School of Molecular Sciences, Arizona State University, Tempe, Arizona 85281, United States.
Department of Materials, University of Oxford, Oxford, OX1 3PH, U.K.
ACS Nano. 2023 Jul 11;17(13):12693-12705. doi: 10.1021/acsnano.3c03395. Epub 2023 Jun 27.
MAX phases with the general formula are layered carbides, nitrides, and carbonitrides with varying stacking sequence of layers of octahedra and the element depending on . While "211" MAXphases ( = 1) are very common, MAX phases with higher , especially ≥ 3, have hardly been prepared. This work addresses open questions regarding the synthesis conditions, structure, and chemical composition of the "514" MAX phase. In contrast to literature reports, no oxide is needed to form the MAX phase, yet multiple heating steps at 1,600 °C are required. Using high-resolution X-ray diffraction, the structure of (MoV)AlC is thoroughly investigated, and Rietveld refinement suggests -62 as the most fitting space group. SEM/EDS and XPS show that the chemical composition of the MAX phase is (MoV)AlC. It was also exfoliated into its MXene sibling (MoV)C using two different techniques (using HF and an HF/HCl mixture) that lead to different surface terminations as shown by XPS/HAXPES measurements. Initial investigations of the electrocatalytic properties of both MXene versions show that, depending on the etchant, (MoV)C can reduce hydrogen at 10 mA cm with an overpotential of 166 mV (HF only) or 425 mV (HF/HCl) after cycling the samples, which makes them a potential candidate as an HER catalyst.
MAX 相具有通式 ，是由不同堆叠顺序的 八面体和 元素层组成的层状碳化物、氮化物和碳氮化物，具体取决于 。虽然“211”MAX 相（ = 1）很常见，但具有更高 的 MAX 相，特别是 ≥ 3，几乎没有被制备出来。这项工作解决了关于“514”MAX 相的合成条件、结构和化学成分的一些问题。与文献报道相反，形成 MAX 相不需要氧化物，但需要在 1600°C 下进行多次加热步骤。使用高分辨率 X 射线衍射，对 (MoV)AlC 的结构进行了彻底研究，Rietveld 精修表明 -62 是最合适的空间群。SEM/EDS 和 XPS 表明 MAX 相的化学成分为 (MoV)AlC。它也被剥离成其 MXene 兄弟体 (MoV)C，使用了两种不同的技术（使用 HF 和 HF/HCl 混合物），这两种技术导致了不同的表面终止，如 XPS/HAXPES 测量所示。对两种 MXene 版本的电催化性能的初步研究表明，根据蚀刻剂的不同，(MoV)C 在 10 mA cm 下可以还原氢气，过电势为 166 mV（仅 HF）或 425 mV（HF/HCl），在循环样品后，这使得它们成为 HER 催化剂的潜在候选物。
