Electrochemical modeling of hydrogen storage in hydride-forming electrodes

Modeling of Electrochemical Hydrogen Storage in Metal Hydride Electrodes

“…The complete electrochemical hydrogen storage process taking place in the MH electrode and the accompanying reaction fluxes are schematically represented in Fig. 1B and consists of four different steps: 12 1. Hydrogen dissociation/recombination at the electrode/ electrolyte interface…”

“…After the charge-transfer reaction at the electrode/electrolyte interface of the hydride-forming material ͑M s ͒ has been initiated, atomic hydrogen is chemically adsorbed ͑H ad ͒ at the electrode surface and is, subsequently, converted into the absorbed state ͑H abs ͒ and transported to the bulk of the hydride-forming material ͑M b ͒ by conventional solid-state diffusion. 9,12,21 In Fig. 1, the normalized hydrogen concentration in the bulk of the MH electrode is represented by x, and the normalized surface concentration is represented by , which is also known as the surface coverage.…”

“…[6][7][8][9][11][12][13] The following set of reaction flux equations has been derived ͑see Fig. 1B͒: 12 1. Mathematical description of the hydrogen absorption/ desorption reaction at the surface of the hydride-forming material ͑Eq.…”

“…A complete set of equations has been derived, describing the equilibrium hydrogen partial pressure and equilibrium electrode potential as a function of hydrogen content in both the solidsolution and two-phase coexistence regions. 12 All above models have been successfully applied to simulate the isotherms of various hydride-forming materials, including AB 5 -based and Mg-based alloys. [6][7][8][9][11][12][13] In the present paper, a further extension of the EKM is proposed to include the dynamic electrochemical ͑de͒hydrogenation kinetics, i.e., to include the exchange current density of the charge-transfer reaction, electrical double-layer charging, and ͑instantaneous͒ phase transition.…”

“…9,11 Finally, an electrochemical kinetic model ͑EKM͒ was developed, describing the electrochemical hydrogen storage in hydride-forming materials under equilibrium conditions. 12 This model was proposed as an extension of the KM. 9 It is also based on the first principles of electrochemical reaction kinetics and statistical thermodynamics and describes the complex, multistage, electrochemical ͑de͒hydrogena-tion process.…”