Efficient Electron Transfer from Electron-Sponge Polyoxometalate to Single-Metal Site Metal-Organic Frameworks for Highly Selective Electroreduction of Carbon Dioxide

Structural Design and Energy and Environmental Applications of Hydrogen-Bonded Organic Frameworks: A Systematic Review

Hydrogen-bonded organic frameworks (HOFs) are emerging porous materials that show high structural flexibility, mild synthetic conditions, good solution processability, easy healing and regeneration, and good recyclability. Although these properties give them many potential multifunctional applications, their frameworks are unstable due to the presence of only weak and reversible hydrogen bonds. In this work, the development history and synthesis methods of HOFs are reviewed, and categorize their structural design concepts and strategies to improve their stability. More importantly, due to the significant potential of the latest HOF-related research for addressing energy and environmental issues, this work discusses the latest advances in the methods of energy storage and conversion, energy substance generation and isolation, environmental detection and isolation, degradation and transformation, and biological applications. Furthermore, a discussion of the coupling orientation of HOF in the cross-cutting fields of energy and environment is presented for the first time. Finally, current challenges, opportunities, and strategies for the development of HOFs to advance their energy and environmental applications are discussed.

Polyoxometalate-Structured Materials: Molecular Fundamentals and Electrocatalytic Roles in Energy Conversion

Polyoxometalates (POMs), a kind of molecular metal oxide cluster with unique physical-chemical properties, have made essential contributions to creating efficient and robust electrocatalysts in renewable energy systems. Due to the fundamental advantages of POMs, such as the diversity of molecular structures and large numbers of redox active sites, numerous efforts have been devoted to extending their application areas. Up to now, various strategies of assembling POM molecules into superstructures, supporting POMs on heterogeneous substrates, and POMs-derived metal compounds have been developed for synthesizing electrocatalysts. From a multidisciplinary perspective, the latest advances in creating POM-structured materials with a unique focus on their molecular fundamentals, electrocatalytic roles, and the recent breakthroughs of POMs and POM-derived electrocatalysts, are systematically summarized. Notably, this paper focuses on exposing the current states, essences, and mechanisms of how POM-structured materials influence their electrocatalytic activities and discloses the critical requirements for future developments. The future challenges, objectives, comparisons, and perspectives for creating POM-structured materials are also systematically discussed. It is anticipated that this review will offer a substantial impact on stimulating interdisciplinary efforts for the prosperities and widespread utilizations of POM-structured materials in electrocatalysis.

Exploring the role of sandwich-type polyoxometalates in {K10(PW9O34)2M4(H2O)2}@PCN-222 (M = Mn, Ni, Zn) for electroreduction of CO2 to CO

To overcome the drawbacks of high solubility and instability of polyoxometalates (POMs) in aqueous solution and to expand their application in the electrocatalytic reduction of CO₂ (ECR), we assemble sandwich-type POMs, K₁₀[(PW₉O₃₄)₂M₄(H₂O)₂] (M = Mn, Ni, Zn, shortened as P₂W₁₈M₄), into the hexagonal channel of a porphyrin-based metal-organic framework (MOF) PCN-222 to form P₂W₁₈M₄@PCN-222 composites. Their ECR behavior displays polyoxoanion-dependent activity. P₂W₁₈Mn₄@PCN-222 demonstrates a faradaic efficiency of 72.6% for the CO product (FE_CO), more than four times that of PCN-222 (FE_CO = 18.1%), and exhibits exceptional electrochemical stability over 36 h. P₂W₁₈Ni₄@PCN-222 and P₂W₁₈Zn₄@PCN-222 slightly increase (26.9%) and decrease (3.2%) in FE_CO, respectively. We combine the results with density functional theory (DFT) calculations to help understand the intrinsic reasons which reveals that the rate-determining step (RDS) reaction energy of P₂W₁₈Mn₄@PCN-222 and P₂W₁₈Ni₄@PCN-222 is significantly reduced compared to that of PCN-222. It is different in P₂W₁₈Zn₄@PCN-222. Frontier molecular orbitals electron distribution results hint at directional electron transfer from P₂W₁₈Mn₄/P₂W₁₈Ni₄ to the porphyrin ring active center in PCN-222, promoting the electro-reduction of CO₂ activity. By contrast, P₂W₁₈Zn₄ may accumulate electrons from PCN-222, thus facilitating the hydrogen evolution reaction (HER). This work reveals the critical role of sandwich-type POMs in manipulating the electron transfer pathway during the electrocatalytic process. Our findings would broaden the scope of POM applications in electrochemical carbon dioxide reduction.

Electrocatalytic Porphyrin/Phthalocyanine-Based Organic Frameworks: Building Blocks, Coordination Microenvironments, Structure-Performance Relationships

Metal-porphyrins or metal-phthalocyanines-based organic frameworks (POFs), an emerging family of metal-N-C materials, have attracted widespread interest for application in electrocatalysis due to their unique metal-N4 coordination structure, high conjugated π-electron system, tunable components, and chemical stability. The key challenges of POFs as high-performance electrocatalysts are the need for rational design for porphyrins/phthalocyanines building blocks and an in-depth understanding of structure-activity relationships. Herein, the synthesis methods, the catalytic activity modulation principles, and the electrocatalytic behaviors of 2D/3D POFs are summarized. Notably, detailed pathways are given for modulating the intrinsic activity of the M-N4 site by the microenvironments, including central metal ions, substituent groups, and heteroatom dopants. Meanwhile, the topology tuning and hybrid system, which affect the conjugation network or conductivity of POFs, are also considered. Furthermore, the representative electrocatalytic applications of structured POFs in efficient and environmental-friendly energy conversion areas, such as carbon dioxide reduction reaction, oxygen reduction reaction, and water splitting are briefly discussed. Overall, this comprehensive review focusing on the frontier will provide multidisciplinary and multi-perspective guidance for the subsequent experimental and theoretical progress of POFs and reveal their key challenges and application prospects in future electrocatalytic energy conversion systems.

A rational design of functional porous frameworks for electrocatalytic CO2 reduction reaction

The electrocatalytic CO₂ reduction reaction (ECO₂RR) is considered one of the approaches with the most potential to achieve lower carbon emissions in the future, but a huge gap still exists between the current ECO₂RR technology and industrial applications. Therefore, the design and preparation of catalysts with satisfactory activity, selectivity and stability for the ECO₂RR have attracted extensive attention. As a classic type of functional porous framework, crystalline porous materials (e.g., metal organic frameworks (MOFs) and covalent organic frameworks (COFs)) and derived porous materials (e.g., MOF/COF composites and pyrolysates) have been regarded as superior catalysts for the ECO₂RR due to their advantages such as designable porosity, modifiable skeleton, flexible active site structure, regulable charge transfer pathway and controllable morphology. Meanwhile, with the rapid development of nano-characterization and theoretical calculation technologies, the structure-activity relationships of functional porous frameworks have been comprehensively considered, i.e., metallic element type, local coordination environment, and microstructure, corresponding to selectivity, activity and mass transfer efficiency for the ECO₂RR, respectively. In this review, the rational design strategy for functional porous frameworks is briefly but precisely generalized based on three key factors including metallic element type, local coordination environment, and microstructure. Then, details about the structure-activity relationships for functional porous frameworks are illustrated in the order of MOFs, COFs, composites and pyrolysates to analyze the effect of the above-mentioned three factors on their ECO₂RR performance. Finally, the challenges and perspectives of functional porous frameworks for the further development of the ECO₂RR are reasonably proposed, aiming to offer insights for future studies in this intriguing and significant research field.

iClick synthesis of network metallopolymers

Described is an approach to preparing the first iClick network metallopolymers with porous properties. Treating digoldazido complex 2-AuN3 with trigoldacetylide 3-AuPPh3 or 3-AuPEt3, trialkyne 3-H, tetragoldacetylide 4-AuPPh3, or tetraalkyne 4-H in CH₂Cl₂ affords five iClick network metallopolymers 5-AuPPh3, 5-AuPEt3, 5-H, 6-AuPPh3, and 6-H. Confirmation of the iClick network metallopolymers comes from FTIR, ¹³C solid-state cross-coupling magic angle spinning (CPMAS) NMR spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and nitrogen and CO₂ sorption analysis. Employing model complexes 7-AuPPh3, 7-AuPEt3, 7-H, 8-AuPPh3, and 8-H provides structural insights due to the insolubility of iClick network metallopolymers.

The Progress of Metal-Organic Framework for Boosting CO2 Conversion

With the rapid development of modern society, environmental problems, including excessive amounts of CO2 released in the atmosphere, are becoming more and more serious. It is necessary to develop new materials and technologies to reduce pollution. Among them, metal–organic frameworks (MOFs) have shown potential for application in the area of catalysis due to their ultra-high specific surface area, structural versatility, and designability as well as ease of modification and post-synthesis. Herein, we summarize recent research advances by use of MOFs for boosting CO2 conversion. Furthermore, challenges and possible research directions related to further exploration are also discussed.

Atomically Dispersed NiN3 Sites on Highly Defective Micro-Mesoporous Carbon for Superior CO2 Electroreduction

Direct electrochemical conversion of CO₂ to CO product powered by renewable electricity is widely advocated as an emerging strategy for alleviating CO₂ emissions while addressing global energy issues. However, the development of low-cost and efficient electrocatalysts with high Faradaic efficiency for CO production (FE_CO ) and high current density remains a grand challenge. Herein, a robust single nickel atomic site electrocatalyst, which features isolated and dense single atomic NiN₃ sites anchored on highly defective hierarchically micro-mesoporous carbon (Ni-SAs/HMMNC-800), to enable enhanced charge transport and more exposed active sites for catalyzing electrochemical CO₂ -to-CO conversion, is reported. The Ni-SAs/HMMNC-800 catalyst achieves excellent activity and selectivity with high FE_CO values of >90% throughout a wide potential range (the FE_CO reaches 99.5% at -0.7 V vs reversible hydrogen electrode) and a CO partial current density as high as 13.0 mA cm^-2 at -0.7 V versus reversible hydrogen electrode, as well as a far outstanding durability during long-term continuous operation, indicating a superior CO₂ electroreduction performance than that of other reference samples and most of previously reported carbon-based single atom electrocatalysts. Experimental and density functional theory calculations reveal that atomic NiN₃ coordination sites coupled adjacent defects are favorable to significantly enhancing the formation of COOH* reaction intermediates while suppressing the competing hydrogen evolution reaction, thereby enhancing the electrocatalytic activity for CO₂ -to-CO reduction. Notably, this work provides a valuable new prospect for designing and synthesizing efficient and cost-effective single atom CO₂ electroreduction catalysts for practical applications.

In Situ Construction of MIL-100@NiMn-LDH Hierarchical Architectures for Highly Selective Photoreduction of CO2 to CH4

Layered double hydroxides (LDHs) are considered a promising catalyst for photocatalytic CO₂ reduction due to their broad photoresponse, facile channels for electron transfer, and the presence of abundant defects. Herein, we reported for the first time the fabrication of a novel photocatalyst MIL-100@NiMn-LDH with a hierarchical architecture by selecting MIL-100 (Mn) as a template to provide Mn³⁺ for the in situ growth of ultrathin NiMn-LDH nanosheets. Moreover, the in situ growth strategy exhibited excellent universality toward constructing MIL-100@LDH hierarchical architectures. When applied in the photocatalytic CO₂ reduction reaction, the as-prepared MIL-100@NiMn-LDH exhibited excellent CH₄ selectivity of 88.8% (2.84 μmol h^-1), while the selectivity of H₂ was reduced to 1.8% under visible light irradiation (λ > 500 nm). Such excellent catalytic performance can be attributed to the fact that (a) the MIL-100@NiMn-LDH hierarchical architectures with exposed catalytic active sites helped to enhance the CO₂ adsorption and activation and (b) the presence of rich oxygen vacancies and coordinately unsaturated metal sites in MIL-100@NiMn-LDH that optimized the band gap and accelerated the separation/transport of photoinduced charges.

POM-based metal organic frameworks with a woven fabric structure for lithium storage

A novel POMOFs with fabric structure possesses high lithium storage capacity, and its long life cycle performance is further enhanced by CNTs.

Exploiting Redox-Complementary Peptide/Polyoxometalate Coacervates for Spontaneously Curing into Antimicrobial Adhesives

Recently, there has been a wave of reports on the fabrication of peptide-based underwater adhesives with the aim of understanding the adhesion mechanism of marine sessile organisms or creating new biomaterials beyond nature. However, the poor shear adhesion performance of the current peptide adhesives has largely hindered their applications. Herein, we proposed to sequentially perform the interfacial adhesion and bulk cohesion of peptide-based underwater adhesives using two redox-complementary peptide/polyoxometalate (POM) coacervates. The oxidative coacervates were prepared by mixing oxidative H₅PMo₁₀V₂O₄₀ and cationic peptides in an aqueous solution. The reductive coacervates consisted of K₅BW₁₂O₄₀ and cysteine-containing reductive peptides. Each of the individual coacervate has well-defined spreading capacity to achieve fast interfacial attachment and adhesion, but their cohesion is poor. However, after mixing the two redox-complementary coacervates at the target surface, effective adhesion and spontaneous curing were observed. We identified that the spontaneous curing resulted from the H₅PMo₁₀V₂O₄₀-regulated oxidization of cysteine-containing peptides. The formed intermolecular disulfide bonds improved the cross-linking density of the dual-peptide/POM coacervates, giving rise to the enhanced bulk cohesion and mechanical strength. More importantly, the resultant adhesives showcased excellent bioactivity to selectively suppress the growth of Gram-positive bacteria due to the presence of the polyoxometalates. This work raises further potential in the creation of biomimetic adhesives through the orchestrating of covalent and noncovalent interactions in a sequential fashion.