Molecular-level insight into interfacial water at a buried electrode interface is essential in electrochemistry, but spectroscopic probing of the interface remains challenging. Here, using surface... Show moreMolecular-level insight into interfacial water at a buried electrode interface is essential in electrochemistry, but spectroscopic probing of the interface remains challenging. Here, using surface-specific heterodyne-detected sum-frequency generation (HD-SFG) spectroscopy, we directly access the interfacial water in contact with the graphene electrode supported on calcium fluoride (CaF2). We find phase transition-like variations of the HD-SFG spectra vs. applied potentials, which arises not from the charging/discharging of graphene but from the charging/discharging of the CaF2 substrate through the pseudocapacitive process. The potential-dependent spectra are nearly identical to the pH-dependent spectra, evidencing that the pseudocapacitive behavior is associated with a substantial local pH change induced by water dissociation between the CaF2 and graphene. Our work evidences the local molecular-level effects of pseudocapacitive charging at an electrode/aqueous electrolyte interface. Show less
Liu, X.; Cecilio de Oliveira Monteiro, M.; Koper, M.T.M. 2023
Insights into how to control the activity and selectivity of the electrochemical CO2 reduction reaction are still limited because of insufficient knowledge of the reaction mechanism and kinetics,... Show moreInsights into how to control the activity and selectivity of the electrochemical CO2 reduction reaction are still limited because of insufficient knowledge of the reaction mechanism and kinetics, which is partially due to the lack of information on the interfacial pH, an important parameter for proton-coupled reactions like CO2 reduction. Here, we used a reliable and sensitive pH sensor combined with the rotating ring-disk electrode technique, in which a functionalized Au ring electrode works as a real-time detector of the OH- generated during the CO2 reduction reaction at a gold disk electrode. Variations of the interfacial pH due to both electrochemical and homogeneous reactions are mapped and the correlation of the interfacial pH with these reactions is inferred. The interfacial pH near the disk electrode increases from 7 to 12 with increasing current density, with a sharp increase at around -0.5 V vs. RHE, which indicates a change of the dominant buffering species. Through scan rate-dependent voltammetry and chronopotentiometry experiments, the homogenous reactions are shown to reach equilibrium within the time scale of the pH measurements, so that the interfacial concentrations of different carbonaceous species can be calculated using equilibrium constants. Furthermore, pH measurements were also performed under different conditions to disentangle the relationship between the interfacial pH and other electrolyte effects. The buffer effect of alkali metal cations is confirmed, showing that weakly hydrated cations lead to less pronounced pH gradients. Finally, we probe to which extent increasing mass transport and the electrolyte buffer capacity can aid in suppressing the increase of the interfacial pH, showing that the buffer capacity is the dominant factor in suppressing interfacial pH variations. Show less
Electrochemical CO2 reduction (CO2R) is an attractive option for storing renewable electricity and for the sustainable production of valuable chemicals and fuels. In this roadmap, we review recent... Show moreElectrochemical CO2 reduction (CO2R) is an attractive option for storing renewable electricity and for the sustainable production of valuable chemicals and fuels. In this roadmap, we review recent progress in fundamental understanding, catalyst development, and in engineering and scale-up. We discuss the outstanding challenges towards commercialization of electrochemical CO2R technology: energy efficiencies, selectivities, low current densities, and stability. We highlight the opportunities in establishing rigorous standards for benchmarking performance, advances in in operando characterization, the discovery of new materials towards high value products, the investigation of phenomena across multiple-length scales and the application of data science towards doing so. We hope that this collective perspective sparks new research activities that ultimately bring us a step closer towards establishing a low- or zero-emission carbon cycle. Show less
Ham, A. van der; Liu, X.; Calvani, D.; Melcrová, A.; Kozdra, M.; Buda, F.; ... ; Schneider, G.F. 2022
Molecularly thin, nanoporous thin films are of paramount importance in material sciences. Their use in a wide range of applications requires control over their chemical functionalities, which is... Show moreMolecularly thin, nanoporous thin films are of paramount importance in material sciences. Their use in a wide range of applications requires control over their chemical functionalities, which is difficult to achieve using current production methods. Here, the small polycyclic aromatic hydrocarbon decacyclene is used to form molecular thin films, without requiring covalent crosslinking of any kind. The 2.5 nm thin films are mechanically stable, able to be free-standing over micrometer distances, held together solely by supramolecular interactions. Using a combination of computational chemistry and microscopic imaging techniques, thin films are studied on both a molecular and microscopic scale. Their mechanical strength is quantified using AFM nanoindentation, showing their capability of withstanding a point load of 26 ± 9 nN, when freely spanning over a 1 μm aperture, with a corresponding Young's modulus of 6 ± 4 GPa. Our thin films constitute free-standing, non-covalent thin films based on a small PAH. Show less
The synthesis, characterization, crystal structure and detailed magnetic properties of a pyrazine (pyz) and azido (N3) bridged cobalt(II) compound of formula [Co(N3)2(pyz)] (1) are reported.... Show moreThe synthesis, characterization, crystal structure and detailed magnetic properties of a pyrazine (pyz) and azido (N3) bridged cobalt(II) compound of formula [Co(N3)2(pyz)] (1) are reported. Compound 1 shows a layered structure formed by Co(II) chains with double μ-N3(κN1,N1) bridges that are further connected by μ-(pyrazine-κN1,N4) bridges. The layers present weak van der Waals interactions between azido terminal groups. The magnetic properties show the presence of a metamagnetic behaviour in 1 with two critical fields of 200 and 400 mT at low temperatures. AC magnetic measurements show the presence of a long-range 2D ferromagnetic order at Tc ≈ 8.0-7.0 K for dc fields above 200 mT and a long-range 3D ferromagnetic order at Tc ≈ 4.5 K for dc fields above 400 mT. Show less
Cecilio de Oliveira Monteira, M.; Liu, X.; Hagedoorn, B.; Snablié, D.; Koper, M.T.M. 2021
Electrochemical reactions in which H+ or OH– ions are produced or consumed, affect the pH near the electrode surface. Probing the pH locally is therefore highly desired to understand and model the... Show moreElectrochemical reactions in which H+ or OH– ions are produced or consumed, affect the pH near the electrode surface. Probing the pH locally is therefore highly desired to understand and model the reaction environment under operando conditions. We carried out interfacial pH measurements under mass transport control using a rotating ring-disc electrode (RRDE) coupled with our recently developed voltammetric pH sensor. The interfacial disc pH is detected by functionalizing the gold ring with a hydroxylaminothiophenol (4-HATP)/4-nitrosothiophenol (4-NSTP) redox couple. As protons only have to interact with a monolayer containing the 4-HATP/4-NSTP, the sensitivity and time resolution that can be achieved are superior to potentiometric sensors. We used hydrogen evolution as a model reaction and performed measurements in buffered and unbuffered electrolytes. The effects of the current density, potential, the buffer capacity of the electrolyte and rotation rate on the local pH were investigated. This work shows a reliable and sensitive method for accurately probing the reaction environment under well-defined mass transport conditions, over a wide pH range. Show less
Liu, X.; He, M.; Calvani, D.; Qi, H.; Sai Sankar Gupta, K.B.; Groot, H.J.M. de; ... ; Schneider, G.F. 2020
The synthesis, characterization and 3D structure determination of Zinc and Cadmium compounds are reported, containing the non-chelating bidentate ligand 4,4'-bipyridine and the anions 1,1,3,3... Show moreThe synthesis, characterization and 3D structure determination of Zinc and Cadmium compounds are reported, containing the non-chelating bidentate ligand 4,4'-bipyridine and the anions 1,1,3,3-tetracyano-2-propoxy-propenide (tcnopr) or 1,1,3,3-tetracyano-2-ethoxy-propenide (tcnoet). The structures consist of linear chains (1D) built from metal ions and 4,4'-bipyridine, where the octahedral coordination around the metals is completed by two trans anions tcnoet (or tcnopr), and two trans-oriented water molecules. Weak interchain interactions are present, based on hydrogen bonds between the water ligands (both hydrogens are involved) and two CN groups of two nearby other chains. Metal-ligand distances appear as uneventful. For the same anion, the Zn and Cd compounds are isomorphous. Possible decomposition of the compounds has been investigated in the temperature range 30-800 degrees C in a static air atmosphere. Thermal analysis studies (TG, DTG, DTA) show that the axial water ligands for all three compounds are gradually lost upon heating above 60 degrees C to about 170 degrees C. Luminescence properties, recorded as powders, are reported as well, and these appear as strong for the Cd compound I, when irradiated at 390 nm, extremely weak for the Cd compound II, when irradiated at wavelengths from 300-400 nm, and moderately weak for the Zn compound III when irradiated at 385 nm. (C) 2019 The Author(s). Published by Elsevier Ltd. Show less
Lehchili, F.; Setifi, F.; Liu, X.; Saneei, A.; Kucerakova, M.; Setifi, Z.; ... ; Reedijk, J. 2017
A luminescent thin film, Eu@glass, has been prepared on the surface of glass substrates from a silylated diamidopyridyl ligand L and the complex [Eu(dbm)3(H2O)2] (Hdbm = dibenzoylmethane) via a sol... Show moreA luminescent thin film, Eu@glass, has been prepared on the surface of glass substrates from a silylated diamidopyridyl ligand L and the complex [Eu(dbm)3(H2O)2] (Hdbm = dibenzoylmethane) via a sol–gel method. The Eu@glass exhibits intense red photoluminescence under the irradiation of near UV light with a quantum yield of 26%. Compared to the compound [Eu(dbm)3(H2O)2], the photoluminescence intensity of Eu@glass is dramatically enhanced, and the emission lifetime of EuIII (0.517 ms) is more than an order of magnitude longer. Show less
Lanthanoid coordination polymers (Ln CPs), self-assembled from organic ligands and lanthanoid ions, combine the promising properties of normal transition metal CPs, such as a well-defined... Show moreLanthanoid coordination polymers (Ln CPs), self-assembled from organic ligands and lanthanoid ions, combine the promising properties of normal transition metal CPs, such as a well-defined structures and large surface areas, with the properties of lanthanoid ions, notably luminescence and magnetism. As the oxidation state and chemical properties of the lanthanoid ions are highly similar, it is possible to prepare mixed-metal Ln CPs which show dual emission from two different lanthanoid ions or lanthanoid ions and ligands. In this research we focused on the preparation of Ln CPs, especially those containing two or more different lanthanoid ions, and the exploration of their applications in sensing. These dual-emission Ln CPs show good performance for temperature sensing: the intensity ratio from two individual emission peaks can be used as parameters for temperature. Furthermore, Gd2O3 was demonstrated to be an excellent substrate for the growth of thin films of Ln CPs. The temperature-sensing properties of these Ln CP films are also reported. Show less
Khan, R.A.; Dielmann, F.; Liu, X.; Hahn FE, Al-Farhan, K.; Alsalme, A.; Reedijk, J. 2016
Three isomorphous compounds have been prepared, i.e. [Cu-I(PPh3)(2)(Hnor)(I)], [Cu-I(PPh3)(2)(Hnor)Cl] and [Cu-I(PPh3)(2)(Hnor)Br]. The compounds are tetrahedrally coordinated, as deduced from the... Show moreThree isomorphous compounds have been prepared, i.e. [Cu-I(PPh3)(2)(Hnor)(I)], [Cu-I(PPh3)(2)(Hnor)Cl] and [Cu-I(PPh3)(2)(Hnor)Br]. The compounds are tetrahedrally coordinated, as deduced from the single-crystal X-ray diffraction analysis of the iodide compound. The chloride and bromide compounds were found to be isomorphous. Significant twinning hampered a detailed X-ray diffraction study of the bromide derivative. All three compounds are highly luminescent in the solid state at room temperature and at 100 K. In addition, in acetonitrile (solution) at room temperature the compounds are luminescent. (C) 2016 Elsevier Ltd. All rights reserved. Show less
Four new compounds containing the (chlorido)((2-x))(cyanido)(x)argentate(I) anion (x = 2, 1.63, 1 and 0.5) are reported. Their solid-state structures with the monocation PPN, bis(triphenylphosphane... Show moreFour new compounds containing the (chlorido)((2-x))(cyanido)(x)argentate(I) anion (x = 2, 1.63, 1 and 0.5) are reported. Their solid-state structures with the monocation PPN, bis(triphenylphosphane) iminium, are described; in a few cases the products also contain solvent molecules. The compounds have the formula (PPN)(2)[Ag2Cl3(CN)], (PPN)[Ag(CN)Cl](CH2Cl2) and (PPN)[Ag(CN)(1.63)Cl-0.37](hexane)(0.5) and (PPN)[Ag(CN)(2)] (CH2Cl2). Apart from the molecular structures and the synthetic process, also the solid-state luminescence has been studied.In the case of (PPN)(2)[Ag2Cl3(CN)], the silver ions are pseudo-trigonally coordinated, with 2 chloride bridges between the Ag+ ions. The terminal Cl and terminal CN ligands are disordered over two positions, but only a single C-13 NMR signal is observed for the cyanide ligands of this compound. The compound (PPN)[Ag(CN)(2)] serves as a reference compound and contains the linear [Ag(CN)(2)] unit.The compound with CN/Cl = 1.0 shows disorder of the [AgCl(CN)] unit, and also in the compounds with other CN/Cl ratios, disorder among the Cl - and CN - ligands is seen. The Ag+ ion is linearly coordinated by two ligands in these two cases, and for cyanides normal Ag-C bond lengths are observed in both cases (1.97-1.99 angstrom). The [Ag(CN)(2)] anion is linear and uneventful. The PPN cation has normal bond lengths in all 4 compounds and no short contacts with other atoms in the lattice are observed. The luminescence properties of the new compounds were explored as solid powders. Only one of the compounds (compound 2, with x = 1) shows luminescence under excitation. The other three compounds do not show emission when irradiated at 320 nm, 350 nm or 380 nm. (C) 2015 Elsevier B. V. All rights reserved. Show less
Ogasawara, D.; Deng, H.; Viader, A.; Baggelaar, M.P.; Breman, A.; Dulk, H. den; ... ; Stelt, M. van der 2016
![A rare example of a double metamagnetic transition leading to 2D and 3D long-range order in the two-dimensional pyrazine- and azido-bridged cobalt(ii) compound [Co(pyz)(N3)2]](/sites/all/modules/custom/islandora_solr_search/images/defaultimg.png?solr_nav%5Bid%5D=6b843e79860e6e784c58&solr_nav%5Bpage%5D=0&solr_nav%5Boffset%5D=4)
