Electrochemical deposition of Fe2O3 in the presence of organic additives: a route to enhanced photoactivity

The photoelectrochemical activity of hematite films prepared by electrochemical deposition (ED) in the presence of organic additives is discussed. The studies focus on the role of small organic additive molecules in the tuning of the morphology of the films and their influence on the photoelectrochemical oxidation of water. The organic additives, namely, coumarin 343 (C343), γ-glucuronic acid (GA) and sodium dodecyl sulfonate (Sds), possess functional moieties to interact with iron ions in the ED bath electrostatically or through metal–ligand complexation reactions. XPS measurements prove that the organic additives are incorporated, and the oxidation state of Fe3+ rules out the presence of mixed valences in the films. SEM and XRD measurements present morphological and structural evidence, respectively. The photoelectrochemical study shows that organically modified hematite films exhibit enhanced photoactivity; the photocurrent density at 1.4 V vs. RHE on a GA-modified electrode is up to 5–6 times higher than on the unmodified electrode. Electrochemical impedance results reveal the role of the organic additives in reducing the charge transfer resistance from the hematite surface to the solution. In addition, a simple Ti post treatment greatly enhances the photoactivity of all electrodes under investigation.DFG/WA 1116/23-

Electrocatalytic CO2 Reduction on CuOx Nanocubes: Tracking the Evolution of Chemical State, Geometric Structure, and Catalytic Selectivity using Operando Spectroscopy

The direct electrochemical conversion of carbon dioxide (CO2) into multi‐carbon (C2+) products still faces fundamental and technological challenges. While facet‐controlled and oxide‐derived Cu materials have been touted as promising catalysts, their stability has remained problematic and poorly understood. Herein we uncover changes in the chemical and morphological state of supported and unsupported Cu2O nanocubes during operation in low‐current H‐Cells and in high‐current gas diffusion electrodes (GDEs) using neutral pH buffer conditions. While unsupported nanocubes achieved a sustained C2+ Faradaic efficiency of around 60 % for 40 h, the dispersion on a carbon support sharply shifted the selectivity pattern towards C1 products. Operando XAS and time‐resolved electron microscopy revealed the degradation of the cubic shape and, in the presence of a carbon support, the formation of small Cu‐seeds during the surprisingly slow reduction of bulk Cu2O. The initially (100)‐rich facet structure has presumably no controlling role on the catalytic selectivity, whereas the oxide‐derived generation of under‐coordinated lattice defects, can support the high C2+ product yields.TU Berlin, Open-Access-Mittel – 2020DFG, 390540038, EXC 2008: Unifying Systems in Catalysis "UniSysCat"BMBF, 033RC004E, CO2Plus - Verbundvorhaben: eEthylen - Nutzung elektrischer Energie aus erneuerbaren Quellen zur elektrochemischen Herstellung von Ethylen aus CO2, Teilvorhaben 5: Charakterisierung und Testung für Synthese-Struktur-WirkungsbeziehungenBMBF, 03SF0523C, Verbundvorhaben CO2EKAT: Elektrokatalysatorsystem für stoffliche Energiespeicherung durch gekoppelte Wasserelektrolyse und CO2-UmwandlungEC/H2020/725915/EU/In situ and Operando Nanocatalysis: Size, Shape and Chemical State Effects/OPERANDOCA

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements