Fuel cell basics

Fuel cells can supply heat and electricity for buildings, as well as energy for automobiles and electronics.

HOW FUEL CELLS FUNCTION

Fuel cells function like batteries, but do not deplete or need recharging. They generate power and heat so long as fuel is available. A fuel cell consists of two electrodes sandwiching an electrolyte: a negative electrode (or anode) and a positive electrode (or cathode). The anode receives a fuel, like as hydrogen, while the cathode receives air. A catalyst in a polymer electrolyte membrane fuel cell splits hydrogen atoms into protons and electrons, which go to the cathode through multiple routes. Electrons move across an external circuit, generating an electric current. The protons go through the electrolyte to the cathode, where they rejoin with oxygen and the electrons to generate water and heat.

VARIETIES OF FUELCELLS

While the fundamental functions of all fuel cells are same, specialized variants have been created to take advantage of different electrolytes and meet the requirements of various applications. The fuel and charged species traveling through the electrolyte may alter, but the underlying concept is same. At the anode, oxidation happens, whereas at the cathode, reduction occurs. A charged species that migrates across the electrolyte and electrons that pass via the external circuit link the two processes.

ELECTROLYTE POLYMER MEMBRANE FUEL CELLS

The electrolyte of polymer electrolyte membrane (PEM) fuel cells, also known as proton exchange membrane fuel cells, is a proton-conducting polymer membrane. Typically, hydrogen is utilized as the fuel. These cells can rapidly adjust their output to suit fluctuating power needs while operating at relatively low temperatures. PEM fuel cells are the most viable option for powering vehicles. They are also suitable for stationary power generation. Due to their low working temperature, however, they cannot directly utilize hydrocarbon fuels such as natural gas, liquefied natural gas, or ethanol. These fuels must be transformed to hydrogen in a fuel reformer in order for a PEM fuel cell to utilise them.

DIRECT-METHANOL FUEL CELLS

Similar to the PEM cell, the direct-methanol fuel cell (DMFC) employs a proton-conducting polymer membrane as its electrolyte. DMFCs, on the other hand, use methanol directly on the anode, eliminating the need for a fuel reformer. DMFCs are useful for powering portable electronic equipment like laptop computers and battery chargers. Methanol has a greater energy density than hydrogen, making it a desirable fuel for portable electronics.

ALKALINE RESOURCE CELLS

Alkaline fuel cells use an alkaline electrolyte, such as potassium hydroxide, or an alkaline membrane that conducts hydroxide ions as opposed to protons. Initially used by the National Aeronautics and Space Administration (NASA) for space missions, alkaline fuel cells are now finding new uses, such as in portable electricity.

PHOSPHORIC ACID CELLS AS FUEL

Phosphoric acid fuel cells employ a phosphoric acid electrolyte that conducts protons contained in a porous matrix and function at around 200 degrees Celsius. In hotels, hospitals, grocery shops, and office buildings, where waste heat may also be used, they are generally utilized in modules of 400 kW or more for stationary power production. Phosphoric acid may also be immobilized in polymer membranes, and fuel cells using these membranes are desirable for several stationary power applications.

COMBUSTIBLE CARBONATE CELLS

As its electrolyte, molten carbonate fuel cells use a molten carbonate salt immobilized in a porous matrix that conducts carbonate ions. They are being used in a range of medium- to large-scale stationary applications, where their great efficiency results in net energy savings. Their high-temperature functioning (about 600°C) allows them to reform fuels such as natural gas and biogas internally.

CELLS OF SOLID OXIDE FUEL

The solid electrolyte in solid oxide fuel cells is a thin layer of ceramic that conducts oxide ions. They are being designed for use in a range of fixed power applications and heavy-duty vehicle auxiliary power devices. Operating at 700°C–1,000°C with zirconia-based electrolytes and as low as 500°C with ceria-based electrolytes, these fuel cells can reform natural gas and biogas internally and can be paired with a gas turbine to achieve electrical efficiencies of up to 75%.

COMBINED THERMAL AND ELECTRICAL FUEL CELLS

In addition to producing electricity, fuel cells generate heat. This heat may be utilized to meet a variety of heating demands, including hot water production and space heating. As their overall efficiency may reach 90 percent, combined heat and power fuel cells are an attractive option for powering homes and buildings. This operation’s great efficiency saves money, conserves energy, and lowers greenhouse gas emissions.

CELLS FOR REGENERATIVE OR REVERSIBLE FUEL

This unique category of fuel cells generates energy from hydrogen and oxygen, but may also be fueled by electricity to generate hydrogen and oxygen. This promising technology might store surplus energy generated by intermittent renewable energy sources, such as wind and solar power plants, and release it during periods of low power generation.