How does the Toyota Mirai fuel cell work?

The Mirai turns hydrogen into electricity using a proton-exchange membrane (PEM) fuel cell, which powers an electric motor. Its exhaust is water vapor, and it can be refueled in minutes at compatible stations.

Beyond this core idea, Toyota pairs the fuel cell stack with a compact high‑voltage battery for energy buffering, uses high‑pressure hydrogen tanks for onboard storage, and relies on a cooling and safety system to manage heat and pressure. This combination underpins Toyota’s broader push toward hydrogen mobility and its role alongside battery electric vehicles in decarbonizing transport.

The basic principle behind the Mirai's fuel cell

At the heart of the Mirai is a PEM fuel cell stack that converts chemical energy from hydrogen directly into electrical energy. The process takes place in a controlled electrochemical reaction, producing electricity, heat, and water as the primary byproduct. The resulting electricity powers the car's traction motor, while the heat is managed by a dedicated cooling loop to maintain optimal temperature for efficiency and longevity.

To deliver smooth, responsive performance, the Mirai blends the fuel cell output with a small on-board battery or energy buffer. This allows for fast acceleration and efficient energy recovery during braking, with the system never directly burning hydrogen in an internal combustion engine. The vehicle remains a zero-emission electric-drive car, with water vapor as its only tailpipe emission.

Key components that power the Mirai's system

The Mirai’s architecture centers on several interlocking hardware pieces that manage hydrogen, electricity, and heat. The following components are the most critical:

• Hydrogen storage tanks (high‑pressure, typically around 70 MPa / 700 bar) that hold onboard fuel in a compact, rugged package


• PEM fuel cell stack (the core device that generates electricity from hydrogen and oxygen)


• Electric traction motor and drivetrain (converts electrical energy into wheel torque)


• Battery pack or energy buffer (assists power delivery and recovers braking energy)


• Power electronics and control systems (inverters, DC–DC converters, and vehicle software)


• Cooling and thermal management system (keeps the stack, battery, and power electronics within their optimum temperature range)


• Safety systems for hydrogen handling (pressure sensors, leak detection, shutoff valves, and venting safeguards)

Together, these parts translate the chemical energy stored in hydrogen into clean, quiet propulsion, with safety and efficiency features designed for real-world driving and variable conditions.

Hydrogen storage and refueling specifics

Understanding the storage and fueling aspects helps explain how the Mirai fits into hydrogen infrastructure. The vehicle carries hydrogen in high‑pressure tanks designed to be light and strong, enabling a practical driving range without frequent stops for fuel.

• Hydrogen is stored at high pressure (around 70 MPa / 700 bar) in durable composite tanks embedded in the chassis


• Onboard storage typically amounts to roughly 5 kilograms of hydrogen, depending on the model


• Real-world range for recent Mirai models generally falls in the vicinity of 350–400 miles (varies with driving conditions and climate)


• Refueling at a compatible hydrogen station typically takes about the same time as a conventional gasoline fill, roughly 3–5 minutes

These storage and refueling characteristics are accompanied by safety features that monitor pressure, detect leaks, and automatically regulate gas flow to protect occupants and infrastructure.

Safety, infrastructure and consumer considerations

Hydrogen vehicles rely on rigorous safety standards and a developing fueling network. The Mirai’s design emphasizes leak detection, robust high‑pressure containment, and rapid shutdown capabilities. While hydrogen refueling infrastructure is growing in regions like Japan, parts of North America and Europe, availability can vary by locale. Toyota positions hydrogen mobility as a complementary option to battery electric vehicles, offering quick refueling and long-range potential where hydrogen ecosystems are well established.

Summary

The Toyota Mirai demonstrates how a hydrogen fuel cell vehicle turns onboard hydrogen and ambient oxygen into electricity through a PEM stack, which then powers an electric drive system. Key advantages include rapid refueling, quiet operation, and near-zero tailpipe emissions (water vapor). The system relies on high-pressure hydrogen tanks, a fuel cell stack, energy buffering from a battery, advanced power electronics, and a thermal management network to deliver practical, real-world performance. As hydrogen infrastructure expands, the Mirai and similar fuel-cell vehicles aim to offer an appealing alternative for those seeking quick fills and long-range capability without combustion engines.

How much does it cost to fill up a Mirai with hydrogen?

The cost to refuel a Toyota Mirai is approximately $200, based on the current average price of about $36 per kilogram and the Mirai's 5.6 kg tank capacity. However, Toyota includes a $15,000 fuel card, which covers complimentary fuel for up to six years for new purchases and three years for leases. After the complimentary period, out-of-pocket refueling costs can be substantial and are subject to significant price fluctuations.
 
Cost breakdown

• Price per kilogram: Approximately $36/kg
• Tank capacity: 5.6 kg
• Cost per fill-up: Approximately $201.60 ($36 x 5.6 kg)
• Cost per mile: Around $0.50 per mile, based on the ~$200 refill and an estimated 400 miles of range. 

Complimentary fuel

• New purchase: The purchase of a new Mirai includes up to $15,000 or six years (whichever comes first) of complimentary hydrogen fuel. 
• Lease: The lease of a new Mirai includes up to $15,000 or three years (whichever comes first) of complimentary hydrogen fuel. 
• Note: The $15,000 credit is based on an estimated 30,000 miles of driving, even at high price points. 

Cost comparison to other vehicles

• EV: It is significantly cheaper to charge a comparable electric vehicle, with estimates suggesting it costs about 14 times less per mile than refueling a Mirai with hydrogen in California. 
• Gasoline: Even compared to a gasoline car, the cost of hydrogen refueling is much higher. For example, fueling a Toyota Corolla Hybrid costs about one-sixth the price per mile of a Mirai. 

Factors to consider

• The cost of hydrogen fuel can fluctuate significantly, and a shortage of stations and supply issues can impact availability and price. 
• The complimentary fuel card is a major benefit for new buyers, but the cost after the card is used can be a significant factor in the total cost of ownership. 

How does the fuel cell work in the Toyota Mirai?

To generate electricity, the fuel cell will strip away the electrons, separating them from the protons. These electrons are then used to create pure electricity. The remaining hydrogen atoms are now ionized and they react with oxygen from the air to create water as well as heat.

What is the lawsuit against Toyota Mirai?

Toyota faces legal action over lack of hydrogen fuel infrastructure. California Mirai owners filed a class-action lawsuit against Toyota seeking $5.7 billion in damages. Plaintiffs allege Toyota concealed reliability issues and misrepresented hydrogen infrastructure.

What is the biggest problem with hydrogen fuel?

Hydrogen is highly flammable, igniting more easily than many other fuels. This presents significant safety challenges, particularly during transportation and storage. Leak detection is especially difficult, as hydrogen is colorless, odorless, and its small molecules can escape through tiny cracks.