Hydrogen purity

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 ICE can tolerate low hydrogen purity where a hydrogen fuel cell requires high hydrogen purity to prevent catalyst poisoning.[1]

Hydrogen purity requirements for fuel cells

In the first generation of fuel cells catalysts 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[2]. 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[3] 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 [4] 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 ([5],[6],[7]).

See also

References
  1. 2007-DOE-Hydrogen Fuel Quality
  2. X. Cheng, Z. Shi, N. Glass, L. Zhang, J. Zhang, D. Song, Z.-S. Liu, H. Wang and J. Shen (2007). "A review of PEM hydrogen fuel cell contamination:Impacts, mechanisms, and mitigation". Journal of Power Sources. 165 (2): 739–756. doi:10.1016/j.jpowsour.2006.12.012.CS1 maint: multiple names: authors list (link)
  3. "Directive 2014/94/EU on the deployment of alternative fuels structure". Retrieved 15 August 2018.
  4. "ISO 14687-2:2012". Retrieved 15 August 2018.
  5. "EMPIR hydrogen project". Retrieved 15 August 2018.
  6. "Hycora workshop" (PDF). Retrieved 15 August 2018.
  7. "Risk assesment impurities ISO 14687-2". Retrieved 15 August 2018.
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