Single‐entity Electrochemistry Unveils Dynamic Transformation during Tandem Catalysis of Cu2O and Co3O4 for Converting NO3− to NH3

Electrochemically converting nitrate to ammonia is an essential and sustainable approach to restoring the globally perturbed nitrogen cycle. The rational design of catalysts for the nitrate reduction reaction (NO3 RR) based on a detailed understanding of the reaction mechanism is of high significance. We report a Cu2 O+Co3 O4 tandem catalyst which enhances the NH3 production rate by ≈2.7-fold compared to Co3 O4 and ≈7.5-fold compared with Cu2 O, respectively, however, most importantly, we precisely place single Cu2 O and Co3 O4 cube-shaped nanoparticles individually and together on carbon nanoelectrodes provide insight into the mechanism of the tandem catalysis. The structural and phase evolution of the individual Cu2 O+Co3 O4 nanocubes during NO3 RR is unveiled using identical location transmission electron microscopy. Combining single-entity electrochemistry with precise nano-placement sheds light on the dynamic transformation of single catalyst particles during tandem catalysis in a direct way.