Boosting selective CO2 reduction via strong spin-spin coupling on dual-atom spin-catalysts

Achieving high selectivity in electrochemical conversion of carbon dioxide (CO2) into valuable products remains a significant challenge. This study investigates the influence of spin states on dual-atom catalysts within two-dimensional metal-organic frameworks (2D-MOFs) and zero-dimensional molecular metal complexes (0D-MMCs), emphasizing their role in the selective electrocatalytic reduction of CO2. Utilizing first-principles calculations, we systematically evaluate dual-atom spin-catalysts (DASCs) TM2S4(NH)2(C6H4)2 0D-MMC and TM2S4(NH)2C4 2D-MOF for CO2 reduction reactions (CO2RR) across various spin states: antiferromagnetic (AFM), ferromagnetic (FM), and non-magnetic (NM). Our analysis confirms that, beyond successfully designing and screening highly active catalysts, the selectivity for various C1 products in CO2 reduction can be readily adjusted by DASCs via spin-spin coupling. Specifically, Mn2 and Fe2 2D-MOF DASCs with an AFM ground state are more inclined to produce formic acid, while their FM counterparts favor the formation of methane, surpassing formic acid among others. Additionally, we demonstrate that 0D-MMCs, as molecular units of 2D-MOFs, achieve comparable catalytic performance. Combining theoretical insights with machine learning highlights the crucial role of electronic and geometric descriptors in the catalytic performance. Our work establishes the correlation between spin-spin coupling and highly selective CO2 reduction in DASCs, offering an effective strategy for designing tunable and efficient electrocatalysts.

Chemical fixation of CO2 conducted by Mg-based materials catalysts to produce cyclic carbonates: A comprehensive review

We are witnessing a surge in CO2 emissions into the atmosphere, leading to serious environmental issues for our planet. If we do not take action, it will harm humanity and the biosphere. Increased levels of CO2 in the atmosphere contribute to global warming, which results in climate upheavals that disrupt ecosystems, alter plant reproduction conditions, and cause numerous related problems. Consequently, the current CO2 levels in the atmosphere must be significantly lowered as soon as possible. CO2 is a plentiful C1 feedstock, and its chemical utilization has inspired chemists in recent years. The reaction of CO2 with epoxide to produce cyclic carbonate (CCs) is highly significant and actively pursued in laboratories worldwide. So, by chemically fixing CO2 into valuable cyclic carbonates, we can achieve two goals at once: reducing atmospheric CO2 and producing essential chemicals. However, CO2's low reactivity and high stability make fixation challenging, leading to the development of innovative heterogeneous catalytic systems to address this. Magnesium-based materials (Mg-based materials) have become an attractive choice for chemical catalysis of CO2 fixation reactions owing to their unique properties enabled by the polar structure of Mg(II) leads to their high CO2 affinity. This research deals with the introduction of Mg-based materials, synthesis methods, and their effect on the performance of the catalytic process in CO2 fixation reactions. Thus, this review can provide researchers with light horizons in utilizing the high potential of Mg-based materials in synthesizing efficient catalysts to achieve excellent yield, conversion, and selectivity in the cycloaddition of CO2 to epoxides into CCs.

Ferrocene unit substitution in nickel(II) porphyrin(2.1.2.1) induces an extremely low oxygen evolution reaction overpotential

This study reports the synthesis, characterization, structure and the oxygen evolution reaction (OER) performance of ferrocene-substituted nickel(II) porphyrin(2.1.2.1) complexes. The Ni-3 complex, functionalized with two ferrocene units, demonstrates exceptional OER activity, achieving an overpotential of 280 mV at 10 mA cm-2 in alkaline media. This enhancement is ascribed to the electron-rich ferrocene moieties, which act as efficient electron-transfer mediators during catalysis. DFT calculations corroborate these findings, revealing a theoretical overpotential of 0.79 eV for the dual-ferrocene-substituted catalyst. These results underscore the critical role of ferrocene in lowering the overpotential of molecular OER catalysts.

Asymmetric heterogeneous catalysis using crystalline porous materials

Asymmetric catalysis has emerged as a pivotal strategy in the synthesis of chiral compounds, offering significant advantages in selectivity and efficiency. In recent years, heterogeneous catalysis has become a focal point in the fields of organic synthesis and materials science due to continuous advancements in science and technology, especially the use of crystalline porous materials (CPMs) as catalysts. This review summarizes recent advances in using CPMs, such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and zeolites, as promising supports for asymmetric catalysts. These materials provide high surface areas, tunable porosity, and the ability to host active catalytic sites, which enhance reaction rates and selectivity. In this review, we summarize the stereostructural properties of chiral CPMs to guide the future design of asymmetric heterogeneous catalysts and the study of catalytic mechanisms. Moreover, we discuss various strategies for incorporating catalytic moieties into these frameworks, including direct synthesis, post-synthesis modification and induced synthesis methods. Additionally, we highlight recent examples where CPMs have been successfully applied in asymmetric transformations, examining their mechanistic insights and the role of substrate diffusion in achieving high enantioselectivity. This review concludes with a perspective on the challenges and future directions in this rapidly evolving field, emphasizing the need for further integration of advanced artificial intelligence techniques and design principles to optimize the synthesis and catalytic performance of chiral CPMs.

Enhancing charge transfer efficiency through carboxyl-modification to improve the photocatalytic activity of covalent organic frameworks for hydrogen evolution from water splitting

The design of photocatalysts based on covalent organic frameworks (COFs) has attracted considerable interest. Nevertheless, the low efficiency in separating photogenerated carriers remains a substantial challenge. Herein, carboxyl modification is employed to enhance the separation efficiency of photogenerated carriers within imine-based porphyrin COFs through the resultant built-in electric field, thereby improving the photocatalytic performance of COFs in hydrogen evolution from water splitting. Spectroscopic and electrochemical analyses reveal that, compared with pristine two-dimensional porphyrin-based COFs (Por-COF), an isostructural carboxyl-modified COF (Por-COOH-COF) exhibits a prolonged excited-state lifetime, reduced exciton binding energy and decreased deactivation probability via radiative processes, and an improved photocurrent response. These improvements result in a hydrogen evolution of 12773 ± 297 μ mol⋅g-1⋅h-1 for Por-COOH-COF, approximately four times higher than that of Por-COF (3351 ± 197 μmol⋅g-1⋅h-1), positioning it among the most efficient metal-free COF photocatalysts reported to date. Density functional theory calculations and in situ X-ray photoelectron spectroscopy analyses indicate that carboxyl modification facilitates charge transfer from the porphine core to the active site of the imine bond (-CN-) under the ultraviolet-visible light irradiation, thereby contributing to the remarkable photocatalytic activity of Por-COOH-COF. This study elucidates how carboxyl groups positively influence photogenerated carrier separation within COFs and provides valuable insights into the development of high-performance metal-free COFs photocatalysts.

Steric factors controlling regioselective and efficient N-methylation of β-tetrabromoporphyrins

N-Methylation is a facile way to tune the structures and the electronic properties of porphyrin macrocycles, which could induce molecular recognition abilities or asymmetric geometric structures for organocatalytic and optoelectronic applications. However, as N-methylation reactions require a strong methylating reagent such as methyl triflate, control over the reactivities including methylation number and positions is still elusive. In this work, we have achieved highly regioselective and efficient 21N,23N-dimethylation of β-tetrabrominated porphyrins by methyl triflate. The experimental and theoretical evidence reveal that steric effects of bulky Br groups and unique tautomerisms of β-substituted porphyrins play essential roles in determining the regioselectivity of the nucleophilic N-methylation. Moreover, the high basicity of the formed 21N,23N-dimethylporphyrins induces the facile protonation of imine nitrogen atoms, which regulates the number of introduced methyl groups to suppress further N-methylation. As Br groups can be easily converted into various types of substituents, this work provides significant insights to expand the synthetic methods of N-methylporphyrins with precisely tunable reactivities and physicochemical properties.

Unveiling the potential of tailored β-substituted iron-porphyrins for highly efficient oxygen reduction reactions (ORR)

A series of β-substituted iron porphyrins, including Fe(III)ClTPPMe4, Fe(III)ClTPPPh4, and Fe(III)ClTPPBr4, featuring electron-withdrawing and electron-donating groups, were synthesized, characterized, and evaluated for their catalytic activity in the oxygen reduction reaction (ORR). These catalysts exhibited onset potentials of 0.77 V, 0.98 V, and 0.79 V (RHE), comparable to platinum-based electrodes, along with high stability over 11 000 s and a 4e-/4H+ transfer pathway. Electron-withdrawing β-substituents combined with steric effects enhance ORR performance, with the phenyl-substituted porphyrin exhibiting unique catalytic behavior due to steric distortions in the porphyrin ring. DFT calculations revealed that a reduced HOMO-LUMO gap facilitates electron transfer which in turn improves catalytic efficiency.

Synthesis and Characterization of Bimetallic Copper(I) Complexes Supported by a Hexadentate Naphthyridine-Based Macrocycle Ligand

Herein, we report the synthesis, characterization, and binding properties of a new ligand, N,N'-di-tert-butyl-3,7-diaza-1,5(2,7)-1,8-naphthyridinacyclooctaphane (tBuN6), with copper (I), CuI, centers. We demonstrate the flexibility and the ability of tBuN6 to adopt various conformations in solution and when coordinated to CuIcenters. NMR studies exhibit the labile coordination nature of CuI. However, the lability of the complexes is blocked by counterion exchange, which enables the use of less coordinating solvents such as tetrahydrofuran (THF) and avoids using acetonitrile. Thus, the exchange of [BF4]- with tetrakis 3,5-bis(trifluoromethyl)phenyl borate, [B(ArF)4]-, in 1·BF4, [Cu2(MeCN)2(tBuN6)][BF4], generates 1·B(ArF)4, which is stable in THF and reacts under a CO atmosphere to generate a syn,syn bis(carbonyl) complex. This complex is sufficiently stable in solution under CO and Ar atmosphere to be characterized by NMR and IR spectroscopy, the latter revealing two stretching bands for the CO bound to the CuI-centers at 2102 and 2088 cm-1.

Modulating Active Center Microenvironment in Phthalocyanine-Based Covalent Organic Frameworks for Enhanced Electrocatalytic CO2 to CH3OH

Developing catalysts for electrocatalytic CO2 to CH3OH still faces great challenge due to the involvement of multiple proton-coupled electron transfer (PCET) processes. Molecular phthalocyanine electrocatalysts on carbon nanotubes have achieved production of methanol as the sole liquid-phase product but with the activity and stability far from meeting industrial demands. Herein, phthalocyaninato cobalt is fabricated into covalent organic frameworks PE-COF via polymerization with ellagic acid. Subsequent hydrolyzation of the ester groups in this framework affords COOH/OH-containing PEH-COF, resulting in the successful modulation over the local microenvironment of Co as electrochemical active center and in turn rendering the production of CH3OH with high yield and durability. Experimental and theoretical investigations reveal that construction of the COOH group and H2O participated catalytic cages in PEH-COF can effectively fix hydrated potassium ions, which efficiently enhances the PCET kinetics and lowers the energy barriers for the conversion of CO2 to CH3OH. The partial current density (j) and Faraday efficiency of methanol for PEH-COF could reach 100.9 mA cm-2 and 38.5%, respectively. Moreover, thej C H 3 O H $\mathrm{j}_{{CH}_3OH}$ of PEH-COF can be maintained at 100.4 mA cm-2 after 9 h of electrocatalysis, superior to the thus far reported catalysts.

Synthesis of the NiO-Faujasite Nanocatalyst for Dry Reforming of Methane: The Effect of the Aniline Additive

Dry reforming of methane (DRM) using a heterogeneous catalyst presents one of the CO2 mitigation pathways to address global warming and climate change challenges. Such a suitable DRM catalyst with optimum activity and stability is still under intense research. We herein present a facile, slightly modified version of the conventional wet impregnation method to synthesize a NiO-faujasite nanocatalyst for DRM with the help of aniline, judiciously chosen based on the hard-soft acid-base (HSAB) principle. The resulting catalyst was characterized by the N2 adsorption isotherm, PXRD, SEM/TEM, XPS, 29Si solid-state NMR, H2-TPR, NH3-TPD, and DRM reaction, and its results were compared with those without aniline assistance. A smaller NiO nanoparticle with better dispersion was observed for our aniline-assisted sample resulting in a significant increase in activity (peaking at 86% CH4 conversion with a H2/CO ratio of 0.93) and stability for a 12 h time on stream. We hope that this work would pave the way to utilize the HSAB principle to synthesize more nanocatalysts with optimum overall performance.

Porphyrin-Based Covalent Organic Framework Encapsulating Multiwalled Carbon Nanotubes: A High-Performance Electrocatalyst for Oxygen Reduction Reaction

The development of efficient and cost-effective oxygen reduction reaction (ORR) catalysts is crucial for advancing fuel cell technologies, given the limitations of platinum-based catalysts. Here, we present a novel nanocomposite, cobalt-based porphyrinic covalent organic framework wrapped on multiwalled carbon nanotubes (Co-pCOF@MWCNTs), synthesized via template-directed in situ polymerization. This composite combines the high porosity and tunable catalytic properties of porphyrinic COFs with the excellent electrical conductivity of MWCNTs. The Co-pCOF@MWCNT demonstrates superior ORR activity, exhibiting an onset potential (Eonset) of 0.86 V vs RHE in 0.1 M KOH, surpassing the performance of its individual components (Co-pCOF and MWCNT) and other related materials. The enhanced catalytic efficiency is attributed to the synergistic interactions between the conductive MWCNT scaffold and the active porphyrinic COF nanolayers, which facilitate efficient charge transfer and increase catalytic site exposure. Furthermore, the nanocomposite exhibits high stability and methanol tolerance, establishing its potential as a cathodic material for fuel cells. This work highlights the promise of integrating COFs with conductive carbon materials and opens new avenues for the design of advanced ORR catalysts for energy conversion applications.

MXene-Regulated Indium-Based Metal-Organic Framework Material for Electrochemical Reduction of CO2 into Pure Formic Acid Aqueous Solution

Electrochemical CO2 reduction reaction provides a mild avenue for resource utilization of CO2. Metal-organic framework (MOF) materials are considered among the promising catalysts due to unique structural advantages. However, the catalytic performance of MOFs is hindered by poor conductivity, making it crucial to enhance the charge transfer for improved efficiency. Herein, a hybrid catalyst was constructed based on the In-based porphyrin framework (In-TCPP) and conducting MXene nanosheets for efficient CO2 conversion. As expected, MXene as a unique conductive support significantly improves the catalytic performance of the hybrid material, achieving a Faraday efficiency for HCOO- of 94.0% with a 2.2-fold increase in the practical current density. Furthermore, a pure formic acid solution with a concentration of ca. 0.22 M was prepared via execution in a solid-state electrolyte-mediated MEA (MEA-SSE) device. Theoretical calculations and in situ ATR-FTIR spectra reveal that the introduction of MXene not only endows the hybrid material with metallic properties to facilitate charge transfer but also modulates the electronic structure to optimize the adsorption of the key intermediate *OCHO. This work enlightens the rational design of MOF-based electrocatalysts via the regulation of MXene and demonstrates the promise of the MEA-SSE device for practical CO2 reduction applications.

Conductivity of a series of (4,8)-connected lanthanide metal-organic frameworks with [Ln4O5] clusters and high selectivity for visual sensing of nitrophenol compounds

A series of lanthanide (Ln) metal-organic frameworks, namely [Nd4(Hdtztp)2O(OH)4(H2O)4]·5(H2O)·DMF (Nd4), [Sm4(Hdtztp)2O(OH)4(H2O)4]·5(H2O)·DMF (Sm4), [Tb4(Hdtztp)2O(OH)4(H2O)2(DMF)2] (Tb4), and [Er4(Hdtztp)2O(OH)4(H2O)2(DMF)2] (Er4), were synthesized by using 2,5-bis-(2H-tetrazol-5-yl)-terephthalic acid (H4dtztp) and lanthanide nitrate as raw materials under solvothermal conditions. X-ray single crystal diffraction reveals that the Ln4 compounds crystallize in the orthorhombic Pmmn space group. In these structures, four Ln ions are interconnected through four μ-3 OH and one μ-2 O bridge to form a [Ln4O5] cubane, which is surrounded by eight ligands to form 8-connected building units. These 8-connected building units are linked to 4-connected Hdtztp3- forming the 4,8-connected three-dimensional (3D) frameworks of Ln4. The phase and purity of Ln4 polycrystalline samples were confirmed by elemental analysis, thermogravimetric analysis (TG) and powder X-ray diffraction (PXRD). The conductivity test proves the existence of π-π stacking electron transfer pathways between tetrazolium and aromatic carbon rings in the crystal, where the conductivity of Nd4 with the largest atomic radius is one order of magnitude higher than that of Er4 with the smallest atomic radius. Due to the excellent fluorescence performance and water stability, Tb4 can be used as a fluorescent probe for nitro compounds, and its detection limit of p-nitrophenol (4-NP) is 38.5 nM.

Selective two-electron and four-electron oxygen reduction reactions using Co-based electrocatalysts

The oxygen reduction reaction (ORR) can take place via both four-electron (4e-) and two-electron (2e-) pathways. The 4e- ORR, which produces water (H2O) as the only product, is the key reaction at the cathode of fuel cells and metal-air batteries. On the other hand, the 2e- ORR can be used to electrocatalytically synthesize hydrogen peroxide (H2O2). For the practical applications of the ORR, it is very important to precisely control the selectivity. Understanding structural effects on the ORR provides the basis to control the selectivity. Co-based electrocatalysts have been extensively studied for the ORR due to their high activity, low cost, and relative ease of synthesis. More importantly, by appropriately designing their structures, Co-based electrocatalysts can become highly selective for either the 2e- or the 4e- ORR. Therefore, Co-based electrocatalysts are ideal models for studying fundamental structure-selectivity relationships of the ORR. This review starts by introducing the reaction mechanism and selectivity evaluation of the ORR. Next, Co-based electrocatalysts, especially Co porphyrins, used for the ORR with both 2e- and 4e- selectivity are summarized and discussed, which leads to the conclusion of several key structural factors for ORR selectivity regulation. On the basis of this understanding, future works on the use of Co-based electrocatalysts for the ORR are suggested. This review is valuable for the rational design of molecular catalysts and material catalysts with high selectivity for 4e- and 2e- ORRs. The structural regulation of Co-based electrocatalysts also provides insights into the design and development of ORR electrocatalysts based on other metal elements.

Integrating Multifunctionalities into a 3D Covalent Organic Framework for Efficient CO2 Photoreduction

Fabrication of highly efficient photocatalysts for CO2 conversion is still challenging. Herein, integrating nitrogen-rich organic cages and the photoactive porphyrin moieties together, a 3D covalent organic framework (COF), Cage-PorCOF, is successfully synthesized. After incorporating metal ions (Co2+ and Ni2+) into the cage-based COF, Cage-PorCOF(Co) and Cage-PorCOF(Ni) are subsequently constructed for the CO2 photoreduction. Catalytic experiments show impressive performance in CO2 photoreduction with CO generation rates of up to 48 748 and 28 446 µmol g-1 h-1 in the first initiating hour for Cage-PorCOF(Co) and Cage-PorCOF(Ni), respectively, which is attributed to the synergistic effects from CO2-affinity of the porous frameworks and incorporated metal atoms, the light-absorption and charge separation ability of metalloporphyrin groups as well as the fully exposed single-atomic catalytic sites confirmed by both experimental and theoretical analyses. This study demonstrates that by the integration of multiple functionalities into 3D porous solids, highly effective photocatalysts for CO2 conversion can be achieved.

Achieving >23% Efficiency Perovskite Solar Minimodules with Surface Conductive Coordination Polymer

Despite the reported high efficiencies of small-area perovskite photovoltaic cells, the deficiency in large-area modules has impeded the commercialization of perovskite photovoltaics. Enhancing the surface/interface conductivity and carrier-transport in polycrystalline perovskite films presents significant potential for boosting the efficiency of perovskite solar modules (PSMs) by mitigating voltage losses. This is particularly critical for multi-series connected sub-cell modules, where device resistance significantly impacts performance compared to small-area cells. Here, an effective approach is reported for decreasing photovoltage loss through surface/interface modulation of perovskite film with a surface conductive coordination polymer. With post-treatment of meso-tetra pyridine porphyrin on perovskite film, PbI2 on perovskite film reacts with pyridine units in porphyrins to generate an iso-structural 2D coordination polymer with a layered surface conductivity as high as 1.14 × 102 S m-1, due to the effect of surface structure reconstruction. Modified perovskite film exhibits greatly increased surface/interface conductivity. The champion PSM obtains a record efficiency up to 23.39% (certified 22.63% with an aperture area of 11.42 cm2) featuring only 0.33-volt voltage loss. Such a modification also leads to substantially improved operational device stability.

Synthesis of Porphyrin Derivatives Bearing Six Carboxylic Acids for the Formation of Three-Dimensional Hydrogen-Bonded Network Structures

we synthesized a series of porphyrin derivatives with six carboxylic acid groups to explore their potential in forming hydrogen-bonded networks (YSHs). By systematically varying the position and structure of these carboxylic acid groups, we observed distinct types of hydrogen-bonded frameworks, including two- and three-dimensional networks. Using single-crystal X-ray crystallography, we confirmed that these derivatives form YSHs with unique structural properties influenced by carboxylic acid positioning and π-π interactions. The 1Zn derivative forms a robust 3D hydrogen-bonded network stabilized by π-π stacking interactions, while the 2Ni derivative, with no such stacking, exhibits reduced stability and collapses upon solvent removal. Structural variations like the terphenylene and biphenyl linkers in 3Zn and 4Zn lead to flexible frameworks, while the 5Zn dimer forms two distinct structures depending on the solvent environment. Our findings reveal that careful control over carboxylic acid orientation and linker structure enables the design of diverse hydrogen-bonded networks with tunable stability and dimensionality. These insights advance our understanding of supramolecular assembly principles in porphyrin-based materials and offer new pathways for developing high-performance frameworks for applications in catalysis, sensing, and materials science.

Precisely tuning the electronic states of organic polymer electrocatalysts via thiophene-based moieties for enhanced oxygen reduction reaction

Optimizing molecular structures in oxygen reduction reaction (ORR) is crucial for enhancing catalytic efficiency and stability, particularly with respect to the effective adsorption and conversion of reaction intermediates. Sulfur-containing heterocyclic compound thiophene can precisely modulate the electronic states and local charge densities, thereby fine-tuning the adsorption and reactivity of microporous polymers, yet, it remains a largely unexplored area. Herein, thiophene-based building blocks featuring diversified linkers into a phenyl-containing model Ph-CMP are developed, affording the thiophene-fused BPT-CMP and the thiophene-linked BCT-CMP. The electron density and adsorption capacity of the frameworks are well regulated through condensation and connecting modification, showing excellent half-wave potentials compared to the reversible hydrogen electrode, surpassing even most metal-free polymer electrocatalysts. Through theoretical calculations and experimental results, we have validated that the thiophene-fused skeleton (BPT-CMP) triggers the activation of thiophene units, with the exposed pentatomic heterocyclic carbon atom (site-3) serving as the catalytic active site.

Improving Electrocatalytic CO2 Reduction over Iron Tetraphenylporphyrin with Triethanolamine as a CO2 Shuttle

Delivering CO2 molecules to catalyst sites is a vital step in the CO2 reduction reaction (CO2RR). Achievements have been made to develop efficient catalysts, but few efforts have been dedicated to improving CO2 delivering in solutions. Herein, we report on electrocatalytic CO2-to-CO conversion using Fe tetraphenylporphyrin (FeTPP) as a catalyst and triethanolamine as a CO2 shuttle. Compared to ethanol, the electrocatalytic CO2RR current with triethanolamine increases by more than three times. We show that triethanolamine can effectively capture a CO2 molecule to form a zwitterionic alkylcarbonate through the collaboration between its tripodal alcohol and amine units. This alkylcarbonate can release the bound CO2 molecule for activation at the Fe site upon its interaction with FeTPP. In addition to shuttling CO2, alkylcarbonates can also provide protons to assist the C-O bond cleavage. Therefore, this work is significant to demonstrate a new strategy to improve electrocatalytic CO2RR by shuttling CO2.

X-ray spectroscopy characterization of cobalt stabilization within a monolayer carbon nitride in the oxygen evolution reaction

Carbon nitride-based catalysts containing earth-abundant metals such as Co have gained attention for the oxygen evolution and reduction reactions (OER and ORR). The catalytic activity of such materials is known to be sensitive to metal dispersion and coordination, which again may depend on reaction conditions, but exact information on the active state and the possible coordination state changes of Co in these materials induced by electrocatalytic conditions are in general lacking. Here, we study the redistribution of Co during the OER in a composite planar model system consisting of a well-defined single-atom Co-doped carbon nitride monolayer and Co nanoparticles on Au(111). Through a combination of electrocatalytic activity measurements and analysis of the catalyst surface pre- and post-electrochemical operation using X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy, we investigate the induced changes in Co species and the carbon nitride network. Our findings indicate significant mobility during the OER of Co atoms originating from the Co nanoparticles, with the presence of the carbon nitride stabilizing Co in a dispersed form. The dispersion of Co leads to a steady increase in OER activity over time, which is only observed when both Co nanoparticles and Co-doped carbon nitride co-exist. We attribute this phenomenon to the carbon nitride's role in dispersing and stabilizing highly mobile cobalt species on the surface, thereby enhancing electrochemical stability.

Tailoring the Electrocatalytic Properties of Porphyrin Covalent Organic Frameworks for Highly Selective Oxygen Sensing In Vivo

In vivo selective sensing of oxygen (O2) dynamics in the central nervous system could provide insights into energy metabolism and neural activities. Although the electrocatalytic four-electron oxygen reduction reaction (ORR) paves an effective way to the electrochemical sensing of O2 in vivo, the concurrent hydrogen peroxide reduction reaction (HPRR) within the potential windows for four-electron ORR unfortunately poses a great challenge to the conventional mechanism employed for selective electrochemical O2 sensing. In this work, we find that regulation of the linkers within the skeleton of porphyrin-based covalent organic frameworks (COFs) could improve the selectivity of the O2 sensor against hydrogen peroxide (H2O2). The electrochemical results reveal that the Co porphyrin active sites facilitate the direct four-electron pathway for ORR and that the Co porphyrin-based COF, enriched with pyrene units, shows enhanced four-electron ORR kinetics and better tolerance to HPRR. The theoretical calculation suggests that introducing pyrene units essentially weakens the adsorption of H2O2, leading to suppression of the HPRR. The microsensor fabricated with the Co porphyrin-based COF as the electrocatalyst features a high selectivity for real-time monitoring of O2 in a living rat brain.

Upgrading the Bioinspired Iron-Polyporphyrin Structures by Abiological Metals Toward New-Generation Reactive Oxygen Biocatalysts

Developing artificial enzymes based on organic molecules or polymers for reactive oxygen biocatalysis has broad applicability. Here, inspired by heme-based enzyme systems, we construct the abiological iron group metal-based polyporphyrin (Ru/Os-coordinated porphyrin-based biocatalyst, Ru/Os-PorBC) to serve as a new generation of efficient and versatile reactive oxygen species (ROS)-related biocatalyst. Due to the structural benefits, including excellent electron configuration, appropriate bandgap, and optimized adsorption and activation of reaction intermediates, Ru/Os-PorBC shows unparalleled ROS-production activities regarding maximum reaction rate and turnover numbers, which also demonstrates superior pH and temperature adaptability compared to natural enzymes. Impressively, the Os-PorBC manifests the most efficacious ROS-production capabilities, surpassing not only Ru/Fe-PorBC but also the existing state-of-the-art ROS-related biocatalyst. Our findings provide a pivotal direction for developing next-generation polyporphyrin-based biocatalysts, setting the stage for a new era of upgrading the artificial metalloenzymes by abiological metals.

Porous Molecular Crystals Derived from Cofacial Porphyrin/Phthalocyanine Heterodimers

Porphyrin-based porous materials are of growing interest as heterogeneous catalysts especially for reactions that are of importance to sustainability. Here we demonstrate that porous molecular crystals can be prepared by the simple co-crystallisation of tetraphenylporphyrin (TPP) with octa(2',6'-di-iso-propylphenoxy)phthalocyanine or some of its metal complexes [(dipPhO)8PcM; M=H2, Al-OH, Ti=O, Mn-Cl, Fe-Cl, Co, Ni, Cu, Zn, Ga-Cl, Ag, In-Cl or Au-Cl]. This process is facilitated by the efficient formation of the supramolecular heterodimer between TPP and (dipPhO)8PcM, which is driven by the complementary shape and symmetry of the two macrocycles. The (dipPhO)8PcM component directs the crystal structure of the heterodimers to form Phthalocyanine Nanoporous Crystals (PNCs) of similar structure to those formed by (dipPhO)8PcM alone. The incorporation of TPP appears to partially stabilise the PNCs towards the removal of included solvent and for cocrystals containing (dipPhO)8PcCo stability can be enhanced further by the insitu addition of 4,4-bipyridyl to act as a "molecular wall tie". These stabilised PNC/TPP cocrystals have a Brunauer-Emmett-Teller surface area (SABET) of 454 m2 g-1 and a micropore volume (Vmp) of 0.22 mL g-1. The reactivity of both macrocycles within the PNC/TPP co-crystals is demonstrated by insitu metal insertion.

The steric hindrance effect of Co porphyrins promoting two-electron oxygen reduction reaction selectivity

A new Co 5,10,15,20-tetrakis(2',6'-dipivaloyloxyphenyl)porphyrin (1) with eight ester groups in all ortho and ortho' positions of phenyl groups was designed, which displayed significantly improved 2e oxygen reduction reaction (ORR) selectivity compared with a 5,10,15,20-tetrakis(para-dipivaloyloxyphenyl) porphyrin (2) without large steric groups. This work is significant to reveal the steric hindrance effect of metal porphyrins on electrocatalytic ORR selectivity.

Synergistic Ultrasound-Activable Artificial Enzyme and Precision Gene Therapy to Suppress Redox Homeostasis and Malignant Phenotypes for Controllably Combating Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) remains one of the most lethal malignant tumors. Multimodal therapeutics with synergistic effects for treating HCC have attracted increasing attention, for instance, designing biocompatible porphyrin-based nanomedicines for enzyme-mimetic and ultrasound (US)-activable reactive oxygen species (ROS) generation. Despite the promise, the landscape of such advancements remains sparse. Here, we propose the de novo design of a π-conjugated, osmium (Os)-coordinated polyporphyrin (P-Por-Os) nanovesicle to serve as an ultrasound-activable artificial enzyme for synergistic therapies to suppress redox homeostasis and malignant phenotypes for controllably combating HCC. Our findings reveal that the P-Por-Os with US showed superior, multifaceted, and controllable ROS-generating activities. This system not only subverts the redox balance within HCC cells but also achieves precise and controlled tumor ablation at remarkably low concentrations, as evidenced across cellular assays and animal models. In the liver orthotopic model, US not only activates the artificial enzyme to catalyze ROS but also facilitates remote-controlled ablation of HCC through precise US positioning. Moreover, the P-Por-Os + US can assist the precision gene therapy by knocking down the ROS resistance factor, MT2A, and down-regulating its downstream oncogene IGFBP2 to attenuate ROS resistance, proliferation, and migration of HCC efficiently. We suggest that the design of this ultrasound-activable artificial enzyme presents a promising avenue for the engineering of innovative tumoricidal materials, offering a synergistic therapeutic approach with high biosecurity for HCC treatment.

Vertically Expanded Covalent Organic Frameworks for Photocatalytic Water Oxidation into Oxygen

Covalent organic frameworks with unique π architectures and pores could be developed as photocatalysts for transformations. However, they usually form π-stacking layers, so that only surface layers function in photocatalysis. Here we report a strategy for developing vertically expanded frameworks to expose originally inaccessible active sites hidden in layers to catalysis. We designed covalently linked two-dimensional cobalt(II) porphyrin layers and explored coordination bonds to connect the cobalt(II) porphyrin layers with bidentate ligands via a three-component one-pot polymerization. The resultant frameworks expand the interlayer space greatly, where both the up and down faces of each cobalt(II) porphyrin layer are exposed to reactants. Unexpectedly, the vertically expanded frameworks increase skeleton oxidation potentials, decrease exciton dissociation energy, improve pore hydrophilicity and affinity to water, and facilitate water delivery. Remarkably, these positive effects work collectively in the photocatalysis of water oxidation into oxygen, with an oxygen production rate of 1155 μmol g-1 h-1, a quantum efficiency of 1.24 % at 450 nm, and a turnover frequency of 1.39 h-1, which is even 5.1-fold as high as that of the π-stacked frameworks and ranks them the most effective photocatalysts. This strategy offers a new platform for designing layer frameworks to build various catalytic systems for chemical transformations.

Direction Modulation of Intramolecular Electric Field Boosts Hole Transport in Phthalocyanines for Perovskite Solar Cells

Tuning the strength of intramolecular electric field (IEF) in conjugated molecules has emerged as an effective approach to boost charge transfer. While direction manipulation of IEF would be a potential way that is still unclear. Here, we leverage the control of peripheral substituents of conjugated phthalocyanines to chemically tune the spatial orientation of IEF. By analyzing the spatial swing of side chains using the Kolmogorov-Arnold representation and least squares algorithm, a comprehensive mathematical-physical model has been established. This model enables rapid evaluation of the IEF and maximum hole transport performance induced by spatial swings. The champion phthalocyanine as dopant-free hole transport material in perovskite solar cell realizes a record performance of 23.41 %. Greatly device stability is also exhibited. This work affords a new way to enhance hole transport capabilities of conjugated molecules by optimizing their IEF vector for photovoltaic devices.

Manganese(II) Porphyrin and Cumyl Hydroperoxide: An Efficient Catalyst for Aryl-Pentazole C-N Bond Cleavage

The selective cleavage of C-N bonds in N-containing compounds holds significant research value in organic synthesis, particularly for the synthesis of promising polynitrogen species. For instance, the discovery of the cyclo-pentazolate (cyclo-N5 -) anion in 2017 as a result of cleavage of the C-N bond has sparked interest within the field of high energy density materials. However, previous methods using ferrous glycinate and m-chloroperoxybenzoic acid generated the cyclo-N5 - anion in a low yield of 19.5 % after 24 hours, and the mechanism remained unclear. In this study, we developed an efficient catalytic system comprising Mn (II) tetraphenylporphyrin and cumyl hydroperoxide. This system enables the cyclo-N5 - anion to be produced from 3,5-dimethyl-4-hydroxyphenylpentazole in 35.4 % yield in 4 hours. Characterization of Mn(IV)-oxo porphyrins, ⋅CH3, and ⋅C8H8ON5 radicals provides evidence for the mechanism whereby the cyclo-N5 - anion forms. Our study underscores the competitive potential of radical-initiated selective C-N bonds cleavage in N-arylazoles and opens avenues for further exploration in this field.

Recent Advances in Bonding Regulation of Metalloporphyrin-Modified Carbon-Based Catalysts for Accelerating Energy Electrocatalytic Applications

Metalloporphyrins modified carbon-based materials, owing to the excellent acid-base resistance, optimal electron transfer rates, and superior catalytic performance, have shown great potential in energy electrocatalysis. Recently, numerous efforts have concentrated on employing carbon-based substrates as platforms to anchor metalloporphyrins, thereby fabricating a diverse array of composite catalysts tailored for assorted electrocatalytic processes. However, the interplay through bonding regulation of metalloporphyrins with carbon materials and the resultant enhancement in catalyst performance remains inadequately elucidated. Gaining an in-depth comprehension of the synergistic interactions between metalloporphyrins and carbon-based materials within the realm of electrocatalysis is imperative for advancing the development of innovative composite catalysts. Herein, the review systematically classifies the binding modes (i.e., covalent grafting and non-covalent interactions) between carbon-based materials and metalloporphyrins, followed by a discussion on the structural characteristics and applications of metalloporphyrins supported on various carbon-based substrates, categorized according to their binding modes. Additionally, this review underscores the principal challenges and emerging opportunities for carbon-supported metalloporphyrin composite catalysts, offering both inspiration and methodological insights for researchers involved in the design and application of these advanced catalytic systems.

Iron Porphyrin-Based Composites for Electrocatalytic Oxygen Reduction Reactions

The oxygen reduction reaction (ORR) is one of the most critical reactions in energy conversion systems, and it facilitates the efficient conversion of chemical energy into electrical energy, which is necessary for modern technology. Developing efficient and cost-effective catalysts for ORRs is crucial for advancing and effectively applying renewable energy technologies such as fuel cells, metal-air batteries, and electrochemical sensors. In recent years, iron porphyrin-based composites have emerged as ideal catalysts for facilitating effective ORRs due to their unique structural characteristics, abundance, advances in synthesis, and excellent catalytic properties, which mimic natural enzymatic systems. However, many articles have focused on reviewing porphyrin-based frameworks or metalloporphyrins in general, necessitating research specifically addressing iron porphyrin. This review discusses iron porphyrin as an effective catalyst in ORRs. It provides a comprehensive knowledge of the application of iron porphyrin-based composites for electrocatalytic ORRs, focusing on their properties, synthesis, structural integration with conductive supports, catalytic mechanism, and efficacy. This review also discusses the challenges of applying iron porphyrin-based composites and provides recommendations to address these challenges.

Improving Active Site Local Proton Transfer in Porous Organic Polymers for Boosted Oxygen Electrocatalysis

Improving proton transfer is vital for electrocatalysis with porous materials. Although several strategies are reported to assist proton transfer in channels, few studies are dedicated to improving proton transfer at the local environments of active sites in porous materials. Herein, we report on new Co-corrole-based porous organic polymers (POPs) with improved proton transfer for electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). By tuning the pore sizes and installing proton relays at Co corrole sites, we designed and synthesized POP-2-OH with improved proton transfer both in channels and at local Co active sites. This POP shows remarkable activity for both electrocatalytic ORR with E1/2=0.91 V vs RHE and OER with η10=255 mV. Therefore, this work is significant to present a strategy to improve active site local proton transfer in porous materials and highlight the key role of such structural functionalization in boosting oxygen electrocatalysis.

Triphenylamine-Substituted Ni(II) Porphyrins for Urea Electro-oxidation

Porphyrin-based molecular catalysts possess a typical aromatic macrocyclic structure regarding their metal centers and coordination frameworks, allowing for the development of promising electrocatalysts through precise selection of the metal and porphyrin ligand. However, reports on metalloporphyrins as catalysts for the electrocatalytic urea oxidation reaction (UOR) remain scarce. With these considerations in mind, the triphenylamine-Ni(II) porphyrin (NiPor-TPA) was synthesized through the solvothermal approach from 5,10,15,20-tetrakis [4-(diphenylamino)phenyl]porphyrin and nickel(II) acetate in this work. Experimental results reveal that the introduction of Ni species can serve as active sites and activate urea oxidation efficiently, and thus the prepared catalysts deliver better electrocatalytic activity than the metal-free TPA. The NiPor-TPA electrode delivers the lowest potential of 1.34 V versus reversible hydrogen electrode (RHE) at 10 mA cm-2 for UOR with a Tafel slope of 44.6 mV dec-1. This work proposes a new porphyrin-based molecular catalyst for effectively boosting electrocatalytic UOR activity. The π-conjugated macroring structure and the excellent electrocatalytic properties both make NiPor-TPA one of the burgeoning electrocatalytic UORs.

Asymmetric Cu-N1O3 Sites Coupling Atop-type and Bridge-type Adsorbed *C1 for Electrocatalytic CO2-to-C2 Conversion

2D functional porous frameworks offer a platform for studying the structure-activity relationships during electrocatalytic CO2 reduction reaction (CO2RR). Yet challenges still exist to breakthrough key limitations on site configuration (typical M-O4 or M-N4 units) and product selectivity (common CO2-to-CO conversion). Herein, a novel 2D metal-organic framework (MOF) with planar asymmetric N/O mixed coordinated Cu-N1O3 unit is constructed, labeled as BIT-119. When applied to CO2RR, BIT-119 could reach a CO2-to-C2 conversion with C2 partial current density ranging from 36.9 to 165.0 mA cm-2 in flow cell. Compared to the typical symmetric Cu-O4 units, asymmetric Cu-N1O3 units lead to the re-distribution of local electron structure, regulating the adsorption strength of several key adsorbates and the following catalytic selectivity. From experimental and theoretical analyses, Cu-N1O3 sites could simultaneously couple the atop-type (on Cu site) and bridge-type (on Cu-N site) adsorption of *C1 species to reach the CO2-to-C2 conversion. This work broadens the feasible C-C coupling mechanism on 2D functional porous frameworks.

Tuning the product selectivity of single-atom catalysts for CO2 reduction beyond CO formation by orbital engineering

Electrochemical CO2 reduction (CO2R) is one of the promising strategies for developing sustainable energy resources. Single-atom catalysts (SACs) have emerged as efficient catalysts for CO2R. However, the efficiency of SACs for the formation of reduction products beyond two-step CO formation is low due to the lower binding strength of the CO intermediate. In this study, we present an orbital engineering strategy based on density functional theory calculations and the fragment molecular orbital approach to tune product selectivity for the CO2R reaction on macrocycle based molecular catalysts (porphyrin and phthalocyanine) and extended SACs (graphene and covalent organic frameworks) with Fe, Co, and Ni dopants. The introduction of neutral axial ligands such as imidazole, pyridine, and trimethyl phosphine to the metal dopants enhances the binding affinity of the CO intermediate. The stability of the catalysts is investigated through the thermodynamic binding energy of the axial ligands and ab initio molecular dynamics simulations (AIMD). The grand canonical potential method is used to determine the reaction free energy values. Using a unified activity volcano plot based on the reaction free energy values, we investigated the catalytic activity and product selectivity at an applied potential of -0.8 V vs. SHE and a pH of 6.8. We found that with the imidazole and pyridine axial ligands, the selectivity of Fe-doped SACs towards the formation of the methanol product is improved. The activity volcano plot for these SACs shows a similar activity to that of the Cu (211) surface. The catalytic activity is found to be directly proportional to the sigma-donating ability of the axial ligands.

Synthesis, Structural, Electrochemical, and DFT Studies of Highly Substituted Nonplanar Ni(II) Porphyrins and Their Intensity-Dependent Third-Order Nonlinear Optical Properties

We designed and successfully synthesized highly substituted electron-deficient nonplanar Ni(II) porphyrins and their derivatives (1-7) in moderate to good yields. These derivatives were comprehensively characterized by various spectroscopic techniques and single-crystal X-ray diffraction (SCXRD) analysis. SCXRD analysis confirmed the structures of compounds 2, 4, and 7, adopting saddle-shape geometry. These nonplanar porphyrins demonstrated significant bathochromic shifts in their absorption spectra compared to parent NiTPP, attributed to the influence of bulky β-substituents and/or peripheral fusion. π-Extended porphyrins 6 and 7 displayed panchromatic absorption spectra extending into the NIR region. Porphyrins 6 and 7 demonstrated a profound anodic shift (∼400 mV) in their first reduction peak potentials compared to precursor NiTPP(NO2)Br6. The experimental absorption spectral pattern matches the simulated absorption spectra obtained from TD-DFT studies. The femtosecond laser intensity-dependent third-order nonlinear optical studies revealed that NiDFP(VCN)2Br6 (6) and NiDFP(VCN)2(PE)6 (7) displayed giant optical nonlinearities compared to the other porphyrins. Among all, NiDFP(VCN)2Br6 (6) possessed the highest two-photon absorption coefficient (β) and cross-section (σTPA) values in the range of 22-33 × 10-10 m/W and 3.77-6.95 × 106 GM, respectively. These findings suggest that the investigated nonplanar π-extended porphyrins are promising candidates for future optoelectronic applications.

Metal Center-Tuned Photocatalytic Carbon Dioxide Reduction for Frameworks with the Tetraphenylethene-Imidazole Ligand

As heterogeneous photocatalysts that can effectively transform CO2 to CO, two MOFs with different metal centers, namely, [M(tipe)(H2O)2](ClO4)2·solvent (M = Ni named as Ni-MOF and M = Co referred to as Co-MOF), were synthesized by reactions of 1,1,2,2-tetrakis(4-(imidazole-1-yl)phenyl)ethene (tipe) with the corresponding metal perchlorate. Both Ni-MOF and Co-MOF have 3D structures, in which the metal centers have the same coordination environment with the N4O2 donor set. Driven by visible light, the CO production catalyzed by Co-MOF is 6734.1 μmol g-1 with 45.3% selectivity, and in contrast, Ni-MOF has 4601.3 μmol g-1 CO production with 97.6% selectivity in 5 h. Through photoelectrochemical characterization, DFT calculations, and in situ FT-IR measurements, the photocatalytic CO2 reduction process catalyzed by Ni-MOF and Co-MOF was investigated. The results show that the metal center of the MOF is crucial for photocatalytic CO2 reduction. This work offers an innovative approach for controlling the performance of photocatalytic CO2 reduction through tuning the metal centers of architectures.

The "Pull Effect" of a Hanging ZnII on Improving the Four-Electron Oxygen Reduction Selectivity with Co Porphyrin

Due to the challenge of cleaving O-O bonds at single Co sites, mononuclear Co complexes typically show poor selectivity for the four-electron (4e-) oxygen reduction reaction (ORR). Herein, we report on selective 4e- ORR catalyzed by a Co porphyrin with a hanged ZnII ion. Inspired by Cu/Zn-superoxide dismutase, we designed and synthesized 1-CoZn with a hanging ZnII at the second sphere of a Co porphyrin. Complex 1-CoZn is much more effective than its Zn-lacking analogues to catalyze the 4e- ORR in neutral aqueous solutions, giving an electron number of 3.91 per O2 reduction. With spectroscopic studies, the hanging ZnII was demonstrated to be able to facilitate the electron transfer from CoII to O2, through an electronic "pull effect", to give CoIII-superoxo. Theoretical studies further suggested that this "pull effect" plays crucial roles in assisting O-O bond cleavage. This work is significant to present a new strategy of hanging a ZnII to improve O2 activation and O-O bond cleavage.

Constructing Co4(SO4)4 Clusters within Metal-Organic Frameworks for Efficient Oxygen Electrocatalysis

Multinuclear metal clusters are ideal candidates to catalyze small molecule activation reactions involving the transfer of multiple electrons. However, synthesizing active metal clusters is a big challenge. Herein, on constructing an unparalleled Co4(SO4)4 cluster within porphyrin-based metal-organic frameworks (MOFs) and the electrocatalytic features of such Co4(SO4)4 clusters for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is reported. The reaction of CoII sulfate and metal complexes of tetrakis(4-pyridyl)porphyrin under solvothermal conditions afforded Co4-M-MOFs (M═Co, Cu, and Zn). Crystallographic studies revealed that these Co4-M-MOFs have the same framework structure, having the Co4(SO4)4 clusters connected by metalloporphyrin units through Co─Npyridyl bonds. In the Co4(SO4)4 cluster, the four CoII ions are chemically and symmetrically equivalent and are each coordinated with four sulfate O atoms to give a distorted cube-like structure. Electrocatalytic studies showed that these Co4-M-MOFs are all active for electrocatalytic OER and ORR. Importantly, by regulating the activity of the metalloporphyrin units, it is confirmed that the Co4(SO4)4 cluster is active for oxygen electrocatalysis. With the use of Co porphyrins as connecting units, Co4-Co-MOF displays the highest electrocatalytic activity in this series of MOFs by showing a 10 mA cm-2 OER current density at 357 mV overpotential and an ORR half-wave potential at 0.83 V versus reversible hydrogen electrode (RHE). Theoretical studies revealed the synergistic effect of two proximal Co atoms in the Co4(SO4)4 cluster in OER by facilitating the formation of O─O bonds. This work is of fundamental significance to present the construction of Co4(SO4)4 clusters in framework structures for oxygen electrocatalysis and to demonstrate the cooperation between two proximal Co atoms in such clusters during the O─O bond formation process.

Unlocking the Potential for Methanol Synthesis via Electrochemical CO2 Reduction Using CoPc-Based Molecular Catalysts

The electrochemical CO2 reduction reaction (CO2RR) to produce methanol (CH3OH) is an attractive yet challenging approach due to a lack of selective electrocatalysts. An immobilized cobalt phthalocyanine (CoPc) molecular catalyst has emerged as a promising electrocatalyst for CH3OH synthesis, demonstrating decent activity and selectivity through a CO2-CO-CH3OH cascade reaction. However, CoPc's performance is limited by its weak binding strength toward the CO intermediate. Recent advancements in molecular modification aimed at enhancing CO intermediate binding have shown great promise in improving CO2-to-CH3OH performance. In this Perspective, we discuss the competitive binding mechanism between CO2 and CO that hinders CH3OH formation and summarize effective molecular modification strategies that can enhance both the binding of the CO intermediate and the conversion of the CO2-to-CH3OH activity. Finally, we offer future perspectives on optimization strategies to inspire further research efforts to fully unlock the potential for methanol synthesis via the CO2RR using molecular catalysts.

Ferrocene-modified covalent organic framework for efficient oxygen evolution reaction and CO2 electroreduction

A ferrocene-modified COF, namely Ni-Tph-COF-Fc, was synthesized and applied in OER. Compared with Ni-Tph-COF-OH, Ni-Tph-COF-Fc shows improved performance with a current density of 99.6 mA cm-2, an overpotential of 450 mV, and a Tafel slope of 73.1 mV dec-1, which may be attributed to a synergy between introduced ferrocene and metalloporphyrin in the COFs. Moreover, the enhanced OER performance leads to an improved CO2RR performance with an FECO of 93.1%. This work represents an effective strategy to enhance the anodic OER performance and realize efficient CO2RR.

Electrocatalytic Reduction of Carbon Dioxide in Acidic Electrolyte with Superior Performance of a Metal-Covalent Organic Framework over Metal-Organic Framework

CO2 electroreduction (CO2RR) to generate valuable chemicals in acidic electrolytes can improve the carbon utilization rate in comparison to that under alkaline conditions. However, the thermodynamically more favorable hydrogen evolution reaction under an acidic electrolyte makes the CO2RR a big challenge. Herein, robust metal phthalocyanine(Pc)-based (M = Ni, Co) conductive metal-covalent organic frameworks (MCOFs) connected by strong metal tetraaza[14]annulene (TAA) linkage, named NiPc-NiTAA and NiPc-CoTAA, are designed and synthesized to apply in the CO2RR in acidic electrolytes for the first time. The optimal NiPc-NiTAA exhibited an excellent Faradaic efficiency (FECO) of 95.1% and a CO partial current density of 143.0 mA cm-2 at -1.5 V versus the reversible hydrogen electrode in an acidic electrolyte, which is 3.1 times that of the corresponding metal-organic framework NiPc-NiN4. The comparison tests and theoretical calculations reveal that in-plane full π-d conjugation MCOF with a good conductivity of 3.01 × 10-4 S m-1 accelerates migration of the electrons. The NiTAA linkage can tune the electron distribution in the d orbit of metal centers, making the d-band center close to the Fermi level and then activating CO2. Thus, the active sites of NiPc and NiTAA collaborate to reduce the *COOH formation energy barrier, favoring CO production in an acid electrolyte. It is a helpful route for designing outstanding conductive MCOF materials to enhance CO2 electrocatalysis under an acidic electrolyte.

Experimentally validating sabatier plot by molecular level microenvironment customization for oxygen electroreduction

Microenvironmental modifications on metal sites are crucial to tune oxygen reduction catalytic behavior and decrypt intrinsic mechanism, whereas the stochastic properties of traditional pyrolyzed single-atom catalysts induce vague recognition on structure-reactivity relations. Herein, we report a theoretical descriptor relying on binding energies of oxygen adsorbates and directly associating the derived Sabatier volcano plot with calculated overpotential to forecast catalytic efficiency of cobalt porphyrin. This Sabatier volcano plot instructs that electron-withdrawing substituents mitigate the over-strong *OH intermediate adsorption by virtue of the decreased proportion of electrons in bonding orbital. To experimentally validate this speculation, we implement a secondary sphere microenvironment customization strategy on cobalt porphyrin-based polymer nanocomposite analogs. Systematic X-ray spectroscopic and in situ electrochemical characterizations capture the pronounced accessible active site density and the fast interfacial/outward charge migration kinetics contributions for the optimal carboxyl group-substituted catalyst. This work offers ample strategies for designing single-atom catalysts with well-managed microenvironment under the guidance of Sabatier volcano map.

Bifunctional oxygen reduction/evolution reaction electrocatalysts achieved by axial ligand modulation on two-dimensional porphyrin frameworks

Exploring efficient and low-cost oxygen reduction and oxygen evolution reaction (ORR/OER) bifunctional catalysts is essential for the development of energy storage and conversion devices. Herein, enlightened by the experimentally synthesized cobalt(II) meso-tetraethynylporphyrins (Co-TEP) molecule, we designed a novel 2D covalent organic framework (COF), namely a 2D Co-TEP monolayer, by dimensional expansion. The 2D Co-TEP monolayer, with Co atoms distributed separately and stabilized by uniform pyrrolic-N coordination, features metal-nitrogen-carbon single-atom catalyst activity and shows tunable catalytic activity for the electrochemical ORR/OER by axial ligand (O, OH, Cl, CN, CH3, NO, F) modulation. By means of the state-of-the-art constant-potential first-principles computations and microkinetic simulations, we demonstrated that 2D Co-TEP-CN exhibits good ORR/OER performance in both acidic and alkaline conditions. The difference between the onset-potential for the OER and the half-wave potential for the ORR is only 0.85 V at pH = 1, smaller than that of Pt/IrO2 electrocatalysts. The good electrocatalytic performance is maintained by replacing the center metal atoms with Mn, Fe and/or Ni. Our investigation highlights the role of the pyrrolic-N coordination and the ligands in improving the catalytic activity of 2D COFs and provides new insights into the rational design of efficient bifunctional ORR/OER catalysts.

Synergistic reductive catalytic effects of an organic and inorganic hybrid covalent organic framework for hydrogen fuel production

Electrocatalytic hydrogen generation in alkaline medium has become widely used in a variety of sectors. However, the possibility for additional performance improvement is hampered by slow kinetics. Because of this restriction, careful control over processes such as water dissociation, hydroxyl desorption and hydrogen recombination is required. Covalent organic frameworks (COFs) based on porphyrin and polyoxometalates (POMs) show encouraging electrocatalytic performance, offering a viable route for effective and sustainable hydrogen generation. Their specific architectures lead to increased electrocatalytic activity, which makes them excellent choices for developing water electrolysis as a clean energy conversion method in the alkaline medium. In this regard, TTris@ZnPor and Lindqvist POM were coordinated to create a new eco-friendly and highly active covalent organic framework (TP@VL-COF). In order to describe TP@VL-COF, extensive structural and morphological investigations were carried out through FTIR, 1H NMR, elemental analysis, SEM, fluorescence, UV-visible, PXRD, CV, N2-adsorption isotherm, TGA and DSC analyses. In an alkaline medium, the electrocatalytic capability of 20%C/Pt, TTris@ZnPor, Lindqvist POM and TP@VL-COF was explored and compared for the hydrogen evolution reaction (HER). The TP@VL-COF showed the best catalytic efficiency for HER in an alkaline electrolyte, requiring just a 75 mV overpotential to drive 10 mA cm-2 and outperforming 20%C/Pt, TTris@ZnPor, Lindqvist POM and other reported catalysts. The Tafel slope value also indicates faster kinetics for TP@VL-COF (114 mV dec-1) than for 20%C/Pt (182 mV dec-1) TTris@ZnPor (116 mV dec-1) and Lindqvist POM (125 mV dec-1).

Monodispersed Molecular Phthalocyanine with Sulfur-Driven Electron Delocalization for Enhanced Electrochemical Biosensing

Heterogenizing the molecular catalysts on conductive scaffolds to achieve the isolated molecular dispersion and expected coordination structures is significant yet still challenging. Herein, a sulfur-driving strategy to anchor monodispersed cobalt phthalocyanine on nitrogen and sulfur co-doped graphene (NSG-CoPc) is demonstrated. Experimental and theoretical analysis prove that the incorporation of S dramatically improves the adsorption capability of NSG and evokes the monodispersion of the CoPc molecule, promoting the axial Co─N coordination and the electron delocalization of the Co catalytic center. Benefiting from the reduced activation energy barrier and boosted electron transfer, as well as the maximized active site utilization, NSG-CoPc exhibits outstanding H2O2 oxidization and sensing performance (used as a representative reaction). Moreover, the usage of NSG as a substrate can be readily extended to other metal (Ni, Cu, and Fe) phthalocyanine molecules with molecular-level dispersion. This work clarifies the mechanism of heteroatoms decoration and provides a new paradigm in devising monodispersed molecular catalysts with modulated chemical surroundings for broad applications.

Constructing 2D Phthalocyanine Covalent Organic Framework with Enhanced Stability and Conductivity via Interlayer Hydrogen Bonding as Electrocatalyst for CO2 Reduction

Fabricating COFs-based electrocatalysts with high stability and conductivity still remains a great challenge. Herein, 2D polyimide-linked phthalocyanine COF (denoted as NiPc-OH-COF) is constructed via solvothermal reaction between tetraanhydrides of 2,3,9,10,16,17,23,24-octacarboxyphthalocyaninato nickel(II) and 2,5-diamino-1,4-benzenediol (DB) with other two analogous 2D COFs (denoted as NiPc-OMe-COF and NiPc-H-COF) synthesized for reference. In comparison with NiPc-OMe-COF and NiPc-H-COF, NiPc-OH-COF exhibits enhanced stability, particularly in strong NaOH solvent and high conductivity of 1.5 × 10-3 S m-1 due to the incorporation of additional strong interlayer hydrogen bonding interaction between the O-H of DB and the hydroxy "O" atom of DB in adjacent layers. This in turn endows the NiPc-OH-COF electrode with ultrahigh CO2-to-CO faradaic efficiency (almost 100%) in a wide potential range from -0.7 to -1.1 V versus reversible hydrogen electrode (RHE), a large partial CO current density of -39.2 mA cm-2 at -1.1 V versus RHE, and high turnover number as well as turnover frequency, amounting to 45 000 and 0.76 S-1 at -0.80 V versus RHE during 12 h lasting measurement.

Selective Electrochemical Oxygen Reduction to Hydrogen Peroxide by Confinement of Cobalt Porphyrins in a Metal-Organic Framework

Sustainable alternatives for the energy intensive synthesis of H2O2 are necessary. Molecular cobalt catalysts show potential but are typically restricted by undesired bimolecular pathways leading to the breakdown of both H2O2 and the catalyst. The confinement of cobalt porphyrins in the PCN-224 metal-organic framework leads to an enhanced selectivity towards H2O2 and stability of the catalyst. Consequently, oxygen can now be selectively reduced to hydrogen peroxide with a stable conversion for at least 5 h, illustrating the potential of catalysts confined in MOFs to increase the selectivity and stability of electrocatalytic conversions.

The meso-substituent electronic effect of Fe porphyrins on the electrocatalytic CO2 reduction reaction

We report Fe porphyrins bearing different meso-substituents for the electrocatalytic CO2 reduction reaction (CO2RR). By replacing two and four meso-phenyl groups of Fe tetraphenylporphyrin (FeTPP) with strong electron-withdrawing pentafluorophenyl groups, we synthesized FeF10TPP and FeF20TPP, respectively. We showed that FeTPP and FeF10TPP are active and selective for CO2-to-CO conversion in dimethylformamide with the former being more active, but FeF20TPP catalyzes hydrogen evolution rather than the CO2RR under the same conditions. Experimental and theoretical studies revealed that with more electron-withdrawing meso-substituents, the Fe center becomes electron-deficient and it becomes difficult for it to bind a CO2 molecule in its formal Fe0 state. This work is significant to illustrate the electronic effects of catalysts on binding and activating CO2 molecules and provide fundamental knowledge for the design of new CO2RR catalysts.

Metalation of metal-organic frameworks: fundamentals and applications

Metalation of metal-organic frameworks (MOFs) has been developed as a prominent strategy for materials functionalization for pore chemistry modulation and property optimization. By introducing exotic metal ions/complexes/nanoparticles onto/into the parent framework, many metallized MOFs have exhibited significantly improved performance in a wide range of applications. In this review, we focus on the research progress in the metalation of metal-organic frameworks during the last five years, spanning the design principles, synthetic strategies, and potential applications. Based on the crystal engineering principles, a minor change in the MOF composition through metalation would lead to leveraged variation of properties. This review starts from the general strategies established for the incorporation of metal species within MOFs, followed by the design principles to graft the desired functionality while maintaining the porosity of frameworks. Facile metalation has contributed a great number of bespoke materials with excellent performance, and we summarize their applications in gas adsorption and separation, heterogeneous catalysis, detection and sensing, and energy storage and conversion. The underlying mechanisms are also investigated by state-of-the-art techniques and analyzed for gaining insight into the structure-property relationships, which would in turn facilitate the further development of design principles. Finally, the current challenges and opportunities in MOF metalation have been discussed, and the promising future directions for customizing the next-generation advanced materials have been outlined as well.

Dialdehyde cellulose films covalently crosslinked with porphyrin-based covalent organic polymers for photodynamic sterilization

Foodborne pathogens result in a great harm to human, which is an urgent problem to be addressed. Herein, a novel cellulose-based packaging films with excellent anti-bacterial properties under visible light were prepared. A porphyrin-based covalent organic polymer (Por-COPs) was constructed, then covalently grafted onto dialdehyde cellulose (DAC). The addition of Por-COPs enhanced the mechanical, hydrophobicity, and water resistance of the DAC-based composite films. DAC/Por-COP-2.5 film exhibited outstanding properties for the photodynamic inactivation of bacteria under visible light irradiation, delivering inactivation efficiencies of 99.90 % and 99.45 % towards Staphylococcus aureus and Escherichia coli within 20 min. The DAC/Por-COPs films efficiently generated •O2- and 1O2 under visible light, thereby causing oxidative stress to cell membranes for bacterial inactivation. The prepared composite film forms a protective barrier against bacterial contamination. Results guide the development of high performance and more sustainable packaging films for the food sector.