Showing papers on "Catalysis published in 2022"

Engineering Dual Single‐Atom Sites on 2D Ultrathin N‐doped Carbon Nanosheets Attaining Ultra‐Low Temperature Zn‐Air Battery

Abstract: Herein, a novel dual single-atom catalyst comprising adjacent Fe-N4 and Mn-N4 sites on 2D ultrathin N-doped carbon nanosheets with porous structure (FeMn-DSAC) was constructed as the cathode for a flexible low-temperature Zn-air battery (ZAB). FeMn-DSAC exhibits remarkable bifunctional activities for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Control experiments and density functional theory calculations reveal that the catalytic activity arises from the cooperative effect of the Fe/Mn dual-sites aiding *OOH dissociation as well as the porous 2D nanosheet structure promoting active sits exposure and mass transfer during the reaction process. The excellent bifunctional activity of FeMn-DSAC enables the ZAB to operate efficiently at ultra-low temperature of -40 °C, delivering 30 mW cm-2 peak power density and retaining up to 86 % specific capacity from the room temperature counterpart.

Regulations of active moiety in single atom catalysts for electrochemical hydrogen evolution reaction

Abstract: Hydrogen production from water splitting using renewable electric energy is an interesting topic towards the carbon neutral future. Single atom catalysts (SACs) have emerged as a new frontier in the field of catalysis such as hydrogen evolution reaction (HER), owing to their intriguing properties like high activity and excellent chemical selectivity. The catalytic active moiety is often comprised of a single metal atom and its neighboring environment from the supports. Recent published reviews about electricdriven HER tend to classify these SACs by the species of active center atom, nevertheless the influence of their neighboring coordinated atoms from the supports is somehow neglected. Thus we classify the SACs for HER through the type of supports, highlighting the electronic metal-support interaction and their coordination environment from support. Then, we put forward some structural designing strategies including regulating of the central atoms, coordination environments, and metal-support interactions. Finally, the current challenges and future research perspectives of SACs for HER are briefly proposed.

Crystalline‐Amorphous Interfaces Coupling of CoSe2/CoP with Optimized d‐Band Center and Boosted Electrocatalytic Hydrogen Evolution

Abstract: Amorphous and heterojunction materials have been widely used in the field of electrocatalytic hydrogen evolution due to their unique physicochemical properties. However, the current used individual strategy still has limited effects. Hence efficient tailoring tactics with synergistic effect are highly desired. Herein, the authors have realized the deep optimization of catalytic activity by a constructing crystalline–amorphous CoSe2/CoP heterojunction. Benefiting from the strong electronic coupling at the interfaces, the d‐band center of the material moves further down compared to its crystalline–crystalline counterpart, optimizing the valence state and the H adsorption of Co and lowering the kinetic barrier of hydrogen evolution reaction (HER). The heterojunction shows an overpotential of 65 mV to drive a current density of 10 mA cm−2 in the acidic medium. Besides, it also shows competitive properties in both neutral and basic media. This work provides inspiration for optimizing the catalytic activity through combining a crystalline and amorphous heterojunction, which can be implemented for other transition metal compound electrocatalysts.

Atomically Dispersed Fe–Co Dual Metal Sites as Bifunctional Oxygen Electrocatalysts for Rechargeable and Flexible Zn–Air Batteries

Abstract: Single-metal site catalysts have exhibited highly efficient electrocatalytic properties due to their unique coordination environments and adjustable local structures for reactant adsorption and electron transfer. They have been widely studied for many electrochemical reactions, including oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, it remains a significant challenge to realize high-efficiency bifunctional catalysis (ORR/OER) with single-metal-type active sites. Herein, we report atomically dispersed Fe–Co dual metal sites (FeCo–NC) derived from Fe and Co co-doped zeolitic imidazolate frameworks (ZIF-8s), aiming to build up multiple active sites for bifunctional ORR/OER catalysts. The atomically dispersed FeCo–NC catalyst shows excellent bifunctional catalytic activity in alkaline media for the ORR (E1/2 = 0.877 V) and the OER (Ej=10 = 1.579 V). Moreover, its outstanding stability during the ORR and the OER is comparable to noble-metal catalysts (Pt/C and RuO2). The atomic dispersion state, coordination structure, and the charge density difference of the dual metal site FeCo–NC were characterized and determined using advanced physical characterization and density functional theory (DFT) calculations. The FeCo–N6 moieties are likely the main active sites simultaneously for the ORR and the OER with improved performance relative to the traditional single Fe and Co site catalysts. We further incorporated the FeCo–NC catalyst into an air electrode for fabricating rechargeable and flexible Zn–air batteries, generating a superior power density (372 mW cm–2) and long-cycle (over 190 h) stability. This work would provide a method to design and synthesize atomically dispersed multi-metal site catalysts for advanced electrocatalysis.

Porphyrin-based Framework Materials for Energy Conversion

Abstract: With the increasing demand for fuel causing serious environmental pollution, it is urgent to develop new and environmentally friendly energy conversion devices. These energy conversion devices, however, require good, inexpensive materials for electrodes and so on. The multifunctional properties of porphyrins enable framework materials (e.g., metal-organic frameworks and covalent organic frameworks) to be applied in energy conversion devices due to their simple synthesis, high chemical stability, abundant metallic active sites, adjustable crystalline structure and high specific surface area. Herein, the types of porphyrin structural blocks are briefly reviewed. They can be used as organic ligands or directly assembled with framework materials to generate high-performance electro-/photo-catalysts. These types of catalysts applied in electro-/photo-catalytic water splitting, electro-/photo-catalytic carbon dioxide reduction, and electrocatalytic oxygen reduction are also summarized and introduced. At the end of the article, we present the challenges of porphyrin-based framework materials in the above application and corresponding solutions. We expect porphyrin-based framework materials to flourish energy conversion in the coming years.

High-efficiency electrocatalytic NO reduction to NH 3 by nanoporous VN

Abstract: Electrocatalytic NO reduction reaction to generate NH₃ under ambient conditions offers an attractive alternative to the energy-extensive Haber–Bosch route; however, the challenge still lies in the development of cost-effective and high-performance electrocatalysts. Herein, nanoporous VN film is first designed as a highly selective and stable electrocatalyst for catalyzing reduction of NO to NH₃ with a maximal Faradaic efficiency of 85% and a peak yield rate of 1.05 × 10^–7 mol·cm^–2·s^–1 (corresponding to 5,140.8 μg·h^–1·mg_cat.^–1) at –0.6 V vs. reversible hydrogen electrode in acid medium. Meanwhile, this catalyst maintains an excellent activity with negligible current density and NH₃ yield rate decays over 40 h. Moreover, as a proof-of-concept of Zn–NO battery, it delivers a high power density of 2.0 mW·cm^–2 and a large NH₃ yield rate of 0.22 × 10^–7 mol·cm^–2·s^–1 (corresponding to 1,077.1 μg·h^–1·mg_cat.^–1), both of which are comparable to the best-reported results. Theoretical analyses confirm that the VN surface favors the activation and hydrogenation of NO by suppressing the hydrogen evolution. This work highlights that the electrochemical NO reduction is an eco-friendly and energy-efficient strategy to produce NH₃.

Protruding Pt single-sites on hexagonal ZnIn2S4 to accelerate photocatalytic hydrogen evolution

Abstract: Abstract Single-site cocatalysts engineered on supports offer a cost-efficient pathway to utilize precious metals, yet improving the performance further with minimal catalyst loading is still highly desirable. Here we have conducted a photochemical reaction to stabilize ultralow Pt co-catalysts (0.26 wt%) onto the basal plane of hexagonal ZnIn 2 S 4 nanosheets (Pt SS -ZIS) to form a Pt-S 3 protrusion tetrahedron coordination structure. Compared with the traditional defect-trapped Pt single-site counterparts, the protruding Pt single-sites on h -ZIS photocatalyst enhance the H 2 evolution yield rate by a factor of 2.2, which could reach 17.5 mmol g −1 h −1 under visible light irradiation. Importantly, through simple drop-casting, a thin Pt SS -ZIS film is prepared, and large amount of observable H 2 bubbles are generated, providing great potential for practical solar-light-driven H 2 production. The protruding single Pt atoms in Pt SS -ZIS could inhibit the recombination of electron-hole pairs and cause a tip effect to optimize the adsorption/desorption behavior of H through effective proton mass transfer, which synergistically promote reaction thermodynamics and kinetics.

Ambient Ammonia Synthesis via Electrochemical Reduction of Nitrate Enabled by NiCo2 O4 Nanowire Array.

Abstract: NiCo2 O4 nanowire array on carbon cloth (NiCo2 O4 /CC) is proposed as a highly active electrocatalyst for ambient nitrate (NO3 - ) reduction to ammonia (NH3 ). In 0.1 m NaOH solution with 0.1 m NaNO3 , such NiCo2 O4 /CC achieves a high Faradic efficiency of 99.0% and a large NH3 yield up to 973.2 µmol h-1 cm-2 . The superior catalytic activity of NiCo2 O4 comes from its half-metal feature and optimized adsorption energy due to the existence of Ni in the crystal structure. A Zn-NO3 - battery with NiCo2 O4 /CC cathode also shows a record-high battery performance.

Emerging low-nuclearity supported metal catalysts with atomic level precision for efficient heterogeneous catalysis

Abstract: Supported atomically dispersed metal catalysts (ADMCs) have received enormous attention due to their high atom utilization efficiency, mass activity and excellent selectivity. Single-atom site catalysts (SACs) with monometal-center as the quintessential ADMCs have been extensively studied in the catalysis-related fields. Beyond SACs, novel atomically dispersed metal catalysts (NADMCs) with flexible active sites featuring two or more catalytically centers including dual-atom and triple-atom catalysts have drawn ever-increasing attention recently. Owing to the presence of multiple neighboring active sites, NADMCs could exhibit much higher activity and selectivity compared with SACs, especially in those complicated reactions with multi-step intermediates. This review comprehensively outlines the recent exciting advances on the NADMCs with emphasis on the deeper understanding of the synergistic interactions among multiple metal atoms and underlying structure–performance relationships. It starts with the systematical introduction of principal synthetic approaches for NADMCs highlighting the key issues of each fabrication method including the atomically precise control in the design of metal nuclearity, and then the state-of-the-art characterizations for identifying and monitoring the atomic structure of NADMCs are explored. Thereafter, the recent development of NADMCs in energy-related applications is systematically discussed. Finally, we provide some new insights into the remaining challenges and opportunities for the development of NADMCs.

High loading of single atomic iron sites in Fe–NC oxygen reduction catalysts for proton exchange membrane fuel cells

Abstract: Non-precious iron-based catalysts (Fe–NCs) require high active site density to meet the performance targets as cathode catalysts in proton exchange membrane fuel cells. Site density is generally limited to that achieved at a 1–3 wt%(Fe) loading due to the undesired formation of iron-containing nanoparticles at higher loadings. Here we show that by preforming a carbon–nitrogen matrix using a sacrificial metal (Zn) in the initial synthesis step and then exchanging iron into this preformed matrix we achieve 7 wt% iron coordinated solely as single-atom Fe–N4 sites, as identified by 57Fe cryogenic Mössbauer spectroscopy and X-ray absorption spectroscopy. Site density values measured by in situ nitrite stripping and ex situ CO chemisorption methods are 4.7 × 1019 and 7.8 × 1019 sites g−1, with a turnover frequency of 5.4 electrons sites−1 s−1 at 0.80 V in a 0.5 M H2SO4 electrolyte. The catalyst delivers an excellent proton exchange membrane fuel cell performance with current densities of 41.3 mA cm−2 at 0.90 ViR-free using H2–O2 and 145 mA cm−2 at 0.80 V (199 mA cm−2 at 0.80 ViR-free) using H2–air.

Splicing the active phases of copper/cobalt-based catalysts achieves high-rate tandem electroreduction of nitrate to ammonia

Abstract: Electrocatalytic recycling of waste nitrate (NO3-) to valuable ammonia (NH3) at ambient conditions is a green and appealing alternative to the Haber-Bosch process. However, the reaction requires multi-step electron and proton transfer, making it a grand challenge to drive high-rate NH3 synthesis in an energy-efficient way. Herein, we present a design concept of tandem catalysts, which involves coupling intermediate phases of different transition metals, existing at low applied overpotentials, as cooperative active sites that enable cascade NO3--to-NH3 conversion, in turn avoiding the generally encountered scaling relations. We implement the concept by electrochemical transformation of Cu-Co binary sulfides into potential-dependent core-shell Cu/CuOx and Co/CoO phases. Electrochemical evaluation, kinetic studies, and in-situ Raman spectra reveal that the inner Cu/CuOx phases preferentially catalyze NO3- reduction to NO2-, which is rapidly reduced to NH3 at the nearby Co/CoO shell. This unique tandem catalyst system leads to a NO3--to-NH3 Faradaic efficiency of 93.3 ± 2.1% in a wide range of NO3- concentrations at pH 13, a high NH3 yield rate of 1.17 mmol cm-2 h-1 in 0.1 M NO3- at -0.175 V vs. RHE, and a half-cell energy efficiency of ~36%, surpassing most previous reports.

Electrocatalysis in Alkaline Media and Alkaline Membrane-Based Energy Technologies.

Abstract: Hydrogen energy-based electrochemical energy conversion technologies offer the promise of enabling a transition of the global energy landscape from fossil fuels to renewable energy. Here, we present a comprehensive review of the fundamentals of electrocatalysis in alkaline media and applications in alkaline-based energy technologies, particularly alkaline fuel cells and water electrolyzers. Anion exchange (alkaline) membrane fuel cells (AEMFCs) enable the use of nonprecious electrocatalysts for the sluggish oxygen reduction reaction (ORR), relative to proton exchange membrane fuel cells (PEMFCs), which require Pt-based electrocatalysts. However, the hydrogen oxidation reaction (HOR) kinetics is significantly slower in alkaline media than in acidic media. Understanding these phenomena requires applying theoretical and experimental methods to unravel molecular-level thermodynamics and kinetics of hydrogen and oxygen electrocatalysis and, particularly, the proton-coupled electron transfer (PCET) process that takes place in a proton-deficient alkaline media. Extensive electrochemical and spectroscopic studies, on single-crystal Pt and metal oxides, have contributed to the development of activity descriptors, as well as the identification of the nature of active sites, and the rate-determining steps of the HOR and ORR. Among these, the structure and reactivity of interfacial water serve as key potential and pH-dependent kinetic factors that are helping elucidate the origins of the HOR and ORR activity differences in acids and bases. Additionally, deliberately modulating and controlling catalyst-support interactions have provided valuable insights for enhancing catalyst accessibility and durability during operation. The design and synthesis of highly conductive and durable alkaline membranes/ionomers have enabled AEMFCs to reach initial performance metrics equal to or higher than those of PEMFCs. We emphasize the importance of using membrane electrode assemblies (MEAs) to integrate the often separately pursued/optimized electrocatalyst/support and membranes/ionomer components. Operando/in situ methods, at multiscales, and ab initio simulations provide a mechanistic understanding of electron, ion, and mass transport at catalyst/ionomer/membrane interfaces and the necessary guidance to achieve fuel cell operation in air over thousands of hours. We hope that this Review will serve as a roadmap for advancing the scientific understanding of the fundamental factors governing electrochemical energy conversion in alkaline media with the ultimate goal of achieving ultralow Pt or precious-metal-free high-performance and durable alkaline fuel cells and related technologies.

High-entropy nanoparticles: Synthesis-structure-property relationships and data-driven discovery

Abstract: High-entropy nanoparticles have become a rapidly growing area of research in recent years. Because of their multielemental compositions and unique high-entropy mixing states (i.e., solid-solution) that can lead to tunable activity and enhanced stability, these nanoparticles have received notable attention for catalyst design and exploration. However, this strong potential is also accompanied by grand challenges originating from their vast compositional space and complex atomic structure, which hinder comprehensive exploration and fundamental understanding. Through a multidisciplinary view of synthesis, characterization, catalytic applications, high-throughput screening, and data-driven materials discovery, this review is dedicated to discussing the important progress of high-entropy nanoparticles and unveiling the critical needs for their future development for catalysis, energy, and sustainability applications. Description BACKGROUND High-entropy nanoparticles contain more than four elements uniformly mixed into a solid-solution structure, offering opportunities for materials discovery, property optimization, and advanced applications. For example, the compositional flexibility of high-entropy nanoparticles enables fine-tuning of the catalytic activity and selectivity, and high-entropy mixing offers structural stability under harsh operating conditions. In addition, the multielemental synergy in high-entropy nanoparticles provides a diverse range of adsorption sites, which is ideal for multistep tandem reactions or reactions that require multifunctional catalysts. However, the wide range of possible compositions and complex atomic arrangements also create grand challenges in synthesizing, characterizing, understanding, and applying high-entropy nanoparticles. For example, controllable synthesis is challenging given the different physicochemical properties within the multielemental compositions combined with the small size and large surface area. Moreover, random multielemental mixing can make it difficult to precisely characterize the individual nanoparticles and their statistical variations. Without rational understanding and guidance, efficient compositional design and performance optimization within the huge multielemental space is nearly impossible. ADVANCES The comprehensive study of high-entropy nanoparticles has become feasible because of the rapid development of synthetic approaches, high-resolution characterization, high-throughput experimentation, and data-driven discovery. A diverse range of compositions and material libraries have been developed, many by using nonequilibrium “shock”–based methods designed to induce single-phase mixing even for traditionally immiscible elemental combinations. The nanomaterial types have also rapidly evolved from crystalline metallic alloys to metallic glasses, oxides, sulfides, phosphates, and others. Advanced characterization tools have been used to uncover the structural complexities of high-entropy nanoparticles. For example, atomic electron tomography has been used for single-atom-level resolution of the three-dimensional positions of the elements and their chemical environments. Finally, high-entropy nanoparticles have already shown promise in a wide range of catalysis and energy technologies because of their atomic structure and tunable electronic states. The development of high-throughput computational and experimental methods can accelerate the material exploration rate and enable machine-learning tools that are ideal for performance prediction and guided optimization. Materials discovery platforms, such as high-throughput exploration and data mining, may disruptively supplant conventional trial-and-error approaches for developing next-generation catalysts based on high-entropy nanoparticles. OUTLOOK High-entropy nanoparticles provide an enticing material platform for different applications. Being at an initial stage, enormous opportunities and grand challenges exist for these intrinsically complex materials. For the next stage of research and applications, we need (i) the controlled synthesis of high-entropy nanoparticles with targeted surface compositions and atomic arrangements; (ii) fundamental studies of surfaces, ordering, defects, and the dynamic evolution of high-entropy nanoparticles under catalytic conditions through precise structural characterization; (iii) identification and understanding of the active sites and performance origin (especially the enhanced stability) of high-entropy nanoparticles; and (iv) high-throughput computational and experimental techniques for rapid screening and data mining toward accelerated exploration of high-entropy nanoparticles in a multielemental space. We expect that discoveries about the synthesis-structure-property relationships of high-entropy nanoparticles and their guided discovery will greatly benefit a range of applications for catalysis, energy, and sustainability. High-entropy nanoparticles and data-driven discovery. Emerging high-entropy nanoparticles feature multielemental mixing within a large compositional space and can be used for diverse applications, particularly for catalysis. High-throughput and machine-learning tools, coupled with advanced characterization techniques, can substantially accelerate the optimization of these high-entropy nanoparticles, forming a closed-loop paradigm toward data-driven discovery. CREDITS: TOP RIGHT: YANG ET AL., NATURE 592, 60–64 (2021); CENTER: JIAQI DAI; BOTTOM RIGHT: XIE ET AL., NAT. COMMUN.10, 4011 (2019) Diversifying nanoparticles Multielement nanoparticles are attractive for a variety of applications in catalysis, energy, and other fields. A more diverse range and larger number of elements can be mixed together because of high-entropy mixing states accessed by a number of recently developed techniques. Yao et al. review these techniques along with characterization methods, high-throughput screening, and data-driven discovery for targeted applications. The wide range of different elements that can be mixed together presents a large number of opportunities and challenges. —BG A review highlights improvements in synthesizing and stabilizing multielement nanoparticles.

Molecularly Engineered Covalent Organic Frameworks for Hydrogen Peroxide Photosynthesis

Abstract: Abstract Synthesizing H2O2 from water and air via a photocatalytic approach is ideal for efficient production of this chemical at small‐scale. However, the poor activity and selectivity of the 2 e− water oxidation reaction (WOR) greatly restricts the efficiency of photocatalytic H2O2 production. Herein we prepare a bipyridine‐based covalent organic framework photocatalyst (denoted as COF‐TfpBpy) for H2O2 production from water and air. The solar‐to‐chemical conversion (SCC) efficiency at 298 K and 333 K is 0.57 % and 1.08 %, respectively, which are higher than the current reported highest value. The resulting H2O2 solution is capable of degrading pollutants. A mechanistic study revealed that the excellent photocatalytic activity of COF‐TfpBpy is due to the protonation of bipyridine monomer, which promotes the rate‐determining reaction (2 e− WOR) and then enhances Yeager‐type oxygen adsorption to accelerate 2 e− one‐step oxygen reduction. This work demonstrates, for the first time, the COF‐catalyzed photosynthesis of H2O2 from water and air; and paves the way for wastewater treatment using photocatalytic H2O2 solution.

Confining and Highly Dispersing Single Polyoxometalate Clusters in Covalent Organic Frameworks by Covalent Linkages for CO2 Photoreduction.

Abstract: Single clusters have attracted extensive research interest in the field of catalysis. However, achieving a highly uniform dispersion of a single-cluster catalyst is challenging. In this work, for the first time, we present a versatile strategy for uniformly dispersed polyoxometalates (POMs) in covalent organic frameworks (COFs) through confining POM cluster into the regular nanopores of COF by a covalent linkage. These COF-POM composites combine the properties of light absorption, electron transfer, and suitable catalytic active sites; as a result, they exhibit outstanding catalytic activity in artificial photosynthesis: that is, CO2 photoreduction with H2O as the electron donor. Among them, TCOF-MnMo6 achieved the highest CO yield (37.25 μmol g-1 h-1 with ca. 100% selectivity) in a gas-solid reaction system. Furthermore, a mechanism study based on density functional theory (DFT) calculations demonstrated that the photoinduced electron transfer (PET) process occurs from the COF to the POM, and then CO2 reduction and H2O oxidation occur on the POM and COF, respectively. This work developed a method for a uniform dispersion of POM single clusters into a COF, which also shows the potential of using COF-POM functional materials in the field of photocatalysis.