SERC: PEM Electrolysis

What good is a PV panel at night? What about windmills when the wind is not blowing? These questions and others like them form the basis for one of the fundamental constraints facing the widespread use of renewable energy power systems: the intermittent nature of renewable energy resources. The solution to this constraint is to store the energy generated by these inexhaustible, yet intermittent, resources. But how?

In the past many storage media have been employed, including batteries, flywheels, ultracapacitors, pumped-storage hydroelectric, and superconducting magnets. These media have had varying degrees of success, but all have significant disadvantages, such as self-discharge, high cost, and the use of toxic materials in their construction. At the Schatz Energy Research Center we have focused our attention on an emerging, better, and more complete energy storage option: hydrogen.
Hydrogen's advantages as a storage medium include:

What is electrolysis?
Electrolysis is the use of electrical energy to produce a chemical change. In the renewable hydrogen cycle, electrical energy (from renewable resources) is used to break the bonds between the hydrogen and oxygen in the water, releasing them as elemental gases. Hydrogen is stored renewable energy.

An electrolyzer is a device that facilitates the electrolysis of water to produce large volumes of hydrogen gas. Electrolyzers most commonly used today generate hydrogen at relatively low pressures (from nearly atmospheric pressure up to 200 pounds per square inch) and use a liquid alkaline electrolyte (KOH or NaOH). At these pressures, storage of large quantities of hydrogen requires extremely large storage vessels. One solution to this problem is to use a compressor to increase the hydrogen pressure. However, the energy investment required to pressurize hydrogen, as well as the maintenance of hydrogen compressors, makes this option infeasible for large-scale application of this technology. Furthermore, the operation of alkaline electrolyzers requires frequent maintenance that includes disposal and replacement of the highly caustic electrolyte. For these reasons, SERC is currently designing and testing a proton exchange membrane electrolyzer.

A proton exchange membrane (PEM) electrolyzer can be designed to electrochemically generate hydrogen at pressures of 2000 psi or greater, thus eliminating the need for mechanical compression. The PEM electrolyzer uses a solid electrolyte membrane that can be expected to last the lifetime of the electrolyzer. No caustic alkaline or acidic fluid electrolyte is required. Additional advantages of PEM electrolysis over alkaline electrolysis include lower parasitic energy losses and higher purity hydrogen output. PEM electrolysis is potentially a simple, sustainable, and cost-effective technology for generating, compressing, and storing hydrogen.