Photocatalytic ammonia production enhanced by a plasmonic near-field and hot electrons originating from aluminium nanostructures

Abstract

Ammonia production at room temperature and atmospheric pressure is in high demand to assist in energy saving and the protection of the environment worldwide, as well as to help reduce CO₂ emissions. Recently, plasmonic nanomaterials have been frequently used for solar to chemical energy conversion, which has the potential to replace existing energy-intensive industrial processes. In our approach, plasmonic aluminium nanotriangles (AlNTs) were used to investigate the impact of plasmonic effects on photocatalytic ammonia production. Plasmonic near-field coupling to a semiconductor and hot electron generation from AlNTs were studied in detail through the use of electrochemical photocurrent measurements. A narrowband LED beam with a central wavelength at 365 nm was used to illuminate the AlNTs and their hot electron generation efficiency was estimated to be 2 × 10⁻⁴%, resulting in an ammonia production rate of 4 × 10⁻⁵ μM h⁻¹ mW⁻¹ cm⁻², which corresponds to a quantum efficiency of 2.5 × 10⁻⁵%. In the case of plasmonic near-field coupling, AlNTs-embedded TiO₂ demonstrates a charge-carrier generation efficiency of 2.7%, which is ∼2.3 times higher than that of bare TiO₂. The ammonia production rate of AlNTs–TiO₂ is 0.1 μM h⁻¹ mW⁻¹ cm⁻² with a quantum efficiency of ∼0.06%, which corresponds to ∼2.4 times that of the rate demonstrated by bare TiO₂ (0.04 μM h⁻¹ mW⁻¹ cm⁻², quantum efficiency ∼ 0.025%). The obtained results confirm successful ammonia production through nitrogen splitting at room temperature and under atmospheric pressure. Moreover, according to the presented results, the use of plasmonic aluminium structures remarkably improves the ammonia production rate.