S. Siracusano

Polymer electrolyte membrane water electrolysis: status of technologies and potential applications in combination with renewable power sources

Technological improvements in polymer electrolyte membrane water electrolysers (PEMWEs) are promoted by their exciting possibilities to operate with renewable power sources. In this paper, a synopsis of the research efforts concerning with the development of electrocatalysts, polymer electrolytes and stack hardware components is presented. The most challenging problem for the development of PEMWEs is the enhancement of oxygen evolution reaction rate. At present, there are no practical alternatives to noble metal-based oxide catalysts such as IrO2 and RuO2. As well as carbon supported Pt nanoparticles are the benchmark cathode catalysts for hydrogen evolution. High noble metal loading on the electrodes and the use of perfluorosulfonic membranes significantly contribute to the cost of these devices. Critical areas include the design of appropriate mixed electrocatalysts and their dispersion on low cost Ti-oxide like supports to increase catalyst utilization. Moreover, the development of alternative membranes with enhanced mechanical properties for high pressure applications, proper conductivity and reduced gas cross-over is strongly required. This latter aspect is also addressed by the development of proper recombination catalysts. The development of anodic mixed non-noble transition metal oxides with spinel or perovskite structure and proper resistance to chemical degradation in the acidic environment and electrochemical corrosion is also an active area of research. Similarly, efforts are also being addressed to Pd and Ru based cathode formulations with cheaper characteristics than Pt. Whereas, concerning with stack hardware, cost reduction may be addressed by replacing Ti-based diffusion media and bipolar plates with appropriate and cost-effective stainless steel materials with enhanced resilience to chemical and electrochemical corrosion. Regarding the combination with renewable power sources, PEM electrolysers can find suitable applications for peak shaving in integrated systems grid connected or in grid independent operating conditions where hydrogen generated through electrolysis is stored and then via fuel cell converted back to electricity when needed or used to refill fuel cell-based cars. Hydrogen is the most promising clean energy carrier to accomplish the sustainable production of energy and a synergy among hydrogen, electricity and renewable energy sources is highly desired.

Advanced (electro) ceramics and innovative energy technologies

The principal drivers of the new direction of research in energy technologies can be exemplified in three major targets: security of supply, environmental pollution issues (with particular reference to the Kyoto protocol), and adherence to the new European legislation related to the deregulation of the energy market. All these drivers contribute to the introduction of new technologies that better fit the requirements of the new scenario in which all the actors in the energy field are working. In this view, the contribution of Advanced Ceramics to such a big effort, with the identification of some development routes needed in terms of new materials and technologies, is analysed. In particular, the possible future trends in Solid Oxide and High Temperature PEM fuel cells, as well as oxygen and hydrogen pumping for hydrogen production connected with R&D in Advanced Ceramics, are discussed.

Polymer Electrolyte Membranes for Water Photo-Electrolysis

Water-fed photo-electrolysis cells equipped with perfluorosulfonic acid (Nafion® 115) and quaternary ammonium-based (Fumatech® FAA3) ion exchange membranes as separator for hydrogen and oxygen evolution reactions were investigated. Protonic or anionic ionomer dispersions were deposited on the electrodes to extend the interface with the electrolyte. The photo-anode consisted of a large band-gap Ti-oxide semiconductor. The effect of membrane characteristics on the photo-electrochemical conversion of solar energy was investigated for photo-voltage-driven electrolysis cells. Photo-electrolysis cells were also studied for operation under electrical bias-assisted mode. The pH of the membrane/ionomer had a paramount effect on the photo-electrolytic conversion. The anionic membrane showed enhanced performance compared to the Nafion®-based cell when just TiO2 anatase was used as photo-anode. This was associated with better oxygen evolution kinetics in alkaline conditions compared to acidic environment. However, oxygen evolution kinetics in acidic conditions were significantly enhanced by using a Ti sub-oxide as surface promoter in order to facilitate the adsorption of OH species as precursors of oxygen evolution. However, the same surface promoter appeared to inhibit oxygen evolution in an alkaline environment probably as a consequence of the strong adsorption of OH species on the surface under such conditions. These results show that a proper combination of photo-anode and polymer electrolyte membrane is essential to maximize photo-electrolytic conversion.

Synthesis and sintering of Ce 1-x Gd x O 2-x/2 nanopowders via chemical routes.

Gd-doped ceria (Ce 0.80 Gd 0.20 O 1.90 ) obtained by several nanopowder synthesis processes are compared structurally, morphologically and electrochemically. The powders have been sintered into pellets and investigated by ac-impedance measurements. The electrochemical properties of the electrolytes have been correlated to the structural morphology of the sintered pellets. When the intergrain region exhibits an elevated interdiffusion, the observation of the grain boundaries becomes difficult while the electrochemical properties are improved. Acrylamide polymerization and oxalic co-precipitation techniques showed the best properties.

Electrochemical Impedance Spectroscopy as a Diagnostic Tool in Polymer Electrolyte Membrane Electrolysis

Membrane–electrode assemblies (MEAs) designed for a polymer electrolyte membrane (PEM) water electrolyser based on a short-side chain (SSC) perfluorosulfonic acid (PFSA) membrane, Aquivion®, and an advanced Ir-Ru oxide anode electro-catalyst, with various cathode and anode noble metal loadings, were investigated. Electrochemical impedance spectroscopy (EIS), in combination with performance and durability tests, provided useful information to identify rate-determining steps and to quantify the impact of the different phenomena on the electrolysis efficiency and stability characteristics as a function of the MEA properties. This technique appears to be a useful diagnostic tool to individuate different phenomena and to quantify their effect on the performance and degradation of PEM electrolysis cells.