Final answer:
A fuel cell is a device that converts combustion fuel energy directly into electrical energy, requiring a continuous supply of fuels such as hydrogen and a catalyst. It is efficient and generates electricity nearly lossless compared to the internal combustion engine, which wastes significant energy.
Step-by-step explanation:
The device that converts energy from the combustion of fuel directly to electrical energy is known as a fuel cell. Unlike an electrolytic cell, which consumes electrical energy to drive a chemical reaction, fuel cells are electrochemical cells where the energy of a combustion reaction is directly turned into electrical energy. This requires a continuous supply of reactants such as hydrogen, methane, or propane for the anode and oxygen for the cathode, with the continual removal of products.
Fuel cells, also referred to as flow batteries, are significantly more efficient than internal combustion engines. This is because they convert the energy released during the reaction almost directly into electrical energy, which can be used with nearly 100-percent efficiency by electric devices. In contrast, thermal energy from direct combustion typically wastes at least half of its energy as per the second law of thermodynamics.
The general reaction in a hydrogen fuel cell involves the oxidation of hydrogen at the anode, with the electrons being transferred through an external circuit. Oxygen at the cathode is reduced and combines with H+ to form water. A solid electrolyte, often KOH, facilitates the proton diffusion from the anode to the cathode. The efficiency and clean energy production of fuel cells are important advantages, despite their current limitations of cost and technological complexity.