Photoelectrochemical (PEC) direct ammonia oxidation is a sustainable alternative to the industrial production of nitrate or nitrite (NO_x⁻), while the highly selective NO_x⁻ synthesis remains challenging due to the intricate kinetics and the inherent competition from the water oxidation reaction (WOR). Herein, we report a high-performance Si-based photoanode modified with Ni–Cu bimetallic nanosheets (NiCuO_x/Ni/n-Si), which presents a benchmark faradaic efficiency of 99% for PEC NO_x⁻ synthesis together with a record partial photocurrent density of ∼12 mA cm⁻² at a low bias of 1.38 V_RHE under AM 1.5G illumination. This results in a NO_x⁻ production rate of 59 μmol h⁻¹ cm⁻² and simultaneously a H₂ production rate of 214 μmol h⁻¹ cm⁻² on the counter electrode. Operando PEC spectroscopic measurements combined with theoretical calculations reveal that water molecules activated at Ni sites produce Ni^IVO species, which bond with the activated ammonia at Cu sites via a nearly barrierless N–O coupling pathway. Such a bimetallic synergetic mechanism presents a first-order hole-transfer kinetics, which kinetically circumvents the competing O₂ production and thus significantly promotes the selectivity to NO_x⁻ on the NiCuO_x/Ni/n-Si photoanode. This work provides a promising strategy for designing advanced photoanodes for cooperative oxidation reactions.

中文翻译：

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NH3 和 H2O 协同氧化通过近乎无障碍的 N-O 偶联途径选择性生产硝酸盐


光电化学（PEC）直接氨氧化是工业生产硝酸盐或亚硝酸盐（NO _x ⁻ ）的可持续替代方案，同时高选择性NO _x <由于复杂的动力学和水氧化反应 (WOR) 的固有竞争，b3> 的合成仍然具有挑战性。在此，我们报道了一种用 Ni-Cu 双金属纳米片 (NiCuO _x /Ni/n-Si) 改性的高性能硅基光阳极，其 PEC NO _x ⁻ 在 AM 1.5G 下进行合成，并在 1.38 V 低偏压 _RHE 下实现约 12 mA cm 的创纪录部分光电流密度 ⁻² 照明。这导致 NO _x ⁻ 生成率为 59 μmol h ⁻¹ cm ⁻² ，同时产生 H ₂ 对电极上的生成率为 214 μmol h ⁻¹ cm ⁻² 。 Operando PEC 光谱测量结合理论计算表明，在 Ni 位点激活的水分子会产生 Ni ^IV O 物种，它通过几乎无势垒的 N- 与 Cu 位点的激活氨结合O偶联途径。这种双金属协同机制呈现出一阶空穴转移动力学，在动力学上规避了竞争性 O ₂ 的产生，从而显着提高了对 NO _x ⁻ 在 NiCuO _x /Ni/n-Si 光阳极上。这项工作为设计用于协同氧化反应的先进光电阳极提供了一种有前途的策略。