Carbon-induced ionocovalence in MgH2 storage material

TL;DR

This study investigates how inserting light elements B and C into MgH2 alters its ionic character and stability, potentially improving hydrogen release kinetics for storage applications.

Contribution

It introduces a novel approach of modifying MgH2 with B and C to tune ionic character and stability, enhancing hydrogen release kinetics.

Findings

B and C insertion destabilizes MgH2 structure.

C reduces ionic character of hydrogen more than B.

Altered ionic character may improve hydrogen release kinetics.

Abstract

The overall large ionic character of MgH2 is reduced by inserting light elements from the first period, B and C, using a trirutile host superstructure. Both elements are found destabilizing to the structure with largely positive cohesive energy with interstitial B and slightly negative cohesive energy with interstitial C. This trend is also observed for low amounts of insertion down to (B,C)0.167MgH2. From the Bader charge analysis the largely ionic character of hydrogen is decreased to an average H-0.37 in the neighborhood of C and H-0.75 for the other hydrogen atoms atoms (resp. H-0.64 and H-0.76 for B insertion). This peculiar behavior should enable enhancing the kinetics of H release for potential applications.