Ulrike Krewer

Future Challenges in Heterogeneous Catalysis: Understanding Catalysts under Dynamic Reaction Conditions

In the future, (electro‐)chemical catalysts will have to be more tolerant towards a varying supply of energy and raw materials. This is mainly due to the fluctuating nature of renewable energies. For example, power‐to‐chemical processes require a shift from steady‐state operation towards operation under dynamic reaction conditions. This brings along a number of demands for the design of both catalysts and reactors, because it is well‐known that the structure of catalysts is very dynamic. However, in‐depth studies of catalysts and catalytic reactors under such transient conditions have only started recently. This requires studies and advances in the fields of 1) operando spectroscopy including time‐resolved methods, 2) theory with predictive quality, 3) kinetic modelling, 4) design of catalysts by appropriate preparation concepts, and 5) novel/modular reactor designs. An intensive exchange between these scientific disciplines will enable a substantial gain of fundamental knowledge which is urgently required. This concept article highlights recent developments, challenges, and future directions for understanding catalysts under dynamic reaction conditions.

Electrochemical Oxidation of Carbon-Containing Fuels and Their Dynamics in Low-Temperature Fuel Cells

Fuel cells can convert the energy that is chemically stored in a compound into electrical energy with high efficiency. Hydrogen could be the first choice for chemical energy storage, but its utilization is limited due to storage and transport difficulties. Carbon-containing fuels store chemical energy with significantly higher energy density, which makes them excellent energy carriers. The electro-oxidation of carbon-containing fuels without prior reforming is a more challenging and complex process than anodic hydrogen oxidation. The current understanding of the direct electro-oxidation of carbon-containing fuels in low-temperature fuel cells is reviewed. Furthermore, this review covers various aspects of electro-oxidation for carbon-containing fuels in non-steady-state reaction conditions. Such dynamic investigations open possibilities to elucidate detailed reaction kinetics, to sense fuel concentration, or to diagnose the fuel-cell state during operation. Motivated by the challenge to decrease the consumption of fossil fuel, the production routes of the fuels from renewable resources also are reviewed.

Real-time model predictive control for the optimal charging of a lithium-ion battery

Li-ion batteries are widely used in industrial applications due to their high energy density, slow material degradation, and low self-discharge. The existing advanced battery management systems (ABMs) in industry employ semiempirical battery models that do not use first-principles understanding to relate battery operation to the relevant physical constraints, which results in conservative battery charging protocols. This article proposes a Quadratic Dynamic Matrix Control (QDMC) approach to minimize the charge time of batteries to reach a desired state of charge (SOC) while taking temperature and voltage constraints into account. This algorithm is based on an input-output model constructed from a first-principles electrochemical battery model known in the literature as the pseudo two-dimensional (P2D) model. In simulations, this approach is shown to significantly reduce charging time.

Simple and reliable model for estimation of methanol cross-over in direct methanol fuel cells and its application on methanol-concentration control

A simplified model of mass-transport phenomena on the anodic side of direct methanol fuel cells (DMFCs) is presented, with the objective of estimating the cross-over flux in order to enable feedforward (sensorless) control of anodic concentration in DMFC systems. The effect of parameter uncertainty on the tracking error of the control system is analysed and several models for temperature dependence are proposed. Experimental data on methanol cross-over was gathered in a DMFC system, and the models were discriminated by means of nonlinear regression. The regression results and an initial test run indicate that feedforward control of anodic methanol concentration in DMFC systems is feasible.

Performance of zinc air batteries with added \hbox {K}_{2}\hbox {CO}_{3} in the alkaline electrolyte

Intentionally adding potassium carbonate to the high molar alkaline electrolyte is one possibility to mitigate the negative impact of carbonation in zinc air batteries (ZABs) that were investigated in this novel study. In this work, an experimental analysis of the electrochemical performance of ZABs with added potassium carbonate in potassium hydroxide electrolyte was conducted. The experiments included polarization curve measurements, electrochemical impedance spectroscopy measurements, and constant current discharge with an in-house battery set-up. In addition, ionic conductivity was measured for mixtures of potassium hydroxide and potassium carbonate solutions. The results implied that up to 50 mol% of added potassium carbonate in the electrolyte had a weaker influence on the cell performance than a decreased amount of hydroxide ions in the electrolyte from 21.9 to 1.8 mol%. However, discharge measurements showed that the cell potential and the maximum state-of-discharge are decreased for the operation with 50.00 mol% of added potassium carbonate. The conductivity measurements revealed that solutions with 9 moll-1K+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}

Model-based analysis of micro-separators for portable direct methanol fuel-cell systems

\hbox {mol} {\mathrm{\,l}}^{-1}\, \hbox {K}^+

Multi-Scale Modeling of Solid Electrolyte Interface Formation in Lithium-Ion Batteries

\end{document} and added potassium carbonate possessed similar ionic conductivity, when compared to the standard 6 M KOH electrolyte. All in all, the analysis showed that it was acceptable to add potassium carbonate to the high molar potassium hydroxide electrolyte, while still obtaining stable cell potential under the premise to increase the practical energy density and the long-term stability of zinc air batteries. The here presented findings might help to establish the zinc air battery as next generation type battery.

A systematic reactor design approach for the synthesis of active pharmaceutical ingredients

A model coupling momentum transport with reaction kinetics within the five-layer membrane electrode assembly has been developed for direct methanol fuel cells (DMFCs). The model accounts for the essential intermediate reaction steps on both anode and cathode catalyst layers, as well as the two-phase phenomena in the anode and cathode gas diffusion layers. The kinetics of the methanol reaction on the cathode catalyst layer that separately account for both chemical and electrochemical pathways are investigated. The model predictions agree with the DMFC experimental data. Simulation results indicate that the transport of methanol is essential in determining both the anode and cathode kinetics. Anode kinetics are not significantly improved for anode concentrations above 2 M. It is also revealed that the transport of methanol to the anode catalyst layer is significantly enhanced by the convection of CO 2 bubbles toward the flow field. The influence of methanol crossover on the cathode potential is quantified by changing the anode feed from methanol to hydrogen. The cathode potential is seen to deteriorate at higher methanol feed concentrations mainly due to the depletion of oxygen by the crossed over methanol on the cathode catalyst. This model should prove useful in optimizing the methanol feed concentration in DMFCs.