A calibrated hydrogen-peroxide direct-borohydride fuel cell model

A numerical model with global reaction rates is calibrated to measurements from a simple hydrogen-peroxide direct-borohydride fuel cell (H2O2-DBFC), and then used to unravel complex electrochemical and competing parasitic reactions. In this H2O2-DBFC, fuel (1-50 mM NaBH4/2 M NaOH) is oxidized at a Au anode and oxidizer (10-40 mM H2O2/1 M H2SO4) is reduced at a Pd:Ir cathode. Polarization curves and electrode potentials, as functions of fuel and oxidizer feeds support global reaction rate parameter fitting. The measurements and calibrated model showed H2O2 decomposition at the cathode depresses open circuit voltage from 3.01 V theoretical to 1.65 V, and when H2O2 supply is limited, cathode potentials are sufficiently negative to make H+ reduction to H2 thermodynamically favorable. Calibrated model results show that thin concentration boundary layers limit reactant utilization and current density. Decreasing the inlet concentrations, flow rates, and cell voltage slow parasitic reactions and favor desirable charge transfer reactions. Peak conversion efficiency and peak power density coincide because thermodynamic efficiency and parasitic reaction rates decrease (relative to charge transfer reaction rates) with increasing current density. We conclude that the performance of a fuel cell with parasitic side reactions can be predicted through numerical modeling.