Cobalt Center Research Articles

Correlating Metal Redox Potentials to Co(III)K(I) Catalyst Performances in Carbon Dioxide and Propene Oxide Ring Opening Copolymerization.

Carbon dioxide copolymerization is a front-runner CO2 utilization strategy but its viability depends on improving the catalysis. So far, catalyst structure-performance correlations have not been straightforward, limiting the ability to predict how to improve both catalytic activity and selectivity. Here, a simple measure of a catalyst ground-state parameter, metal reduction potential, directly correlates with both polymerization activity and selectivity. It is applied to compare performances of 6 new heterodinuclear Co(III)K(I) catalysts for propene oxide (PO)/CO2 ring opening copolymerization (ROCOP) producing poly(propene carbonate) (PPC). The best catalyst shows an excellent turnover frequency of 389 h-1 and high PPC selectivity of >99 % (50 °C, 20 bar, 0.025 mol% catalyst). As demonstration of its utility, neither DFT calculations nor ligand Hammett parameter analyses are viable predictors. It is proposed that the cobalt redox potential informs upon the active site electron density with a more electron rich cobalt centre showing better performances. The method may be widely applicable and is recommended to guide future catalyst discovery for other (co)polymerizations and carbon dioxide utilizations.

Further Perspectives on the Teflate versus Fluoride Analogy: The Case of a Co(II) Pentafluoroorthotellurate Complex.

The pentafluoroorthotellurate group (teflate, OTeF5) is considered as a bulky analogue of fluoride, yet its coordination behavior in transition metal complexes is not fully understood. By reaction of [CoCl4]2- and neat ClOTeF5, we synthesized the first cobalt teflate complex, [Co(OTeF5)4]2-, which exhibits moisture-resistant Co-OTeF5 bonds. Through a combined experimental and theoretical (DFT and NEVPT2) study, the properties and electronic structure of this species have been investigated. It exhibits a distorted tetrahedral structure around the cobalt center and can be described as a d7 system with a quartet (S = 3/2) ground state. A comparative bonding analysis of the (pseudo)tetrahedral [CoX4]2- anions (X = OTeF5, F, Cl) revealed that the strength of the Co-X interaction is similar in the three cases, being the strongest in [Co(OTeF5)4]2-. In addition, an analysis of the charge of the Co center reinforced the similar electron-withdrawing properties of the teflate and fluoride ligands. Therefore, the [Co(OTeF5)4]2- anion constitutes an analogue of the polymeric [CoF4]2- in terms of electronic properties, but with a monomeric structure.

Structurally Rigid (8-(Arylimino)-5,6,7-trihydroquinolin-2-yl)-methyl Acetate Cobalt Complex Catalysts for Isoprene Polymerization with High Activity and cis-1,4 Selectivity

A series of cobalt complexes bearing (8-(arylimino)-5,6,7-trihydroquinolin-2-yl)methyl acetate ligand framework were prepared using a one-pot synthesis method. These complexes were then extensively investigated for their catalytic performance in isoprene polymerization. In addition to the complexes being characterized via FT-IR spectrum and elemental analysis, the molecular structure of Co1 and Co5 was determined via X-ray diffraction analysis. The analysis revealed a chloride-bridged centrosymmetric binuclear species in which each cobalt center exhibited a distorted square pyramidal geometry. Among the prepared complexes, Co1 demonstrated the highest catalytic activity of 1.37 × 105 g (mol of Co)−1(h)−1, achieving complete monomer conversion and resultant polyisoprene showed high molecular weight (Mn ≥ 2.6 × 105 g/mol). All of the complexes showed preference for the cis-1,4 configuration ranging from 65% to 72%, while the 3,4 monomer insertion units constituted between 27% and 34% of the polymer structure. Moreover, extensive investigations were conducted to assess the impact of reaction parameters and ligand properties on the catalytic activities and microstructural characteristics of the resulting polymer.

Water‐Solvation‐Dependent Spin Transitions in Cobalt(II)‐Octacyanidometallate Complexes

AbstractThe spin‐crossover (SCO) and charge‐transfer (CT) phenomena, the switching processes between two distinguishable magnetic states, are promising for developing materials capable of sophisticated memory and sensing functionalities. The majority of SCO systems are based on iron(II) complexes. However, cobalt(II)‐2,2′:6′,2′′‐terpyridine (terpy) systems emerge as a promising alternative. In this work, new complex salts [CoII(terpy)2]2[MoIV(CN)8] ⋅ 15H2O, Co2Mo(H2O), and [CoII(terpy)2]3[WV(CN)8]2 ⋅ 12H2O, Co3W2(H2O) were synthesized and physiochemically characterized. Structural studies for both compounds revealed [Co(terpy)2]2+ layers pillared by octacyanidometallate anions and completed with water molecules between them. Magnetic studies confirmed that the (de)solvated phases of both complexes exhibit partial SCO on the cobalt(II) centers: CoII−LS (SCo(II)‐LS=1/2)↔CoII−HS (SCo(II)‐HS=3/2). Moreover, handling dehydrated samples in a high‐humidity environment leads to partial recovery of previous magnetic properties via humidity‐induced SCO for Co2Mo: CoII−HS→CoII−LS, and the new phenomenon of isothermal humidity‐activated charge‐transfer‐induced spin transition, which we define here as HACTIST, for Co3W2: CoII−HS⋅⋅⋅WV (SCo(II)‐HS=3/2 and SW(V)=1/2)→CoIII−LS⋅⋅⋅WIV (SW(IV)=0 and SCo(III)‐LS=0). These comprehensive studies shed light on the water‐solvation‐dependent spin transitions in Co(II)‐octacyanidometallate(IV/V) complexes.

Intramolecular charge transfer in bulky “diazabutadiene-M(II)-catecholate” chromophores (M = Ni, Co): A role of a molecular geometry

Two monomeric heteroleptic charge transfer (CT) complexes NiII(3,6-Cat)(DADdipp) (1) and CoII(3,6-Cat)(DADdipp) (2) of “α-diimine-MII-catecholate” general type were prepared in the course of two-step synthetic procedures, based on 3,6-di-tert-butyl-o-benzoquinone (3,6-DTBQ) and 1,4-bis(2,6-di-isopropylphenyl)-1,4-diaza-1,3-butadiene (DADdipp). Square-planar coordination environment in complex 1 enables an implementation of a low energy ligand-to-ligand charge transfer (LL’CT), thus making NIR NiII chromophore (λmax = 1107 nm, in toluene) with high absorptivity of light and a fine sensitivity of CT energy towards solvent polarity (red solvatochromic shift from CH3CN to toluene at 192 nm). Energy of frontiers orbitals and HOMO-LUMO gap of 1 is evaluated in synergy of UV-vis-NIR spectroscopy, cyclic voltammetry, and DFT calculations, with a good accordance of data sets. A significant ligands’ bulkiness provided a tetrahedral distortion of square-planar N2O2 polyhedron of 2 in solutions (CH3CN, CH2Cl2, THF, toluene), that changed CT nature drastically with a concomitant decrease of absorptivity and an elimination of solvatochromism. Electrochemical behavior of studied complexes is defined by the differences in geometry of a coordination environment and corresponding mutual arrangement of metal and ligand orbitals (in solution): one-electron redox processes of square-planar NiII derivative 1 are predominantly ligand-centered, while redox transitions in tetrahedral CoII complex 2 proceed with the substantial participation of cobalt center.

Ligand-Field Directed Electronic Effects in Heterogenized Bifunctional Co(II) Molecular Clusters Accomplish Efficient Overall Water Splitting

We demonstrate a hitherto unknown approach of employing cobalt organophosphate D4R cage-clusters, [(RO) PO3Co(L)]4 (1–4) and [nBu4N][F@{(RO)PO3Co(L)}4], (1F–4F), where L = DMSO (1 or 1F), pyridine (2 or 2F), 4-formylpyridine (3 or 3F), and 4-cyanopyridine (4 or 4F), as bifunctional heterogeneous catalysts for electrochemical water splitting in near-neutral conditions. Electronic and steric modifications on the clusters are achieved through a synergistic combination of endohedral trapping of fluoride ion and exohedral functionalization of pyridines. This two-pronged approach significantly reduces the charge density at the metal leading to energetically favorable water coordination with a perceptible enhancement in the kinetics of overall water splitting, with 4F exhibiting the lowest cell overpotential of 0.949 V (overall cell potential 2.179 V), observed among molecular catalysts. Density functional calculations highlight the importance of cooperativity between the cobalt centers. The unique D4R geometry stabilizes the high-valent metal-oxo/hydroperoxo species, emphasizing the need for polynuclear clusters to catalyze such challenging reactions, as has been well-established in the evolutionary PS-II.

Manipulating Electron-Transfer Events in [Fe4 Co4 ] Cubes via a Mixed-Ligand Approach: The Impact of Elastic Frustration.

The engineering of intermolecular interaction is challenging but critical for magnetically switchable molecules. Here, we prepared two cyanide-bridged [Fe4 Co4 ] cube complexes via the alkynyl- and alcohol-functionalized trispyrazoyl capping ligands. The alkynyl-functionalized complex 1 exhibited a thermally-induced incomplete metal-to-metal electron transfer (MMET) behaviour at around 220 K, while the mixed alkynyl/alcohol-functionalized cube of 2 showed a complete and abrupt MMET behaviour at 232 K. Remarkably, both compounds showed a long-lived photo-induced metastable state up to 200 K. The crystallographic study demonstrated that the incomplete transition of 1 was likely due to the possible elastic frustration originating from the competition between the anion-propagated elastic interactions and inter-cluster alkynyl-alkynyl & CH-alkynyl interactions, whereas the latter are eliminated in 2 as a result of the partial substitution by the alcohol-functionalized ligand. Additionally, the introduction of chemically distinguishable cobalt centers within the cube unit of 2 did not lead to a two-step but a one-step transition, possibly because of the strong ferroelastic intramolecular interaction through the cyanide bridges.

Manipulating Electron‐Transfer Events in [Fe4Co4] Cubes via a Mixed‐Ligand Approach: The Impact of Elastic Frustration

AbstractThe engineering of intermolecular interaction is challenging but critical for magnetically switchable molecules. Here, we prepared two cyanide‐bridged [Fe4Co4] cube complexes via the alkynyl‐ and alcohol‐functionalized trispyrazoyl capping ligands. The alkynyl‐functionalized complex 1 exhibited a thermally‐induced incomplete metal‐to‐metal electron transfer (MMET) behaviour at around 220 K, while the mixed alkynyl/alcohol‐functionalized cube of 2 showed a complete and abrupt MMET behaviour at 232 K. Remarkably, both compounds showed a long‐lived photo‐induced metastable state up to 200 K. The crystallographic study demonstrated that the incomplete transition of 1 was likely due to the possible elastic frustration originating from the competition between the anion‐propagated elastic interactions and inter‐cluster alkynyl‐alkynyl & CH‐alkynyl interactions, whereas the latter are eliminated in 2 as a result of the partial substitution by the alcohol‐functionalized ligand. Additionally, the introduction of chemically distinguishable cobalt centers within the cube unit of 2 did not lead to a two‐step but a one‐step transition, possibly because of the strong ferroelastic intramolecular interaction through the cyanide bridges.

Novel Co5 Cluster Based Triazole Bridged Cobalt‐Fluorophosphate: Synthesis, Structure, Magnetic and Heterogeneous Catalytic Epoxidation Studies

AbstractA novel triazole bridged cobalt fluorophosphate coordination polymer with the formula {Co5(1,2,4‐triazole)2(OH)2(PO3F)4}n has been synthesized. Single crystal X‐ray studies reveal that the compound comprises of Co5 clusters which ultimately build the whole framework, here all cobalt centers are in octahedral geometry established from continuous shape analysis. All the cobalt centers are in Co(II) oxidation state and the results are supported by the bond valence sum (BVS) calculation. The sample has been characterized by single crystal X‐ray, powder X‐ray, FTIR and TGA analysis. The compound was tested for olefin catalysis performance and magnetism. Magnetization measurements reveal overall antiferromagnetic interactions among the Co(II) ions. The compound is very active in the catalytic transformation of olefins to their corresponding epoxides. Catalytic epoxidation studies reveal that cyclohexene and styrene can be converted up to 97 % with almost 65 % selectivity of products with higher TON numbers.

Syntheses and Structures of Arenethiolato Cobalt(II) Complexes Containing Acylamino Groups: Steric Effects of Bulky Ligands on Coordination and Geometry.

Bulky thiolato ligands have been developed for creating biomimetic model complexes of active sites in metalloenzymes. Herein, we report a series of di-ortho-substituted arenethiolato ligands containing bulky acylamino groups (RCONH; R = t-Bu-, (4-t-BuC6H4)3C-,{3,5-(Me2CH)2C6H3}3C-, and {3,5-(Me3Si)2C6H3}3C-) that were developed for biomimetics. Bulky hydrophobic substituents generate a hydrophobic space around the coordinating sulfur atom through the NHCO bond. This steric environment induces the formation of low-coordinate mononuclear thiolato Co(II) complexes. The well-positioned NHCO moieties in the hydrophobic space coordinate to the vacant sites of the cobalt center with different coordination modes, viz., the S,O-chelate of the carbonyl C═O or the S,N-chelate of the acylamido CON-. The solid (crystalline) and solution structures of the complexes were investigated in detail using single-crystal X-ray crystallography, 1H NMR, and absorption spectroscopic analyses. The spontaneous deprotonation of NHCO, which is commonly observed in metalloenzymes but requires a strong base in artificial systems, was simulated by forming a hydrophobic space in the ligand. This new ligand design strategy is advantageous for creating model complexes that have never been constructed artificially.

Regulated High‐Spin State and Constrained Charge Behavior of Active Cobalt Sites in Covalent Organic Frameworks for Promoting Electrocatalytic Oxygen Reduction

AbstractA novel type of covalent organic frameworks has been developed by assembling definite cobalt‐nitrogen‐carbon configurations onto carbon nanotubes using linkers that have varying electronic effects. This innovative approach has resulted in an efficient electrocatalyst for oxygen reduction, which is understood by a combination of in situ spectroelectrochemistry and the bond order theorem. The strong interaction between the electron‐donating carbon nanotubes and the electron‐accepting linker mitigates the trend of charge loss at cobalt sites, while inducing the generation of high spin state. This enhances the adsorption strength and electron transfer between the cobalt center and reactants/intermediates, leading to an improved oxygen reduction capability. This work not only presents an effective strategy for developing efficient non‐noble metal electrocatalysts through reticular chemistry, but also provides valuable insights into regulating the electronic configuration and charge behavior of active sites in designing high‐performance electrocatalysts.

Regulated High-Spin State and Constrained Charge Behavior of Active Cobalt Sites in Covalent Organic Frameworks for Promoting Electrocatalytic Oxygen Reduction.

A novel type of covalent organic frameworks has been developed by assembling definite cobalt-nitrogen-carbon configurations onto carbon nanotubes using linkers that have varying electronic effects. This innovative approach has resulted in an efficient electrocatalyst for oxygen reduction, which is understood by a combination of in situ spectroelectrochemistry and the bond order theorem. The strong interaction between the electron-donating carbon nanotubes and the electron-accepting linker mitigates the trend of charge loss at cobalt sites, while inducing the generation of high spin state. This enhances the adsorption strength and electron transfer between the cobalt center and reactants/intermediates, leading to an improved oxygen reduction capability. This work not only presents an effective strategy for developing efficient non-noble metal electrocatalysts through reticular chemistry, but also provides valuable insights into regulating the electronic configuration and charge behavior of active sites in designing high-performance electrocatalysts.

Cobalt(II) and nickel(II) complexes based on 2,5-di(pyridine-4-yl)thiazolo[5,4-d]thiazole and dicarboxylate ligands: synthesis, structures and properties

Abstract Two metal coordination polymers [Ni(oba)(Py2TTz)1.5(H2O)]·2H2O·DMF (1) and [Co(oba)(Py2TTz)(H2O)4]·2H2O (2) have been synthesized under solvothermal conditions [H2oba = 4,4′-oxybis(benzoic acid) and Py2TTz = 2,5-di(pyridine-4-yl)thiazolo[5,4-d]thiazole]. Crystals of compound 1 belong to the orthorhombic system, space group Ibam, with a = 38.928(8), b = 7.7113(14), c = 28.508(6) Å, V = 8558(3) Å3, Z = 8. Compound 2 crystallizes in the monoclinic crystal system, space group C2/c, with a = 33.816(3), b = 6.2697(6), c = 13.5821(13) Å, β = 96.393(3)°, V = 2861.7(5) Å3, Z = 4. The oba2− dianions link two Ni atoms through unidentate carboxylate moieties in a μ 1 − η 1:η 0 coordination mode. Compound 1 features a three-dimensional (3D) framework structure with Py2TTz and oba2− ligands. In compound 2, the central cobalt ion is in an octahedral geometry, which is defined by four oxygen atoms from four different coordinated water molecules and two nitrogen atoms from two different Py2TTz ligands. It is noteworthy that the dicarboxylate ligands oba2− with four oxygen atoms do not directly coordinate with the cobalt ion, and only act as a counter-anion. The luminescence properties of 1 and 2 were also investigated.

Synthesis and Structural Elucidation of Pom-based Hybrid with a Common Cobalt Centre: It’s Antibacterial Activity and Future Perspectives

A novel hybrid Keggin tungstocobaltate [Co(H2O)6][C5H6N] H4[CoW12O40][NO3].3H2O was prepared by the hydrothermal method and was characterized by elemental analyses, IR spectra, TG-DTA and single crystal X-ray diffraction techniques. This might be the first example of transition metal fuctionalised POM where the same cobalt metal resides at the centre of both of the cationic and anionic complexes. Furthermore, their antibacterial efficacy was determined by MIC and MBC on Gram-negative (Escherichia coli, Salmonella typhi) and Gram-positive (Streptococcus pneumoniae, Bacillus cereus) bacteria. The results indicated an acceptable bacteriostatic and bactericidal effects of this hybrid polyoxometalate.

Control of chirality inversion kinetics of triple-helical metallocryptands

Abstract Dynamic helical molecules, which can undergo a reversible chirality inversion between the P and M forms, are useful as a platform for switchable chiral functional molecules. The chirality inversion of these molecules has been extensively studied. However, it has mostly been discussed from the viewpoint of the equilibrated P/M ratios before and after the inversion; control of the response speeds or kinetic profiles has rarely been explored. In order to construct helical structures with controllable kinetic profiles, triple-helical metallocryptands, LM3, have been designed and synthesized. These molecules can undergo a relatively slow dynamic P/M chirality inversion (helicity inversion) to produce an equilibrated mixture. The P/M equilibration was accelerated or decelerated based on the following two strategies. One is based on the guest binding in the cryptand cavity. The P/M racemization kinetics of LNi3 was significantly decelerated by recognition of guanidinium ion in the cavity. The other strategy is based on the ligand exchange reactions at the octahedral cobalt(III) centers in LCo3(amine)6. The P/M chirality inversion speeds were controlled by changing the initial and entering amine ligands. In addition, a unique transient chirality inversion behavior was observed when chiral amine ligands were removed from the metallocryptand by the ligand exchange reaction with piperidine.

Role of benzene tricarboxylic acid in regulating cobalt-titania interface-interaction to access highly dispersed cobalt nanoparticles catalyst

Finding a robust cobalt catalyst with highly exposed metallic, active sites has been challenging but highly desirable. Extending our in-situ hybridization route, herein we prepared a highly dispersed and accessible CoOx#TiO2 catalyst via interface engineering induced by the benzene tricarboxylic acid (BTC). At the optimized content of BTC (molar ratio of BTC/Co=1), the introduced BTC exerted two vital roles in providing active cobalt center, one is retarding the creation of hard-reducible cobalt titanate (CoTiO3) to facilitate the reduction of CoOx species, the other is stabilizing the anatase phase and retaining a relatively high surface area to well-disperse the cobalt nanoparticles. As a result, the selected CoOx#TiO2, affording a large number of accessible metallic cobalt sites, showed an excellent furfuryl alcohol productivity of 31 gFOL·gCo-1·h-1 at 140 oC and 2.0 MPa, which is among the top values reported by other scientists. SynopsisThe BTC ligands can stabilize the anatase and retard the creation of hard-reducible cobalt titanate (CoTiO3), affording high number of accessible metallic cobalt species. An excellent FOL productivity of 31 gFUR·gCo-1·h-1 at 140 oC and 2.0 MPa was achieved.

Cobalt(II) complexes containing mefenamic acid with imidazole and pyridine based auxiliary ligands: Synthesis, structural investigation and cytotoxic evaluation

The interaction between CoCl2.6H2O and mefenamic acid (2-[(2,3-dimethylphenyl)amino]benzoic acid) in the presence of imidazole and pyridine based ligands resulted in the formation of [Co(mef)2(imi)2]; C-1, [Co(mef)2(nic)2(H2O)2].2H2O; C-2, [Co2(µ-H2O)(µ-mef-O,O')2(mef)2(py)4].CH3CN; C-3, and [Co2(µ-mef-O,O')4(apy)2].2CH3CN; C-4, (mef is monodentate mefenamato, µ-H2O is bridging aqua ligand, µ-mef-O, O' is bridging bidentate mefenamato, imi is imidazole, nic is nicotinamide, py is pyridine, and apy is 2-aminopyridine). The complexes were characterized spectroscopically and by physicochemical properties. Single-crystal X-ray diffraction studies confirmed the structures of the complexes. In C-1, Co(II) is in four-coordinate geometry, while in C-2, Co(II) is in hexa-coordination with two mefenamato carboxylate oxygen atoms, two nitrogen atoms, and two oxygen atoms from two solvent ligands. Complex C-3 consists of two cobalt centers linked by an aqua ligand and bridged by two mefenamato ligands. Furthermore, the octahedral geometry in each Co(II) in C-3 was completed by coordinating two monodentate mefenamato ligands and monodentate pyridine ligands. Similarly, in C-4, a Co-Co bond connects two Co(II) centers in six-coordinate geometry, with four bidentate mefenamato ligands acting as bridges between the two Co(II) and two 2-aminopyridine nitrogen, in monodentate coordination to each Co(II). The lattice solvents in C-2 to C-4 participated in intermolecular hydrogen bonding interactions with the mefenamato ligand. FTIR studies showed the presence of both monodentate and bidentate coordination of the deprotonated carboxylate oxygen atoms of the mefenamato ligand, as well as the coordination of the nitrogen donor ligands in the complexes. TG analysis determined the complexes' thermal stability and decomposition steps and ascertained their compositions, which agreed with the analytical and X-ray crystallography studies. Furthermore, the cytotoxicity of mefenamic acid and the cobalt (II) complexes on lung carcinoma cells (NCIH-460) and breast cells (MDAMB) were assessed using MTT assay. The complexes showed higher cytotoxicity than mefenamic acid against the MDAMB cell line.

Improving Co(II) separation from Ni(II) by solvent extraction using phosphonium-based ionic liquids

The solvent extraction of Co(II) from its aqueous solutions free of acids or chloride salts at high concentration by the ionic liquids trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate ([P66614][C272]) and trihexyl(tetradecyl)phosphonium thiocyanate ([P66614][SCN]) was characterised at saturation of the organic phase with Co(II) using toluene as diluent. The ionic liquids’ cation participated in the formation of two ion-pairs in the organic phase, i.e., one with the complex anion containing cobalt, and the other with the cobalt counter anion, thus preserving electroneutrality in both the organic and aqueous phases. This was considered to be an example of bifurcated extraction.UV–visible spectral studies of the intensively blue organic phase after Co(II) extraction demonstrated that the Co(II) coordination sphere geometry in the case of both extractants was tetrahedral. The Co(II) extraction stoichiometry was experimentally determined for the first time by saturating the organic phase with Co(II). The [P66614][C272] to Co(II) stoichiometric mole ratio in the extracted adduct was found to be 2.8:1, suggesting that eight phosphinate anions acted as bridging ligands around three cobalt centres. For the [P66614][SCN], the stoichiometric mole ratio was found to be 2.5:1 with the Co(II)-thiocyanate adduct consisting of two Co(II)-thiocyanate tetrahedra linked by a bridging thiocyanate ion.The Co(II) extraction was enhanced when the aqueous phase contained an anion with high lipophilicity (e.g., nitrate, thiocyanate). [P66614][SCN] did not extract Ni(II) from nitrate or chloride solutions, thus demonstrating its potential for the separation of Co(II) from Ni(II) without requiring the addition of high concentrations of acids or chloride salts to the aqueous phase.

Effects of Group IB Metals of Au/Ag/Cu on Boosting Oxygen Evolution Reaction of Cobalt Hydroxide

AbstractDeveloping high‐activity, good‐stability oxygen evolution reaction (OER) catalysts is the key to solving the problem of hydrogen production from electrolytic water. Cobalt hydroxide (Co(OH)2) is a hopeful OER catalyst, but its poor conductivity and low inherent activity limit its OER performance. Herein, we used group IB metals of Au, Ag, and Cu to increase the OER performance of Co(OH)2via the electrodeposition method. All three metals can increase the carrier concentration and proportion of high‐valence cobalt ions. The analysis results disclose that the construction of Ag−Co(OH)2heterostructure can optimize the electronic structure through interfacial interactions, produce a moderate proportion of high‐valence cobalt centers, enhance the charge transport capacity and the adsorption of hydroxyl species, thus accelerating the OER kinetics and effectively improving the inherent catalytic activity. This work not only develops effective and steady catalysts but also provides a facile method to enhance the OER performance through interface engineering.

Understanding the potential-induced activation of a cobalt MOF electrocatalyst for the oxygen evolution reaction

Metal–organic frameworks (MOFs) are attractive porous materials for electrocatalytic applications associated with carbon-free energy storage and conversion. This type of material usually requires a post-treatment to be used as electrocatalyst. The present work comprehensively investigates the electrochemical activation of a cobalt-MOF@Nafion composite that produces outstanding electrocatalytic performance for the water oxidation reaction at neutral pH. A detailed electrochemical characterization reveals that the electroactivation of the composite requires the participation of the oxygen evolution reaction (OER) and leads to a significant increase in the electroactive population of cobalt centers. It is shown that an increase of the applied activation potential in the OER region results in a faster electroactivation of the Co-MOF without affecting the intrinsic electrocatalytic properties of the active cobalt centers, as evidenced by the unique linear correlation between the electrocatalytic OER current and the population of electroactive cobalt. In addition, at structural level, it is shown that the electrochemical activation causes the partial disruption of the Nafion adlayer, as well as morphological changes of the Co–MOF particles from a compact, rounded morphology, before electrochemical activation, to a more open and expanded structure, after electroactivation; with the concomitant increase of the number of surface–exposed cobalt centers. Interestingly, these cobalt centers retain their coordinative chemistry and their laminar distribution in the nanosheets at the nanoscale, which is consistent with the preservation of their intrinsic electrocatalytic activity after potential–induced activation. In this scenario, these results suggest that only the electroactivated cobalt centers with good accessibility to the electrolyte are electrochemically active. This work provides a better understanding of the processes and structural changes underlying the electrochemical activation at neutral pH of a Co–MOF for boosting the electrocatalytic water oxidation reaction.