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Gas diffusion electrodes are used for many purposes, for example in fuel cells, in synthesis and as anodes in electrodeposition processes. The behaviour of gas diffusion electrodes has been the subject of many studies. In this work the transport of gas in the gas diffusion electrode, characterized by the overall mass transport coefficient, has been investigated using hydrogen-nitrogen mixtures. A reactor model for the gas compartment of the gas diffusion electrode test cell is proposed to calculate the concentration of hydrogen in the gas compartment as a function of the input concentration of hydrogen and the total volumetric gas flow rate. The mass transport coefficient is found to be independent of variations in hydrogen concentration and volumetric gas flow rate. The temperature dependence of the mass transport coefficient has been determined. A maximum was found at 40 ° C. /hp volumetric flow rate at the inlet of the gas k~ compartment (m -3s l) volumetric flow rate at the outlet of the gas n compartment (m -3 s 1) volumetric flow rate of reactive component T into the gas diffusion electrode (m-3s 1) Vm q NotationFaraday constant (A s mol ~) current for gas diffusion electrode (A) current density for gas diffusion electrode (A m -2) diffusion limited current for gas diffusion electrode (A) diffusion limited current density for gas diffusion electrode (A m -a) calculated diffusion limited current for gas diffusion electrode (A) calculated diffusion limited current density for gas diffusion electrode (A m -2) current for hydrogen production (A) mass transport coefficient calculated from Cout (m s 1) number of electrons involved in electrode reaction temperature (°C) molar volume of gas (m 3 mol-1 ) overpotential (V)

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) ©

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