Other meanings of cell
ENERGY TECHNOLOGY
A fuel cell is an electrochemical device that converts the chemical energy of a fuel and an oxidant directly into electricity, usually producing water and heat as by-products. Unlike a battery, it does not store a finite charge: it generates power while reactants are supplied. Hydrogen is the most common fuel, although some fuel-cell systems process methanol, natural gas, or other hydrocarbons internally.
A fuel cell produces electricity by separating oxidation and reduction reactions across an electrolyte. At the anode, a catalyst helps split the fuel; in a hydrogen cell, hydrogen releases electrons and becomes protons. The electrons travel through an external circuit, while ions cross the electrolyte to the cathode, where they react with oxygen and form water. This arrangement resembles a battery’s electrochemistry, but the electrodes are continuously supplied rather than gradually consumed.
A complete system includes a cell stack, fuel and air delivery, thermal management, power electronics, sensors, and controls. Individual cells generate less than a few volts, so many are connected in series. Water and heat must be removed or recovered, and impurities such as carbon monoxide can poison catalysts in some designs.
Fuel-cell types are chiefly distinguished by their electrolyte and operating temperature. Proton-exchange membrane fuel cells use a polymer electrolyte, operate at relatively low temperatures, and respond quickly; they are prominent in vehicles and backup power. Alkaline fuel cells were used in NASA spacecraft, but their sensitivity to carbon dioxide limits broader terrestrial use. Phosphoric-acid fuel cells operate at moderate temperatures and have served in stationary combined-heat-and-power installations.
High-temperature systems include molten-carbonate and solid-oxide fuel cells. They can use hydrogen-rich fuels and, in some configurations, internally reform natural gas or other hydrocarbons. Solid-oxide cells employ ceramic electrolytes and can also run in reverse as electrolyzers, while direct-methanol cells feed liquid methanol to the anode and suit some portable applications. Each design trades efficiency, durability, cost, start-up speed, and fuel flexibility.
Fuel cells are used where quiet operation, high efficiency, long operating duration, or low local emissions are valuable. Hydrogen fuel-cell vehicles emit water at the vehicle, and fuel cells provide electricity for buses, forklifts, telecommunications backup, remote installations, spacecraft, and distributed power. Stationary units can capture their substantial heat in combined-heat-and-power systems, raising total energy utilization well above electrical efficiency alone.
Climate performance depends on how the fuel is made and delivered. Hydrogen produced with renewable electricity or low-carbon energy can reduce lifecycle emissions, whereas hydrogen made from unabated fossil fuels retains significant emissions. Fuel-cell vehicles also require costly hydrogen infrastructure, and hydrogen storage, transport, catalyst supply, stack durability, and overall system cost remain important constraints. Battery-electric systems are often more energy-efficient for light-duty road transport because they avoid several conversion steps.12
The fuel cell has a longer history than its modern vehicle image suggests. William Grove demonstrated a hydrogen–oxygen device in 1839, but practical development accelerated only when space programs needed reliable electricity and potable water. Apollo spacecraft used alkaline fuel cells, whose water was a useful co-product for crews. NASA’s later fuel-cell work helped establish engineering methods for stacks, reactant control, and space-qualified power systems.3
Fuel cells are also reversible in a broader energy-system sense: solid-oxide and some proton-conducting devices can operate as electrolyzers, converting electricity into hydrogen when power is abundant and returning electricity later. Microbial fuel cells use microorganisms to oxidize organic matter and have been studied for wastewater treatment and low-power sensing, although they remain a specialized research technology. Fuel-cell efficiency is not governed by combustion limits alone; its theoretical ceiling follows thermodynamics, while real losses arise from activation, ohmic, and mass-transport effects.4
Electrical efficiency varies substantially with fuel-cell chemistry, operating temperature, system design, load, and fuel-processing pathway; quoted ranges are indicative rather than universal.
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