The role (or lack thereof) of nitrogen or ammonia adsorption-induced hydrogen flux inhibition on palladium membrane performance

• Pd/YSZ membrane exposed to N2 and NH3 soaks for 24 h, 1 MPa between 598 K and 773 K.
• H2 flux corrected for Knudsen flow through defects, pressure dependence calculated.
• No H2 flux inhibition observed for pure N2, NH3 or equimolar H2/N2, H2/NH3 exposure.
• Apparent H2 flux inhibition after He soak, linked to Pd surface restructuring.
• Air exposure to roughen Pd surface prevented further H2 flux reduction.

The potential impact of nitrogen and ammonia exposure on hydrogen permeance through thin palladium membranes (1.3 µm to 4.1 µm thick) fabricated by electroless plating was studied. Additionally, a robust approach is introduced to quantify the pressure exponent which accounts for contributions to Knudsen flow through defects present in very thin membranes. In sharp contrast to previously published results, no flux inhibition was observed due to nitrogen or ammonia exposure. Studies included 24 h exposures to both pure gases and equimolar hydrogen/nitrogen or hydrogen/ammonia mixtures at trans-membrane pressures ranging up to 1.0 MPa and temperatures of 598 K to 773 K. One membrane did exhibit significant flux inhibition after helium exposure, but this was attributed to changes in surface microstructure associated with hydrogen departing the lattice. This apparent hydrogen flux inhibition behavior was permanently eliminated by air exposure which roughens the surface, and it is suggested that this surface structure mechanism is a more probable explanation for flux inhibition than adsorption of nitrogen–based species.