A novel alternative to high-pressure mechanical hydrogen compression has been proposed. The alternative technology employs a two-stage, hybrid, thermo-electrochemical system based on electrochemical and metal hydride hydrogen compression technologies. A technical analysis was performed to evaluate the performance of both the electrochemical low-pressure stage (100 bar) and the metal hydride high-pressure stage (875 bar). The performance of several membrane and metal hydride candidate materials was evaluated and the best candidate materials were identified. A model of the integrated, two-stage system was developed that found that all or most of the waste heat from the electrochemical stage can be used to fully drive the metal hydride stage, thereby, improving the overall efficiency of the combined process.
a b s t r a c t a r t i c l e i n f o Available online xxxx Keywords: Platinum Catalysts Hydrogen pumping Fluidized bed Fluidization Atomic layer depositionPlatinum nanoparticle catalysts for electrochemical hydrogen pumping were synthesized on a functionalized powder carbon substrate (XC72R) using atomic layer deposition (ALD) in a fluidized bed reactor (FBR). Trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPtMe 3 ) was used as the reagent for platinum delivery. Following deposition, MeCpPtMe 3 ligands were combusted or hydrogenated to yield platinum on the XC72R surface. Reactions throughout the ALD cycle were monitored using mass spectrometry and IR spectroscopy to clarify the deposition chemistry. The resultant platinum catalysts were compared to commercial products in hydrogen pumping tests. Hydrogenation made finer, more dispersed, platinum nanoparticles that performed similarly to their commercial equivalent when pumping hydrogen. Conversely, oxygenation made a coarser catalyst that underperformed its commercial equivalent. Thus, altering chemistries shows potential for improving ALD catalyst performance.
Proton exchange membrane fuel cell (PEMFC) catalysts manufactured using atomic layer deposition (ALD) on unmodified and functionalized carbon were compared to a commercial catalyst in half-and whole-cell tests. Half-cell tests showed the ALD catalyst performed better or comparable to a commercial catalyst. Conversely, whole-cell tests revealed flooding in the ALD catalyst produced on functionalized carbon. Residual functional groups had reduced the hydrophobicity, and rendered this catalyst impractical for use in whole-cell PEMFC applications. However, the ALD catalyst produced on unmodified carbon performed better than the commercial catalyst, which illustrates the power of ALD on appropriate catalyst supports.
In micro satellites, delicate instrumentations are compacted into a limited space. It raises concerns of active cooling and remote cooling. Silicon based micro-pump arrays are employed thanks to manufacturing simplicity, a small cryogen charge, etc., which keeps the instrumentations within a narrow cryogenic temperature range. The mechanical performance of the silicon diaphragm, the key component of the micro-pump, is critical in terms of heat balance calculation and life time evaluation. This paper examines the mechanical performance of the silicon diaphragm under cryogenic temperature for micro satellite applications. In this work, differential pressure was used for the actuation of a single-crystal silicon diaphragm. Diaphragm deflection and stress distribution were achieved using interferometry and micro Raman spectroscopy, respectively. As a result, a higher elastic modulus was associated with the diaphragm under cryogenic temperature, comparing to that under room temperature, indicating a stiffer material. From stress mapping, the edge centers were believed to be the most vulnerable to fracture, which was further validated by analyzing the fracture diaphragm. Moreover, a fatigue testing was conducted for 1.8 million cycles with no damage found, verifying thin film silicon as a viable material for long time operation in a cryogenic environment.
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