Investigation of Electrochemical Gas Generation in Ion Electrospray Thrusters

Abstract

This work investigates the electrochemical formation of gas-phase species in passively-fed ion electrospray thrusters biased with porous distal electrodes. Volatile reaction products of the ionic liquid propellants EMI-BF4, EMI-Im, and EMI-CF3BF3 are identified using differential electrochemical mass spectrometry. Trace amounts of the same species are independently detected in tests of the electrospray thrusters, where gas appears to be generated at the distal electrode site after 6 hour periods of continuous emission at a beam current of about 200 µA. We find that higher beam currents, smaller electrodes, and singlepolarity emission results in more gas being produced. No solid-phase products or hardware damage are observed in any of these tests. These findings suggest that electrochemistry could be an important efficiency loss in ion electrospray thrusters, even when no visible degradation occurs.