Hierarchical Nanospheres with Polycrystalline Ir&Cu and Amorphous Cu₂ O toward Energy-Efficient Nitrate Electrolysis...

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 Cu₂ 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 NH₃ yield rate (YR) up to 0.423 mmol h^-1  cm^-2 (or 4.8 mg h^-1  mg_cat ^-1 ) and a high NH₃ 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 NO₃ ^- 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.