Developing efficient and stable Pt‐based oxygen reduction reaction (ORR) catalysts is a way to promote the large‐scale application of fuel cells. Pt‐based alloy nanowires are promising ORR catalysts, ...but their application is hampered by activity loss caused by structural destruction during long‐term cycling. Herein, the preparation of ordered PtFeIr intermetallic nanowire catalysts with an average diameter of 2.6 nm and face‐centered tetragonal structure (fct‐PtFeIr/C) is reported. A silica‐protected strategy prevents the deformation of PtFeIr nanowires during the phase transition at high temperature. The as‐prepared fct‐PtFeIr/C exhibited superior mass activity for ORR (2.03 A mgPt−1) than disordered PtFeIr nanowires with face‐centered cubic structure (1.11 A mgPt−1) and commercial Pt/C (0.21 A mgPt−1). Importantly, the structure and electrochemical performance of fct‐PtFeIr/C were maintained after stability tests, showing the advantages of the ordered structure.
Ordered PtFeIr intermetallic nanowires supported on commercial carbon were synthesized. Coating with SiO2 and the addition of Ir enabled the integrity of the nanowire structure to be maintained during their transformation from a disordered fcc‐phase to an ordered fct‐phase. The fct‐phase nanowires exhibited much better ORR activity and structural and electrochemical stability than the fcc‐phase ones.
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The development of Fe single‐atom catalysts (Fe SACs) with abundant, accessible Fe sites is a key step toward enhancing the efficiency of the oxygen reduction reaction (ORR) in proton exchange ...membrane fuel cells (PEMFCs). In this study, Zn4O(1,4‐benzenedicarboxylate)3 (MOF‐5), which has a 3D microporous cubic structure, is used as the precursor to prepare highly‐porous carbon (denoted as C‐MOF‐5) with an ultrahigh specific surface area (2751 m2 g–1) and high external surface area (1651 m2 g–1). C‐MOF‐5 is demonstrated as an effective carbon support to yield Fe SAC‐MOF‐5 with a large amount of accessible FeNx sites (2.35 wt%). Fe SAC‐MOF‐5 delivers a half‐wave potential of 0.83 V (vs RHE) in a 0.5 m H2SO4 electrolyte, and achieves a peak power density of 0.84 W cm–2 in a 0.2 MPa H2‐O2 PEMFC. This excellent performance originates from the ultrahigh specific surface area of C‐MOF‐5 for the formation of a high density of single Fe atoms, and high external surface area for the increased exposure of active sites. This work may inspire the rational design of metal single‐atom catalysts derived from a wider range of MOF precursors with ultrahigh specific area to improve the performance of the oxygen reduction reaction in PEMFCs.
A Fe single‐atom catalyst (Fe SAC‐MOF‐5) is successfully synthesized using MOF‐5 derived porous carbon (C‐MOF‐5) as a precursor. C‐MOF‐5 possesses an ultrahigh specific surface area to afford large amounts of FeNx sites, and a large external surface area to enable active sites to be fully accessible. Fe SAC‐MOF‐5 demonstrates superior oxygen reduction reaction activity and excellent performance in proton exchange membrane fuel cells.
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Fe single‐atom catalysts (Fe SACs) with atomic FeNx active sites are very promising alternatives to platinum‐based catalysts for the oxygen reduction reaction (ORR). The pyrolysis of metal–organic ...frameworks (MOFs) is a common approach for preparing Fe SACs, though most MOF‐derived catalysts reported to date are microporous and thus suffer from poor mass transfer and a high proportion of catalytically inaccessible FeNx active sites. Herein, NH2‐MIL‐101(Al), a MOF possessing a mesoporous cage architecture, is used as the precursor to prepare a series of N‐doped carbon supports (denoted herein as NC‐MIL101‐T) with a well‐defined mesoporous structure at different pyrolysis temperatures. The NC‐MIL101‐T supports are then impregnated with a Fe(II)‐phenanthroline complex, and heated again to yield Fe SAC‐MIL101‐T catalysts rich in accessible FeNx single atom sites. The best performing Fe SAC‐MIL101‐1000 catalyst offers outstanding ORR activity in alkaline media, evidenced by an ORR half‐wave potential of 0.94 V (vs RHE) in 0.1 m KOH, as well as excellent performance in both aqueous primary zinc–air batteries (a near maximum theoretical energy density of 984.2 Wh kgZn−1) and solid‐state zinc–air batteries (a peak power density of 50.6 mW cm−2 and a specific capacity of 724.0 mAh kgZn−1).
Mesoporous Fe single‐atom catalysts (Fe SAC‐MIL101‐T) are successfully synthesized using NH2‐MIL‐101(Al)‐derived N‐doped carbon as supports. The abundant mesopores in the supports promote mass transport during the oxygen reduction reaction (ORR) and ensure a high proportion of FeNx sites are accessible. Fe SAC‐MIL101‐1000 demonstrates outstanding activity for ORR and excellent performance in both aqueous and solid‐state zinc–air batteries.
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There is interest in metal single atom catalysts due to their remarkable activity and stability. However, the synthesis of metal single atom catalysts remains somewhat ad hoc, with no universal ...strategy yet reported that allows their generic synthesis. Herein, we report a universal synthetic strategy that allows the synthesis of transition metal single atom catalysts containing Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Pt or combinations thereof. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and extended X-ray absorption fine structure spectroscopy confirm that the transition metal atoms are uniformly dispersed over a carbon black support. The introduced synthetic method allows the production of carbon-supported metal single atom catalysts in large quantities (>1 kg scale) with high metal loadings. A Ni single atom catalyst exhibits outstanding activity for electrochemical reduction of carbon dioxide to carbon monoxide, achieving a 98.9% Faradaic efficiency at -1.2 V.
A challenging but pressing task to design and synthesize novel, efficient, and robust pH‐universal hydrogen evolution reaction (HER) electrocatalysts for scalable and sustainable hydrogen production ...through electrochemical water splitting. Herein, we report a facile method to prepare an efficient and robust Ru‐M (M=Ni, Mn, Cu) bimetal nanoparticle and carbon quantum dot hybrid (RuM/CQDs) for pH‐universal HER. The RuNi/CQDs catalysts exhibit outstanding HER performance at all pH levels. The unexpected low overpotentials of 13, 58, and 18 mV shown by RuNi/CQDs allow a current density of 10 mA cm−2 in 1 m KOH, 0.5 m H2SO4, and 1 m PBS, respectively, for Ru loading at 5.93 μgRu cm−2. This performance is among the best catalytic activities reported for any platinum‐free electrocatalyst. Theoretical studies reveal that Ni doping results in a moderate weakening of the hydrogen bonding energy of nearby surface Ru atoms, which plays a critical role in improving the HER activity.
How low can Ru go: A scalable and general synthetic method for the preparation of transition‐metal‐doped RuM/carbon quantum dots (CQDs; M=Ni, Mn, Cu) has been developed through metal‐mediated CQD condensation and carbonization. The low‐ruthenium‐content RuM/CQD catalysts exhibit outstanding activity and stability in catalyzing hydrogen evolution at all pH values.
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Rechargeable zinc–air batteries (ZABs) are presently attracting a lot of attention for electrical energy storage, owing to their low manufacturing cost and very high theoretical specific energy ...density. Currently, the large‐scale application of ZABs is hampered by the sluggish kinetics of the oxygen‐reduction reaction (ORR) and oxygen evolution reaction (OER), which underpin battery discharging and charging processes, respectively. In recent years, metal single‐atom catalysts (SACs) have emerged as promising candidates for driving oxygen electrocatalysis in ZABs, offering both high electrocatalytic activity and high metal atom utilization through unique metal coordination environments (typically porphyrin‐like MNx species on N‐doped carbon supports). Herein, recent breakthroughs in the design of SACs for ORR and OER electrocatalysis are summarized, with a general view towards improving ZAB performance. This Review begins by introducing the operating principles of ZABs and the reaction mechanisms of the ORR and the OER on the air electrode, after which the various types of SAC‐based materials developed to date for oxygen electrocatalysis and ZABs are discussed. Special emphasis is placed on the relationships between the structure of the SAC active site and electrocatalytic performance. Finally, challenges and opportunities for SACs in practical ZABs are explored.
Recent breakthroughs in the development of metal single‐atom catalysts (SACs) for the oxygen reduction reaction and the oxygen evolution reaction are reviewed, with the goal of improving the future performance of zinc–air batteries. Particular emphasis is placed on the relationships between the structure of the metal SAC sites and electrocatalytic performance in oxygen electrocatalysis.
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Abstract
The electrochemical CO
2
reduction reaction (CO
2
RR) represents a very promising future strategy for synthesizing carbon-containing chemicals in a more sustainable way. In spite of great ...progress in electrocatalyst design over the last decade, the critical role of wettability-controlled interfacial structures for CO
2
RR remains largely unexplored. Here, we systematically modify the structure of gas-liquid-solid interfaces over a typical Au/C gas diffusion electrode through wettability modification to reveal its contribution to interfacial CO
2
transportation and electroreduction. Based on confocal laser scanning microscopy measurements, the Cassie-Wenzel coexistence state is demonstrated to be the ideal three phase structure for continuous CO
2
supply from gas phase to Au active sites at high current densities. The pivotal role of interfacial structure for the stabilization of the interfacial CO
2
concentration during CO
2
RR is quantitatively analysed through a newly-developed in-situ fluorescence electrochemical spectroscopic method, pinpointing the necessary CO
2
mass transfer conditions for CO
2
RR operation at high current densities.
The selective hydrogenation of acetylene to ethylene in an ethylene‐rich gas stream is an important process in the chemical industry. Pd‐based catalysts are widely used in this reaction due to their ...excellent hydrogenation activity, though their selectivity for acetylene hydrogenation and durability need improvement. Herein, the successful synthesis of atomically dispersed Pd single‐atom catalysts on nitrogen‐doped graphene (Pd1/N‐graphene) by a freeze‐drying‐assisted method is reported. The Pd1/N‐graphene catalyst exhibits outstanding activity and selectivity for the hydrogenation of C2H2 with H2 in the presence of excess C2H4 under photothermal heating (UV and visible‐light irradiation from a Xe lamp), achieving 99% conversion of acetylene and 93.5% selectivity to ethylene at 125 °C. This remarkable catalytic performance is attributed to the high concentration of Pd active sites on the catalyst surface and the weak adsorption energy of ethylene on isolated Pd atoms, which prevents C2H4 hydrogenation. Importantly, the Pd1/N‐graphene catalyst exhibits excellent durability at the optimal reaction temperature of 125 °C, which is explained by the strong local coordination of Pd atoms by nitrogen atoms, which suppresses the Pd aggregation. The results presented here encourage the wider pursuit of solar‐driven photothermal catalyst systems based on single‐atom active sites for selective hydrogenation reactions.
Pd single‐atom catalysts on nitrogen‐doped graphene are successfully fabricated. A Pd1/N‐graphene catalyst (Pd loading of 2.3 wt%) exhibits outstanding activity and selectivity for the selective hydrogenation of acetylene in the presence of excess ethylene under photothermal or direct thermal heating at 125 °C, which is attributed to the suppression of C2H4 hydrogenation to C2H6 by Pd‐N4 surface sites.
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Nanozymes have attracted extensive interest owing to their high stability, low cost and easy preparation, especially in the field of cancer therapy. However, the relatively low catalytic activity of ...nanozymes in the tumor microenvironment (TME) has limited their applications. Herein, we report a novel nanozyme (PtFe@Fe3O4) with dual enzyme‐like activities for highly efficient tumor catalytic therapy. PtFe@Fe3O4 shows the intrinsic photothermal effect as well as photo‐enhanced peroxidase‐like and catalase‐like activities in the acidic TME, thereby effectively killing tumor cells and overcoming the tumor hypoxia. Importantly, a possible photo‐enhanced synergistic catalytic mechanism of PtFe@Fe3O4 was first disclosed. We believe that this work will advance the development of nanozymes in tumor catalytic therapy.
Double attack: A novel nanozyme (PtFe@Fe3O4) with dual enzyme‐like activities was developed for deep pancreatic cancer catalytic therapy. The PtFe@Fe3O4 nanozyme shows photo‐enhanced peroxidase‐like and catalase‐like activities under the acidic tumor microenvironment, as well as intrinsic photothermal effect, effectively killing tumor cells and overcoming the tumor hypoxia.
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A series of novel CoFe‐based catalysts are successfully fabricated by hydrogen reduction of CoFeAl layered‐double‐hydroxide (LDH) nanosheets at 300–700 °C. The chemical composition and morphology of ...the reaction products (denoted herein as CoFe‐x) are highly dependent on the reduction temperature (x). CO2 hydrogenation experiments are conducted on the CoFe‐x catalysts under UV–vis excitation. With increasing LDH‐nanosheet reduction temperature, the CoFe‐x catalysts show a progressive selectivity shift from CO to CH4, and eventually to high‐value hydrocarbons (C2+). CoFe‐650 shows remarkable selectivity toward hydrocarbons (60% CH4, 35% C2+). X‐ray absorption fine structure, high‐resolution transmission electron microscopy, Mössbauer spectroscopy, and density functional theory calculations demonstrate that alumina‐supported CoFe‐alloy nanoparticles are responsible for the high selectivity of CoFe‐650 for C2+ hydrocarbons, also allowing exploitation of photothermal effects. This study demonstrates a vibrant new catalyst platform for harnessing clean, abundant solar‐energy to produce valuable chemicals and fuels from CO2.
Three unique CoFe‐based catalysts are successfully fabricated via direct H2 reduction of a CoFeAl layered‐double‐hydroxide (CoFeAl‐LDH) nanosheets precursor by varying the reduction temperature. LDH precursor reduction at temperatures above 600 °C results in the formation of CoFe‐alloy nanoparticles, thereby affording a remarkable CO2 hydrogenation selectivity toward high‐value (C2+) hydrocarbons under simulated solar excitation through photothermal effects.
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