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

Lead ruthenate pyrochlore showed exceptional OER activity and stability when tested in a solid-state alkaline water electrolyzer.

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.

Alkaline stability of benzyl trimethylammonium (BTMA)-functionalized polyaromatic membranes was investigated by computational modeling and experimental methods. The barrier height of hydroxide initiated aryl-ether cleavage in the polymer backbone was computed to be 85.8 kJ/mol, a value lower than the nucleophilic substitution of the αcarbons on the benzylic position of BTMA cationic functional group, computed to be 90.8 kJ/mol. The barrier heights of aryl− aryl cleavage (polymer backbone) are 223.8−246.0 kJ/mol. The computational modeling study suggests that the facile aryl−ether cleavage is not only due to the electron deficiency of the aryl group but also due to the low bond dissociation energy arising from the ether substituent. Ex situ degradation studies using Fourier transform infrared (FTIR) and 1 H nuclear magnetic resonance (NMR) spectroscopy indicated that 61% of the aryl−ether groups degraded after 2 h of treatment in 0.5 M NaOH at 80 °C. BTMA cationic groups degraded slowly over 48 h under the same conditions. In situ degradation studies validate the calculated results: anion exchange membrane fuel cells and water electrolyzer using poly(arylene ether) membranes exhibit a catastrophic, premature failure during lifetime tests, while no sudden performance loss is observed with an ether-free poly(phenylene) membrane. Despite the gradual performance loss due to the degradation of BTMA cation functional group, the membrane electrode assembly using the poly(phenylene) membrane exhibited a lifetime of >2000 h in the alkaline water electrolyzer mode at 50 °C.

Hydrogen is one of the world's most important chemicals, with global production of about 50 billion kg/yr. Currently, hydrogen is mainly produced from fossil fuels such as natural gas and coal, producing CO 2. Water electrolysis is a promising technology for fossilfree, CO 2-free hydrogen production. Proton exchange membrane (PEM)-based water electrolysis also eliminates the need for caustic electrolyte, and has been proven at megawatt scale. However, a major cost driver is the electrode, specifically the cost of electrocatalysts used to improve the reaction efficiency, which are applied at high loadings (>3 mg/cm 2 total platinum group metal (PGM) content). Core shell catalysts have shown improved activity for hydrogen production, enabling reduced catalyst loadings, while reactive spray deposition techniques (RSDT) have been demonstrated to enable manufacture of catalyst layers more uniformly and with higher repeatability than existing techniques. Core shell catalysts have also been fabricated with RSDT for fuel cell electrodes with good performance. Manufacturing and materials need to go hand in hand in order to successfully fabricate electrodes with ultra-low catalyst loadings (<0.5 mg/cm 2 total PGM content) without significant variation in performance. This paper describes the potential for these two technologies to work together to enable low cost PEM electrolysis systems.

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Iridium oxide is one of the most common anode catalysts in commercial proton exchange membrane (PEM) electrolyzers because of its strong mix of high activity and stability under oxygen evolution reaction (OER) conditions. Unfortunately, benchmarking iridium oxide OER catalysts has proven difficult since IrO 2 cannot undergo proton underpotential deposition like platinum and other transition metal eletrocatalysts, making it difficult to estimate the electrochemically active surface area (ECSA), as well as OER specific and mass activity. In this work, we propose a method to calculate the ECSA of iridium oxide in an operating PEM electrolyzer. A universal constant, 596 (± 21) μC/cm 2 , was obtained from the correlation of pseudocapacitive charge and ECSA of iridium oxide. In the membrane electrode assembly (MEA), the calculated ECSA (1.81 (±0.065) m 2 over a 25-cm 2 geometric area) showed an iridium oxide catalyst utilization of ∼93%. Additionally, the IrO 2 OER specific and mass activities at 80 • C, 1.6 V in an operating PEM electrolyzer were 0.401 (±0.014) mA/cm 2 and 132 mA/mg, respectively.