ASTM D7941/D7941M-23 PDF

SIGNIFICANCE AND USE 5.1 Proton exchange membranes (PEM) used in fuel cells are susceptible to contamination from a number of species that can be found in hydrogen. It is critical that these contaminants be measured and verified to be present at or below the amounts stated in SAE J2719 and ISO 14687 to ensure both fuel cell longevity and optimum efficiency. Contaminant concentrations as low as single-figure ppb(v) for some species can seriously compromise the life span and efficiency of PEM fuel cells. The presence of contaminants in fuel-cell-grade hydrogen can, in some cases, have a permanent adverse impact on fuel cell efficiency and usability. It is critical to monitor the concentration of key contaminants in hydrogen during the production phase through to delivery of the fuel to a fuel cell vehicle or other PEM fuel cell application. In ISO 14687, the upper limits for the contaminants are specified. Refer to SAE J2719 (see 2.3) for specific national and regional requirements. For hydrogen fuel that is transported and delivered as a cryogenic liquid, there is additional risk of introducing impurities during transport and delivery operations. For instance, moisture can build up over time in liquid transfer lines, critical control components, and long-term storage facilities, which can lead to ice buildup within the system and subsequent blockages that pose a safety risk or the introduction of contaminants into the gas stream upon evaporation of the liquid. Users are reminded to consult Practice D7265 for critical thermophysical properties such as the ortho/para hydrogen spin isomer inversion that can lead to additional hazards in liquid hydrogen usage. SCOPE 1.1 This test method describes contaminant determination in fuel cell grade hydrogen as specified in relevant ASTM and ISO standards using cavity ring-down spectroscopy (CRDS). This standard test method is for the measurement of one or multiple contaminants including, but not limited to, water (H2O), oxygen (O2), methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), ammonia (NH3), and formaldehyde (H2CO), henceforth referred to as “analyte.” 1.2 This test method applies to CRDS analyzers with one or multiple sensor modules (see 6.2 for definition). This test method describes sampling apparatus design, operating procedures, and quality control procedures required to obtain the stated levels of precision and accuracy. 1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.