A General Metal Ion Recognition Strategy to Mediate Dual-Atomic-Site Catalysts.

Heterogeneous dual-atomic-site catalysts (DACs) hold great potential for diverse applications. However, to date, the synthesis of DACs primarily relies on different atoms freely colliding on the support during synthesis, principally leading to low yields. Herein, we report a general metal ion recognition (MIR) strategy for constructing a series of DACs, including but not limited to Fe1Sn1, Fe1Co1, Fe1Ni1, Fe1Cu1, Fe1Mn1, Co1Ni1, Co1Cu1, Co2, and Cu2. This strategy is achieved by coupling target inorganometallic cations and anions as ion pairs, which are sequentially adsorbed onto a nitrogen-doped carbon substrate as the precursor. Taking the oxygen reduction reaction as an example, we demonstrated that the Fe1Sn1-DAC synthesized through this strategy delivers a record peak power density of 1.218 W cm-2 under 2.0 bar H2-O2 conditions and enhanced stability compared to the single-atom-site FeN4. Further study revealed that the superior performance arises from the synergistic effect of Fe1Sn1 dual vicinal sites, which effectively optimizes the adsorption of *OH and alleviates the troublesome Fenton-like reaction.

Atomization-Induced High Intrinsic Activity of a Biocompatible MgAl-LDH Supported Ru Single-Atom Nanozyme for Efficient Radicals Scavenging.

Developing efficient nanozymes to mimic natural enzymes for scavenging reactive radicals remains a significant challenge owing to the insufficient activity of conventional nanozymes. Herein, we report a novel Ru single-atom nanozyme (SAE), featuring atomically dispersed Ru atoms on a biocompatible MgAl-layered double hydroxide (Ru1 /LDH). The prepared Ru1 /LDH SAE shows high intrinsic peroxidase (POD)-like catalytic activity, which outperforms the Ru nanoclusters (NCs) nanozyme by a factor of 20 and surpasses most SAEs. The density functional theory calculations reveal that the high intrinsic POD-like activity of Ru1 /LDH can be attributed to a heterolytic path of H2 O2 dissociation on the single Ru sites, which requires lower free energy (0.43 eV) compared to the homolytic path dissociation on Ru NC (0.63 eV). In addition, the Ru1 /LDH SAE shows excellent multiple free radicals scavenging ability, including superoxide anion radical (O2 ⋅- ), hydroxyl radical (⋅OH), nitric oxide radical (NO⋅) and 2, 2-diphenyl-1-picrylhydrazyl radical (DPPH⋅). Given the advantages of Ru1 /LDH with high enzymatic activities, biosafety, and ease to scale up, it paves the way for exploring SAEs in the practical biological immunity system.

Single-atomic cobalt sites embedded in hierarchically ordered porous nitrogen-doped carbon as a superior bifunctional electrocatalyst.

Exploring efficient and cost-effective catalysts to replace precious metal catalysts, such as Pt, for electrocatalytic oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) holds great promise for renewable energy technologies. Herein, we prepare a type of Co catalyst with single-atomic Co sites embedded in hierarchically ordered porous N-doped carbon (Co-SAS/HOPNC) through a facile dual-template cooperative pyrolysis approach. The desirable combination of highly dispersed isolated atomic Co-N4 active sites, large surface area, high porosity, and good conductivity gives rise to an excellent catalytic performance. The catalyst exhibits outstanding performance for ORR in alkaline medium with a half-wave potential (E1/2) of 0.892 V, which is 53 mV more positive than that of Pt/C, as well as a high tolerance of methanol and great stability. The catalyst also shows a remarkable catalytic performance for HER with distinctly high turnover frequencies of 0.41 and 3.8 s-1 at an overpotential of 100 and 200 mV, respectively, together with a long-term durability in acidic condition. Experiments and density functional theory (DFT) calculations reveal that the atomically isolated single Co sites and the structural advantages of the unique 3D hierarchical porous architecture synergistically contribute to the high catalytic activity.

Atomically Dispersed Nickel(I) on an Alloy-Encapsulated Nitrogen-Doped Carbon Nanotube Array for High-Performance Electrochemical CO2 Reduction Reaction.

Single-atom catalysts (SACs) show great promise for electrochemical CO2 reduction reaction (CRR), but the low density of active sites and the poor electrical conduction and mass transport of the single-atom electrode greatly limit their performance. Herein, we prepared a nickel single-atom electrode consisting of isolated, high-density and low-valent nickel(I) sites anchored on a self-standing N-doped carbon nanotube array with nickel-copper alloy encapsulation on a carbon-fiber paper. The combination of single-atom nickel(I) sites and self-standing array structure gives rise to an excellent electrocatalytic CO2 reduction performance. The introduction of copper tunes the d-band electron configuration and enhances the adsorption of hydrogen, which impedes the hydrogen evolution reaction. The single-nickel-atom electrode exhibits a specific current density of -32.87 mA cm-2 and turnover frequency of 1962 h-1 at a mild overpotential of 620 mV for CO formation with 97 % Faradic efficiency.

A General Method to Ultrathin Bimetal-MOF Nanosheets Arrays via In Situ Transformation of Layered Double Hydroxides Arrays.

Structure engineering of ultrathin metal-organic framework (MOF) nanosheets to self-supporting and well-aligned MOF superstructures is highly desired for diverse applications, especially important for electrocatalysis. In this work, a facile layered double hydroxides in situ transformation strategy is developed to synthesize ultrathin bimetal-MOF nanosheets (BMNSs) arrays on conductive substrates. This approach is versatile, and applicable to obtain various BMNSs or even trimetal-MOF nanosheets arrays on different substrates. As a proof of concept application, the obtained ultrathin NiCo-BDC BMNSs array exhibits an excellent catalytic activity toward the oxygen evolution reaction with an overpotential of only 230 mV to reach a current density of 10 mA cm-2 in 1 m KOH. The present work demonstrates a strategy to prepare ultrathin bimetal-MOF nanosheets arrays, which might open an avenue for various promising applications of MOF materials.

A Bimetallic Zn/Fe Polyphthalocyanine-Derived Single-Atom Fe-N4 Catalytic Site:A Superior Trifunctional Catalyst for Overall Water Splitting and Zn-Air Batteries.

Developing an efficient single-atom material (SAM) synthesis and exploring the energy-related catalytic reaction are important but still challenging. A polymerization-pyrolysis-evaporation (PPE) strategy was developed to synthesize N-doped porous carbon (NPC) with anchored atomically dispersed Fe-N4 catalytic sites. This material was derived from predesigned bimetallic Zn/Fe polyphthalocyanine. Experiments and calculations demonstrate the formed Fe-N4 site exhibits superior trifunctional electrocatalytic performance for oxygen reduction, oxygen evolution, and hydrogen evolution reactions. In overall water splitting and rechargeable Zn-air battery devices containing the Fe-N4 SAs/NPC catalyst, it exhibits high efficiency and extraordinary stability. This current PPE method is a general strategy for preparing M SAs/NPC (M=Co, Ni, Mn), bringing new perspectives for designing various SAMs for catalytic application.

A Vacuum Vapor Deposition Strategy to Fe Single-Atom Catalysts with Densely Active Sites for High-Performance Zn-Air Battery.

Iron single-atom catalysts (SACs) have garnered increasing attention as highly efficient catalysts for the oxygen reduction reaction (ORR), yet their performance in practical devices remains suboptimal due to the low density of accessible active sites. Anchoring iron single atoms on 2D support is a promising way to increase the accessible active sites but remains difficult attributing to the high aggregation tendency of iron atoms on the 2D support. Herein, a vacuum vapor deposition strategy is presented to fabricate an iron SAC supported on ultrathin N-doped carbon nanosheets with densely active sites (FeSAs-UNCNS). Experimental analyses confirm that the FeSAs-UNCNS achieves densely accessible active sites (1.11 × 1020 sites g-1) in the configuration of Fe─N4O. Consequently, the half-wave potential of FeSAs-UNCNS in 0.1 m KOH reaches a remarkable value of 0.951 V versus RHE. Moreover, when employed as the cathode of various kinds of Zn-air batteries, FeSAs-UNCNS exhibits boosting performances by achieving a maximum power density of 306 mW cm-2 and long cycle life (>180 h) at room temperature, surpassing both Pt/C and reported SACs. Further investigations reveal that FeSAs-UNCNS facilitates the mass and charge transfer during catalysis and the atomic configuration favors the desorption of *OH kinetically.

ZnS/C Dual-Quantum-Dots Heterostructural Nanofibers for High-Performance Photocatalytic H2O2 Production.

Constructing heterostructures of dual quantum-dots (QDs) is a promising way to achieve high performance in photocatalysis, but it still faces substantial synthetic challenges. Herein, we developed an in situ transformation strategy to coassemble ZnS QDs and C QDs into dual-quantum-dot heterostructural nanofibers (ZnS/C-DQDH). Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy results revealed the formation of strong Zn-O-C bonds at the interface between ZnS QDs and C QDs, improving the separation efficiency of photogenerated charge carriers. The ZnS/C-DQDH demonstrated remarkable photocatalytic activity in H2O2 production, with generation rates of 2896.4 µmol gcat-1 h-1 without sacrificial agents and 9879.3 µmol gcat-1 h-1 with ethanol as the sacrificial agent, significantly higher than the QD counterparts and surpassed state-of-the-art photocatalysts. Moreover, due to the nanofibrous feature, ZnS/C-DQDH demonstrated excellent stability and facile recyclability. This work provides a facile and large scalable method to gain dual-quantum-dot heterostructures and a promising alternative for photocatalytic H2O2 production.

Modulating the Electronic Metal-Support Interactions to Anti-Leaching Pt Single Atoms for Efficient Hydrosilylation.

Modulating the electronic metal-support interaction (EMSI) of the single-atomic sites against leaching via microenvironment regulation is critical to achieving high activity and stability but remains challenging. Herein, this work selectively confines Pt single atoms on CoFe layered double hydroxide (LDH) by three oxygen atoms around cation vacancy (Pt1 /LDHV ) or one oxygen atom at the regular surface (Pt1 /LDH) via cation vacancy engineering. By characterizing the structural evolution of the obtained catalysts before and after vacancy construction and single-atom anchoring, this work demonstrates how the microenvironments modulate the EMSI and the catalytic performance. Theoretical simulations further reveal a significantly enhanced EMSI effect by the three-coordinated Pt1 atoms on cation vacancies in Pt1 /LDHV , which endows a more prominent anti-leaching feature than the one-coordinated ones on the regular surface. As a result, the Pt1 /LDHV catalyst shows exceptional performance in anti-Markovnikov alkene hydrosilylation, with a turnover frequency of 1.3 × 105 h-1 . More importantly, the enhanced EMSI of Pt1 /LDHV effectively prevented the leaching of Pt atom from the catalyst surface and can be recycled at least ten times with only a 3.4% loss of catalytic efficiency with minimal Pt leaching, and reach a high turnover number of 1.0 × 106 .

Defect-Rich CoFe-Layered Double Hydroxides as Superior Peroxidase-like Nanozymes for the Detection of Ascorbic Acid.

The development of artificial enzymes with superior catalytic properties to natural enzymes has been a long-standing goal of chemists. Herein, defect-rich CoFe-layered double hydroxides (d-CoFe-LDHs) nanosheets are developed and used as superior peroxidase-like nanozymes for the detection of ascorbic acid (AA). The d-CoFe-LDHs with an average thickness of ∼3 nm and a lateral size of ∼20 nm are synthesized through rapid nucleation in a colloid mill, which exhibited abundant unsaturated sites (oxygen vacancies and cobalt vacancies). Impressively, d-CoFe-LDHs exhibited excellent peroxidase-mimicking performance with strong substrate affinity and robustness in a wide pH range. Density functional theory calculations show that d-CoFe-LDHs have lower H2O2 adsorption energy, which promotes the decomposition of H2O2, thereby improving the catalytic activity. The chromogenic system of d-CoFe-LDHs and 3,3',5,5'-tetramethylbenzidine can be used to accurately detect the content of AA, and the detection limit is about 3.6 µM. This study opens up a new approach for the construction of highly active defective LDH peroxidases for the detection of biomolecules.

Hollow mesoporous atomically dispersed metal-nitrogen-carbon catalysts with enhanced diffusion for catalysis involving larger molecules.

Single-atom catalysts (SACs) show great promise in various applications due to their maximal atom utilization efficiency. However, the controlled synthesis of SACs with appropriate porous structures remains a challenge that must be overcome to address the diffusion issues in catalysis. Resolving these diffusion issues has become increasingly important because the intrinsic activity of the catalysts is dramatically improved by spatially isolated single-atom sites. Herein, we develop a facile topo-conversion strategy for fabricating hollow mesoporous metal-nitrogen-carbon SACs with enhanced diffusion for catalysis. Several hollow mesoporous metal-nitrogen-carbon SACs, including Co, Ni, Mn and Cu, are successfully fabricated by this strategy. Taking hollow mesoporous cobalt-nitrogen-carbon SACs as a proof-of-concept, diffusion and kinetic experiments demonstrate the enhanced diffusion of hollow mesoporous structures compared to the solid ones, which alleviates the bottleneck of poor mass transport in catalysis, especially involving larger molecules. Impressively, the combination of superior intrinsic activity from Co-N4 sites and the enhanced diffusion from the hollow mesoporous nanoarchitecture significantly improves the catalytic performance of the oxidative coupling of aniline and its derivatives.

Multi-shelled hollow layered double hydroxides with enhanced performance for the oxygen evolution reaction.

Hollow materials with a sophisticated structure are promising for various applications with boosted performances and innovative properties. Herein, we report an in situ transformation strategy using multi-layered MOFs as templates to fabricate multi-shelled hollow NiZnCoFe layered double hydroxides (LDHs), which outperformed the double- and single-shelled hollow LDHs and commercial IrO2 in the oxygen evolution reaction.

Construction of Pd-Zn dual sites to enhance the performance for ethanol electro-oxidation reaction.

Rational design and synthesis of superior electrocatalysts for ethanol oxidation is crucial to practical applications of direct ethanol fuel cells. Here, we report that the construction of Pd-Zn dual sites with well exposure and uniformity can significantly improve the efficiency of ethanol electro-oxidation. Through synthetic method control, Pd-Zn dual sites on intermetallic PdZn nanoparticles, Pd-Pd sites on Pd nanoparticles and individual Pd sites are respectively obtained on the same N-doped carbon coated ZnO support. Compared with Pd-Pd sites and individual Pd sites, Pd-Zn dual sites display much higher activity for ethanol electro-oxidation, exceeding that of commercial Pd/C by a factor of ~24. Further computational studies disclose that Pd-Zn dual sites promote the adsorption of ethanol and hydroxide ion to optimize the electro-oxidation pathway with dramatically reduced energy barriers, leading to the superior activity. This work provides valuable clues for developing high-performance ethanol electro-oxidation catalysts for fuel cells.

VO2(B) nanobelts/reduced graphene oxide composites for high-performance flexible all-solid-state supercapacitors.

Vanadium oxide has attracted extensive attention for electrochemical capacitors due to its wide range of versatility. However, due to the relative poor conductivity and chemical stability of vanadium oxide, severe losses of capacitance often occur during charge and discharge processes. Herein, a free-standing vanadium dioxide (VO2(B)) nanobelts/reduced graphene oxide (VO2/rGO) composite film was fabricated by assembly of VO2(B) nanobelts and rGO for supercapacitors. The flexible rGO sheets and VO2(B) nanobelts intertwined together to form a porous framework, which delivered a 353 F g-1 specific capacitance at 1 A g-1, and after 500 cycles, the specific capacitance retention rate was 80% due to the enhanced conductivity of the VO2(B) nanobelts by rGO and increased transport of ions and electrons by the porous structures. An all-solid-state symmetrical supercapacitor was assembled from the VO2/rGO composites, which exhibited good energy storage performance with a maximum voltage of 1.6 V. The maximum power density is 7152 W kg-1 at the energy density of 3.13 W h kg-1, ranking as one of the highest power densities for reported materials. In addition, after 10000 cycles, it still has a specific capacitance retention rate of 78% at 10 A g-1.

Strain Regulation to Optimize the Acidic Water Oxidation Performance of Atomic-Layer IrOx.

Strain regulation has become an important strategy to tune the surface chemistry and optimize the catalytic performance of nanocatalysts. Herein, the construction of atomic-layer IrOx on IrCo nanodendrites with tunable IrO bond length by compressive strain effect for oxygen evolution reaction (OER) in acidic environment is demonstrated. Evidenced from in situ extended X-ray absorption fine structure, it is shown that the compressive strain of the IrOx layer on the IrCo nanodendrites decreases gradually from 2.51% to the unstrained state with atomic layer growth (from ≈2 to ≈9 atomic layers of IrOx ), resulting in the variation of the IrO bond length from shortened 1.94 Å to normal 1.99 Å. The ≈3 atomic-layer IrOx on IrCo nanodendrites with an IrO bond length of 1.96 Å (1.51% strain) exhibits the optimal OER activity compared to the higher-strained (2.51%, ≈2 atomic-layer IrOx ) and unstrained (>6 atomic-layer IrOx ) counterparts, with an overpotential of only 247 mV to achieve a current density of 10 mA cm-2 . Density functional theory calculations reveal that the precisely tuned compressive strain effect balances the adsorbate-substrate interaction and facilitates the rate-determining step to form HOO*, thus assuring the best performance of the three atomic-layer IrOx for OER.

Isolating contiguous Pt atoms and forming Pt-Zn intermetallic nanoparticles to regulate selectivity in 4-nitrophenylacetylene hydrogenation.

Noble metals play a momentous role in heterogeneous catalysis but still face a huge challenge in selectivity control. Herein, we report isolating contiguous Pt atoms and forming Pt-Zn intermetallic nanoparticles as an effective strategy to optimize the selectivity of Pt catalysts. Contiguous Pt atoms are isolated into single atoms and Pt-Zn intermetallic nanoparticles are formed which are supported on hollow nitrogen-doped carbon nanotubes (PtZn/HNCNT), as confirmed by aberration-corrected high-resolution transmission electron microscopy and X-ray absorption spectrometry measurements. Interestingly, this PtZn/HNCNT catalyst promotes the hydrogenation of 4-nitrophenylacetylene to 4-aminophenylacetylene with a much higher conversion ( > 99%) and selectivity (99%) than the comparison samples with Pt isolated-single-atomic-sites (Pt/HNCNT) and Pt nanoparticles (Pt/CN). Further density functional theory (DFT) calculations disclose that the positive Zn atoms assist the adsorption of nitro group and Pt-Zn intermetallic nanoparticles facilitate the hydrogenation on nitro group kinetically.

Efficient photodegradation of chlorophenols by BiOBr/NaBiO3 heterojunctioned composites under visible light.

Forming heterojunctioned composites is an effective way to develop visible-light-driven photocatalysts. A series of BiOBr/NaBiO3 composites were synthesized by surface transformation of NaBiO3 with hydrobromic acid. Commensurate planes of BiOBr and NaBiO3 enabled the formation of a closely bound interface. Composites with <20wt.% BiOBr exhibited excellent photocatalytic activity towards the degradation of chlorophenols under low intensity visible light (λ>400nm). The best photocatalyst was 9% BiOBr/NaBiO3 with a quantum yield of 0.365. No photocorrosion was observed after three cycles. Using radical scavengers and inert atmosphere, holes, superoxide and hydroxyl radicals were found to be involved in the photoactivity of the BiOBr/NaBiO3 composite. Hydroxylated and open-ring diacid molecules were identified as intermediates in the mineralization of 4-chlorophenol.

A Polymer Encapsulation Strategy to Synthesize Porous Nitrogen-Doped Carbon-Nanosphere-Supported Metal Isolated-Single-Atomic-Site Catalysts.

A novel polymer encapsulation strategy to synthesize metal isolated-single-atomic-site (ISAS) catalysts supported by porous nitrogen-doped carbon nanospheres is reported. First, metal precursors are encapsulated in situ by polymers through polymerization; then, metal ISASs are created within the polymer-derived p-CN nanospheres by controlled pyrolysis at high temperature (200-900 °C). Transmission electron microscopy and N2 sorption results reveal this material to exhibit a nanospheric morphology, a high surface area (≈380 m2 g-1 ), and a porous structure (with micropores and mesopores). Characterization by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure confirms the metal to be present as metal ISASs. This methodology is applicable to both noble and nonprecious metals (M-ISAS/p-CN, M = Co, Ni, Cu, Mn, Pd, etc.). In particular, the Co-ISAS/p-CN nanospheres obtained using this method show comparable (E1/2 = 0.838 V) electrochemical oxygen reduction activity to commercial Pt/C with 20 wt% Pt loading (E1/2 = 0.834 V) in alkaline media, superior methanol tolerance, and outstanding stability, even after 5000 cycles.

ZIF-derived porous carbon supported Pd nanoparticles within mesoporous silica shells: sintering- and leaching-resistant core-shell nanocatalysts.

A facile strategy to prepare sintering- and leaching-resistant core-shell nanocatalysts is reported. ZIF-derived porous carbon supported Pd nanoparticles are coated with a mesoporous silica shell, preventing Pd nanoparticles from sintering at high temperature and leaching in a catalytic process. This nanocatalyst exhibits excellent catalytic activity and recyclability for the oxidation of benzyl alcohol.