N2 solar activation: ammonia as a hydrogen vector for energy storage

From the plethora of energy-intensive synthetic processes, ammonia production has a particularly negative impact due to the high-energy consumption caused by the Haber–Bosch process and the high greenhouse gas (GHG) emission rate. Thus, new and effective ways to activate N2 and synthesise NH3 are crucial to reduce production costs and the anthropogenic footprint derived from the current harsh reaction conditions. In this study, two-dimensional materials have been employed in the photoactivation of nitrogen in an aqueous medium; MI(ii)MII(iii) (with MI = Cu or CuNi, and MII = Cr or Al) layered double hydroxides have been synthesised using a simple, economical and scalable co-precipitation/filtration method. The structural and functional properties were systematically investigated by XRD, SEM, TPR and BET; the results indicate that the prepared LDHs were successfully synthesised, possess high surface areas and, in the case of CuAl LDH, the material showed a nanoplate-like structure, thus confirming the two-dimensional nature of this class of catalyst. The N2 fixation performances were evaluated using a scalable, cost-effective and low-energy-consuming setup; from the catalytic tests, a NH3 production rate of 99 μmol g−1 h−1 was observed, demonstrating LDHs’ high potential and the scalability of the overall process.