Coordination Configuration Research Articles

Exclusive separation of Cu(II) with aminophosphonic acid-functionalized hydrogel from strong acidic media

Strong acidic heavy metal ions (HMIs) wastewater (pH < 3.0) is characterized by widespread source, mixed composition and high toxicity, which is extremely difficult to control and meet the requirements of HMIs separation and resource recovery. Herein, a novel aminophosphonic acid-functionalized hydrogel (CMC/PEI-P) was prepared successfully and applied to highly-selective separate Cu(II) from strong acidic media (SAM) (pH = 2.0). Thanks to the abundant and outward amino phosphonic acid groups, the maximum adsorption capacity and the initial adsorption rate constant were 119.41% and 116.64% higher than those of the precursor CMC/PEI. Most importantly, the exclusive separation with the super-high selectivity coefficients (+∞) could unexpectedly achieve with CMC/PEI-P even from the mixed polymetallic SAM. Furthermore, the purity of Co(II) in strong acidic cobalt-rich solution could be increased to more than 99.50%, with the benefit of about 200 times higher than the cost. The predominant mechanisms existed in the coordination with various active groups such as phosphonate, amine and hydroxyl. According to Density Functional Theory (DFT) calculations, the tetradentate coordination configuration with the best stability could be formed involving CMC/PEI-P and Cu(II). Therefore, this work explored a new pathway for the cost-effective separation and purification toward Cu(II) directly especially from SAM.

Vanadium as Auxiliary for Fe-V Dual-Atom Electrocatalyst in Lithium-Sulfur Batteries: "3D in 2D" Morphology Inducer and Coordination Structure Regulator.

The undesirable shuttling behavior, the sluggish redox kinetics of liquid-solid transformation, and the large energy barrier for decomposition of Li2S have been the recognized problems impeding the practical application of lithium-sulfur batteries. Herein, inspired by the spectacular catalytic activity of the Fe/V center in bioenzyme for nitrogen/sulfur fixation, we design an integrated electrocatalyst comprising N-bridged Fe-V dual-atom active sites (Fe/V-N7) dispersed on ingenious "3D in 2D" carbon nanosheets (denoted as DAC), in which vanadium induces the laminar structure and regulates the coordination configuration of active centers simultaneously, realizing the redistribution of the 3d-orbital electrons of Fe centers. The high coupling/conjunction between Fe/V 3d electrons and S 2p electrons shows strong affinity and enhanced reactivity of DAC-Li2Sn (1 ≤ n ≤ 8) systems. Thus, DAC presents strengthened chemisorption ability toward polysulfides and significantly boosts bidirectional sulfur redox reaction kinetics, which have been evidenced theoretically and experimentally. Besides, the well-designed "3D in 2D" morphology of DAC enables uniform sulfur distribution, facilitated electron transfer, and abundant active sites exposure. Therefore, the assembled Li-S cells present outstanding cycling stability (637.3 mAh g-1 after 1000 cycles at 1 C) and high rate capability (711 mAh g-1 at 4 C) under high sulfur content (70 wt %).

Assisted wet deposition targeted synthesis of Co-N coordination single-atom catalysts for efficient Fenton-like catalytic degradation of micropollutants

Assisted wet deposition methods to localize the active phase metal on the carrier surface and prevent atomic aggregation during conventional heat treatment are strongly preferred. Herein, single-atom cobalt catalysts (SA-Co-PCN) with different metal-central content were target-prepared using a combination of impregnation and secondary annealing on polymerized carbon nitride (PCN) through reticular confinement. Fitting the coordination configuration of the Co-N pathway within the first coordination shell according to quantitative EXAFS indicated that the ligancy of Co-N was 4. The removal efficiency of representative micropollutants in the SA-Co-PCN/PMS system achieved 100% within 15 min. The outstanding degradation properties of micropollutants were ascribed to the SA-Co-PCN boosts PMS to a 1O2-dominated system. Moreover, the effects of substituents on the degradation behavior and ecotoxicology of sulfonamides (SAs) in PMS-activated systems were investigated in depth. The combination of DFT theoretical calculations and LC-MS further confirmed that the similar electron-rich sites on the SAs molecules allowed for commonality in the degradation pathway. Both S-N bond and C-S bond fragments became the initial attack and cleavage sites in the series of SAs. Ecotoxicity predictions indicated that most intermediates of SAs exhibited lower acute and chronic toxicity, especially acute toxicity, than the parent compounds. Environmental ImplicationAssisted wet deposition to localize the active phase metal on the carrier surface allows easy target formation of single-atom cobalt catalysts (SA-Co-PCN), which could boost PMS to a 1O2-dominated system for efficient oxidation of typical micropollutants. The degradation behavior and ecotoxicology of sulfonamides in the SA-Co-PCN/PMS system were investigated in depth, revealing that most intermediates of sulfonamides exhibited lower acute and chronic toxicity, especially acute toxicity, than the parent compounds. This work provides a strategy for the development of facilely prepared single-atom catalysts and contributes to the development and application potential of PMS advanced oxidation technology for water pollution control.

Evolution of Ni coordination configuration during one-pot pyrolysis synthesis of Ni-g-C3N4 single atom catalyst

In this paper, the unclear Ni atom coordination structure evolution in one-pot pyrolysis method synthesizing Ni single atom catalyst using graphitic carbon nitride as support (Ni-g-C3N4) was deeply discussed. In-situ X-ray absorption fine structure spectra and other assisted methods were used to characterize the structural evolution. The results demonstrate that the pyrolysis process can be divided into three stages. In the first stage from room temperature to 183 °C (Stage I), the NiCl2⋅6H2O was mixed with the supporting material (dicyandiamide) to form the precursor with Ni-(H2O)6 octahedral coordination configuration. In the second stage from 183 to 350 °C (Stage II), the H2O molecules have been removed and the supporting material was converted to melamine. The melamine molecules were polycondensed to melem during 308–350 °C. The intermediates labeled Ni-melamine and Ni-melem was formed with Ni-N4 planar quadrilateral coordination configuration. In the third stage from 350 to 600 °C (Stage III), the supporting material (melem) was gradually converted to g-C3N4, and the Ni-N4 coordination configurations were replaced by Ni-N6 planar hexagon coordination configuration one by one. The three Ni coordination configurations were further confirmed by Reverse Monte Carlo simulations and ab initio calculations.

Redistribution of d-orbital in Fe-N4 active sites optimizing redox kinetics of the sulfur cathode

Redistributing the d-orbital of single Fe atom catalysts (SFeACs) has been challenging to optimize redox kinetics of lithium sulfur batteries (LSBs). Here, the Fe-N4/S2C with mounting energy level of dz2 and partial occupation of dxz is controllably fabricated. The increased dz2, originating from thiophene sulfur, upshifts d band center compared to the Fe-N4/C with planar symmetric structure. That promotes electron transfer between Fe-N4 and sulfur, enhancing conversion of polysulfides and solid products. The lower fill of dxz develops hybridization between Fe and S atoms via the form of bonding and antibonding, with alleviating the loss of sulfur. Thus, the sulfur cathode with Fe-N4/S2C delivers a high capacity of 749 mAh g−1 at 2.0 C, accompanied by excellent stability with a lower capacity decay of 0.07% per cycle. This work has developed a novel coordination configuration towards SFeACs and uncovered the intrinsic mechanism of facilitated redox kinetics with SFeACs for LSBs.

O, N Coordination-Mediated Nickel Single-Atom Catalysts for High-Efficiency Generation of H2O2.

Electrochemical selective two-electron oxygen reduction shows great potential for on-site electrochemical production of hydrogen peroxide (H2O2). Herein, we demonstrated the synthesis of Ni single-atom sites coordinated by three oxygen atoms and one nitrogen atom (i.e., Ni-N1O3) supported by oxidized carbon black (OCB) by pyrolyzing nickel-(pyridine-2,5-dicarboxylate) coordination complexes. Aberration-corrected scanning transmission electron microscopy (AC-STEM) combined with X-ray absorption spectroscopy (XAS) proves the presence of atomically dispersed Ni atoms attached on OCB (labeled as Ni-SACs@OCB), in which Ni single atoms are stabilized by a N, O-mediated coordination configuration. This Ni-SACs@OCB catalyst shows high H2O2 selectivity (95%) in a range of 0.2-0.7 V undergoing a two-electron oxygen reduction process, with a kinetic current density of 2.8 mA cm-2 and a mass activity of 24 A gcat.-1 at 0.65 V (vs RHE). In practice, H-cells with Ni-SACs@OCB as catalysts displayed a high H2O2 production rate of 98.5 mmol gcat.-1 h-1 with negligible current loss during testing, suggesting the high H2O2 generation efficiency and robust stability. DFT theoretical calculations revealed that Ni single-atom sites coordinated by O, N coordination exhibit advantages in oxygen adsorption and increased reactivity toward the intermediate species, *OOH, which is beneficial to high selectivity for H2O2 production. This work provides a novel N, O-mediated four-coordinate nickel single-atom catalyst as a promising candidate for practical decentralized production of H2O2.

High loads of rare earth single-atom lanthanum anchored carbon nitride with special double-layer coordination structure for efficient photocatalysis

A special two-layer coordination configuration anchored single-atom La (SALa) catalyst is synthesized to realize the effective separation of electrons in space and efficient active sites for the activation of O2 to produce more active species. The special SALa microenvironment is obtained by a novel and facile reduction method that avoids the formation of rare earth oxides and the concentration of loaded SALa (10.34 wt%) exceeds that in most previous studies. The photodegradation test results show that antibiotics are almost completely removed within 30 min by SALa/CN. The first-order kinetic constant of SALa/CN (0.10661 min−1) is approximately 9.81 times higher than that of 3DA-CN (0.01087 min−1). SALa can be considered as a bridge to transfer electrons and •O2−, 1O2 and h+ are the main active species to degrade tetracycline into some pollution-free small molecules. This work provides an efficient rare earth single-atom catalyst activity strategy possessing certain potential in practical applications.

Europium(III) Ion-Based photoluminescence complexes of Indole-Derivative β-diketone dominated by ancillary ligands

One pot reaction of β-diketone EIFD, EuCl3·6H2O and ancillary ligand yield a sequence of five luminescence β-diketone EIFD europium complexes, including Eu(EIFD)3(H2O)·CH2Cl2 (1), Eu(EIFD)3(DMSO) (2), Eu(EIFD)3(DMF)·CH2Cl2 (3), Eu(EIFD)3(phen)·CH2Cl2 (4) and Eu(EIFD)3(bpy) (5) (EIFD: 1-(1-ethyl-1H-indol-3-yl)-4,4,4-trifluorobutane-1,3-dione, phen = 1, 10-phenanthroline, bpy = 2,2′-bipyridine,). The molecular crystals reveal five mononuclear structures with the central Eu(III) ions of seven/eight coordination configuration furnished by three EIFD ligands and ancillary ligands for complexes 1–5. All the five complexes display room-temperature strong characteristic photoluminescence emissions of Eu(III) ions. The coordination environment of Eu(III) ion is a crucial factor in the optical performance of the complex. Herein, the way to introduce of oxygen and nitrogen ancillary ligands plays an important role in characteristic photoluminescence. The luminescence lifetime and quantum yields of the complexes can vary essentially by substituting the solvent molecules with oxygen and nitrogen ligands, leading to a strong luminescence intensity, as observed experimentally.

Layer-by-layer enriching active Ni-N3C sites in nickel-nitrogen-carbon electrocatalysts for enhanced CO2-to-CO reduction

Transition metal and nitrogen co-doped carbons (M-N-C) have proven to be promising catalysts for CO2 electroreduction into CO because of the high activity and selectivity. Effective enrichment of the active transition metal coordinated nitrogen sites is desirable but is challenging for a practical volumetric productivity. Herein, we report four kinds of model electrocatalysts to unveil this issue, which include the NC structures with surface N-functionalities, Ni-N-C_I with one layer of surface Ni-N3C sites, NC@Ni-N-C_I with surface N-functionalities and underneath Ni-N3C sites as well as Ni-N-C_II with doubled surface Ni-N3C sites. The X-ray absorption spectroscopy indicates the coordination configuration of Ni-N3C. For NC catalysts, when N-doping level increased from 3.5 at% to 8.4 at%, the CO partial current density increased from below 0.1 mA/cm2 to 3 mA/cm2. Introducing one layer of Ni-N3C onto the NC structures leads to a 54 times higher CO partial current density than that of NC, in the meantime the FECO is 66 times higher. Furthermore, doubling the density of surface Ni-N3C sites by a layer-by-layer method doubles the CO partial current density (jCO), indicating its potential to achieve a high density of active coordinated sites and current densities.

Auxiliary coordination strategy designed poly(chloranil-squaricamide) cathode achieving enhanced specific capacity utilization and Zn2+ insertion/extraction for aqueous zinc ion batteries

High-performance organic cathodes with sustainable advantages are suitable for low-carbon and secure applications in aqueous zinc ion batteries (AZIB). Herein, we propose an improved auxiliary coordination facilitating Zn2+ insertion/extraction strategy to design a novel poly(chloranil-squaricamide) (PCSA) as AZIB cathode. The auxiliary coordination squaraine groups with appropriate Zn2+ coordination configuration can facilitate Zn2+ insertion/extraction, so that PCSA presents enhanced stable cycle performance and specific capacity utilization. Particularly, PCSA can perform maximum 98.4% specific capacity utilization and 93% capacity retention after 400 cycles under 0.02 A g−1, even under 0.1 A g−1 the capacity retention can still reach 80% after 1000 cycles. The ex-situ X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectra (FTIR) reveal that quinone units can undertake redox function in PCSA and the auxiliary coordination of the squaraine groups can facilitate Zn2+ insertion/extraction. The ex-situ XRD indicates that slight H+ is involved in the Zn2+ storage process. Such an auxiliary coordination strategy can provide a prospective design method to construct high-performance organic cathode materials for AZIB.

Multiport Current-Limiting Hybrid DC Circuit Breaker for MTdc Grids

The coordination configuration of current-limiting inductors (CLIs) and hybrid dc circuit breakers (HCBs) is currently the most commonly used fault handling method to ensure fault ride-through of multi-terminal dc (MTdc) grids after the dc-side fault occurs. However, the high cost of HCB limits its large-scale application. In addition, the installation of the large CLIs will adversely affect the HCB performance, such as extending the fault current interruption time and increasing the energy dissipation pressure of the arrester. To solve these problems, a multiport current-limiting hybrid dc circuit breaker (MCL-HCB) is proposed in this paper. Compared with the typical HCBs, the MCL-HCB can achieve full selective protection of all connected dc lines with significantly reduced investment costs. Besides, it can suppress the rising speed of the fault current by embedded CLIs, while eliminating their negative impacts on the fault current interruption. The feasibility and superiority of the proposed MCL-HCB are verified by simulations in the PSCAD&#x002F;EMTDC software and experiments in the scaled-down experimental setup. Besides, the performance comparison between the MCL-HCB and existing solutions is elaborated.

Unveiling the Critical Role of Ion Coordination Configuration of Ether Electrolytes for High Voltage Lithium Metal Batteries

AbstractAlbeit ethers are favorable electrolyte solvents for lithium (Li) metal anode, their inferior oxidation stability (&lt;4.0 V vs. Li/Li+) is problematic for high‐voltage cathodes. Studies of ether electrolytes have been focusing on the archetype glyme structure with ethylene oxide moieties. Herein, we unveil the crucial effect of ion coordination configuration on oxidation stability by varying the ether backbone structure. The designed 1,3‐dimethoxypropane (DMP, C3) forms a unique six‐membered chelating complex with Li+, whose stronger solvating ability suppresses oxidation side reactions. In addition, the favored hydrogen transfer reaction between C3 and anion induces a dramatic enrichment of LiF (a total atomic ratio of 76.7 %) on the cathode surface. As a result, the C3‐based electrolyte enables greatly improved cycling of nickel‐rich cathodes under 4.7 V. This study offers fundamental insights into rational electrolyte design for developing high‐energy‐density batteries.

Unveiling the Critical Role of Ion Coordination Configuration of Ether Electrolytes for High Voltage Lithium Metal Batteries.

Albeit ethers are favorable electrolyte solvents for lithium (Li) metal anode, their inferior oxidation stability (<4.0 V vs. Li/Li+ ) is problematic for high-voltage cathodes. Studies of ether electrolytes have been focusing on the archetype glyme structure with ethylene oxide moieties. Herein, we unveil the crucial effect of ion coordination configuration on oxidation stability by varying the ether backbone structure. The designed 1,3-dimethoxypropane (DMP, C3) forms a unique six-membered chelating complex with Li+ , whose stronger solvating ability suppresses oxidation side reactions. In addition, the favored hydrogen transfer reaction between C3 and anion induces a dramatic enrichment of LiF (a total atomic ratio of 76.7 %) on the cathode surface. As a result, the C3-based electrolyte enables greatly improved cycling of nickel-rich cathodes under 4.7 V. This study offers fundamental insights into rational electrolyte design for developing high-energy-density batteries.

Atomically Dispersed Silver‐Cobalt Dual‐Metal Sites Synergistically Promoting Photocatalytic Hydrogen Evolution

AbstractRegulating the coordination environment of single‐atom sites is of high necessity to promote the catalytic performances of the photocatalysts. Herein, the preparation of atomically dispersed Co‐Ag dual‐metal sites anchored on P‐doped carbon nitride (Co1Ag1‐PCN) via supramolecular and solvothermal approaches is reported, which demonstrates desirable performance for photocatalytic H2 evolution from water splitting. The optimal Co1Ag1‐PCN catalyst achieves a remarkable hydrogen production rate of 1190 µmol g−1 h−1 with an apparent quantum yield (AQY) of 1.49% at 365 nm, superior to most of the newly reported metal‐N‐coordinated photocatalysts. Systematic experimental characterizations and density functional theoretic studies attribute the enhanced photocatalytic activity to the synergistic effect of Co‐Ag dual sites with exclusive coordination configuration of Co‐N6 and Ag‐N2C2, which enhances the charge density and promotes oriented electrons transport to the metal centers with reduced free energy barriers by facilitating the formation of H* intermediates as the key step in hydrogen evolution. This study reveals a versatile strategy to tailor the electronic structures of dual‐metal sites with synergies by engineering the neighboring coordination environment.

A spherical capped square antiprismatic DyIII complex encapsulated three acylhydrazone Schiff base ligands behaving field-induced single-ion magnet behaviour

One mononuclear DyIII based complex, [Dy(L)3]·0·25H2O (1) (HL= N'-(2-hydroxybenzoyl)pyridine-2-carbohydrazonamide) has been successfully synthesized and systematically characterized. Single-crystal X-ray diffraction reveals that 1 crystallizes in the orthorhombic system with space group P/21. The nine-coordinated DyIII ion in 1 adopts distorted spherical capped square antiprism configuration (C4v-CSAPR) with three tridentate coordination pockets. In addition, the alternating-current (ac) magnetic susceptibility investigations show that 1 exhibits slow magnetic relaxation behavior under an applied 1000 Oe field with effective energy barrier (Ueff) of 83.10 K. To understand the magnetic behaviour in depth, the magnetic axes and magneto-structural correlations are analyzed to reveal that the coordination of three ligands effectively enhances the axiality of the nine-coordinated mononuclear DyIII complexes, thereby exhibiting the slow magnetic relaxation behaviour. This work provides a strategy to effectively improve the performance of single-ion magnets (SIMs) by introducing more ligands around the DyIII ion, and regularizing the coordination configuration of the DyIII ion towards an axial-type structure.

Altering the Site of Electron Abstraction in Cobalt Corroles via meso-Trifluoromethyl Substituents

A mono-DMSO cobalt meso-CF3 corrole, formulated as (CF3)3CorCo(DMSO), where (CF3)3Cor is the trianion of 5,10,15-tris(trifluoromethyl)corrole, was synthesized and characterized as to its spectral and electrochemical properties in nonaqueous media with a focus on its coordination chemistry and electronic structure. Cyclic voltammetric measurements showed more facile reductions and difficult oxidations compared to the cobalt triarylcorrole possessing p-CF3Ph units at the meso-positions, a result consistent with the enhanced inductive effect of the electron-withdrawing trifluoromethyl substituents linked directly at the meso-carbon atoms of the macrocycle. The effects of DMSO, pyridine, and cyanide anions (CN-) on the electrochemistry and spectral properties of the compound were investigated, and it was found that only two molar equivalents are needed to form the bis-CN adduct, which exhibited two 1-electron oxidations at 0.27 and 0.95 V vs saturated calomel electrode (SCE) in CH2Cl2/0.1 M TBAP. The sites of electron transfer in the first oxidation and reduction were investigated by spectroelectrochemistry and confirmed that the first electron addition affords a Cor3-CoII complex under all solution conditions independent of the initial coordination and/or electronic configuration (i.e., innocent Cor3-CoIII or noninnocent Cor•2-CoII). In contrast, data for the first oxidation suggests that the site of electron abstraction (ligand or metal) depended upon coordination of the neutral and in situ generated complexes under the various solution conditions, leading to a Co(IV)-corrole3- product for both the bis-pyridine and bis-cyanide adducts.

Modulating photogenerated electron density of Pr single-atom sites by coordination environment engineering for boosting photoreduction of CO2 to CH3OH

The performance of photocatalytic reduction CO2 to CH3OH is intimately tied to the photogenerated electron density of the active center, because CH3OH formation involves a 6-electron transfer process. However, the random migration of photocarriers in the photocatalysts is severely not conducive to the directional delivery and enrichment of photogenerated electrons to active sites, leading to poor photocatalytic activity for CO2 to CH3OH. Herein, we reported a coordination environment engineered Pr single-atom catalyst for boosting the photogenerated electron density of the active sites, achieving the high-efficiency photoreduction of CO2 to CH3OH. The carbon nitride (CN) supported Pr single-atom with oxygen coordination was designed via a three-step pyrolysis process. Then, the engineered oxygen coordination configuration for the Pr single-atom (Pr1-N4O2) was successfully achieved. Importantly, this Pr1-N4O2 sites can induce photogenerated electrons more easily to accumulate on the Pr atom as compared to the reference catalyst of the Pr atom without oxygen coordination (Pr1-N6). Moreover, the formed atomically dispersed Pr1-N4O2 active centers with ultra-high Pr loading (21.05 wt%) can promote CO2 adsorption and activation, and provide a high density of active sites for CO2 photoreduction. As a result, the optimized Pr1-N4O2/CN exhibited a boosted photoreduction of CO2 to CH3OH activity (511.1 μmol g−1 h−1), which was up to 28.9 and 1.9 times higher than those of CN (17.7 μmol g−1 h−1) and Pr1-N6/CN (274.1 μmol g−1 h−1), and preferable to most reported work under similar catalytic conditions. Our findings can provide a fresh prospect for developing innovative SACs to enhance the photoreduction of CO2 to CH3OH activity.

A novel strategy of engineering genetically encoded probe for ultrasensitive sensing Hg2+ with unusual planar trigonometric coordination configuration

At present, few genetically encoded fluorescent probes are currently available for the analysis of toxic heavy metal ions, and most have poor performance that cannot meet the requirements of sensitive and dynamic detection in living cells. In this study, we designed a single fluorescent protein-based probe sfGFP-MerBD, which can specifically response to Hg2+ with high binding affinity and wide dynamic range. More importantly, the developing probe can timely and reversibly monitor changes of Hg2+ concentration in living mammalian cells. The excellent performance of this probe is largely due to the recognition element of the probe, MerBD, which adopts an unusual planar trigonometric coordination configuration with Hg2+, and the coordination can cause enough conformational change to influence the fluorescence of skeleton protein sfGFP coupled with it. The small peptide MerBD was delicately designed based on the three-dimensional structure of metalloprotein MerR. This novel design strategy solves the challenging problems that there are few natural functional proteins in the process of constructing fluorescent probes for toxic metal ions and some functional proteins cannot be directly used as recognition elements. Based on the new strategy, more genetically encoded fluorescent probes of toxic heavy metal ions can be efficiently constructed and applied in the future.

Molecular engineering of Fe-MIL-53 electrocatalyst for effective oxygen evolution reaction

Homogeneous molecular catalysts have obtained considerable attention in electrocatalytic fields owing to the easily accessible catalytic sites and well-defined structure. However, they are generally regarded as less practical application compared to heterogeneous catalysts due to the challenge to integrate molecular catalysts onto electrodes and poor durability. Here, the “heterogenization” of homogeneous Ni-based molecular catalyst with the definite coordination configuration of NiN2Cl2 is achieved by covalently grafting it into the framework of solid Fe-MIL-53-NH2 on the basis of the imine condensation reaction, which effectively integrates the advantages of homogeneous and heterogeneous catalysis. Electrochemical results of oxygen evolution reaction (OER) indicate that the overpotential at 10 mA cm−2 in NiN2Cl2@Fe-MIL-53 (287 mV) is obviously lower than that of parent Fe-MIL-53-NH2 (466 mV). This significantly improved OER activity in NiN2Cl2@Fe-MIL-53 confirms that the Ni-based molecular catalyst is the key active sites. The kinetic analysis reveals that the Eapp in Ni-based molecular catalyst (31.6 kJ/mol) is obviously lower than that in NiN2Cl2@Fe-MIL-53 (60.3 kJ/mol), proving that incorporating Ni-based molecular catalyst can regulate the rate-determining step and thus improve the OER activity. This work provides a novel covalent grafting strategy for molecular engineering of metal–organic-framework (MOF) and demonstrates their huge potential in electrocatalytic fields.

Recent progress of iron-based electrocatalysts for nitrogen reduction reaction

• xyz • Tuning electronic structure improves Fe-based catalytic performance • Coordination effect and synergistic effect simultaneously module Fe-based catalysts • Combining DFT and experiments is a promising method to advance electrocatalysts. Ammonia is a critical feedstock for modern industry and agriculture, which is also a promising carbon-free energy carrier. Electrochemical nitrogen reduction reaction (ENRR) is a sustainable and efficient approach to synthesize ammonia under ambient reaction conditions. ENRR relies on the development of highly efficient electrocatalysts. So far various strategies have been applied to enhance the performance of catalysts including tuning the electronic structure, binding strength, coordination configuration as well as the introduction of multiple active sites and defects. In this review, the recent progress of Fe-based electrocatalysts and their coordination effect, synergistic effect and defect effect for nitrogen reduction reaction have been summarized. Our critical review focuses on the discussion of theoretical advancement, the performance origin of ENRR activity and selectivity of Fe-based electrocatalysts.