Metal-organic frameworks (MOFs) exhibited great potential in the electrocatalytic reduction of nitrate to ammonia (eNORR), but the structural transformation and the identification of the active sites in the electrochemical process have rarely been reported. Herein, a series of MOFs have been fabricated for eNORR. The Co-based MOF (Co-TPA) is selected as a representative for exploration through - and - techniques to reveal the structural evolution during eNORR. The structural transformation from the Co-TPA to electrochemically activated catalyst (Co-TPA-E) is verified, and it is found that the - formed high-valent Co species (CoOOH) are the active sites for eNORR. Moreover, the formation of the high-valence CoOOH species can be further facilitated by introducing highly electronegative Cu ions into the Co-TPA-E, resulting in excellent catalytic activity with an NH yield rate of 1.12 mmol h cm at − 0.326 V vs. RHE and a maximum Faradaic efficiency of 99.62 %.

中文翻译：

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来自金属有机框架电化学活化的高价钴活性位点，用于有效地将硝酸盐还原为氨

金属有机框架（MOF）在硝酸盐电催化还原为氨（eNORR）方面表现出巨大的潜力，但电化学过程中的结构转变和活性位点的识别却鲜有报道。在此，我们为 eNORR 制造了一系列 MOF。选择Co基MOF（Co-TPA）作为代表，通过-and-技术进行探索，以揭示eNORR过程中的结构演化。验证了从Co-TPA到电化学活化催化剂（Co-TPA-E）的结构转变，发现形成的高价Co物种（CoOOH）是eNORR的活性位点。此外，通过将高负电性铜离子引入Co-TPA-E中，可以进一步促进高价CoOOH物质的形成，从而产生优异的催化活性，在- 0.326 V vs. 1.12 mmol h cm的NH产率为1.12 mmol h cm。 RHE 和最大法拉第效率为 99.62%。