Electrocatalytic synthesis of C–N coupling compounds from CO2 and nitrogenous species

The authors gratefully acknowledge financial support from the National Natural Science Foundation of China (Nos. 42277485, 21976141, 22272197, 22102184, 22102136, andU22A20392), the Natural Science Foundation of Hubei Province (2022CFB1001 and 2021CFA034), the Department of Education of Hubei Province (Q20221701 and Q20221704), and the Joint Fund of Yulin University and Dalian National Laboratory for Clean Energy (YLU-DNL Fund 2022008).The electrocatalytic synthesis of C–N coupling compounds from CO2 and nitrogenous species not only offers an effective avenue to achieve carbon neutrality and reduce environmental pollution, but also establishes a route to synthesize valuable chemicals, such as urea, amide, and amine. This innovative approach expands the application range and product categories beyond simple carbonaceous species in electrocatalytic CO2 reduction, which is becoming a rapidly advancing field. This review summarizes the research progress in electrocatalytic urea synthesis, using N2, NO2−, and NO3− as nitrogenous species, and explores emerging trends in the electrosynthesis of amide and amine from CO2 and nitrogen species. Additionally, the future opportunities in this field are highlighted, including electrosynthesis of amino acids and other compounds containing C–N bonds, anodic C–N coupling reactions beyond water oxidation, and the catalytic mechanism of corresponding reactions. This critical review also captures the insights aimed at accelerating the development of electrochemical C–N coupling reactions, confirming the superiority of this electrochemical method over the traditional techniques.publishersversionpublishe

Nanocarbons and their hybrids as catalysts for non-aqueous lithium-oxygen batteries

Rechargeable lithium-oxygen (Li-O-2) batteries have been considered as the most promising candidates for energy storage and conversion devices because of their ultra high energy density. Until now, the critical scientific challenges facing Li-O-2 batteries are the absence of advanced electrode architectures and highly efficient electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which seriously hinder the commercialization of this technology. In the last few years, a number of strategies have been devoted to exploring new catalysts with novel structures to enhance the battery performance. Among various of oxygen electrode catalysts, carbon-based materials have triggered tremendous attention as suitable cathode catalysts for Li-O-2 batteries due to the reasonable structures and the balance of catalytic activity, durability and cost. In this review, we summarize the recent advances and basic understandings related to the carbon-based oxygen electrode catalytic materials, including nanostructured carbon materials (one-dimensional (1D) carbon nanotubes and carbon nanofibers, 2D graphene nanosheets, 3D hierarchical architectures and their doped structures), and metal/metal oxide-nanocarbon hybrid materials (nanocarbon supporting metal/metal oxide and nanocarbon encapsulating metal/metal oxide). Finally, several key points and research directions of the future design for highly efficient catalysts for practical Li-O-2 batteries are proposed based on the fundamental understandings and achievements of this battery field. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved

Structural and electronic optimization of graphene encapsulating binary metal for highly efficient water oxidation

Encapsulating non-precious metals within graphene layers represents a promising strategy to substitute precious metal catalyst towards the oxygen evolution reaction (OER). The surface electronic structure of graphene can significantly affect the OER performance, which depends on the types of encapsulated metal and their proportion but it still lacks efficient methods to modulate them. Herein, we report a universal strategy to encapsulate FeNi binary metal nanoalloy within ultrathin graphene layers, which can efficiently optimize the electronic properties and the OER activity on the graphene surface via modulating Fe/Ni ratio. The optimized catalyst with Fe/Ni of 1 shows a low overpotential of 280 mV at the current density of 10 mA cm(-2). Both the catalytic activity and durability of the catalyst are better than the commercial IrO2. Theoretical calculations indicate that the adsorption strength of each intermediate on graphene can be optimally balanced by modulating the metal proportion of the encapsulated FeNi, leading to an enhanced OER activity with reduced overpotential on the graphene surface

Effect of heat treatment on microstructure and mechanical properties of Fe60 coating by laser cladding on 304 stainless steel

Heat treatment has a direct effect on the microstructure and mechanical properties of laser cladding coatings. To investigate the influence of heat treatment on the microstructure and mechanical properties of Fe60 coating, the surface of 304 stainless steel was coated with Fe60 coating by laser cladding technology, and then normalizing treatments were conducted on the coatings at temperatures of 950 °C, 1000 °C, and 1050 °C, as well as a solution treatment at 1050 °C. The microstructure and phase composition of the coatings before and after heat treatment were analyzed using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffractometry (XRD). In addition, the microhardness, tensile properties, and impact toughness of the coating were evaluated through experimental testing. Furthermore, SEM examination was performed to observe the tensile fracture morphology with subsequent analysis. The results show that no phase transition occurs in the coatings after heat treatment. Subsequent to normalizing treatments, the grains are gradually refined with the increase of normalizing temperature. Solution treatment leads to grain refinement in the coating and significantly eliminates precipitated phases. The heat treatment effectively reduces residual stress and lattice distortion in the coating, which reduces the microhardness and significantly improves tensile properties and impact resistance at the same time. Observation of the tensile fracture microstructure reveals ductile dimple fractures in the substrate and brittle cleavage fractures within the coated region. The results can provide a valuable reference for enhancing the mechanical properties of Fe60 coatings by laser cladding

Low charge overpotential of lithium-oxygen batteries with metallic Co encapsulated in single-layer graphene shell as the catalyst

Rechargeable lithium-oxygen (Li-O-2) battery has triggered tremendous attention as a promising candidate power source for portable electronics and light vehicles. Until now, a critical scientific challenge facing Li-O-2 battery is the high charge overpotential due to the sluggish oxygen evolution reaction (OER) on the oxygen electrode, which results in low energy efficiency and poor cyclability. Here, we demonstrated that nitrogen-doped single layer graphene shell encapsulating non-precious metal Co can be used as a highly efficient catalyst for Li-O-2 batteries. The catalyst showed significantly enhanced OER catalytic activity, with a charge overpotential of 0.58 V, which was remarkably lower compared with the corresponding N-free graphene encapsulating metal, metal oxide and metal-free carbon materials. DFT calculations revealed that the nitrogen dopants and enclosed metal clusters can synergistically modulate the electronic properties of the graphene surface, resulting in a dramatic reduction of the overpotentials. This study provides the possibility of the rational non-precious metal electrocatalysts designing for Li-O-2 batteries. (C) 2016 Published by Elsevier Ltd

Tuning the Activities of Cu2O Nanostructures via the Oxide-Metal Interaction

Despite tremendous importance in catalysis, the design and improvement of the oxide- metal interface has been hampered by the limited understanding on the nature of interfacial sites, as well as the oxide-metal interaction (OMI). Through the construction of well-defined Cu2O-Pt, Cu2O-Ag, Cu2O-Au interfaces, we found that Cu2O Nanostructures (NSs) on Pt exhibit much lower thermal stability than on Ag and Au, although they show the same surface and edge structures, as identified by element-specific scanning tunneling microscopy (ES-STM) images. The activities of the Cu2O-Pt and Cu2O-Au interfaces for CO oxidation were further compared at the atomic scale and showed in general that the interface with Cu2O NSs could annihilate the CO-poisoning problem suffered by Pt group metals and enhance the interaction with O2, which is a limiting step for CO oxidation catalysis on group IB metals. While both interfaces could react with CO at room temperature, the OMI was found to determine the reactivity of supported Cu2O NSs by 1) tuning the activity of interfacial oxygen atoms and 2) stabilizing oxygen vacancies or vice versa, the dissociated oxygen atoms at the interface. Our study provides new insight for OMI and for the development of Cu-based catalysts for low temperature oxidation reactions

Three-dimensionally hierarchical MoS2/graphene architecture for high-performance hydrogen evolution reaction

Molybdenum disulfide (MoS2) has been considered as a potential alternative to precious metal catalysts for the hydrogen evolution reaction (HER). However, the performance of MoS2 is still limited due to the poor electron conductivity, scarce active sites and low structural stability. A multiscale design of MoS2 in the structure and atomic composition is needed but still a great challenge. Herein, we report a well-organized three-dimensionally (3D) mesoporous hybrid structure of Co-doped MoS2 and graphene for highly efficient electrocatalytic HER. The mesoporous morphology ensures the well-dispersion of MoS2 layers and exposure of abundant edge sites. Doping of Co atoms into the MoS2 lattice improves the intrinsic HER activity of in-plane sulfur sites. The highly conductive and robust graphene network enhances the conduction of electrons and simultaneously improves the stability of the hybrid structure. The catalyst achieves a current density of 10 mA cm(-2) at an overpotential of 143 mV versus the reversible hydrogen electrode (RHE) which is 200 mV lower compared with pure 2D MoS2, and maintains the activity for over 5000 cyclic voltammetry sweeps. This work provides a promising strategy for efficiently enhancing both the activity and stability of MoS2-based catalyst for HER

Multiscale carbon foam confining single iron atoms for efficient electrocatalytic CO2 reduction to CO

Electrocatalytic CO2 reduction to CO is a sustainable process for energy conversion. However, this process is still hindered by the diffusion-limited mass transfer, low electrical conductivity and catalytic activity. Therefore, new strategies for catalyst design should be adopted to solve these problems and improve the electrocatalytic performance for CO production. Herein, we report a multiscale carbon foam confining single iron atoms prepared with the assistant of SiO2 template. The pore-enriched environment at the macro-scale facilitates the diffusion of reactants and products. The graphene nanosheets at the nano-scale promote the charge transfer during the reaction. The single iron atoms confined in carbon matrix at the atomic-scale provide the active sites for electrocatalytic CO2 reduction to CO. The optimized catalyst achieves a CO Faradaic efficiency of 94.9% at a moderate potential of -0.5 V vs. RHE. Furthermore, the performance can be maintained over 60 hours due to the stable single iron atoms coordinated with four nitrogen atoms in the carbon matrix. This work provides a promising strategy to improve both the activity and stability of single atom catalysts for electrocatalytic CO2 reduction to CO