--- title: "Fuel cell and its working" subject: "Energy Environment and Society" chapter: 3 key: "semester_7/energy_environment_and_society:fuel-cell-working" source: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/fuel-cell-working site: BCT Engineering --- # Fuel cell and its working Energy Environment and Society · Chapter 3: Renewable Energy Sources - Asked in: 2069 Chaitra, 4 marks; 2071 Shrawan, 3 marks; year not given (asked 2 times) - Video: [How Do Hydrogen Fuel Cells Work?](https://www.youtube.com/watch?v=R6AdX-bdDaw) — Reactions - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/fuel-cell-working - Whole chapter: https://www.bctengineer.com/md/semester_7/energy_environment_and_society/chapter-3 ## Question What is a fuel cell? Explain briefly how it works (how does a hydrogen fuel cell function?). ## Short answer A fuel cell is an electrochemical device that converts hydrogen and oxygen directly into electricity, heat, and water. At the anode, H2 splits into H+ and e-; H+ cross the electrolyte while e- flow externally. At the cathode, O2 combines with them to form water. Overall: 2H2 + O2 → 2H2O. ## Answer A **fuel cell** is an electrochemical device that converts the chemical energy of a fuel (usually hydrogen) and an oxidant (oxygen or air) directly into electricity, heat and water, without combustion. It works as long as fuel is supplied, unlike a battery, which stores a fixed amount of energy. #### Construction Two electrodes (anode and cathode) separated by an **electrolyte**, with a catalyst (platinum) on each electrode. ```text H2 in --> [ANODE | ELECTROLYTE | CATHODE] <-- O2/air in (-) H+ -> (+) \__ e- through load __/ Output: electricity + water + heat ``` #### Working of a hydrogen fuel cell (PEM type) 1. Hydrogen is fed to the anode. The catalyst splits it into protons and electrons: **Anode: 2H₂ → 4H⁺ + 4e⁻** 2. The electrolyte (a proton-exchange membrane) lets only H⁺ pass to the cathode. The electrons cannot pass through the membrane and take the external circuit, producing DC current. 3. At the cathode, oxygen combines with the protons and returning electrons to form water: **Cathode: O₂ + 4H⁺ + 4e⁻ → 2H₂O** 4. Overall: **2H₂ + O₂ → 2H₂O + electricity + heat** One cell gives about 0.6–0.8 V, so many cells are stacked in series to form a stack with higher voltage. #### Features - Efficiency 40–60% (higher with heat recovery), quiet, no moving parts. - Pollution-free at the point of use (only water). - Used in vehicles, backup power, space missions and portable devices. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How does a fuel cell differ from a battery? A. It stores more energy in a closed cell B. It burns fuel in a combustion chamber C. It works as long as fuel is supplied; a battery stores a fixed amount of energy D. It produces AC directly Answer: C. A fuel cell converts supplied fuel electrochemically without combustion and does not run down like a battery. (Key point: Fuel cell vs battery) 2. What does the PEM electrolyte do? A. Lets electrons pass through directly B. Lets only H+ pass; electrons must go through the external circuit C. Passes oxygen to the anode D. Splits hydrogen into protons Answer: B. The membrane conducts protons only, forcing electrons through the load to give DC current. (Key point: Electrolyte role) 3. What happens at the cathode of a hydrogen PEM fuel cell? A. O2 + 4H+ + 4e- gives 2H2O B. 2H2 gives 4H+ + 4e- C. H2O splits to H2 and O2 D. O2 gives 2O2- Answer: A. Oxygen combines with protons and returning electrons to form water at the cathode. (Key point: Cathode reaction) 4. Why are cells stacked in series? A. To increase fuel efficiency to 100% B. To avoid use of a catalyst C. One cell cannot produce current D. One cell gives only about 0.6-0.8 V Answer: D. Series stacking adds cell voltages to get a useful voltage. (Key point: Stack voltage) ## Related in Energy Environment and Society - [Hydrogen fuel advantages and disadvantages](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Ahydrogen-fuel-adv-disadv) — Energy Environment and Society, chapter 3, asked 3× - [Hydrogen fuel compared with solar](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Ahydrogen-fuel-solar-comparison) — Energy Environment and Society, chapter 3 - [Solid oxide fuel cell](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Asofc-construction-working) — Energy Environment and Society, chapter 3, asked 2× - [Proton exchange membrane fuel cell](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Apemfc-working) — Energy Environment and Society, chapter 3 - [Working of a solar cell](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Asolar-cell-working) — Energy Environment and Society, chapter 3 - [Hydrogen production and storage](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Ahydrogen-production-storage) — Energy Environment and Society, chapter 3 ## Related in other subjects - [Fuel cell voltage, efficiency and hydrogen use](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Afuel-cell-stack-numerical) — Energy Resources, chapter 6 - [Working principle and types of fuel cells](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Apem-fuel-cell-working-types) — Energy Resources, chapter 6 - [Standard hydrogen electrode; Mg/Ag cell emf](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Ashe-mg-ag-cell) — Engineering Chemistry, chapter 1 - [Normal hydrogen electrode; Ni/Cu cell emf](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Anhe-ni-cu-cell) — Engineering Chemistry, chapter 1