A Multi-Paradigm Computational Model of Materials Electrochemical Reactivity for Energy Conversion and Storage

Abstract

In this paper we report a new multi-paradigm modeling approach devoted to the investigation of the electrochemical reactivity of materials in electrodes for energy conversion or storage applications. The approach couples an atomistically-resolved Kinetic Monte Carlo (KMC) modeling module describing the electrochemical kinetics in an active material, with continuum modeling modules describing reactants transport at the active material/electrolyte nanoscopic interface (electrochemical double layer region) and along the mesoscale electrode thickness. The KMC module is developed by extending the so-called Variable Step Size Method (VSSM) algorithm (called here Electrochemical-VSSM) and constitutes the first VSSM extension reported so far which allows calculating the electrode potential as function of the imposed current density. The KMC module can be parameterized with activation energies calculated from Density Functional Theory (DFT), and thanks to the coupling with the transport modules, it describes the materials reactivity in electrochemical conditions. This approach allows us to study how the surface morphology (e.g. distribution of inactive sites, size of the active material particle, etc.) impacts the performance of the electrode. As an application example, we report here a computational investigation of the Oxygen Reduction Reaction (ORR) kinetics in a Pt (111) Because of the global warming and the fossil fuels depletion, zeroemission electrochemical devices for energy conversion and storage, such as fuel cells and secondary batteries, are called to play a significant role in the sustainable development of the Humanity. The operation principles of these devices involve complex competitions and synergies between electrochemical, transport and thermo-mechanical mechanisms occurring at multiple spatial and temporal scales. Multiscale modeling techniques can help on establishing correlations between their materials chemical and microstructural properties, operation conditions, performance and durability.1-3 Such correlations are important in order to suggest enhanced materials and cells designs. [4][5][6][7] Several multiscale modeling approaches have been reported so far. The most popular one consists in extracting data from a lower-scale and using it as input for the upper-scale via their parameters. For example, activation barriers for elementary reaction steps can be extracted from Density Functional Theory (DFT) calculations 8 and then injected into Transition State Theory (TST) Eyring's expressions to estimate the parameters which are used to solve Mean Field (MF) kinetic models simulating the evolution of the reactants, intermediate reaction species and products. 9,10 Alternatively, direct multiparadigm multiscale models consist in coupling "on-the-fly" models developed in the frame of different paradigms. For instance, continuum equations describing the transport phenomena of multiple reactants in a porous electrode may be coupled with atomistically-resolved simulations describing electrochemical reacti...

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A Multiparadigm Modeling Investigation of Membrane Chemical Degradation in PEM Fuel Cells

“…As it was previ- ously predicted 67 the H 2 O is the dominant adspecie (with an initial coverage value of ∼0.6 ML for H 2 O, 0.3 ML for O 2 and 0.03 ML for O). The PEM degradation process at non-zero current leads to the cathode coverage evolution.…”

“…67 for the cathode CL. This approach resolves the adsorption/desorption, adspecies surface diffusion and reactions on the catalyst surface during the PEMFC operation, and allows calculating the electrodes and cell potential.…”

“…62 Parameter values of the associated electrochemical double layer sub-model and of the surface diffusion processes are identical to the ones used in our previous work. 67 For the H 2 O 2 production within the ORR pathway in the cathode CL, we have considered the elementary kinetic reaction in Table II, still within our KMC E-VSSM approach, with the same parameters values for the activation barriers, diffusion barriers and electrochemical double layer sub-model that in Ref. 67.…”

“…For the adsorption steps we follow the same approach as in our previous publication: 67 according to the collision theory, the kinetic …”