Self-template synthesis of hierarchically structured Co3O4@NiO bifunctional electrodes for selective nitrate reduction and tetrahydroisoquinolines semi-dehydrogenation

The rational design and synthesis of hierarchically hollow nanostructures with controlled spatial architecture and composition are significant in electrocatalysis owing to their abundant active sites and the expedited electron/mass transfer. Electrocatalytic nitrate reduction to ammonia is of great interest from the points of environmental protection and energy saving. However, the development of this technology is hindered by the lack of efficient nitrate-to-ammonia electrocatalysts and the kinetically sluggish oxygen evolution reaction at the anode. Herein, a novel self-template conversion method was developed for the synthesis of Co3 O4@NiO hierarchical nanotubes (Co3O4@NiO HNTs) with NiO porous nanosheets assembled on Co3O4 nanotubes. The as-obtained Co3O4@NiO HNTs exhibited an outstanding performance for both the cathodic nitrate electroreduction to ammonia reaction and the anodic tetrahydroisoquinolines (THIQs) semi-dehydrogenation to dihydroisoquinolines (DHIQs). Importantly, a two-electrode system of Co3O4@NiO HNTs ∥ Co3O4@NiO HNTs was constructed for the simultaneous synthesis of ammonia and DHIQs with high selectivity and robust stability.