NiTiFe and NiTiZn LDHs with affinity for hydrogen – Role of the surface basicity

Abstract

NiTi-based layered double hydroxides modified by isomorphic substitution of nickel by iron or zinc showed appreciable affinity towards hydrogen under ambient conditions. This affinity was correlated to their surface basicity, expressed in terms of CO2 retention capacity (CRC). The latter was assessed through thermal programmed desorption (TPD), and was found to vary almost linearly with the partial negative charge of lattice oxygen (PNCLO). Incorporation of iron or zinc induced a basicity enhancement, which was markedly affected by excessive amount of incorporated iron. This was explained in terms of structure compaction that reduces the amount of accessible basic sites. NiTiFe and NiTiZn LDHs showed almost similar affinity towards hydrogen, which appears to be enhanced by increasing amount of incorporated metal. However, both LDH types displayed thoroughly opposite HRC-CRC correlations presumably due to the different polarizing power of Fe and Zn cations within the LDH frameworks. These findings demonstrate that optimum basicity is an essential requirement for improved affinity towards hydrogen. This basicity can be judiciously tailored through adequate chemical composition for envisaging potential use in hydrogen storage.