Development of Standards in Support of Hydrogen-Fueled Vehicles

The Society of Automotive Engineers International (SAE) has proposed a Hydrogen Fuel Quality Specification Guideline. Several contaminants, in particular sulfur-containing compounds, have been identified that will be detrimental to the performance of the hydrogen fuel cell. NIST has begun the development of standard preparation and analytical methodology for: hydrogen sulfide (H₂S), carbonyl sulfide (COS), methyl mercaptan (CH₃SH), and ammonia (NH₃). NIST participated in an ASTM Committee D03 round robin study of sulfur compounds in nitrogen.

The performance of hydrogen-fueled vehicles is dictated by the performance of the fuel cell, which in turn is affected by the quality of the hydrogen gas used. Several contaminants have been identified that will decrease the performance of the fuel cell. Among these are hydrogen sulfide (H₂S), carbonyl sulfide (COS), methyl mercaptan (CH₃SH), and ammonia (NH₃). Currently, there are no nationally recognized standards for these components either in nitrogen or hydrogen as the balance gas. NIST’s objective is to develop accurate, stable standards of these components in balance nitrogen, then in balance hydrogen. In this way the quality (purity) of the hydrogen used for vehicles can be accurately determined.

During the participation in the ASTM round robin study of H₂S, COS, and CH₃SH, NIST developed analytical methods to certify these components in the 1 µmol/mol to 25 µmol/mol range with a typical accuracy of 1% or better. Further, a novel technique was established, whereby an effluent from a permeation tube was cryotrapped to form an accurate, high-pressure gas standard. The permeation rate was measured throughout the trapping process by a system consisting of a very sensitive mass balance (10^-10 g sensitivity) and a MolBloc flow meter. Mass loss of the permeation tube was linear over the trapping time and allowed the permeation rate to be calculated to less than 0.5 % uncertainty. This is the uncertainty of the standards produced by this method. To date, 2 µmol/mol to 20 µmol/mol standards have been produced for CH₃SH, H₂S, and NH₃. Future work will include: 1) stability testing of these standards; 2) improving analytical methodology to increase accuracy; 3) establishing standards in the 0.1 µmol/mol to 1 µmol/mol range; and 4) extending the components to other contaminants that affect the hydrogen cell, e.g. carbonyl disulfide (CS₂) and formaldehyde (HCHO).

• Prepared accurate high-pressure CH₃SH, H₂S, and NH₃ standards by cryotrapping permeation tube effluent in aluminum cylinders
• Developed analytical methods to analyze COS, CH₃SH, and H₂S in the 1 µmol/mol to 25 µmol/mol range
• Participated as reference laboratory in ASTM sulfur gas round robin