Theoretical Design of Catalysts for the Heterolytic Splitting of H₂

Here, we briefly review recent advances in H 2 storage technologies relying on mixed proton–hydride and destabilized hydride materials. We establish a general relationship across different materials: the higher the effective H content, the higher the temperatures needed to completely desorb H 2 . Nevertheless, several systems show promising thermodynamics for H 2 desorption; however, the desorption kinetics still needs to be improved by the use of appropriate catalysts. Prompted by the importance of heterolytically splitting stable dihydrogen molecules for proton–hydride technologies, we attempt to theoretically design novel H 2 transfer catalysts. We focus mainly on M 4 Nm 4 H 8 catalysts (M = V, Ti, Zr, Hf, and Nm = Si, C, B, N), which should be able to preserve their functionality in the strongly reducing environment of a H 2 storage system. We are able to determine the energy of H 2 detachment from these molecules, as well as the associated energy barriers. In order to optimize the properties of the catalysts, we use isoelectronic atom‐by‐atom substitutions, vary the valence electron count, and borrow the concept of near‐surface alloys from extended solids and apply it to molecular systems. We are able to obtain control over the enthalpy and electronic barriers for H 2 detachment. Molecules with the coordinatively unsaturated > TiSi < unit exhibit particularly favorable thermodynamics and show unusually small electronic barriers for H 2 detachment (> 0.27 eV) and attachment (> 0.07 eV). These and homologous ZrSi frameworks may serve as novel H 2 transfer catalysts for use with emerging lightweight hydrogen storage materials holding 5.0–10.4 wt % hydrogen, such as Li 2 NH, Li 2 Mg(NH) 2 , Mg 2 Si, and LiH/MgB 2 (discharged forms). Catalytic properties are also anticipated for appropriate defects on the surfaces and crystal edges of solid Ti and Zr silicides, and for TiSi ad‐units chemisorbed on other support materials.