Glucose can form carbon material under hydrothermal conditions. Thus, carbon-layer-coated nickel sulfide nanoparticles were prepared using a one-step hydrothermal method with nickel sulfide as the primary phase. The effect of the glucose mass on the structure and electrochemical properties of nickel sulfide was studied in detail. The size of nanoparticles decreased after the nickel sulfide surface was coated by using the carbon layer, forming uniform spherical particles of 200-300 nm. The carbon layer thickness on the surface was similar to 3 nm. The nitrogen adsorption-desorption test revealed that the specific surface area of the pristine nickel sulfide was 2.7 m(2) g(-1). Under optimal conditions, the prepared carbon-layer-coated nickel sulfide (NixSy-0.5) depicted a surface area of 15.2 m(2) g(-1). The high specific surface area provided additional electrochemically active sites. The glucose-derived carbon layer could be utilized as a conductive agent to enhance electron transport in the electrode. Electrochemical test results depicted a high capacitance of NixSy-0.5 of 612.5 C g(-1) at 1 A g(-1), higher than that of pristine nickel sulfide (381.7 C g(-1)). The hybrid supercapacitor (HSC) assembled with NixSy-0.5 as the positive electrode and commercial activated carbon (AC) as the negative electrode exhibited a high energy density of 47 Wh kg(-1). The capacitance retention rate is high (99%) after 20 000 cycles. This study demonstrated the simultaneous preparation of nickel sulfide-carbon layer composites and provided a feasible strategy for preparing economical and efficient electrode materials.

In this study, we fabricated LiMn0.6Fe0.4PO4/C (LMFP/C) materials employing the spray drying method. Subsequently, the LMFP/C composites underwent surface modification with Li4Ti5O12 (LTO) using the rheological phase reaction method. LTO demonstrates high electrochemical activity and possesses significantly greater lithium-ion conductivity compared to LMFP. The developed composite coating serves a dual purpose by safeguarding the LMFP material against electrolyte erosion and facilitating the swift transfer of lithium ions and electrons. The results from transmission electron microscopy and energy-dispersive X-ray spectroscopy validated the successful coating of LTO onto the LMFP/C surface after the surface modification treatment. A comparative analysis was conducted between the pristine LMFP/C powder and the LMFP-LTO composite that underwent surface modification. The results reveal that the 2 wt% LTO-coated LMFP/C composite has the best electrochemical performance, manifesting specific capacities of 156 and 132.6 mAh g−1 at 0.2 and 5 C rate, respectively. Furthermore, the material demonstrated excellent cycle retention, with 95.4% capacity retention after 100 cycles at 1 C. Hence, LTO coating can be considered an efficacious strategy for enhancing the electrochemical performance of LMFP.

The extensive combustion of fossil fuels along with uncontrolled release of carbon dioxide (CO2) has led to severe environmental contamination and global greenhouse effects. Carbon neutrality and low-carbon development are urgent demands for the enduring progress of human society. The utilization of electrocatalytic and photocatalytic reduction reaction to convert CO2 into valuable chemicals is viewed as a hopeful approach for addressing environmental issues and energy crises. Metal-organic frameworks (MOFs) are discovered to have extensive applications in the areas of electrocatalysis and photocatalysis because of their high porosity, versatile compositions and structural tunability. With the help of designed MOF structures and specific synthesis methods, it is convenient and targeted to regulate the morphologies and electronic structures of MOF-derived materials with higher stability, further affecting their catalytic performance towards CO2 reduction. In order to enhance catalytic performance to meet application requirements, it is essential to investigate the relationship between the morphologies, electronic structures of MOF-derived materials and their performances. In this review, to reveal the reaction mechanisms and provide theoretical support for catalyst design, the fundamentals of CO2 reduction through electrocatalytic and photocatalytic pathways are discussed. Subsequently, an overview of the developments in MOF-derived materials for electrocatalytic and photocatalytic CO2 reduction is presented, focusing on different optimization strategies such as morphology control and electronic modification. Finally, we outline the difficulties and opportunities for advancing MOF-derived materials in electrocatalytic and photocatalytic CO2 reduction, along with the strategies for developing electrocatalysts and photocatalysts with excellent performance.

Electrochemical activation usually accompanies in situ atom rearrangement forming new catalytic sites with higher activity due to reconstructed atomic clusters or amorphous phases with abundant dangling bonds, vacancies, and defects. By harnessing the pre-catalytic process of reconstruction, a multilevel structure of CuNi alloy nanoparticles encapsulated in N-doped carbon (CuNi nanoalloy@N/C) transforms into a highly active compound of Ni-doped CuO nanocluster supported on (N/O-C) co-doped C. Both the exposure of accessible active sites and the activity of individual active sites are greatly improved after the pre-catalytic reconstruction. Manipulating the Cu/Ni ratios of CuNi nanoalloy@N/C can tailor the electronic property and d-band center of the high-active compound, which greatly optimizes the energetics of oxygen evolution reaction (OER) intermediates. This interplay among Cu, Ni, C, N, and O modifies the interface, triggers the active sites, and regulates the work functions, thereby realizing a synergistic boost in OER.

Conductive metal-organic frameworks (MOFs) are a type of porous material. It consists of metal ions coordinated with highly conjugated organic ligands. The high density of carriers and orbital overlap contribute to the amazing conductivity. Additionally, conductive MOFs inherit the advantages of large specific surface area, structural diversity, and adjustable pore size from MOFs. These excellent properties have attracted many researchers to explore controllable synthesis and electrochemical applications over the past decade. This work provides an overview of the recent advances in the synthesis strategies of conductive MOFs and highlights their applications in electrocatalysis, supercapacitors, sensors, and batteries. Finally, the challenges faced by the synthesis and application of conductive MOFs are discussed, as well as the views on promising solutions for them are presented. This work summarizes the latest strategies for synthesizing conductive metal-organic frameworks (MOFs) and discusses their impact on the structure and conductivity of the conductive MOFs. In the field of electrocatalysts, supercapacitors, batteries, and sensors, the applications and corresponding electrochemical mechanisms of conductive MOFs are discussed in depth based on the structure-performance relationship.image

Cu-based materials are seldom reported as oxygen evolution reaction (OER) electrocatalysts due to their inherent electron orbital configuration, which makes them difficult to adsorb oxygen-intermediates during OER. Reasonably engineering the hierarchical architectures and the electronic structures can improve the performance of Cu-based OER catalysts, such as constructing multilevel morphology, inducing the porous materials, improving the Cu valence, building heterostructures, doping heteroatoms, etc. In this work, copper-1,3,5-benzenetricarboxylate (HKUST-1) octahedra in-situ grow on the Cu nanorod (NR)-supported N-doped carbon microplates, meanwhile an active layer of Cu(OH)2 forms on the surface of the original conductive Cu NRs. The octahedral HKUST-1, serving as a spacer between the microplates, greatly improves the porosity and increases the available active sites, facilitating the mass transport and electron transfer, thus resulting in greatly enhanced OER performance.

The development of clean sustainable energy conversion technologies to deal with energy shortage and environmental pollution has aroused a widespread concern. To improve the rate and selectivity of the pivotal chemical reactions involved in these technologies, high-performance electrocatalysts are crucial. Alloys have sparked research hotspot in electrocatalysis because of their higher catalytic activity, stability, and selectivity than their single-metal counterparts. In this review, the design strategies for alloy electrocatalysts are firstly introduced with a focus on how to achieve optimal performance by composition regulation, size optimization and morphology control. Subsequently, we offer a comprehensive overview of the electrocatalytic applications of binary, ternary, quaternary, and high-entropy alloys to different types of electrochemical energy conversion processes, including the hydrogen evolution, oxygen evolution, oxygen reduction, CO2 reduction, formic acid oxidation, methanol oxidation, and ethanol oxidation reactions. Finally, the challenges and future outlook are presented for the rational design of advanced alloy electrocatalysts.

The tailoring of intrinsic electronic structures and extrinsic hierarchical morphologies is widely recognized as a promising strategy to enhance the oxygen evolution reaction (OER) performance of electrocatalysts. It is generally accepted that the surface of the transition metal-based electrocatalyst exposed to the alkaline electrolyte is highly oxidized and reconstructed, forming an amorphous layer during the electrochemical process. This amorphous active phase is favorable for OER due to its abundant dangling bonds, vacancies and defects, which is tricky to be rationally prepared by conventional methods. Herein, a facile access to crystalline / amorphous NiOx microbelt superstructure of core-shell nanoparticles is presented, which is assembled of crystalline NiO nanoparticles coated with amorphous Ni3+/Ni2+ oxide layer. Electrochemical activation induces the in-situ surface reconstruction of the NiOx microbelt superstructure, resulting in a thicker outer amorphous Ni3+/Ni2+ layer further facilitating OER. Owing to the optimization of the in-situ surface reconstruction, the NiOx microbelt superstructure with crystalline / amorphous dual phases exhibited both high electrocatalytic activity and superior durability for OER, with the original microbelt superstructure retained after 50000 s I-t test.

Lithium-ion capacitor (LICs) is expected to replace the traditional double-layer capacitor and lithium-ion battery as a new energy storage device. However, the slow de/intercalation of Li + in battery-type electrodes (anode) limits the power density of lithium-ion capacitors (LICs). In this work, a high specific surface area porous carbon skeleton (Z-T-PC) is synthesized derived from MOF (Zn-TFBDC). Benefit from the large specific surface area and 3D conductive skeleton, the Z-T-PC shows that the sample has a high specific capacity and stable cycling performance as the LIC anode. The assembled asymmetric LICs exhibit high power density and energy density with Z-T-PC anode. The work provides new thinking for the application of the novel anode material of LICs.

Metal-organic frameworks（MOFs） with porous crystal structures have attracted extensive attention in application of energy storage and conversion, owing to their regularity, porosity, large specific surface area, etc. In this work, Co-MOF-74 microflower has been successfully prepared via a controllable solvent regulation strategy. Through modulating the polarity of the solvent, crystals grow in certain preferred orientation and Co-MOF-74 with various morphologies were obtained. Thereinto, the energy storage performance of Co-MOF-74 microflower was measured in both three-electrode system and asymmetric supercapacitor device（specific capacitance of 164.2 F/g at 0.5 A/g in the three-electrode system and 62.5 F/g at 1 A/g in the asymmetric supercapacitor device）. This can be attributed to the preferred crystal orientation resulting in a regular and uniform microflower, which is of great significance to electronic interfacial exchange and ion transfer during electrochemical reactions.

Currently, under the background of urgent energy crisis, the water splitting, especially oxygen evolution reaction (OER), is of significance in application of clean energy storage and conversion. To further optimize electrocatalytic performance of materials, many researchers purposely design heteroatom functionalization strategy during synthesizing catalysts. Nitrogen (N) functionalization can alter the electronic structures to optimize the coordination environment of the active metal centers in the catalysts and improve the intermediate adsorption/desorption on the interface. Herein, we review the recent progress on synthetic approaches of N-functionalized catalysts for OER, including solution (small molecular complexes, metal-organic frameworks, etc. as precursors), solid-state (ball milling and chemical vapor deposition), interface, and noncovalent chemistry synthesis. Furthermore, the catalytic mechanism of N-coordinated active metal sites and the influence factors of OER performance are discussed, and the current challenges and outlook of OER catalysts with N-optimized coordination are also presented. (C) 2020 Elsevier B.V. All rights reserved.

The urea oxidation reaction has attracted increasing attention. Here, porous rod-like Ni2P/Ni assemblies, which consist of numerous nanoparticle subunits with matching interfaces at the nanoscale have been synthesized via a simple phosphating approach. Density functional theory calculations and density of states indicate that porous rod-like Ni2P/Ni assemblies can significantly enhance the activity of chemical bonds and the conductivity compared with NiO/Ni toward the urea oxidation reaction. The optimal catalyst of Ni2P/Ni can deliver a low overpotential of 50 mV at 10 mA·cm−2 and Tafel slope of 87.6 mV·dec−1 in urea oxidation reaction. Moreover, the constructed electrolytic cell exhibits a current density of 10 mA·cm−2 at a cell voltage of 1.47 V and an outstanding durability in the two-electrode system. This work has provided a new possibility to fabricate metal phosphides-metal assemblies with advanced performance.

Nowadays, Cu-based materials have attracted extensive attention as electrocatalysts, while the inherent reason of the filling of high anti-bonding state of Cu d band (3d(10)4s(1)) makes it difficult to hybridize with O 2p band of oxygen intermediates during the adsorption process of oxygen evolution reaction (OER). To increase the efficiency of Cu-based electrocatalysts, efforts have been made to optimize the electronic structures and to create surface defects and hierarchical nanostructures with more exposed accessible active sites. Herein, we report a facile method for preparing CuO electrocatalysts with hierarchical nanostructures using the Cu-alanine complex as a precursor through room-temperature chemical precipitation and subsequent calcination in air. Investigations of products obtained at different calcination temperatures reveal the relationship between OER activities and the material characteristics such as specific surface areas, crystal growth orientations, and element components. The product obtained at 500 degrees C exhibits the smallest overpotential of 290 mV in 1.0 mol/L KOH for electrocatalyzing OER. Combining with various characterizations of CuO electrocatalysts after OER activities, the possible catalytic mechanism and the influence factors of their OER performance are also discussed. (C) 2021 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.

Metal-organic frameworks (MOFs), an emerging class of porous materials, have shown intriguing and promising properties in a wide range of applications due to their versatile structures, large surface areas, tunable porosity and tailorable chemistry. In recent years one of the most active research fields is to explore energy applications of MOF-based materials. In this review, we present a critical overview on the recent progress of the use of MOF-based materials for gaseous fuel storage, chemical hydrogen storage, solar and electrochemical energy storage and conversion. The challenges and opportunities towards advanced energy technologies with the MOF-based materials are discussed.

This work summarizes the use of graphene/Co3O4 composites in electrochemical energy conversion and storage applications. Graphene is considered the most promising carbon material for accommodating multifarious nanoparticles and achieving excellent electrochemical performance, such as a high electrolyte contact area, electron transport rate and structural stability. This work presents different nanostructures of Co3O4 that consist of nanowires, nanotubes and ordered mesoporous structures, many of which have been poorly synthesized by facile strategies. Graphene can effectively house Co3O4 nanoparticles inside its 3D structure and greatly enhance the electrochemical performance of these nanoparticles. The synergistic effects of graphene and Co3O4 lead to a variety of attractive properties, such as excellent reversible capacity and good cycling stability. In addition, these unique properties are due to the many short diffusion pathways and active sites of nanosized Co3O4 and the elastic buffer space and conductive pathways provided by graphene. This comprehensive review outlines the excellent electrochemical performance of graphene/Co3O4 composites in electrocatalysis, supercapacitors, lithium-ion batteries and other batteries.

Taking advantage of the self‐assembling function of amino acids, cobalt–alanine complexes are synthesized by straightforward process of chemical precipitation. Through a controllable calcination of the cobalt–alanine complexes, N‐doped Co 3 O 4 nanostructures (N‐Co 3 O 4 ) and N‐doped CoO composites with amorphous carbon (N‐CoO/C) are obtained. These N‐doped cobalt oxide materials with novel porous nanostructures and minimal oxygen vacancies show a high and stable activity for the oxygen evolution reaction. Moreover, the influence of calcination temperature, electrolyte concentration, and electrode substrate to the reaction are compared and analyzed. The results of experiments and density functional theory calculations demonstrate that N‐doping promotes the catalytic activity through improving electronic conductivity, increasing OH − adsorption strength, and accelerating reaction kinetics. Using a simple synthetic strategy, N‐Co 3 O 4 reserves the structural advantages of micro/nanostructured complexes, showing exciting potential as a catalyst for the oxygen evolution reaction with good stability.

With the ever increasing demand for clean, sustainable energy, electrochemical supercapacitors with the advantages of high power density, high efficiency and long life expectancy have become one of the major devices for energy storage and power supply, and have found wide application in hybrid power sources, backup power sources, starting power for fuel cells and burst-power generation in electronic devices. Metal phosphates with the advantages of abundance, environmental friendliness and low cost are emerging as a novel class of promising electrode materials for supercapacitors. This review summarizes recent progress with respect to cobalt and nickel phosphate based micro/nanomaterials applied as supercapacitors, covering ammonium/bimetallic phosphates, cobalt phosphates, nickel phosphates and cobalt/nickel phosphates. Much progress has been made using metal phosphate materials as supercapacitors; however, there is still much room for further improvement.

Electrochemical capacitors (supercapacitors, SCs), have been deemed to be one of the most promising powerful electrochemical energy storage devices, owing to that SCs have long cycle lives, high power densities, and fast recharge capabilities. Transition metal oxide is one of the most promising electrode materials in the application of SCs, but the poor active surface areas limit their electrochemical performances. Particularly, hollow structures can enhance their active surface areas and porosity for better transportation. In this review, the development regarding hollow structures of the metal oxide, metal oxide complex, and carbon–metal oxide complex is discussed. Furthermore, performances of these materials applied in SCs are tested in various systems, and their electrochemical performances are introduced and compared. The disadvantages of SCs based on hollow metal oxide materials are also discussed, and the various solutions are provided.

High‐performance electric energy storage material has recently developed due to the attention for sustainable development. As ecofriendly energy storage device, lithium ion batteries and sodium ion batteries deserve more concern today. FePO 4 and NaFePO 4 share similar advantages such as easy preparation, abundant, and inexpensive, so they can be ideal materials for lithium/sodium ion batteries. This review is focused on recent progresses in nanostructured FePO 4 /NaFePO 4 ‐based nanomaterial as cathode materials for lithium/sodium ion batteries. FePO 4 ‐based materials contain crystalline and amorphous pure FePO 4 nanomaterial, FePO 4 /C compounds, and other novel materials with unique morphologies. NaFePO 4 ‐based materials contain olivine NaFePO 4 , Na 4 FeP 2 O 7 , and so on. They own unique properties, including preferable energy density, cycling performance, electrical conductivity, and charge/discharge stability. This review is designed to summarize the synthesis, morphology, and electrochemical property and application of FePO 4 ‐based and NaFePO 4 ‐based nanomaterials. There exist relations among the structure, property, and storage, which is also introduced. Furthermore, this review assesses the challenges and outlooks of FePO 4 /NaFePO 4 ‐based nanomaterial for future development; it also sheds light on appropriate development direction of advanced rechargeable batteries with a focus on FePO 4 /NaFePO 4 ‐based nanomaterial.