Several application fields can benefit from solar-hydrogen technologies via specific short-term and long-term pathways.

Water electrolysis has benefits over other hydrogen generation technologies due to the lack of carbon footprint when integrated with a renewable source of energy. Specifically, proton exchange membrane (PEM) electrolysis is a promising technology for hydrogen generation applications because of the lack of corrosive electrolytes, small footprint, and ability to generate at high pressure, requiring only deionized water and an energy source. PEM electrolysis also produces very pure hydrogen, with none of the typical catalyst poisons that may be found in hydrogen produced from reforming. However, significant advances are required in order to in order to provide a cost-competitive hydrogen source for energy markets. This paper will discuss the current limitations and recent work by Proton Energy Systems towards reaching the DOE Hydrogen Program objective for distributed production of hydrogen from distributed water electrolysis of $3.70/gge by 2012. Status of TechnologyProton exchange membrane (PEM) electrolysis has been known for over 50 years, starting from GE technology. Proton Energy Systems is currently the world leader in manufacturing of PEM hydrogen generation products using electrolysis, with over 1300 units in the field. Pure hydrogen is used in a variety of industrial applications, including acting as a cooling fluid for power plant turbine generators, a reducing atmosphere for heat treating and semiconductor processing, and as a carrier gas for spectroscopic applications such as gas chromatography. Proton's on site hydrogen generators are costcompetitive with delivered hydrogen for these applications. However, interest in hydrogen for energy applications has increased the need to decrease capital cost and increase efficiency of electrolysis and other generation methods. PEM vs. AlkalineThere are two main types of low temperature electrolysis currently commercially available. Alkaline electrolysis uses liquid electrolyte, with high concentrations of potassium hydroxide to provide ionic conductivity and to participate in the electrochemical reactions. PEM electrolysis replaces the liquid electrolyte with a solid polymer electrolyte, which selectively conducts positive ions such as protons. The protons participate in the water-splitting reaction instead of hydroxide, creating a locally acidic environment in the cell.There are advantages and disadvantages of each system. One advantage of KOH electrolyzers is the stability of nickel and stainless steel in this environment, enabling elimination of expensive materials of construction. However, in the KOH system, the

Solid-state alkaline water electrolysis using a pure water feed offers several distinct advantages over liquid alkaline electrolyte water electrolysis and proton exchange membrane water electrolysis. These advantages include a larger array of electrocatalyst available for oxygen evolution, no electrolyte management, and the ability to apply differential pressure. To date, there have been only a handful of reports on solid-state alkaline water electrolyzers using anion exchange membranes (AEMs), and there have been no reports that investigate loss in system performance over time. In this work, a solidstate alkaline water electrolyzer was successfully demonstrated with several types of polysulfone-based AEMs using a relatively expensive but highly active lead ruthenate pyrochlore electrocatalyst for the oxygen evolution reaction. The electrolysis of ultrapure water at 50 C resulted in a current density of 400 mA cm À2 at 1.80 V. We demonstrated that the short-term degradation of water electrolyzer performance over time was largely a consequence of carbon dioxide intrusion into the system and could be easily remedied, while longterm deterioration was a consequence of irreversible AEM polymer degradation.