Analytical evaluation of heat sources and electrical resistance of a cermet electrode for the production of hydrogen in a membrane reactor

• Analytical expressions for mass and energy transport and transfer inside a cermet electrode.
• Dimensionless number A governs the electrochemical reaction repartition in the electrode.
• Heat sources and the effective resistivity are dominated by electrochemical reaction for A << 1.
• Heat sources and the effective resistivity are dominated by ohmic losses for A >> 1.

This work focuses on the calculation of transfers inside a cermet electrode for solid oxide membrane fuel cells and electrolysers for hydrogen production. A validation of the analytical model previously developed by our group for the calculation of transport quantities inside a cermet electrode was carried out. This model showed that the transport and transfer phenomena in the electrode are controlled by a new dimensionless number named A. This characteristic number is expressed with the parameters of the electrode and governs the repartition of the electrochemical reaction inside the volumetric electrode. The exploitation of this model was extended to predict heat sources and the effective electrical resistance in the membrane electrode in a direct manner and without numerical calculation. The results showed that the behaviour of these quantities follows two regimes: heat sources and the effective resistivity are dominated by the effects related to the electrochemical reaction for A << 1, and by ohmic losses for A >> 1. The effective resistivity and heat sources are lower and less dependent on A in the ohmic regime. This means that increasing the electrochemical capabilities of the electrode, i.e the exchange current density and the density of the number of triple boundary points, along with decreasing the thickness of the electrolyte, is more beneficial than increasing the electrical conductivity of the solid oxide. This model provided guidelines and relevant orders of magnitude for the design of electrodes without using numerical calculation.

Effective resistivity of different phases as a function of A in a symmetrical MEAFigure optionsDownload as PowerPoint slide