Coupling Single-Atom Sites and Ordered Intermetallic PtM Nanoparticles for Efficient Catalysis in Fuel Cells.

The design of an efficient catalytic system with low Pt loading and excellent stability for the acidic oxygen reduction reaction is still a challenge for the extensive application of proton-exchange membrane fuel cells. Here, a gas-phase ordered alloying strategy is proposed to construct an effective synergistic catalytic system that blends PtM intermetallic compounds (PtM IMC, M = Fe, Cu, and Ni) and dense isolated transition metal sites (M-N4 ) on nitrogen-doped carbon (NC). This strategy enables Pt nanoparticles and defects on the NC support to timely trap flowing metal salt without partial aggregation, which is attributed to the good diffusivity of gaseous transition metal salts with low boiling points. In particular, the resulting Pt1 Fe1 IMC cooperating with Fe-N4 sites achieves cooperative oxygen reduction with a half-wave potential up to 0.94 V and leads to a high mass activity of 0.51 A  mgPt -1 and only 23.5% decay after 30 k cycles, both of which exceed DOE 2025 targets. This strategy provides a method for reducing Pt loading in fuel cells by integrating Pt-based intermetallics and single transition metal sites to produce an efficient synergistic catalytic system.

Coplanar Pt/C Nanomeshes with Ultrastable Oxygen Reduction Performance in Fuel Cells.

Developing highly stable and efficient catalysts toward the oxygen reduction reaction is important for the long-term operation in proton exchange membrane fuel cells. Reported herein is a facile synthesis of two-dimensional coplanar Pt-carbon nanomeshes (NMs) that are composed of highly distorted Pt networks (neck width of 2.05±0.72 nm) and carbon. X-ray absorption fine structure spectroscopy demonstrated the metallic state of Pt in the coplanar Pt/C NMs. Fuel cell tests verified the excellent activity of the coplanar Pt/C NM catalyst with the peak power density of 1.21 W cm-2 and current density of 0.360 A cm-2 at 0.80 V in the H2 /O2 cell. Moreover, the coplanar Pt/C NM electrocatalysts showed superior stability against aggregation, with NM structures preserved intact for a long-term operation of over 30 000 cycles for electrode measurement, and the working voltage loss was negligible after 120 h in the H2 /O2 single cell operation. Density-functional theory analysis indicates the increased vacancy formation energy of Pt atoms for coplanar Pt/C NMs, restraining the tendency of Pt dissolution and aggregation.

Single Iron Site Nanozyme for Ultrasensitive Glucose Detection.

Nanomaterials with enzyme-mimicking characteristics have engaged great awareness in various fields owing to their comparative low cost, high stability, and large-scale preparation. However, the wide application of nanozymes is seriously restricted by the relatively low catalytic activity and poor specificity, primarily because of the inhomogeneous catalytic sites and unclear catalytic mechanisms. Herein, a support-sacrificed strategy is demonstrated to prepare a single iron site nanozyme (Fe SSN) dispersed on the porous N-doped carbon. With well-defined coordination structure and high density of active sites, the Fe SSN performs prominent peroxidase-like activity by efficiently activating H2 O2 into hydroxyl radical (•OH) species. Furthermore, the Fe SSN is applied in colorimetric detection of glucose through a multienzyme biocatalytic cascade platform. Moreover, a low-cost integrated agarose-based hydrogel colorimetric biosensor is designed and successfully achieves the visualization evaluation and quantitative detection of glucose. This work expands the application of single-site catalysts in the fields of nanozyme-based biosensors and personal biomedical diagnosis.

2D PbS Nanosheets with Zigzag Edges for Efficient CO2 Photoconversion.

The rational design of transition-metal sulfide with two-dimensional (2D) structure and tunable edges on the nanoscale can effectively improve their activity for variously catalytic reactions. Herein, the 2D PbS nanosheets with abundant zigzag edges (e-PbS NS), which exhibited an excellent performance for CO2 photoconversion to CO, were constructed. The zigzag edges on the PbS NS are beneficial for exposing more active sites and promoting charge separation, thereby accelerating the kinetics process of CO2 photoreduction. This study provides a strategy to regulate structure with effective edge sites for the CO2 reduction.

Two-Step Carbothermal Welding To Access Atomically Dispersed Pd1 on Three-Dimensional Zirconia Nanonet for Direct Indole Synthesis.

Herein, we report a novel carbothermal welding strategy to prepare atomically dispersed Pd sites anchored on a three-dimensional (3D) ZrO2 nanonet (Pd1@ZrO2) via two-step pyrolysis, which were evolved from isolated Pd sites anchored on linker-derived nitrogen-doped carbon (Pd1@NC/ZrO2). First, the NH2-H2BDC linkers and Zr6-based [Zr6(µ3-O)4(µ3-OH)4]12+ nodes of UiO-66-NH2 were transformed into amorphous N-doped carbon skeletons (NC) and ZrO2 nanoclusters under an argon atmosphere, respectively. The NC supports can simultaneously reduce and anchor the Pd sites, forming isolated Pd1-N/C sites. Then, switching the argon to air, the carbonaceous skeletons are gasified and the ZrO2 nanoclusters are welded into a rigid and porous nanonet. Moreover, the reductive carbon will result in abundant oxygen (O*) defects, which could help to capture the migratory Pd1 species, leaving a sintering-resistant Pd1@ZrO2 catalyst via atom trapping. This Pd1@ZrO2 nanonet can act as a semi-homogeneous catalyst to boost the direct synthesis of indole through hydrogenation and intramolecular condensation processes, with an excellent turnover frequency (1109.2 h-1) and 94% selectivity.

Thermal Emitting Strategy to Synthesize Atomically Dispersed Pt Metal Sites from Bulk Pt Metal.

Developing a facile route to access active and well-defined single atom sites catalysts has been a major area of focus for single atoms catalysts (SACs). Herein, we demonstrate a simple approach to generate atomically dispersed platinum via a thermal emitting method using bulk Pt metal as a precursor, significantly simplifying synthesis routes and minimizing synthesis costs. The ammonia produced by pyrolysis of Dicyandiamide can coordinate with platinum atoms by strong coordination effect. Then, the volatile Pt(NH3) x can be anchored onto the surface of defective graphene. The as-prepared Pt SAs/DG exhibits high activity for the electrochemical hydrogen evolution reaction and selective oxidation of various organosilanes. This viable thermal emitting strategy can also be applied to other single metal atoms, for example, gold and palladium. Our findings provide an enabling and versatile platform for facile accessing SACs toward many industrial important reactions.

A Supported Nickel Catalyst Stabilized by a Surface Digging Effect for Efficient Methane Oxidation.

A surface digging effect of supported Ni NPs on an amorphous N-doped carbon is described, during which the surface-loaded Ni NPs would etch and sink into the underneath carbon support to prevent sintering. This process is driven by the strong coordination interaction between the surface Ni atoms and N-rich defects. In the aim of activation of C-H bonds for methane oxidation, those sinking Ni NPs could be further transformed into thermodynamically stable and active metal-defect sites within the as-generated surface holes by simply elevating the temperature. In situ transmission electron microscopy images reveal the sunk Ni NPs dig themselves adaptive surface holes, which would largely prevent the migration of Ni NPs without weakening their accessibility. The reported two-step strategy opens up a new route to manufacture sintering-resistant supported metal catalysts without degrading their catalytic efficiency.

Multicarbons generation factory: CuO/Ni single atoms tandem catalyst for boosting the productivity of CO2 electrocatalysis.

Tandem electrocatalysis is an emerging concept for effective electrochemical CO2 reduction reaction (CO2RR) towards multicarbons (C2+). This decouples the multiple steps of CO2-to-C2+ into two steps of CO2-to-CO and CO-to-C2+ catalyzed by individual catalysts, to improve the Faradic efficiency (FE). However, due to the mass-transport limitation of CO from the generation site to the long-distance consumption site, such a strategy still remains challenge for high-rate production of C2+ products. Herein, we designed CuO/Ni single atoms tandem catalyst, which made the catalytic sites of Ni and Cu for independently catalyzing CO2-to-CO and CO-to-C2+ compactly neighbored, enabling the in-situ generation and rapid consumption of CO. The CuO/Ni SAs tandem catalyst achieved a particularly high partial current density of C2+ products (1220.8 mA/cm2), while still maintained outstanding C2+ products FE (81.4%) and excellent selectivities towards ethylene (FE 54.1%) and ethanol (FE 28.8%), enabling the profitable production of multicarbons by CO2RR.

Dual confinement of high-loading enzymes within metal-organic frameworks for glucose sensor with enhanced cascade biocatalysis.

The intrinsically fragile nature and leakage of the enzymes is a major obstacle for the commercial sensor of a continuous glucose monitoring system. Herein, a dual confinement effect is developed in a three dimensional (3D) nanocage-based zeolite imidazole framework (NC-ZIF), during which the high-loading enzymes can be well encapsulated with unusual bioactivity and stability. The shell of NC-ZIF sets the first confinement to prevent enzymes leakage, and the interior nanocage of NC-ZIF provides second confinement to immobilize enzymes and offers a spacious environment to maintain their conformational freedom. Moreover, the mesoporosity of the formed NC-ZIF can be precisely controlled, which can effectively enhance the mass transport. The resulted GOx/Hemin@NC-ZIF multi-enzymes system could not only realize rapid detection of glucose by colorimetric and electrochemical sensors with high catalytic cascade activity (with an 8.3-fold and 16-fold enhancements in comparison with free enzymes in solution, respectively), but also exhibit long-term stability, excellent selectivity and reusability. More importantly, the based wearable sweatband sensor measurement results showed a high correlation (>0.84, P < 0.001) with the levels measured by commercial glucometer. The reported dual confinement strategy opens up a window to immobilize enzymes with enhanced catalytic efficiency and stability for clinical-grade noninvasive continuous glucose sensor.

Integrating single-cobalt-site and electric field of boron nitride in dechlorination electrocatalysts by bioinspired design.

The construction of enzyme-inspired artificial catalysts with enzyme-like active sites and microenvironment remains a great challenge. Herein, we report a single-atomic-site Co catalyst supported by carbon doped boron nitride (BCN) with locally polarized B-N bonds (Co SAs/BCN) to simulate the reductive dehalogenases. Density functional theory analysis suggests that the BCN supports, featured with ionic characteristics, provide additional electric field effect compared with graphitic carbon or N-doped carbon (CN), which could facilitate the adsorption of polarized organochlorides. Consistent with the theoretical results, the Co SAs/BCN catalyst delivers a high activity with nearly complete dechlorination (~98%) at a potential of -0.9 V versus Ag/AgCl for chloramphenicol (CAP), showing that the rate constant (k) contributed by unit mass of metal (k/ratio) is 4 and 19 times more active than those of the Co SAs/CN and state-of-the-art Pd/C catalyst, respectively. We show that Co single atoms coupled with BCN host exhibit high stability and selectivity in CAP dechlorination and suppress the competing hydrogen evolution reaction, endowing the Co SAs/BCN as a candidate for sustainable conversion of organic chloride.

Biocompatible Ruthenium Single-Atom Catalyst for Cascade Enzyme-Mimicking Therapy.

Rationally constructing single-atom enzymes (SAEs) with superior activity, robust stability, and good biocompatibility is crucial for tumor therapy but still remains a substantial challenge. In this work, we adopt biocompatible carbon dots as the carrier material to load Ru single atoms, achieving Ru SAEs with superior multiple enzyme-like activity and stability. Ru SAEs behave as oxidase, peroxidase, and glutathione oxidase mimics to synchronously catalyze the generation of reactive oxygen species (ROS) and the depletion of glutathione, thus amplifying the ROS damage and finally causing the death of cancer cells. Notably, Ru SAEs exhibit excellent peroxidase-like activity with a specific activity of 7.5 U/mg, which surpasses most of the reported SAEs and is 20 times higher than that of Ru/C. Theoretical results reveal that the electrons of the Ru 4d orbital in Ru SAEs are transferred to O atoms in H2O2 and then efficiently activate H2O2 to produce •OH. Our work may provide some inspiration for the design of SAEs for cancer therapy.

Room-Temperature Synthesis of Single Iron Site by Electrofiltration for Photoreduction of CO2 into Tunable Syngas.

Developing a convenient and effective method to prepare single-atom catalysts at mild synthetic conditions remains a challenging task. Herein, a voltage-gauged electrofiltration method was demonstrated to synthesize single-atom site catalysts at room temperature. Under regulation of the graphene oxide membrane, a bulk Fe plate was directly converted into Fe single atoms, and the diffusion rate of Fe ions was greatly reduced, resulting in an ultralow concentration of Fe2+ around the working electrode, which successfully prevented the growing of nuclei and aggregating of metal atoms. Monatomic Fe atoms are homogeneously anchored on the as-prepared nitrogen-doped carbon. Owing to the fast photoelectron injection from photosensitizers to atomically dispersed Fe sites through the highly conductive supported N-C, the Fe-SAs/N-C exhibits an outstanding photocatalytic activity toward CO2 aqueous reduction into syngas with a tunable CO/H2 ratio under visible light irradiation. The gas evolution rates for CO and H2 are 4500 and 4950 µmol g-1 h-1, respectively, and the tunable CO/H2 ratio is from 0.3 to 8.8. This article presents an efficient strategy to develop the single-atom site catalysts and bridges the gap between heterogeneous and homogeneous catalysts toward photocatalytic CO2 aqueous reduction into syngas.

In Situ Topotactic Transformation of an Interstitial Alloy for CO Electroreduction.

Electrochemical reduction of CO to value-added products holds promise for storage of energy from renewable sources. Copper can convert CO into multi-carbon (C2+ ) products during CO electroreduction. However, developing a Cu electrocatalyst with a high selectivity for CO reduction and desirable production rates for C2+ products remains challenging. Herein, highly lattice-disordered Cu3 N with abundant twin structures as a precursor electrocatalyst is examined for CO reduction. Through in situ activation during the CO reduction reaction (CORR) and concomitant release of nitrogen, the obtained metallic Cu° catalyst particles inherit the lattice dislocations present in the parent Cu3 N lattice. The de-nitrified catalyst delivers an unprecedented C2+ Faradaic efficiency of over 90% at a current density of 727 mA cm-2 in a flow cell system. Using a membrane electrode assembly (MEA) electrolyzer with a solid-state electrolyte (SSE), a 17.4 vol% ethylene stream and liquid streams with concentration of 1.45 m and 230 × 10-3 m C2+ products at the outlet of the cathode and SSE-containment layer are obtained.

Construction of highly accessible single Co site catalyst for glucose detection.

The development of high-performance glucose sensors is an urgent need, especially for diabetes mellitus diagnosis. However, the glucose monitoring is conventionally operated in an invasive finger-prick manner and their noninvasive alternatives largely suffered from the relatively poor sensitivity, selectivity, and stability, resulted from the lack of robust and efficient catalysts. In this paper, we design a concave shaped nitrogen-doped carbon framework embellished with single Co site catalyst (Co SSC) by selectively controlling the etching rate on different facet of carbon substrate, which is beneficial to the diffusion and contact of analyte. The Co SSC prompts a significant improvement in the sensitivity of the solution-gated graphene transistor (SGGT) devices, with three orders of magnitude better than those of SGGT devices without catalysts. Our findings expand the field of single site catalyst in the application of biosensors, diabetes diagnostics and personalized health-care monitoring.

Recover the activity of sintered supported catalysts by nitrogen-doped carbon atomization.

The sintering of supported metal nanoparticles is a major route to the deactivation of industrial heterogeneous catalysts, which largely increase the cost and decrease the productivity. Here, we discover that supported palladium/gold/platinum nanoparticles distributed at the interface of oxide supports and nitrogen-doped carbon shells would undergo an unexpected nitrogen-doped carbon atomization process against the sintering at high temperatures, during which the nanoparticles can be transformed into more active atomic species. The in situ transmission electron microscopy images reveal the abundant nitrogen defects in carbon shells provide atomic diffusion sites for the mobile atomistic palladium species detached from the palladium nanoparticles. More important, the catalytic activity of sintered and deactivated palladium catalyst can be recovered by this unique N-doped carbon atomization process. Our findings open up a window to preparation of sintering-resistant single atoms catalysts and regeneration of deactivated industrial catalysts.

Trifunctional Self-Supporting Cobalt-Embedded Carbon Nanotube Films for ORR, OER, and HER Triggered by Solid Diffusion from Bulk Metal.

The development of robust and efficient trifunctional catalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen reaction (HER) is central to regenerative metal-air batteries and overall water splitting. It is still a big challenge to achieve an efficient integration of three functions in one freestanding electrode. Herein, a facile and upscalable strategy is demonstrated, to construct cobalt nanoparticle-encapsulated 3D conductive films (Co/CNFs), which were induced by in situ solid diffusion from bulk cobalt metal. Under high-temperature, volatile cobalt species from bulk cobalt foil are trapped by the contacted nitrogen-rich carbons, followed by catalytic growth of interconnected carbon tubes, forming the 3D structured film. This resulting film can be directly preformed as self-supporting and binder-free electrode, which simultaneously facilitates the ORR, OER, and HER with excellent activities and superior stability. Furthermore, such "all-in-one" film also exhibits remarkable performance for Zn-air batteries and overall water splitting, demonstrating its feasibility for practical applications.

Directly transforming copper (I) oxide bulk into isolated single-atom copper sites catalyst through gas-transport approach.

Single-atom metal catalysts have sparked tremendous attention, but direct transformation of cheap and easily obtainable bulk metal oxide into single atoms is still a great challenge. Here we report a facile and versatile gas-transport strategy to synthesize isolated single-atom copper sites (Cu ISAS/NC) catalyst at gram levels. Commercial copper (I) oxide powder is sublimated as mobile vapor at nearly melting temperature (1500 K) and subsequently can be trapped and reduced by the defect-rich nitrogen-doped carbon (NC), forming the isolated copper sites catalyst. Strikingly, this thermally stable Cu ISAS/NC, which is obtained above 1270 K, delivers excellent oxygen reduction performance possessing a recorded half-wave potential of 0.92 V vs RHE among other Cu-based electrocatalysts. By varying metal oxide precursors, we demonstrate the universal synthesis of different metal single atoms anchored on NC materials (M ISAS/NC, where M refers to Mo and Sn). This strategy is readily scalable and the as-prepared sintering-resistant M ISAS/NC catalysts hold great potential in high-temperature applications.

Ambient Synthesis of Single-Atom Catalysts from Bulk Metal via Trapping of Atoms by Surface Dangling Bonds.

Single-atom catalysts (SACs) feature the maximum atom economy and superior performance for various catalysis fields, attracting tremendous attention in materials science. However, conventional synthesis of SACs involves high energy consumption at high temperature, complicated procedures, a massive waste of metal species, and poor yields, greatly impeding their development. Herein, a facile dangling bond trapping strategy to construct SACs under ambient conditions from easily accessible bulk metals (such as Fe, Co, Ni, and Cu) is presented. When mixing graphene oxide (GO) slurry with metal foam and drying in ambient conditions, the M0 would transfer electrons to the dangling oxygen groups on GO, obtaining Mδ+ (0 < δ < 3) species. Meanwhile, Mδ+ coordinates with the surface oxygen dangling bonds of GO to form MO bonds. Subsequently, the metal atoms are pulled out of the metal foam by the MO bonds under the assistance of sonication to give M SAs/GO materials. This synthesis at room temperature from bulk metals provides a versatile platform for facile and low-cost fabrication of SACs, crucial for their mass production and practical application in diverse industrial reactions.

Unraveling the enzyme-like activity of heterogeneous single atom catalyst.

Herein, we report a heterogeneous single iron atom catalyst exhibiting excellent peroxidase, oxidase and catalase enzyme-like activities (defined as single atom enzymes, SAEs), exceeding those of Fe3O4 nanozymes by a factor of 40. Our findings open up a new family of artificial materials that mimic natural enzymes.