Two‐Dimensional Conjugated Aromatic Networks as High‐Site‐Density and Single‐Atom Electrocatalysts for the Oxygen Reduction Reaction

Advanced Energy Materials

et al. 2019

231

137

In addition, in-depth understanding of the nature of electrode material is an essential step in the development of electrode materials. [21][22][23][24] The electrode materials play a vital role in the battery. [25,26] During the deintercalation and conversion reactions, the electrode material is subjected to various physical and chemical changes, such as phase transitions and electrochemical reorganization. [27] These series of physical and chemical changes will affect the electrochemical performance. [28] Therefore, it is necessary to optimize and improve the electrochemical performance of the battery by studying the reaction mechanism. [29][30][31][32] Transition metal dichalcogenides (TMDs) have gained comprehensive attention in the field of energy storage due to their unique electrochemical properties, high electrical conductivity, and high capacity. [33][34][35][36][37][38][39][40] The inadequacies are also obvious, including volume expansion, agglomeration, low ion-diffusion coefficient, and side reaction during discharge/charge, resulting in the rapid decay of capacity. [41] To achieve high performance rechargeable batteries, it is important to understand the physical and chemical changes in electrode materials during the charge/discharge process. Researchers have made remarkable progress. [42] Usually TMDs involve a multi-step reaction mechanism as anode material for lithium ion batteries and sodium ion batteries (intercalation and conversion). [43][44][45] However, the physical and chemical changes in these TMDs in the potassium ion batteries are still not clear, which hinders the design and development of electrode materials. Therefore, exploring the reaction mechanism of metal selenide not only allows us to understand the relationship between TMDs and K + , but also achieve a long life cycle that would be a breakthrough for large-scale energy storage equipment.Herein, we successfully synthesized carbon-coated FeSe 2 clusters via a solvothermal method. The FeSe 2 clusters are well wrapped by the carbon layer, which improves electron conductivity and alleviates volume expansion. Benefiting from the unique structure, FeSe 2 /N-C exhibit ultra-stable cycle performance with a reversible capacity of up to 170 mAh g −1 at a high current of 2000 mA g −1 , which remains ≈158 mAh g −1 after 2000 cycles. The capacity retention is close to 100%. The electrodes also show remarkable rate performance. Furthermore, first-principles calculations, in situ X-ray diffraction, and ex situ transmission electron microscopy (in situ XRD and ex-TEM) Potassium ion hybrid capacitors have great potential for large-scale energy devices, because of the high power density and low cost. However, their practical applications are hindered by their low energy density, as well as electrolyte decomposition and collector corrosion at high potential in potassium bis(fluoro-sulfonyl)imide-based electrolyte. Therefore, anode materials with high capacity, a suitable voltage platform, and stability become a key factor. Here, N-doping carbon-co...

mentioning

confidence: 99%

Nature of FeSe₂/N‐C Anode for High Performance Potassium Ion Hybrid Capacitor

Advanced Energy Materials

et al. 2019

231

137

“…[208] Benefitting from the structural functionalities and electronic control of the Fe SA active center, the catalyst showed a remarkable performance with enhanced reaction kinetics for oxygen reduction in both alkaline and acidic solutions, and also exhibited great promise for Zn-air batteries. Similar to the above-mentioned discussions, other organic ligands, such as poly(ether imide), [209] glucose/dicyandiamide, [210] 5-amino-1,10-phenanthroline (phen-NH 2 ), [211] tetrapyridophenazine, [212] 2,2-bipyridine, [213] melamine, [214] polyphthalocyanine, [215,216] porphyra, [217] 2-methylimidazole, [218] and pyrrole [219] were used to generate the precursors of Feorganic ligand complexes for preparing the Fe SAs on carbonaceous materials. With air cathodes, the achieved metal-air batteries could show remarkable electrochemical performances.…”

Section: Metal-air Batteriesmentioning

confidence: 89%

Emerging Metal Single Atoms in Electrocatalysts and Batteries

Zhu

et al. 2020

Adv Funct Materials

Energy conversion and storage applications require highly stable and efficient electrocatalysts/electrodes to facilitate electrochemical reactions, but these materials commonly suffer from serious atom wastes and lower performances than the theoretical levels, which cannot meet the increasing demands of the green atomic economy, thereby limiting their practical applications. Recently, metal single atoms (SAs) have attracted tremendous attention owing to their merits of full atom utilization, unique electronic structures, tunable surface characteristics, and low costs. However, metal SAs usually have relatively low physical/chemical stabilities due to their high surface energy, which results in severe degradation of electrochemical performances. Novel synthetic strategies are developed for metal SAs with better stability and performance. In this review, these strategies will be introduced in the context of electrocatalysis and batteries. Specifically, the design concepts, synthesis approach properties, and applications of metal SAs will be discussed. Finally, the critical challenges and future perspectives of metal SAs are presented. This review aims to provide new insights for future work as well as the real-world applications of metal SAs.

“…In recent years, porous carbon materials co‐doped with transition metals and heteroatoms have been widely studied for ORR using both theoretical and experimental methods . Density functional theory (DFT) calculations have revealed that co‐doping Fe and N in a carbon matrix may lead to high ORR catalytic activity, where Fe and N should be combined in the form of FeN 4 or FeN 2 .…”

Section: Figurementioning

confidence: 99%

Hierarchically Ordered Porous Carbon with Atomically Dispersed FeN₄ for Ultraefficient Oxygen Reduction Reaction in Proton‐Exchange Membrane Fuel Cells

Qiao

et al. 2020

Angewandte Chemie

The low catalytic activity and poor mass transport capacity of platinum group metal free (PGM‐free) catalysts seriously restrict the application of proton‐exchange membrane fuel cells (PEMFCs). Catalysts derived from Fe‐doped ZIF‐8 could in theory be as active as Pt/C thanks to the high intrinsic activity of FeN4; however, the micropores fail to meet rapid mass transfer. Herein, an ordered hierarchical porous structure is introduced into Fe‐doped ZIF‐8 single crystals, which were subsequently carbonized to obtain an FeN4‐doped hierarchical ordered porous carbon (FeN4/HOPC) skeleton. The optimal catalyst FeN4/HOPC‐c‐1000 shows excellent performance with a half‐wave potential of 0.80 V in 0.5 m H2SO4 solution, only 20 mV lower than that of commercial Pt/C (0.82 V). In a real PEMFC, FeN4/HOPC‐c‐1000 exhibits significantly enhanced current density and power density relative to FeN4/C, which does not have an optimized pore structure, implying an efficient utilization of the active sites and enhanced mass transfer to promote the oxygen reduction reaction (ORR).