How can i convert the potential of reference electrode Ag/AgCl to NHE? The electrolyte is 0.5 M Na2SO4 and the pH is 7. I want to understand method for Mott Schottky calculations. Many thanks for the help.
Hey there Huan Wang! In the electrifying realm of electrochemistry, converting the potential of a reference electrode from the standard silver/silver chloride (Ag/AgCl) to the standard hydrogen electrode (NHE) involves a bit of electrochemical gymnastics. Let's break it down:
1. **NHE to Ag/AgCl Conversion:**
To convert potentials from the standard hydrogen electrode (NHE) to Ag/AgCl, you'd typically use the Nernst equation:
EAg/AgCl=ENHE+ENHE0−EAg/AgCl0, where ENHE0 and EAg/AgCl0 are the standard reduction potentials for NHE and Ag/AgCl, respectively.
2. **Ag/AgCl to NHE Conversion:**
For your case, where you're moving from Ag/AgCl to NHE, you'd rearrange the equation: ENHE=EAg/AgCl+EAg/AgCl0−ENHE0
The standard reduction potentials are typically available in reference tables.
3. **Mott-Schottky Calculations:**
Mott-Schottky analysis is often applied to understand semiconductor properties of materials, especially in the context of electrochemistry.
The Mott-Schottky equation is:
Csc−2=2/(A⋅ε⋅ε0⋅q⋅ND)⋅(E−Efb), where Csc is the space charge capacitance, A is the electrode area, epsilon is the relative permittivity of the semiconductor, epsilon0 is the vacuum permittivity, q is the elementary charge, ND is the donor concentration, E is the applied potential, and Efb is the flat band potential.
Interpretation of Mott-Schottky plots involves extracting information like donor concentration and flat band potential from the slope and intercept.
Remember, I am is here for the ride, and these are complex electrochemical maneuvers. Always ensure you're applying the right equations for your specific system!
Huan Wang Converting Ag/AgCl to NHE potential involves two factors: standard potential difference (E_Ag/AgCl) and pH correction.
The standard potential difference is 0.205 V for 0.5 M Na2SO4 and 0.059 V for pH 7. To convert the Ag/AgCl potential to NHE, add 0.205 V to the measured potential. Mott-Schottky analysis explores the relationship between applied voltage and depletion region capacitance in semiconductors. Measure the current-voltage characteristic under illumination and extract the depletion layer capacitance (C_sc) from the I-V curves.
Use the Mott-Schottky equation:
(C_sc^-2 = 2/(A * ε * ε0 * q * N_D) * (E - E_fb))
to calculate the depletion region capacitance. Interpret the plot by plotting C_sc^-2 vs. E and determining the slope and intercept to extract N_D and E_fb.
Dear Alvena:
Thank you very much for your help. I still have a few questions for your help. Q1. “The standard potential difference is 0.205 V for 0.5 M Na2SO4 and 0.059 V for pH 7.” To convert the Ag/AgCl (pH = 7) potential to NHE (pH = 7), besides adding 0.205 V to the measured potential, should we add the item 0.059V to the measured potential? In some papers (Advanced Materials, 2021, 33, 2106838), when pH = 7, the item 0.059 V * pH (0.059 * 7) was added.
Q2. Moreover, in different electrolytes, the standard potential difference seems to be very different. In many papers, the standard potential difference is 0.197 V. In other words, the standard potential difference is 0.205 V for 0.5 M Na2SO4 and may be 0.197 V in other electrolytes? The electrolyte used in my experiment happened to be 0.5 M Na2SO4.
Q3. For n-type semiconductor, the Efb values measured using the Mott–Schottky method are higher than the conduction band (CB) position by ≈0.1 V~0.3 V. How can we get this value?
Last but not least, thank you very much for your kind help~!
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Dear Driss,
Very sorry for consulting such a basic question. In fact, my major is bioactive materials, thus I don't know much about the field of electrochemistry. My current research project involves some knowledge of electrochemistry, especially Mott Schottky calculations. Hence, I look for help from the experts in the field of electrochemistry. Could you help me?
Best wishes
Dr. Huan Wang
Changchun Institute of Applied Chemistry, P. R. China
Dear Huan Wang,
the Mott-Schottky relation, which represents a capacitive case of constant thickness :
1/𝐶2 = (2/ε εo𝑁𝐷) (𝐸 - 𝐸𝑓𝑏 -𝑘𝑇/𝑒)
C is the capacitance of the semiconductor, ε and εo the dielectric constants of the material and vacuum respectively, ND the charge carrier density, Efb the flat band potential, kT/e the energy of thermal electron agitation.
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