fuel cell

A fuel cell generates electrical current by combining hydrogen fuel with oxygen in a controlled electrochemical reaction. Unlike a battery, which stores a fixed charge, a fuel cell operates as long as fuel is supplied. The reaction occurs across a membrane that separates a hydrogen-rich anode from an oxygen-rich cathode. Electrons flow from anode to cathode through an external circuit, creating usable direct current, while ions travel through the membrane itself. The only emissions are heat and water vapor.

Proton exchange membrane (PEM) fuel cells are the most common industrial type. These use a polymer membrane that conducts protons but blocks electrons, forcing current to flow through the external load. Operating temperatures run 50 to 100 degrees Celsius. Solid oxide fuel cells (SOFC) work hotter, between 600 and 1000 degrees Celsius, making them efficient for stationary industrial power generation and able to run on various hydrocarbon fuels with internal reforming. Alkaline fuel cells, phosphoric acid cells, and molten carbonate cells serve specialized applications where higher temperature, better tolerance of fuel impurities, or waste heat recovery matter more than compact size.

Stack design and system integration

Individual fuel cells produce roughly 0.7 volts under load. Practical systems stack dozens or hundreds of cells in series to reach required voltage and power output. A 50 kW fuel cell system might contain 400 individual cells. Current density at the electrodes typically ranges from 200 to 1000 mA per square centimeter depending on cell type and operating point. Heat management is critical: fuel cells convert only 40 to 60 percent of the fuel's chemical energy into electricity, so cooling subsystems, humidifiers, and pressure regulation are essential components.

Hydrogen supply presents the main practical constraint. Most hydrogen today comes from steam reforming of natural gas, making fuel cells part of an existing fossil fuel supply chain rather than a standalone clean energy source. On-site electrolysis or sourcing hydrogen from industrial processes adds cost but decouples the system from fossil fuels. Impurities in fuel streams, particularly carbon monoxide and sulfur compounds, poison catalysts and degrade performance, so fuel conditioning and purity control are non-negotiable in continuous operation.

Fuel cells appear in materials handling (forklift propulsion), stationary backup power for telecommunications sites, distributed energy generation at industrial facilities, and experimental automotive applications. They compete with internal combustion engines where silence, long runtime without refueling, and minimal emissions justify higher capital cost and operational complexity. System lifespan depends on membrane degradation and catalyst deactivation; current targets aim for 40,000 to 60,000 operating hours in vehicle applications and 80,000 hours or more for stationary units.