I made several ORR catalyst for PEMFC but after putting the catalyst in vial/glass bottle/polybags, I observe decrease in onset/peak potentials with the passage of time. e.g. if I test my catalyst today then its performance is good but after some days/month in a vial, I make fresh catalyst ink and its performance is very bad. Is it normal that every NPMC degrades like this (attached) with the passage of time? what's the cause of this sort of degradation and how should we store catalyst powder so that we may test it in future without any performance loss?
Dear Muhammad,
NPMC are susceptible to various forms of deactivation, particularly oxidation in ambient environments. For instance, if you are looking at a concrete building or wall and notice streaks of reddish brown scattered about, you are observing solubilized iron oxide products (mostly Fe3+) that have spontaneously formed from the metallic iron supports and leached through the concrete.
Humidity, light, and ambient oxygen are all it takes to create these oxide products which may deactivate your material, therefore it is suggested that you purge your containment vessels with an inert gas such as N2 or Ar, and keep them in a dark refrigerator to minimize the rate of these processes.
Furthermore, if you are working with alloy NPMCs you may want to investigate their relative standard potentials (chart link here: https://en.wikipedia.org/wiki/Standard_electrode_potential_(data_page) ). Various transition metals that are in direct contact can spontaneous oxidize others over time, which may be a contributing factor to the deactivation. This idea forms the basis for many batteries!
I hope these suggestions provide a good basis for a better understanding your system, good luck!