Department of Chemistry and Biochemistry, Freie Universität Berlin , Taku Straße 3, 14195 Berlin, Germany.
Department of Materials and Earth Science, Institute of Applied Geosciences, Department of Geometrical Science, TU Darmstadt , Schnittspahn Straße 9, 64287 Darmstadt, Germany.
ACS Appl Mater Interfaces. 2017 Aug 2;9(30):25184-25193. doi: 10.1021/acsami.7b01647. Epub 2017 Jul 18.
In this work, we present a comprehensive study on the role of metal species in MOF-based Me-N-C (mono- and bimetallic) catalysts for the hydrogen evolution reaction (HER). The catalysts are investigated with respect to HER activity and stability in alkaline electrolyte. On the basis of the structural analysis by X-ray diffraction, X-ray-induced photoelectron spectroscopy, and transmission electron microscopy, it is concluded that MeN sites seem to dominate the HER activity of these catalysts. There is a strong relation between the amount of MeN sites that are formed and the energy of formation related to these sites integrated at the edge of a graphene layer, as obtained from density functional theory (DFT) calculations. Our results show, for the first time, that the combination of two metals (Co and Mo) in a bimetallic (Co,Mo)-N-C catalyst allows hydrogen production with a significantly improved overpotential in comparison to its monometallic counterparts and other Me-N-C catalysts. By the combination of experimental results with DFT calculations, we show that the origin of the enhanced performance of our (Co,Mo)-N-C catalyst seems to be provided by an improved hydrogen binding energy on one MeN site because of the presence of a second MeN site in its close vicinity, as investigated in detail for our most active (Co,Mo)-N-C catalyst. The outstanding stability and good activity make especially the bimetallic Me-N-C catalysts interesting candidates for solar fuel applications.
在这项工作中，我们对基于 MOF 的单金属和双金属 Me-N-C（单金属和双金属）催化剂中金属物种在析氢反应（HER）中的作用进行了全面研究。研究了催化剂在碱性电解质中对 HER 活性和稳定性的影响。基于 X 射线衍射、X 射线光电子能谱和透射电子显微镜的结构分析，得出结论认为 MeN 位似乎主导了这些催化剂的 HER 活性。从密度泛函理论（DFT）计算中获得的，形成的 MeN 位的数量与与这些位相关的形成能之间存在很强的关系，这些位在石墨烯层的边缘处整合。我们的结果首次表明，双金属（Co 和 Mo）在双金属（Co，Mo）-N-C 催化剂中的结合允许与单金属对应物和其他 Me-N-C 催化剂相比，以显著降低的过电势生产氢气。通过将实验结果与 DFT 计算相结合，我们表明，由于在其附近存在第二个 MeN 位，我们最活跃的（Co，Mo）-N-C 催化剂中一个 MeN 位上的氢结合能得到改善，从而提高了我们（Co，Mo）-N-C 催化剂性能的起源。出色的稳定性和良好的活性使双金属 Me-N-C 催化剂特别成为太阳能燃料应用的有吸引力的候选者。
