Analysis of the Purity of Hydrogen at Public Hydrogen Refuelling Stations in Germany

Kurzfassung

Abundant contaminants in hydrogen are responsible for numerous degradation modes within the fuel cell. In particular, for proton exchange membrane (PEM) based fuel cells for mobile applications a strong impact of contaminations on the longterm stability and thereby performance is well-known. Although these influences have been intensively studied, predominantly the purity of the hydrogen provided at public hydrogen refuelling stations (HRS) is rarely analyzed. To avoid damaging processes initiated by harmful compounds, international standards for the quality of hydrogen set precise limits for contaminations present in hydrogen [1, 2]. Whereas single pathways of contamination, e.g. the synthesis route, have been individually studied in detail elsewhere [3], the provision of hydrogen with different storage processes, as well as transport and compression at the HRS are considered in these investigations as a holistic system. For the investigation of hydrogen at HRS and the analysis of contaminations in the parts per billion (ppb) range, only a couple of mobile devices for the sampling at 70 MPa exist since no conventional gas cylinder can be used. Moreover, there are no general protocols available for the contamination-free sampling of hydrogen. In this study, a specially designed mobile composite high-pressure hydrogen tank similar to that in fuel cell vehicles is used. With this tank, it is possible to use the standardized dispenser at public HRS with up to 70 MPa. To ensure that the fuelled hydrogen and the subsequent analyses of the contaminants are referable to the so-sampled hydrogen, a specifically developed method is applied. In that regard, the first kilogram of hydrogen is fuelled to purge the system and subsequently, the tank is on-site carefully emptied again following mandatory safety regulations. Finally, the module is refuelled with the amount of hydrogen necessary for the laboratory analysis. By this, contaminants like water and sulphur compounds will be removed from within the module and sampling lines [4]. For investigating the purity of hydrogen, a high-performance gas analyzer based on an ion-molecule reaction mass spectrometer (IMR-MS) is employed. With this state-of-the-art equipment, i.e. the mobile hydrogen tank and the capable gas analysis, selected HRS in Germany were approached, hydrogen was sampled, and finally analysed for contaminants in the laboratory. Some HRS are supplied with hydrogen from steam reforming of natural gas via delivery by trailer; others produce the hydrogen directly at the refuelling station by on-site electrolysis without the necessary use of trailers. Thus, by investigating the hydrogen with the gas analysis in the laboratory a dependency of the manufacturing processes on the purity can be shown. In the first approach series, HRS supplied by on-site electrolysis showed high purity as expected, in general, but also noteworthy contamination above the threshold of ISO 14687 [1] in the form of water (19.3 ppm), carbon dioxide (2.9 ppm), and nitrogen (751.8 ppm). With this study, it can be estimated whether the dispensed hydrogen at HRS meets the purity requirements of fuel cells for mobile applications specified in ISO 14687 [1]. [1] International Organization for Standardization. 2019. ISO 14687:2019 Hydrogen fuel quality - Product specification. [2] SAE International Surface Vehicle Standard. 2016. SAE Standard J2601. Fueling Protocols for Light Duty Gaseous Hydrogen Surface Vehicles. [3] Bacquart T, Arrhenius K, Persijn S, Rojo A, Auprêtre F, Gozlan B, Moore N, Morris A, Fischer A, Murugan A, Bartlett S, Doucet G, Laridant F, Gernot E, Fernández T E, Gómez C, Carré M, De Reals G, Haloua F. 2019. Hydrogen fuel quality from two main production processes: Steam methane reforming and proton exchange membrane water electrolysis. Journal of Power Sources 444:227170.[4] ASTM International. 2017. ASTM D7606-17. Standard Practice for Sampling of High Pressure Hydrogen and Related Fuel Cell Feed Gases.