Electrocatalytic selectivity for nitrogen reduction vs. hydrogen evolution: a comparison of vanadium and cobalt oxynitrides at different pH values
Electrocatalytic selectivity for nitrogen reduction vs. hydrogen evolution: a comparison of vanadium and cobalt oxynitrides at different pH values
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氮还原与析氢的电催化选择性：不同 pH 值下钒和钴氮氧化物的比较
DOI：
10.1039/d2ta05180j
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发表时间：
2022
影响因子：
11.9
通讯作者：
Kelber, Jeffry A.
中科院分区：
文献类型：
--
作者：
Chukwunenye, Precious;Ganesan, Ashwin;Gharaee, Mojgan;Balogun, Kabirat;Anwar, Fatima;Adesope, Qasim;Cundari, Thomas R.;D'Souza, Francis;Kelber, Jeffry A.
电催化氮还原反应（NRR）作为用于农业和清洁能源应用的NH3生产的环境友好方法具有显著的兴趣。然而，NRR维斯维斯析氢反应（HER）的选择性被认为不利地影响许多潜在的催化剂，包括地球上丰富的过渡金属氮氧化物。因此，直接比较具有不同金属亲氧性的两种过渡金属氮氧化物-Co和V的相对HER/NRR选择性。电催化电流-电势测量、操作荧光、吸收和H2和NH3产生的GC测量，非原位X射线光电子能谱（XPS），和密度泛函理论（DFT）计算相结合，直接比较在相同的反应条件下的NRR和HER活性。结果表明，钴氮氧化物-与钴主要在钴（II）的氧化态-NRR活性在pH值为10，与电化学还原的晶格氮和溶解的N2，后者发生没有N纳入晶格。晶格N的去除然后产生Co（II）氧化物，其仍然是NRR活性的。这些结果的补充计算表明，N2在Co（II）的网站结合是积极的有利于在Co（III）网站的结合。GC分析表明，H2的产生与氨的产生一致，但以更高的速率发生。相比之下，氧钒膜在相同（pH 10）条件下以及在pH 7下是HER非活性的，但在pH 7下是NRR活性的。DFT计算表明，在两种材料中的一个主要区别是阻碍O-H解离的H2O吸附在O-连接的Co与V阳离子中心。组合的研究表明HER与NRR选择性作为所采用的过渡金属氮氧化物的函数的显著变化，以及V和Co氮氧化物中的不同HER机制。
The electrocatalytic nitrogen reduction reaction (NRR) is of significant interest as an environmentally friendly method for NH3 production for agricultural and clean energy applications. Selectivity of NRR vis-à-vis the hydrogen evolution reaction (HER), however, is thought to adversely impact many potential catalysts, including Earth-abundant transition metal oxynitrides. Relative HER/NRR selectivities are therefore directly compared for two transition metal oxynitrides with different metal oxophilicities—Co and V. Electrocatalytic current–potential measurements, operando fluorescence, absorption, and GC measurements of H2 and NH3 production, ex situ X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations are combined to directly compare NRR and HER activities under identical reaction conditions. Results show that cobalt oxynitrides – with Co primarily in the Co(II) oxidation state – are NRR active at pH 10, with electrochemical reduction of both lattice nitrogen and dissolved N2, the latter occurring without N incorporation into the lattice. Removal of lattice N then yields Co(II) oxide, which is still NRR active. These results are complemented by calculations showing that N2 binding at Co(II) sites is energetically favored over binding at Co(III) sites. GC analysis demonstrates that H2 production occurs in concert with ammonia production but at a far greater rate. In contrast, vanadium oxynitride films are HER inactive under the same (pH 10) conditions, as well as at pH 7, but are NRR active at pH 7. DFT calculations indicate that a major difference in the two materials is hindered O–H dissociation of H2O adsorbed at O-ligated Co vs. V cation centers. The combined studies indicate significant variation in HER vs. NRR selectivity as a function of employed transition metal oxynitrides, as well as different HER mechanisms in V and Co oxynitrides.