Hierarchical Nanospheres with Polycrystalline Ir&Cu and Amorphous Cu 2 O toward Energy-Efficient Nitrate Electrolysis to Ammonia.

Electrochemical reduction reaction of nitrate (NITRR) provides a sustainable route toward the green synthesis of ammonia. Nevertheless, it remains challenging to achieve high-performance electrocatalysts for NITRR especially at low overpotentials. In this work, hierarchical nanospheres consisting of polycrystalline Iridium&copper (Ir&Cu) and amorphous Cu 2 O (Cu x Ir y O z NS) have been fabricated. The optimal species Cu 0.86 Ir 0.14 O z delivers excellent catalytic performance with a desirable NH 3 yield rate (YR) up to 0.423 mmol h -1  cm -2 (or 4.8 mg h -1  mg cat -1 ) and a high NH 3 Faradaic efficiency (FE) over 90% at a low overpotential of 0.69 V (or 0 V RHE ), where hydrogen evolution reaction (HER) is almost negligible. The electrolyzer toward NITRR and hydrazine oxidation (HzOR) is constructed for the first time with an electrode pair of Cu 0.86 Ir 0.14 O z //Cu 0.86 Ir 0.14 O z , yielding a high energy efficiency (EE) up to 87%. Density functional theory (DFT) calculations demonstrate that the dispersed Ir atom provides active site that not only promotes the NO 3 - adsorption but also modulates the H adsorption/desorption to facilitate the proton supply for the hydrogenation of *N, hence boosting the NITRR. This work thus points to the importance of both morphological/structural and compositional engineering for achieving the highly efficient catalysts toward NITRR.