TECHNOLOGY AREA(S): Materials/Processes

ACQUISITION PROGRAM: PMS450, VIRGINIA Class Submarine Program Office

OBJECTIVE: Develop advanced non-noble metal PEM electrocatalysts and engineered nanostructures to improve submarine oxygen generators and significantly reduce cost.

DESCRIPTION: Oxygen is generated onboard submarines utilizing electrolysis conducted within a stack of Proton Exchange Membranes (PEM) cells known as a cell stack. Within the electrolysis cell stack, the PEM material is a subcomponent of the Membrane Electrode Assembly (MEA) and it is within this MEA that electrocatalysts are employed to encourage both the oxidation and reduction processes. The electrocatalysts currently used are noble metal catalysts, which add significant cost to the submarine electrolysis cell stack valued at $1M each.

Noble metals are also known as strategic metals as defined by the National Research Council and are often referred to as such in electrolysis studies. At an estimated 25% of the cost of an electrolysis cell stack, the MEA is a prime candidate for catalytic improvement with significant and measureable cost benefit. Recently reported basic research (references 1, 2, and 3) discusses the successful use of a non-noble metal catalyst for the electrolysis. The reported successes utilizing molybdenum phosphide (MoP) and molybdenum phosphide with a phosphosulfide surface (MoP/S) are extremely promising and directly applicable to PEM electrolyzers, however additional research is required to evaluate how these materials or similar non-noble metal catalysts perform at high current densities of approximately 1000 amps per square foot (ASF). By eliminating or reducing the use of costly precious metals as the electrocatalysts, the Navy will achieve significant cost reductions in acquisition and maintenance to the order of roughly $200,000 per electrolysis stack.

Additionally, the development of an improved and novel MEA such as an engineered nanostructure to enhance activity (references 4 and 5), will achieve a reduction in the catalyst loading, which will also result in significant cost reductions by reducing the amount of catalyst required. PEM fuel cells and the PEM electrolysis cell stacks have unique requirements. They have already achieved loading reductions of at least an order of magnitude below the current submarine PEM electrolysis cell stack design from on the order of 1 mg of catalyst / cm^2 of active area to on the order of 0.1 mg of catalyst / cm^2 of active areas. These unique requirements include alternative catalyst morphologies and compositions, support characteristics such as wetting properties and the porosity for gas and fluid transport, and deposition methods to form a highly active and stable electrode at low catalyst loading.

Current submarine electrolysis cell stacks are capable of operating at oxygen generation rates of 225 standard cubic feet per hour (SCFH) and a current density of 1000 ASF which are required to operate for a minimum of 30,000 hours prior to failure. Future submarine oxygen generators currently in development have these same operational requirements and will utilize a PEM electrolysis cell stack. It is critical to the Navy to invest in advancements in technology to realize benefits from potential performance improvements, to reduce the cost, and improve affordability of a known high dollar acquisition and maintenance component. Qualification of a new cell stack for submarine use would most likely involve shock/vibration testing and a 2,000-hour endurance test or equivalent testing to show that the cell stack will last the required 30,000 hours of operation.

The target platform for implementation of these improvements would be on all current and planned VIRGINIA Class submarines. Additionally, these improvements would be beneficial to the PEM electrolyzer on Ohio Replacement and may even stand to benefit the PEM electrolyzer on SEAWOLF and OHIO Class submarines. The objective is to meet current performance requirements while achieving a reduction in acquisition cost by $200K per electrolysis cell stack, which will have additional affordability benefits to the Navy’s operation and maintenance costs on the order of magnitude of $10M’s.

PHASE I: The company will develop a concept that will demonstrate and report on achieved and anticipated optimized performance of non-noble metal electrocatalysts as compared to noble metal electrocatalysts and improved or novel MEA structures capable of operating in the described submarine operational environment. The company will perform modeling and simulation to provide the initial feasibility assessment of the concept performance. The Phase I Option if exercised, will include the initial layout and capabilities description to build the MEA structures.

PHASE II: Based on the results of Phase I and the Phase II Statement of Work (SOW), the company will develop and build a prototype 4-cell stack incorporating the improved electrocatalyst and novel MEA structures developed in Phase I. This prototype should be capable of operating at equivalent current density of 1000 ASF and at an equivalent oxygen generation rate of 225 SCFH. Results from the prototype 4-cell stack testing will be compared to a 4-cell stack utilizing a noble metal electrocatalyst representative to those currently deployed on VIRGINIA Class submarines. The company will deliver the prototype at the end of the Phase II to the Navy.

PHASE III DUAL USE APPLICATIONS: The company will design and develop a process for manufacturing a 225 SCFH electrolysis cell stack which will operate in the VIRGINIA Class PEM electrolyzers capable of meeting the acquisition needs and the future maintenance requirements for potentially all other Navy submarine PEM electrolyzers. Depending on the need and similarity to the existing cell stack, the improved PEM electrolysis cell stack would optimally be qualified for submarine use as a standalone component as part of a submarine electrolyzer first article unit, or strictly by analysis, pending qualification. Private Sector Commercial Potential: This area of research and technologic improvements has direct importance to commercial PEM electrolyzers and PEM fuel cells. PEM electrolyzers and PEM fuel cells compete in markets such as automotive propulsion as an alternative to gasoline-powered engines (alternative energy source), supplying power to our nation’s electrical grid (energy efficiency), and even use as a clean water-splitting energy source as an alternative to fossil fuel-based power generation (alternative energy source). Adaptions of these improvements are also relevant for use in solar photo electrochemical cells in energy generation (alternative energy source) and all other market in which solar cells compete. All of these applications rely on the same limited noble metal electrocatalysts so all improvements will uniformly benefit all of these applications.

REFERENCES:

• Gao, Min-Rui et al. “An efficient molybdenum disulfide/cobalt diselenide hybrid catalyst for electrochemical hydrogen generation.” Nature Communications 6, Article Number 5982, DOI: 10.1038/ncomms6982, 14 January 2015.
• Kibsgaard, Jakob and Jaramillo, Thomas. “Molybdenum Phosphosulfide: An Active, Acid-Stable, Earth-Abundant Catalyst for the Hydrogen Evolution Reaction.” Angewandte Chemie International Edition Volume 53, Issue 52, 22 December 2014, Pages 14433-14437.
• Jaramillo, Thomas. “Low Cost Catalyst for Hydrogen Production and Renewable Energy Storage.” Stanford University Office of Technology Licensing. Stanford Reference: 14-317. http://techfinder.stanford.edu/technology_detail.php?ID=31394
• Lu, Qi et al. “Highly porous non-precious bimetallic electrocatlysts for efficient hydrogen evolution.” Nature Communications 6 Article Number 6567, DOI: 10.1038/ncomms7567, 16 March 2015. http://www.nature.com/ncomms/2015/150316/ncomms7567/full/ncomms7567.html
• Zhao, Zhenlu. “Bacteriorhodopsin/Ag Nanoparticle-Based Hybrid Nano-Bio Electrocatalyst for Efficient and Robust H2Evolution from Water.” Journal of the American Chemical Society, 2015, 137, 8, Pages 2840-2843. http://pubs.acs.org/doi/abs/10.1021/jacs.5

KEYWORDS: Non-noble metal catalyst; electrocatalyst for oxygen generation; electrochemical; hydrogen evolution; proton exchange membrane; fuel cell molybdenum phosphide with a phosphosulfide surface

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