Should we invest in hydrogen technology for automobiles?

Water to hydrogen and back: the balanced equations

It takes the same amount of energy to split water into hydrogen and oxygen as is released when that hydrogen burns back into water. These equations compare the same conditions, with liquid water at the start and finish. The reaction energy is the same in either direction. In practice, we recover less useful energy because of inefficiencies in the equipment and conversion steps.

Here, (l) means liquid and (g) means gas. The energy figures apply at 25°C and 1 bar, with liquid water as the starting and final state. Energy input can include electricity and heat.

Both sides contain four hydrogen atoms and two oxygen atoms. Two moles of water yield two moles of hydrogen gas and one mole of oxygen gas. Approximately 9 kg of water supplies the atoms for 1 kg of H₂.

The equations show two moles of hydrogen. Divide the energy by two to express it per mole:

• Produce 1 mole of H₂ from liquid water: absorb 285,830 joules (285.83 kJ/mol); ΔH = +285.83 kJ/mol.
• React 1 mole of H₂ with oxygen to form liquid water: release 285,830 joules (285.83 kJ/mol); ΔH = −285.83 kJ/mol.
• Complete the cycle: +285,830 J − 285,830 J = 0 J of net energy gained.

This corresponds to about 39.4 kWh per kg of hydrogen, its higher heating value. NIST thermochemical data.

A worked example: how much electricity comes back?

Use 55 kWh of electricity to produce 1 kg of hydrogen, the system figure in DOE's 2022 status column for PEM electrolysis. Use an assumed fuel-cell efficiency of 50%, measured against the hydrogen's lower heating value.

This calculation excludes compression or liquefaction, delivery, refueling, and the motor and drivetrain. Those steps require additional energy or reduce energy reaching the wheels. The unrecovered energy has not vanished; much becomes heat instead of useful vehicle work.

DOE electrolysis reference. The 50% fuel-cell efficiency is an assumption for this calculation, not a universal efficiency.

What does this mean for cars?

• Burning hydrogen: an engine uses combustion heat to produce mechanical work. Only part of the fuel energy reaches the wheels.
• Using a fuel cell: hydrogen reacts electrochemically with oxygen to produce electricity, water, and heat. An electric motor drives the car; the fuel cell does not burn hydrogen in a flame. How a fuel-cell car works.
• Charging a battery: using electricity directly avoids the electrolysis and hydrogen-to-electricity conversion steps. The hydrogen route adds conversion steps and losses before electricity reaches the motor.
• Comparing with gasoline or gas: count extraction, processing, delivery, and engine losses too. Compare energy delivered to the wheels from the same starting energy source.

The abundance argument does not establish feasibility. For hydrogen made from water, identify the original energy source, then calculate useful energy at the wheels, total cost, and the infrastructure required. Hydrogen can move or store energy; this cycle cannot create it.

What happens in a crash?

Hydrogen is highly flammable. A leak that mixes with air and ignites can cause a fire or explosion. It can ignite more easily than gasoline vapor or natural gas. Its flame can be difficult to see. DOE: hydrogen fire hazards.

A hydrogen car carries fuel in high-pressure tanks, with systems commonly using about 5,000 or 10,000 psi. The pressure itself is another hazard if a tank fails. A crash must not turn a damaged fuel system into an uncontrolled gas release.

• Damage and leaks: check whether the tank, pipes, and connections survive the impact and whether fuel flow shuts off after damage.
• Fire: escaping gas can ignite. Pressure-relief devices are designed to vent fuel when a tank is heated, reducing the risk of rupture; that release must also be managed.
• Trapped gas: hydrogen can collect near the ceiling of an enclosed space. Leak detection and ventilation matter. Outdoors, its buoyancy helps it disperse upward.
• Protection: examine tank impact and fire tests, shutoff valves, leak detection, and pressure relief. These are essential parts of the vehicle, not optional extras.

A crash does not automatically cause an explosion. The outcome depends on damage, leakage, air mixing, ignition, and the protection systems. Tanks are engineered and tested to resist failure. The question is how well the complete system protects occupants and bystanders in a real crash or fire. DOE: tank pressures, testing, and fire protection.

Natural hydrogen: reserves and actual extraction

Proved reserves: natural hydrogen versus crude oil

I could not find any published tonnage of proved natural-hydrogen reserves. Compare proved reserves with proved reserves, not an estimate of all the hydrogen that might be underground.

Estimates of hydrogen underground are not proved reserves. They cannot be substituted for the missing proved-reserve tonnage.

Annual natural-hydrogen extraction versus world oil use

IEA reports 5 tonnes per year of natural hydrogen, equivalent to about 100 barrels of oil per year. OPEC reports worldwide oil demand of 105.15 million barrels per day in 2025.

Worldwide annual oil use is about 384 million times larger than the oil-energy equivalent of reported natural-hydrogen extraction. Calculation: 38,379,750,000 ÷ 100 ≈ 384 million. The hydrogen conversion uses IEA's rounded energy equivalence.

The separate comparison with worldwide passenger-car energy use is 78 million times larger. That calculation and its sources are in the evidence section.

IEA Global Hydrogen Review 2025, Box 5.3, printed page 190; OPEC Annual Statistical Bulletin 2026: 2025 world oil demand.

Reported natural-hydrogen extraction supplies no meaningful amount of the energy used by the world's cars. The fuel still needs processing, storage, transport, and refueling facilities. Those steps add cost.

Conserve instead of counting on a hydrogen breakthrough

Hydrogen is not free energy. A large estimate of gas underground is not fuel at a filling station. The numbers show the energy losses, the tiny scale of natural extraction, and the gap between a project announcement and a usable fuel supply.

Spending money does not make a project feasible. Funding projects that cannot deliver useful results is a money pit. Public funding must be justified by measured output, delivered fuel cost, reliability, and safety. Stop funding projects that fail those tests.

• Drive less. Combine errands instead of making repeated trips.
• Combine riders. Share trips to the same destination.
• Use less heating and cooling. Accept a cooler house in winter and a warmer house in summer while keeping conditions safe.
• Cut waste. Turn off equipment you do not need and reduce unnecessary purchases.

Do not use a promised hydrogen breakthrough as permission to waste energy. Conserve rather than waiting for a technology to remove the consequences of consumption. Read Conservation.