Driving the Oxygen Evolution Reaction by Nonlinear Cooperativity in Bimetallic Coordination Catalysts

Electrically transmissive alkyne-anchored monolayers on gold

Well-ordered, tightly-packed (surface coverage 0.97 × 10-9 mol cm-2) monolayer films of 1,4-bis((4-ethynylphenyl)ethynyl)benzene (1) on gold are prepared via a simple self-assembly process, taking advantage of the ready formation of alkynyl C-Au σ-bonds. Electrochemical measurements using [Ru(NH3)6]3+, [Fe(CN)6]3-, and ferrocenylmethanol [Fe(η5-C5H4CH2OH)(η5-C5H5)] redox probes indicate that the alkynyl C-Au contacted monolayer of 1 presents a relatively low barrier for electron transfer. This contrasts with monolayer films on gold of other oligo(phenylene ethynylene) derivatives of comparable length and surface coverage, but with different contacting groups. Additionally, a low voltage transition (Vtrans = 0.51 V) from direct tunneling (rectangular barrier) to field emission (triangular barrier) is observed. This low transition voltage points to a low tunneling barrier, which is consistent with the facile electron transport observed through the C-Au contacted self-assembled monolayer of 1.

A trinuclear cobalt-based coordination polymer as an efficient oxygen evolution electrocatalyst at neutral pH

The dearth of an efficient, robust, abundant and cost-effective water oxidation catalyst is debatably the major hurdle for the technological advancement of artificial photosynthesis devices. Herein, a three dimensional (3D) cobalt-based coordination polymer {[Co₃(pyz)(fa)₃(dmso)₂]·2H₂O}_n, (1) (pyz = pyrazine, fa = fumarate, dmso = dimethyl sulfoxide) has been synthesized and demonstrated to act as an efficient electrocatalyst towards water oxidation at neutral pH. Compound 1 displays a stair-like arrangement parallel to the b-axis, with the cobalt clusters arranged in a zigzag fashion, and contains small, honeycomb-like channels parallel to the c-axis. Compound 1 shows a remarkable activity for water oxidation and attains a current density of 1 mA.cm^-2 at low overpotential (η = 257 mV) with a Tafel slope value of 80.5 mV.dec^-1. This high performance of 1 in catalysing the water oxidation reaction is attributed to its unique 3-D architecture. The results of electrochemical investigations, including long-term and controlled potential electrolysis, are anticipated to guide the forthcoming advancement in creating efficient, cheap and noble metal (Pt/Ru/Ir) free catalysts for the water oxidation reaction.

Computational Approach to Molecular Catalysis by 3d Transition Metals: Challenges and Opportunities

Computational chemistry provides a versatile toolbox for studying mechanistic details of catalytic reactions and holds promise to deliver practical strategies to enable the rational in silico catalyst design. The versatile reactivity and nontrivial electronic structure effects, common for systems based on 3d transition metals, introduce additional complexity that may represent a particular challenge to the standard computational strategies. In this review, we discuss the challenges and capabilities of modern electronic structure methods for studying the reaction mechanisms promoted by 3d transition metal molecular catalysts. Particular focus will be placed on the ways of addressing the multiconfigurational problem in electronic structure calculations and the role of expert bias in the practical utilization of the available methods. The development of density functionals designed to address transition metals is also discussed. Special emphasis is placed on the methods that account for solvation effects and the multicomponent nature of practical catalytic systems. This is followed by an overview of recent computational studies addressing the mechanistic complexity of catalytic processes by molecular catalysts based on 3d metals. Cases that involve noninnocent ligands, multicomponent reaction systems, metal-ligand and metal-metal cooperativity, as well as modeling complex catalytic systems such as metal-organic frameworks are presented. Conventionally, computational studies on catalytic mechanisms are heavily dependent on the chemical intuition and expert input of the researcher. Recent developments in advanced automated methods for reaction path analysis hold promise for eliminating such human-bias from computational catalysis studies. A brief overview of these approaches is presented in the final section of the review. The paper is closed with general concluding remarks.

A General Method to Ultrathin Bimetal-MOF Nanosheets Arrays via In Situ Transformation of Layered Double Hydroxides Arrays

Structure engineering of ultrathin metal-organic framework (MOF) nanosheets to self-supporting and well-aligned MOF superstructures is highly desired for diverse applications, especially important for electrocatalysis. In this work, a facile layered double hydroxides in situ transformation strategy is developed to synthesize ultrathin bimetal-MOF nanosheets (BMNSs) arrays on conductive substrates. This approach is versatile, and applicable to obtain various BMNSs or even trimetal-MOF nanosheets arrays on different substrates. As a proof of concept application, the obtained ultrathin NiCo-BDC BMNSs array exhibits an excellent catalytic activity toward the oxygen evolution reaction with an overpotential of only 230 mV to reach a current density of 10 mA cm^-2 in 1 m KOH. The present work demonstrates a strategy to prepare ultrathin bimetal-MOF nanosheets arrays, which might open an avenue for various promising applications of MOF materials.

Stability of metallo-porphyrin networks under oxygen reduction and evolution conditions in alkaline media

Transition metal atoms stabilised by organic ligands or as oxides exhibit promising catalytic activity for the electrocatalytic reduction and evolution of oxygen. Built-up from earth-abundant elements, they offer affordable alternatives to precious-metal based catalysts for application in fuel cells and electrolysers. For the understanding of a catalyst's activity, insight into its structure on the atomic scale is of highest importance, yet commonly challenging to experimentally access. Here, the structural integrity of a bimetallic iron tetrapyridylporphyrin with co-adsorbed cobalt electrocatalyst on Au(111) is investigated using scanning tunneling microscopy and X-ray absorption spectroscopy. Topographic and spectroscopic characterization reveals structural changes of the molecular coordination network after oxygen reduction, and its decomposition and transformation into catalytically active Co/Fe (oxyhydr)oxide during oxygen evolution. The data establishes a structure-property relationship for the catalyst as a function of electrochemical potential and, in addition, highlights how the reaction direction of electrochemical interconversion between molecular oxygen and hydroxyl anions can have very different effects on the catalyst's structure.

Efficacious Electrochemical Oxygen Evolution from a Novel Co(II) Porphyrin/Pyrene-Based Conjugated Microporous Polymer

Oxygen evolution reaction (OER) is energetically challenging from the platform of making many photovoltaic devices such as metal-air batteries and water splitting systems because of its poor kinetics even when precious metals are used. Herein, a Co(II)-porphyrin/pyrene-comprised conjugated microporous polymer Co-MPPy-1 has been developed which shows efficient OER in alkaline medium. The material was characterized by Fourier transform infrared, solid-state ¹³C cross-polarization magic angle spinning nuclear magnetic resonance, N₂ volumetric adsorption/desorption analysis, scanning electron microscopy, ultra high resolution-transmission electron microscopy, X-ray photoelectron spectroscopy, and other physical studies. Co-MPPy-1 showed Brunauer-Emmett-Teller surface area of ∼501 m² g^-1. Co-MPPy-1 achieved a current density of 1 and 10 mA/cm^-2 at 340 and 420 mV, respectively. The turnover frequency calculated for the OER is 0.43 s^-1. The heterogeneity of this electrocatalyst was tested by chronoamperometric measurement and 1000 cycle recyclability test with retainment of the excellent electrochemical catalytic activity. This can be attributed to the presence of high density of Co(II) porphyrin unit and efficient charge transport in the π-conductive conjugated polymeric backbone.

A squaraine-linked metalloporphyrin two-dimensional polymer photocatalyst for hydrogen and oxygen evolution reactions

A squaraine–metalloporphyrin 2D-polymer based bifunctional catalyst for photocatalytic water splitting.

Trinuclear Ni(ii) oriented highly dense packing and π-conjugation degree of metal–organic frameworks for efficient water oxidation

Trinuclear nickel cluster based MOF shows highly denser crystal packing and π-conjugation degree as well as outstanding OER performance with an overpotential of 270 mV at 10 mA cm⁻².

On-surface transmetalation of metalloporphyrins

Increasing the complexity of 2D metal-organic networks has led to the fabrication of structures with interesting magnetic and catalytic properties. However, increasing complexity by providing different coordination environments for different metal types imposes limitations on their synthesis if the controlled placement of one metal type into one coordination environment is desired. Whereas metal insertion into free-base porphyrins at the vacuum/solid interface has been thoroughly studied, providing detailed insight into the mechanisms at play, the chemical interaction of a metal atom with a metallated porphyrin is rarely investigated. Herein, the breadth of metalation reactions is augmented towards the metal exchange of a metalloporphyrin through the deliberate addition of atomic metal centers. The cation of Fe(ii)-tetraphenylporphyrins can be replaced by Co in a redox transmetalation-like reaction on a Au(111) surface. Likewise, Cu can be replaced by Co. The reverse reaction does not occur, i.e. Fe does not replace Co in the porphyrin. This non-reversible exchange is investigated in detail by X-ray absorption spectroscopy complemented by scanning tunneling microscopy. Density functional theory illuminates possible reaction pathways and leads to the conclusion that the transmetalation proceeds through the adsorption of initially metallic (neutral) Co onto the porphyrin and the expulsion of Fe towards the surface accompanied by Co insertion. Our findings have important implications for the fabrication of porphyrin layers on surfaces when subject to the additional deposition of metals. Mixed-metal porphyrin layers can be fabricated by design in a solvent-free process, but conversely care must be taken that the transmetalation does not proceed as an undesired side reaction.

Application of In Situ Techniques for the Characterization of NiFe-Based Oxygen Evolution Reaction (OER) Electrocatalysts

Developing high-efficiency and affordable electrocatalysts for the sluggish oxygen evolution reaction (OER) remains a crucial bottleneck on the way to the practical applications of rechargeable energy storage technologies and water splitting for producing clean fuel (H₂ ). In recent years, NiFe-based materials have proven to be excellent electrocatalysts for OER. Understanding the characteristics that affect OER activity and determining the OER mechanism are of vital importance for the development of OER electrocatalysts. Therefore, in situ characterization techniques performed under OER conditions are urgently needed to monitor the key intermediates together with identifying the OER active centers and phases. In this Minireview, recent advances regarding in situ techniques for the characterization of NiFe-based electrocatalysts are thoroughly summarized, including Raman spectroscopy, X-ray absorption spectroscopy, ambient pressure X-ray photoelectron spectroscopy, Mössbauer spectroscopy, Ultraviolet-visible spectroscopy, differential electrochemical mass spectrometry, and surface interrogation scanning electrochemical microscopy. The results from these in situ measurements not only reveal the structural transformation and the progressive oxidation of the catalytic species under OER conditions, but also disclose the crucial role of Ni and Fe during the OER. Finally, the need for developing new in situ techniques and theoretical investigations is discussed to better understand the OER mechanism and design promising OER electrocatalysts.

Carbon-Supported Single Atom Catalysts for Electrochemical Energy Conversion and Storage

Single atoms of select transition metals supported on carbon substrates have emerged as a unique system for electrocatalysis because of maximal atom utilization (≈100%) and high efficiency for a range of reactions involved in electrochemical energy conversion and storage, such as the oxygen reduction, oxygen evolution, hydrogen evolution, and CO₂ reduction reactions. Herein, the leading strategies for the preparation of single atom catalysts are summarized, and the electrocatalytic performance of the resulting samples for the various reactions is discussed. In general, the carbon substrate not only provides a stabilizing matrix for the metal atoms, but also impacts the electronic density of the metal atoms due to strong interfacial interactions, which may lead to the formation of additional active sites by the adjacent carbon atoms and hence enhanced electrocatalytic activity. This necessitates a detailed understanding of the material structures at the atomic level, a critical step in the construction of a relevant structural model for theoretical simulations and calculations. Finally, a perspective is included highlighting the promises and challenges for the future development of carbon-supported single atom catalysts in electrocatalysis.

Carbon Nanotubes with Cobalt Corroles for Hydrogen and Oxygen Evolution in pH 0-14 Solutions

Water splitting is promising to realize a hydrogen-based society. The practical use of molecular water-splitting catalysts relies on their integration onto electrode materials. We describe herein the immobilization of cobalt corroles on carbon nanotubes (CNTs) by four strategies and compare the performance of the resulting hybrids for H₂ and O₂ evolution. Co corroles can be covalently attached to CNTs with short conjugated linkers (the hybrid is denoted as H1) or with long alkane chains (H2), or can be grafted to CNTs via strong π-π interactions (H3) or via simple adsorption (H4). An activity trend H1≫H3>H2≈H4 is obtained for H₂ and O₂ evolution, showing the critical role of electron transfer ability on electrocatalysis. Notably, H1 is the first Janus catalyst for both H₂ and O₂ evolution reactions in pH 0-14 aqueous solutions. Therefore, this work is significant to show potential uses of electrode materials with well-designed molecular catalysts in electrocatalysis.

Supramolecular Assemblies on Surfaces: Nanopatterning, Functionality, and Reactivity

Understanding how molecules interact to form large-scale hierarchical structures on surfaces holds promise for building designer nanoscale constructs with defined chemical and physical properties. Here, we describe early advances in this field and highlight upcoming opportunities and challenges. Both direct intermolecular interactions and those that are mediated by coordinated metal centers or substrates are discussed. These interactions can be additive, but they can also interfere with each other, leading to new assemblies in which electrical potentials vary at distances much larger than those of typical chemical interactions. Earlier spectroscopic and surface measurements have provided partial information on such interfacial effects. In the interim, scanning probe microscopies have assumed defining roles in the field of molecular organization on surfaces, delivering deeper understanding of interactions, structures, and local potentials. Self-assembly is a key strategy to form extended structures on surfaces, advancing nanolithography into the chemical dimension and providing simultaneous control at multiple scales. In parallel, the emergence of graphene and the resulting impetus to explore 2D materials have broadened the field, as surface-confined reactions of molecular building blocks provide access to such materials as 2D polymers and graphene nanoribbons. In this Review, we describe recent advances and point out promising directions that will lead to even greater and more robust capabilities to exploit designer surfaces.

Towards molecular electronic devices based on 'all-carbon' wires

Nascent molecular electronic devices based on linear 'all-carbon' wires attached to gold electrodes through robust and reliable C-Au contacts are prepared via efficient in situ sequential cleavage of trimethylsilyl end groups from an oligoyne, Me₃Si-(C[triple bond, length as m-dash]C)₄-SiMe₃ (1). In the first stage of the fabrication process, removal of one trimethylsilyl (TMS) group in the presence of a gold substrate, which ultimately serves as the bottom electrode, using a stoichiometric fluoride-driven process gives a highly-ordered monolayer, Au|C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CSiMe₃ (Au|C₈SiMe₃). In the second stage, treatment of Au|C₈SiMe₃ with excess fluoride results in removal of the remaining TMS protecting group to give a modified monolayer Au|C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CH (Au|C₈H). The reactive terminal C[triple bond, length as m-dash]C-H moiety in Au|C₈H can be modified by 'click' reactions with (azidomethyl)ferrocene (N₃CH₂Fc) to introduce a redox probe, to give Au|C₆C₂N₃HCH₂Fc. Alternatively, incubation of the modified gold substrate supported monolayer Au|C₈H in a solution of gold nanoparticles (GNPs), results in covalent attachment of GNPs on top of the film via a second alkynyl carbon-Au σ-bond, to give structures Au|C₈|GNP in which the monolayer of linear, 'all-carbon' C₈ chains is sandwiched between two macroscopic gold contacts. The covalent carbon-surface bond as well as the covalent attachment of the metal particles to the monolayer by cleavage of the alkyne C-H bond is confirmed by surface-enhanced Raman scattering (SERS). The integrity of the carbon chain in both Au|C₆C₂N₃HCH₂Fc systems and after formation of the gold top-contact electrode in Au|C₈|GNP is demonstrated through electrochemical methods. The electrical properties of these nascent metal-monolayer-metal devices Au|C₈|GNP featuring 'all-carbon' molecular wires were characterised by sigmoidal I-V curves, indicative of well-behaved junctions free of short circuits.

The Design of Water Oxidation Electrocatalysts from Nanoscale Metal-Organic Frameworks

Metal-organic frameworks (MOFs), as the shining stars in field of materials science, have become an important class of highly efficient catalysts for electrochemical oxygen evolution reaction (OER). Although tremendous progresses have been achieved by exploring two MOF-based groups: the MOF-derived electrocatalysts and the direct MOF electrocatalysts in recently years, it appears that both activity and stability of these two kinds of MOF-based electrocatalysts have big rooms for improvement. In order to overcome these issues, a comprehensive summary of the advanced designs of catalysts is timely urgent. Here, the advanced engineering strategies including structural, carbon-based, metal-based and substrate-engineered strategies of MOF-derived catalysts have been introduced. In addition, the detailed explorations of the nanostructured direct MOF catalysts for OER are also reviewed. Finally, short comments and perspectives about the future development of the MOF-based OER electrocatalysts are provided.

Remote functionalization in surface-assisted dehalogenation by conformational mechanics: organometallic self-assembly of 3,3',5,5'-tetrabromo-2,2',4,4',6,6'-hexafluorobiphenyl on Ag(111)

Even though the surface-assisted dehalogenative coupling constitutes the most abundant protocol in on-surface synthesis, its full potential will only become visible if selectivity issues with polybrominated precursors are comprehensively understood, opening new venues for both organometallic self-assembly and on-surface polymerization. Using the 3,3',5,5'-tetrabromo-2,2',4,4',6,6'-hexafluorobiphenyl (Br4F6BP) at Ag(111), we demonstrate a remote site-selective functionalization at room temperature and a marked temperature difference in double- vs. quadruple activation, both phenomena caused by conformational mechanical effects of the precursor-surface ensemble. The submolecularly resolved structural characterization was achieved by Scanning Tunneling Microscopy, the chemical state was quantitatively assessed by X-ray Photoelectron Spectroscopy, and the analysis of the experimental signatures was supported through first-principles Density-Functional Theory calculations. The non-planarity of the various structures at the surface was specifically probed by additional Near Edge X-ray Absorption Fine Structure experiments. Upon progressive heating, Br4F6BP on Ag(111) shows the following unprecedented phenomena: (1) formation of regular organometallic 1D chains via remote site-selective 3,5'-didebromination; (2) a marked temperature difference in double- vs. quadruple activation; (3) an organometallic self-assembly based on reversibility of C-Ag-C linkages with a thus far unknown polymorphism affording both hexagonal and rectangular 2D networks; (4) extraordinary thermal stability of the organometallic networks. Controlled covalent coupling at the previously Br-functionalized sites was not achieved for the Br4F6BP precursor, in contrast to the comparatively studied non-fluorinated analogue.

Sulfur-driven switching of the Ullmann coupling on Au(111)

We demonstrate a method to selectively switch the Ullmann coupling reaction of 2,8-dibromodibenzothiophene on a Au(111) support. The Ullmann coupling reaction is effective already at low temperature, but the complete inhibition of the same reaction can be achieved on Au(111) pre-exposed to H2S. The marked difference in reactivity of pretreated Au(111) is explained by the S-passivation of free Au atoms emerging from reconstruction sites. The inhibited state can be fully lifted by removing the S via hydrogen gas post-exposure.

Cobalt Covalent Doping in MoS2 to Induce Bifunctionality of Overall Water Splitting

The layer-structured MoS2 is a typical hydrogen evolution reaction (HER) electrocatalyst but it possesses poor activity for the oxygen evolution reaction (OER). In this work, a cobalt covalent doping approach capable of inducing HER and OER bifunctionality into MoS2 for efficient overall water splitting is reported. The results demonstrate that covalently doping cobalt into MoS2 can lead to dramatically enhanced HER activity while simultaneously inducing remarkable OER activity. The catalyst with optimal cobalt doping density can readily achieve HER and OER onset potentials of -0.02 and 1.45 V (vs reversible hydrogen electrode (RHE)) in 1.0 m KOH. Importantly, it can deliver high current densities of 10, 100, and 200 mA cm-2 at low HER and OER overpotentials of 48, 132, 165 mV and 260, 350, 390 mV, respectively. The reported catalyst activation approach can be adapted for bifunctionalization of other transition metal dichalcogenides.

Cobalt-Bridged Ionic Liquid Polymer on a Carbon Nanotube for Enhanced Oxygen Evolution Reaction Activity

By taking inspiration from the catalytic properties of single-site catalysts and the enhancement of performance through ionic liquids on metal catalysts, we exploited a scalable way to place single cobalt ions on a carbon-nanotube surface bridged by polymerized ionic liquid. Single dispersed cobalt ions coordinated by ionic liquid are used as heterogeneous catalysts for the oxygen evolution reaction (OER). Performance data reveals high activity and stable operation without chemical instability.

Electrocatalytic water oxidation by a molecular catalyst incorporated into a metal-organic framework thin film

A molecular water oxidation catalyst, [Ru(tpy)(dcbpy)(OH₂)](ClO₄)₂ (tpy = 2,2':6',2''-terpyridine, dcbpy = 2,2'-bipyridine-5,5'-dicarboxylic acid) [1], has been incorporated into FTO-grown thin films of UiO-67 (UiO = University of Oslo), by post-synthetic ligand exchange. Cyclic voltammograms (0.1 M borate buffer at pH = 8.4) of the resulting UiO67-[RuOH₂]@FTO show a reversible wave associated with the Ru^III/II couple in the anodic scan, followed by a large current response that arises from electrocatalytic water oxidation beyond 1.1 V vs. Ag/AgCl. Water oxidation can be observed at an applied potential of 1.5 V over the timescale of hours with a current density of 11.5 μA cm^-2. Oxygen evolution was quantified in situ over the course of the experiment, and the Faradaic efficiency was calculated as 82%. Importantly, the molecular integrity of [1] during electrocatalytic water oxidation is maintained even on the timescale of hours under turnover conditions and applied voltage, as evidenced by the persistence of the wave associated with the Ru^III/II couple in the CV. This experiment highlights the capability of metal organic frameworks like UiO-67 to stabilize the molecular structure of catalysts that are prone to form higher clusters in homogenous phase.

Two-dimensional metal–organic framework nanosheets: synthesis and applications

Synthesis and applications of two-dimensional metal–organic framework nanosheets and their composites are summarized.

Polymorphism and metal-induced structural transformation in 5,5′-bis(4-pyridyl)(2,2′-bispyrimidine) adlayers on Au(111)

Addition of iron to a self-assembled molecular network can lift polymorphism and leads to the expression of one single metal–organic structure on a surface.

A Porous Cobalt (II) Metal⁻Organic Framework with Highly Efficient Electrocatalytic Activity for the Oxygen Evolution Reaction

A 3D porous framework ([Co_1.5(tib)(dcpna)]·6H₂O) (1) with a Wei topology has been synthesized by solvothermal reaction of 1,3,5-tris(1-imidazolyl)-benzene (tib), 5-(3′,5′-dicarboxylphenyl)nicotinic acid (H₃dcpna) and cobalt nitrate. The electrocatalytic activity for water oxidation of 1 has been investigated in alkaline solution. Compound 1 exhibits good oxygen evolution reaction (OER) activities in alkaline solution, exhibiting 10 mA·cm⁻² at η = 360 mV with a Tafel slope of 89 mV·dec⁻¹. The high OER activity can be ascribe to 1D open channels along b axis of 1, which expose more activity sites and facilitate the electrolyte penetration.

In Situ Fabrication of Defective CoNx Single Clusters on Reduced Graphene Oxide Sheets with Excellent Electrocatalytic Activity for Oxygen Reduction

A facile one-step strategy for anchoring defective CoN_x single clusters on partly reduced graphene oxide (RGO) is constructed to significantly improve the catalytic performance of non-noble metal complexes toward oxygen reduction reaction (ORR). Sequent loading with trace amounts of metal-free porphyrin and Co²⁺ in RGO can dramatically enhance both the half-wave potential and the peak current density. Intriguingly, the RGO/P/2Co single cluster exhibits the best ORR catalytic performance with the half-wave potential of 0.834 V, extremely approaching that of commercial Pt/C (0.836 V). This half-wave potential surpasses most of the reported half-wave potentials of RGO supported non-noble metal ORR catalysts through low-temperature synthesis. Furthermore, the as-prepared RGO/P/2Co delivers a peak current density of 1.3 times higher than that of Pt/C at the same loading, together with a high mass activity of 2.76 A mg_Co^-1. During the durability test, a cathodic current loss less than 10% is recorded after 8000 continuous potential cycles. Insights into this successful example will be conducive to the development of elegant routes for constructing metal nitrogen (MN)-based ORR catalysts with high efficiency, outstanding stability, and excellent selectivity.

Dinuclear Complexes Formed by Hydrogen Bonds: Synthesis, Structure and Magnetic and Electrochemical Properties

The synthesis is reported of a series of homo- and hetero-dinuclear octahedral complexes of the ligand 1, 1,2-bis(1-methyl-benzimidazol-2-yl) ethanol, where the two metal centres are linked by hydrogen bonds between coordinated alcohols and coordinated alkoxides. Homonuclear divalent M^II M^II , mixed-valent M^II M^III and heteronuclear M^II M'^III species are prepared. The complexes have been characterised by X-ray crystallography and show unusually short O⋅⋅⋅O distances for the hydrogen bonds. Magnetic measurements show the hydrogen-bond bridges can lead to ferromagnetic or antiferromagnetic coupling. The electrochemistry of the dinuclear species is significantly different from the mononuclear systems: the latter show irreversible waves in cyclic voltammograms as a result of the need to couple proton and electron transfer. The dinuclear species, in contrast, show reversible waves, which are attributed to rapid intramolecular proton transfer facilitated by the hydrogen-bonded structure.

Molecular Chessboard Assemblies Sorted by Site-Specific Interactions of Out-of-Plane d-Orbitals with a Semimetal Template

We show that highly ordered two-dimensional (2D) chessboard arrays consisting of a periodic arrangement of two different molecules can be obtained by self-assembly of unsubstituted metal-phthalocyanines (metal-Pcs) on a suitable substrate serving as the template. Specifically, CuPc + MnPc and CuPc + CoPc mixtures sort into highly ordered Cu/Mn and Cu/Co chessboard arrays on the square p(10 × 10) reconstruction of bismuth on Cu(100). Such created bimolecular chessboard assemblies emerge from the site-specific interactions between the central transition-metal ions and the periodically reconstructed substrate. This work provides a conceptually new approach to induce 2D chessboard patterns in that no functionalization of the molecules is needed.

Cu(OH)2 @CoCO3 (OH)2 ·nH2 O Core-Shell Heterostructure Nanowire Array: An Efficient 3D Anodic Catalyst for Oxygen Evolution and Methanol Electrooxidation

A Cu(OH)₂ @CoCO₃ (OH)₂ ·nH₂ O (CCHH) core-shell heterostructure nanowire array acts as robust 3D oxygen evolution reaction catalyst. It needs an overpotential of 270 mV to drive 50 mA cm^-2 in 1.0 m KOH, outperforming CCHH nanowire arrays on copper foam and most reported Co-based oxygen evolution reaction catalysts in alkaline media. It is also efficient for methanol electrooxidation.

Radical induced intermolecular linkage and energy level modifications of a porphyrin monolayer

A new method to directly modify the surface structure and energy levels of a porphyrin monolayer was examined in the molecular scale using scanning tunneling microscopy and spectroscopy (STM and STS) and presented in this communication. The exposure to atomic oxygen has induced highly ordered surface cross-linking and changed the occupied and unoccupied orbital levels of a cobalt(ii) octaethyl porphyrin (CoOEP) monolayer, and as a result, the HOMO-LUMO gap was reduced by ∼10%. Counterintuitively, the STM/STS data indicated that the reactive central Co atoms did not participate in the gas-surface reactions. Reflection-absorption infrared spectroscopy (RAIRS) measurements further indicated that the STM observed intermolecular linkages are stabilized via hydrogen bonding. This CoOEP + O˙ system also illustrates an example that the six-fold surface packing symmetry predominates the four-fold molecular symmetry in producing a three-fold symmetric surface cross-linking structure.

Hybrids of Cobalt/Iron Phosphides Derived from Bimetal-Organic Frameworks as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction

The electrochemical splitting of water, as an efficient and large-scale method to produce H₂, is still hindered by the sluggish kinetics of the oxygen evolution reaction (OER) at the anode. Considering the synergetic effect of the different metal sites with coordination on the surface of electrocatalysts, the hybrids of Co/Fe phosphides (denoted as Co-Fe-P) is prepared by one-step phosphorization of CoFe metal-organic frameworks for the first time as highly efficient electrocatalysts for OER. Benefiting from the synergistic effect of Co and Fe, the high valence of Co ions induced by strongly electronegative P and N and the large electrochemical active surface area (ECSA) originated from exposed nanowires on the surface of Co/Fe phosphides, the resultant Co-Fe-P-1.7 exhibits remarkable electrocatalytic performances for OER in 1.0 M KOH, affording an overpotential as low as 244 mV at a current density of 10 mA/cm², a small Tafel slope of 58 mV/dec, and good stability, which is superior to that of the state-of-the-art OER electrocatalysts. In addition, the two-electrode cell with Co-Fe-P-1.7 modified Ni foam as anode and cathode in an alkaline electrolyte, respectively, exhibits the decomposition potential of ca. 1.60 V at a current density of 10 mA/cm² and excellent stability.

A general synthesis of abundant metal nanoparticles functionalized mesoporous graphitized carbon

A general coordination–polymerization strategy combining flexible coordination mode with stable polymer network is reported to construct metal–gallic acid resin and mesoporous graphitized carbon materials with abundant metal nanoparticles.