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When studying electrochemical oxygen reduction reactions in homogeneous media, special attention must be given to the significant background activity present with conventional electrode materials. The intrinsic electrocatalytic activity of different materials can be investigated using complementary methods, such as the rotating ring-disc electrode (RRDE) technique and chronoamperometric electrolysis with product quantification. This report presents a detailed investigation of the electrocatalytic ability of hydroxy anthraquinone derivatives and riboflavin towards hydrogen peroxide (H2O2) production via a novel RRDE subtraction method together with chronoamperometric electrolysis. Qualitative trends linking the two methods were obtained, such as a higher excess current correlating with both higher productivity and selectivity. As such, a valuable tool is provided to increase the understanding of the electrocatalytic ability of homogeneous solutions toward improving the oxygen reduction reaction. Version of record

The majority of energy storage devices like batteries, fuel cells or electrolyzers require heterogeneous electrodes. Immobilization of redox-active organic molecules by a polymeric approach seems to be a promising route towards organic electrodes for electrocatalytic energy storage or in batteries. Although numerous reports on synthesis and application of new poly-anthraquinones exist, a universal guideline or tool for selection of the best polymer, concerning several energy storage applications, is still underdeveloped. Moving into the direction of developing such a tool, we have selected and synthesized three poly(anthraquinones). NMR, FTIR, UV-Vis, TGA, contact angle measurement and SEM revealed certain structure-property trends, which can be correlated with the performance in the electrochemical investigation. The insights gained within this work demonstrate correlations between the FTIR frequencies and the electrochemical reduction potential, as well as between the polymer hydrophobicity and the electrochemical performance. Fonds zur Förderung der Wissenschaftlichen Forschung Z222-N19 Version of record

The state-of-the-art procedure for investigating homogenous and heterogeneous electrocatalysts is cyclic voltammetry (CV). However, this technique usually requires an inactive electrode material. One common problem arising e. g. in studying the oxygen reduction reaction (ORR) is the significant background contribution to the overall ORR current provided by many carbon-based and metal-based electrode materials. Furthermore, rotating ring-disc electrodes (RRDEs) made of common materials like glassy carbon/platinum (GC/Pt) can be affected by overlapping reduction potentials on the disc. Interference from overlapping reactions on the ring might also occur, particularly in connection with oxygen reduction and hydrogen peroxide oxidation in ORR studies. We present herein a novel subtraction method which allows a semi-quantitative description of homogeneous electrocatalysts and helps to overcome the overlapping problems described above using anthraquinone-2-sulfonate (AQS) as a “case study material” for the ORR. Fonds zur Förderung der Wissenschaftlichen Forschung Z222-N19 Version of record

In this report, we present results on the electrocatalytic activity of conducting polymers [polyaniline (PANI) and polypyrrole (PPy)] toward the electrochemical oxygen reduction reaction (ORR) to hydrogen peroxide (H2O2). The electropolymerization of the polymers and electrolysis conditions were optimized for H2O2 production. On flat glassy carbon (GC) electrodes, the faradaic efficiency (FE) for H2O2 production was significantly improved by the polymers. Rotating disc electrode (RDE) studies revealed that this is mainly a result of blocking further H2O2 to the water reduction pathway by the polymers. PPy on carbon paper (CP) significantly increased the molar production of H2O2 by over 250% at an average FE of above 95% compared to bare CP with a FE of 25%. Thus, the polymers are acting as catalysts on the electrode for the ORR, although their catalytic mechanisms differ from other electrocatalysts. Version of record

Developing efficient methods for capture and controlled release of carbon dioxide is crucial to any carbon capture and utilization technology. Herein we present an approach using an organic semiconductor electrode to electrochemically capture dissolved CO2 in aqueous electrolytes. The process relies on electrochemical reduction of a thin film of a naphthalene bisimide derivative, 2,7-bis(4-(2-(2-ethylhexyl)thiazol-4-yl)phenyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (NBIT). This molecule is specifically tailored to afford one-electron reversible and one-electron quasi-reversible reduction in aqueous conditions while not dissolving or degrading. The reduced NBIT reacts with CO2 to form a stable semicarbonate salt, which can be subsequently oxidized electrochemically to release CO2. The semicarbonate structure is confirmed by in situ IR spectroelectrochemistry. This process of capturing and releasing carbon dioxide can be realized in an oxygen-free environment under ambient pressure and temperature, with uptake efficiency for CO2 capture of ∼2.3 mmol g–1. This is on par with the best solution-phase amine chemical capture technologies available today.

In the recent decade, CO2 has increasingly been regarded not only as a greenhouse gas but even more as a chemical feedstock for carbon‐based materials. Different strategies have evolved to realize CO2 utilization and conversion into fuels and chemicals. In particular, biological approaches have drawn attention, as natural CO2 conversion serves as a model for many processes. Microorganisms and enzymes have been studied extensively for redox reactions involving CO2. In this review, we focus on monitoring nonliving biocatalyzed reactions for the reduction of CO2 by using enzymes. We depict the opportunities but also challenges associated with utilizing such biocatalysts. Besides the application of enzymes with co‐factors, resembling natural processes, and co‐factor recovery, we also discuss implementation into photochemical and electrochemical techniques.

Ellipsometric measurements in a wide spectral range (from 0.05 to 6.5 eV) have been carried out on the organic semiconducting polymer, poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene-vinylene] (MDMO-PPV), in both undoped and doped states. The real and imaginary parts of the dielectric function and the refractive index are determined accurately, provided that the layer thickness is measured independently. After doping, the optical properties show the presence of new peaks, which could be well-resolved by spectroscopic ellipsometry. Also for the doped material, the complex refractive index, with respect to the dielectric function, has been determined. The broadening of the optical transitions is due to the delocalization of polarons at higher doping level. The detailed information about the dielectric function as well as refractive index function obtained by spectroscopic ellipsometry allows not only qualitative but also quantitative description of the optical properties of the undoped/doped polymer. For the direct characterization of the optical properties of MDMO-PPV, ellipsometry turns out to be advantageous compared to conventional reflection and transmission measurements.