Definition of Operational Regimes for PEMFC through Dimensionless Numbers

I. SCHMIDHALTER; P. AGUIRRE

Buenos Aires

Congreso; 20th Topical Meeting of the International Society of Electrochemistry; 2017

Division 3 Electrochemical Energy Conversion and Storage Division 4 Electrochemical Materials Science ISE Region Argentina

Through the present work a dimensionless number relating, the diffusive flux, the convective flow, and reaction rate for reactants (H2/O2/H2O) in Proton Exchange Membrane Fuel Cells (PEMFC) is defined. It allows determining the operational regime for PEMFCs previous to any simulation of the entire system. This number is defined as the ratio maximum reaction rates to maximum diffusion rates. The data needed for its calculus are, geometric dimensions, physical properties of the electrode, feeding conditions, and operational conditions. The maximum reaction rate is computed assuming no diffusion limitation in the Gas Diffusion Layer (GDL). Thus, no variation in composition of the reactants through GDL is obtained. The maximum current density is achieved when output potential of the cell attain zero. This calculus includes the solution of a simple algebraic system of equations containing the electrochemical relationships of the PEMFC. The maximum diffusion rate is computed when depletion of the reactants at membrane-GDL interphase is achieved. The dimensionless number obtained has been checked by means of the solution of the whole PEMFC model, showing a significant agreement. Maximum reaction rates and maximum diffusion rates can be computed for different cells arrangements and different utilization factors of reactants giving raise to the definition of inlet and outlet numbers. Some study cases are presented showing changes of the limiting regime along the cell length according to the dimensionless number calculated at both cell ends.