Feature Report: Hydrogen as an Energy Carrier

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The Different Types of Fuel Cell

Fuel cells convert energy from a fuel into electricity via an electrochemical reaction. The most commonly used fuels are natural gas and hydrogen, which is discussed here.  

An engineer demonstrates a PEMFC at Université de Belfort-Montbéliard in France. © AFP PHOTO / SEBATIEN BOZON

A fuel cellA device that produces electricity by oxidizing a reducing agent (fuel) in one electrode (the anode) and reducing an oxidizing agent in another... using hydrogenThe simplest and lightest atom, the most abundant element in the universe. consists of two electrodes:

  • One positive, known as the anode, containing hydrogen.
  • One negative, known as the cathode, containing oxygen.

An electrolyte — a solid or liquid able to control the flow of electrons — is sandwiched between the two. It is usually a polymer containing a platinum catalyst.

The hydrogen molecules separate in the anode: the ions are diffused in the electrolyte, while the electrons circulate in an external circuit, generating usable direct current.

At the cathode, electrons from the external circuit, the hydrogen ions (protons) and the oxygen combine to form water and heatIn the field of statistical thermodynamics today, heat refers to the transfer of the thermal agitation of the particles making up matter... that can be recovered.

Ultimately, with hydrogen on one side and oxygen on the other, the fuel cell generates both electricityForm of energy resulting from the movement of charged particles (electrons) through a conductor... and heat. The only byproduct of hydrogen combustion is water vapor.

Two Main Pathways

There are many fuel cell technologies, but the two main ones have already found significant industrial applications: protonA positively charged particle. Protons and neutrons form the nucleus of an atom. exchange membrane fuelFuel is any solid, liquid or gaseous substance or material that can be combined with an oxidant... cells (PEMFC) and solid oxide fuel cells (SOFC):1/2

  • Solid oxide fuel cell (SOFC) technology is well suited to cogenerationThe simultaneous production of both heat (thermal energy) and power... (combined heat and powerIn physics, power is the amount of energy supplied by a system per unit time. In simpler terms, power can be viewed as energy output...). These fuel cells have an yttria-stabilized zirconia electrolyte. Their operating temperature of 800 °C enables any fuel containing hydrogen to be used, thanks to internal reforming processes that eliminate the need for pure hydrogen. This means that they could even run on municipal natural gas. SOFCs offer excellent power conversion efficiency — between 40 and 70% — as well as good thermal efficiency. The heat produced is reused in part to operate the fuel cell, while the very hot residual heat can be easily recovered. SOFCs are very heavy, have a low tolerance for vibrations and are easily disrupted by frequent stops. They are therefore intended for stationary applications, such as power generation for apartment buildings.
  • Proton exchange membrane fuel cells (PEMFC) are compact and operate at low temperatures (80 °C) with a polymer electrolyte. They mainly provide electricity, with an average efficiency of 40 to 60%. This “all-terrain” technology can be used for both portable and stationary applications. R&D continues, especially to reduce its cost, which is high because platinum is used for both the anode and the cathode. PEMFCs are the only fuel cells suitable for transportation applications. They can also be used for niche stationary applications, such as supplying power to isolated sites or emergency power generation.

Among the other technologies, direct methanolMethanol or methyl alcohol is the simplest alcohol, with a chemical formula of CH3-OH. It is used in the production of methyl tert-butyl ether... fuel cells (DMFC) and direct ethanol fuel cells (DEFC) can easily be miniaturized. They use the hydrogen contained in the respective alcohol molecules directly. Their main applications are mobile devices, such as cell phones and laptops.

There are two main types of fuel cell: PEMFCs and SOFCs

Lifespan

Lifespan — the period of time during which the fuel cell performs optimally — is an important factor for industrial applications. It varies considerably depending on the type of fuel cell and the way it is used. For stationary fuel cells, the average lifespan today is between 30,000 and 40,000 hours. For fuel cells designed for cars, manufacturers have obtained lifespans of around 5,000 hours.

It should also be noted that fuel cells are very quiet — 40 to 50 decibels at a distance of a meter, which is lower than the volume of a normal conversation.

 

Sources:

(1) La Recherche (In French)