Hi,
I am trying to determine which parameter (current or voltage) is more important for electrochemical hydrogenation. I understand that current is directly related to the rate of electron flow but the voltage at the applied current also determines how the reaction proceeds. Essentially, I want to know that when to determine which parameter is more important for hydrogenation from a CV.
Without knowing your system, I would say, that it is the voltage you should control.
The reaction rate (the current) will be dependent on many parameters that may vary (also with time,) e.g. reactant concentration, convection/stirring, catalytic conditions etc.
The voltage controls the thermodynamic condition - the oxidation potential, and thereby what reaction(s) that can occur at the electrode.
Hello,
Thank you for your responses. Keld West, the reasons for using either makes a lot of sense since I would like to control the selectivity of my reaction.
I am using 20% Pt/C as my anode and Pd black as my cathode; the set up is similar to H2/O2 fuel cells except the O2 is replaced with an inert gas saturated with my organic molecule.
While taking your system into consideration, I would suggest to apply constant potential for selective electrode reaction. You may need to go for CV curve first to get oxidation peak potential .
I agree with going for voltage control. It is the potential, that is relevant for the theoretical calculations, as already mentioned by Keld West in the first reply in this thread.
Dear Sarah Carl,
as Prof. Keld West (and Ole L. Trinhammer) Voltage control. More specifically, Voltage vs Ref. electrode, is more clear.
It was very important what prof. Samaras said. If you work in a 3 electrodes cell, choose constant voltage control. But if you use a 2 electrodes cell, the only chance is to use constant current density (to compare different runs).
I am using a 2 electrode set up but when at constant current, the voltage is extremely high that I believe it is destroying the electrodes. Also, I thought that if my counter (Pt) has a high enough surface area compared to the working (Pd), my counter can also be a stable reference electrode, allowing me to be able to reliably run at constant voltage?
The voltage WORK - COUNTER is not so relevant, but the potential of your working electrode is critical.
Add to your 2 electrodes set up a REF electrode and a common voltmeter between REF and WORK. Increase voltage until you have a relevant high current. Verify if the potential of WORK electrode vs. REF is in agreement with the intended electrochemical process. The value for current is correct only if it is confirmed by the potential of the WORK electrode.
The current value is the same in any section of your circuit (including the redox process at electrodes). Thus if you want a constant rate for the electrochemical process, choose to maintain/control a constant current density. Monitor the voltage measured between WORK and REF.
The voltage between WORK and COUNTER is relevant only to calculate how efficiently the energy is spent. It is not an appropriate way to control the rate of the electrochemical process.
Voltage and potential are very different things.
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