School of Chemistry, Monash University, Clayton, VIC 3800, Australia.
CSIRO Energy, Private Bag 10, Clayton South, Victoria 3169, Australia.
ChemSusChem. 2022 Oct 21;15(20):e202200614. doi: 10.1002/cssc.202200614. Epub 2022 Sep 29.
Studies of the ammonia oxidation reaction (AOR) for the synthesis of nitrite and nitrate (NO ) have been limited to a small number of catalytic materials, majorly Pt based. As the demand for nitrate-based products such as fertilisers continues to grow, exploration of alternative catalysts is needed. Herein, 19 metals immobilised as particles on carbon fibre electrodes were tested for their catalytic activity for the ammonia electrooxidation to NO under alkaline conditions (0.1 m KOH). Nickel-based electrodes showed the highest overall NO yield with a rate of 5.0±1.0 nmol s cm , to which nitrate contributed 62±8 %. Cu was the only catalyst that enabled formation of nitrate, at a rate of 1.0±0.4 nmol s cm , with undetectable amounts of nitrite produced. Previously unexplored in this context, Fe and Ag also showed promise and provided new insights into the mechanisms of the process. Ag-based electrodes showed strong indications of activity towards NH oxidation in electrochemical measurements but produced relatively low NO yields, suggesting the formation of alternate oxidation products. NO production over Fe-based electrodes required the presence of dissolved O and was more efficient than with Ni on longer timescales. These results highlight the complexity of the AOR mechanism and provide a broad set of catalytic activity and nitrate versus nitrite yield data, which might guide future development of a practical process for the distributed sustainable production of nitrates and nitrites at low and medium scales.
对氨氧化反应（AOR）用于合成亚硝酸盐和硝酸盐（NO ）的研究仅限于少数几种催化材料，主要是基于 Pt 的材料。随着对硝酸盐基产品（如肥料）的需求持续增长，需要探索替代催化剂。在此，我们测试了 19 种金属固定在碳纤维电极上的颗粒的催化活性，以研究它们在碱性条件（0.1 m KOH）下将氨电氧化为 NO 的活性。基于镍的电极表现出最高的总 NO 产率，为 5.0±1.0 nmol s cm ，其中硝酸盐的贡献为 62±8%。Cu 是唯一能够形成硝酸盐的催化剂，其产率为 1.0±0.4 nmol s cm ，且未检测到亚硝酸盐的生成。在这种情况下，以前未被探索过的 Fe 和 Ag 也表现出了希望，并为该过程的机制提供了新的见解。Ag 基电极在电化学测量中表现出对 NH 氧化的强烈活性迹象，但产生的 NO 产率相对较低，这表明形成了替代的氧化产物。Fe 基电极上的 NO 生成需要溶解氧的存在，并且在较长的时间内比 Ni 更有效。这些结果突出了 AOR 机制的复杂性，并提供了广泛的催化活性和硝酸盐与亚硝酸盐产率数据，这可能为未来在低中和中等规模下实现硝酸盐和亚硝酸盐的分布式可持续生产的实用工艺的发展提供指导。
