Insight into Selectivity Differences of Glycerol Electro-Oxidation on Pt(111) and Ag(111)

Electro-oxidation is a way to utilize glycerol, a byproduct of biodiesel production, to produce fuels and feedstock chemicals for the chemical industry. A significant challenge is to get products with high selectivity, so it is desirable to understand the glycerol oxidation mechanisms in further detail. Using density functional theory calculations, we investigated possible glycerol oxidation intermediates on Pt(111) and Ag(111). We find that the different adsorption preferences of the intermediates on Pt (adsorption via carbon atoms) and Ag (adsorption via oxygen atoms) lead to different preferred reaction pathways, resulting in different products. The reaction pathways on both surfaces involve glyceraldehyde as a key intermediate; however, upon further oxidation, Pt(111) preferentially produces glyceric acid (CH2OH–CHOH–COOH), while on Ag(111) C–C bonds are broken, which leads to the production of glycolaldehyde and formic acid (CH2OH–CHO and HCOOH). These predictions agree well with the experimental outcome of the electro-oxidation of glycerol on Pt and Ag surfaces. Our study therefore provides useful insights for optimizing the selectivity of glycerol oxidation and improving the utilization of glycerol

Positivitat in Kultur und Religion (1) : Ein Gesichtspunkt aus dem wir die europaische Kultur anzusehen haben

In the field of energy storage devices the pursuit for cheap, high energy density, reliable secondary batteries is at the top of the agenda. The Li–O₂ battery is one of the possible technologies that, in theory, should be able to close the gap, which exists between the present state-of-the-art Li-ion technologies and the demand placed on batteries by technologies such as electrical vehicles. Here we present a redox probing study of the charge transfer across the main deposition product lithium peroxide, Li₂O₂, in the Li–O₂ battery using outer-sphere redox shuttles. The change in heterogeneous electron transfer exchange rate as a function of the potential and the Li₂O₂ layer thickness (∼depth-of-discharge) was determined using electrochemical impedance spectroscopy. The attenuation of the electron transfer exchange rate with film thickness is dependent on the probing potential, providing evidence that hole transport is the dominant process for charge transfer through Li₂O₂ and showing that the origin of the sudden death observed upon discharge is due to charge transport limitations

Razvoj eksplozivne moči v košarki, pri kadetih v predtekmovalnem obdobju

Lithium–O₂ (Li–O₂) batteries are currently limited by a large charge overpotential at practically relevant current densities, and the origin of this overpotential has been heavily debated in the literature. This paper presents a series of electrochemical impedance measurements suggesting that the increase in charge potential is not caused by an increase in the internal resistance. It is proposed that the potential shift is instead dictated by a mixed potential of parasitic reactions and Li₂O₂ oxidation. The measurements also confirm that the rapid potential loss near the end of discharge (“sudden death”) is explained by an increase in the charge transport resistance. The findings confirm that our theory and conclusions in ref , based on experiments on smooth small-area glassy carbon cathodes, are equally valid in real Li–O₂ batteries with porous cathodes. The parameter variations performed in this paper are used to develop the understanding of the electrochemical impedance, which will be important for further improvement of the Li–air battery

An Electrochemical Impedance Study of the Capacity Limitations in Na–O₂ Cells

Electrochemical impedance spectroscopy, pressure change measurements, and scanning electron microscopy were used to investigate the nonaqueous Na–O₂ cell potential decrease and rise (sudden deaths) on discharge and charge, respectively. To fit the impedance spectra from operating cells, an equivalent circuit model was used that takes into account the porous nature of the positive electrode and is able to distinguish between the electrolyte resistance in the pores and the charge-transfer resistance of the pore walls. The results obtained indicate that sudden death on discharge is caused by, depending on the current density, either accumulation of large NaO₂ crystals that eventually block the electrode surface and/or a thin film of NaO₂ forming on the cathode surface at the end of discharge, which limits charge-transfer. The commonly observed sudden rise in potential toward the end of charge may be caused by a concentration depletion of NaO₂ dissolved in the electrolyte near the cathode surface and/or an accumulation of degradation products on the cathode surface

Electrochemical Switching of Conductance with Diarylethene-Based Redox-Active Polymers

Reversible switching of conductance using redox triggered switching of a polymer-modified electrode is demonstrated. A bifunctional monomer comprising a central electroswitchable core and two bithiophene units enables formation of a film through anodic electropolymerization. The conductivity of the polymer can be switched electrochemically in a reversible manner by redox triggered opening and closing of the diarylethene unit. In the closed state, the conductivity of the modified electrode is higher than in the open state