Work-Function-Dependent Reduction of Transition Metal Nitrides in Hydrogen Environments

Abstract: Amidst the growing importance of hydrogen in a sustainable future, it is crucial to develop coatings that can protect hydrogen-sensitive system components in reactive hydrogen environments. However, the prediction of the chemical stability of materials in hydrogen is not fully understood. In this study, we show that the work function is a key parameter determining the reducibility (i.e., de-nitridation) of transition metal nitrides (TMNs) in hydrogen radicals (H*) at elevated temperatures. We demonstrate that when the work function of a TMN system drops below a threshold limit, its reduction effectively stops. We propose that this is due to the preferential binding of H* to TM-atoms rather than N-atoms, which makes the formation of volatile species (NHx) unfavourable. This finding provides a novel perspective for comprehending the interaction of hydrogen with transition metal compounds and allows predicting the chemical stability of hydrogen-protective coatings.