Nitrous Oxide As an Oxidizer for Dual Use Fuel Cell / Thrust Systems in Space Applications

Abstract

Nitrous oxide (N2O), a non-toxic chemical which can be stored in a liquefied state under moderate pressures(52 bar) without cryogenic storage, is a reactant which can be used to generate electricity or propel aspacecraft. It has been investigated as a cold gas propellant, monopropellant, and bipropellant; particularlyin the field of small satellites.[1,2] Nitrous oxide can also be used to generate electricity by acting as theoxidizer in a fuel cell where N2O reduction occurs at the cathode and a fuel such as H2 is oxidized at theanode.[3] Although the equilibrium potential in standard state aqueous electrolytes is 1.76 V vs SHE,[3] large overpotentials in aqueous electrolytes make it difficult to efficiently extract power from this reaction. Theelectrochemical reduction can be more readily achieved in a solid-oxide fuel cell (SOFC) with an oxygenion conductor for an electrolyte following the reactions in equations 1 and 2.[4] SOFCs also enable the useof alternative fuels such as hydrocarbons, CO, and NH3. Additionally, the reaction product N2 is expectedto be usable as a cold gas propellant. Cathode: \U0001d4412\U0001d442 + 2\U0001d452− → \U0001d4412 + \U0001d4422− (1)Anode: \U0001d43b2 + \U0001d4422− → \U0001d43b2\U0001d442 + 2\U0001d452− (2) We report on a SOFC device consisting of a Ni anode, a LaSrMnO3 cathode, and a Sc-doped ZrO2 electrolyte substrate. The maximum operating power which can be extracted from this system using N2Oas an oxidizer and H2 as a fuel, the conversion efficiency of N2O to N2, and a comparison of the performanceof N2O with air and O2 are all evaluated under a range of operating temperatures and flow rates.