Development of a Full Layer Pore-Scale Model for the Simulation of Electro-Active Material Used in Power Sources

Abstract

A general pore-scale model was developed which mimics the electro-active layer formation process. The model was used to simulate the active material loading on battery, fuel cell and supercapacitor electrodes. The active layer was reconstructed by coating 10 8 particles with different interparticle interactions onto a smooth surface. Instead of simulating each generated layers at macro scale, scaling analysis was applied to reduce the complexity of the system. It was shown, that the generated layers belong to the same universality class and can be normalized by a self-affine transformation. The non-linear scaling function, obtained at mesoscale, was incorporated into the macrohomogeneous model to simulate the impact of ultra-low Pt loading on specific activity of fuel cells and of thickness of supercapacitors layers on volumetric capacitance. The analysis of experimental data and modeling results revealed that (measurable) specific activity and volumetric capacitance increase at ultra-low loading, because the surface area in unit volume (or porosity) and the thickness scale differently with loading. Finally a general relationship was proposed, which describes the evolution of volumetric surface area density of fuel cells, batteries and supercapacitor with loading, and can be used to build a bridge between mesoscale morphology and macroscopic simulation. Electrochemical energy storage and conversion devices, such as batteries, fuel cells and supercapacitors are key enabling technologies to store electricity, in a form of chemical energy, for an electric vehicle with desirable driving range and power.1 Even if state-of-the-art electrochemical storage devices can provide enough stored electricity, the cost of zero emission vehicles (battery, and fuel cell vehicles) is still too high for widespread application. Helou and Brodd 2 analyzed the cost structure of battery production and found that at mass production level the cost of active materials used is 50-60% of the total cost per battery cell. In fuel cells only one component, the Pt catalyst, is responsible for ca. 35% of the total cost of the stack.3 The limited stock of Pt is another bottleneck 4 to cost reduction. Consequently, the reduction of active material loading is a requirement to meet market expectations for all systems. The development of higher capacity Li materials with nano-sized particles 5,6 and more active and extended surface area electrocatalysts for fuel cells 4,7,8 can pave the way for reducing material costs. Numerical modeling is one of the most prospective techniques to find the optimal electrode structure to accommodate lower material loading.In spite of the different nature of fuel cells, batteries and supercapacitors, very similar models are used to study and optimize their performance. The most widely used simulation method is the macrohomogeneous model, 9,10 because it can predict the macroscopic behavior of a fuel cell stack, 11,12 a battery cell 13,14 and a supercapacitor. 15,16 It does not describe however, the exact geometric det...

Mesoscale Elucidation of the Influence of Mixing Sequence in Electrode Processing

“…Kriston et al developed a pore-scale model accompanied by a stochastic method to mimic the electroactive layer formation process in energy storage devices, and they employed a scaling analysis to reduce the complexity of the system. 57 Their work demonstrated that the interparticle interaction and material loading affected the morphological properties of electroactive layer. However, their work did not consider multiphase interaction which is important in electrode preparation.…”

(Invited)Development of Highly Active and Durable Hybrid Compressive Platinum for Polymer Electrolyte Membrane (PEM) Fuel Cells at USC

“…The activated carbon support (ACCS) was prepared using the procedure developed in the Center for Electrochemical Engineering at University of South Carolina (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). The Pt/ACCS was synthesized using a modified polyol method (7,9,11).…”

“…Compressive platinum lattice catalyst (Pt*/ACCS) was prepared using a methodologies developed at USC (4)(5)(6)(7)(8)(9)(10)(11)(12)(13). The amount of Co used as a doping material targeted different atomic ratio of PtCo in Pt*/ACCS catalyst.…”