Hydrogen-Bond-Network Breakdown Boosts Selective CO2 Photoreduction by Suppressing H2 Evolution.

Conventional strategies for highly efficient and selective CO2 photoreduction focus on the design of catalysts and cocatalysts. In this study, we discover that hydrogen bond network breakdown in reaction system can suppress H2 evolution, thereby improving CO2 photoreduction performance. Photosensitive poly(ionic liquid)s are designed as photocatalysts owing to their strong hydrogen bonding with solvents. The hydrogen bond strength is tuned by solvent composition, thereby effectively regulating H2 evolution (from 0 to 12.6 mmol g-1 h-1). No H2 is detected after hydrogen bond network breakdown with trichloromethane or tetrachloromethane as additives. CO production rate and selectivity increase to 35.4 mmol g-1 h-1 and 98.9 % with trichloromethane, compared with 0.6 mmol g-1 h-1 and 26.2 %, respectively, without trichloromethane. Raman spectroscopy and theoretical calculations confirm that trichloromethane broke the systemic hydrogen bond network and subsequently suppressed H2 evolution. This hydrogen bond network breakdown strategy may be extended to other catalytic reactions involving H2 evolution.

Contact-Electro-Catalysis for Direct Oxidation of Methane under Ambient Conditions.

The conversion of methane under ambient conditions has attracted significant attention. Although advancements have been made using active oxygen species from photo- and electro- chemical processes, challenges such as complex catalyst design, costly oxidants, and unwanted byproducts remain. This study exploits the concept of contact-electro-catalysis, initiating chemical reactions through charge exchange at a solid-liquid interface, to report a novel process for directly converting methane under ambient conditions. Utilizing the electrification of commercially available Fluorinated Ethylene Propylene (FEP) with water under ultrasound, we demonstrate how this interaction promote the activation of methane and oxygen molecules. Our results show that the yield of HCHO and CH3OH can reach 467.5 and 151.2 µmol ⋅ gcat -1, respectively. We utilized electron paramagnetic resonance (EPR) to confirm the evolution of hydroxyl radicals (⋅OH) and superoxide radicals (⋅OOH). Isotope mass spectrometry (MS) was employed to analyze the elemental origin of CH3OH, which can be further oxidized to HCHO. Additionally, we conducted density functional theory (DFT) simulations to assess the reaction energies of FEP with H2O, O2, and CH4 under these conditions. The implications of this methodology, with its potential applicability to a wider array of gas-phase catalytic reactions, underscore a significant advance in catalysis.

Metal-Organic Frameworks: Direct Synthesis by Organic Acid-Etching and Reconstruction Disclosure as Oxygen Evolution Electrocatalysts.

Metal-organic frameworks (MOFs) have emerged as promising oxygen evolution reaction (OER) electrocatalysts. Chemically bonded MOFs on supports are desirable yet lacking in routine synthesis, as they may allow variable structural evolution and the underlying structure-activity relationship to be disclosed. Herein, direct MOF synthesis is achieved by an organic acid-etching strategy (AES). Using π-conjugated ferrocene (Fc) dicarboxylic acid as the etching agent and organic ligand, a series of MFc-MOF (M=Ni, Co, Fe, Zn) nanosheets are synthesized on the metal supports. The crystal structure is studied using X-ray diffraction and low-dose transmission electron microscopy, which is quasi-lattice-matched with that of the metal, enabling in situ MOF growth. Operando Raman and attenuated total reflectance Fourier transform infrared spectroscopy disclose that the NiFc-MOF features dynamic structural rebuilding during OER. The reconstructed one showing optimized electronic structures with an upshifted total d-band center, high M-O bonding state occupancy, and localized electrons on adsorbates indicated by density functional theory calculations, exhibits outstanding OER performance with a fairly low overpotential (130 mV at 10 mA cm-2 ) and good stability (144 h). The newly established approach for direct MOF synthesis and structural reconstruction disclosure stimulate the development of more prudent catalysts for advancing OER.

MXene-Derived Na+ -Pillared Vanadate Cathodes for Dendrite-Free Potassium Metal Batteries.

Cation-intercalated vanadates, which have considerable promise as the cathode for high-performance potassium metal batteries (PMBs), suffer from structural collapse upon K+ insertion and desertion. Exotic cations in the vanadate cathode may ease the collapse, yet their effect on the intrinsic cation remains speculative. Herein, a stable and dendrite-free PMB, composed of a Na+ and K+ co-intercalated vanadate (NKVO) cathode and a liquid NaK alloy anode, is presented. A series of NKVO with tuneable Na/K ratios are facilely prepared using MXene precursors, in which Na+ is testified to be immobilized upon cycling, functioning as a structural pillar. Due to stronger ionic bonding and lower Fermi level of Na+ compared to K+ , moderate Na+ intercalation could reduce K+ binding to the solvation sheath and favor K+ diffusion kinetics. As a result, the MXene-derived Na+ -pillared NKVO exhibits markedly improved specific capacities, rate performance, and cycle stability than the Na+ -free counterpart. Moreover, thermally-treated carbon paper, which imitates the microscopic structure of Chinese Xuan paper, allows high surface tension liquid NaK alloy to adhere readily, enabling dendrite-free metal anodes. By clarifying the role of foreign intercalating cations, this study may lead to a more rational design of stable and high-performance electrode materials.

Photocatalytic CO2 reduction to syngas using metallosalen covalent organic frameworks.

Metallosalen-covalent organic frameworks have recently gained attention in photocatalysis. However, their use in CO2 photoreduction is yet to be reported. Moreover, facile preparation of metallosalen-covalent organic frameworks with good crystallinity remains considerably challenging. Herein, we report a series of metallosalen-covalent organic frameworks produced via a one-step synthesis strategy that does not require vacuum evacuation. Metallosalen-covalent organic frameworks possessing controllable coordination environments of mononuclear and binuclear metal sites are obtained and act as photocatalysts for tunable syngas production from CO2. Metallosalen-covalent organic frameworks obtained via one-step synthesis exhibit higher crystallinity and catalytic activities than those obtained from two-step synthesis. The optimal framework material containing cobalt and triazine achieves a syngas production rate of 19.7 mmol g-1 h-1 (11:8 H2/CO), outperforming previously reported porous crystalline materials. This study provides a facile strategy for producing metallosalen-covalent organic frameworks of high quality and can accelerate their exploration in various applications.

Optimized synthesis of anti-COVID-19 drugs aided by retrosynthesis software.

Considering the millions of COVID-19 patients worldwide, a global critical challenge of low-cost and efficient anti-COVID-19 drug production has emerged. Favipiravir is one of the potential anti-COVID-19 drugs, but its original synthetic route with 7 harsh steps gives a low product yield (0.8%) and has a high cost ($68 per g). Herein, we demonstrated a low-cost and efficient synthesis route for favipiravir designed using improved retrosynthesis software, which involves only 3 steps under safe and near-ambient air conditions. A yield of 32% and cost of $1.54 per g were achieved by this synthetic route. We also used the same strategy to optimize the synthesis of sabizabulin. We anticipate that these synthetic routes will contribute to the prevention and treatment of COVID-19.

Protocol for ambient CO2 capture and conversion into HCOOH and NH4H2PO4.

CO2 capture and utilization into liquid fuels and high-added-value chemicals has been regarded as an attractive strategy to mitigate excessive carbon emissions. Here, we present a protocol to capture and convert CO2 into pure formic acid (HCOOH) solution and solid fertilizer (NH4H2PO4). We describe steps for synthesis of an IRMOF3-derived carbon-supported PdAu heterogeneous catalyst (PdAu/CN-NH2), which can efficiently catalyze (NH4)2CO3-captured CO2 into formate under ambient conditions. For complete details on the use and execution of this protocol, please refer to Jiang et al. (2023).1.

Nb2 CTx MXene Derived Polymorphic Nb2 O5.

Previously, heat treatment was the only feasible route for tuning the crystal phases of niobium pentoxide (Nb2 O5 ). With the use of Nb2 CTx MXene precursors, the first case of phase tuning of Nb2 O5 in the low-temperature hydrothermal synthesis using sulfuric acid regulating agents is presented. By varying the amount of the agent, four pure-phase Nb2 O5 crystals and mixed phases in-between are obtained. The required amount is found to be related to the H-covered surface energy calculated based on density functional theory. Overall, MXene-derived B-phase Nb2 O5 is of particular interest due to its exceptionally high capacities as lithium-ion battery anodes, which are three times higher than the routine synthesized one. Oxygen vacancies induced by crystallographic shear would be responsible for the extraordinary performance. The proposed phase tuning strategy encourages the prudent synthesis of difficult-to-obtain crystal phases.

Single-atom alloy Ir/Ni catalyst boosts CO2 methanation via mechanochemistry.

A new catalytic approach is pioneered to achieve CO2 methanation via a single atom alloy Ir/Ni catalyst using a ball-milling method. This Ir/Ni catalyst exhibits a TOFCH4 of 10244 h-1 and a 220 h lifetime at 350 °C without deactivation, illustrating excellent catalytic efficiency in the presence of mechanical energy.

Distilling universal activity descriptors for perovskite catalysts from multiple data sources via multi-task symbolic regression.

Developing activity descriptors via data-driven machine learning (ML) methods can speed up the design of highly active and low-cost electrocatalysts. Despite the fact that a large amount of activity data for electrocatalysts is stored in the literature, data from different publications are not comparable due to different experimental or computational conditions. In this work, an interpretable ML method, multi-task symbolic regression, was adopted to learn from data in multiple experiments. A universal activity descriptor to evaluate the oxygen evolution reaction (OER) performance of oxide perovskites free of calculations or experiments was constructed and reached high accuracy and generalization ability. Utilizing this descriptor with Bayesian-optimized parameters, a series of compelling double perovskites with excellent OER activity were predicted and further evaluated using first-principles calculations. Finally, the two ML-predicted nickel-based perovskites with the best OER activity were successfully synthesized and characterized experimentally. This work opens a new way to extend machine-learning material design by utilizing multiple data sources.

Poly(ionic liquid)s for Photo-Driven CO2 Cycloaddition: Electron Donor-Acceptor Segments Matter.

CO2 cycloaddition with epoxides is a key catalytic procedure for CO2 utilization. Several metal-based catalysts with cocatalysts are developed for photo-driven CO2 cycloaddition, while facing difficulties in product purification and continuous reaction. Here, poly(ionic liquid)s are proposed as metal-free catalysts for photo-driven CO2 cycloaddition without cocatalysts. A series of poly(ionic liquid)s with donor-acceptor segments are fabricated and their photo-driven catalytic performance (conversion rate of 83.5% for glycidyl phenyl ether) outstrips (≈4.9 times) their thermal-driven catalytic performance (17.2%) at the same temperature. Mechanism studies confirm that photo-induced charge separation is promoted by the donor-acceptor segments and can accelerate the CO2 cycloaddition reaction. This work paves the way for the further use of poly(ionic liquid)s as catalysts in photo-driven CO2 cycloaddition.

Heterogenization of Salen Metal Molecular Catalysts in Covalent Organic Frameworks for Photocatalytic Hydrogen Evolution.

Integrating a molecular catalyst with a light harvester into a photocatalyst is an effective strategy for solar light conversion. However, it is challenging to establish a crystallized framework with well-organized connections that favour charge separation and transfer. Herein, we report the heterogenization of a Salen metal complex molecular catalyst into a rigid covalent organic framework (COF) through covalent linkage with the light-harvesting unit of pyrene for photocatalytic hydrogen evolution. The chemically conjugated bonds between the two units contribute to fast photogenerated electron transfer and thereby promote the proton reduction reaction. The Salen cobalt-based COF showed the best hydrogen evolution activity (1378 µmol g-1 h-1 ), which is superior to the previously reported nonnoble metal based COF photocatalysts. This work provides a strategy to construct atom-efficient photocatalysts by the heterogenization of molecular catalysts into covalent organic frameworks.

Hydrogenation Reactions with Synergistic Catalysis of Pd single atoms and nanoparticles under Near-Ambient Conditions.

Due to the limited resources and high cost of noble metals, boosting their catalytic activities is highly desired in the current catalysis industry. Here, we report a synergetic catalyst, combining Pd2+ and Pd0 species in a nitrogen-doped porous carbons (NPC), which shows boosted catalytic activities in hydrogenation reactions of organic nitro compounds (nitrobenzene, 4-nitrophenol, 1-nitronaphthalene and 1-nitropropane) under near ambient conditions. This synergetic catalyst NPC-[Pd] was synthesized by partial reduction of a palladium-loaded NPC. The catalytic activities and selectivity of NPC-[Pd] for hydrogenation were enhanced significantly compared with those of NPC-Pd2+ or NPC-Pd0 nanoparticles. Theoretical calculations show that H2 preferentially dissociates on Pd nanoparticles, and then organic molecules (nitrobenzene) can be captured and react with the dissociated H atom on Pd2+ sites. Similar reaction procedure also occur on Pt or Rh. Hydrogenation of different aromatic compounds with different functional groups (naphthalene, 4-nitrochlorobenzene, benzaldehyde and acetophenone) confirmed the broad excellent catalytic activity of this synergistic catalyst.

MXene-Derived Metal-Organic Framework@MXene Heterostructures toward Electrochemical NO Sensing.

The electrochemical sensing of nitric oxide (NO) molecules by metal-organic framework (MOF) catalysts has been impeded, to a large extent, owing to their poor electrical conductivity and weak NO adsorption. In this work, incomplete in situ conversion of V2 CTx (T = terminal atoms) MXene to MOF is adopted, forming MOF@MXene heterostructures, which outperform MXene and MOF monocomponents toward electrochemical NO sensing. Density functional theory (DFT) calculation results indicate metal-like electronic characters for the heterostructure benefiting from the dominating contribution of the V 3d orbitals of the metallic MXene. Moreover, plane-averaged charge density difference shows substantial charge redistribution occurs at the heterointerfaces, producing a built-in field, which facilitates charge transfer. Besides, molecular mechanics-based simulated annealing calculation reveals greatly enhanced adsorption energies of NO molecules on the heterointerfaces than that on separate MOFs and MXenes. Hence, the facilitated charge transfer and preferential NO adsorption are responsible for the dramatically promoted performance toward NO sensing. The prudent design of MOF@MXene heterostructure may spur advanced electrocatalysts for electrochemical sensing.

Ultrasensitive NO Sensor Based on a Nickel Single-Atom Electrocatalyst for Preliminary Screening of COVID-19.

A new coronavirus, SARS-CoV-2, has caused the coronavirus disease-2019 (COVID-19) epidemic. A rapid and economical method for preliminary screening of COVID-19 may help to control the COVID-19 pandemic. Here, we report a nickel single-atom electrocatalyst that can be printed on a paper-printing sensor for preliminary screening of COVID-19 suspects by efficient detection of fractional exhaled nitric oxide (FeNO). The FeNO value is confirmed to be related to COVID-19 in our exploratory clinical study, and a machine learning model that can accurately classify healthy subjects and COVID-19 patients is established based on FeNO and other features. The nickel single-atom electrocatalyst consists of a single nickel atom with N2O2 coordination embedded in porous acetylene black (named Ni-N2O2/AB). A paper-printed sensor was fabricated with the material and showed ultrasensitive response to NO in the range of 0.3-180 ppb. This ultrasensitive sensor could be applied to preliminary screening of COVID-19 in everyday life.

Liquid Sunshine: Formic Acid.

"Liquid sunshine" is the conceptual green liquid fuel that is produced by a combination of solar energy, CO2, and H2O. Alcohols are commonly regarded as the preferred candidates for liquid sunshine because of their advantages of high energy density and extensive industrial applications. However, both the alcohol synthesis and H2 release processes require harsh reaction conditions, resulting in large external energy input. Unlike alcohols, the synthesis and dehydrogenation of formic acid (FA)/formate can be performed under mild conditions. Herein, we propose liquid sunshine FA/formate as a promising supplement to alcohol. First, we outline the vision of using FA/formate as liquid sunshine and discuss its feasibility. Then, we concentrate on the application of FA/formate as liquid organic hydrogen carrier and summarize the recent developments of CO2 hydrogenation to FA/formate and FA/formate dehydrogenation under mild conditions. Finally, we discuss the current applications, challenges, and opportunities surrounding the use of FA/formate as liquid sunshine.

Flavanthrene derivatives as photostable and efficient singlet exciton fission materials.

Singlet exciton fission (SF) is believed to have the potential to break the Shockley-Queisser limit for third-generation solar cell devices, so it has attracted great attention. Conventional linear acene based SF materials generally suffer from low triplet energy and poor photostability. We report herein two flavanthrene derivatives, EH-Fla and TIPS-Fla, as new photostable singlet exciton fission materials. These N-doped two-dimensional angular fused acenes have three sets of aromatic Clar sextets, making them significantly more stable than linear acenes with only one sextet. Time-resolved spectroscopy characterization reveals that the SF process occurs in the polycrystalline films of EH-Fla and TIPS-Fla, with maximal triplet yields of 32% and 159%, respectively. The SF processes of these two molecules are mediated by excimer states. In EH-Fla, the low-lying excimer prevents the SF process from occurring effectively, resulting in a low triplet yield. In contrast, the excimer state in TIPS-Fla is mixed with strong CT coupling, which prompts efficient SF and results in a high triplet yield. Our results show that flavanthrene is a promising SF chromophore for photoenergy conversion applications, while a fine-tune of the intermolecular interaction is crucial for achieving high SF efficiency.

First-principles study of CO2 hydrogenation to formic acid on single-atom catalysts supported on SiO2.

The hydrogenation of CO2 into valuable chemical fuels reduces the atmospheric CO2 content and also has broad economic prospects. Support is essential for catalysts, but many of the reported support materials cannot meet the requirements of accessibility and durability. Herein, we theoretically designed a series of single-atom noble metals anchored on a SiO2 surface for CO2 hydrogenation using density functional theory (DFT) calculations. Through theoretical evaluation of the formation energy, hydrogen dissociation capacity, and activity of CO2 hydrogenation, we found that Ru@SiO2 is a promising candidate for CO2 hydrogenation to formic acid. The energy barrier of the rate-determining step of the entire conversion process is 23.9 kcal mol-1; thus, the reaction can occur under mild conditions. In addition, active and stable origins were revealed through electronic structure analysis. The charge of the metal atom is a good descriptor of the catalytic activity. The Pearson correlation coefficient (PCC) between metal charge and its CO2 hydrogenation barrier is 0.99. Two solvent models were also used to investigate hydrogen spillover processes and the reaction path was searched by the climbing image nudged-elastic-band (CI-NEB) method. The results indicated that the explicit solvent model could not be simplified into a few solvent molecules, leading to a large difference in the reaction paths. This work will serve as a reference for the future design of more efficient catalysts for CO2 hydrogenation.

Protocol for fabrication and characterization of Fe-SAC@COF for electrocatalytic oxygen evolution reaction.

Single-atom catalysts (SACs) have promising atomic utilization efficiency and catalytic activity, but their construction with a specific coordination mode remains challenging. This protocol describes the synthesis of a coordinated Fe-SAC@COF for boosted electrocatalytic oxygen evolution reaction (OER). We also detail the steps for single iron atoms confinement and characterization of the COF and Fe-SAC@COF with X-ray diffraction and transmission electron microscopy technique. For complete details on the use and execution of this protocol, please refer to Wang et al. (2022).

In situ photodeposition of platinum clusters on a covalent organic framework for photocatalytic hydrogen production.

Photocatalytic hydrogen production has been considered a promising approach to obtain green hydrogen energy. Crystalline porous materials have arisen as key photocatalysts for efficient hydrogen production. Here, we report a strategy to in situ photodeposit platinum clusters as cocatalyst on a covalent organic framework, which makes it an efficient photocatalyst for light-driven hydrogen evolution. Periodically dispersed adsorption sites of platinum species are constructed by introducing adjacent hydroxyl group and imine-N in the region of the covalent organic framework structural unit where photogenerated electrons converge, leading to the in situ reduction of the adsorbed platinum species into metal clusters by photogenerated electrons. The widespread platinum clusters on the covalent organic framework expose large active surface and greatly facilitate the electron transfer, finally contributing to a high photocatalytic hydrogen evolution rate of 42432 µmol g-1 h-1 at 1 wt% platinum loading. This work provides a direction for structural design on covalent organic frameworks to precisely manipulate cocatalyst morphologies and positions at the atomic level for developing efficient photocatalysts.