The open circuit voltage of any storage cell depends wholly upon

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Examoogle · Accepted Answer

all of the above

Explanation: The open circuit voltage (electromotive force) of a storage cell is not a fixed constant but is determined by the electrochemical potential difference between the electrodes, which is inherently influenced by the materials used, the chemical state of the electrolyte, and the thermal energy of the system.

Working Principle: The cell potential is governed by the Nernst equation, which explicitly relates the cell voltage to the activity (concentration) of the reactants and products in the electrolyte. Furthermore, temperature affects the reaction kinetics and the standard electrode potentials according to the Gibbs free energy relation, $\Delta G = -nFE$, explaining why temperature fluctuations alter the output voltage.

Key Formulas: $E = E^0 - \frac{RT}{nF} \ln(Q)$ — Nernst equation showing dependence on Temperature ($T$) and Reaction Quotient ($Q$ or electrolyte concentration); $\Delta G = \Delta H - T\Delta S$ — Thermodynamic relation showing the temperature dependence of cell potential

Key Points: The standard potential $E^0$ is defined by the chemical constituents (Anode/Cathode materials).; Electrolyte strength (concentration) changes the activity of ions, shifting the potential.; Temperature affects both the Nernst term and the equilibrium constant of the chemical reaction.; The open circuit voltage represents the maximum potential difference when no current is flowing.

Advantages: Predictable behavior under known environmental conditions.; Allows for state-of-charge (SoC) estimation using voltage measurements.

Disadvantages: Voltage readings alone can be misleading without temperature compensation.; Electrolyte degradation over time shifts the nominal OCV.

Applications: Battery Management Systems (BMS) for EVs.; Portable electronics power monitoring.

Additional Info: Option A is true as the choice of electrodes (e.g., Pb-PbO2 vs Ni-Cd) dictates the basic EMF.. Option B is true because electrolyte concentration directly influences the ion activity coefficients.. Option C is true because thermodynamics dictates that cell potential varies with temperature.

Answer: D is correct — The open circuit voltage of a storage cell is a function of its chemical material composition, electrolyte concentration, and operating temperature.

Exam Tip: Always remember that in battery technology, OCV is a state function—it depends on the current internal state variables ($c, T$) and not on the history of the cell.

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