'''Hydrogen purity''' or hydrogen quality is a term to describe the lack of impurities in [[hydrogen]] as a [[fuel gas]]. The purity requirement varies with the application, for example a H₂ [[Internal combustion engine|ICE]] can tolerate low hydrogen purity where a hydrogen fuel cell requires high hydrogen purity to prevent [[catalyst poisoning]].<ref>[http://www.nrel.gov/docs/fy07osti/41541.pdf 2007-DOE-Hydrogen Fuel Quality]</ref>

==Hydrogen purity requirements for fuel cells==

In the first generation of [[fuel cell]]s [[catalyst]]s like [[palladium]], [[ruthenium]] and [[platinum]] are used in combination with [[hydrogen production]] from hydrocarbons which results in performance degradation.

The catalyst poisoning induced by some impurities like [[carbon monoxide]], [[formic acid]], or [[formaldehyde]] can be reversed with a high purity hydrogen stream. Presence of other impurities like sulfurs may lead to permanent degradation of the fuel cells<ref>{{Cite journal|last=X. Cheng, Z. Shi, N. Glass, L. Zhang, J. Zhang, D. Song, Z.-S. Liu, H. Wang and J. Shen|title=A review of PEM hydrogen fuel cell contamination:Impacts, mechanisms, and mitigation|journal=Journal of Power Sources|volume=165|issue=2|pages=739–756|doi=10.1016/j.jpowsour.2006.12.012|year=2007}}</ref>^. The kind of impurities and their level depends on the H₂ production process (e.g., steam methane reforming, electrolysis) but impurities can also be introduced due to transport, cleaning of the refueling station, leakages or maintenance.

In Europe, the Directive 2014/94/EU<ref>{{Cite web|url=https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32014L0094&from=EN|title=Directive 2014/94/EU on the deployment of alternative fuels structure|access-date=15 August 2018}}</ref> on the deployment of alternative fuels infrastructure states that the hydrogen purity dispensed by hydrogen refuelling points shall comply with the technical specifications included in the ISO 14687-2 standard. ISO 14687-2 <ref>{{Cite web|url=https://www.iso.org/standard/55083.html|title=ISO 14687-2:2012|access-date=15 August 2018}}</ref> specifies maximum impurities levels for particles and several gaseous impurities. For many compounds the limit values are very low including total sulfur (4 nmol/mol) or carbon monoxide (200 nmol/mol). The least stringent limits are for helium (300 µmol/mol) and total nitrogen/argon (300 µmol/mol).  The sum of the impurities should be less than 300 µmol/mol (e.g. H₂ purity is 99.97%).

== Analytical methods for hydrogen purity analysis ==

As the limit values for many impurities are very low this sets stringent demands on the sensitivity of the analytical methods. Moreover, the high reactivity of some impurities requires use of a properly passivated sampling and analytical systems. A combination of different instruments (e.g. gas chromatography, infrared spectroscopy and mass spectroscopy) is now needed to cover all components listed in ISO 14687-2. Currently, several research efforts are directed to address the existing problems focusing on new multi-component analytical methods, risk assessments to limit the number of impurities to be analyzed (e.g. by using information from the H₂ production process) and lay the metrological foundation for H₂ purity analysis (<ref>{{Cite web|url=http://projects.lne.eu/jrp-hydrogen/|title=EMPIR hydrogen project|access-date=15 August 2018}}</ref>,<ref>{{Cite web|url=http://hycora.eu/workshops/09102015/Aarhaug_WP2.pdf|title=Hycora workshop|access-date=15 August 2018}}</ref>,<ref>{{Cite web|url=https://www.sciencedirect.com/science/article/pii/S0360319918308450|title=Risk assesment impurities ISO 14687-2|access-date=15 August 2018}}</ref>).

==See also==

*[[Glossary of fuel cell terms]]

==References==

{{reflist|refs=}}

==External links==

*[http://www.fuelcellstandards.com/H2Quality.ppt H2 Quality]

{{DEFAULTSORT:Hydrogen Purity}}

[[Category:Hydrogen]]

[[Category:Hydrogen technologies]]