A Bio-Inspired Dendritic MoOx Electrocatalyst for Efficient Electrochemical Nitrate Reduction to Ammonia

Drawing inspiration from the nitrate reductase enzymes, which catalyze nitrate to nitrite in nature, here a bio-inspired, reduced molybdenum oxide (MoOx) shell is introduced that is grown on top of a dendritic nickel foam core (NiNF). The resulting MoOx/NiNF material is prepared via a facile, two-step electrodeposition strategy using commercially available, low-cost precursors. This catalytic material displays a remarkable faradaic efficiency (FE) of 99% at −0.5 V versus RHE and a high ammonia (NH3) yield rate of up to 4.29 mmol h−1 cm−2 at −1.0 V versus RHE in neutral media. Most importantly, MoOx/NiNF exhibits exceptional stability for the nitrate reduction reaction (NO3RR), maintaining operation for over 3100 h at a high current density of −650 mA cm−2, with a yield rate of 2.6 mmol h−1 cm−2 and a stable average NH3 FE of ≈83%. Through combined XPS and in situ Raman spectroscopy it is shown that the pronounced affinity of MoOx/NiNF for nitrate is associated with a substantial presence of oxygen vacancies within the material.