Spatial reactant distribution in CO2 electrolysis: Balancing CO2 utilization and Faradaic Efficiency

The production of value added C1 and C2 compounds within CO2 electrolyzers has reached sufficient catalytic performance that system and process performance – such as CO2 utilization – have come...

Enhanced Reactant Distribution in Redox Flow Cells

Redox flow batteries (RFBs), provide a safe and cost-effective means of storing energy at grid-scale, and will play an important role in the decarbonization of global electricity networks. Several approaches have been explored to improve their efficiency and power density, and recently, cell geometry modification has shown promise in efforts to address mass transport limitations which affect electrochemical and overall system performance. Flow-by electrode configurations have demonstrated significant power density improvements in laboratory testing, however, flow-through designs with conductive felt remain the standard at commercial scale. Concentration gradients exist within these cells, limiting their performance. A new concept of redistributing reactants within the flow frame is introduced in this paper. This research shows a 60% improvement in minimum V3+ concentration within simulated vanadium redox flow battery (VRB/VRFB) cells through the application of static mixers. The enhanced reactant distribution showed a cell voltage improvement by reducing concentration overpotential, suggesting a pathway forward to increase limiting current density and cycle efficiencies in RFBs.

Flame stability and behavior inside meso-scale combustor with different flame holder

Flame stability and behavior inside meso-scale combustor with different flame holder was investigated experimentally. Three types of flame holder i.e. wire mesh, flat plate with circular holes and flat plate with narrow slits, were used to improve the flame stability inside the meso-scale combustor. Combustor with flat plate - narrow slits flame holder has the best flame stability, i.e. stable flame established inside the combustor at the highest reactant velocity compared to the other combustor with the different flame holder. Furthermore, combustor with wire mesh and flat plate with narrow slits have a relatively uniform flame colour at the combustor cross section, compared to flame visualization inside meso-scale combustor with flame holder of flat plate with circular holes. This phenomena is related to non-uniform reactant distribution on the combustor cross section.

The Effect of Nonuniform Under-Rib Convection on Reactant and Liquid Water Distribution in Proton Exchange Membrane Fuel Cells

The performance of a proton exchange membrane (PEM) fuel cell strongly depends on the nature of reactant distribution and the effectiveness of liquid water removal. In this work, three different configurations of a mixed flow distributor are studied analytically and numerically to find out the effect of nonuniform under-rib convection on reactant and liquid water distribution in the cell. In a mixed flow distributor, the rate of under-rib convection is found to be different under each rib in the same flow sector which results in different rates of removal of liquid water. This helps to retain some water to hydrate the membrane, whereas the excess is removed to avoid flooding. It is found that under-rib convection aids to get better reactant distribution, reduces pressure drop, and provides better control over liquid water removal which is helpful in developing efficient water management strategies for PEM fuel cells.

Graduated Resistance to Gas Flow Through a GDL in an Unconventional PEM Stack

The goal of this study is to design a gas diffusion layer (GDL) for a polymer electrolyte membrane (PEM) fuel cell with a graduated permeability and thereby graduating the resistance to flow throughout the GDL. It has been shown that in using conventional materials, the GDL exhibits a higher resistance in the through-plane direction due to the orientation of the small carbon fibers that make up the carbon paper or carbon cloth. In this study, a GDL is designed for an unconventional PEM fuel cell stack where the reactant gases are supplied through the side of the GDL rather than through flow field channels machined into a bipolar plate. The effects of changing in-plane permeability, through-plane permeability, GDL thickness, and oxygen utilization on the expected current density distribution at the catalyst layer are studied. Three different thicknesses and three different utilizations are investigated. It has been found that a thinner GDL with a lower utilization yields a higher current density on the electrode. A quantitative metric to measure uniformity of reactant distribution and the ratio of the standard deviation of the current density to the average current density was introduced, and it was found that while the uniformity of the reactant distribution is independent of thickness of the GDL, it is inversely proportional to utilization.

Numerical Simulation of an Innovative PEM Fuel Cell Stack

This paper describes a novel design approach for a fuel cell stack to address the uniformity of reactant streams and eliminate the bipolar plate to reduce cost, size, volume, and weight. Computational analysis for a novel PEM fuel cell stack and two conventional stacks is conducted. Preliminary results based on a comparison study have shown that eliminating bipolar plates from the fuel cell drastically increases power density, while maintaining uniformity in reactant distribution. Specifically, preliminary case studies suggest that the power density using the novel design is four times that of conventional approaches.