Modulation of Co-N4 active sites in 1D-2D heterostructure as bifunctional electrocatalyst for nitrate and nitrogen reduction reaction

Ammonia (NH3) is a key agricultural component and a source of clean energy as a hydrogen mediator. Ammonia is produced by Haber Bosch process, resulting in massive energy consumption and severe environmental impact. It is a thriving challenge to design and develop efficient nitrogen reduction reaction (NRR) and nitrate reduction reaction (NO3RR) electrocatalysts using variable reactants sources for ammonia synthesis at STP. 2D graphene sheets wrapped cobalt phthalocyanine nanotube to obtain (1D-2D) heterostructure, which serve as an active bifunctional electrocatalyst for NRR and NO3RR. At –0.2 V vs RHE, the electrocatalyst displayed NH3 yield rate of 58.82 μg h−1 mg−1 cat and a Faradaic efficiency (FE) of 95.12 % for NO3RR and 143.38 μg h−1 mg−1 cat and 43.69 % for NRR. Isotope tracing experiment confirmed the origin of ammonia synthesis. DFT calculations through Bader charge analysis revealed that charge transfer from the RGO to the Co-N4 sites in CoPc aided in the formation of NNH* @ NRR and *NOH @ NO3RR intermediates while impeding the competitive HER, resulting in high selectivity and FE. This study provides new mechanistic insights on the interfacial charge transfer, effect of work function and overpotential of electrocatalyst for their NO3RR and NRR utility.