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.
High purity hydrogen
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 carbon monoxide, formic acid, or formaldehyde can be reversed with a high purity hydrogen stream. Sulfur dioxide is problematic
References
Hydrogen purity Wikipedia(Text) CC BY-SA