Effect of oxygen and nitrogen on hydrogen adsorption and permeation processes

• Dissolved gas variations negligibly affect D eff during hydrogen charging. • High H surface coverage and slow Tafel reaction rate occurred in N2 condition. • N and O atoms shown lower adsorption energies than H atom on Fe (100). • The adsorbed N atoms maintain the availability of hydrogen hollow sites. This study investigated the effect of oxygen and nitrogen on hydrogen adsorption and permeation by combining electrochemical hydrogen permeation tests with density functional theory calculations. During electrochemical hydrogen charging, variations in the dissolved gas medium have a negligible influence on the hydrogen diffusion rate. However, adsorbed N atoms significantly enhanced hydrogen adsorption energy at neighboring hollow site and preserved hydrogen hollow site availability, whereas O atoms exhibited the opposite behaviors. These distinctions illustrated the increased hydrogen surface coverage and diminished Tafel desorption kinetics on the iron surface under N 2 conditions compared with those under O 2 conditions. Moreover, the accelerated Tafel desorption kinetics under O 2 conditions might improve both OH − mass transport efficiency and the electrochemically active surface area, consequently accelerating Volmer reaction kinetics under O 2 condition.