Engineering Zinc-Organic Frameworks-Based Artificial Carbonic Anhydrase with Ultrafast Biomimetic Centers for Efficient Hydration Reactions

Constructing effective and robust biocatalysts with carbonic anhydrase (CA)-mimetic activities offers an alternative and promising pathway for diverse CO2-related catalytic applications. However, there is very limited success has been achieved in controllably synthesizing CA-mimetic biocatalysts. Here, inspired by the 3D coordination environments of CAs, this study reports on the design of an ultrafast ZnN3-OH2 center via tuning the 3D coordination structures and mesoporous defects in a zinc-dipyrazolate framework to serve as new, efficient, and robust CA-mimetic biocatalysts (CABs) to catalyze the hydration reactions. Owing to the structural advantages and high similarity with the active center of natural CAs, the double-walled CAB with mesoporous defects displays superior CA-like reaction kinetics in p-NPA hydrolysis (V0 = 445.16 nM s-1, Vmax = 3.83 µM s-1, turnover number: 5.97 × 10-3 s-1), which surpasses the by-far-reported metal-organic frameworks-based biocatalysts. This work offers essential guidance in tuning 3D coordination environments in artificial enzymes and proposes a new strategy to create high-performance CA-mimetic biocatalysts for broad applications, such as CO2 hydration/capture, CO2 sensing, and abundant hydrolytic reactions.

Optimizing the Activation Energy of Reactive Intermediates on Single-Atom Electrocatalysts: Challenges and Opportunities

Single-atom catalysts (SACs) have made great progress in recent years as potential catalysts for energy conversion and storage due to their unique properties, including maximum metal atoms utilization, high-quality activity, unique defined active sites, and sustained stability. Such advantages of single-atom catalysts significantly broaden their applications in various energy-conversion reactions. Given the extensive utilization of single-atom catalysts, methods and specific examples for improving the performance of single-atom catalysts in different reaction systems based on the Sabatier principle are highlighted and reactant binding energy volcano relationship curves are derived in non-homogeneous catalytic systems. The challenges and opportunities for single-atom catalysts in different reaction systems to improve their performance are also focused upon, including metal selection, coordination environments, and interaction with carriers. Finally, it is expected that this work may provide guidance for the design of high-performance single-atom catalysts in different reaction systems and thereby accelerate the rapid development of the targeted reaction.

Temperature-Induced Low-Coordinate Ni Single-Atom Catalyst for Boosted CO2 Electroreduction Activity

Single-atom catalysts (SACs) exhibit remarkable potential for electrochemical reduction of CO2 to value-added products. However, the commonly pursued methods for preparing SACs are hard to scale up, and sometimes, lack general applicability because of expensive raw materials and complex synthetic procedures. In addition, the fine tuning of coordination environment of SACs remains challenging due to their structural vulnerability. Herein, a simple and universal strategy is developed to fabricate Ni SACs with different nitrogen coordination numbers through one-step pyrolysis of melamine, Ni(NO3 )∙6H2 O, and polyvinylpyrrolidone at different temperatures. Experimental measurements and theoretical calculations reveal that the low-coordinate Ni SACs exhibit outstanding CO2 reduction performance and stability, achieving a Faradic efficiency (FECO ) of 98.5% at -0.76 V with CO current density of 24.6 mA cm-2 , and maintaining FECO of over 91.0% at all applied potential windows from -0.56 to -1.16 V, benefiting from its coordinatively unsaturated structure to afford high catalytic activity and low barrier for the formation of *COOH intermediate. No significant performance degradation is observed over 50 h of continuous operation. Additionally, several other metallic single-atom catalysts are successfully prepared by this synthetic method, demonstrating the universality of this strategy.

Geometric and Electronic Structural Engineering of Isolated Ni Single Atoms for a Highly Efficient CO2 Electroreduction

Tuning the coordination environment and geometric structures of single atom catalysts is an effective approach for regulating the reaction mechanism and maximize the catalytic efficiency of single-atom centers. Here, a template-based synthesis strategy is proposed for the synthesis of high-density NiN_x sites anchored on the surface of hierarchically porous nitrogen-doped carbon nanofibers (Ni-HPNCFs) with different coordination environments. First-principles calculations and advanced characterization techniques demonstrate that the single Ni atom is strongly coordinated with both pyrrolic and pyridinic N dopants, and that the predominant sites are stabilized by NiN₃ sites. This dual engineering strategy increases the number of active sites and utilization efficiency of each single atom as well as boosts the intrinsic activity of each active site on a single-atom scale. Notably, the Ni-HPNCF catalyst achieves a high CO Faradaic efficiency (FE_CO ) of 97% at a potential of -0.7 V, a high CO partial current density (j_CO ) of 49.6 mA cm^-2 (-1.0 V), and a remarkable turnover frequency of 24 900 h^-1 (-1.0 V) for CO₂ reduction reactions (CO₂ RR). Density functional theory calculations show that compared to pyridinic-type NiN_x , the pyrrolic-type NiN₃ moieties display a superior CO₂ RR activity over hydrogen evolution reactions, resulting in their superior catalytic activity and selectivity.

Highly Luminescent Earth-Benign Organometallic Manganese Halide Crystals with Ultrahigh Thermal Stability of Emission from 4 to 623 K

The phosphor-converted light-emitting diode (PC-LED) has become an indispensable solid-state lighting and display technologies in the modern society. Nevertheless, the use of scarce rare-earth elements and the thermal quenching (TQ) behavior are still two most crucial issues yet to be solved. Here, this work successfully demonstrates a highly efficient and thermally stable green emissive MnI₂ (XanPO) crystals showing a notable photoluminescence quantum yield (PLQY) of 94% and a super TQ resistance from 4 to 623 K. This unprecedented superior thermal stability is attributed to the low electron-phonon coupling and the unique rigid crystal structure of MnI₂ (XanPO) over the whole temperature range based on the temperature-dependent photoluminescence (PL) and single crystal X-ray diffraction (SCXRD) analyses. Considering these appealing properties, green PC-LEDs with a power efficacy of 102.5 lm W^-1 , an external quantum efficiency (EQE) of 22.7% and a peak luminance up to 7750 000 cd m^-2 are fabricated by integrating MnI₂ (XanPO) with commercial blue LEDs. Moreover, the applicability of MnI₂ (XanPO) in both micro-LEDs and organic light-emitting diodes (OLEDs) is also demonstrated. In a nutshell, this study uncovers a candidate of highly luminescent and TQ resistant manganese halide suitable for a variety of emission applications.

Atomic Tungsten on Graphene with Unique Coordination Enabling Kinetically Boosted Lithium-Sulfur Batteries

Use of catalytic materials is regarded as the most desirable strategy to cope with sluggish kinetics of lithium polysulfides (LiPSs) transformation and severe shuttle effect in lithium-sulfur batteries (LSBs). Single-atom catalysts (SACs) with 100 % atom-utilization are advantagous in serving as anchoring and electrocatalytic centers for LiPSs. Herein, a novel kind of tungsten (W) SAC immobilized on nitrogen-doped graphene (W/NG) with a unique W-O₂ N₂ -C coordination configuration and a high W loading of 8.6 wt % is proposed by a self-template and self-reduction strategy. The local coordination environment of W atom endows the W/NG with elevated LiPSs adsorption ability and catalytic activity. LSBs equipped with W/NG modified separator manifest greatly improved electrochemical performances with high cycling stability over 1000 cycles and ultrahigh rate capability. It indicates high areal capacity of 6.24 mAh cm^-2 with robust cycling life at a high sulfur mass loading of 8.3 mg cm^-2 .

Low-Temperature Synthesis of Single Palladium Atoms Supported on Defective Hexagonal Boron Nitride Nanosheet for Chemoselective Hydrogenation of Cinnamaldehyde

Metal-support interactions are of great importance in determining the support-activity in heterogeneous catalysis. Here we report a low-temperature synthetic strategy to create atomically dispersed palladium atoms anchored on defective hexagonal boron nitride (h-BN) nanosheet. Density functional theory (DFT) calculations suggest that the nitrogen-containing B vacancy can provide stable anchoring sites for palladium atoms. The presence of single palladium atoms was confirmed by spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurement. This catalyst showed exceptional efficiency in chemoselective hydrogenation of cinnamaldehyde, along with excellent recyclability, sintering-resistant ability, and scalability. We anticipate this synthetic approach for the synthesis of high-quality SACs based on h-BN support is amenable to large-scale production of bench-stable catalysts with maximum atom efficiency for industrial applications.

Engineering Ag-Nx Single-Atom Sites on Porous Concave N-Doped Carbon for Boosting CO2 Electroreduction

The electrochemical CO₂ reduction reaction (CO₂RR) offers an environmentally benign pathway for renewable energy conversion and further regulation of the environmental CO₂ concentration to achieve carbon cycling. However, developing desired electrocatalysts with high CO Faradaic efficiency (FE_CO) at an ultralow overpotential remains a grand challenge. Herein, we report an effective CO₂RR electrocatalyst that features Ag single-atom coordinated with three nitrogen atoms (Ag₁-N₃) anchored on porous concave N-doped carbon (Ag₁-N₃/PCNC), which is identified by X-ray absorption spectroscopy. Ag₁-N₃/PCNC shows a low CO₂RR onset potential of -0.24 V, high maximum FE_CO of 95% at -0.37 V, and high CO partial current density of 7.6 mA cm^-2 at -0.55 V, exceeding most of the previous Ag electrocatalysts. The in situ infrared absorption spectra technique proves that Ag₁-N₃ single-atom sites have sole linear-adsorbed CO and can easily desorb *CO species to achieve the highest CO selectivity in comparison with the corresponding counterparts. This work provides significant inspiration on boosting CO₂RR by tuning the active center at an atomic level to achieve a specific absorption with an intermediate.

The Limited Predictive Power of the Pauling Rules

The Pauling rules have been used for decades to rationalise the crystal structures of ionic compounds. Despite their importance, there has been no statistical assessment of the performances of these five empirical rules so far. Here, we rigorously and automatically test all five Pauling rules for a large data set of around 5000 known oxides. We discuss each Pauling rule separately, stressing their limits and range of application in terms of chemistries and structures. We conclude that only 13 % of the oxides simultaneously satisfy the last four rules, indicating a much lower predictive power than expected.

Single-Site AuI Catalyst for Silane Oxidation with Water

Single-site Au anchored on mpg-C₃ N₄ (519 ppm Au loading) is developed as a highly active, selective, and stable catalyst for the oxidation of silanes with water with a turnover frequency as high as 50 200 h^-1 , far exceeding most known catalysts based on total gold content. Other hydrosilanes bearing unsaturated functional groups also lead to corresponding silanols under mild reaction conditions without formation of any side products in good or excellent yields. The spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements both confirm the atomic dispersion of Au atoms stabilized by mpg-C₃ N₄ . The coordination of the catalytically active Au^I by three nitrogen or carbon atoms in the tri-s-triazine repeating units not only prevents the Au atoms from aggregation, but also renders the surface Au^I highly active, which is completely different than homogeneous Au^I species.