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 (NO3RR) based on a detailed understanding of the reaction mechanism is of high significance. We report a Cu2O+Co3O4 tandem catalyst which enhances the NH3 production rate by ~2.7-fold com-pared to Co3O4 and ~7.5-fold compared with Cu2O, respectively. Most importantly, we precisely place single Cu2O and Co3O4 cube-shaped nanoparticles individually and together on carbon nano-electrodes provide insight into the mechanism of the tandem catalysis. The structural and phase evolution of the individual Cu2O+Co3O4 nanocubes during NO3RR is unveiled using identical location trans-mission electron microscopy. Combining single-entity electrochemis-try with precise nano-placement sheds light on the dynamic transfor-mation of single catalyst particles during tandem catalysis in a direct way.