  We present a generalised framework for resolving the
electrochemistry-diffusion interface and modelling hydrogen transport near a
crack tip. The adsorption and absorption kinetics are captured by means of
Neumann-type generalised boundary conditions. The diffusion model includes the
role of trapping, with a constant or evolving trap density, and the influence
of the hydrostatic stress. Both conventional plasticity and strain gradient
plasticity are used to model the mechanical behaviour of the solid. Notable
differences are found in the estimated crack tip hydrogen concentrations when
comparing with the common procedure of prescribing a constant hydrogen
concentration at the crack surfaces.
