High Atom Utilization Efficiency Research Articles

Recent progress on the synthesis and oxygen reduction applications of Fe-based single-atom and double-atom catalysts

Single-atom and double-atom catalysts have emerged as a new Frontier in many fields due to their high atom-utilization efficiency, excellent catalytic properties and good durability.

Achievements in Pt nanoalloy oxygen reduction reaction catalysts: strain engineering, stability and atom utilization efficiency.

The Pt nanoalloy surfaces often show unique electronic and physicochemical properties that are distinct from those of their parent metals, which provide significant room for manipulating their oxygen reduction reaction (ORR) behaviour. In this Feature Article, we present the progress of our recent research and that of other groups in Pt nanoalloy catalysts for ORR from three aspects, namely, strain engineering, stability and atom utilization efficiency. Some new insights into Pt surface strain engineering will be firstly introduced, with a focus on discussing the effect of compressive and tensile strain on the chemisorption properties. Secondly, the design concepts and synthetic methodologies to intensify the inherent stability of Pt nanoalloys will be summarized. Then, the exciting research push in developing nanostructured alloys with high atom utilization efficiency of Pt will be presented. Finally, a brief illumination of challenges and future developing perspectives of Pt nanoalloy catalysts will be provided.

Micelles of Mesoporous Silica with Inserted Iron Complexes as a Platform for Constructing Efficient Electrocatalysts for Oxygen Reduction.

Iron, N-codoped carbon materials (Fe-N-C) are promising electrocatalysts toward oxygen reduction reactions due to their high atom utilization efficiency and intrinsic activity. Nanostructuring of the Fe-N-C materials, such as introducing porosity into the carbon structure, would be conducive to further increasing the exposure of active sites as well as improving the mass transfer. Herein, we explore the potential of iron complex-functionalized micelles of mesoporous SiO2 as a platform for constructing porous Fe-N-C materials. The classical three-dimensional MCM-48 was selected as a proof-of-concept example, which was utilized as the hard template, and cetyltrimethylammonium bromide micelles inside it played the role of the main carbon source. Fe-Nx sites were derived from Fe-1,10-phenanthroline complexes in the micelles introduced by in situ incorporation of 1,10-phenanthroline and post Fe2+ insertion in an aqueous solution. After thermal annealing in a nitrogen atmosphere and subsequent removal of the MCM-48 framework, a carbon material that possesses porous structural features with uniformly dispersed Fe-Nx sites (MPC@PhFe) was obtained, which shows superior ORR activity in a 0.1 M KOH solution and great potential for Zn-air battery applications as well. This work demonstrates the feasibility as well as the effectiveness of turning micelles of mesoporous SiO2 into porous carbon structures and might offer a universal strategy for manufacturing carbon materials for future application in energy storage and conversion.

Recent advances in electrocatalysts for neutral and large-current-density water electrolysis

Hydrogen as a clean energy resource is considered as one of the most promising alternatives to alleviate energy crisis and environmental pollution, which induces the urgent requirement for electrochemical water splitting that contains the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Compared with alkaline or acidic electrolytes, the water splitting in neutral media is more daunting and less explored, which is mainly attributed to the additional challenge in improving the sluggish kinetics of water dissociation in neutral pH. However, if the neutral water splitting system could be realized, it would bring about the opportunity to direct splitting of less corrosive saline water that is the most abundant resource, which allows a massive and sustainable hydrogen fuel production. Here we review recent research in the development of both HER and OER electrocatalysts that are operated in neutral conditions from the perspective of the reaction mechanisms, rate-determining steps, and component-structure-activity correlations. Single-atom catalysts as an emerging field are also highlighted for their high atom utilization efficiency and high activity. In view of large-current-density operating conditions, three-dimensional freestanding electrodes where catalysts grow directly on the conductive substrates become the main tendency. In addition, superhydrophilic and superaerophobic electrode surfaces are summarized with regard to rapid ion diffusions and gas bubbles release, especially under large current densities. Finally, we address the challenges associated with neutral water electrolysis and future pathways in the hope of guiding the design of the electrocatalysts and electrode materials to make large-scale hydrogen production easier and more efficient. • Reaction mechanisms and design strategies of HER/OER electrocatalysts in neutral media are summarized. • Design principles of electrodes are pointed out regarding efficient charge transfer, especially at high current densities. • Surface engineering for superhydrophilic and superaerophobic electrodes are discussed in view of rapid gas bubble release. • Challenges and future perspectives on neutral and large-current-density water electrolysis are presented.

Hollow Mesoporous Carbon Sphere Loaded Ni-N4 Single-Atom: Support Structure Study for CO2 Electrocatalytic Reduction Catalyst.

Single-atom catalysts have become a hot spot because of the high atom utilization efficiency and excellent activity. However, the effect of the support structure in the single-atom catalyst is often unnoticed in the catalytic process. Herein, a series of carbon spheres supported Ni-N4 single-atom catalysts with different support structures are successfully synthesized by the fine adjustment of synthetic conditions. The hollow mesoporous carbon spheres supported Ni-N4 catalyst (Ni/HMCS-3-800) exhibits superior catalytic activity toward the electrocatalytic CO2 reduction reaction (CO2 RR). The Faradaic efficiency toward CO is high to 95% at the potential range from -0.7 to -1.1V versus reversible hydrogen electrode and the turnover frequency value is high up to 15 608 h-1 . More importantly, the effect of the geometrical structures of carbon support on the CO2 RR performance is studied intensively. The shell thickness and compactness of carbon spheres regulate the chemical environment of the doped-N species in the carbon skeleton effectively and promote CO2 molecule activation. Additionally, the optimized mesopore size is beneficial to improve diffusion and overflow of the substance, which enhances the CO2 adsorption capacity greatly. This work provides a new consideration for promoting the catalytic performance of single-atom catalysts.

Single atom alloy: An emerging atomic site material for catalytic applications

Abstract The development of low-cost, high-performance catalysts at the atomic level has become a challenging issue for large-scale applications of renewable clean energy technologies. Atomic sites catalysts, such as single atoms catalysts (SAC), single clusters catalysts (SCC), single-atom alloys (SAA), have proved their performance in various catalytic reactions due to their extremely high atom utilization efficiency, unique structure, and exceptional catalytic selectivity. A deep understanding and design of the active center of the catalyst at the atomic level has become a top priority for current research. Compared with SAC and SCC, SAA has its own uniqueness. In this review, we focused on the recent progress on the preparation methods of SAA and discussed the key factors controlling the structure of SAA. In addition, several important catalytic reactions performed over well-defined SAA are analyzed. Finally, the challenges and the perspectives of this cutting-edge field are suggested. We believe that this critical review provides a guidance for the rational design of SAA for catalytic applications.

Ultrafine Ir Nanowires with Microporous Channels and Superior Electrocatalytic Activity for Oxygen Evolution Reaction

AbstractHydrogen energy is considered as an ideal candidate energy of traditional fossil fuels. Oxygen evolution reaction (OER) is a crucial reaction for the sustainable hydrogen generation as a half reaction of water splitting. It is important to develop efficient electrocatalysts for the OER. Herein, the porous iridium nanowires (Ir PNWs) with polyallylamine hydrochloride (PAH) as a complex‐forming agent and capping agent have been successfully synthesized through a one‐pot hydrothermal approach. Benefiting from the inherent anisotropic characteristic of one‐dimensional nanowires structure, abundant microporous channels and high atom utilization efficiency, the synthesized Ir PNWs possess very large electrochemically active surface area (118.2 m2 g−1), and thus exhibit superior electrocatalytic activity and stability towards the OER compared with commercial RuO2 catalyst and other Ir nanocrystals.

Preparation and catalytic performance of ZrO2‐supported Pt single‐atom and cluster catalyst for hydrogenation of 2,4‐dinitrotoluene to 2,4‐toluenediamine

AbstractBACKGROUNDThe catalytic hydrogenation of 2,4‐dinitrotoluene is an environmentally benign technology for the production of 2,4‐toluenediamine, which is a key intermediate in production of polyurethane foams, elastomers and sealants. Most of the existing precious metal nanocatalysts, however, suffer from low catalytic efficiency and high catalyst costs. Single metal atoms and clusters anchored on carriers, with high atom utilization efficiency, provide a good strategy for creating cost‐effective catalysts. In the work reported, a ZrO2‐supported Pt single‐atom and cluster catalyst was successfully prepared using a facile adsorption method for hydrogenation of 2,4‐dinitrotoluene to 2,4‐toluenediamine.RESULTSPt concentration in solution and reduction temperature had a substantial effect on the Pt loadings, dispersion and the corresponding catalytic performance. The 15Pt/ZrO2‐300 catalyst exhibited the highest catalytic activity. At 80 °C and hydrogen pressure of 1 MPa, the initial hydrogenation rate reached as high as 4583.33 molH2 molPt−1 min−1, which was more than 40 times that for a conventional Pd/C catalyst.CONCLUSIONSZrO2‐supported Pt single‐atom and cluster catalyst was successfully fabricated. The method was implemented on the foundation of strong charge adsorption between Pt ions and ZrO2 carrier. The prepared Pt single‐atom and cluster catalyst showed excellent catalytic activity for hydrogenation of 2,4‐dinitrotoluene to 2,4‐toluenediamine. © 2020 Society of Chemical Industry

One‐pot synthesis of 3‐(sulfonyl)‐5,6,7,8‐tetrahydro‐4H‐pyrano[3,2‐c]pyridines through a cascade Michael/cyclization reaction

AbstractIn this paper, a straightforward and valid three‐component Michael/cyclization reaction of (E)‐1‐methyl‐3‐(arylidene)piperidin‐4‐ones, 2‐(sulfonyl)acetonitriles, and aromatic aldehydes was explored for the preparation of potentially biologically active 3‐(sulfonyl)‐5,6,7,8‐tetrahydro‐4H‐pyrano[3,2‐c]pyridines under mild reaction conditions. More diverse 3‐(sulfonyl)‐5,6,7,8‐tetrahydro‐4H‐pyrano[3,2‐c]pyridine derivatives were constructed in satisfactory yields (up to 97%). The chemical structure of newly synthesized 3‐(sulfonyl)‐5,6,7,8‐tetrahydro‐4H‐pyrano[3,2‐c]pyridines were identified with 1H‐NMR, 13C‐NMR, and mass spectrometry analysis. The recommendable method features a simple and direct workup, easy access to initial materials, high atom utilization efficiency, high final product yields, and a wide range of substrate adaptability.

Atomically Transition Metals on Self-Supported Porous Carbon Flake Arrays as Binder-Free Air Cathode for Wearable Zinc-Air Batteries.

Metal single-atom materials with their high atom utilization efficiency and unique electronic structures usually show remarkable catalytic performances in many crucial chemical reactions. Herein, a facile and easily scalable "impregnation-carbonization-acidification" strategy for fabricating a class of single-atom-anchored (including cobalt and nickel single atoms) monolith as superior binder-free electrocatalysts for developing high-performance wearable Zn-air batteries is reported. The as-prepared single atoms, supported by N-doped carbon flake arrays grown on carbon nanofibers assembly (M SA@NCF/CNF), demonstrate the dual characteristics of excellent catalytic activity (reversible oxygen overpotential of 0.75 V) and high stability, owing to the greatly improved active sites' accessibility and optimized single-sites/pore-structures correlations. Furthermore, wearable Zn-air battery based on Co SA@NCF/CNF air electrode displays superior stability under deformation, satisfactory energy storage capacity, and good practicality to be utilized as an integrated battery system. Theoretical calculations reveal a mechanism for the promotion of the catalytic performances on single atomic sites by lowering the overall oxygen reduction/evolution reaction barriers comparing to metal cluster co-existing configuration. These findings provide a facile strategy for constructing free-standing single-atom materials as well as the engineering of high-performance binder-free catalytic electrodes.

Nano-Cu-Mediated Multi-Site Approach to Ultrafine MoO2 Nanoparticles on Poly(diallyldimethylammonium chloride)-Decorated Reduced Graphene Oxide for Hydrogen Evolution Electrocatalysis.

Catalysts with high atom utilization efficiency accompanied by improved reactivity and durability are highly desired. Metallic MoO2 with its small size easily agglomerates, making it difficult to use in water splitting to obtain hydrogen by electrolysis. Here, the nano-Cu-mediated multi-site method is proposed to prepare ultrafine MoO2 nanoparticles (NPs) dispersed on poly(diallyldimethylammonium chloride)-decorated reduced graphene oxide (denoted as MoO2 /PDDA-rGO). The introduction of Cu NPs increases the number of growth sites for MoO2 on the PDDA-rGO and simultaneously promotes the growth rate of MoO2 on PDDA-rGO. As a consequence, the resulting size of the MoO2 NPs is only 2 nm and these are evenly dispersed on PDDA-rGO. Significantly, the optimized catalyst has a low onset potential of -42 mV versus reversible hydrogen electrode (RHE), a calculated Tafel slope of only 42 mV dec-1 , and good cycling stability of more than 40 h. This favored hydrogen evolution reaction (HER) activity is caused by the synergistic effects of MoO2 and PDDA-rGO, rapid charge transport, and sufficient exposed active sites of MoO2 /PDDA-rGO.

Pt-Based electrocatalysts with high atom utilization efficiency: from nanostructures to single atoms

This review presents recent developments in the design and synthesis of Pt-based catalysts with high atom utilization efficiency and their enhanced catalytic performance in electrochemical catalytic reactions.

Edge-Site Engineering of Atomically Dispersed Fe-N4 by Selective C-N Bond Cleavage for Enhanced Oxygen Reduction Reaction Activities.

Single-atom metal-nitrogen-carbon (M-N-C) catalysts have sparked intense interests, but the catalytic contribution of N-bonding environment neighboring M-N4 sites lacks attention. Herein, a series of Fe-N-C nanoarchitectures have been prepared, which confer adjustable numbers of atomically dispersed Fe-N4 sites, tunable hierarchical micro-mesoporous structures and intensified exposure of interior active sites. The optimization between Fe-N4 single sites and carbon matrix delivers superior oxygen reduction reaction activity (half-wave potential of 0.915 V vs RHE in alkaline medium) with remarkable stability and high atom-utilization efficiency (almost 10-fold enhancement). Both experiments and theoretical calculations verified the selective C-N bond cleavage adjacent to Fe center induced by porosity engineering could form edge-hosted Fe-N4 moieties, and therefore lower the overall oxygen reduction reaction barriers comparing to intact atomic configuration. These findings provide a new pathway for the integrated engineering of geometric and electronic structures of single-atom materials to improve their catalytic performance.

Hypervalent Iodine(III)‐Mediated Benzannulation of Enamines with Alkynes: an Efficient Synthesis of Substituted Aminonaphthoic Acid Derivatives

Abstract An intermolecular two CC bond formation procedure for the synthesis of carbocycles mediated by hypervalent iodine(III) reagents was developed. This metal free protocol provided a new approach for the synthesis of useful substituted 1‐amino‐2‐naphthoic acid derivatives via benzannulation reactions. Various N‐unsubstituted and N‐alkyl substituted aromatic enamines with terminal alkynes and non‐terminal alkynes can be converted into corresponding 1‐amino‐2‐naphthoic acid derivatives under mild reaction conditions. When meta‐substituted phenyl enamines were employed in the reaction, two cyclization paths were detected in the reaction and ortho‐cyclization products were the only or major products. Good functional group tolerance, readily available material and high atom utilization efficiency make this method a potential procedure which may find broad application in organic synthesis.