Hydrogen is a carrier, not a source
Hydrogen is the most abundant element in the universe, but on Earth it is almost always bound to something else, such as oxygen in water or carbon in natural gas. There are no large natural reserves of pure hydrogen gas to dig up in the way there are of coal or oil, so it has to be made. That makes hydrogen an energy carrier, like a battery: you put energy in at one point and get it out later.
This distinction explains much of the debate. Any fuel made from other energy has to be judged by how much energy is lost along the way, not just by what happens at the point of use.
How a fuel cell works
A fuel cell converts the chemical energy in hydrogen into electricity directly, without combustion. The most common type for vehicles and small systems is the proton exchange membrane (PEM) fuel cell.
In simple terms:
- Hydrogen gas is fed to one side of the cell, the anode, where a catalyst helps split each hydrogen molecule into protons and electrons.
- The membrane in the middle lets protons pass through but blocks electrons.
- The electrons are forced to travel around an external circuit, which is the electric current you use.
- At the other side, the cathode, oxygen from the air combines with the protons and returning electrons to form water.
The main by-products are water and heat. At the point of use there are no carbon dioxide emissions, which is a large part of the appeal. A single cell produces a modest voltage, so many are stacked together to make a useful power source, and the system also needs pumps, humidifiers or cooling, and control electronics.
A fuel cell is not a battery: it does not store energy itself. It keeps producing electricity as long as fuel and air are supplied. Many practical systems pair a fuel cell with a small battery to handle sudden changes in demand.
Where the promise lies
- Quick refuelling and long range. For heavy vehicles, ships or trains, refuelling a tank can be faster and lighter than carrying very large batteries.
- Storing energy for long periods. In principle, surplus renewable power could be turned into hydrogen and held for days or seasons, something batteries are not well suited to.
- Industry. Some industrial processes already use hydrogen and need a low-carbon version.
- Backup power. Fuel cells can provide power for remote sites.
How significant any of these will be is still debated, and the answer differs by sector.
Production: not all hydrogen is equal
Most hydrogen today is made from natural gas, in a process that releases carbon dioxide. Hydrogen can also be made by electrolysis, which uses electricity to split water into hydrogen and oxygen. If that electricity is from low-carbon sources, the hydrogen can have a much smaller footprint.
People use colour labels such as green, blue and grey to describe production routes, but the labels are not applied consistently, so check what a claim actually means. Electrolysis itself has costs and efficiency limits, and it needs a lot of electricity.
Storage and handling
Hydrogen is very light, so a given volume holds comparatively little energy. To make it practical, it is usually compressed to high pressure, cooled to a liquid at very low temperatures, or bound into other compounds. Each option needs energy and specialised equipment.
Hydrogen molecules are small and can leak through tiny gaps. They can also make some metals brittle over time, which affects how tanks and pipes are designed. Hydrogen is flammable across a wide range of concentrations, so ventilation, leak detection and safety standards matter. This is not an area for home experimentation with gas cylinders or improvised storage.
The efficiency question
Consider the chain from electricity to hydrogen and back to electricity: electrolysis, then compression or liquefaction, then storage and transport, then a fuel cell. Each step loses energy. Overall, only a fraction of the original electricity usually returns, and it is typically lower than for charging and discharging a battery. Exact values depend on the equipment, so be wary of any single figure presented without conditions, as covered in reading efficiency claims critically.
This is why hydrogen is often considered most promising where batteries struggle, such as long-distance heavy transport or seasonal storage, and less compelling for ordinary passenger cars where charging infrastructure is expanding. That view could change as technology and costs evolve.
Other hurdles
- Infrastructure. Refuelling stations, pipelines and distribution networks are limited in most regions.
- Cost and materials. Catalysts often use expensive metals, and cost reductions are ongoing research.
- Durability. Membranes and catalysts wear, and impurities in the fuel can damage them.
- Cold climates. Water produced in a cell can freeze, which designers must manage.
What this means for makers
Small educational fuel cell kits exist and can demonstrate the principle safely when used as directed. Beyond that, hydrogen at any scale needs training, certified components and compliance with local regulations. Follow manufacturer guidance and treat the gas with respect.
Hydrogen is one piece of a bigger puzzle, and how it fits alongside batteries, generation and the power grid is covered in our overview of how clean energy technology fits together.