Perspectives on hydrogen uptake, diffusion and trapping

•Advanced hydrogen diffusion model with generalised boundary conditions.•Electrochemical recombination shown to be reason for limited hydrogen uptake with increase cathodic current.•Concept of irreversible trapping challenged and acceptable leakage rate of hydrogen from traps proposed.•Applicability of beneficial traps discussed.

Contentious issues in relation to hydrogen uptake and diffusion in metals (primarily steels) are discussed in relation to recent modelling predictions and current understanding. Topics highlighted include optimising charging conditions in hydrogen permeation measurements, limits to hydrogen uptake with increase in charging current density, irreversible traps and beneficial traps, the effective diffusion coefficient, the primary source of hydrogen in relation to hydrogen assisted cracking, and outstanding challenges in modelling hydrogen diffusion.