(a) Adsorbed coverage of H and D as a function of time for Fe exposed to hydrogen gas pressures of 1.7 and 5.5 MPa, respectively. It can be observed that fully adsorbed hydrogen coverage occurs in tens of nanoseconds. (b) Chemisorption of H from the adsorbed H2 state, which occurs on the order of seconds. Note that for pressures above ≈1 Pa, the chemisorption rate is independent of pressure. The rate of adsorption is orders of magnitude faster than the rate of chemisorption, where full adsorption saturation of the surface occurs on the timescale of nanoseconds while dissociation of the adsorbed molecule occurs on the order of seconds. Reprinted from Connolly et al., Mater. Sci. Eng., A 753, 331 (2019).37 Copyright 2019 Elsevier.