Onset potentials for different reaction mechanisms of nitrogen activation to ammonia on transition metal nitride electro-catalysts
Onset potentials for different reaction mechanisms of nitrogen activation to ammonia on transition metal nitride electro-catalysts
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DOI：
10.1016/j.cattod.2016.11.047
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发表时间：
2017-05-15
期刊：
影响因子：
5.3
通讯作者：
Skulason, Egill
中科院分区：
文献类型：
--
作者：
Abghoui, Younes;Skulason, Egill
最近的 DFT 理论计算表明，过渡金属氮化物 (TMN) 是在环境条件下催化 N-2 电还原成氨的有前途的材料。为了了解哪种机制更有利，我们进行DFT计算，通过传统的缔合（AM）和解离（DM）机制探索这些材料在最稳定结构下的催化活性，然后将相应的结果与我们最近报道的Mars-van Krevelen（MvK）机制的结果进行比较。大多数氮化物在清洁表面上的 N-2 解离是吸热的，并且在所有情况下活化势垒都很大，这抑制了这些材料上的 DM。通过 MvK 预测的这些 TMN 上氨形成的起始电位总是比 AM 的负值要小，但在少数情况下，两种机制具有相似的起始电位。在这些情况下，AM 不如 MvK 有利，因为 N-2 分子的吸附是吸热的。因此，MvK 几乎总是有利的机制。我们在这项工作中使用了计算氢电极方法，并忽略了任何质子-电子转移反应势垒，但包括这些势垒是必要的，以做出更明确的陈述，这是未来工作的主题。 (C) 2016 Elsevier B.V. 保留所有权利。
Recent theoretical calculations with DFT suggest that transition metal nitrides (TMNs) are promising materials to catalyze N-2 electroreduction to ammonia at ambient conditions. To realize which mechanism is more favourable, we conduct DFT calculations to explore the catalytic activity of these materials in their most stable structures via conventional associative (AM) and dissociative (DM) mechanisms, and then compare the corresponding results with that of Mars-van Krevelen (MvK) mechanism we recently reported. The dissociation of N-2 on the clean surfaces is endothermic on most of these nitrides and the activation barriers large in all cases, which is inhibitive of a DM on these materials. The onset potential predicted for ammonia formation on these TMNs is always less negative via MvK than with AM, except a few cases, where both mechanisms have similar onset potentials. In those cases, the AM is less favourable than MvK since the adsorption of N-2 molecule is endothermic. Therefore, the MvK is almost always the favourable mechanism. We used the computational hydrogen electrode method and neglected any proton-electron transfer reaction barriers in this work but including those will be necessary to make a more definitive statement, which is the subject of future work. (C) 2016 Elsevier B.V. All rights reserved.