In Situ Observation of Hydrogen Interactions with Highly Strained Ni Twin Boundaries

Transitioning from catalysis based on platinum group elements (PGE) to earth-abundant metal catalysts is crucial for sustainable large-scale hydrogen production. Due to its abundance, low price, and ability to promote hydrogenation reactions, nickel has been considered as a promising substitute for PGE catalysts, especially with enhanced catalytic activity achieved by tailored nanostructures such as grain size, defects, and strain. Among many defective structures, twin boundaries (TBs) have been noted to boost the hydrogen evolution reaction. However, the understanding of the kinetics of hydrogen incorporation and the formation of Ni hydride phases is limited due to the lack of direct microscopic evidence of hydrogen interaction with highly twinned areas and quantification of the effect of these interactions on the local structure.<br/>We employed in-situ environmental transmission electron microscopy to directly observe the interaction of highly strained nickel films with hydrogen, along with the resultant structural changes and strain redistribution. These films contain high densities of TBs and their intersections. The distribution of pre-existing strain around highly twinned Ni was examined, and the evolution of defective structures around the Ni TBs due to the volumetric expansion associated with the formation of hydrides was studied under a hydrogen gas environment. Subsequently, the structural change of highly twinned Ni area by the absorption and desorption of hydrogen was explored repeatedly over time. Density functional theory calculations elucidate the influence of the kinetics of hydrogen incorporation and the formation of hydride phases in highly strained multi-twinned areas, which is responsible for the enhanced catalytic activity. This work illuminates the role of defects in the formation of hydrides and the consequent effects of hydrogen absorption on the Ni nanostructure, providing insight into the design of PGE alternatives.