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

TL;DR

This study reveals that the work function of transition metal nitrides determines their stability in hydrogen environments, with lower work functions leading to reduced nitridation and improved material stability.

Contribution

It introduces the work function as a key parameter for predicting the reducibility of transition metal nitrides in hydrogen, offering a new approach to designing hydrogen-resistant coatings.

Findings

Work function influences nitridation in TMNs.

Reduction stops below a certain work function threshold.

Hydrogen binds preferentially to metal atoms, preventing volatile species formation.

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.