ASTM D7941/D7941M-14

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, ISO 14687-2 and ISO 14687-3 to ensure both fuel cell longevity and optimum efficiency. Contaminant concentrations as low as single-figure ppb 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 14687-2 and ISO 14687-3, the upper limits for the aforementioned contaminants are specified. Refer to SAE J2719 and the California Code of Regulations (see 2.3) for example 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 icing up 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 property such as the ortho/para hydrogen spin isomer inversion that can lead to additional hazards in liquid hydrogen usage. In addition to this test method employing CRDS, test methods such as D7649 (carbon dioxide, argon, nitrogen, oxygen and water) and D7653 (IR active species) are used to measure impurities in hydrogen fuel.

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 (CO_{1.2 This test method applies to CRDS analyzers with one or multiple sensor modules (see 3.3 for definition), each of which is designed for a specific analyte. 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 may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.

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 and health practices and determine the applicability of regulatory limitations prior to use.