Tailoring the interior structure of Cu₂O Shell-in-Shell nanospheres for high-performance electrocatalytic nitrate-to-ammonia conversion

Electrocatalytic nitrate reduction is one of the most promising technology for removing harmful nitrate from water while simultaneously producing value-added ammonia. Regulating the internal structure of the benchmark electrocatalyst copper can further improve nitrate-to-ammonia conversion performance. Herein, we synthesized a series of hollow multi-shell structured Cu2O nanospheres (NSs) via a multistep Ostwald ripening method, and evaluated their nitrate-to-ammonia conversion performance. Results show that 2-shell Cu2O NSs demonstrated the highest nitrate conversion (98.1 %), ammonia selectivity (80.2 %), ammonia Faradic efficiency (70.3 %) and reaction rate constant (0.03 min(-1)) for nitrate-to-ammonia conversion. Important influencing factors are also examined including applied potentials and nitrate concentrations. Mechanistic study unravels that the outstanding electrocatalytic performance of 2-shell Cu2O NSs originates from the strongest nitrite adsorption so as to enhance nitrate-to-ammonia conversion. Materials characterizations verify that Cu2O NSs were reduced to metallic copper that severed as the real active site during electrocatalytic nitrate reduction. This work unveils the interior structure-dependent electrocatalytic performance of Cu2O NSs for nitrate-to-ammonia conversion, which offers a practical strategy to design structurally novel heterogeneous catalysts for various applications.