Several cost reduction areas should be explored. Corrosion resistant materials such as Nb and Mo might prove useful as cladding materials that can be hot stamped. Some alternative to the metals we used in the cell, Mo and 316 SS, are potentially useful. In particular, alternatives to carbon paper GDLs such as metal felts and alternatives to carbon supports for Pt such as TiC and TiB2 might also be worthwhile and would be helpful to fuel cells as well. Alternatives to carbon in the cell may be helpful in any context. Alternative materials should be explored. This will insure uniform resistance perpendicular to the plane of the cell and eliminate some of the dependence of the resistance on high stack compression. A simple cure for the very high, localized corrosion of the anode might be to diffusion bond the metal electrode support screen to bipolar plate. These may be especially useful in conjunction with metal felt replacement of carbon paper. Ultra thin silane/siloxane polymer coatings should be tried. Corrosion solutions should be investigated such as surface passivation of 316 SS parts using nitric acid.
Investigation into the effects of conductivity enhancers such as carbon microlayers on supporting carbon paper is also needed. This would reveal the existence of organic compounds. The contaminated cell parts can be placed in an oxidizing atmosphere at high temperature and the weight loss can be observed. An investigation of possible electro-organic sythesis mechanisms with emphasis on oxalates formation is warranted. This may be due to the deposition of organic compounds, which may be produced electrochemically on the surface of the metal support screens that contact carbon gas diffusion layers (GDLs) or catalyst supports. In addition to corrosion there is evidence of high component resistivity.
Shunt currents at hydraulic cathode ports were problematic, but are not difficult to cure. The mechanisms involved in this phenomenon are poorly understood. We suspect that the corrosion includes more than simple galvanic mechanisms. The diagnosis of experimental cells with titration to determine the loss of membrane active sites is recommended.
First, we need a better understanding of the corrosion mechanisms involved. The experiments and analysis conducted lead to several recommended future research directions. It is an important area for scientific investigation. Our research suggests that there is more to the corrosion process in fuel cells and electrochemical compressors than simple, steady state, galvanic stability. The problem of corrosion resistant metal bipolar plates is vital to the development of an inexpensive, commercial PEM fuel cell. more » The development and successful demonstration of the hydraulic cathode is also important. This is one of the promising aspects of the redesigned EHC. The program produced a design with an extraordinary high cell pitch, and a very low part count. The nature of the corrosion mechanisms are not well understood, but locally high potentials within the unit cell package are probably involved. The use of carbon paper in combination with a perforated thin metal electrode demonstrated adequate anode support strength, but is suspect in promoting galvanic corrosion. It also showed that: molybdenum bipolar plates, photochemical etching processes, and Gortex Teflon seals are too costly for a commercial EHC. The research performed did not completely investigate Molybdenum as a hydrogen anode or cathode, it did show that photoetched 316 stainless steel is inadequate for an EHC. If the EHC can be made inexpensive, reliable and long lived then it can satisfy all these applications save pipelines where the requirements for platinum catalyst exceeds the annual world production. It was also evaluated as a modular replacement for the compressors used in petrochemical refineries. The Electrochemical Hydrogen Compressor EHC was evaluated against DOE applications for compressing hydrogen at automobile filling stations, in future hydrogen pipelines and as a commercial replacement for conventional diaphragm hydrogen compressors.