Single-atom Electrocatalysts Research Articles

Multiatom activation of single-atom electrocatalysts via remote coordination for ultrahigh-rate two-electron oxygen reduction

Electrocatalytic oxygen reduction via a two-electron pathway (2e−-ORR) is a promising and eco-friendly route for producing hydrogen peroxide (H2O2). Single-atom catalysts (SACs) typically show excellent selectivity towards 2e−-ORR due to their unique electronic structures and geometrical configurations. The very low density of single-atom active centers, however, often leads to unsatisfactory H2O2 yield rate, significantly inhibiting their practical feasibility. Addressing this, we herein introduce fluorine as a secondary doping element into conventional SACs, which does not directly coordinate with the single-atom metal centers but synergize with them in a remote manner. This strategy effectively activates the surrounding carbon atoms and converts them into highly active sites for 2e−-ORR. Consequently, a record-high H2O2 yield rate up to 27 mol g−1 h−1 has been achieved on the Mo–F–C catalyst, with high Faradaic efficiency of 90%. Density functional theory calculations further confirm the very kinetically facile 2e−-ORR over these additional active sites and the superiority of Mo as the single-atom center to others. This strategy thus not only provides a high-performance electrocatalyst for 2e−-ORR but also should shed light on new strategies to significantly increase the active centers number of SACs.

Binary Metal Single Atom Electrocatalysts with Synergistic Catalytic Activity toward High‐Rate and High Areal‐Capacity Lithium–Sulfur Batteries

AbstractLithium–sulfur (Li–S) batteries with high theoretical energy density have been long considered as an alternative energy storage device to lithium‐ion batteries. Nevertheless, the polysulfide shuttle effects trigger fast capacity decay and short battery lifespan, severely hampering their practical utilizations. Herein, an efficient electrocatalyst comprising of nitrogen (N)‐coordinated binary metal single atoms (SAs) implanted within a hierarchical porous carbon skeleton (Fe/CoNHPC) is constructed to trap and catalyze polysulfides conversion through a separator coating strategy. It is demonstrated that the introduction of Co atom can enrich the electron number of Fe active center, thereby realizing the distinct synergistic catalytic effect of binary metal SAs and improving the bidirectional catalysis of Li–S redox reaction. As a result, Li–S batteries with the Fe/CoNHPC‐modified separator exhibit outstanding rate capability (740 mAh g−1 at 5.0 C), and superior long‐term cyclic stability (694 mAh g−1 after 600 cycles at 1.0 C). Increasing the sulfur loading to 4.8 mg cm−2, a remarkable areal capacity of 6.13 mAh cm−2 is achieved. Furthermore, in situ X‐ray diffraction and theoretical simulation results verify the catalysis mechanism of binary metal SAs by changing the rate‐determining steps, providing new directions for constructing high‐performance Li–S batteries.

Isolation anchoring strategy for in situ synthesis of iron single-atom catalysts towards long-term rechargeable zinc-air battery

The reasonable design and construction of single-atom electrocatalysts with low-cost and excellent intrinsic activity for oxygen reduction reaction (ORR) is indispensable in metal-air batteries. Herein, a facile isolation anchoring strategy was reported for in situ formation of porous N-doped carbon catalysts (Fe1/NC) rich in Fe single atoms. The d-glucose, zinc gluconate and N-rich histidine were deployed as spatial isolation agents and anchoring agents to inhibit iron atom aggregation during the high-temperature pyrolysis. The as-synthesized Fe1/NC catalyst shows remarkable stability and superior ORR electrocatalytic activity under both alkaline and acidic conditions owing to highly dispersed Fe–N4 sites, especially with a half-wave potential up to 0.91 V in 0.1 M KOH, exceeding 60 mV compared with Pt/C. Notably, the Fe1/NC-based Zn-air battery exhibits maximal power density of 164 mW cm−2, large specific capacities of 769 mA h gZn−1, excellent cycle stability over 300 h, and great potential in renewable energy conversion electronics.

Single Atom Catalysts with Out-of-Plane Coordination Structure on Conjugated Covalent Organic Frameworks.

Adjusting the local coordination environment of single-atom electrocatalysts is a viable way to improve catalytic performance. The diversity of coordination geometric structures is limited to the traditional in-plane configuration, with only a little consideration paid to out-of-plane configurations due to the lack of suitable carriers and fabrication methods. This study reports out-of-plane coordination of Co-based single-atom catalysts mediated by the conjugated bipyridine-rich covalent organic framework (COF). The bipyridine nitrogen on the COF layer backbone of these catalysts serves as the linker center for cobalt sites anchoring, while the complementary moieties are coordinated at the other side of the Co metal and reside beyond the COF backbone plane, thus yielding out-of-plane coordination. The electrochemical experiments and density functional theory calculations reveal that catalysts with multiple out-of-plane coordinations exhibit different electrocatalytic oxygen evolution activities and catalytic pathways. The out-of-plane coordination enabled by COFs provides a strategy for designing single-atom electrocatalysts, expanding the application of COFs in the field of electrocatalysis.

Protein-mediated synthesis of iron single atom electrocatalyst with highly accessible active sites for enhanced pH-universal oxygen reduction

Facile synthesis of highly efficient non-precious metal electrocatalysts is intriguing as these catalysts are used in the oxygen reduction reaction (ORR). Herein, we describe an effective protein-mediated approach to access atomically dispersed iron electrocatalyst (Fe SAs/NC) with enhanced accessible metal active sites. This Fe catalyst achieves an exceptional ORR activity in the pH-universal range, especially in alkaline and acid electrolytes with half-wave potentials of 0.93 and 0.84 V (vs RHE), respectively. The unique electronic structure of Fe sites with enhanced electron/proton transportation ability contributes to the optimized adsorption/desorption of oxygen intermediates. In addition, it shows robust durability and excellent tolerance to methanol crossover in pH-universal media. Impressively, it displays encouraging performance when employed in a zinc-air battery, demonstrating a peak power density of 275.1 mW cm−2 and a specific capacity of 753.8 mAh g−1. The extremely long-term operational stability of more than 250 h further provides significant potential for its application.

Insight into the Evolution of Ordered Mesoporous sp2 Carbonaceous Material Derived from Self-Assembly of a Block Copolymer.

Block-copolymer-derived ordered mesoporous carbon (OMC) materials have great potential in many applications, such as adsorption, catalysis, and energy conversions; however, their formation process and the kinetic mechanism remain unclear. Herein, a N-doped OMC (N-OMC) with sp2-bonded C atoms is developed via self-assembly of the polystyrene-block-poly(4-vinyl pyridine) block copolymer. By correlating the external morphologies with the internal chemical states, the formation process can be concluded as follows: (1) pore evolution via polystyrene domain degradation and (2) regularization and graphitization of the residual carbon via the removal of sp3 C atoms. In addition, the thickness of the N-OMC shows a power function relationship with the spin-coating rate, and the N content can be incredibly increased up to 26.34 at. % in an NH3 carbonization atmosphere. With the as-prepared N-OMC as the support for loading of the pseudo-atomic-scale Pt (Pt/N-OMC), a high electrochemical active surface area value of 99.64 m2·g-1 and a half-wave potential (E1/2) of 0.850 VRHE are achieved, showing great potential in developing single-atom electrocatalysts.

Recent advances in the design of single-atom electrocatalysts by defect engineering.

Single-atom catalysts (SACs) with isolated metal atoms dispersed on supports have attracted increasing attention due to their maximum atomic utilization and excellent catalytic performance in various electrochemical reactions. However, SACs with a high surface-to-volume ratio are fundamentally less stable and easily agglomerate, which weakens their activity. In addition, another issue that restricts the application of SACs is the low metal loading. Defect engineering is the most effective strategy for the precise synthesis of nanomaterials to catch and immobilize single atoms through the modulation of the electronic structure and coordination environment. Herein, in this mini-review, the latest advances in designing SACs by defect engineering have been first highlighted. Then, the heteroatom doping or intrinsic defects of carbon-based support and anion vacancies or cation vacancies of metal-based supports are systematically evaluated. Subsequently, the structure–activity relationships between a single-atom coupled defect structure and electrocatalytic performance are illustrated by combining experimental results and theoretical calculations. Finally, a perspective to reveal the current challenges and opportunities for controllable preparation, in situ characterization, and commercial applications is further proposed.

3D Nanoporous Graphene Based Single-Atom Electrocatalysts for Energy Conversion and Storage

ConspectusThis Account will provide an overview and analysis on recent research of 3D nanoporous graphene based single-atom electrocatalysts for energy conversion and storage applications. In order to meet the increasing energy demands and assist in the transition from a global economy that relies heavily on fossil fuels to one that utilizes more renewable energy sources, there is urgent need to develop high-performing electrocatalysts toward renewable energy related reactions. These catalysts are expected to have low overpotentials, high reaction selectivity, long cycling stability, and, importantly, lower materials costs to address the challenges of traditional nanoparticulate noble metal catalysts. One approach to conquering a transition of such scale is the use of single-atom electrocatalysts which can bring benefits of lowered materials cost, increased reaction selectivity, and improved catalytic activity. However, despite some success in recent years there remain challenges such as the stability of single-atom catalysts over time, especially at high operating temperatures and potentials, and the limited loading of single-atom catalysts on a support matrix. This Account will discuss the use of graphene as the support matrix with heavy focus on the progress in developing 3D nanoporous graphene, synthesized by chemical vapor deposition. We will cover how 3D nanoporous graphene possesses a large specific surface area, open porosity, high electric conductivity, and bound geometric and topological defects and analyze how it is emerging as an excellent support material for developing chemically stable and catalytically active single-atom catalysts with a large loading amount and high electrocatalytic efficiency. Additionally, we will highlight the benefits of the presence of topological and geometric defects, from curved graphene in the 3D structure, and how they can bring more chemically active sites, and how, together with chemical dopants, they can improve the catalytic performance, stability, and loading amount of single-atom catalysts via their strong chemical affinity with transition metals and the formation of active M–Nx–Cy (M = transition metals, N-nitrogen, C-carbon) moieties. Furthermore, we will discuss two common methods for fabrication of single-atom catalysts on nanoporous graphene: (1) controlled etching for non-noble and noble metal catalysts and (2) atomic layer deposition for noble metal catalysts. The electrochemical performances of these single-atom catalysts will be reviewed with the applications toward hydrogen evolution reaction, oxygen reduction reaction and oxygen evolution reaction. This Account highlights advances made in solving the challenges of developing 3D nanoporous graphene based single-atom catalysts and the benefits that the new single-atom catalysts can bring to the applications in energy storage and conversion.

Construction of hierarchically porous carbon spheres supported nonprecious metal single-atom electrocatalysts for oxygen reduction reaction

Design of a highly efficient nonprecious metal electrocatalysts towards oxygen reduction reaction (ORR) is essential for the commercialization of sustainable and economical energy conversion and storage devices containing metal-air batteries and fuel cells. Herein, we present a facile strategy to fabricate the hierarchical porous carbon nanospheres with isolated single-atom iron sites by using the dual-template method of combination of triblock polymers F127 and silica as soft and hard templates, respectively. Owing to the simultaneous hydrolysis of tetraethoxysilane (TEOS) and polymerization of 2,6-diaminopyridine (DAP), the Fe-Nx active sites are protected and the micro-mesoporous structures are constructed. Benefiting from the synergistic effects of the high loaded contents of Fe-Nx active sites and the hierarchically porous nanostructure, Fe–N/C-SA exhibits the excellent electrocatalytic performance over ORR with E1/2 of 0.89 V, which is superior than that of Pt/C (0.84 V). In addition, the as-obtained catalyst exhibits excellent stability and methanol tolerance compared to commercial Pt/C catalysts. Most importantly, the Zn-air battery assembled with Fe–N/C-SA exhibits a gratifying peak power density of 265.0 mW cm−2, large specific capacity of 798.2 mAh g−1, excellent long-term stability and remarkable rate capability.

Theoretical and Experimental Understanding of Metal Single-Atom Electrocatalysts for Accelerating the Electrochemical Reaction of Lithium-Sulfur Batteries.

Metal single-atom materials have attracted tremendous attention in the research field of lithium-sulfur (Li-S) batteries because they can effectively improve the reaction kinetics of sulfur cathodes. However, it is still difficult to determine the best metal single-atom catalyst for Li-S batteries, due to the lack of a unified measurement and evaluation method. Herein, a series of metal single-atom- and nitrogen-doped graphene materials (M-NG, M = Fe, Co, Ni, Ir, Ru) have been prepared as the catalysts for promoting the reaction kinetics of the sulfur reduction reaction process. Using rotating disk electrode measurements and density functional theory-based theoretical calculations, Ni-NG was screened out to be the best catalyst. It is found that Ni-NG materials can provide a kinetically favorable pathway for the reversible conversion of polysulfide conversion, thus increasing the utilization of sulfur. By coating the Ni-NG materials on the separator as a multifunctional interlayer, a commercially available sulfur cathode presents a stable specific capacity of 701.8 mAh g-1 at a current rate of 0.5C over 400 cycles. Even with a high sulfur loading of 3.8 mg cm-2, a high areal capacity of 4.58 mAh cm-2 can be achieved. This work will provide a fundamental understanding of efficient single-atom catalyst materials for Li-S batteries.

Theoretical inspection of TM-P4C single-atom electrocatalysts: High performance for oxygen reduction and evolution reactions

Developing the cost-effective or even bifunctional electrocatalysts for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) with industrially relevant activity is highly desired for metal-air batteries at the current stage. Herein, in this work, the catalytic performances of the single transition metal (TM) atom embeds graphene sheet with the tetra-coordinates Phosphorus (TMP4) for ORR and OER are investigated based on the density functional theory method. The results demonstrate that the most promising ORR and OER catalytic activity can be achieved on the CoP4 with the smallest potential gap ΔE and the lowest overpotential of 0.37 and 0.32 eV among all TMP4 systems, respectively, and the catalytic activity is even better than that of the traditional Pt and IrO2 catalysts. Furthermore, the AIMD and phonon dispersion calculations are conducted to confirm the thermodynamics and dynamics stability of CoP4. This work screens out promising candidates for novel graphene-based bifunctional ORR and OER catalysts and offers detailed microscopic insights into the mechanism of OER/ORR, provides a theoretical guidance for the development of further single-atom catalysts.

Pt Single Atom Electrocatalysts at Graphene Edges for Efficient Alkaline Hydrogen Evolution

AbstractGraphene edges exhibit a highly localized density of states that result in increased reactivity compared to its basal plane. However, exploiting this increased reactivity to anchor and tune the electronic states of single atom catalysts (SACs) remains elusive. To investigate this, a method to anchor Pt SACs with ultra‐low mass loadings at the edges of edge‐rich vertically aligned graphene (as low as 0.71 µg Pt cm–2) is developed. Angle‐dependent X‐ray absorption spectroscopy and density‐functional theory calculations reveal that edge‐anchored Pt SACs has a robust coupling with the π‐electrons of graphene. This interaction results in a higher occupancy of the Pt 5d orbital, shifting the d‐band center toward the Fermi level, improving the adsorption of *H for the hydrogen evolution reaction (HER). Pt primarily coordinated to the graphene edge shows improved alkaline HER performance compared to Pt coordinated in mixed environments (turnover frequencies of 22.6 and 10.9 s–1 at an overpotential of 150 mV, respectively). This work demonstrates an effective route to engineering the coordination environment of Pt SACs by using the graphene edge for enhanced energy conversion reactions.

(Invited) New Bioinspired Nanomaterials for Biosensing and Cancer Theranostics

Nature is an excellent source of inspiration for the widespread application of science and technology. Researchers learn from biological principles and gradually develop from the earliest direct use of biological materials to the design and development of new biomimetic materials inspired by nature. Therefore, the innovation of bioinspired nanomaterials will enable tremendous advances in biology and biochemistry with biomimetic capabilities, such as biosensing, cell imaging, and drug delivery. In this presentation, I will discuss my group’s recent work on two bioinspired nanomaterials: nano-peptoids and single-atom nanozymes.The first type of bioinspired materials is a sequence-defined peptide-like materials that can mimic the structure and function of peptides and proteins. Compared with peptides and proteins, peptoids have a high degree of thermal and chemical stability, and are resistant to proteolytic degradation. In addition, due to the lack of intramolecular and intermolecular backbone hydrogen bond donors, it is possible to precisely control the peptoid and peptoid-substrate interactions, leading to bio-inspired synthesis of nanomaterials with a layered structure. As a peptide mimic, the peptoids has biocompatibility, non-toxicity and sequence-specific heteropolymers. Nano-peptoids can be synthesized with polar and hydrophobic monomers and have the following advantages: They can be easily processed into desired shapes (e.g. dendritic, sheets, tubes and vesicles), and the size range is 2-100 nm to enhance cell targeting and uptake. The application of nano-peptoids in cell imaging and cancer theranostics will be discussed.Another type of bioinspired nanomaterials with enzyme-like properties is single-atom nanoenzymes. As a biocatalyst, natural enzymes have the ability to accelerate various reaction rates with extremely high activity and selectivity under mild conditions. However, due to the temperature and pH-related denaturation of proteins and the possibility of contamination by bacteria or other reagents, the shelf life of natural enzymes is limited or uncertain, and their purification and production costs are high. Therefore, natural enzymes must narrow the range of conditions under which they can be used, limiting their further applications in biosensing and biomedicine. R Recent research has focused on the rational design of nanomaterials with inherent enzyme-like catalytic properties (for example, oxidase, peroxidase, catalase, superoxide dismutase, and so on) and exploration of their applications in various fields. Although much progress has been made, the development of nanozymes is still hampered by several challenges. Catalytic activity and substrate selectivity are the two most important issues that need to be resolved to allow the technology to reach full maturity. Therefore, rational design and tuning of nanomaterials is highly desirable for the development of novel enzyme-mimic nanomaterials with precise catalytic sites. We have developed various Fe-N-C based single atomic site catalysts which have similar structure with active site of peroxidase. These atomically-dispersed Fe-N-C materials have enzyme-like properties, therefore they are classified as single-atom nanozymes. Together with their abundantly exposed active sites and specific structures, these single atomic nanozymes have great potential for the enhancement of biocatalytic activity and selectivity in biosensing. Jiao, H. Yan, Y. Wu, W. Gu, C. Zhu, D. Du, Y. Lin. When Nanozymes Meet Single-Atom Catalysis. Angew. Chem. Int. Ed. 2020,132, 2585-2596Zhu, S. Fu, Q. Shi, D. Du, Y. Lin. Single-Atom Electrocatalysts. Angew. Chem. Int. Ed. 2017, 56, 13944-13960.Cheng, J. Li, D. Liu, Y. Lin, D. Du. Single-Atom Nanozyme Based on Nanoengineered Fe-N-C Catalyst with Superior Peroxidase-Like Activity for Ultrasensitive Bioassays. Small, 2019, 1901485.Niu, Q. Shi, W. Zhu, D. Liu, H. Tian, S. Fu, N. Cheng, S. Li, J. N Smith, D. Du, Y. Lin. Unprecedented Peroxidase-mimicking Activity of Single-atom Nanozyme with Atomically Dispersed Fe-Nx Moieties Hosted by MOF Derived Porous Carbon. Biosensors & Bioelectronics, 2019, 142, 111495.Jiao, W. Xu, Y. Wu, H. Yan, W. Gu, D. Du, Y Lin, C. Zhu, Single-atom Catalysts Boost Signal Amplification for Biosensing. Chemical Society Reviews 2021, 50, 750-765Luo, Y. Song, M. Wang, T. Jian, S. Ding, P. Mu, Z. Liao, Q. Shi, X. Cai, H. Jin, D. Du, W. Dong, C. Chen, Y. Lin. Bioinspired Peptoid Nanotubes for Targeted Tumor Cell Imaging and Chemo-Photodynamic Therapy. Small 2019, 1902485.Song, M. Wang, S. Akkineni, W. Yang, J.J. Hettige, H. Jin, Z. Liao, P. Mu, F. Yan, M. Baer, J. De Yoreo, D. Du, Y. Lin, C. Chen. Highly Bright and Photostable Two-Dimensional Nanomaterials Assembled from Sequence-Defined Peptoids. ACS Materials Letters 2021, 3, 420-427.Cai, M. Wang, P. Mu, T. Jian, D. Liu, S. Ding, Y. Luo, D. Du, Y. Song, C. Chen, Y. Lin. Sequence-Defined Nanotubes Assembled from IR780-Conjugated Peptoids for Chemophototherapy of Malignant Glioma. Research 2021, Article ID 9861384.

Single-Atom Electrocatalyst for Engineered Cathode Interfaces in Sodium-Sulfur Batteries

The demand for portable rechargeable energy storage devices is ever increasing, especially because of the advent of electric vehicles and widespread usage of portable electronics. The lithium-ion batteries are currently leading the battery market; however, the high-cost and potentially depleting storage of lithium metals are stimulating the search for alternative technologies. Metal-sulfur batteries are deemed to be promising candidates to supplant the ubiquitously used lithium-ion batteries owing to their high energy density, specific capacity, low cost of sulfur, and environmental benignity. Room temperature sodium sulfur batteries (RT Na-S) is a technologically viable alternative candidate which possesses astounding advantages such as low cost (both sodium and sulfur), non–toxicity, natural abundance, and high theoretical energy density (1274 Whkg-1). However, the inevitable problems such as the solubility of higher order polysulfides to the electrolyte, known as shuttle effect, and the slow kinetics of electrochemical conversion reactions of intermediate sodium polysulfides (Na2Sn) significantly impede the practical realization of Na-S batteries. The conventionally used various forms of carbonaceous nanomaterials for cathode design have floundered to overcome the challenges because their nonpolar nature cannot produce adequate anchoring and enhanced polysulfides reaction kinetics. The polar anchoring materials (AM) have exhibited promising performance to improve sulfur chemistry. It is generally understood that catalytic performance is directly connected to the surface area of catalytic particles, and the single-atomic level provides the maximum surface area, resulting in the highest catalytic efficacy. Herein, we use first principles-based density functional theory (DFT) simulations to investigate the interfacial interactions between Na2Sn and novel transition metal (TM) single-atom catalysts (SACs) embedded on nitrogen doped graphene and various lattice sites of transition metal chalcogenides (TMDC) (chalcogenides- and Metal-substitution, Metal-top sites). For example, the pristine and Mo-sub sites of MoS2 are found to be ineffective for efficient confinement of the polysulfides within the cathode material. We demonstrate that SACs on both S-site and Mo-top sites of MoS2 and on nitrogen doped graphene possess strong adsorption strength with the Na2Sn which are superior to the commonly used ether electrolyte solvents, a requisite to prevent shuttle effect. We illustrate the influence of d-band center of SACs as an important descriptor in describing Na2Sn interactions with them. The underlying anchoring mechanism of polysulfide adsorption over AM is examined through Bader charge, charge density difference and projected density of states (PDOS) analysis. We also investigate the effect of SACs in improving the kinetics of sulfur reduction reactions (SRRs) and catalytic decomposition of short-chain polysulfides which are crucial for achieving excellent rate capability and longer cycle life. Overall, the unprecedented insights obtained on the role of SACs in tailoring the polysulfides redox chemistry at the interfaces and their relation to their TM’s d-band center is an important step towards rational design cathode materials for high-performance Na-S batteries, in particular, but metal-chalcogenide batteries, in general.

Pyrolysed Co-N4 Macrocycles on Carbon Supports for the Efficient Electroreduction of CO2

Converting CO2 into materials such as chemicals or synfuels is an attractive way to mitigate greenhouse gas emissions while producing value-added products1-4. Even though the intrinsic chemical stability of CO2 significantly limits its reactivity, the use of electrocatalysts allows its efficient reduction in a mild environment and at relatively low overpotentials5,6. Cobalt phthalocyanine (CoPC), cobalt tetra-phenyl porphyrin (CoTPP) and Vitamin B12 (VB12) are well-defined Co-N4 macrocycles whose incorporation into heterogeneous catalyst setups have led to materials with outstanding CO2 electroreduction reaction (CO2ERR) properties, most notably in the selective formation of CO at high current densities7-11.These Co-N4 macrocycles have also been used to manufacture catalysts efficient for the oxygen reduction reaction (ORR). Notably, the pyrolysis of the macrocyclic precursor supported by carbon materials allowed the fabrication of heterogeneous ORR catalysts with high loadings of catalytically active components, controlled local environments and enhanced stabilities12,13. While these properties could lead to these materials also being efficient catalysts for CO2ERR, to the best of our knowledge, such pyrolyzed catalysts have not been investigated for the CO2 reduction reaction.In this work, we report materials based on CoPC, CoTPP and VB12, supported by carbon black and pyrolyzed under argon, as efficient catalysts for the CO2ERR. The catalytic precursors were dispersed on carbon powders with ball-milling before being annealed at different temperatures chosen from the positions of the significant steps and plateaus observed by thermogravimetric analysis of the pure precursors. The structures of the resulting materials were analyzed by powder X-ray diffraction and X-ray absorption spectroscopy. The electrochemical behaviour of these materials for the CO2ERR were characterized in CO2-saturated potassium bicarbonate (KHCO3) electrolyte using a custom-made flow cell at a range of potentials, and the products of the reaction were analyzed with gas chromatography, 1H NMR spectroscopy and high-performance liquid chromatography.The high reactivity of the catalysts for the reduction of CO2 into CO was maintained for all materials treated at temperatures as high as 700 °C, even though the structures of their active sites were drastically different from that of the precursor molecules. The pyrolyzed materials also exhibited a change in correlation between the CO current densities and the KHCO3 concentration of the electrolyte, indicating that the reaction mechanism had changed compared to that of the pristine materials.1 Peter, S. C. Reduction of CO2 to Chemicals and Fuels: A Solution to Global Warming and Energy Crisis. ACS Energy Letters 3, 1557-1561, doi:10.1021/acsenergylett.8b00878 (2018).2 Lee, Z. H., Sethupathi, S., Lee, K. T., Bhatia, S. & Mohamed, A. R. An overview on global warming in Southeast Asia: CO2 emission status, efforts done, and barriers. Renewable and Sustainable Energy Reviews 28, 71-81, doi:10.1016/j.rser.2013.07.055 (2013).3 Saeidi, S., Amin, N. A. S. & Rahimpour, M. R. Hydrogenation of CO2 to value-added products - A review and potential future developments. Journal of CO2 Utilization 5, 66-81, doi:10.1016/j.jcou.2013.12.005 (2014).4 Zhao, G., Huang, X., Wang, X. X. & Wang, X. X. Progress in catalyst exploration for heterogeneous CO2 reduction and utilization: A critical review. Journal of Materials Chemistry A 5, 21625-21649, doi:10.1039/c7ta07290b (2017).5 Finn, C., Schnittger, S., Yellowlees, L. J. & Love, J. B. Molecular approaches to the electrochemical reduction of carbon dioxide. Chemical Communications 48, 1392-1399, doi:10.1039/c1cc15393e (2012).6 Torbensen, K., Boudy, B., Joulié, D., von Wolff, N. & Robert, M. Emergence of CO2 electrolyzers including supported molecular catalysts. Current Opinion in Electrochemistry 24, 49-55, doi:10.1016/j.coelec.2020.07.001 (2020).7 Wang, M. et al. CO2 electrochemical catalytic reduction with a highly active cobalt phthalocyanine. Nature Communications 10, doi:10.1038/s41467-019-11542-w (2019).8 Ni, W. et al. Dual single-cobalt atom-based carbon electrocatalysts for efficient CO2-to-syngas conversion with industrial current densities. Applied Catalysis B: Environmental 291, doi:10.1016/j.apcatb.2021.120092 (2021).9 Jia, C. et al. Vitamin B12 on Graphene for Highly Efficient CO2 Electroreduction. ACS Appl Mater Interfaces 12, 41288-41293, doi:10.1021/acsami.0c10125 (2020).10 Hu, B. et al. How does the ligands structure surrounding metal-N4 of Co-based macrocyclic compounds affect electrochemical reduction of CO2 performance? Electrochimica Acta 331, 135283, doi:10.1016/j.electacta.2019.135283 (2020).11 Hu, X. M., Ronne, M. H., Pedersen, S. U., Skrydstrup, T. & Daasbjerg, K. Enhanced Catalytic Activity of Cobalt Porphyrin in CO2 Electroreduction upon Immobilization on Carbon Materials. Angew Chem Int Ed Engl 56, 6468-6472, doi:10.1002/anie.201701104 (2017).12 Wan, G. et al. Tuning the Performance of Single-Atom Electrocatalysts: Support-Induced Structural Reconstruction. Chemistry of Materials 30, 7494-7502, doi:10.1021/acs.chemmater.8b02315 (2018).13 Wan, G. et al. Anion-Regulated Selective Generation of Cobalt Sites in Carbon: Toward Superior Bifunctional Electrocatalysis. Adv Mater 29, doi:10.1002/adma.201703436 (2017).

Porphyrinic MOF derived Single-atom electrocatalyst enables methanol oxidation

Electrochemical methanol oxidation reaction (MOR) serves as a key route for renewable energy technologies. However, unmet challenges remain in the preparation of low-cost, efficient and robust electrocatalysts for MOR. Herein, a porphyrinic metal–organic framework (MOF) with spatially isolated Ni centres is prepared. Upon pyrolysis, this affords a single-atom Ni implanted nitrogen-doped porous carbon (20% Ni-N-C). Integrating abundant and accessible single-atom Ni sites, hierarchical porosity, excellent conductivity with stable Ni-N4 moieties all in one, the derived ultra-stable 20% Ni-N-C exhibits high MOR activity, impressive durability and CO tolerance, thereby outperforming state-of-the-art nonprecious metal based electrocatalysts. Computational insights reveal a low energy barrier of 1.19 eV for the rate-determining step, in agreement with the experimental observations of superior MOR activity. As the first foray into improving MOR efficiency with nonprecious metal based single-atom electrocatalysts, the yet-unrealized potential for MOFs and related modular hybrids is demonstrated.

1+1>2: Learning from the interfacial modulation on single-atom electrocatalysts to design dual-atom electrocatalysts for dinitrogen reduction

Developing efficient electrocatalysts for converting dinitrogen to ammonia through electrocatalysis is of significance to the decentralized ammonia production. Here, through high-throughput density functional theory calculations, we demonstrated that the interfacial modulation of hexagonal boron nitride/graphene (hBN-graphene) could sufficiently improve the catalytic activity of the single transition metal atom catalysts for nitrogen reduction reaction (NRR). It was revealed that Re@hBN-graphene and Os@hBN-graphene possessed remarkable NRR catalytic activity with low limiting potentials of 0.29 V and 0.33 V, respectively. Furthermore, the mechanism of the enhanced catalytic activity was investigated based on various descriptors of the adsorption energies of intermediates, where the synergistic effect of hBN and graphene in the hybrid substrate was found to play a key role. Motivated by the synergistic effect of hybrid substrate in single-atom catalysts, a novel strategy was proposed to efficiently design dual-atom catalysts by integrating the merits of both metal components. The as-designed dual-atom catalyst Fe-Mo@hBN exhibited more excellent NRR catalytic performance with a limiting potential of 0.17 V, manifesting the solidity of the design strategy. Our findings open new avenues for the search of heterostructure substrates for single-atom catalysts and the efficient design of dual-atom catalysts for NRR.

Single-atom transition metals supported on defective graphene for electrochemical reduction of acetonitrile to ethylamine

The electrochemical acetonitrile (CH3CN) reduction reaction provides an alternative to produce ethylamine (CH3CH2NH2) under ambient conditions but remains challenging. Using density functional theory (DFT) calculations, we explored the catalytic performance of four types of graphene-based single-atom catalysts (SACs) total of 32 materials toward the CH3CN reduction reaction. We identified that two highly stable SACs, namely Cr@N4 and Mn@N4, can greatly accelerate both reaction thermodynamics and kinetics with small energy barriers. In particular, these two SACs can effectively suppress the competitive hydrogen evolution reaction (HER) by selective adsorption of key intermediate of *CH3CN rather than *H, which feature superior catalytic selectivity. More impressively, the activity trends of various candidates can be directly correlated to the adsorption energy of *CH3CHN (ΔE(*CH3CHN)), and the underlying activity origin is ascribed by the enhancement of the adsorption for the *CH3CHN. Furthermore, detailed electronic property analyses indicate that the bonding/anti-bonding interactions of different active metal centers with *CH3CHN are the key factor determining the adsorption strength. The more bonding contributions below the Fermi level (Ef) lead to the stronger *CH3CHN combination on active metal centers, while the anti-bonding state is opposite. As a result, Cr@N4 stands out among these candidates, which can tune the performance of acetonitrile reduction reaction by balancing the reactivity of CH3CN and the desorption of CH3CH2NH2. Our results unveil that the excellent catalytic activity of Cr@N4 for CH3CN reduction reaction can be further confirmed by calculating the bond lengths and charge variations. With the elongation of CN bond in the adsorbed CH3CHxNHy, CH3CN molecule can be effectively activated on Cr@N4. Overall, this work addresses a promising active catalyst and will be of a guidance of great theoretical significance to construct carbon-based materials supported transition metal single-atom electrocatalysts for the CH3CN reduction reaction.

Computational Insight into Metallated Graphynes as Single Atom Electrocatalysts for Nitrogen Fixation.

The electrochemical nitrogen reduction reaction (NRR) is expected to achieve sustainable ammonia synthesis via direct nitrogen fixation; however, the high-quality catalysts that play a crucial role in the NRR are still lacking. The emerging transition metal-1,3,5-triethynylbenzene (TM-TEB) frameworks offer attractive possibilities in the electrochemical catalysis due to the featured atomic and electronic structures. This work presents a comprehensive first-principles study of the TM-TEB systems for TMs from the first three d-block series and systematically explores their potential applications as NRR electrocatalysts. By designing a hierarchical screening strategy, the TM-TEB systems are evaluated based on the NRR catalytic activity as well as the competition from the hydrogen evolution reaction. In addition, in order to have a deeper understanding of the catalytic activities of the TM-TEB systems, diverse possible NRR paths on the TM-TEB surfaces are completely analyzed as well. Our analysis reveals that the TM-TEB systems with TM = V, Mo, Tc, W, and Os are electrocatalysts with a high NRR catalytic activity, while among them, only Mo- and V-TEB show promising NRR selectively. This work demonstrates the great potential of the TM-TEB systems as electrocatalysts in the NRR process, which improves the understanding of the TM-TEB systems and can motivate further exploration of their application in catalysis.

Total conversion of centimeter-scale nickel foam into single atom electrocatalysts with highly selective CO2 electrocatalytic reduction in neutral electrolyte

Total conversion of centimeter-scale nickel foam into single atom electrocatalysts with highly selective CO2 electrocatalytic reduction in neutral electrolyte