Kuznetsov Denis A, Chen Zixuan, Abdala Paula M, Safonova Olga V, Fedorov Alexey, Müller Christoph R
Department of Mechanical and Process Engineering, Eidgenössische Technische Hochschule (ETH) Zürich, 8092 Zürich, Switzerland.
Paul Scherrer Institute, 5232 Villigen, Switzerland.
J Am Chem Soc. 2021 Apr 21;143(15):5771-5778. doi: 10.1021/jacs.1c00504. Epub 2021 Mar 31.
This work critically assesses the electrocatalytic activity, stability, and nature of the active phase of a two-dimensional molybdenum carbide (MXene) with single-atomic iron sites, MoC:Fe ( are surface terminating groups O, OH, and F), in the catalysis of the oxygen reduction reaction (ORR). X-ray absorption spectroscopy unequivocally confirmed that the iron single sites were incorporated into the MoC structure by substituting Mo atoms in the molybdenum carbide lattice with no other detectable Fe-containing phases. MoC:Fe, the first two-dimensional carbide with isolated iron sites, demonstrates a high catalytic activity and selectivity in the oxygen reduction to hydrogen peroxide. However, an analysis of the electrode material after the catalytic tests revealed that MoC:Fe transformed into a graphitic carbon framework with dispersed iron oxyhydroxide (ferrihydrite, Fh) species (Fh/C), which are the actual active species. This experimental observation and the results obtained for the titanium and vanadium 2D carbides challenge previous studies that discuss the activity of the native MXene phases in oxygen electrocatalysis. Our work showcases the role of 2D metal carbides as precursors for active carbon-based (electro)catalysts and, more fundamentally, highlights the intrinsic evolution pathways of MXenes in electrocatalysis.
本工作批判性地评估了具有单原子铁位点的二维碳化钼（MXene），即MoC:Fe（表面端基为O、OH和F）在氧还原反应（ORR）催化中的电催化活性、稳定性和活性相的性质。X射线吸收光谱明确证实，铁单原子位点通过取代碳化钼晶格中的钼原子而融入MoC结构，未检测到其他含Fe相。MoC:Fe是首个具有孤立铁位点的二维碳化物，在氧还原为过氧化氢的过程中表现出高催化活性和选择性。然而，催化测试后对电极材料的分析表明，MoC:Fe转变为具有分散的羟基氧化铁（水铁矿，Fh）物种（Fh/C）的石墨碳骨架，这些是实际的活性物种。这一实验观察结果以及钛和钒二维碳化物的实验结果对先前讨论原生MXene相在氧电催化中活性的研究提出了挑战。我们的工作展示了二维金属碳化物作为活性碳基（电）催化剂前体的作用，更重要的是，突出了MXene在电催化中的内在演化途径。
