A series of stable heterometallic Fe2M cluster‐based MOFs (NNU‐31‐M, M=Co, Ni, Zn) photocatalysts are presented. They can achieve the overall conversion of CO2 and H2O into HCOOH and O2 without the ...assistance of additional sacrificial agent and photosensitizer. The heterometallic cluster units and photosensitive ligands excited by visible light generate separated electrons and holes. Then, low‐valent metal M accepts electrons to reduce CO2, and high‐valent Fe uses holes to oxidize H2O. This is the first MOF photocatalyst system to finish artificial photosynthetic full reaction. It is noted that NNU‐31‐Zn exhibits the highest HCOOH yield of 26.3 μmol g−1 h−1 (selectivity of ca. 100 %). Furthermore, the DFT calculations based on crystal structures demonstrate the photocatalytic reaction mechanism. This work proposes a new strategy for how to design crystalline photocatalyst to realize artificial photosynthetic overall reaction.
A series of stable heterometallic Fe2M cluster‐based MOFs achieve the overall conversion of CO2 and H2O into HCOOH and O2 without the assistance of additional sacrificial agent and photosensitizer. A strategy is proposed to design crystalline photocatalysts to realize the overall artificial photosynthetic reaction.
Abstract
The electrochemical CO
2
reduction to high-value-added chemicals is one of the most promising and challenging research in the energy conversion field. An efficient ECR catalyst based on a ...Cu-based conductive metal-organic framework (Cu-DBC) is dedicated to producing CH
4
with superior activity and selectivity, showing a Faradaic efficiency of CH
4
as high as ~80% and a large current density of −203 mA cm
−2
at −0.9 V vs. RHE. The further investigation based on theoretical calculations and experimental results indicates the Cu-DBC with oxygen-coordinated Cu sites exhibits higher selectivity and activity over the other two crystalline ECR catalysts with nitrogen-coordinated Cu sites due to the lower energy barriers of Cu-O
4
sites during ECR process. This work unravels the strong dependence of ECR selectivity on the Cu site coordination environment in crystalline porous catalysts, and provides a platform for constructing highly selective ECR catalysts.
2D nanomaterials with flexibly modifiable surfaces are highly sought after for various applications, especially in room‐temperature chemiresistive gas sensing. Here, we have prepared a series of COF ...2D nanomaterials (porphyrin‐based COF nanosheets (NS)) that enabled highly sensitive and specific‐sensing of NO2 at room temperature. Different from the traditional 2D sensing materials, H2‐TPCOF was designed with a largely reduced interlayer interaction and predesigned porphyrin rings as modifiable sites on its surfaces for post‐metallization. After post‐metallization, the metallized M‐TPCOF (M=Co and Cu) showed remarkably improved sensing performances. Among them, Co‐TPCOF exhibited highly specific sensing toward NO2 with one of the highest sensitivities of all reported 2D materials and COF materials, with an ultra‐low limit‐of‐detection of 6.8 ppb and fast response/recovery. This work might shed light on designing and preparing a new type of surface‐highly‐modifiable 2D material for various chemistry applications.
A series of metalloporphyrin covalent organic framework based nanosheets has been synthesized and successfully applied in specific sensing of NO2 at room temperature.
Despite wide applications of bimetallic electrocatalysis in oxygen evolution reaction (OER) owing to their superior performance, the origin of the improved performance remains elusive. The underlying ...mechanism was explored by designing and synthesizing a series of stable metal–organic frameworks (MOFs: NNU‐21–24) based on trinuclear metal carboxylate clusters and tridentate carboxylate ligands. Among the examined stable MOFs, NNU‐23 exhibits the best OER performance; particularly, compared with monometallic MOFs, all the bimetallic MOFs display improved OER activity. DFT calculations and experimental results demonstrate that introduction of the second metal atom can improve the activity of the original atom. The proposed model of bimetallic electrocatalysts affecting their OER performance can facilitate design of efficient bimetallic catalysts for energy storage and conversion, and investigation of the related catalytic mechanisms.
An iron atom in an Fe3 cluster is replaced by a second metal to form Fe2M clusters, which can serve as nodes to bridge with organic ligands and construct stable bimetallic MOFs. The introduction of the second metal atom can improve the activity of the original atom and thus improve the oxygen evolution reaction performance of electrocatalysts.
The exploration of new application forms of covalent organic frameworks (COFs) in Li−S batteries that can overcome drawbacks like low conductivity or high loading when typically applied as sulfur ...host materials (mostly ≈20 to ≈40 wt % loading in cathode) is desirable to maximize their low‐density advantage to obtain lightweight, portable, or high‐energy‐density devices. Here, we establish that COFs could have implications as microadditives of binders (≈1 wt % in cathode), and a series of anthraquinone‐COF based hollow tubes have been prepared as model microadditives. The microadditives can strengthen the basic properties of the binder and spontaneously immobilize and catalytically convert lithium polysulfides, as proved by density functional calculations, thus showing almost doubly enhanced reversible capacity compared with that of the bare electrode.
Covalent organic frameworks could have implications as microadditives of binders (≈1 wt % in cathode) and a series of anthraquinone‐COF based hollow tubes have been prepared as model microadditives to obtain a high‐performance binder in Li−S batteries.
In the electrochemical CO2 reduction reaction (CO2RR), it is challenging to develop a stable, well‐defined catalyst model system that is able to examine the influence of the synergistic effect ...between adjacent catalytic active sites on the selective generation of C1 or C2 products. We have designed and synthesized a stable crystalline single‐chain catalyst model system for electrochemical CO2RR, which involves four homomorphic one‐dimensional chain‐like compounds (Cu‐PzH, Cu‐PzCl, Cu‐PzBr, and Cu‐PzI). The main structural difference of these four chains is the substituents of halogen atoms with different electronegativity on the Pz ligands. Consequently, different synergistic effects between bi‐copper centers lead to changes in the faradic efficiency (FECH4
:FEC2H4
). This work provides a simple and stable crystalline single‐chain model system for systematically studying the influence of coordination microenvironment on catalytically active centers in the CO2RR.
During the process of the electrochemical CO2 reduction reaction, the different synergistic effects (the distance DCu‐Cu and the dihedral angle βCu‐Cu) between neighboring catalytic copper (bi‐copper) active sites induced by the variations of coordination microenvironment lead to regular FECH4: FEC2H4 changes in crystalline single‐chain models (Cu‐PzH, Cu‐PzCl, Cu‐PzBr, and Cu‐PzI).
Over the past 200 years, the most famous and important heteroatom Keggin architecture in polyoxometalates has only been synthesized with Mo, W, V, or Nb. Now, the self‐assembly of two phosphate ...(PO43−)‐centered polyoxo‐titanium clusters (PTCs) is presented, PTi16 and PTi12, which display classic heteroatom Keggin and its trivacant structures, respectively. Because TiIV has lower oxidate state and larger ionic radius than MoVI, WVI, VV, and NbV, additional TiIV centres in these PTCs are used to stabilize the resultant heteroatom Keggin structures, as demonstrated by the cooresponding theoretical calculation results. These photoactive PTCs can be utilized as efficient photocatalysts for highly selective CO2‐to‐HCOOH conversion. This new discovery indicates that the classic heteroatom Keggin family can be assembled with Ti, thus opening a research avenue for the development of PTC chemistry.
One of the family: A TiIV‐based heteroatom Keggin and its trivacant lacunary architectures were structurally synthesized as a polyoxo‐titanium cluster. They exhibited a very high selectivity and activity for photocatalytic CO2‐to‐HCOOH conversion.
Photocatalytic synthesis of hydrogen peroxide (H2O2) is a potential clean method, but the long distance between the oxidation and reduction sites in photocatalysts hinders the rapid transfer of ...photogenerated charges, limiting the improvement of its performance. Here, a metal‐organic cage photocatalyst, Co14(L−CH3)24, is constructed by directly coordinating metal sites (Co sites) used for the O2 reduction reaction (ORR) with non‐metallic sites (imidazole sites of ligands) used for the H2O oxidation reaction (WOR), which shortens the transport path of photogenerated electrons and holes, and improves the transport efficiency of charges and activity of the photocatalyst. Therefore, it can be used as an efficient photocatalyst with a rate of as high as 146.6 μmol g−1 h−1 for H2O2 production under O2‐saturated pure water without sacrificial agents. Significantly, the combination of photocatalytic experiments and theoretical calculations proves that the functionalized modification of ligands is more conducive to adsorbing key intermediates (*OH for WOR and *HOOH for ORR), resulting in better performance. This work proposed a new catalytic strategy for the first time; i.e., to build a synergistic metal‐nonmetal active site in the crystalline catalyst and use the host–guest chemistry inherent in the metal‐organic cage (MOC)to increase the contact between the substrate and the catalytically active site, and finally achieve efficient photocatalytic H2O2 synthesis.
Two stable CoII‐based metal‐organic cages are efficient catalysts for photocatalytic synthesis of H2O2 in pure water and O2 or air atmospheres. The metal‐nonmetal active site operates synergistically during photocatalytic H2O2 synthesis and the reaction substrate can more fully contact the catalytically active site through host–guest chemistry of cages, ultimately achieving a high H2O2 production rate.
Electrochemical water splitting is one of the most economical and sustainable methods for large-scale hydrogen production. However, the development of low-cost and earth-abundant non-noble-metal ...catalysts for the hydrogen evolution reaction remains a challenge. Here we report a two-dimensional coupled hybrid of molybdenum carbide and reduced graphene oxide with a ternary polyoxometalate-polypyrrole/reduced graphene oxide nanocomposite as a precursor. The hybrid exhibits outstanding electrocatalytic activity for the hydrogen evolution reaction and excellent stability in acidic media, which is, to the best of our knowledge, the best among these reported non-noble-metal catalysts. Theoretical calculations on the basis of density functional theory reveal that the active sites for hydrogen evolution stem from the pyridinic nitrogens, as well as the carbon atoms, in the graphene. In a proof-of-concept trial, an electrocatalyst for hydrogen evolution is fabricated, which may open new avenues for the design of nanomaterials utilizing POMs/conducting polymer/reduced-graphene oxide nanocomposites.
Imidazole molecules were frequently incorporated into porous materials to improve their proton conductivity. To investigate how different arrangements of imidazoles in metal–organic frameworks (MOFs) ...affect the overall proton conduction, we designed and prepared a MOF-based model system. It includes an Fe–MOF as the blank, an imidazole@Fe–MOF (Im@Fe–MOF) with physically adsorbed imidazole, and an imidazole–Fe–MOF (Im–Fe–MOF), which contains chemically coordinated imidazole molecules. The parent Fe–MOF, synthesized from the exchange of carboxylates in the preformed Fe3(μ3–O)(carboxylate)6 clusters and multitopic carboxylate ligands, serves as a control. The Im@Fe–MOF was prepared by encapsulating free imidazole molecules into the pores of the Fe–MOF, whereas the Im–Fe–MOF was obtained in situ, in which imidazole ligands coordinate to the metal nodes of the framework. Proton-conductivity analyses revealed that the proton conductivity of Im–Fe–MOF was approximately two orders of magnitude greater than those of Fe–MOF and Im@Fe–MOF at room temperature. The high proton conductivity of 1.21 × 10–2 S cm–1 at 60 °C for Im–Fe–MOF ranks among the highest performing MOFs ever reported. The results of the density functional theory calculations suggest that coordinated imidazole molecules in Im–Fe–MOF provide a greater concentration of protons for proton transportation than do coordinated water molecules in Fe–MOF alone. Besides, Im–Fe–MOF exhibits steadier performance than Im@Fe–MOF does after being washed with water. Our investigation using the above ideal crystalline model system demonstrates that compared to disorderly arranged imidazole molecules in pores, the immobilized imidazole molecules by coordination bonds in the framework are more prone to form proton–conduction pathways and thus perform better and steadier in water-mediated proton conduction.
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