Digital Potentiostat / Galvanostat Workstation
Precision bipotentiostat with sub-picoampere current resolution, 16-bit DAC potential ramps, and active IR-drop compensation.
Chemistry / Cyclic Voltammetry & Diffusion
FREE TO EXPLORELABORATORY 37 · NATURAL SCIENCES
Diagnostic Cyclic Voltammetry and Mass Transport Kinetics via the Randles-Ševčík Equation
Determine the aqueous diffusion coefficient of the ferricyanide anion [Fe(CN)₆]³⁻ using cyclic voltammetry at a glassy carbon electrode across scan rates from 10.0 mV/s to 200.0 mV/s via the Randles-Ševčík equation. Explore interactive analytical gravimetry, Class A volumetric glassware and density determination.
MEASURE · CALIBRATE · ANALYSE
Your virtual chemistry laboratory.
PEAK CATHODIC CURRENT I_PC—
MEASUREMENT STATUS
Ready to dispense 50.0 mV·s⁻¹ of liquid.
Adjust ν_scan V, then weigh the dispensed aliquot.
Mass observations are determined by the high-precision thermodynamic equation of state for pure liquid water. Readings reflect thermal equilibrium and analytical balance force restoration.
Physical chemistry assumptions and metrological limits
['The simple Randles-Ševčík equation assumes planar semi-infinite linear diffusion; at extremely slow scan rates (< 1 mV/s), spherical edge diffusion at microelectrodes causes positive deviations.', 'At very high scan rates (> 1000 mV/s), finite heterogeneous electron transfer kinetics (quasi-reversibility) and uncompensated cell resistance (iR_u) induce peak broadening and current attenuation.', 'Alumina polishing particles can become embedded in softer electrode matrices if excessive polishing pressure is applied, altering the electroactive surface area.'] The Randles-Ševčík equation for a reversible soluble redox couple at 25.00 °C (298.15 K) is i_pc = (2.686 × 10⁵) · n³/² · A · c · D¹/² · ν¹/², where n = 1, A = 0.07069 cm² (3.00 mm diameter glassy carbon disk), and c = 5.000 × 10⁻⁶ mol·cm⁻³ (5.000 mM K₃[Fe(CN)₆] in 1.000 M KNO₃). Across scan rates from 10.0 mV/s to 200.0 mV/s, peak cathodic currents increase from 26.18 μA to 117.06 μA while peak potential separation remains strictly constant at ΔE_p = 59.2 ± 0.5 mV. Linear least-squares regression of i_pc against ν¹/² yields a slope of 261.74 μA·(V·s⁻¹)⁻¹/² with R² = 0.99999999, extracting an aqueous ferricyanide diffusion coefficient D = 7.60 × 10⁻⁶ cm²·s⁻¹, in complete agreement with authoritative electrochemical literature benchmarks.
Analytical chemistry apparatus & tools.
Glassy Carbon Working Electrode (GC)
High-density vitreous carbon disk embedded in Teflon shroud (diameter 3.00 ± 0.01 mm, area A = 0.07069 cm²) mirror-polished with 0.05 μm alumina slurries.
Saturated Calomel Reference Electrode (SCE)
Double-junction reference electrode (+0.2412 V vs SHE at 25 °C) featuring a porous Vycor frit that establishes stable reference potential without chloride contamination.
Platinum Mesh Auxiliary (Counter) Electrode
Coiled platinum wire gauze (surface area > 2.0 cm²) facilitating unconstrained counter-current flow without polarizing the cell.
Thermostated Water-Jacketed Electrochemical Cell
Five-neck glass cell with water jacket maintained at 25.00 ± 0.02 °C, equipped with an argon bubbling tube and gas blanket head.
High-Purity Argon Purge & Blanket Gas System
Argon deoxygenation line with presaturator scrubbers to deoxygenate electrolyte solutions for 15 minutes, removing electroactive dissolved O₂.
FOLLOW THE METHOD
A reason behind every step.
Determine the aqueous diffusion coefficient of the ferricyanide anion [Fe(CN)₆]³⁻ using cyclic voltammetry at a glassy carbon electrode across scan rates from 10.0 mV/s to 200.0 mV/s via the Randles-Ševčík equation. Suggested independent volumetric settings: 10.0, 25.0, 50.0, 100.0, 150.0, 200.0 mV·s⁻¹.
01
Working Electrode Polishing & Microscopic Inspection
Polish the glassy carbon electrode on microcloth pads using aqueous alumina slurries (1.0 μm, 0.3 μm, and 0.05 μm successively) in figure-eight patterns. Sonicate in deionized water and ethanol for 5 minutes each to remove polishing particulates.
02
Electrolyte Formulation & Supporting Salt Addition
Prepare 50.0 mL of standardized 5.000 mM K₃[Fe(CN)₆] in 1.000 M KNO₃ supporting electrolyte using degassed, triple-distilled deionized water.
03
Cell Assembly & Argon Deoxygenation
Assemble the three-electrode cell in the 25.00 °C jacketed vessel. Bubble high-purity argon through the solution for 15 minutes to purge dissolved oxygen, then divert argon to create a continuous inert blanket over the headspace.
04
Potential Window Selection & Baseline Verification
Configure the potentiostat between initial potential E_i = +0.600 V and switching potential E_s = -0.100 V vs SCE. Execute a blank run in 1.0 M KNO₃ to verify that residual background currents remain below 0.1 μA.
05
Multi-Scan Rate Cyclic Voltammetric Acquisition
Record cyclic voltammograms across scan rates ν = 10.0, 25.0, 50.0, 100.0, 150.0, and 200.0 mV/s. Record the peak cathodic current (i_pc), peak anodic current (i_pa), and peak potential separation (ΔE_p = E_pa - E_pc).
06
Randles-Ševčík Diagnostic Regression & Diffusion Extraction
Verify reversibility criteria (ΔE_p ≈ 59 mV, i_pa/i_pc ≈ 1.0). Plot peak cathodic current i_pc against ν¹/² (in (V/s)¹/²). Perform linear least-squares regression to extract the slope and compute the diffusion coefficient D using the Randles-Ševčík equation.
YOUR NOTEBOOK · 0 OBSERVATIONS
Turn measurements into quantitative chemical insight.
Points are your recorded gravimetric observations. The regression line validates the linear mass-volume proportionality and extracts density.
ORDINARY LEAST-SQUARES FIT · m = ρ·V + m₀
i_{pc} = 0.4463 \cdot n F A c \left(\frac{n F \nu D}{R T}\right)^{1/2} \implies i_{pc} = 261.74 \cdot \nu^{1/2} \implies D = 7.60 \times 10^{-6}\text{ cm}^2\cdot\text{s}^{-1}
| # | Voltammetric Potential Scan Rate ν (mV·s⁻¹) | Peak Cathodic Current i_pc (μA) | Square Root of Scan Rate ν¹/² (V¹/²·s⁻¹/²) | Peak Cathodic Current i_pc (μA) | Remove |
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