I am working with platinum nanoparticles entrapped polymer for fuel cells. For measuring its ORR activity, glassy carbon modified with polymer entrapped Pt nanoparticles is used as WE, Pt wire as CE and Ag/AgCl, KCl(sat.) as RE in the 0.5 M sulfuric acid. Scan rate 20 mV/s. What could be the reasons for not observing steady state current?
Why Current is not increasing after increasing the rotation speed?
Please inform me possible reasons and how to obtain steady state current which will depend on different rotation speed for tafel plot calculations.
Bhushan San,
I guess, you performed your experiment in O2 saturated solution and were continuously purging during experiment. Did you repeat ORR activity at 100 rpm just after 1200 rpm? Did you find any difference after repeating at 100 rpm? Make sure that your Pt nanoparticles are not falling off during the rotation or it is surely entrapped Pt nanoparticles. Because the polarization curves that you provided showed poor ORR activity (onset potential) compare to many reported Pt catalyst. You can compare the characteristic CVs in N2-H2SO4 solution before and after ORR activity. BTW, you should run experiment high rotation to low rotation speed.
Have fun!
Thank you for your reply and suggestions. I will check for it. Since particles density is too low. It is very hard to observe characteristic CV but from XPS, TEM and edax we are sure that there are Pt nanoparticles. So it is really very difficult to confirm whether Pt particles are detached or still present on the surface. Yes, the solution was O2 saturated and continuously bubbling during the experiment. But when I check the similar experiment with bare Pt electrode I did not have any problem so I just continued with the same set up for modified electrode. I will do the experiment as per your suggestions from high to low rpm.
Check TEM/EDX of your catalyst after activity from where you can confirm the stability (detached of Pt). As you provided the polarization curves, first two rpm (100 & 200) current was increased and rest of rpm almost same current. This is might due to the detachment of Pt nanoparticles. Another possibility, the polymer that you used has any negative effect (may reduce the Pt activity). Sometimes electrode needs to soak in the same electrolyte solution for a while to wet the electrode surface which may help to easy access of your electrolyte to catalyst surface.
Dear Masud san,
Thank you very much for your suggestions. Now I can observe steady state current with different rotations. There was not leaching of pt particles but poor conductivity of polymer was the problem so after reducing amount of loading on electrode surface it worked.
I am following your other suggestions. Thank you very much!
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