Characterization of organic molecules at metal/electrolyte interfaces

The spontaneous self-assembly of organic molecules is considered a promising “bottom-up” approach in nanotechnology to create surface patterns, molecular sensors, and molecular logic devices with nanometer dimension, and complex organic structures. Porphyrins, for example, have attracted much attention of surface electrochemists within the last few decades due to the wide range of potential applications of this class of molecules, for instance, as catalysts in the field of “green energy”, as devices in state-of-the-art electronics, as sensors and collectors or emitters of light etc. to name only a few. However, in particular, larger organic molecules tend to be thermally labile, these molecules are better deposited from solution. Furthermore, if these molecules are deposited electrochemically in the form of ions (from their solvable salts) the electrochemical potential is a further very useful control parameter which allows to influence the self-assembly process. Thus, the electrochemical solid-liquid interfaces is a good choice in order to study the 2D self-organization process of organic molecules. It is well-know that the solid/liquid interface plays a fundamental role in a diverse range of phenomena encountered in biological, chemical and physical processes, for example in many electrochemical, electrocatalytic and biological reactions. In the case of a metal in contact with an electrolyte, a lot of interesting processes can be carried out on the metal surface, such as adsorption/desorption of species from the electrolyte like anions and cations, e.g. organic ions, surface reactions like corrosion/passivation, deposition/growth of new compounds, etching/plating etc.. Unraveling the atomic structure at a solid/liquid interface and of processes occurring at this interface with atomic/molecular resolution is, therefore, one of the major challenges of today's surface science to investigate and to understand the elementary steps of these processes with model systems in order to apply them effectively in our daily life. In this dissertation has been explored the electrochemical deposition route to study the self-assembly of Tetra(N-methyl-4-pyridyl)-porphyrin molecules (TMPyP) and Tetra(4-trimethylammoniophenyl) porphyrin molecules (TTMAPP) on an iodide-modified Au(100) electrode surface by means of in-situ Electrochemical Scanning Tunneling Microscopy (EC-STM) with submolecular resolution. This enables unprecedented insight into such self-assembly phenomena at solid-liquid interfaces in the presence of anions and organic molecules as a function of electrode potential. Results of the investigations of TMPyP and TTMAPP molecules on an iodide-modified Au(100) surface in both cases show a long-range periodic superstructures beyond the molecular arrangement with phase transitions which is dependent on the substrate structure and applied electrode potential. The resultant structures, imaged with submolecular resolution by in situ STM, are clearly correlated with the redox state of the molecules as indicated by cyclic voltammetry. As a result, detailed structure models are derived and are discussed in terms of the prevailing interactions

Porphyrin Layers at Cu/Au(111)–Electrolyte Interfaces: In Situ EC-STM Study

The coadsorption of porphyrin molecules (TMPyP: tetra(N-methyl-4-pyridyl)-porphyrin), sulfate anions and copper on a Au(111) electrode was investigated by the use of cyclic voltammetry (CV) and in situ electrochemical scanning tunneling microscopy. With decreasing electrode potential the following sequence of surface phases was found: (I) an ordered $$\left( {\sqrt 3 \times \sqrt 7 } \right)R19.1^\circ - {\text{S}}{{\text{O}}_4}^{{2 - }}$$ structure on the unreconstructed Au(111)-(1 × 1) surface; (II) a disordered SO42−-layer on the still unreconstructed Au(111)-(1 × 1); (III) a $$\left( {\sqrt 3 \times \sqrt 3 } \right)R30^\circ$$ coadsorption structure of 2/3 ML Cu and 1/3 ML SO42−; (IV) a completed 1 ML Cu covered by a layer of mobile, i.e. not imaged, SO42− anions, moreover, a coadsorption layer of disordered porphyrin molecules and still mobile SO42− anions; (V) overpotentially deposited Cu-multilayers terminated by the well known Moire-type modulated $$\left( {\sqrt 3 \times \sqrt 7 } \right)R19.1^\circ - {\text{S}}{{\text{O}}_4}^{{2 - }}$$ structure (similar to bulk Cu(111)) and covered by a dense layer of flat lying TMPyP molecules showing a growing square as well as hexagonally ordered arrangement, and at even more negative potential values and low Cu concentrations in the solution (VI) a pseudomorphic underpotentially deposited Cu-monolayer covered by a $$\left( {\sqrt 3 \times \sqrt 7 } \right)R19.1^\circ - {\text{S}}{{\text{O}}_4}^{{2 - }}$$ layer and a dense, ordered porphyrin layer ontop. The formation of the various phases is driven by the potential dependent surface charge density and the resultant electrostatic interaction with the respective ions. A severe imbalance between the copper deposition and desorption current in the CV spectra suggests also the formation of CuTMPyP-metalloporphyrin on the surface which diffuses into the bulk solution

Markov risk mappings and risk-sensitive optimal stopping

In contrast to the analytic approach to risk for Markov chains based on transition risk mappings, we introduce a probabilistic setting based on a novel concept of regular conditional risk mapping with Markov update rule. We confirm that the Markov property holds for the standard measures of risk used in practice such as Value at Risk and Average Value at Risk. We analyse the dual representation for convex Markovian risk mappings and a representation in terms of their acceptance sets. The Markov property is formulated in several equivalent versions including a strong version, opening up additional risk-sensitive optimisation problems such as optimal stopping with exercise lag and optimal prediction. We demonstrate how such problems can be reduced to a risk-sensitive optimal stopping problem with intermediate costs, and derive the dynamic programming equations for the latter. Finally, we show how our results can be extended to partially observable Markov processes.Comment: 29 pages. New: extension of one-step ahead Markov property to entire "future", Markov property in terms of acceptance sets, VaR and AVaR examples, convex Markov risk mappings, application to optimal stopping with exercise lag. Notable changes: Stopping cost in the partially observable optimal stopping problem can depend on the unobservable stat

Organizational resilience as a response to the energy crisis: Systematic literature review

In this paper, we provide a literature review on the topic of organizational resilience, in relation to the energy crisis. The concept of organizational resilience refers to the capability to respond and adapt to shocks. Undoubtedly, the recent energy crisis may be considered an external shock, as it has raised energy prices and exerts a significant pressure on decision makers. Although the energy crisis has impacted organizations significantly in recent months, there is little knowledge on how companies should respond to this threat. Thus, to fill in this research gap, we apply the method of a systematic literature review (SLR), combined with text mining tools, to map the topics covered by 124 works in the field. Based on our results, we uncover several important gaps in the existing studies. We also provide suggestions on relevant future research directions that could broaden the scope of the management of energy crisis, in line with the concept of organizational resilience.Web of Science162art. no. 70

Chitosan-derived nitrogen-doped carbon electrocatalyst for a sustainable upgrade of oxygen reduction to hydrogen peroxide in UV-assisted electro-Fenton water treatment

The urgency to move from critical raw materials to highly available and renewable feedstock is currently driving the scientific and technical developments. Within this context, the abundance of natural resources like chitosan paves the way to synthesize biomass-derived nitrogen-doped carbons. This work describes the synthesis of chitosan-derived N-doped mesoporous carbon in the absence (MC-C) and presence (N-MC-C) of 1,10-phenanthroline, which acted as both a porogen agent and a second nitrogen source. The as-prepared MC-C and N-MC-C were thoroughly characterized and further employed as catalytic materials in gas-diffusion electrodes (GDEs), aiming to develop a sustainable alternative to conventional GDEs for H2O2 electrogeneration and photoelectro-Fenton (PEF) treatment of a drug pollutant. N-MC-C presented a higher content of key surface N-functionalities like the pyrrole group, as well as an increased graphitization degree and surface area (63 vs 6 m2/g), comparable to commercial carbon black. These properties entailed a superior activity of N-MC-C for the oxygen reduction reaction, as confirmed from its voltammetric behavior at a rotating ring-disk electrode. The GDE prepared with the N-MC-C catalyst showed greater H2O2 accumulation, attaining values close to those obtained with a commercial GDE. N-MC-C- and MC-C-derived GDEs were employed to treat drug solutions at pH 3.0 by the PEF process, which outperformed electro-oxidation. The fastest drug removal was achieved using N-MC-C, requiring only 16 min at 30 mA/cm2 instead of 20 min required with MC-C. The replacement of the dimensionally stable anode by a boron-doped diamond accelerated the degradation process, reaching an almost complete mineralization in 360 min. The main degradation products were identified, revealing the formation of six different aromatic intermediates, alongside five aliphatic compounds that comprised three nitrogenated structures. The initial N was preferentially converted into ammonium

High soluble transferrin receptor in patients with heart failure:a measure of iron deficiency and a strong predictor of mortality

Background: Iron deficiency (ID) is frequent in heart failure (HF), linked with exercise intolerance and poor prognosis. Intravenous iron repletion improves clinical status in HF patients with LVEF≤45%. However, uncertainty exists about the accuracy of serum biomarkers in diagnosing ID. Study Aims: 1) to identify the iron biomarker with the greatest accuracy for the diagnosis of ID in bone marrow in patients with ischaemic HF; 2) to establish the prevalence of ID using this biomarker and its prognostic value in HF patients. Methods and Results: Bone marrow was stained for iron in 30 patients with ischaemic HF with LVEF≤45% and 10 healthy controls, and ID was diagnosed for 0‐1 grades (Gale scale). 791 patients with HF with LVEF≤45% were prospectively followed‐up for 3 years. Serum ferritin, transferrin saturation, soluble transferrin receptor (sTfR) were assessed as iron biomarkers. Most patients with HF (25, 83%) had ID in bone marrow, but none of the controls (p<0.001). Serum sTfR had the best accuracy in predicting ID in bone marrow (AUC: 0.920, 95%CI: 0.761‐0.987, for cut‐off 1.25 mg/L sensitivity 84%, specificity 100%). Serum sTfR was ≥1.25 mg/L in 47% of HF patients, in 56% and 46% of anaemics and non‐anaemics, respectively (p<0.05). The reclassification methods revealed that serum sTfR significantly added the prognostic value to the baseline prognostic model, and to the greater extent than plasma NT‐proBNP. Based on internal derivation and validation procedures, serum sTfR ≥1.41 mg/L was the optimal threshold for predicting 3‐year mortality, independent of other established variables. Conclusions: High serum sTfR accurately reflects depleted iron stores in bone marrow in patients with HF, and identifies those with a high 3‐year mortality

Establishing reactivity descriptors for platinum group metal (PGM)-free Fe–N–C catalysts for PEM fuel cells

We report a comprehensive analysis of the catalytic oxygen reduction reaction (ORR) reactivity of four of today's most active benchmark platinum group metal-free (PGM-free) iron/nitrogen doped carbon electrocatalysts (Fe–N–Cs). Our analysis reaches far beyond previous such attempts in linking kinetic performance metrics, such as electrocatalytic mass-based and surface area-based catalytic activity with previously elusive kinetic metrics such as the active metal site density (SD) and the catalytic turnover frequency (TOF). Kinetic ORR activities, SD and TOF values were evaluated using in situ electrochemical NO2− reduction as well as an ex situ gaseous CO cryo chemisorption. Experimental ex situ and in situ Fe surface site densities displayed remarkable quantitative congruence. Plots of SD versus TOF (“reactivity maps”) are utilized as new analytical tools to deconvolute ORR reactivities and thus enabling rational catalyst developments. A microporous catalyst showed large SD values paired with low TOF, while mesoporous catalysts displayed the opposite. Trends in Fe surface site density were linked to molecular nitrogen and Fe moieties (D1 and D2 from 57Fe Mössbauer spectroscopy), from which pore locations of catalytically active D1 and D2 sites were established. This cross-laboratory analysis, its employed experimental practices and analytical methodologies are expected to serve as a widely accepted reference for future, knowledge-based research into improved PGM-free fuel cell cathode catalysts.EC/H2020/779366/EU/Critical Raw material ElectrocatalystS replacement ENabling Designed pOst-2020 PEMFC/CRESCENDOTU Berlin, Open-Access-Mittel - 202