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The Rh/BINAPa and ZSM-35(10) co-catalyzed tandem hydroformylation–acetalization of olefins has been developed. A series of olefins with various alcohols performed well in the process, affording the corresponding acetals with high regioselectivities (l/b ≥ 30.5) and excellent catalytic activities (TON of the Rh catalyst up to 4.3 × 104). Control experiments and DFT calculations indicated that the Rh/L11-catalyzed hydroformylation occurred in the solvent outside the molecular sieve, while the acetalization of intermediate aldehydes with alcohols takes place mainly in the interior of the molecular sieve. [ABSTRACT FROM AUTHOR]

A PPh3 modified-chitosan support was synthesized by the acid-mediated addition reaction of the tris(4-vinylphenyl)phosphane ligand (3vPPh3) and chitosan (CS). The material was loaded with Pd(OAc)2 to furnish a supported Pd catalyst (Pd/PPh3-CS), which was characterized by FT-IR, ICP-MS, TGA, XPS, SEM, TEM and N2 adsorption–desorption analysis. The catalyst showed a high catalytic activity, wide substrate compatibility and good recyclability in heterogeneous Suzuki–Miyaura cross coupling reactions. [ABSTRACT FROM AUTHOR]

2D materials are attracting much attention in the field of cathode catalysts for lithium–oxygen batteries (LOBs) due to their layered structure, unique electronic properties, and high stability. However, different stacking layer structures trigger different catalytic capabilities in LOBs. In this work, tin selenide nanosheets with a black phosphorus‐like 2D structure are synthesized and used as the cathode catalyst for LOBs. SnSe nanosheets with exposed stack (200) facets and stack edge facets exhibit superior specific capacity over 20 783 mAh g−1 and ultralong cycle stability over 380 cycles at 500 mA g−1 in LOBs. This demonstrates that the growth of discharge products is mainly concentrated on the 2D surface (200) facets, rather than the stack edge facets. Experimental and theoretical studies reveal that the confined adsorption of Li2O2 on the stack edge facets of SnSe, due to the 2D layer structure and the unique electron distribution, restricts the growth of discharge products. The 2D surface facets of SnSe benefit for the formation and stabilization of LiO2 intermediates, leading to the efficient formation/decomposition of discharge products. The findings provide in‐depth insight into the elusive electrocatalytic mechanism for 2D layer‐structures materials in LOBs. [ABSTRACT FROM AUTHOR]

Highlights: X-ray photoelectron spectroscopy results confirmed the increased number of M–N sites in the bimetallic Fe–Co catalyst. Synchrotron-based X-ray absorption fine structure demonstrated that the interaction in the coordination environments of the different transition metal sites facilitated the CO production in electroreduction reaction of CO2 (ECO2RR). This bimetallic strategy has also been extended to fabricate other catalysts such as Cu–Co and Ni–Co, which also exhibited enhanced performance for ECO2RR. The electroreduction reaction of CO2 (ECO2RR) requires high-performance catalysts to convert CO2 into useful chemicals. Transition metal-based atomically dispersed catalysts are promising for the high selectivity and activity in ECO2RR. This work presents a series of atomically dispersed Co, Fe bimetallic catalysts by carbonizing the Fe-introduced Co-zeolitic-imidazolate-framework (C–Fe–Co–ZIF) for the syngas generation from ECO2RR. The synergistic effect of the bimetallic catalyst promotes CO production. Compared to the pure C–Co–ZIF, C–Fe–Co–ZIF facilitates CO production with a CO Faradaic efficiency (FE) boost of 10%, with optimal FECO of 51.9%, FEH2 of 42.4% at − 0.55 V, and CO current density of 8.0 mA cm−2 at − 0.7 V versus reversible hydrogen electrode (RHE). The H2/CO ratio is tunable from 0.8 to 4.2 in a wide potential window of − 0.35 to − 0.8 V versus RHE. The total FECO+H2 maintains as high as 93% over 10 h. The proper adding amount of Fe could increase the number of active sites and create mild distortions for the nanoscopic environments of Co and Fe, which is essential for the enhancement of the CO production in ECO2RR. The positive impacts of Cu–Co and Ni–Co bimetallic catalysts demonstrate the versatility and potential application of the bimetallic strategy for ECO2RR. [ABSTRACT FROM AUTHOR]

The electrochemical oxygen evolution reaction (OER) is an important half‐cell reaction in many renewable energy conversion and storage technologies, including electrolyzers, nitrogen fixation, CO2 reduction, metal‐air batteries, and regenerative fuel cells. Among them, proton exchange membrane (PEM)‐based devices exhibit a series of advantages, such as excellent proton conductivity, high durability, and good mechanical strength, and have attracted global interest as a green energy device for transport and stationary sectors. Nevertheless, with a view to rapid commercialization, it is urgent to develop highly active and acid‐stable OER catalysts for PEM‐based devices. In this Review, based on the recent advances in theoretical calculation and in situ/operando characterization, the OER mechanism in acidic conditions is first discussed in detail. Subsequently, recent advances in the development of several types of acid‐stable OER catalysts, including noble metals, non‐noble metals, and even metal‐free OER materials, are systematically summarized. Finally, the current key issues and future challenges for materials used as acidic OER catalysis are identified and potential future directions are proposed. [ABSTRACT FROM AUTHOR]

An Fe/N/C catalyst derived from the pyrolysis of metal–organic frameworks, for example, a zeolitic‐imidazolate‐framework‐8 (ZIF‐8), has been regarded as one of the most promising non‐precious metal catalysts toward oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, its ORR mass activity is still much inferior to that of Pt, partly because of the lack of general and efficient synthetic strategies. Herein, a general carboxylate‐assisted strategy that dramatically enhances the ORR mass activity of ZIF‐derived Fe/N/C catalysts is reported. The carboxylate is found to promote the formation of Fe/N/C catalysts with denser accessible active sites and entangled carbon nanotubes, as well as a higher mesoporosity. These structural advantages make the carboxylate‐assisted Fe/N/C catalysts show a 2–10 fold higher ORR mass activity than the common carboxylate‐free one in various cases. When applied in H2–O2 PEMFCs, the active acetate‐assisted Fe/N/C catalyst generates a peak power density of 1.33 W cm−2, a new record of peak power density for a H2–O2 PEMFC with non‐Pt ORR catalysts. [ABSTRACT FROM AUTHOR]

The worldwide fossil fuel shortage and resultant environmental issues urgently require renewable and clean energy technologies. Electrocatalytic oxygen reduction/evolution reactions (ORR/OER) are the cornerstone for renewable energy conversion and storage devices, such as fuel cells, electrolyzers, unitized regenerative fuel cells, and metal‐air batteries. High‐performance electrocatalysts are required to improve the ORR and OER activity and stability, and thus the device performance. Therefore, appropriate strategies and methods are crucial for the rational design and synthesis of highly efficient ORR/OER electrocatalysts. On the other hand, the conventional platinum‐group‐metal‐based (PGM‐based) catalysts, such as Pt and Ir/Ru (oxides), have been facing great challenges, including limited resources and high cost, leading to them being less competitive in the market. Thus, a lot of effort has been devoted to developing alternative PGM‐free ORR/OER catalysts, which, however, still suffer from low activity and insufficient stability. In this review paper, the strategies for engineering high‐performance PGM‐free ORR and OER electrocatalysts are discussed by reviewing the most recent advances. At the end, perspectives on the methods to rationally design PGM‐free ORR and OER catalysts are provided. [ABSTRACT FROM AUTHOR]

Highlights: All the important single-atom catalysts (SACs) synthetic strategies, such as wet-chemistry method, atomic layer deposition, metal–organic framework-derived method, electrodeposition, high-temperature atom trapping from bulk particles, and vacancies/defects immobilized strategy, have been summarized and discussed in detail. Various metal-based (especially Pt, Pd, Ru, Fe, Co, Ni, Mo, W, V) SACs in electrocatalytic hydrogen evolution reaction (HER) have been systematically reviewed. The current key challenges in SACs for electrochemical HER are pointed out, and some potential strategies/perspectives are proposed. Hydrogen, a renewable and outstanding energy carrier with zero carbon dioxide emission, is regarded as the best alternative to fossil fuels. The most preferred route to large-scale production of hydrogen is by water electrolysis from the intermittent sources (e.g., wind, solar, hydro, and tidal energy). However, the efficiency of water electrolysis is very much dependent on the activity of electrocatalysts. Thus, designing high-effective, stable, and cheap materials for hydrogen evolution reaction (HER) could have a substantial impact on renewable energy technologies. Recently, single-atom catalysts (SACs) have emerged as a new frontier in catalysis science, because SACs have maximum atom-utilization efficiency and excellent catalytic reaction activity. Various synthesis methods and analytical techniques have been adopted to prepare and characterize these SACs. In this review, we discuss recent progress on SACs synthesis, characterization methods, and their catalytic applications. Particularly, we highlight their unique electrochemical characteristics toward HER. Finally, the current key challenges in SACs for HER are pointed out and some potential directions are proposed as well. [ABSTRACT FROM AUTHOR]

Fluorination is considered as a means of reducing the degradation of Fe/N/C, a highly active FeNx-doped disorganized carbon catalyst for the oxygen reduction reaction (ORR) in PEM fuel cells. Our recent experiments have, however, revealed that fluorination poisons the FeNx moiety of the Fe/N/C catalytic site, considerably reducing the activity of the resulting catalyst to that of carbon only doped with nitrogen. Using the density functional theory (DFT), we clarify in this work the mechanisms by which fluorine interacts with the catalyst. We studied 10 possible FeNx site configurations as well as 2 metal-free sites in the absence or presence of fluorine molecules and atoms. When the FeNx moiety is located on a single graphene layer accessible on both sides, we found that fluorine binds strongly to Fe but that two F atoms, one on each side of the FeNx plane, are necessary to completely inhibit the catalytic activity of the FeNx sites. When considering the more realistic model of a stack of graphene layers, only one F atom is needed to poison the FeNx moiety on the top layer since ORR hardly takes place between carbon layers. We also found that metal-free catalytic N-sites are immune to poisoning by fluorination, in accordance with our experiments. Finally, we explain how most of the catalytic activity can be recovered by heating to 900 °C after fluorination. This research helps to clarify the role of metallic sites compared to non-metallic ones upon the fluorination of FeNx-doped disorganized carbon catalysts. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) is one of the end products of fuel combustion and the major component of the greenhouse gases. The reduction of atmospheric CO2 not only decreases environmental pollution but also produces value‐added chemicals, solving energy and environment issues simultaneously. One significant challenge is the low conversion efficiency of CO2 reduction due to the inertness of the CO2 molecule. The design of the catalyst nanomaterials with the high selectivity, stability, and the activation capabilities for the conversion of CO2 is needed. Atomic layer deposition (ALD), capable of constructing catalysts with atomic‐level precision in a highly controllable manner, is a promising technique to address the key problems in CO2 reduction. This review explores the application of ALD in CO2 reduction, emphasizing the designs of the efficient catalyst nanomaterials fabricated by the ALD technique and their applications in CO2 reduction and capture. The significance of the ALD catalysts with the fine structures is highlighted to obtain a better understanding of the catalytic performance–aimed benefits as well as an outlook on the ALD‐designed catalysts for the reduction of CO2. [ABSTRACT FROM AUTHOR]

The electrocatalytic oxygen reactions, i.e. oxygen reduction/evolution reactions (ORR/OER), play a key role in electrochemical energy conversion and storage devices, including fuel cells, electrolyzers, and metal-air batteries, and have attracted significant attention in the past decades. Platinum-group metal (PGM)-free materials have been intensively investigated as alternatives to replace the well-accepted but costly PGM-based catalysts such as Pt for ORR and Ir/Ru (oxides) for OER. Particularly, metal-organic framework (MOF)-derived carbon materials are emerging PGM-free catalysts for ORR/OER. So far, excellent works have been achieved to enhance the activity and durability of the MOF-derived PGM-free catalysts. It is the occasion to promote the PGM-free catalysts to the next level of application, i.e. in real devices. However, ORR/OER in real devices are potentially subject to the porosity related challenges, e.g. electron/mass transfer issue and active site isolation in organic Li-air batteries. To address these challenges, the rational design of porous electrocatalyst for devices is required. In this review, we summarize the most recent progress of MOF-derived carbon materials for ORR/OER with the focus on not only the active site engineering but also the design of porous structure. We also provide perspectives on the rational design of PGM-free catalysts using MOF as precursors. Image 102 [ABSTRACT FROM AUTHOR]

The graphene-supported Na2Ta8O21-x electrocatalyst (50 wt% Ta2O5, 50 wt% graphene) is obtained by sonicating graphene in an aqueous TaCl5 solution at pH 10.9 (adjusted with NaOH) followed by drying and heating under Ar (900 °C, 90 min). [ABSTRACT FROM AUTHOR]

Electrochemical CO 2 reduction reaction (ECO 2 RR) offers an opportunity to sustainably convert CO 2 into value-added fuels and chemicals by using the electricity that could be generated by renewable energies. Recently, enormous efforts are focused on the development of metal-based catalysts for the selective ECO 2 RR with high efficiency. Multi-metallic catalyst design emerges as one of the most promising strategies for the promotion of the Faradaic efficiency (FE), the current density, and the lowering of the overpotential of the catalysts for ECO 2 RR. The synergistic effects of the different metal sites in the hybrid catalysts are of significance for the enhancement of the ECO 2 RR performance. This review summarizes the rational design of multi-metallic catalysts, including alloy, atomically dispersed multi-metallic sites, and others, along with the popular metal elements studied in multi-metallic catalysts to clarify the advantages of different metal elements for ECO 2 RR. The density functional theory (DFT) simulations and advanced in-situ characterizations that contribute to demystifying the synergies between metal elements are highlighted. Challenges and outlook concerning the catalyst design and reaction mechanism of multi-metallic catalysts for ECO 2 RR are also discussed. • A review of the multi-metallic catalysts for the electroreduction of CO 2 is reported. • The catalyst design of multi-metallic catalysts and the popular metal elements are illustrated. • The advantages of multi-metallic catalysts for the electroreduction of CO 2 are discussed. • Future perspectives regarding multi-metallic catalysts for the electroreduction of CO 2 are presented. [ABSTRACT FROM AUTHOR]

A novel atomically dispersed Pt into SnO 2 nanocatalyst has been designed by a facile hydrothermal crystallization process to achieve high selective electrochemical reduction of CO 2. Such catalyst can could induce charge redistribution and the formed low-coordinated Pt atoms tune the product selectivity, resulting in the high Faradaic efficiency of HCOOH of 82.1% at −1.2 V vs. RHE. [Display omitted] • Atomically dispersed Pt into SnO 2 nanocatalyst (Pt atom/SnO 2). • Pt atom/SnO 2 promotes the adsorption of intermediates CO 2 *, HCOO* and HCOOH*. • Pt atom/SnO 2 facilitates the conversion of CO 2 to HCOO* rather than HER. • FE HCOO - reaches 82.1% on the obtained sample at −1.2 V vs. RHE. Electrochemical reduction of CO 2 into fuels offers an attractive approach to environmental and energy sustainability. Herein, we designed atomically dispersed Pt into SnO 2 catalyst (Pt atom/SnO 2). Such catalyst dramatically improves the adsorption performance of CO 2 and lowers the activation energy of CO 2. DFT calculations indicate that the doping of Pt in SnO 2 could induce charge redistribution and tune active electronic state, showing higher adsorption energy for intermediates CO 2 *, HCOO* and HCOOH*, which is different from the Pt NPs loaded SnO 2 mainly for H 2 generation. As a result, a higher Faradaic efficiency (82.1 ± 1.4%) and the production rate (5105 μmol h−1 cm−2) of HCOO– are achieved at −1.2 V vs. RHE. Moreover, the current density and Faradaic efficiency of HCOO– nearly remain unchanged in 8 h on the Pt atom/SnO 2 , indicating its high stability. This work opens up a new avenue to tune product selectivity by atomically dispersed catalysts. [ABSTRACT FROM AUTHOR]

• Recent developments of regenerative fuel cells (RFC) are reviewed. • Recent progress and challenges in unitized RFC (URFC) are discussed. • Applications of URFC in space energy storage and transportation are summarized. • Challenges and future perspectives for RFC in space application are highlighted. Energy storage and transportation technologies play an important role in space exploration missions. Regenerative fuel cells are among the most promising sustainable energy power sources. Compared to secondary batteries, regenerative fuel cells possess unique advantages, including high power density, high specific energy density, light-weight, low-cost, high-efficiency, long-life, and zero environmental impact. More importantly, an regenerative fuel cell is an electrochemical device that can collect and store solar energy during the daytime and release it gradually whenever is needed, making energy available 24/7. Therefore, the development of high-performance regenerative fuel cells in the aerospace sector is becoming more and more important. Herein, in this review, various types of fuel cells are briefly introduced, followed by a detailed discussion and comparison between different unitized regenerative fuel cells. Electrocatalysts and membranes are two of the essential components in the unitized regenerative fuel cells that play a key role in enhancing the system's efficiency. Thus, recent progress and challenges on bifunctional hydrogen and oxygen electrodes are systematically summarized and discussed, respectively. More importantly, the progress and challenges of proton and anion electrolyte membranes are discussed. Further, power performance and durability are two important measures for the application of regenerative fuel cells in space energy systems. Therefore, the current progress of fuel cells in power performance and durability are summarized and discussed. In the end, the key issues and future perspectives of unitized regenerative fuel cells toward space energy storage and transportation are presented. [ABSTRACT FROM AUTHOR]