Regenerative Solid Oxide Fuel Cells for Mars Exploration

Abstract

A regenerative solid oxide fuel cell was designed, built, and tested for Mars exploration. The fuel cell operates at night on CO and excess O2 generated from the Mars atmospheric C02 during the day. The primary objective of the device was to generate O2 from the Mars atmosphere for use as ascent vehicle propellant. The cells tested were composed of a 8-mole percent yttria stabilized zirconia (YSZ) electrolyte and 2 platinum electrodes. The fuel cell was tested by connecting it to an external circuit with adjustable resistance and then measuring cell voltage and current for different load points. The results obtained were consistent with the theoretical relations predicted by thermodynamics and electrochemistry. The performance loss of the fuel cell, observed during the first 40 hours of operation in the fuel cell mode, was attributed to chemisorbtion of CO in the platinum electrodes. It was found that the concentration overpotential was negligible and the calculated activation overpotential fit well with the Tafel equation. The results suggest that operating O2 generator cells as fuel cells with low fuel utilization at night has distinct advantages for Mars missions.