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 compared to Co₃O₄ and ≈7.5-fold compared with Cu₂O, respectively, however, most importantly, we precisely place single Cu₂O and Co₃O₄ 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 Cu₂O+Co₃O₄ nanocubes during NO₃RR 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.