Morphology Changes of Cu₂O Catalysts During Nitrate Electroreduction to Ammonia**

This manuscript reports the electrosynthesis of ammonia from nitrate catalysed Cu derived from Cu₂O materials. Cu₂O (111) and (100) preferential grain orientations were prepared through electrodeposition. Cu derived from Cu₂O (111) is more active and selective for ammonia formation than Cu₂O (100) derived Cu. The highest faradaic efficiency (FE) was achieved for both catalysts at −0.3 V vs RHE, with Cu derived from Cu₂O (111) reaching up to 80 %. Additional measurements with quasi-in situ X-ray photoelectron spectroscopy and in situ Raman spectroscopy revealed that Cu⁰ is the active phase during the reaction. The stability of the catalysts was examined by ex situ methods such as SEM, XRD and ICP elemental analysis. The catalysts underwent severe morphological changes as a function of the applied potential and the reaction time, most likely due to the dissolution and redeposition of Cu. After 3 hours of reaction, the entire surface of the catalysts was reconstructed into nanoneedles. The FE after 3 hours remained higher for the Cu derived from Cu₂O (111), suggesting that the activity is dependent on the initial structure and the different rates of dissolution and re-deposition.