest photocatalytic efficiency and allow 100% degradation of RhB after being exposed for 60 min under a Xenon lamp irradiation, which is four times faster than that of pure g-C₃N₄ nanosheets.

Enhanced cyclability of Li-O2 batteries with cathodes of Ir and MnO2 supported on well-defined TiN arrays

The cycling stability of Li-O₂ batteries has been impeded by the lack of high-efficiency, and durable oxygen cathodes for the oxygen-reduction reaction (ORR) and the oxygen-evolution reaction (OER). Herein we report a novel TiN nanorod array-based cathode, which was firstly prepared by growing a TiN nanorod array on carbon paper (CP), and then followed by depositing MnO₂ ultrathin sheets or Ir nanoparticles on the TiN nanorods to form well-ordered, three-dimensional (3D), and free-standing structured cathodes: TiN@MnO₂/CP and TiN@Ir/CP. Both cathodes exhibited good specific capacity and excellent cycling stability. Their specific discharge capacities were up to 2637 and 2530 mA h g^-1, respectively. After 200 cycles for 2000 h at a current density of 100 mA g^-1, no obvious decays were observed for TiN@MnO₂/CP and TiN@Ir/CP cathodes, while significant decreases were observed after the 80^th and 30^th cycles for the Pt/C and TiN/CP cathodes, respectively. Such high performance can be ascribed to the 3D array structure with enough microspace and high surface area, which facilitated the high dispersion of active components and prevented the formation of large/irreversible Li₂O₂.

Recent developments of aprotic lithium-oxygen batteries: functional materials determine the electrochemical performance

Lithium oxygen battery has the highest theoretical capacity among the rechargeable batteries and it can reform energy storage technology if it comes to commercialization. However, many critical challenges, mainly embody as low charge/discharge round-trip efficiency and poor cycling stability, impede the development of Li-O₂ batteries. The electrolyte decomposition, lithium metal anode corrosion and sluggish oxygen reaction kinetics at cathode are all responsible for poor electrochemical performances. Particularly, the catalytic cathode of Li-O₂ batteries, playing a crucial role to reduce the oxygen during discharging and to decompose discharge products during charging, is regarded as a breakthrough point that has been comprehensive investigated. In this review, the progress and issues of electrolyte, anode and cathode, especially the catalysts used at cathode, are systematically summarized and discussed. Then the perspectives toward the developments of a long life Li-O₂ battery are also presented at last.

NiMn2O4 as an efficient cathode catalyst for rechargeable lithium–air batteries

Intermediate spinel structured NiMn₂O₄-FT performs better than normal spinel oxide NiMn₂O₄-PH as a cathode bi-functional catalyst for Li–air batteries.

In situ growth of NiO nanoparticles on carbon paper as a cathode for rechargeable Li–O2 batteries

In situ growth of NiO nanoparticles on carbon paper as a cathode for rechargeable Li–O₂ batteries that shows excellent electrocatalytic performance.

Self-Assembled 3D Foam-Like NiCo2O4 as Efficient Catalyst for Lithium Oxygen Batteries

A self-assembled 3D foam-like NiCo2O4 catalyst has been synthesized via a simple and environmental friendly approach, wherein starch acts as the template to form the unique 3D architecture. Interestingly, when employed as a cathode for lithium oxygen batteries, it demonstrates superior bifunctional electrocatalytic activities toward both the oxygen reduction reaction and the oxygen evolution reaction, with a relatively high round-trip efficiency of 70% and high discharge capacity of 10 137 mAh g(-1) at a current density of 200 mA g(-1), which is much higher than those in previously reported results. Meanwhile, rotating disk electrode measurements in both aqueous and nonaqueous electrolyte are also employed to confirm the electrocatalytic activity for the first time. This excellent performance is attributed to the synergistic benefits of the unique 3D foam-like structure and the intrinsically high catalytic activity of NiCo2O4 .

Preparation of a graphitic N-doped multi-walled carbon nanotube composite for lithium–sulfur batteries with long-life and high specific capacity

One of the challenges for lithium–sulfur batteries is a rapid capacity fading owing to the insulating of sulfur and Li₂S₂/Li₂S compounds, the dissolving and consequent shuttling of polysulfide.