A Catalyst for Sodium Borohydride Dehydrogenation Based on a Mixed-Valent Iron Hydroxide Platform

Abstract

Although sodium borohydride (NaBH4, SBH) has been investigated extensively as a high-capacity hydrogen-storage material that can be used to move toward a hydrogen-powered society, the development of efficient and cost-effective catalysts for the generation of hydrogen from SBH remains challenging. Here, we report that a mixed-valent [FeII-FeIII] iron hydroxide, which we term green rust (GR), treated with a CuCl2 solution shows a good solar-light-assisted catalytic activity toward SBH hydrolysis at room temperature that is higher than those of existing catalysts, including Pt nanoparticle-modified titanium dioxide (TiO2). Even without solar light, the GR-based catalyst exhibits turnover frequency (TOF) of up to 5000 min-1 for the hydrolysis of SBH at a higher temperature, which is comparable to or one or two orders of magnitude higher than those of existing catalysts based on precious and noble metals under similar or identical conditions. Comprehensive spectral and microscopic analyses revealed that our catalyst was composed of GR plate-like particles with edges that were decorated with aggregated Cu2O clusters with particle sizes down to 5 nm. Molecular dynamics simulations, combined with experimental results, demonstrate that the Cu2O modifier not only provides adsorption sites for SBH molecules but also acts as a cocatalyst for the transfer of photoexcited electrons in the GR component to the adsorbed SBH, both of which enable the effective activation of the reactant (BH4-).