Hi All,
I am investigating the electrochemical oxygen evolution reaction in alkaline solution.1.5 V vs RHE is required to reach the anodic current density of 10 mA cm-2 when cyclic voltammetry is carried out. At the same potential (1.5 V vs RHE) when CA is measured, the current density starts from 8 mA cm-2 and produces constant current for few hours. Why this difference is observed in CV and CA?.
Basically, there is no different current densities like CV current density and CA current density. Current density is the same whatever be the type of technique.
The possible reasons for the difference you observed are
1. Your material could be highly capacitive in nature so that the capacitance current might have been added up to your gas evolution current CV. In case of CA, we let the system to reach a steady state and does not allow to polarize. Hence, there could not be such addition.
2. In case when your material is capacitive, the scan rate at which you acquired your CV could also be the issue. Try the slowest possible scan rate (for example 0.1 to 1 mVs-1). Remember that the gas evolution reaction and the associated current density are independent of scan rate. If you see any small increase in OER current with increasing scan rate, that could be due to the addition of capacitive current which increases with increasing scan rate.
3. The CA current density is the steady state current and that represents your catalytic interface's property on overpotential at a defined current density more precisely than the one measured with the polarization curves where we keep on polarizing the interface and does not allow the system to reach an equilibriated steady state. (the data acquired at slowest scan rate like 0.1 mVs-1 in CV or LSV would be 99.99% closer to the data acquired with CA)
4. If you had run simultaneous iR comp during CV measurements, the system would have shown you the iR corrected potential for 10 mAcm-2. In such case, there will always be difference in between the current densities measured at a certain overpotential by CV and CA (during CA such simultaneous iR compensation is not available with the electrochemical workstation that I familiarized with).
Hope it clarifies.
Basically, there is no different current densities like CV current density and CA current density. Current density is the same whatever be the type of technique.
The possible reasons for the difference you observed are
1. Your material could be highly capacitive in nature so that the capacitance current might have been added up to your gas evolution current CV. In case of CA, we let the system to reach a steady state and does not allow to polarize. Hence, there could not be such addition.
2. In case when your material is capacitive, the scan rate at which you acquired your CV could also be the issue. Try the slowest possible scan rate (for example 0.1 to 1 mVs-1). Remember that the gas evolution reaction and the associated current density are independent of scan rate. If you see any small increase in OER current with increasing scan rate, that could be due to the addition of capacitive current which increases with increasing scan rate.
3. The CA current density is the steady state current and that represents your catalytic interface's property on overpotential at a defined current density more precisely than the one measured with the polarization curves where we keep on polarizing the interface and does not allow the system to reach an equilibriated steady state. (the data acquired at slowest scan rate like 0.1 mVs-1 in CV or LSV would be 99.99% closer to the data acquired with CA)
4. If you had run simultaneous iR comp during CV measurements, the system would have shown you the iR corrected potential for 10 mAcm-2. In such case, there will always be difference in between the current densities measured at a certain overpotential by CV and CA (during CA such simultaneous iR compensation is not available with the electrochemical workstation that I familiarized with).
Hope it clarifies.
I think, it might due to resitance of the electrolde/electrolyte interface. If you use 3D substrate or high conduct substrate we might not get it. However, I got similar problem bcoz I used GCE for HER.
The concept is same wherever we apply. I beleive the internal resistnce might be problem or reference electrode. Very recently, Ag/AgCl used for HER they founf silver leakge through capilatryto reduce the current density, and they used Hg/Hg2SO4 they observed no current loss during CA studies.
You can see the paper from "Silver Leakage from Ag/AgCl Reference Electrodes as a Potential Cause of Interference in the Electrocatalytic Hydrogen Evolution Reaction"
A good piece of work from this Dr. Symes
group.
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