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 CuO nanospheres (NSs) via a multistep Ostwald ripening method, and evaluated their nitrate-to-ammonia conversion performance. Results show that 2-shell CuO NSs demonstrated the highest nitrate conversion (98.1 %), ammonia selectivity (80.2 %), ammonia Faradic efficiency (70.3 %) and reaction rate constant (0.03 min) 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 CuO NSs originates from the strongest nitrite adsorption so as to enhance nitrate-to-ammonia conversion. Materials characterizations verify that CuO 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 CuO NSs for nitrate-to-ammonia conversion, which offers a practical strategy to design structurally novel heterogeneous catalysts for various applications.

中文翻译：

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定制 Cu2O 壳中壳纳米球的内部结构以实现高性能电催化硝酸盐至氨的转化


电催化硝酸盐还原是去除水中有害硝酸盐同时生产增值氨的最有前途的技术之一。调节基准电催化剂铜的内部结构可以进一步提高硝酸盐到氨的转化性能。在此，我们通过多步奥斯特瓦尔德熟化方法合成了一系列空心多壳结构的氧化铜纳米球（NSs），并评估了它们的硝酸盐到氨的转化性能。结果表明，2 壳层 CuO NS 表现出最高的硝酸盐转化率 (98.1%)、氨选择性 (80.2%)、氨法拉第效率 (70.3%) 和硝酸盐至氨转化的反应速率常数 (0.03 分钟)。还检查了重要的影响因素，包括施加的电位和硝酸盐浓度。机理研究表明，2壳CuO NSs优异的电催化性能源于最强的亚硝酸盐吸附，从而增强硝酸盐到氨的转化。材料表征验证了 CuO NSs 被还原为金属铜，金属铜在电催化硝酸盐还原过程中作为真正的活性位点被切断。这项工作揭示了 CuO NSs 在硝酸盐至氨转化中的内部结构依赖性电催化性能，为设计用于各种应用的结构新颖的多相催化剂提供了实用策略。