Current ex-situ electrochemical characterisation techniques for measuring the hydrogen reaction are insufficient to effectively characterise catalytic behaviour under CO containing environments. We show the high mass transport, floating electrode technique offers a solution as it adequately describes hydrogen oxidation (HOR) and evolution over a wide potential range, as needed for various electrochemical systems. The peak HOR mass activities measured on the floating electrode were 68–93 A.mgmetal-1 - significantly higher than achieved in an experimental setup of an electrochemical hydrogen pump (EHP, 6–12 A.mgmetal−1). This implies that the EHPs operate with a significant mass transport limitation. Additionally, poison tolerances of catalysts using low concentrations of 20 ppm CO produced transient responses over ca. 500 s which correctly followed the CO tolerances determined from EHPs (PtRu/C > Pt/C > PtNi/C). A model of the kinetic transient responses on the floating electrode is provided which aids in describing the catalytic behaviour in poisoned environments.