Generally, we can get the semicircle plot of nyquist plot by EIS study. However, sometimes we can also obtain non-semicircle plot(in the figure below). So i wonder that if nyquist plot doesn't have semicircle, how we can interpret it.
Thanks in advance,
Sanghyun.
To get the semicircle you have to start your impedance measurement at zero frequency and then at low frequency. The value of your real part at zero frequency according to inset = Rct +Rrec + Rs. As i see from your impedance spectroscopy curve it is not complete. The part at low frequencies is absent. Do, you have to measure your impedance at low frequencies.
However, if you have an equivalent circuit similar to that shown in the inset you will have to circles which are intervening with each other.
Best wishes
Hi Sanghyun Bae,
Absence of semicircle in Nyquist plot demonstrates minimal distribution of charge storage and Ohmic contact of the studied material with substrates
References:
1. Premathilake, D., Outlaw, R. A., Parler, S. G., Butler, S. M. & Miller, J. R. Electric double layer capacitors for ac filtering made from vertically oriented graphene nanosheets on aluminum. Carbon 111, 231-237, http://dx.doi.org/10.1016/j.carbon.2016.09.080 (2017).
2. Bo, Z. et al. One-step fabrication and capacitive behavior of electrochemical double layer capacitor electrodes using vertically-oriented graphene directly grown on metal. Carbon 50, 4379-4387 (2012). Article One-step fabrication and capacitive behavior of electrochemi...
With regards
Subrata
Thanks for your answer Artur Braun.
I think 'Generally' might give you some confusion.
I wanted to say 'generally' just in my research. sorry
In my research(PEC cell, BiVO4 photoanode), i am able to get the semicircle when i set applied potential above 1.0V vs RHE. However, below 1.0V, i cannot obtain semicircle. So i want to know why i cannot have semicircle at low applied potential.
My measurement condition is
- Amplitude : 20 mV
- Frequency : 100 kHz – 0.1 Hz
Sincerely
Sanghyun Bae
Your answer is a great help for me
Thank you for your answer Artur Braun.
Sanghyun Bae
Hi Sanghyun Bae,
I feel, I hope, that you get the semicircle[1,2], under illumination, only.
Otherwise[2], in high potential you risk (>>1V, near ~1.23 V vs. RHE) to start in developing a bit of some new puzzled[3] mixed current (iphotocurrent+ioxidation), e.g. a developing risk from another upsetting current (ioxidation), due to the water oxidation[4] (partial) current, also.
1. Recall from you (your quote) : "In my research(PEC cell, BiVO4 photoanode), i am able to get the semicircle when i set applied potential above 1.0V vs RHE."
2. CV & EIS not in the dark. Check and compare CV & EIS : 1)in the dark and 2)under illumination.
3. The performance[4] of the photoanode is commonly compared at 1.23 V vs. RHE, the theoretical water oxidation potential.
4. Single-crystalline, wormlike hematite photoanodes for efficient solar water splitting. https://openi.nlm.nih.gov/detailedresult.php?img=PMC3775410_srep02681-f3&req=4
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