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Defective UiO-66-NH2 Functionalized with Stable Superoxide Radicals toward Electrocatalytic Nitrogen Reduction with High Faradaic Efficiency
ACS Applied Materials & Interfaces ( IF 8.3 ) Pub Date : 2022-06-06 , DOI: 10.1021/acsami.1c23643 Xiaobo He 1 , Fengxiang Yin 1 , Xuerui Yi 2 , Tong Yang 2 , Biaohua Chen 1, 3 , Xiang Wu 1 , Shang Guo 1 , Guoru Li 1 , Zhichun Li 1
ACS Applied Materials & Interfaces ( IF 8.3 ) Pub Date : 2022-06-06 , DOI: 10.1021/acsami.1c23643 Xiaobo He 1 , Fengxiang Yin 1 , Xuerui Yi 2 , Tong Yang 2 , Biaohua Chen 1, 3 , Xiang Wu 1 , Shang Guo 1 , Guoru Li 1 , Zhichun Li 1
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The electrocatalytic nitrogen reduction reaction (NRR) to NH3 is limited by low Faradaic efficiency (FE). Herein, defective UiO-66-NH2 functionalized with quite stable superoxide radicals (O2•) is developed as a highly active NRR catalyst. The experimental and computational results show that one linker per Zr6 node is missed and two Zr atoms are exposed in the defective UiO-66-NH2. One of the two exposed Zr atoms can stably adsorb O2•, and thus, a Zr-OO• site forms during the preparations without light excitation or postoxidation, while the other Zr atom is activated as an active site. The synergistic effects of the two Zr sites in the defective UiO-66-NH2 suppress hydrogen and hydrazine evolutions considerably. They are as follows: (i) due to repulsion of the proton on the active Zr site and stabilization of the proton on the Zr-OO• site, the active Zr site is unfavorable for the adsorption of the proton with a high energy barrier, which is the HER rate-determining step (RDS); (ii) under the assistance of the OO• of the Zr-OO• site, the first hydrogenation step of *N2 (i.e., NRR RDS) on the active Zr site is promoted; and (iii) relying on the assistance of the OO• of the Zr-OO• site, the continuous hydrogenation of *NH2NH2 to produce NH3 on the active Zr site is spontaneously exothermic, whereas its desorption to hydrazine is blocked. Accordingly, an extremely high FE of ∼85.21% has been realized along with a high yield rate of NH3 (∼52.81 μg h–1 mgcat–1). To the best of our knowledge, it is the highest FE that has been achieved in recent years. Radical scavenging treatment of the defective UiO-66-NH2 and detailed investigations of two categories of control samples further verify the favorable effects of the O2• that closely correlates with the missed linkers on the performance of the NRR to NH3. This work opens a new way toward highly efficient NRR catalysts, i.e., stable radical-activating defective metal–organic frameworks.
中文翻译：
用稳定的超氧自由基功能化的缺陷 UiO-66-NH2 可实现高法拉第效率的电催化氮还原
电催化氮还原反应(NRR)生成NH 3受到低法拉第效率(FE)的限制。在此，用相当稳定的超氧自由基(O 2 • )功能化的有缺陷的UiO-66-NH 2被开发为高活性的NRR催化剂。实验和计算结果表明，在有缺陷的UiO-66-NH 2中，每个Zr 6节点丢失了一个连接子并且暴露了两个Zr原子。两个暴露的Zr原子之一可以稳定地吸附O 2 • ，因此，在制备过程中无需光激发或后氧化即可形成Zr-OO •位点，而另一个Zr原子则被激活作为活性位点。有缺陷的UiO-66-NH 2中两个Zr位点的协同效应显着抑制氢气和肼的释放。它们如下：（i）由于活性Zr位上质子的排斥和Zr-OO •位上质子的稳定，活性Zr位不利于具有高能垒的质子的吸附，这是 HER 速率决定步骤 (RDS)； (ii)在Zr-OO •位的OO •的辅助下，促进了活性Zr位上*N 2 (即NRR RDS)的第一氢化步骤； (iii)依靠Zr-OO •位的OO •的辅助，*NH 2 NH 2在活性Zr位上连续加氢生成NH 3 ，是自发放热的，但其解吸到肼的过程被阻断。因此，实现了~85.21%的极高FE以及NH 3的高收率（~52.81 µg h –1 mg cat –1 )。据我们所知，这是近年来达到的最高FE。对有缺陷的UiO-66-NH 2的自由基清除处理和对两类对照样品的详细研究进一步验证了O 2 •的有利影响，其与缺失的连接子对NH 3的NRR 性能密切相关。这项工作为高效NRR催化剂（即稳定的自由基激活缺陷金属有机框架）开辟了一条新途径。
更新日期：2022-06-06
中文翻译：
用稳定的超氧自由基功能化的缺陷 UiO-66-NH2 可实现高法拉第效率的电催化氮还原
电催化氮还原反应(NRR)生成NH 3受到低法拉第效率(FE)的限制。在此，用相当稳定的超氧自由基(O 2 • )功能化的有缺陷的UiO-66-NH 2被开发为高活性的NRR催化剂。实验和计算结果表明，在有缺陷的UiO-66-NH 2中，每个Zr 6节点丢失了一个连接子并且暴露了两个Zr原子。两个暴露的Zr原子之一可以稳定地吸附O 2 • ，因此，在制备过程中无需光激发或后氧化即可形成Zr-OO •位点，而另一个Zr原子则被激活作为活性位点。有缺陷的UiO-66-NH 2中两个Zr位点的协同效应显着抑制氢气和肼的释放。它们如下：（i）由于活性Zr位上质子的排斥和Zr-OO •位上质子的稳定，活性Zr位不利于具有高能垒的质子的吸附，这是 HER 速率决定步骤 (RDS)； (ii)在Zr-OO •位的OO •的辅助下，促进了活性Zr位上*N 2 (即NRR RDS)的第一氢化步骤； (iii)依靠Zr-OO •位的OO •的辅助，*NH 2 NH 2在活性Zr位上连续加氢生成NH 3 ，是自发放热的，但其解吸到肼的过程被阻断。因此，实现了~85.21%的极高FE以及NH 3的高收率（~52.81 µg h –1 mg cat –1 )。据我们所知，这是近年来达到的最高FE。对有缺陷的UiO-66-NH 2的自由基清除处理和对两类对照样品的详细研究进一步验证了O 2 •的有利影响，其与缺失的连接子对NH 3的NRR 性能密切相关。这项工作为高效NRR催化剂（即稳定的自由基激活缺陷金属有机框架）开辟了一条新途径。
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