This simulation shows the concentration profiles (H2 grey, oxygen red, oxidised and reduced viologen pink and blue, and inactive enzyme black) within the depth of a film of redox polymer embedding the H2-oxidation catalyst hydrogenase. xi is the normalised distance to the electrode (xi=0 is the electrode/film interface; xi=1 is the film/solution interface). The first part of the simulation shows the system reaching steady-state under anaerobic condition. When the film is exposed to O2, O2 penetrates, inactivates the enzyme, oxidises the viologen; catalytic H2 oxidation by the enzyme produces reductive equivalents that diffuse outward, and reduce the incoming O2, preventing further penetration. Note the non linear time scale (the simulation accelerates, the evolution of the system slows down). Kappa=13 https://pubs.acs.org/doi/10.1021/jacs.9b06790.