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 http://les.kaist.ac.kr/B_Lecture

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?

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

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.

Three Electrode Measurement

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

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

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

Energy Scale of Reference Electrodes Ag/AgCl = 0.197 V vs. NHE

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

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

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

Next Meeting Solid-liquid interfaces