Atomically dispersed single-atom catalysts have the potential to bridge heterogeneous and homogeneous catalysis. Dozens of single-atom catalysts have been developed, and they exhibit notable ...catalytic activity and selectivity that are not achievable on metal surfaces. Although promising, there is limited knowledge about the boundaries for the monometallic single-atom phase space, not to mention multimetallic phase spaces. Here, single-atom catalysts based on 37 monometallic elements are synthesized using a dissolution-and-carbonization method, characterized and analysed to build the largest reported library of single-atom catalysts. In conjunction with in situ studies, we uncover unified principles on the oxidation state, coordination number, bond length, coordination element and metal loading of single atoms to guide the design of single-atom catalysts with atomically dispersed atoms anchored on N-doped carbon. We utilize the library to open up complex multimetallic phase spaces for single-atom catalysts and demonstrate that there is no fundamental limit on using single-atom anchor sites as structural units to assemble concentration-complex single-atom catalyst materials with up to 12 different elements. Our work offers a single-atom library spanning from monometallic to concentration-complex multimetallic materials for the rational design of single-atom catalysts.
Modulating the coordination environment of active sites on catalyst surfaces is crucial to developing effective catalysts and controlling catalysis. However, this may be a highly challenging ...procedure. Guided by the first‐principles calculations, the modification of the coordination environment of active sites on MoC nanoparticle surfaces is experimentally accomplished by anchoring pyridinic N atom rings of holey graphene on Mo atoms. The rings produce electrostatic forces that enable the tuning of the Mo sites′ affinity to reaction intermediates, which passivates Mo hollow sites, activates Mo top sites, and reduces the overadsorption of OH on the Mo active sites, as predicted by calculations. The atomic‐level modification is well confirmed by atomic‐resolution imaging, high‐resolution electron tomography, synchrotron soft X‐ray spectroscopy, and operando electrochemical infrared spectroscopy. Consequently, the Faradaic efficiency for CO2 reduction to CH4 is enhanced from 16% to 89%, a record high efficiency so far, in aqueous electrolytes. It also exhibits a negligible activity loss over 50 h.
The coordination environment of active sites on the surfaces of MoC nanoparticles is modified by anchoring pyridinic N rings on Mo atoms adjacent to hollow sites, reducing the overadsorption of OH on the Mo active sites. The sites after modification exhibit high‐efficiency and durable performance for electrocatalytic reduction of CO2 to CH4.
Anion exchange membrane fuel cells are limited by the slow kinetics of alkaline hydrogen oxidation reaction (HOR). Here, we establish HOR catalytic activities of single-atom and diatomic sites as a ...function of *H and *OH binding energies to screen the optimal active sites for the HOR. As a result, the Ru-Ni diatomic one is identified as the best active center. Guided by the theoretical finding, we subsequently synthesize a catalyst with Ru-Ni diatomic sites supported on N-doped porous carbon, which exhibits excellent catalytic activity, CO tolerance, and stability for alkaline HOR and is also superior to single-site counterparts. In situ scanning electrochemical microscopy study validates the HOR activity resulting from the Ru-Ni diatomic sites. Furthermore, in situ x-ray absorption spectroscopy and computational studies unveil a synergistic interaction between Ru and Ni to promote the molecular H
dissociation and strengthen OH adsorption at the diatomic sites, and thus enhance the kinetics of HOR.
The electrochemical nitrogen (N2) reduction reaction (N2RR) under mild conditions is a promising and environmentally friendly alternative to the traditional Haber‐Bosch process with high energy ...consumption and greenhouse emission for the synthesis of ammonia (NH3), but high‐yielding production is rendered challenging by the strong nonpolar N≡N bond in N2 molecules, which hinders their dissociation or activation. In this study, disordered Au nanoclusters anchored on two‐dimensional ultrathin Ti3C2Tx MXene nanosheets are explored as highly active and selective electrocatalysts for efficient N2‐to‐NH3 conversion, exhibiting exceptional activity with an NH3 yield rate of 88.3±1.7 μg h−1 mgcat.−1 and a faradaic efficiency of 9.3±0.4 %. A combination of in situ near‐ambient pressure X‐ray photoelectron spectroscopy and operando X‐ray absorption fine structure spectroscopy is employed to unveil the uniqueness of this catalyst for N2RR. The disordered structure is found to serve as the active site for N2 chemisorption and activation during the N2RR process.
Order from disorder: Au nanoclusters with disordered Au atoms anchored on two‐dimensional ultrathin Ti3C2Tx MXene nanosheets are synthesized and prove to be a highly efficient catalyst for the electrochemical synthesis of ammonia. In situ near‐ambient pressure X‐ray photoelectron spectroscopy and operando XAFS spectroscopy are used to investigate the catalyst.
As the lightest and cheapest transition metal dichalcogenide, TiS2 possesses great potential as an electrode material for lithium batteries due to the advantages of high energy density storage ...capability, fast ion diffusion rate, and low volume expansion. Despite the extensive investigation of its electrochemical properties, the fundamental discharge–charge reaction mechanism of the TiS2 electrode is still elusive. Here, by a combination of ex situ and operando X-ray absorption spectroscopy with density functional theory calculations, we have clearly elucidated the evolution of the structural and chemical properties of TiS2 during the discharge–charge processes. The lithium intercalation reaction is highly reversible and both Ti and sulfur are involved in the redox reaction during the discharge and charge processes. In contrast, the conversion reaction of TiS2 is partially reversible in the first cycle. However, TiO related compounds are developed during electrochemical cycling over extended cycles, which results in the decrease of the conversion reaction reversibility and the rapid capacity fading. In addition, the solid electrolyte interphase formed on the electrode surface is found to be highly dynamic in the initial cycles and then gradually becomes more stable upon further cycling. Such understanding is important for the future design and optimization of TiS2 based electrodes for lithium batteries.
Effects of electronic and atomic structures of V‐doped 2D layered SnS2 are studied using X‐ray spectroscopy for the development of photocatalytic/photovoltaic applications. Extended X‐ray absorption ...fine structure measurements at V K‐edge reveal the presence of VO and VS bonds which form the intercalation of tetrahedral OVS sites in the van der Waals (vdW) gap of SnS2 layers. X‐ray absorption near‐edge structure (XANES) reveals not only valence state of V dopant in SnS2 is ≈4+ but also the charge transfer (CT) from V to ligands, supported by V Lα,β resonant inelastic X‐ray scattering. These results suggest V doping produces extra interlayer covalent interactions and additional conducting channels, which increase the electronic conductivity and CT. This gives rapid transport of photo‐excited electrons and effective carrier separation in layered SnS2. Additionally, valence‐band photoemission spectra and S K‐edge XANES indicate that the density of states near/at valence‐band maximum is shifted to lower binding energy in V‐doped SnS2 compare to pristine SnS2 and exhibits band gap shrinkage. These findings support first‐principles density functional theory calculations of the interstitially tetrahedral OVS site intercalated in the vdW gap, highlighting the CT from V to ligands in V‐doped SnS2.
The interstitially tetrahedral O–V–S site in the vdW gap of V‐doped 2D SnS2 establishes the origin of the charge transfer mechanism between metal ion V4+ 3d and ligand O2‐ 2p/S2‐ 3p states and the decrease in the band gap by studying synchrotron‐based techniques and first‐principles density functional theory.
As a model system for hydrogen storage, magnesium hydride exhibits high hydrogen storage density, yet its practical usage is hindered by necessarily high temperatures and slow kinetics for ...hydrogenation–dehydrogenation cycling. Decreasing particle size has been proposed to simultaneously improve the kinetics and decrease the sorption enthalpies. However, the associated increase in surface reactivity due to increased active surface area makes the material more susceptible to surface oxidation or other side reactions, which would hinder the overall hydrogenation–dehydrogenation process and diminish the capacity. Previous work has shown that the chemical stability of Mg nanoparticles can be greatly enhanced by using reduced graphene oxide as a protecting agent. Although no bulklike crystalline MgO layer has been clearly identified in this graphene-encapsulated/Mg nanocomposite, we propose that an atomically thin layer of honeycomb suboxide exists, based on first-principles interpretation of Mg K-edge X-ray absorption spectra. Density functional theory calculations reveal that in contrast to conventional expectations for thick oxides this interfacial oxidation layer permits H2 dissociation to the same degree as pristine Mg metal with the added benefit of enhancing the binding between reduced graphene oxide and the Mg nanoparticle, contributing to improved mechanical and chemical stability of the functioning nanocomposite.
Electrochemical conversion of CO2 into formate is a promising strategy for mitigating the energy and environmental crisis, but simultaneously achieving high selectivity and activity of ...electrocatalysts remains challenging. Here, we report low-dimensional SnO2 quantum dots chemically coupled with ultrathin Ti3C2Tx MXene nanosheets (SnO2/MXene) that boost the CO2 conversion. The coupling structure is well visualized and verified by high-resolution electron tomography together with nanoscale scanning transmission X-ray microscopy and ptychography imaging. The catalyst achieves a large partial current density of −57.8 mA cm−2 and high Faradaic efficiency of 94% for formate formation. Additionally, the SnO2/MXene cathode shows excellent Zn–CO2 battery performance, with a maximum power density of 4.28 mW cm−2, an open-circuit voltage of 0.83 V, and superior rechargeability of 60 h. In situ X-ray absorption spectroscopy analysis and first-principles calculations reveal that this remarkable performance is attributed to the unique and stable structure of the SnO2/MXene, which can significantly reduce the reaction energy of CO2 hydrogenation to formate by increasing the surface coverage of adsorbed hydrogen.
Electrochemical N2 reduction reaction (NRR) has long been regarded as a promising process to generate NH3 under ambient conditions. Therefore, developing cost-effective and high-performance ...non-noble-metal catalysts for NRR is highly desirable. Inspired by the biological nitrogenase structure, we here designed and synthesized a catalyst with iron-molybdenum sub-nanoclusters and single atoms on porous nitrogen-doped carbon (FeMo/NC). The catalyst features porous structure beneficial to active site exposure and accessibility to electrolyte as well as FeMo sub-nanoclusters and single atoms enabling to activate N2 molecular. In situ near-ambient pressure X-ray photoelectron spectroscopy tests reveal that during the process from vacuum to nitrogen saturation, N2 was close to, adsorbed on and interacted with Fe and Mo in FeMo/NC. The Fe and Mo through electron transfer play a key role in activating the N2 molecules. Therefore, when tested for NRR, FeMo/NC achieves the maximum Faradaic efficiency (FE) of 11.8 ± 0.8% at −0.25 V and NH3 yield rate of 26.5 ± 0.8 μg h−1 mgcat.−1 at −0.3 V in neutral electrolyte. Moreover, the catalyst exhibits ignorable variations in the FE and a slight decrease in current density for 100,000 s. This work develops a non-precious bimetallic electrocatalyst with synergetic effect capability for efficient NH3 production and provides a guideline for the design of efficient and robust catalysts with coexistence of sub-nanoclusters and single atoms.
Inspired by the biological nitrogenase, we have designed a novel catalyst composed of FeMo sub-nanoclusters/single atoms on N-doped carbon that can effectively catalyse electroreduction of N2 to generate NH3 in neutral media. Display omitted
•FeMo sub-nanoclusters/single atoms are developed from the inspiration of biological nitrogenase.•The catalyst shows excellent activity toward neutral NH3 electrosynthesis.•The catalyst also displays an outstanding stability during the electrolysis.•Near-ambient pressure X-ray photoelectron spectroscopy confirms that the coexistence of Fe and Mo activates the N2 molecules.
Zeolitic imidazolate framework (ZIF‐8)‐derived single‐atom catalysts (SACs) are widely studied in many catalytic reactions such as hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), ...and CO2 reduction reactions (CO2RR). Grinding procedures involved in the synthesis of ZIF‐8‐derived SACs could affect the catalytic performance but are less evaluated in the literature. Herein, a series of ZIF‐8‐derived cobalt SACs (C–Co–ZIFs) with different grinding processes to investigate the impact of the grinding degrees on the performance of the electrochemical reduction reaction of CO2 (ECO2RR) is presented. The moderate grinding process affords a boost in CO Faradaic efficiency (FE, around 15% higher than that of the original C–Co–ZIF) and the highest current densities among all the samples. The variations in the electronic structure of the Co active sites in the ground catalysts are confirmed by X‐Ray absorption spectroscopy (XAS) and X‐Ray emission spectroscopy (XES) for improved catalytic performance. The increased micropores in the moderately ground catalyst provide more exposed active sites while the increased meso‐ and macropores promote the mass transfer, benefiting the ECO2RR performance. It suggests that the impact of grinding processes on the synthesis of ZIF‐8‐derived SACs should be considered for the evaluation of the catalytic performance.
A series of ZIF‐8‐derived cobalt single‐atom catalysts (C–Co–ZIF) with different grinding processes are synthesized to investigate the impact of grinding degrees on the performance of the electrochemical reduction reaction of CO2 (ECO2RR). The moderate grinding process affords the best ECO2RR performance, due to the modified electronic structure of the Co active sites and the optimized pore structures.
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