Synthesis, Characterization, and Properties of a Titanium(IV)-Tetrathiafulvalene-Based Complex.

To deeply investigate the interaction between a tetrathiafulvalene (TTF) unit and a Ti(IV) center, a monomeric heteroleptic octahedral Ti(IV) complex containing a diimine ligand composed of a 1,10-phenanthroline core fused with a TTF fragment (ligand 2a) was prepared. The stable complex formulated as Ti(1)2(2a), where 1 is a 2,2'-biphenolato derivative, was efficiently synthesized by following a one-step approach. This complex and its model species [Ti(1)2(2b)] were fully characterized in solution, and their solid-state structures were established by single-crystal X-ray diffraction analysis. Density functional theory calculations allowed the assignment of the frontier orbitals involved in the electronic transitions characterized by ultraviolet-visible absorption spectroscopy. Electrochemical and spectroelectrochemical studies revealed that the TTF unit within Ti(1)2(2a) can undergo two reversible one-electron oxidation processes; a reversible one-electron reduction of the Ti(IV) atom was highlighted. The photophysical measurements performed for this donor-acceptor molecular system indicated that an electron transfer process upon light excitation occurred within Ti(1)2(2a).

A photo-switchable molecular capsule: sequential photoinduced processes.

The metastable trilacunary heteropolyoxomolybdate [PMo9O31(py)3]3- - {PMo9}; py = pyridine) and the ditopic pyridyl bearing diarylethene (DAE) (C25H16N2F6S2) self-assemble via a facile ligand replacement methodology to yield the photo-active molecular capsule [(PMo9O31)2(DAE)3]6-. The spatial arrangement and conformation of the three DAE ligands are directed by the surface chemistry of the molecular metal oxide precursor with exclusive ligation of the photo-active antiparallel rotamer to the polyoxometalate (POM) while the integrity of the assembly in solution has been verified by a suite of spectroscopic techniques. Electrocyclisation of the three DAEs occurs sequentially and has been investigated using a combination of steady-state and time-resolved spectroscopies with the discovery of a photochemical cascade whereby rapid photoinduced ring closure is followed by electron transfer from the ring-closed DAE to the POM in the latent donor-acceptor system on subsequent excitation. This interpretation is also supported by computational and detailed spectroelectrochemical analysis. Ring-closing quantum yields were also determined using a custom quantum yield determination setup (QYDS), providing insight into the impact of POM coordination on these processes.

Polymerization/depolymerization of chiral metallo-supramolecular assembly induced by redox change.

We report on the polymerization/depolymerization of chiral metallo-supramolecular assembly by CuI /CuII redox change. By combining a monotopic enantiopure ligand with a ditopic ligand of opposite configuration, ML2 -type complexes are generated with chiral self-recognition or self-discrimination depending on the oxidation state of copper. In presence of CuI , the formation of heterochiral complexes is favored, thus generating dinuclear species whereas CuII advocates for the formation of homochiral species, namely, a mixture of mononuclear species and metallo-supramolecular polymeric species. Thus, cyclic voltammetry was used to study such a chirality-induced stimulus sensitive polymerization/depolymerization process.

Enhancement of photocurrent by incorporation of Preyssler type polyoxometalate protected nanoparticles in polyporphyrin films.

The introduction of nanoparticles (MNPs) at the surface of cationic poly-porphyrin films, obtained by electrostatic interaction between the bis-porphyrin copolymer and the Preyssler type polyoxometalate P5W30@MNPs, enhances the photocurrent (up to 2.5-3 times greater as a function of the used nanoparticle).

Chiral stimuli-responsive metallo-supramolecular assembly induced by CuII/CuI redox change.

We investigated the selective formation of homoleptic and heteroleptic metal complexes controlled by means of the chiral molecular instruction of the ligand and the coordination geometry of the metal. Our results showed that chiral self-recognition or self-discrimination may be induced by the CuI/CuII redox transition using cyclic voltammetry. The further use of chiral ditopic ligands led to metallo-supramolecular copolymers with stimuli-responsive controlled arrangement.

An Efficient Electrochromic Supercapacitor Based on Solution-Processable Nanoporous Poly{tris[4-(3,4-ethylenedioxythiophene)phenyl]amine}.

A new green synthetic route to tris[4-(3,4-ethylenedioxythiophene)phenyl]amine (TEPA) monomer has been developed and the molecular structure of TEPA has been determined by using single-crystal XRD. Solution-processable nanoporous poly{tris[4-(3,4-ethylenedioxythiophene)phenyl]amine} (PTEPA) is prepared by a chemical oxidative polymerization in a microemulsion. Based on the distorted structure of TEPA in the solid state, it is proposed that dendritic PTEPA has a distorted 3 D conformation with multiple twisted channels and pores that are narrowed and blocked by bifurcation and distortion of PTEPA, which is consistent with the observed hierarchical pore structure. As a cathode material, PTEPA exhibits a discharge capacity of 89.5 mAh g-1 in the initial cycle with a highly sloping two-stage discharge curve and relatively stable cycling performance. Beyond its excellent energy storage properties, PTEPA also shows relatively good electrochromic performance. Furthermore, an efficient all-solid-state electrochromic supercapacitor (ECSC) with good electrochromic performance and high energy storage capacity (13.3 mF cm-2 ) is assembled from PTEPA and nanoporous graphene films. During charge-discharge processes, the color of the ECSC changes between yellow-green and steel blue. Thus, the energy storage level of the ECSC can be monitored by the corresponding color changes. The fabricated ECSC may have practical applications, for example, in self-powered electrochromic smart windows.

Recycling Iron-Containing Sludges from the Electroflocculation of Printing and Dyeing Wastewater into Anode Materials for Lithium-Ion Batteries.

Iron-containing sludges (DW/Fe) were prepared by the electroflocculation of industrial printing and dyeing wastewater (DW). To investigate the formation process and the properties of the DW/Fe sludges and their application in anode materials in Li-ion batteries, the DW/Fe sludges were compared to three other sludges (MB/Fe, RB/Fe, Ta/Fe) prepared from model solutions that contained either methyl blue (MB), rhodamine B (RB), or tartrazine (Ta). The DW/Fe sludges were calcined at 500 °C under N2 to form iron oxide/carbon composite C-DW/Fe. The composition and structure of the sludges and the C-DW/Fe composite were analyzed by using FTIR spectroscopy, XRD, thermogravimetric analysis, SEM, TEM, and X-ray photoelectron spectroscopy, and their performances as anodes of Li-ion batteries were studied by adding different proportions of conductive agent (super P® conductive carbon black). Our results show that the sludges are a complex mixture of Fe3 O4 and organic matter. The specific capacity and stability can be improved during the charge-discharge test by increasing the amount of carbon black. Importantly, this improvement is more pronounced on DW/Fe that does not require high-temperature carbonization, which means that the sludges cannot only protect the environment and avoid the waste of resources but also can be used directly and widely in decentralized energy storage devices.

Decoupling the roles of carbon and metal oxides on the electrocatalytic reduction of oxygen on La1-xSrxCoO3-δ perovskite composite electrodes.

Perovskite oxides are active room-temperature bifunctional oxygen electrocatalysts in alkaline media, capable of performing the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with lower combined overpotentials relative to their precious metal counterparts. However, their semiconducting nature necessitates the use of activated carbons as conductive supports to generate applicably relevant current densities. In efforts to advance the performance and theory of oxide electrocatalysts, the chemical and physical properties of the oxide material often take precedence over contributions from the conductive additive. In this work, we find that carbon plays an important synergistic role in improving the performance of La1-xSrxCoO3-δ (0 ≤ x ≤ 1) electrocatalysts through the activation of O2 and spillover of radical oxygen intermediates, HO2- and O2-, which is further reduced through chemical decomposition of HO2- on the perovskite surface. Through a combination of thin-film rotating disk electrochemical characterization of the hydrogen peroxide intermediate reactions (hydrogen peroxide reduction reaction (HPRR), hydrogen peroxide oxidation reaction (HPOR)) and oxygen reduction reaction (ORR), surface chemical analysis, HR-TEM, and microkinetic modeling on La1-xSrxCoO3-δ (0 ≤ x ≤ 1)/carbon (with nitrogen and non-nitrogen doped carbons) composite electrocatalysts, we deconvolute the mechanistic aspects and contributions to reactivity of the oxide and carbon support.

Conjugated hybrid films based on a new polyoxotitanate monomer.

Electropolymerisation of the novel polyoxotitanate (POT) hexamer [Ti(µ3-O)(OiPr)(TA)]6 (TA = thiophene-3-acetate) with 3,4-ethylenedioxythiophene (EDOT) gives films of hybrid conjugated copolymer, Poly-(EDOT-POT)s, the morphologies of which are, uniquely, influenced by the electropolymerisation potential. Nanoporous Poly-(EDOT-POT)-1 is a fast-ion electrode material and has improved electrochromic properties and significantly higher capacitance than that of the parent poly(3,4-ethylenedioxythiophene) (PEDOT).

Exploring diversity in platinum(iv) N-heterocyclic carbene complexes: synthesis, characterization, reactivity and biological evaluation.

Platinum(iv) complexes stabilized by N-heterocyclic carbene ligands of the type [(NHC)PtX4L], where L is a neutral nitrogen-based ligand and X is a halide anion (Br, Cl), were prepared by using straightforward and high-yielding synthetic routes and the scope was extended to amphiphilic derivatives. The complexes were fully characterized and the molecular structure of the three derivatives was determined by single-crystal X-ray analyses. The complexes demonstrated in vitro antiproliferative activities against several cancer cell lines. In particular, a representative Pt(iv) complex, namely, [(NHC)PtCl4(pyridine)], displayed efficient antiproliferative activity against cisplatin-resistant cancer cells. These results were correlated with their physicochemical properties, namely, solubility, stability and redox behavior by means of UV-vis spectroscopy, NMR or cyclic voltammetry, whereas in DMSO/water, these Pt(iv) complexes transform into biologically less active cis[(NHC)PtX2(DMSO)] species, in the presence of a bioreductant such as glutathione which quickly leads to the formation of a biologically active trans[(NHC)PtX2L] complex. Overall, these data show that NHC-Pt(iv) compounds are good candidates as anti-cancer prodrugs.

Heteroanionic Materials Based on Copper Clusters, Bisphosphonates, and Polyoxometalates: Magnetic Properties and Comparative Electrocatalytic NO(x) Reduction Studies.

Three compounds associating for the first time polyoxotungstates, bisphosphonates, and copper ions were structurally characterized. They consist in heteropolyanionic monodimensional materials where [Cu6(Ale)4(H2O)4](4-) (Ale = alendronate = [O3PC(O)(C3H6NH3)PO3](4-)) complexes alternate with polyoxometalate (POM) units. In Na12[{SiW9O34Cu3(Ale)(H2O)}{Cu6(Ale)4(H2O)4}]·50H2O (SiW9CuAle), the polyoxometalate core consists in a {SiW9Cu3} monomer capped by a pentacoordinated Ale ligand, while sandwich-type Keggin {(SbW9O33)2Cu3(H2O)(2.5)Cl(0.5)} and Dawson {(P2W15O56)2Cu4(H2O)2} complexes are found in Na8Li29[{(SbW9O33)2Cu3(H2O)(2.5)Cl(0.5)}2{Cu6(Ale)4(H2O)4}3]·163H2O (SbW9CuAle) and Na20[{(P2W15O56)2Cu4(H2O)2}{Cu6(Ale)4(H2O)4}]·50H2O (P2W15CuAle), respectively. A comparative magnetic study of the SiW9CuAle and SbW9CuAle compounds enabled full quantification of the Cu(II) superexchange interactions both for the POM and non-POM subunits, evidencing that, while the paramagnetic centers are anti-ferromagnetically coupled in the polyoxometalate units, both anti-ferromagnetic and ferromagnetic interactions coexist in the {Cu6(Ale)4(H2O)4} cluster. All the studied compounds present a good efficiency upon the reduction of HNO2 or NO2(-), the POM acting as a catalyst. However, it has been found that SbW9CuAle is inactive toward the reduction of nitrates, highlighting that both the {(SbW9O33)2Cu3} unit and the {Cu6(Ale)4(H2O)4} cluster do not act as electrocatalysts for this reaction. In contrast, SiW9CuAle and P2W15CuAle have shown a significant activity upon the reduction of NO3(-) and thus both at pH 1 and pH 5, evidencing that the chemical nature of the polyoxometalate is a crucial parameter even if it acts as precatalyst. Moreover, comparison of the activities of P2W15CuAle and [(P2W15O56)2Cu4(H2O)2](16-) evidenced that if the [Cu6(Ale)4(H2O)4](4-) cluster does not act as electrocatalyst, it acts as a cofactor, significantly enhancing the catalytic efficiency of the active POM.

Dissipative solitons and backfiring in the electrooxidation of CO on Pt.

Collisions of excitation pulses in dissipative systems lead usually to their annihilation. In this paper, we report electrochemical experiments exhibiting more complex pulse interaction with collision survival and pulse splitting, phenomena that have rarely been observed experimentally and are only poorly understood theoretically. Using spatially resolved in-situ Fourier transform infrared spectroscopy (FTIR) in the attenuated total reflection configuration, we monitored reaction pulses during the electrochemical oxidation of CO on Pt thin film electrodes in a flow cell. The system forms quasi-1d pulses that align parallel to the flow and propagate perpendicular to it. The pulses split once in a while, generating a second solitary wave in the backward moving direction. Upon collision, the waves penetrate each other in a soliton-like manner. These unusual pulse dynamics could be reproduced with a 3-component reaction-diffusion-migration model with two inhibitor species, one of them exhibiting a long-range spatial coupling. The simulations shed light on existence criteria of such dissipative solitons.

Electrocatalytic oxygen reduction reaction on perovskite oxides: series versus direct pathway.

The mechanism of the oxygen reduction reaction (ORR) on LaCoO(3) and La(0.8)Sr(0.2)MnO(3) perovskite oxides is studied in 1 M NaOH by using the rotating ring disc electrode (RRDE) method. By combining experimental studies with kinetic modeling, it was demonstrated that on perovskite, as well as on perovskite/carbon electrodes, the ORR follows a series pathway through the intermediate formation of hydrogen peroxide. The escape of this intermediate from the electrode strongly depends on: 1) The loading of perovskite; high loadings lead to an overall 4 e(-) oxygen reduction due to efficient hydrogen peroxide re-adsorption on the active sites and its further reduction. 2) The addition of carbon to the catalytic layer, which affects both the utilization of the perovskite surface and the production of hydrogen peroxide. 3) The type of oxide; La(0.8)Sr(0.2)MnO(3) displays higher (compared to LaCoO(3)) activity in the reduction of oxygen to hydrogen peroxide and in the reduction/oxidation of the latter.

Cooperative behaviour of Pt microelectrodes during CO bulk electrooxidation.

Cooperative behaviour of an array of microelectrodes: The interplay of bistable reaction kinetics with global coupling results in a spontaneous sequential activation of electrodes when the applied current is increased.

Using ordered carbon nanomaterials for shedding light on the mechanism of the cathodic oxygen reduction reaction.

Insufficient understanding of the mechanism of the cathodic oxygen reduction reaction puts constraints on the improvement of the efficiency of polymer electrolyte fuel cells (PEMFCs). We apply ordered catalytic layers based on vertically aligned carbon nanofilaments and combine experimental rotating ring-disk studies with mathematical modeling for shedding light on the mechanism of the oxygen reduction reaction on Pt nanoparticles. Based on the experimental and simulation evidence we propose a dual path ORR mechanism which comprises a "direct 4e(-)" and a "series 2e(-) + 2e(-)" pathway and explains switching between the two. For the first time we show that below 0.8 V the "direct" path may be discarded and the ORR predominantly occurs via H(2)O(2) mediated pathway, while in the potential interval between ca. 0.8 V and the onset of the ORR the "direct" path is dominating.

Mass transport effects in CO bulk electrooxidation on Pt nanoparticles supported on vertically aligned carbon nanofilaments.

In this work we report on the influence of the catalytic layer architecture on the autocatalytic reaction of CO-bulk oxidation in liquid electrolyte by employing two types of nanomaterials: 2D arrays of Pt particles prepared on the surface of glassy carbon by colloidal lithography and 3D arrays of Pt nanoparticles supported on vertically aligned carbon nanofilaments. Oxidation of dissolved CO is studied experimentally using RDE approach and computationally using finite element method. For the first time, the influence of 3D architecture of the electrode on a complex bistable electrochemical system was investigated. The modelling results are in qualitative agreement with the experiment and explain the influence of nanostructure of the electrodes on such key characteristics of CO electrooxidation as the ignition potential, the width and the shape of the bistability region, and the value of the limiting current. Analysis of the experimental RDE curves suggests spontaneous formation of active and passive reaction zones along the fibre length which is supported by modelling.

Spatially resolved ATR-FTIRS study of the formation of macroscopic domains and microislands during CO electrooxidation on Pt.

Electrooxidation of CO in CO-saturated sulfuric acid electrolyte solutions with controlled mass transport is investigated with spatially resolved attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy under galvanostatic and potentiostatic conditions. The reaction conditions are chosen such that steady states with intermediate current densities and intermediate average CO coverages are accessible. We demonstrate that under these conditions the reaction never proceeds uniformly on the electrode surface. Instead, macroscopic domains form spontaneously, composed of areas with high CO coverage and areas essentially free of adsorbed CO molecules. The average coverage within the CO-covered domains depends on the electrolyte concentration and the applied potential and can vary between saturation coverage and a few tenths of a monolayer. However, the absence of a red-shift of the CO vibrational band points to a further substructuring of the domains in densely packed CO microislands. These microislands most likely also form in the boundary layer between the CO-rich and CO-free electrode domains. This hierarchical patterning of the electrode surface is attributed to the interplay of autocatalytic reaction steps, spatial coupling through migration or the galvanostatic control of the experiment, and molecular interactions between molecules co-adsorbed on the electrode surface.

The role of the support in CO(ads) monolayer electrooxidation on Pt nanoparticles: Pt/WO(x)vs. Pt/C.

The electrocatalytic properties of home-made Pt nanoparticles supported onto WO(x) were determined for the electrooxidation of a CO(ads) monolayer and compared with that of a commercial Pt/C having the same Pt particle size. By combining electrochemical and spectroscopic techniques, we found that Pt/WO(x) nanoparticles exhibit a very high tolerance to CO at low electrode potentials (E = 0.1 V vs. RHE), which was never reported in the literature before. CO adsorption at E = 0.1 V vs. RHE on Pt/WO(x) yields CO(2) production as observed by Fourier-transform infrared spectroscopy (FTIR). When the gas bubbling in solution changes from CO to Ar, the current attenuates and the CO(2) production vanishes. This points towards a limited number of "active sites" and a slow step in the electrocatalytic process. When H(2) is used to purge the electrolyte from CO, a steep and continuous increase of the H(2) electrooxidation current is observed pointing towards continuous liberation of the Pt catalytic sites. The high tolerance to CO of Pt/WO(x) is discussed in terms of strong metal-support interaction (SMSI), which involves formation of a metal-oxide film partially covering the Pt nanoparticles (encapsulation) and creation of W-OH groups upon H(+) insertion at low electrode potentials.

A hierarchy of global coupling induced cluster patterns during the oscillatory H2-electrooxidation reaction on a Pt ring-electrode.

We report experimental results on spatiotemporal pattern formation during the oscillatory hydrogen electrooxidation reaction on a Pt ring-electrode under negative (desynchronizing) global coupling (GC). Spatially one-dimensional profiles of the interfacial potential drop along the angular direction of the ring electrode are recorded by means of a potential probe. The dynamics is investigated as a function of two control parameters, the applied voltage U and the strength of the global coupling. The latter is adjusted either by varying the distance between the working electrode (WE) and the reference electrode (RE) or by inserting a negative impedance device in series with the WE. In the absence of global coupling, uniform oscillations were destabilized by migration coupling, and electrochemical turbulence developed at large values of U (H. Varela, C. Beta, A. Bonnefont and K. Krischer, Phys. Rev. Lett., 2005, 94, 174104; ). Already low global coupling strengths sufficed to suppress turbulence. Instead, regular two-phase clusters formed. At higher coupling strength, a second type of two-phase cluster was observed as well as two types of irregular cluster patterns, which were connected with an irregular motion of the cluster boundaries and the emergence and disappearance of clusters through splitting and merging of the boundaries, respectively. Upon increasing the coupling strength even further, five-phase clusters were stabilized and at the highest coupling strength applied the cluster patterns transformed into strongly modulated pulses. The two types of two-phase clusters and the five-phase clusters are analyzed employing several signal processing techniques.

Transitions to electrochemical turbulence.

We report experimental evidence of transitions from limit cycle oscillations through a phase turbulent regime to space-time defect turbulence in a spatially (quasi-)one-dimensional electrochemical system with nonlocal coupling. The transitions are characterized in terms of the defect density, the Karhunen-Loève decomposition dimension, and a measure of the degree of spatial correlation in the data. Furthermore, these quantities give the first experimental confirmation that the spatial coupling range in electrochemical systems indeed depends on the distance between the working and the counterelectrode.