Unsaturated Sites Research Articles

Surface oxygen vacancy enhanced the activation of peroxymonosulfate on α-Ni0.2Fe1.8O3 for water decontamination: The overlooked role of H2O in interface mechanism

Oxygen vacancies (OVs)-rich α-Ni0.2Fe1.8O3 with dual metal sites was synthesized by Ni2+ isomorphously substituted α-Fe2O3 to activate peroxymonosulfate (PMS) for aceclofenac (ACF) degradation. A novel insight was proposed for the overlooked role of H2O in the surface-complexed process between PMS and unsaturated metal sites induced by OVs. The surface-bond SO4∙- and ∙OH were demonstrated as the dominant reactive oxygen species (ROS). In situ ATR and Raman spectra revealed the reaction of HSO5- with the surface metal sites by replacing the surface-bonded -OH. The DFT study revealed the spontaneous formation of hydrolyzed -OH on OVs (∆G=−1.45 eV), which was further replaced by HSO5- to complex with metal sites (∆G=−3.58 eV). The OⅠ of the H-OⅠ-OⅡ-SO3- was more readily bonded with the Ni or Fe sites around OVs, causing the O-O cleavage for SO4∙- generation. This study proposed a brand-new perspective for the interfacial behavior of PMS activation.

Self-assembly, structure and catalytic activity of Ni3 on TiO2: A triple-atom catalyst for hydrogen evolution

Triple-atom catalysts (TACs), structurally derived from single-atom catalysts (SACs) but beyond SACs in the active sites, have received increasing attention but are still in their infant stage. Using density functional theory, we study the self-assembly of the Ni3 trimer on TiO2 (Ni3/TiO2) by atom-by-atom deposition. Coordinatively unsaturated sites on the TiO2 surface are responsible for this self-assembly, resulting in different configurations of Ni3. According to the orientation relationship and lattice mismatch, an embryo of Ni crystal is thought to be born of triangle Ni3 trimer on TiO2. The hydrogen evolution reaction activity and mechanism of Ni3/TiO2 with different H coverages are evaluated using thermochemistry and kinetics calculations. Only at high H coverage would Ni3/TiO2 TACs exhibit a hydrogen production activity higher than that of Ni1/TiO2 SACs, indicating the matching relationship between multiple active sites and multi-step reaction intermediates for the active-site utilization. The quantum confinement effect throughout Nin/TiO2 (n = 1–3) is evidenced by the localization of metallic states of Nin. Our results not only open the possibility for synthesizing multimers on oxides by self-assembly, but also enrich the quantum control toolbox in few-atom catalysts by coordination modulation.

Nitrogen-doped carbon aerogel framework with in situ encapsulated ZrO2 nanoparticles as pseudocapacitive anode for phosphorus uptake

Phosphorus reduction is crucial for controlling eutrophication and protecting the aquatic environment. Nonetheless, traditional methods suffer from secondary pollution and high costs. Capacitive deionization (CDI) is a novel electrochemical approach for phosphorus removal, which is low-cost and environmentally friendly. Its performance is highly correlated with the electrode material. Herein, a novel nitrogen-doped carbon aerogel framework encapsulated with ZrO2 nanoparticles (ZrNC) was rationally fabricated and employed as an anode for phosphorus removal. The experimental results revealed that the N site and ZrO2 could enhance the physicochemical properties, electrochemical activity, and additional pseudocapacitive contribution, thus raising the phosphorus removal capacity. The optimal ZrNC-3 electrode demonstrated superior phosphorus capture (18.26 mg P/g), low energy consumption at 1.2 V (0.0256 kWh/m3 and 4.159 kWh/kg), outstanding phosphorus selectivity, and excellent stability. Mechanism investigation suggested phosphorus can form mono- or bi-dentate inner-sphere complexes (Zr–O–P) by ligand exchange with ZrO2 sites under an electric field and combined with unsaturated Zr sites and N species by electrostatic attraction. This study presents a promising conception for designing and applying metal oxide/carbon complexes in selective phosphorus uptake electrodes.

High-performance carbon@ metal oxide nanocomposites derived metal–organic framework-perovskite hybrid boosted microwave-induced catalytic degradation of norfloxacin: Performance, degradation pathway and mechanism

Herein, FeCo@C-LFCx (FeCo@C-xLaFeCoO3) materials were prepared by high-temperature carbonation based on the construction of Fe/Co metal–organic framework columns with LaCoO3 (FeCo-MOF-LFCx) by in-situ extraction and synchronous coordination growth strategy. This strategy could improve the defects of perovskite materials such as easy aggregation, poor stability and poor specific surface area. The results demonstrated that the degradation rate of FeCo@C-LFC1.0 for norfloxacin (NOR, 20 mg/L) was 93.81% within 15 min. Co-BTC column nanocolumns and spongy Fe-BTC were successfully formed. Compared with LaFeCoO3, the specific surface area (89.9 m2/g) and pore volume (0.101 cm3/g) of FeCo@C-LFC1.0 after carbonization were increased by 16.3 times and 9.2 times, respectively. FeCo@C-LFCx could produce more structural defects and coordination unsaturated sites, promote microwave absorption. Vo and C = O on the material surface were involved in the activation of PMS. Moreover, quenching experiments and EPR verified that 1O2, OH, and SO4− were the main reactive radicals in the degradation process. The FeCo@C-LFC1.0 showed excellent reusability and stability. After five experiments, the removal rate of NOR remained at 91.15%. The toxicity of intermediate products was reduced. This work provided new avenues for using FeCo@C-LFC1.0 for environmental remediation.

Electron Delocalization Realizes Speedy Fenton-Like Catalysis over a High-Loading and Low-Valence Zinc Single-Atom Catalyst.

A zinc (Zn)-based single-atom catalyst (SAC) is recently reported as an active Fenton-like catalyst; however, the low Zn loading greatly restricts its catalytic activity. Herein, a molecule-confined pyrolysis method is demonstrated to evidently increase the Zn loading to 11.54 wt.% for a Zn SAC (ZnSA -N-C) containing a mixture of Zn-N4 and Zn-N3 coordination structures. The latter unsaturated Zn-N3 sites promote electron delocalization to lower the average valence state of Zn in the mix-coordinated Zn-Nx moiety conducive to interaction of ZnSA -N-C with peroxydisulfate (PDS). A speedy Fenton-like catalysis is thus realized by the high-loading and low-valence ZnSA -N-C for PDS activation with a specific activity up to 0.11min L-1 m-2 , outstripping most Fenton-like SACs. Experimental results reveal that the formation of ZnSA -N-C-PDS* complex owing to the strong affinity of ZnSA -N-C to PDS empowers intense direct electron transfer from the electron-rich pollutant toward this complex, dominating the rapid bisphenol A (BPA) elimination. The electron transfer pathway benefits the desirable environmental robustness of the ZnSA -N-C/PDS system for actual water decontamination. This work represents a new class of efficient and durable Fenton-like SACs for potential practical environmental applications.

Controllable Synthesis of Defective UiO-66 for Efficient Degradation and Detection of Ozone.

Metal-organic framework (MOF) structures have gained significant attention for their exceptional catalytic performance in ozone degradation, even under high humidity conditions, which is attributed to the presence of unsaturated metal sites (MOF defects). However, the correlation between MOF defects and catalytic ozone remains ambiguous, and a general approach for the controllable synthesis of high-performance MOF structures is currently lacking. Herein, different defective UiO-66 materials with cluster or ligand defects were obtained by precisely controlling small molecular acid modulators. Their catalytic performance can be analyzed in real time through the specific cataluminescence (CTL) signal of ozone at the interface. The presence of ligand defects was found to be crucial for both catalytic degradation and luminescence of ozone, and the CTL signal exhibited a positive correlation with the endogenous hydroxyl group content in the material (R2 = 0.982), while external humidity further supplemented internal water molecules within the material. Furthermore, theoretical calculations were conducted to compare the adsorption behaviors of ozone on the defective UiO-66 under dry/wet conditions, leading to the proposal of two potential reaction pathways. Subsequently, UiO-66-DA with superior catalytic performance was employed to develop a highly efficient CTL sensor capable of accurately detecting ozone (LOD = 23.3 ppb). This study held significant value in elucidating the reaction site of ozone on MOFs and achieving optimal catalytic effects through the careful selection of modulators and humidity levels.

Synthesis of Quaternary (Ni, Co, Cu)Se2 Nanosheet Arrays on Carbon Cloth for Non-Enzymatic Glucose Determination

Unlike transition metal oxides and sulfides, transition metal-based selenides display higher electrical conductivity, more electroactive unsaturated edge sites, and better chemical stability, which have found extensive usage in electrocatalysis. In this work, simple hydrothermal and solvothermal procedures were employed to synthesize quaternary (Ni, Co, Cu)Se2 nanosheet arrays on carbon cloth (CC) to measure glucose. The conductivity of the material can be effectively elevated by adding Se element to form selenides, and the synergistic effect between the three selenides can improve the electrocatalytic performance. Consequently, in the ranges of 0.01–600 μM and 600–9000 μM, respectively, the current response of the synthesized material to glucose concentration exhibited linear relationships. The sensor demonstrated excellent sensitivity and a low detection limit of 5.82 nM. Furthermore, the practical applicability of the constructed biosensor was proved by using it to quantify the amount of glucose in human serum.

Amorphization-induced abundant coordinatively unsaturated Ni active sites in NiCo(OH)2 for boosting catalytic OER and HER activities at high current densities for water-electrolysis

The large overpotential required for oxygen evolution reaction (OER) is one of the major factors limiting the efficiency of electrochemical water-electrolysis for hydrogen production. In this work, to decrease OER energy barrier and obtain low overpotential, amorphous-crystalline NiCo(OH)2 nanoplates are in-situ grown on nickel foam surface to form a catalyst-based electrode (ac-NiCo(OH)2/NF) for water-electrolysis application. As the inner amorphization of NiCo(OH)2 results in increased electron density of the metal sites, leading to the formation of tensile Ni-O bond, the coordinatively unsaturated Ni sites in the down-shift d-band centers toward Fermi level can lower the antibonding states. This can lead to optimized adsorption and desorption energies for oxygen-containing intermediates for OER. As expected, the prepared ac-NiCo(OH)2/NF electrode presents a low overpotential of 364 mV to deliver 1000 mA cm−2 toward OER with impressively high robust stability. When this electrocatalyst electrode serves as both the anode and cathode, the assembled anion exchange membrane (AEM) electrolyser only needs a cell voltage of 1.68 V to drive the overall water-electrolysis process at a current density of 10 mA cm−2.

Effect of Linker Substituent Nature on Performance of Active Sites in UiO-66: Combined FT-IR and DFT Study.

The nature of organic linker substituents plays an important role in gas sorption and separation as well as in catalytic applications of metal-organic frameworks. Zirconium-based UiO-66 is one of the most tunable members of this class of materials. However, the prediction of its properties is still not a fully solved problem. Here, the infrared spectroscopic measurements using highly sensitive CO probe molecules, combined with DFT calculations, are used in order to characterize the performance of different acidic sites caused by the presence of different organic linker substituents. The proposed model allowed differentiation between various active sites over the UiO-66 and clarification of their behavior. The experimental IR bands related to CO adsorption can be unambiguously assigned to one type of site or another. The previously undescribed highly red-shifted band is attributed to CO adsorbed on coordinatively unsaturated zirconium sites through an O atom. The results confirm the lower and higher Lewis's acidity of coordinatively unsaturated Zr sites on linker defects in the UiO-66 structure when electron-withdrawing and electron-donating groups are, respectively, included in a terephthalate moiety, whilst the Brønsted acidity of zirconium oxo-cluster remains almost unchanged.

Study on the decarbonization mechanism of composite adsorbent by Mg-MOF-74-based modified biochar

In this paper, the composite adsorbent by MOFs-based modified biochar was prepared by in-situ growth method based on the structural design of modified biochar and Mg-MOF-74, both of which contained unsaturated metal centers and oxygen-containing functional groups. The coupling mechanism between MOFs and biochar was investigated by CO2 adsorption properties and various characterizations. Based on the density functional theory (DFT), the three-dimensional model of composite adsorbent was constructed by combining the characterization of various microscopic properties to reveal CO2 adsorption mechanism of the composite adsorbent. Finally, the correctness of the microscopic mechanism of the composite adsorbent was verified by using surface element analysis. The results reveal that biochar causes lattice defects in MOFs, improving the pore structure, and the composite of biochar and MOFs increases the CO2 adsorption performance. Biochar is connected with Mg-MOF-74 through oxygen-containing functional groups and unsaturated metal centers to form a composite adsorbent. The four adsorption sites constructed with electron-bearing oxygen vacancies, metal ions, lattice oxygen, and chemisorbed oxygen are coupled to act on CO2 adsorption, chemisorption properties of the composite adsorbent are enhanced. MOFs are affected by the spatial site resistance effect brought by the biochar to produce oxygen defects, which couples with the unsaturated metal adsorption sites to realize the composite adsorption of metals. There is electron transfer during CO2 adsorption by the composite adsorbent and the stable carbonate is generated.

Yolk@shell nanoreactor with coordinately unsaturated metal sites on MOF surface inside polypyrrole capsule: Enhanced catalytic activity and lowered metal leaching in fenton-like reaction

Yolk@shell nanoreactor with coordinately unsaturated metal sites on MOF surface inside polypyrrole capsule: Enhanced catalytic activity and lowered metal leaching in fenton-like reaction

The tunable effect of the second metal site on the hydroformylation of propylene over Rh-M-BTC (M= Fe, Ru, Mn, Rh, Pt, Pd, Re, Cu, Ni)

Hydroformylation is one of the most important homogeneous reactions in industry. Cu-BTC, as a kind of MOFs material with coordinate unsaturated metal sites, has strong interaction with adsorption molecules and is widely used in adsorption and catalytic research fields. The open metal sites in it can be adjusted according to the demand. In this work, Rh-BTC was selected as the catalyst for the hydroformylation of propylene. In order to regulate the electronic properties of Rh metal center, eight Rh-M-BTC materials (M= Fe, Ru, Mn, Rh, Pt, Pd, Re, Cu, Ni) were investigated. The Mulliken charge of Rh-M metal nodes and the reaction energy barrier of the key steps of propylene hydroformylation on Rh-M-BTC were calculated, including the step of propylene insertion, CO insertion, and aldehyde formation. The results showed that on Rh-Pd-BTC, the energy barrier difference between linear and branched path for the regional decisive step propylene insertion step is the lowest, only 0.04 eV. The reaction energy barrier of the linear path for CO insertion is only half of that of the branched path. The linear path has obvious advantages. Therefore, Rh-Pd-BTC was suggested as the most suitable model studied in the work for hydroformylation of propylene.

Interface mediated CO2 hydrogenation on inverse supported ZrO2/Ni(1 1 1) nanocluster catalyst

To tune the activity and selectivity of CO2 hydrogenation, inverse supported Zr9O18/Ni(111) catalysts are designed based on ab initio molecular dynamics simulation and density functional theory calculation under the consideration of the number of interfacial O and Zr atoms as well as the interaction between O and Zr atoms. For the most stable catalyst with coordinatively unsaturated interface Zr sites, charge transfer from surface to oxide has been found. The Ni(111) surface is pre-covered by H atoms and the interface Zr sites can activate CO2 to a large extent, and their interaction results in the spontaneous formation of surface formate. Further hydrogenation of surface formate leads to the selective formation of methanol with an apparent Gibbs free energy barrier of 0.62 eV, lower than that of methane formation (1.09 eV). On the contrary to metallic nickel and supported nickel catalysts, the most favoured methanol formation route [HCOO → CHO → CH2O → CH3O → CH3OH] does not involve CO as intermediate, revealing the mediated interface effect.

A novel approach to environmental pollution management/remediation techniques using derived advanced materials

The carbon dioxide (CO2) crisis is one of the world's most urgent issues. Meeting the worldwide targets set for CO2 capture and storage (CCS) is crucial. Because it may significantly reduce energy consumption compared to traditional amine-based adsorption capture, adsorption dependant CO2 capture is regarded as one of the most hopeful techniques in this paradigm. The expansion of unique, critical edge adsorbent materials has received most of the research attention to date, with the main objective of improving adsorption capacity and lifespan while lowering the temperature of adsorption, thereby lowering the energy demand of sorbent revival. There are specific materials needed for each step of the carbon cycle, including capture, regeneration, and conversion. The potential and efficiency of metal-organic frameworks (MOFs) in overcoming this obstacle have recently been proven through research. In this study, we pinpoint MOFs' precise structural and chemical characteristics that have contributed to their high capture capacity, effective regeneration and separation processes, and efficient catalytic conversions. As prospective materials for the next generation of energy storage and conversion applications, carbon-based compounds like graphene, carbon nanotubes, and fullerenes are receiving a lot of interest. Their distinctive physicochemical characteristics make them suitable for these popular study topics, including structural stability and flexibility, high porosity, and customizable physicochemical traits. It is possible to precisely design the interior of MOFs to include coordinatively unsaturated metal sites, certain heteroatoms, covalent functionalization, various building unit interactions, and integrated nanoscale metal catalysts. This is essential for the creation of MOFs with improved performance. Utilizing the accuracy of MOF chemistry, more complicated materials must be built to handle selectivity, capacity, and conversion all at once to achieve a comprehensive solution. This review summarizes, the most recent developments in adsorption-based CO2 combustion capture, the CO2 adsorption capacities of various classes of solid sorbents, and the significance of advanced carbon nanomaterials for environmental remediation and energy conversion. This review also addresses the difficulties and potential of developing carbon-based electrodes for energy conversion and storage applications.

Directional Shunting of Photogenerated Carriers in POM@MOF for Promoting Nitrogen Adsorption and Oxidation.

The efficient catalysis of nitrogen (N2 ) into high-value N-containing products plays a crucial role in the N economic cycle. However, weak N2 adsorption and invalid N2 activation remain two major bottlenecks in rate-determining steps, leading to low N2 fixation performance. Herein, an effective dual active sites photocatalyst of polyoxometalates (POMs)-based metal-organic frameworks (MOFs) is highlighted via altering coordination microenvironment and inducing directional shunting of photogenerated carriers to facilitate N2 /catalyst interaction and enhance oxidation performance. MOFs create more open unsaturated metal cluster sites with unoccupied d orbital possessing Lewis acidity to accept electrons from the 3σg bonding orbital of N2 for storage by combining with POMs to replace bidentate linkers. POMs act as electron sponges donating electrons to MOFs, while the holes directional flow to POMs. The hole-rich POMs with strong oxidation capacity are easily involved in oxidizing adsorbed N2 . Taking UiO-66 (C48 H28 O32 Zr6 ) and Mo72 Fe30 ([Mo72 Fe30 O252 (CH3 COO)12 {Mo2 O7 (H2 O)}2 {H2 Mo2 O8 (H2 O)}(H2 O)91 ]·150H2 O) as an example, Mo72 Fe30 @UiO-66 shows twofold enhanced adsorption of N2 (250.5cm3 g-1 ) than UiO-66 (122.9cm3 g-1 ) at P/P0 =1. And, the HNO3 yield of Mo72 Fe30 @UiO-66 is 702.4µgg-1 h-1 , ≈7times and 24 times higher than UiO-66 and Mo72 Fe30 . This work provides reliable value for the storage and relaying artificial N2 fixation.

Ethylenediamine-entrapped defective UiO-66(Zr) frameworks for improved CO2 adsorption and selectivity

In this work, ethylenediamine was entrapped to defected UiO-66(Zr) frameworks to harvest defective amine@UiO-66(Zr) adsorbent (ED@DUiO) that showed improved CO2 performance and good renewability owing to a synergetic effect of creating defects and introducing amine molecules. The UiO-66(Zr) framework was in-situ modified using an acetic acid modulator, followed by grafting of ethylenediamine into the defected UiO-66(Zr) in n-hexane media. Results indicated that the defected UiO-66(Zr) framework had enhanced porosity and exposed more coordinatively unsaturated sites of Zr4+, favouring grafting amine molecules. Gas adsorption experiments revealed that ED@UiO exhibited significantly enhanced CO2 performance compared to the pristine MOF. At 25 °C and 100 kPa, the optimized ED@DUiO entrapped with ∼ 38.3 wt% amines exhibited a CO2-absorbing amount of ∼ 3.48 mmol/g, and IAST-CO2/CO and CO2/N2 selectivity of ∼ 46 and ∼ 78, respectively. Furthermore, the defected UiO-66 entrapped with ethylenediamine exhibited good separation of CO2 in the mixture with CO or N2 under dynamic flow adsorption conditions. The study provides a new strategy combining engineering defects and grafting alkylamine within MOF, which is a promising strategy for developing CO2-selective adsorbent materials.

Construction of metal-organic frameworks with unsaturated Cu sites for efficient and fast reduction of nitroaromatics: A combined experimental and theoretical study

Metal-organic frameworks (MOFs) functionalized with open metal sites (OMSs) have received widespread attention in various applications due to their fascinating electronic properties and unique interactions with guest molecules. However, rational tailoring of the coordination environment of metal nodes during the synthesis of MOFs remains a great challenge due to their tendency of saturated coordination with linkers. Herein, we reported the construction of three new MOFs featuring unsaturated Cu(II) sites, namely [Cu(HCOO)(pzta)]n (HL-1), {[Cu(PTA)0.5(pzta)(H2O)]·2H2O}n (HL-2) and [Cu(NA)0.5(pzta)]n (HL-3) (Hpzta = 3-pyrazinyl-1,2,4-triazole; PTA = terephthalic acid; NA = 1,4-naphthalene dicarboxylic acid), based on the mixed-linker strategy via specific selection of versatile Hpzta ligand and carboxylate ligands. Remarkably, the obtained MOFs exhibited excellent activity and good recyclability for the catalytic reduction of nitroaromatics under mild conditions (25 °C and 1 atm). In particular, the complete conversion of 4-nitrophenol (4-NP) took only 30 s on HL-2, reaching a record-high TOF value compared with previously reported metal catalysts. The combined experimental and theoretical studies on HL-2 revealed that the open Cu site with positive-charged nature could improve the adsorption and subsequent electron transport between the substrates, and was responsible for the outstanding performance. This work shined lights on the further enhancement of performance for MOFs through rational OMSs construction.

Morphological Effect on the Surface Activity and Hydrogen Evolution Catalytic Performance of Cu2O and Cu2O/rGO Composites

Different cuprous oxide (Cu2O) particle forms, including the octahedron, truncated octahedron, cube, and star-like forms, are synthesized through chemical reduction under different reaction conditions. The correlation between the morphology and the catalytic activity of hydrogen evolution reactions (HERs) is investigated. It is discovered that the Cu2O particles with a higher 111/100 facets (r) ratio have a higher oxidation resistance and higher activity in HER catalysis, as supported by the density functional theory (DFT) calculation results. This improvement is attributed to the fact that more Cu+ terminated atoms on facet 111 provide more active sites, as measured using their electroactive area, as well as the lower H2 adsorption energy on that facet. To enhance Cu2O’s HER performance, cuprous oxide particles are deposited on reduced graphene oxide (rGO) through a hydrothermal method. XPS and XRD show a CuO layer on the composite surface, which reduces the Cu2O corrosion in the reaction. Overall, Cu2O/rGO composites exhibit a better particle distribution, increased active sites, and improved charge separation. The best electrocatalyst in this study is the Cu2O/rGO with a star-shaped form, with an overpotential of −458 mV. Its improved performance is attributed to the presence of unsaturated active sites with a higher reactivity, such as the edges and corners. SEM studies of this composite after catalysis indicate that Cu2O undergoes structural reconstruction during the reaction and reaches a more stable structure.

Highly Water-Stable Zinc Based Metal-Organic Framework: Antibacterial, Photocatalytic Degradation and Photoelectric Responses.

A reported water-stable Zn-MOF ([Zn(L)2(bpa)(H2O)2]·2H2O, H2L = 5-(2-cyanophenoxy) isophthalic acid has been prepared via a low-cost, general and efficient hydrothermal method. It is worth noting the structural features of Zn-MOF which exhibit the unsaturated metal site and the main non-covalent interactions including O⋯H, N⋯H and π-π stacking interactions, which lead to strong antibacterial and good tetracycline degradation ability. The average diameter of the Zn-MOF inhibition zone against Escherichia coli and Staphylococcus aureus was 12.22 mm and 10.10 mm, respectively. Further, the water-stable Zn-MOF can be employed as the effective photocatalyst for the photodegradation of tetracycline, achieving results of 67% within 50 min, and it has good cyclic stability. In addition, the photodegradation mechanism was studied using UV-vis diffuse reflection spectroscopy (UV-VIS DRS) and valence-band X-ray photoelectron spectroscopy (VB-XPS) combined with the ESR profile of Zn-MOF, which suggest that ·O2- is the main active species responsible for tetracycline photodegradation. Also, the photoelectric measurement results show that Zn-MOF has a good photocurrent generation performance under light. This provides us with a new perspective to investigate Zn-MOF materials as a suitable multifunctional platform for future environmental improvement applications.

Defect Engineered Metal–Organic Framework with Accelerated Structural Transformation for Efficient Oxygen Evolution Reaction

AbstractMetal–organic frameworks (MOFs) have been increasingly applied in oxygen evolution reaction (OER), and the surface of MOFs usually undergoes structural transformation to form metal oxyhydroxides to serve as catalytically active sites. However, the controllable regulation of the reconstruction process of MOFs remains as a great challenge. Here we report a defect engineering strategy to facilitate the structural transformation of MOFs to metal oxyhydroxides during OER with enhanced activity. Defective MOFs (denoted as NiFc′xFc1‐x) with abundant unsaturated metal sites are constructed by mixing ligands of 1,1′‐ferrocene dicarboxylic acid (Fc′) and defective ferrocene carboxylic acid (Fc). NiFc′xFc1‐x series are more prone to be transformed to metal oxyhydroxides compared with the non‐defective MOFs (NiFc′). Moreover, the as‐formed metal oxyhydroxides derived from defective MOFs contain more oxygen vacancies. NiFc′Fc grown on nickel foam exhibits excellent OER catalytic activity with an overpotential of 213 mV at the current density of 100 mA cm−2, superior to that of undefective NiFc′. Experimental results and theoretical calculations suggest that the abundant oxygen vacancies in the derived metal oxyhydroxides facilitate the adsorption of oxygen‐containing intermediates on active centers, thus significantly improving the OER activity.