As a new and popular material, single‐atom catalysts (SACs) exhibit excellent activity, selectivity, and stability for numerous important reactions, and show great potential in heterogeneous ...catalysis due to their high atom utilization efficiency and the controllable characteristics of the active sites. The composition and coordination would determine the geometric and electronic structures of SACs, and thus greatly influence the catalytic performance. Based on atom economy, rational design and controllable synthesis of SACs have become central tasks in the fields of low‐cost and green catalysis. Herein, an introduction to the recent progress in the precise synthesis of SACs including the regulation of the coordination structure and the choice of different systems is presented. Thereafter, the potentials of SACs in different applications are comprehensively summarized and discussed. Furthermore, a detailed discussion of the recent developments regarding the large‐scale preparation of SACs is provided, including the major issues and prospects for industrialization. Finally, the main challenges and opportunities of rapid large‐scale industrialization of SACs are briefly discussed.
The development and exploration of highly efficient single‐atom catalysts (SACs) is of enormous significance for achieving industrialization. The advanced progress of precise synthesis and practical application of SACs is summarized. Thereafter, the main challenges and future opportunities of large‐scale synthesis of SACs are discussed.
The rational design of metal–organic frameworks (MOFs) with hollow features and tunable porosity at the nanoscale can enhance their intrinsic properties and stimulates increasing attentions. In this ...Communication, we demonstrate that methanol can affect the coordination mode of ZIF‐67 in the presence of Co2+ and induces a mild phase transformation under solvothermal conditions. By applying this transformation process to the ZIF‐67@ZIF‐8 core–shell structures, a well‐defined hollow Zn/Co ZIF rhombic dodecahedron can be obtained. The manufacturing of hollow MOFs enables us to prepare a noble metal@MOF yolk‐shell composite with controlled spatial distribution and morphology. The enhanced gas storage and porous confinement that originate from the hollow interior and coating of ZIF‐8 confers this unique catalyst with superior activity and selectivity toward the semi‐hydrogenation of acetylene.
A mild phase transformation of ZIF‐67@ZIF‐8 core–shell structures is achieved under solvothermal conditions to generate unique hollow Zn/Co ZIF particles, which were used to generate Pd@MOF yolk‐shell composites. They exhibit enhanced gas storage and high catalytic activity and selectivity in the semi‐hydrogenation of acetylene.
Abstract
The search for constructing high-performance catalysts is an unfailing topic in chemical fields. Recently, we have witnessed many breakthroughs in the synthesis of single-atom catalysts ...(SACs) and their applications in catalytic systems. They have shown excellent activity, selectivity, stability, efficient atom utilization and can serve as an efficient bridge between homogeneous and heterogenous catalysis. Currently, most SACs are synthesized via a bottom-up strategy; however, drawbacks such as the difficulty in accessing high mass activity and controlling homogeneous coordination environments are inevitably encountered, restricting their potential use in the industrial area. In this regard, a novel top-down strategy has been recently developed to fabricate SACs to address these practical issues. The metal loading can be increased to 5% and the coordination environments can also be precisely controlled. This review highlights approaches to the chemical synthesis of SACs towards diverse chemical reactions, especially the recent advances in improving the mass activity and well-defined local structures of SACs. Also, challenges and opportunities for the SACs will be discussed in the later part.
Single-atom catalysts often exhibit unexpected catalytic activity for many important chemical reactions because of their unique electronic and geometric structures with respect to their bulk ...counterparts. Herein we adopt metal–organic frameworks (MOFs) to assist the preparation of a catalyst containing single Ni sites for efficient electroreduction of CO2. The synthesis is based on ionic exchange between Zn nodes and adsorbed Ni ions within the cavities of the MOF. This single-atom catalyst exhibited an excellent turnover frequency for electroreduction of CO2 (5273 h–1), with a Faradaic efficiency for CO production of over 71.9% and a current density of 10.48 mA cm–2 at an overpotential of 0.89 V. Our findings present some guidelines for the rational design and accurate modulation of nanostructured catalysts at the atomic scale.
The design of active, selective, and stable CO2 reduction electrocatalysts is still challenging. A series of atomically dispersed Co catalysts with different nitrogen coordination numbers were ...prepared and their CO2 electroreduction catalytic performance was explored. The best catalyst, atomically dispersed Co with two‐coordinate nitrogen atoms, achieves both high selectivity and superior activity with 94 % CO formation Faradaic efficiency and a current density of 18.1 mA cm−2 at an overpotential of 520 mV. The CO formation turnover frequency reaches a record value of 18 200 h−1, surpassing most reported metal‐based catalysts under comparable conditions. Our experimental and theoretical results demonstrate that lower a coordination number facilitates activation of CO2 to the CO2.− intermediate and hence enhances CO2 electroreduction activity.
A remarkable carbon dioxide electroreduction catalytic performance with superior activity and high selectivity was achieved on atomically dispersed Co sites through coordination environment regulating. First step in picture: C–N fragments, 1000 °C; second step: NH3 treatment.
Herein, a series of porous nano‐structured carbocatalysts have been fused and decorated by Mo‐based composites, such as Mo2C, MoN, and MoP, to form a hybrid structures. Using the open porosity ...derived from the pyrolysis of metal–organic frameworks (MOFs), the highly dispersive MoO2 small nanoparticles can be deposited in porous carbon by chemical vapor deposition (CVD). Undergoing different treatments of carbonization, nitridation, and phosphorization, the Mo2C‐, MoN‐, and MoP‐decorated carbocatalysts can be selectively prepared with un‐changed morphology. Among these Mo‐based composites, the MoP@Porous carbon (MoP@PC) composites exhibited remarkable catalytic activity for the hydrogen evolution reaction (HER) in 0.5 m H2SO4 aqueous solution versus MoO2@PC, Mo2C@PC, and MoN@PC. This study gives a promising family of multifunctional lab‐on‐a‐particle architectures which shed light on energy conversion and fuel‐cell catalysis.
Decorated for HER: Using the open porosity derived from the pyrolysis of metal–organic frameworks (MOFs), MoO2 small nanoparticles can be deposited in the porous carbon by chemical vapor deposition. Carbonization, nitridation, or phosphorization, selectively gives Mo2C‐, MoN‐, and MoP‐decorated carbocatalysts with unchanged morphology. The catalysts are promising for the hydrogen evolution reaction.
Single-atom metal catalysts have sparked tremendous attention, but direct transformation of cheap and easily obtainable bulk metal oxide into single atoms is still a great challenge. Here we report a ...facile and versatile gas-transport strategy to synthesize isolated single-atom copper sites (Cu ISAS/NC) catalyst at gram levels. Commercial copper (I) oxide powder is sublimated as mobile vapor at nearly melting temperature (1500 K) and subsequently can be trapped and reduced by the defect-rich nitrogen-doped carbon (NC), forming the isolated copper sites catalyst. Strikingly, this thermally stable Cu ISAS/NC, which is obtained above 1270 K, delivers excellent oxygen reduction performance possessing a recorded half-wave potential of 0.92 V vs RHE among other Cu-based electrocatalysts. By varying metal oxide precursors, we demonstrate the universal synthesis of different metal single atoms anchored on NC materials (M ISAS/NC, where M refers to Mo and Sn). This strategy is readily scalable and the as-prepared sintering-resistant M ISAS/NC catalysts hold great potential in high-temperature applications.
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•Personal thermal management can be applied for building energy saving and improving occupant thermal comfort.•A thermoelectric unit is proposed for personal thermal ...management.•Relationship established between personal energy requirement and thermoelectric energy supply.•Weight minimization of the thermoelectric unit is achieved.
Heating and cooling of buildings consume approximately 15% of all energy used in the United States. Such a large energy demand is primarily due to heating and cooling of the entire building space to temperature setpoints usually between 21.1 °C (70 °F) and 23.9 °C (75 °F). However, even with such a narrow range of temperature setpoints, more than 20% of the occupants do not feel thermally comfortable due to individual differences (e.g. age, gender, clothing, or physiology). The personal thermal management techniques, which create a local thermal envelope around a human body instead of heating or cooling the entire building space, have the potential to greatly reduce the building energy consumption and to enhance thermal comfort of individuals. In this study, a portable thermoelectric energy conversion unit (TECU) that converts electricity into cooling and heating energy is developed. The TECU supplies cool air (in the cooling mode) or warm air (in the heating mode) to regulate the thermal comfort of a human body. The cool or warm air is supplied through a tree-like rubber tube network that is knitted into a thermoregulatory undergarment. To achieve a cooling/heating target that provides satisfactory thermal comfort, the required cooling/heating power supply from the TECU is determined first while a theoretical model is then developed to guide the design of the TECU. To minimize the TECU weight and make it suitable for portable applications, relationships between weight and thermal resistances of commercial off-the-shelf heat sinks are established first, and a method to find the minimal weight of heat sinks for the TECU is then developed. This methodology is also applicable for other applications where heat sink weight needs to be minimized. The thermal manikin tests demonstrate that 24.6 W of personal cooling power and 18.5 W of personal heating power are achieved by using the TECU.
Platinum (Pt)-based catalysts have been unanimously considered the most efficient catalysts for the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells (PEMFCs). Unfortunately, the ...exorbitant cost of Pt hampers the widespread adoption and development of PEMFCs. Scientists have devoted tremendous efforts to achieving higher catalytic activity with less Pt usage by constructing delicate nanostructures. Substituting Pt with cheaper metals may be a feasible solution but suffers from a relatively low intrinsic activity. Recently, single-atom catalysts (SACs), which possess the highest metal utilization and excellent activity because of the minimum size of metal and unique coordination structure, are developing rapidly and have been regarded as a potential alternative to Pt-based materials. Here, we review the development of conventional Pt- and nonprecious-metal-based ORR catalysts and summarize recent achievement in SACs for the ORR. A brief perspective on the remaining challenges and future directions of SACs is also presented.
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Proton-exchange membrane fuel cells (PEMFCs) are now of great interest because of zero emission and high efficiency. Current PEMFCs require an unaffordable amount of Pt-based catalysts to overcome the sluggish kinetics of the oxygen reduction reation (ORR) on cathodes, hampering the widespread adoption of PEMFCs. Tremendous efforts have been devoted to achieving higher catalytic activity with less Pt usage by nanoscale engineering. Substituting Pt with cheaper metals may be also a feasible solution but suffers from low intrinsic activity. Recently, single-atom catalysts (SACs), which possess the highest metal utilization and excellent activity because of the minimum size of metal and unique coordination structure, have been regarded as potential alternatives. Here, we review the development of Pt- and nonprecious-metal-based ORR nanocatalysts and summarize recent achievements in SACs for the ORR. At last, a brief perspective on the remaining challenges and future directions of SACs for the ORR is presented.
Proton-exchange membrane fuel cells (PEMFCs) are considered the ideal devices for direct chemical-to-electrical energy conversion but suffer from the sluggish kinetics of the oxygen reduction reaction (ORR) on cathodes. For an overview of the recent progress in this field, this review introduces the mechanism and electrochemical evaluation of the ORR, elaborates on the development of conventional Pt- and nonprecious-metal-based catalysts for the ORR, summarizes recent achievements in the ORR, and presents the remaining challenges as well as future directions of single-atom catalysts.
We develop a host-guest strategy to construct an electrocatalyst with Fe-Co dual sites embedded on N-doped porous carbon and demonstrate its activity for oxygen reduction reaction in acidic ...electrolyte. Our catalyst exhibits superior oxygen reduction reaction performance, with comparable onset potential (E onset, 1.06 vs 1.03 V) and half-wave potential (E 1/2, 0.863 vs 0.858 V) than commercial Pt/C. The fuel cell test reveals (Fe,Co)/N-C outperforms most reported Pt-free catalysts in H2/O2 and H2/air. In addition, this cathode catalyst with dual metal sites is stable in a long-term operation with 50 000 cycles for electrode measurement and 100 h for H2/air single cell operation. Density functional theory calculations reveal the dual sites is favored for activation of O-O, crucial for four-electron oxygen reduction.
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