Kinetic analysis in the micropolarization region. The micropolarization region is a common starting point for kinetic analyses. Due to the small magnitude of the currents around the equilibrium potential, mass transport effects are negligible and the measured current density, j, can be regarded as being under purely kinetic control, j ≈ j kin . It is thus assumed to correspond to the kinetic current density, j kin , observable under ideal conditions, i.e., with the surface reactant concentrations equal to the bulk concentrations in the electrolyte. The measured micropolarization currents for the different hydrogen pressures are depicted in Fig. along with linear fits (dashed lines) in the region ±5 mV on an overpotential scale, i.e., around the respective equilibrium potential for each H 2 partial pressure. For small overpotential η, the Butler-Volmer equation for the kinetic current density can be linearized after a Taylor expansion, 24