NASA requires a durable and efficient catalyst for the electrolysis of water in a polymer-electrolyte-membrane (PEM) cell. Ruthenium oxide in a slightly reduced form is known to be a very efficient catalyst for the anodic oxidation of water to oxygen, but it degrades rapidly, reducing efficiency. To combat this tendency of ruthenium oxide to change oxidation states, it is combined with iridium, which has a tendency to stabilize ruthenium oxide at oxygen evolution potentials. The novel oxygen evolution catalyst was fabricated under flowing argon in order to allow the iridium to preferentially react with oxygen from the ruthenium oxide, and not oxygen from the environment.
Nanoparticulate iridium black and anhydrous ruthenium oxide are weighed out and mixed to 5–18 atomic percent. They are then heat treated at 300 °C under flowing argon (in order to create an inert environment) for a minimum of 14 hours. This temperature was chosen because it is approximately the creep temperature of ruthenium oxide, and is below the sintering temperature of both materials. In general, the temperature should always be below the sintering temperature of both materials. The iridiumdoped ruthenium oxide catalyst is then fabricated into a PEM-based membrane-electrode assembly (MEA), and then mounted into test cells.
The result is an electrolyzer system that can sustain electrolysis at twice the current density, and at the same efficiency as commercial catalysts in the range of 100–200 mA/cm2. At 200 mA/cm2, this new system operates at an efficiency of 85 percent, which is 2 percent greater than commercially available catalysts. Testing has shown that this material is as stable as commercially available oxygen evolution catalysts. This means that this new catalyst can be used to regenerate fuel cell systems in space, and as a hydrogen generator on Earth.
This work was done by Thomas I. Valdez, Sri R. Narayan, and Keith J. Billings of Caltech for NASA’s Jet Propulsion Laboratory. In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to: Innovative Technology Assets Management JPL Mail Stop 202-233 4800 Oak Grove Drive Pasadena, CA 91109-8099 E-mail:
This Brief includes a Technical Support Package (TSP).
Iridium-Doped Ruthenium Oxide Catalyst for Oxygen Evolution
(reference NPO-46387) is currently available for download from the TSP library.
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Overview
The document presents a Technical Support Package detailing the development of an Iridium-Doped Ruthenium Oxide Catalyst for Oxygen Evolution, primarily aimed at enhancing the efficiency of electrolysis systems for water splitting. This research, conducted at the Jet Propulsion Laboratory (JPL) and supported by NASA, addresses the need for durable and efficient catalysts in polymer-electrolyte membrane (PEM) cells, which are crucial for regenerative fuel cells, particularly for lunar applications.
The motivation behind this work stems from the challenges associated with existing catalysts, which often lack the necessary durability and efficiency for sustained operation in electrolysis. The novel catalyst developed in this study demonstrates superior electrochemical performance compared to commercially available iridium-ruthenium oxide catalysts. Specifically, it can operate at an efficiency of 85% at a current density of 200 mA/cm², which is 2% higher than its commercial counterparts.
The fabrication process of the iridium-doped ruthenium oxide catalyst involves careful preparation of starting materials, which are mixed and heat-treated in a controlled environment (argon atmosphere) to ensure optimal reaction conditions. The choice of a heat treatment temperature of 300 °C is strategic, as it is below the sintering temperature of the materials involved, allowing for effective catalyst formation without compromising structural integrity.
The document emphasizes the novelty of the catalyst's electrochemical efficiency, which enables it to sustain the oxygen evolution reaction (OER) at twice the current density of commercial catalysts while maintaining comparable efficiency. This advancement is significant for applications in regenerative fuel cells, which are essential for providing power to manned lunar bases and could also contribute to the development of carbon-free energy sources on Earth.
In summary, the iridium-doped ruthenium oxide catalyst represents a significant technological advancement in the field of electrolysis, with potential implications for both space exploration and terrestrial energy solutions. The research highlights the collaborative efforts of JPL and the University of Southern California, showcasing the importance of innovative technology in addressing future energy challenges.
