MgAl2O4-based humidity-sensing material for potential application in PEM fuel cells

MgAl2O4 ceramic pellets have been investigated as the in situ humidity sensing elements for proton exchange membrane (PEM) fuel cells. The MgAl2O4 powder was synthesized through EDTA-citrates method. When the temperature increased from 50 °C to 80 °C, the ohmic resistance (R) at the whole relative humidity (RH) range decreased by about one order of magnitude while the linearity of Log(R) vs. RH remained constant. The MgAl2O4 specimens sintered at 1200 °C with ball-milled powder show the highest humidity sensitivity with 3.3 orders of magnitude change from RH 40% to RH 100%. Homogenous meso-pore (around 50 nm) might be the root cause for high sensitivity and the macro-pore (>50 nm) is the cause for decreasing the sensitivity of the sensing material. A precise optimization criterion for pore size has been proposed for this RH range. The MgAl2O4-based ceramic pellets show promising performance for the in situ RH sensing for PEM fuel cells.