Where does the water go in a hydrogen fuel cell car?
In a hydrogen fuel cell car, the water produced by the fuel cell is mostly expelled as water vapor through the exhaust, while a portion helps keep the fuel cell membrane hydrated and the rest is managed by the vehicle’s water handling system. In short, the car emits clean water and uses a small amount internally for membrane hydration.
How water is produced and what happens inside the stack
Inside a PEM (proton exchange membrane) fuel cell stack, hydrogen from the tanks reacts with oxygen from the air to generate electricity, heat, and water. The reaction creates water primarily at the cathode and the water helps keep the membrane hydrated, which is crucial for efficient operation. The system carefully manages humidity and temperature to avoid drying out or flooding the membrane.
Key details about water production
- The chemical reaction H2 + 1/2 O2 → H2O produces water as a byproduct.
- Most water forms at the cathode and can appear as liquid droplets or water vapor depending on operating conditions.
- The produced water helps maintain membrane hydration and thus fuel-cell performance.
- Excess water is removed through the vehicle’s water management pathways and typically exits as water vapor via the exhaust, or as condensate in cooler conditions.
The balance of humidity, temperature, and flow is a central design consideration to keep the stack efficient and durable while ensuring that water does not flood the channels or dry out the membrane.
Where the water goes when the car is running
During normal operation, the bulk of the water produced inside the stack leaves the vehicle through the exhaust as water vapor. The exhaust outlet releases steam that quickly dissipates into the atmosphere. In cold weather, some of this water may condense into liquid water in the tailpipe before it evaporates or drains away, but it is not stored as a long-term liquid inside the car.
Water recirculation and byproducts
- Some water is used to humidify the incoming air and hydrogen streams, which helps keep the membrane adequately hydrated.
- A small amount of condensate can accumulate in piping and must be drained as part of the vehicle’s water management system.
- The vehicle’s cooling system circulates water to remove heat from the stack; this is a separate loop and does not represent the water produced by the electrochemical reaction.
In practice, the water produced by the reaction is largely a clean byproduct that is vented as vapor, with careful internal management to maintain membrane hydration and prevent flooding.
Practical considerations for drivers
For drivers, the water aspect of hydrogen fuel cell cars is largely invisible. The cars do not burn water; they convert hydrogen and oxygen into electricity and a small amount of water as a byproduct. There is no need for users to manage water intake or disposal, aside from the car’s routine maintenance of its cooling and humidification systems.
Summary
Hydrogen fuel cell vehicles generate water as a byproduct of converting hydrogen and oxygen into electricity. Most of this water exits the car as water vapor through the exhaust, while a portion contributes to keeping the fuel cell membrane hydrated. The remainder is managed by the vehicle’s water handling and cooling systems, with minimal liquid water that may condense in cold conditions. This water byproduct helps illustrate the clean-emission promise of hydrogen-powered cars while highlighting the importance of proper water management within the fuel-cell stack.
