Mass transport in a hydrogen gas diffusion electrode

Abstract

Experimental data are presented concerning the diffusion-limited current density for hydrogen oxidation in a gas diffusion electrode (GDE) under various conditions. These current densities were obtained using mixtures of hydrogen and inert gases. To elucidate the dependence of the overall mass transport coefficient on the gas phase diffusion coefficient and the liquid phase diffusion coefficient of the hydrogen, a simplified model was derived to describe the transport of hydrogen in a GDE based on literature models. The GDE consists of a hydrophobic and a hydrophilic layer, namely a porous backing and a reaction layer. The model involves gas diffusion through the porous backing of the GDE combined with gas diffusion, gas dissolution and reaction in the reaction layer of the electrode. It was found that the transport rate of hydrogen under the experimental circumstances is determined by hydrogen gas diffusion in the pores of the porous backing, as well as in the macropores of the reaction layer. Diffusion of dissolved hydrogen in the micropores of the reaction layer, through the liquid, is shown to be of little significance. geometric electrode surface area (m 2) concentration of reactive component at the inlet of the gas compartment (tool m -3) concentration of reactive component in and at the outlet of the gas compartment (mol m -3) concentration of sulphuric acid in the solution compartment (tool m -3) concentration of reactive component in a gas diffusion electrode (mol m -3) interdiffusion coefficient for gas i in gasj at a temperature T (m 2 s -1) diffusion coefficient for electroactive species in solution (m 2 s -1) electrode potential (V) equilibrium electrode potential (V) upper limit electrode potential (V) volumetric flow rate at the inlet of the gas compartment (m 3 s -1) volumetric flow rate of nitrogen at the inlet of the gas compartment (m -3 s -1) mass flow rate at the inlet of the gas compartment (kg s -l) Faraday constant (A s mo1-1) Henry's constant defined by Equation 9 (-) diffusion limited current density for gas diffusion electrode (A m -2) calculated diffusion limited current density for gas diffusion electrode (A m -2) local current density for hydrogen oxidation reaction in a micropore of the gas diffusion electrode (Am -2) current for hydrogen production (A) ©

Hydrogen Mass Transport in Fuel Cell Gas Diffusion Electrodes

“…Thus, the hydrogen mass transport coefficients from Ref. [26,27] are generally larger than values derived from the present model (Table 1, Figure 10). Figure 10 k CSTR values are calculated using a CSTR model [26,27] and all data pertaining to Figures 6-9:…”

“…(10) indicates that the hydrogen concentration steeply varies along the flow field length. Therefore, a CSTR model [26,27] is not adequate to derive a mass transport coefficient because it assumes that the hydrogen concentration is constant and fixed to the outlet value (ŷ 1). As the concentration is underestimated along the flow channel, Eq.…”

“…Previous studies' data [26][27][28][29] are reanalysed to: (i) fulfil the need for hydrogen mass transport coefficients, (ii) highlight shortcomings of previous treatment methods, including error estimates due to the use of a model either neglecting or improperly taking into account reactant consumption along the channel length, and (iii) emphasize an already proven analysis alternative [6]. Necessary precautions to ensure experimental data quality are stated.…”

“…Hydrogen transport within the ionomer layer is a diffusion-controlled process [25]. Gas diffusion electrodes (GDEs) were studied by circulating different fuel compositions on one of their side while the catalysed side was in contact with an aqueous sulphuric acid solution [26,27]. The method used to extract the mass transport coefficient was derived under the continuous stirred tank reactor (CSTR) assumption.…”

Reduction of chromate in dilute solution using hydrogen in a GBC-cell

“…1 and is called a GBC-cell, a Gas diffusion electrodepacked Bed electrode Cell. This cell is similar to that described in [10], except for the packed bed of carbon rods in the solution compartment of the cell. The cell has two compartments, viz.…”