first-principles, ab-initio molecular dynamics, metal nanoparticles, extended metal surfaces, hydride, energy conversion and storage
One of the attractive hydride compounds is the borohydride which exhibits high hydrogen content in NaBH4 form (~10.6 wt%). Thus, significant number of experimental research have been devoted to investigate its applicability as a hydrogen source and as anodic fuel in direct borohydride fuel cell (DBFC) for direct electricity generation. Recently, a non-Pt catalyst (Osmium) is used in the DBFC anode, yielding very high mass-specific activity of ~1240 A/g. The wide application of this hydride in energy storage/conversion and the feasibility of using non-Pt metal as catalyst necessitate atomic level information regarding structures and electrochemical reactions such as oxidation. Thus, our present work employs first-principles electronic structure calculations as well as ab-initio molecular dynamics to determine borohydride structures on the widely used metal catalyst morphologies: extended surfaces and nanoparticles and reveal the role of facets and size. Moreover, for the first time, we show the oxidation reaction on a ~2nm metal nanoparticle as a function of electrode potential and differentiate such reaction from that of typical model surfaces. Here, the role of solvation in the local sites of the nanoparticle is revealed, which then poses important factors to consider in both modeling and synthesis of metal nanostructures.