“…The first one is the classical two-step indirect absorption process, via the H ads adsorbed intermediate, first proposed by Bockris et al [20], whose rate constants are k 1 , k −1 , k 4 , k −4 . The second one can be seen as a generalization of the one-step Frumkin direct insertion process [21][22][23], which generates the H * abs in a thin sublayer, which was already proposed for the Pd/H system, and whose rate constants are k 5 , k −5 . In the sublayer, the absorbed monoatomic hydrogen, H abs , and the "trapped" hydrogen, H * abs , are supposed to interact through k t , k r .…”