A process was carried on with Hg/HgO as a reference and with a continuous passage of CO2, and the CV was recorded before and after passage of CO2 (pH changes from 13 to 8). Also, in both the cases a fresh RHE was prepared and potential of reference vs RHE was measured, so that findings could be reported as per vs RHE instead of vs Hg/HgO, but then I am confused because the RHE reference itself changes with pH. So is it sufficient to just ignore RHE shift because of pH changes or does it need to be considered, because with RHE shift considered, observation is quite correct and with RHE shift ignored, the observation is meaningless.
The conversion between Hg/HgO and RHE depends on the pH of the electrolyte.
The below equation gives the conversion between Ag/AgCl and RHE.
E(RHE) = E(Ag/AgCL)+0.0591*pH+0.197 V.
Thanks Santosh this info is helpful, i still have a doubt that what if two RHE's are prepared "freshly" in solutions with diff pH and reference electrode is measured,
..How will the above equation then respond..??
You can see the potential difference between NHE, Ag/AgCl and SHE in Allen J Bard book.preparation and difference in their potentials are clearly given.
If you prepare two different RHE (NHE) they should have similar valur of potential even if they are prepared in two different solutions. Because it is reference electrode who's potential is dependent on solution pH but it should change -59 mV per unit pH according Nernstian equation.
As your solution pH is changing during the course of the experiment, so will also the RHE value. If the reaction you are interested in would change with pH you will be in trouble. My suggestion is that you measure the pH continuously and present the data vs the RHE. Observe that the RHE value vs Hg/HgO will not be constant but change during the course of the experiment.(Venkataraman gave the equation)
thank u for info, Qijin Chi,.. I am using RHE as to standardize all at the data against the single reference only, and, its property to nullify the effect of change of pH in the solution by keeping all reference level to the same zero level.
I could not get the meaning of the phrase "uncertain RHE", could you please explain?
Hi everyone, I am working on characterizing the E1/2 of different catalysts. But I am confused about the reference electrode. Why most researchers convert their potential data with respect to RHE no mater what actual reference electrode they used? Since RHE is dependent on the pH value of the electrolyte, it is not possible to compare the E1/2 values obtained in different electrolytes. Why not convert all the potential data with respect to SHE? More specifically, I am working on the oxygen reduction catalysts. Some researchers test the ORR property in 0.5 M sulfuric acid (pH=0.3) someone prefer 0.1 M perchloric acid (pH=1). When they convert the E1/2 with respect to RHE. The experiment done in the perchloric acid would benefit ~40mV from the electrolyte for the same catalyst. Therefore, I am wondering why the reference point is not set to SHE for the direct comparison of different catalysts?
Hi,
Can anyone help me in the conversion of the SCE to RHE in case of the -ve SCE potentials as in case of HER. Let I have values extending from -0.8V to -0.1 on SCE and I have to convert it to RHE if I use the same formula E(RHE) = E(Ag/AgCL)+0.0591*pH+0.197 V
Then I get more +ve positive (when ph is 14) values. So how can I show it for for RHE in case of HER.
Thanks in advance!
I have seen your question by pure chance. I suggest you to post it as a new topic to allow more researchers to see it. Or read first this discussion:
https://www.researchgate.net/post/How_can_I_convert_RHE_from_the_measured_potentials_in_different_reference_electrodes_and_electrolytes
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