1. Lecture 09 Experimental Techniques - Two vs. Three Electrode Setup -
Reference.
Zhebo Chen et al, Journal of Materials Research 25, 3 (2010).
A.J. Bard and L.R. Faulkner, Electrochemical Methods: Fundamentals and Applications, Wiley, 2001.
R. Memming, Semiconductor Electrochemistry, Wiley-VCH, 2000 (e-book).
Lecture note

2. Photoelectrochemical (PEC) cells
Solar H2 Production :
Photoelectrochemical (PEC) cells
2H2O O2
4H+ + 4e-
2H2 H2
p-Semiconductor
Counter Electrode
4H+
4e-
As we’ve seen this week, there are many interesting talks about producing Hydrogen fuels using sunlight and water at semiconductor interfaces. Briefly in ideal photoelectrochemical cells as schematically shown here, a semiconductor with band-gap over 1.7 eV can split water to produce H2 at semiconductor/water interface with sunlight. But unfortunately, there are very few photoelectrochemical materials and systems satisfies reliable and efficient PEC water splitting. So there are intense research on searching materials and systems, such as III-V and metal oxide semiconductors.
How to measure H2 production in a PEC cell?

3. PEC Experimental Setup
For PEC measurement, we need only anode and cathode, but why reference electrode?

4. Two Electrode Measurement
Counter
electrode
In two electrode measurement, independent potential drop occurs at both WE and CE.
And those potential drop can not be independently resolved. In other word, we can only measure the sum of potential drop at WE and CE.

5. Three Electrode Measurement

6. Reference Electrode (RE) - Normal Hydrogen Electrode -
Standard to measure a potential at a working electrode
Difficult to measure electrochemical reaction in other pH solution
But set-up is very difficult

7. Requirements of Reference Electrode
Ideal polarizable electrode
Ideal non-polarizable electrode

8. Other Reference Electrodes
Standard Calomel Electrode (SCE)
Ag/AgCl Electrode

9. Energy Scale of Reference Electrodes
Ag/AgCl = V vs. NHE

10. In pH = 1, at what potential vs
In pH = 1, at what potential vs. Ag/AgCl reference electrode does hydrogen evolution reaction occurs?

11. OK.
Now we know why we use a reference electrode.
But for water splitting efficiency, what electrode setup should we use?

12. PEC Water Splitting Efficiency - Solar to Hydrogen (STH) Efficiency -or
Only in two electrode measurement
No pH biasing!
No sacrificial donors/acceptors!

13. Next Meeting
Solid-liquid interfaces