I was wondering if I need to widen my window since I do not see any peaks for my electrocatalyst? There is a noticeable hydrogen evolution tail so I know I am on the right track but I expected the hydrogenation peak to be closer to that end instead. The CV I obtain is attached, depicting a linear increase as the voltage increases. If I don't need to widen my voltage window, does that mean that my catalyst is kinetically slow at hydrogen oxidation?
Thanks in advance!
There is no oxidation peak of hydrogen in aqueous solution in cyclic voltammetry. in the cathodic side there is a reduction of H+ protons (2H+ + 2e- === H2) and release of hydrogen gas. This gas is insoluble in electrolytic solution. so, there is no hydrogen in the solution, there is no peak of hydrogen oxidation.
Cordially.
As Oualid pointed out, you won't see electrochemical reactions that involve H2 as a reactant (substrate) unless there is a significant concentration of H2 at the electrode. I don't think that H2 dissolves in aqueous solution to any more than about 15 ppm (and that's under 1 atm of H2).
You might be able to observe this by switching to a solvent that hydrogen is soluble in ( http://pubs.acs.org/doi/abs/10.1021/je00041a010 )
Is hydrogen oxidation the purpose of your catalyst?
Hi Aaron and Oualid,
I apologize for the misunderstanding but I am running it in a solid polymer reactor (like a fuel cell) so there shouldn't be any issues with insolubility. Does this new information change the situation? I am aiming to see HOR and HER on my catalyst.
Yes, thank you Sarah, that changes the picture entirely!
New questions: What pH, pressure and temperature are you operating at? And what is the potential shown at the bottom of the CV is relative to?
Also, what is your counter electrode? Are you sure that it will do HER (or ORR) when your working electrode is trying to do HOR? (probably not a problem, but just checking)
Also, just looking at the shape of your CV, I have some questions:
1) Just to be sure we are on the same page: a higher potential shown on the x axis means more oxidizing, and a positive current indicates HOR or competing reaction while a negative current indicates HER or competing reaction? (if this is incorrect, the rest of my questions are moot)
2) In the range above about 200 mV we some non-negligible currents in the CV. Is this due to capacitance or Faradaic current? If you perform chronoamperometry at say 500 mV for 20 minutes, does the current hold steady at an unambiguously non-zero value, or does it drop off very quickly?
3) It looks like the HER wave that is just starting at the bottom left is much steeper. If you sweep to slightly more reducing potentials, what sort of current densities do you get? What is the ratio between the j/v slope for HOR vs HER?
4) This one is just a comment: despite the concept of microscopic reversibility, most catalysts are much more effective for a given reaction than they are for the reverse reaction. This is usually much more of an issue with OER/ORR than HER/HOR, but you might also just have a catalyst that is particularly bad at HOR...
Hi Aaron,
The pH is acid (probably around 1), the pressure is atmospheric, and the temperature is 30C. The humidifiers are set to 35C so the membrane should be well humidified.The anode is Pt/C, acting both as a counter and reference. I have tested the same anode catalyst with a different cathode (Pd black) and the CV does show hydrogen adsorbed and desorbed. The CV I attached is not what I have personally obtained but what I expect to see where the hydrogen peaks are below 0.4V; the hydrogen adsorption is when it is at the negative currents and the hydrogen desorption is when it is at the positive currents.
1) Yes, I believe we are on the same page but to make sure I attached a CV of what I expect to see where the hydrogen peaks are below 0.4V; the hydrogen adsorption is when it is at the negative currents and the hydrogen desorption is when it is at the positive currents. But I could be wrong to expect to see those peaks since I saw it with Pd black.
2) I think it is just the Faradaic current but I'm not sure. I haven't held it at a constant voltage but I have held it at constant current where the voltage is relatively stable.
3) I have swept it below 0V and I observe a linear hydrogen evolution tail. At -100mV, I get about -12mA/cm2 but since I don't see any HOR behavior, I'm not sure how to obtain that ratio.
4) That's very true and I want to make sure that I have done what I can before deeming it a bad catalyst for HER/HOR. Thank you for providing me some insight on how to look at the CV.
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