Unveiling Local Aging Patterns Following Accelerated Stress Testing of High-Performance Polymer Electrolyte Fuel Cells.

This study presents an in-depth analysis of heterogeneous aging patterns in membrane electrode assemblies (MEAs) subjected to diverse accelerated stress test (AST) conditions, simulating carbon corrosion (CC AST) and Pt particle size growth in fully humidified (Pt AST-Wet) and underhumidified (Pt AST-Dry) H2/N2 atmospheres. Multimodal characterization techniques are used to focus on heterogeneous aging patterns, primarily examining the variations in current distributions and Pt particle size maps. The findings reveal distinct characteristics of current distributions for all the AST cases, with substantial changes and strong current gradients in the CC AST case, indicative of severe performance degradation. Notably, despite significant differences in Pt particle size growth at the end-of-life (EOL), the Pt AST-Wet and Pt AST-Dry cases show minor changes in spatial current distributions. Moreover, a preferential growth of Pt particles under serpentine flow field bends in the Pt AST-Wet case is observed for the first time. This study provides crucial insights into the role of mass transport properties in shaping fuel cell performance, and highlights the need to consider factors beyond electrochemically-active surface area (ECSA) when assessing fuel cell durability.

Investigation of nutrient feeding strategies in a countercurrent mixed-acid multi-staged fermentation: experimental data.

Nutrients are essential for microbial growth and metabolism in mixed-culture acid fermentations. Understanding the influence of nutrient feeding strategies on fermentation performance is necessary for optimization. For a four-bottle fermentation train, five nutrient contacting patterns (single-point nutrient addition to fermentors F1, F2, F3, and F4 and multi-point parallel addition) were investigated. Compared to the traditional nutrient contacting method (all nutrients fed to F1), the near-optimal feeding strategies improved exit yield, culture yield, process yield, exit acetate-equivalent yield, conversion, and total acid productivity by approximately 31%, 39%, 46%, 31%, 100%, and 19%, respectively. There was no statistical improvement in total acid concentration. The traditional nutrient feeding strategy had the highest selectivity and acetate-equivalent selectivity. Total acid productivity depends on carbon-nitrogen ratio.

The slope method: a tool for analyzing semi-continuous data.

The MixAlco process is a biorefinery that converts lignocellulose into useful chemicals and hydrocarbon fuels via mixed-acid fermentation. For a semi-continuous-staged fermentation train, during each transfer, discrete amounts of material are moved between fermentors and data are tabulated. Because of natural day-to-day variations, the data are inherently noisy. To calculate performance parameters (e.g., yield, conversion, selectivity, productivity), the average flowrate of each stream component must be determined. To minimize error associated with noise, three data analysis methods were compared: Average, Accumulation, and Slope. The Average method determines the flowrate by averaging the amounts moved each transfer. The Accumulation method stores the solids and liquids that exit the fermentation train in separate vessels. After an extended time period, the mass in each storage vessel is measured so the average flowrate can be calculated. The Slope method calculates the flowrate of material in each stream from the slope of the moving cumulative sum with respect to time. For all three methods, the measured rates were virtually identical; thus accuracy was not affected by the method. However, for the examples presented, the Average method had >40% error and the Slope method <4% error; thus, precision was significantly affected by the method. The Accumulation method calculated the flowrate with a single data point so it is not possible to determine the statistical error.

Investigating microbial fuel cell bioanode performance under different cathode conditions.

A compact, three-in-one, flow-through, porous, electrode design with minimal electrode spacing and minimal dead volume was implemented to develop a microbial fuel cell (MFC) with improved anode performance. A biofilm-dominated anode consortium enriched under a multimode, continuous-flow regime was used. The increase in the power density of the MFC was investigated by changing the cathode (type, as well as catholyte strength) to determine whether anode was limiting. The power density obtained with an air-breathing cathode was 56 W/m(3) of net anode volume (590 mW/m(2)) and 203 W/m(3) (2160 mW/m(2)) with a 50-mM ferricyanide-based cathode. Increasing the ferricyanide concentration and ionic strength further increased the power density, reaching 304 W/m(3) (3220 mW/m(2), with 200 mM ferricyanide and 200 mM buffer concentration). The increasing trend in the power density indicated that the anode was not limiting and that higher power densities could be obtained using cathodes capable of higher rates of oxidation. The internal solution resistance for the MFC was 5-6 Omega, which supported the improved performance of the anode design. A new parameter defined as the ratio of projected surface area to total anode volume is suggested as a design parameter to relate volumetric and area-based power densities and to enable comparison of various MFC configurations.