Abstract: Hydrogen will be at the basis of the World's energy policy in forthcoming decades, owing to its decarbonized nature, at least when produced from renewables. For now, hydrogen is still essentially produced from fossil feedstock (and to a minor extent from biomass); in consequence the present hydrogen gas on the market is containing non-negligible amounts of impurities that prevent its immediate usage in specialty chemistry or as an energy carrier in fuel cells, e.g. in transportation applications (cars, buses, trains, boats, etc.) that gradually spread on the planet. For these purposes, hydrogen must be of sufficient purity but also sufficiently compressed (at high pressures, typically 70 MPa), rendering purification and compression steps unavoidable in the hydrogen cycle. As shown in the first part of this contribution "Electrochemical hydrogen compression and purification versus competing technologies: Part I. pros and cons", electrochemical hydrogen compressors (EHCs), which enable both hydrogen purification and compression, exhibit many theoretical (thermodynamic) and practical (kinetics) advantages over their mechanical counterparts. However, in order to be competitive, EHCs must operate in very intensive conditions (high current density and low cell voltage) that can only be reached if their core materials, e.g. the membrane and the electrodes/electrocatalysts, are optimized. This contribution will particularly focus on the properties electrocatalysts must exhibit to be used in EHCs:they shall promote (very) fast hydrogen oxidation reaction (HOR) in presence of impurities, which implies that they are (very) tolerant to poisons as well. This consists of a prerequisite for the operation of the anode of an EHC used for the purification-compression of hydrogen, and the materials developed for poison-tolerance in the vast literature on low-temperature fuel cells, may not always satisfy these two criteria, as this contribution will review.

Key words: Electrochemical hydrogen compression, Electrochemical hydrogen purification, Electrocatalysts, Hydrogen oxidation, Poison tolerance