How does a hydrogen fuel cell work step by step?
A hydrogen fuel cell converts chemical energy from hydrogen and oxygen directly into electricity, with water and heat as the main byproducts. In its core, hydrogen’s electrons flow through an external circuit to create electrical power, while protons move through a membrane to combine with oxygen at the other electrode.
Hydrogen fuel cells operate without combustion, using electrochemical reactions rather than burning fuel. This article explains the step-by-step process, the key components involved, and practical considerations for use in cars, power stations, and portable devices.
What a fuel cell does
At a high level, a fuel cell takes in a fuel (hydrogen) and an oxidant (oxygen from air) and converts their chemical energy into electricity. The process is generally quiet, highly efficient relative to combustion engines, and produces water as the main liquid byproduct. The exact sequence depends on the cell type, but the steps below describe the common flow for a polymer electrolyte membrane (PEM) hydrogen fuel cell used in many vehicles and stationary systems.
Step-by-step operation
Below is a step-by-step sequence of how a typical PEM hydrogen fuel cell operates, from fuel intake to electricity, water, and heat byproducts.
- Hydrogen is delivered to the anode (negative electrode) from storage tanks or a reformer that can convert hydrocarbon fuel to hydrogen on-site.
- The anode catalyst splits hydrogen molecules into protons (H+) and electrons (e−).
- Protons migrate through the proton exchange membrane (the electrolyte) toward the cathode, while electrons travel through an external circuit, creating an electric current that can power devices.
- Electrons return to the stack at the cathode (positive electrode) after passing through the external circuit, providing useful electrical power along the way.
- At the cathode, oxygen from the air combines with the incoming protons and electrons to form water (and some heat). In PEM cells, the half-reaction is O2 + 4H+ + 4e− → 2H2O.
- The water produced is managed by the system, helping to humidify the membrane and, in many installations, is vented or collected as liquid water.
- Heat is generated by the electrochemical reactions and must be removed through cooling systems to keep temperatures within an optimal range (typically around 60–80°C for PEM cells).
- The cell stack, made of many individual fuel cells, shares electrical current and voltage to meet the power needs of the application.
- During start-up or high-load transients, the system adjusts gas flow, humidity, and temperature to maintain membrane hydration and performance.
The overall chemical reaction in a PEM hydrogen fuel cell is 2H2 + O2 → 2H2O, meaning electricity is produced as hydrogen is oxidized and oxygen is reduced, with water as the primary byproduct.
Key components and how they fit
Before outlining the components, note that a PEM fuel cell is built from repeating units within a larger stack, designed to maximize surface area for the reactions while distributing reactants and removing products efficiently.
A solid, proton-conducting layer that lets H+ pass from the anode to the cathode while blocking most electrons, forcing them to travel through the external circuit. Thin coatings (often platinum-based) on the anode and cathode that accelerate the electrochemical reactions without being consumed. A porous support that distributes gas evenly to the catalyst, conducts electrons, and helps remove water. Conduct electricity between cells and channel the flow of hydrogen, air (oxygen), and exhaust water, while helping to remove heat. Maintain membrane hydration for optimal proton conductivity and remove excess heat to keep operating temperatures stable. Systems designed to handle the produced water—critically, to balance humidity without flooding the cell or drying out the membrane. Monitoring for pressure, temperature, hydrogen leaks, and overall performance to ensure safe operation.
Together, these components convert the chemical energy of hydrogen and oxygen into direct current electricity, with water and heat as the primary byproducts. The stack design and supporting systems determine efficiency, durability, and suitability for a given application.
Summary
Hydrogen fuel cells generate electricity through a straightforward electrochemical process: hydrogen is oxidized at the anode to release protons and electrons, protons migrate through a membrane to the cathode where they combine with electrons and oxygen to form water, while electrons travel through an external circuit to power devices. A PEM stack with catalysts, diffusion layers, and flow channels handles reactant delivery, product removal, and heat management. The result is clean, efficient power with water as the main byproduct, calibrated by temperature control, humidity management, and system design to meet specific energy needs.
