Which device uses an electrochemical reaction to generate an electric current at a constant voltage?

• A. Battery
• B. Electrochemical cells
• C. Fuel cell
• D. Capacitor

Answer: (B)

At the heart of this question is how chemical energy is turned into electrical energy through a redox reaction. An electrochemical cell provides a defined potential difference between two electrodes in an electrolyte. When you complete the circuit, electrons flow from one electrode to the other, producing an electric current. The cell’s emf sets a value for the voltage that remains essentially constant while reactants are available, so the current is drawn at a steady potential during operation. That direct conversion of chemical energy into electrical energy with a stable voltage is the hallmark of an electrochemical cell.

A capacitor, on the other hand, stores energy electrostatically and does not rely on a chemical reaction to generate current. A battery is made up of multiple cells, so while it also uses chemical reactions, the fundamental unit that matches the description of generating current from a chemical reaction with a stable voltage is the electrochemical cell. A fuel cell is a specialized type of electrochemical cell that continuously consumes fuel, but the basic concept remains the same: chemical energy converted to electrical energy via a redox process.