A strategy to covalently connect crystalline covalent organic frameworks (COFs) with semiconductors to create stable organic–inorganic Z‐scheme heterojunctions for artificial photosynthesis is ...presented. A series of COF–semiconductor Z‐scheme photocatalysts combining water‐oxidation semiconductors (TiO2, Bi2WO6, and α‐Fe2O3) with CO2 reduction COFs (COF‐316/318) was synthesized and exhibited high photocatalytic CO2‐to‐CO conversion efficiencies (up to 69.67 μmol g−1 h−1), with H2O as the electron donor in the gas–solid CO2 reduction, without additional photosensitizers and sacrificial agents. This is the first report of covalently bonded COF/inorganic‐semiconductor systems utilizing the Z‐scheme applied for artificial photosynthesis. Experiments and calculations confirmed efficient semiconductor‐to‐COF electron transfer by covalent coupling, resulting in electron accumulation in the cyano/pyridine moieties of the COF for CO2 reduction and holes in the semiconductor for H2O oxidation, thus mimicking natural photosynthesis.
Here comes the sun: A strategy to covalently connect covalent organic frameworks with semiconductors to create organic–inorganic Z‐scheme heterojunctions was developed and applied for the CO2 photoreduction with H2O. This work delivers new insights for the future design of Z‐scheme organic–inorganic heterojunctions for artificial photosynthesis.
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.
Zn‐based aqueous batteries have attracted much attention because of their high theoretical‐capacity, safety, and low‐cost, yet the H2‐evolution, qualification or inhibition mechanism investigations ...that are closely related to the dendrite‐growth are rare and challenging. Herein, a series of zincophilic metal‐covalent organic frameworks (e.g., Zn‐AAn‐COF, Zn‐DAAQ‐COF, and Zn‐DAA‐COF) have been explored as model‐platforms to manipulate the H2‐evolution and Zn2+ flux. Best of them, Zn‐AAn‐COF based cell only produces 0.002 mmol h−1 cm−2 H2, which is >2 orders of magnitude lower than bare Zn. Noteworthy, it affords high stability for 3000 cycles (overpotential, <79.1 mV) at 20 mA cm−2 in symmetric‐cell and enhanced cycling‐stability up to 6000 cycles at 2000 mA g−1 in the assembled full‐battery. Besides, mechanistic characterizations show that Zn‐AAn‐COF can enhance the energy‐barrier of H2‐evolution and homogenize the ion‐distribution or electric‐filed to achieve high performance.
A series of porous Zn‐COF@Zn anodes have been fabricated to synergistically manipulate the H2 evolution and Zn2+ flux, during which the closely related H2 qualification/inhibition and Zn dendrite‐growth in zinc‐based aqueous batteries have been studied.
The inhomogeneous consumption of anions and direct contact between electrolyte and anode during the Zn‐deposition process generate Zn‐dendrites and side reactions that can aggravate the space‐charge ...effect to hinder the practical implementation of zinc‐metal batteries (ZMBs). Herein, electrospray has been applied for the scalable fabrication (>10 000 cm2 in a batch‐experiment) of hetero‐metallic cluster covalent‐organic‐frameworks (MCOF‐Ti6Cu3) nanosheet‐coating (MNC) with integrated micro space electrostatic field for ZMBs anode protection. The MNC@Zn symmetric cell presents ultralow overpotential (≈72.8 mV) over 10 000 cycles at 1 mAh cm−2 with 20 mA cm−2, which is superior to bare Zn and state‐of‐the‐art porous crystalline materials. Theoretical calculations reveal that MNC with integrated micro space electrostatic field can facilitate the deposition‐kinetic and homogenize the electric field of anode to significantly promote the lifespan of ZMBs.
Electrospray has been applied for scalable fabrication (>10 000 cm2 in a batch‐experiment) of hetero‐metallic cluster covalent‐organic‐frameworks (MCOF‐Ti6Cu3) nanosheet‐coating (MNC) with integrated micro space electrostatic field for ZMBs anode protection.
As hot topics in the chemical conversion of CO2, the photo‐/electrocatalytic reduction of CO2 and use of CO2 as a supporter for energy storage have shown great potential for the utilization of CO2. ...However, many obstacles still exist on the road to realizing highly efficient chemical CO2 conversion, such as inefficient uptake/activation of CO2 and mass transport in catalysts. Covalent organic frameworks (COFs), as a kind of porous material, have been widely explored as catalysts for the chemical conversion of CO2 owing to their unique features. In particular, COF‐based functional materials containing diverse active sites (such as single metal sites, metal nanoparticles, and metal oxides) offer great potential for realizing CO2 conversion and energy storage. This Minireview discusses recent breakthroughs in the basic knowledge, mechanisms, and pathways of chemical CO2 conversion strategies that use COF‐based functional catalysts. In addition, the challenges and prospects of COF‐based functional catalysts for the efficient utilization of CO2 are also introduced.
This Minireview discusses recent developments in the basic knowledge, mechanisms, and CO2 utilization strategies regarding the use of functional materials based on covalent‐organic frameworks (COFs) with diverse active sites as catalysts. Insight is provided into the challenges and prospects of COF‐based catalysts for the design of the next‐generation photo‐/electrocatalysts for the utilization of CO2.
In this work, we rationally designed a series of crystalline and stable dioxin‐linked metallophthalocyanine covalent organic frameworks (COFs; MPc‐TFPN COF, M=Ni, Co, Zn) under the guidance of ...reticular chemistry. As a novel single‐site catalysts (SSCs), NiPc/CoPc‐TFPN COF exhibited outstanding activity and selectivity for electrocatalytic CO2 reduction (ECR; Faradaic efficiency of CO (FECO)=99.8(±1.24) %/ 96.1(±1.25) % for NiPc/CoPc‐TFPN COF). More importantly, when coupled with light, the FECO and current density (jCO) were further improved across the applied potential range (−0.6 to −1.2 V vs. RHE) compared to the dark environment for NiPc‐TFPN COF (jCO increased from 14.1 to 17.5 A g−1 at −0.9 V; FECO reached up to ca. 100 % at −0.8 to −0.9 V). Furthermore, an in‐depth mechanism study was established by density functional theory (DFT) simulation and experimental characterization. For the first time, this work explored the application of COFs as photo‐coupled electrocatalysts to improve ECR efficiency, which showed the potential of using light‐sensitive COFs in the field of electrocatalysis.
A series of stable dioxin‐linked metallophthalocyanine covalent organic frameworks (COFs) were developed and applied for photo‐coupled electrocatalytic CO2 reduction. This work represents a new insight for the future rational design of light sensitive crystalline materials for CO2 reduction.
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.
Strategies that enable simultaneous morphology‐tuning and electroreduction performance boosting are much desired for the exploration of covalent organic frameworks in efficient CO2 electroreduction. ...Herein, a kind of functionalizing exfoliation agent has been selected to simultaneously modify and exfoliate bulk COFs into functional nanosheets and investigate their CO2 electroreduction performance. The obtained nanosheets (Cu−Tph−COF−Dct) with large‐scale (≈1.0 μm) and ultrathin (≈3.8 nm) morphology enable a superior FECH4 (≈80 %) (almost doubly enhanced than bare COF) with large current‐density (−220.0 mA cm−2) at −0.9 V. The boosted performance can be ascribed to the immobilized functionalizing exfoliation agent (Dct groups) with integrated amino and triazine groups that strengthen CO2 absorption/activation, stabilize intermediates and enrich the CO concentration around the Cu active sites as revealed by DFT calculations. The point‐to‐point functionalization strategy for modularly assembling Dct‐functionalized COF catalyst for CO2 electroreduction will open up the attractive possibility of developing COFs as efficient CO2RR electrocatalysts.
A kind of functionalizing exfoliation agent has been selected to simultaneously modify and exfoliate bulk COFs into functional nanosheets and the obtained materials can be applied in highly selective CO2 electroreduction into CH4.
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.
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