基于钼镉相分离的多孔碳化钼晶体结构调控及产氢催化位点研究

The development of hydrogen evolution reaction (HER) electrocatalysts with high activity, high stability and low cost is of great significance for the wide application of hydrogen energy. Molybdenum carbide has attracted much attention as a kind of electrocatalyst whose theoretical HER activity is close to platinum. Exposing more catalytically active sites, play an important role in increasing electrocatalytic activity for electrocatalysts. In this study, cadmium molybdate was used as the precursor. During the high-temperature carbonization process, the chemical bonding between Cd atom and the Mo atom was beneficial to the molybdenum atoms free from being covered by the excess carbon. The Mo catalytic sites were exposed by the phase separation between molybdenum and cadmium, as well as the volatilization of Cd. The porous crystal structure and catalytic site regulation of molybdenum carbide were finally realized. By exploring the crystal structure evolution and phase transformation regularity from cadmium molybdate to molybdenum carbide, a controllable preparation method for synthesizing porous molybdenum carbide based on phase separation and Cd volatilization is realized. By discussing the exposure of catalytic site for molybdenum carbide and the corresponding electrocatalytic activity, the regulation mechanism of Cd on the catalytic site of molybdenum carbide was revealed, and high HER activity was achieved. The favoring development of the project is expected to realize a controllable technology for synthesizing porous molybdenum carbide with high activity based on the phase separation between cadmium and cadmium, and provide a new way and theoretical basis for the regulation of catalytic sites of other porous transition metal carbides.

开发高活性、高稳定性、低成本的析氢反应电催化剂，对氢能源的广泛应用具有重要意义。碳化钼作为一类电解水产氢理论活性接近铂的电催化剂备受关注。对电催化剂来说，暴露更多的催化活性位点是提高其电催化活性的主要因素。本研究以钼酸镉作为前驱体，利用钼酸镉中Cd-Mo原子成键作用，避免高温碳化过程中钼原子被多余碳覆盖，利用钼镉相分离Cd金属挥发充分暴露Mo催化位点，实现碳化钼的多孔晶体结构和催化位点调控。通过研究此过程中钼酸镉到碳化钼的晶体结构演化关系与物相转化规律，实现基于钼镉相分离金属Cd挥发合成多孔碳化钼的可控制备方法。通过探讨镉挥发造孔调控碳化钼的催化位点显露以及对应的电催化活性变化规律，阐明Cd对碳化钼催化位点的调控机理，实现高效电催化产氢。该项目的顺利开展有望实现一种基于钼镉相分离Cd挥发制备高效催化活性多孔碳化钼的可控工艺，并为其他多孔过渡金属碳化物的催化位点调控提供新的途径和理论依据。

开发高活性、高稳定性、低成本的析氢反应电催化剂，对氢能源的广泛应用具有重要意义。碳化钼作为一类电解水产氢理论活性接近铂的电催化剂备受关注。对碳化钼电催化剂来说，产氢活性位点主要位于钼原子，因此暴露更多的钼催化活性位点是提高其电催化活性的主要因素。. 本项目通过调控反应条件实现不同尺寸钼酸镉的可控制备，进而以钼酸镉作为模板和前驱体，制备了多孔、晶体结构高度对齐的Cd、N共掺杂碳化钼电催化剂。研究证明，镉元素的存在对形成多孔的高度排列的Cd, N-Mo2C起到了关键作用，增加了电化学活性面积，暴露了Mo活性位点。首先，利用钼镉相分离Cd金属升华可以产生多孔结构，有效地暴露Mo活性位点，增加有效活性面积；其次，Cd的掺杂会调节Mo原子的电子态密度，从而获得适当的Mo-H键合强度，阐明了Cd对碳化钼催化位点的调控机理，实现高效电催化产氢。第三，研究了钼酸镉到碳化钼的晶体结构演化关系与物相转化规律，得到具有高度对齐结构的Cd, N-Mo2C，这有利于内部电子转移，提升HER性能。第四，Cd的存在可以有效调控Mo2C的暴露晶面，因此我们提出了(200)/(121)晶面比值判断碳化钼电催化活性的评价方式。最后，利用钼酸镉中Cd-Mo原子成键作用，可以有效避免高温碳化过程中钼原子被多余碳覆盖，有利于暴露钼催化位点。该项目的顺利开展实现了一种基于钼镉相分离Cd挥发制备高效催化活性多孔碳化钼的可控工艺，并为其他多孔过渡金属碳化物的催化位点调控提供新的途径和理论依据。