Modulation on Surface Termination Groups to Optimize the Adsorption Energy and Work Function of Nb2CTx for Enhanced Hydrogen Storage in Magnesium Hydride

Abstract Exploring high‐performance catalysts for hydrogen storage in magnesium hydride (MgH 2 ) is crucial but still a challenge. Herein, Nb 2 CT x with controllable surface termination groups is developed as an efficient catalyst and the bifunctional modulation (adsorption energy and work function) of different surface termination groups (F, O, OH, or defects) is explored. First, compared to F and O, the introduction of OH on the surface or the direct removal of functional groups both leads to a significant increase in the adsorption of H by Nb 2 CT x . Second, compared to the surface bare, OH‐rich Nb 2 CT x has a lower work function, making it easier for hydrogen to enter Mg/MgH 2 from the Nb 2 CT x surface or escape from the Mg/MgH 2 surface into the Nb 2 CT x , thus facilitating the hydrogen ad/desorption properties of MgH 2 , i.e., the rate‐determining step (RDS) shifts from penetration to diffusion. The Nb 2 CT x ‐KOH‐catalyzed MgH 2 with optimal surface termination groups, therefore exhibits a release of 6.56 wt.% H 2 in 5 min at 250 °C, and 6.46 wt.% H 2 uptake within 5 min at 150 °C. The dehydrogenation and hydrogen uptake activation energies show 49.5% and 60.1% enhancements over pristine MgH 2 . In addition, a storage capacity of 5.51 wt.% is maintained after 50 dehydrogenation/hydrogenation cycles.