Molybdenum carbides are considered as one type of privileged noble-metal-free electrocatalysts for hydrogen evolution reactions (HER) due to their d-band electron structure, which is similar to Pt. Especially, the electronic structure of such materials can be further adjusted by elemental doping to improve their electrocatalytic activity. Herein, we selected the Anderson-type polyoxometalates (POMs) (NH₄)_n[TMMo₆O₂₄H₆]·5H₂O (TM = Ni²⁺, Co²⁺, n = 4; TM = Fe³⁺, Cr³⁺, n = 3) as precursors to prepare new transition-metal-doped Mo₂C materials. When these POMs were mixed with dicyandiamide (DCA) by solid grinding, and carbonized at a high temperature, a series of Ni-, Co-, Fe-, and Cr-doped Mo₂C composite nanoparticles covered by few-layer graphitic carbon shells (abbr. TM-Mo₂C@C) were obtained. All these nanoparticles possess a similar size, morphology, and TM/Mo component ratio, and thus it is feasible to systematically investigate the influence of different TM dopants on the electrocatalytic activity of Mo₂C for HER. Both electrocatalytic experiments and DFT calculations reveal that TM dopants have a significant effect on the hydrogen binding energy (ΔG_H*) and the catalytic activity of Mo₂C. The sequence of HER electrocatalytic activity is as follows: Ni-Mo₂C > Co-Mo₂C > Fe-Mo₂C > Cr-Mo₂C. As a result, Ni-Mo₂C@C possesses the best HER performance, which required an overpotential of 72 mV at a current density of 10 mA cm⁻² and the Tafel slope is 65.8 mV dec⁻¹. This work suggests a shortcut to reasonably investigate the effects of elemental doping on molybdenum carbides and explore new high-efficient and low-cost electrocatalysts for HER.

中文翻译：

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不同过渡金属掺杂剂影响 的超小型Mo ₂ C在析氢反应中的电催化性能†

碳化钼由于其d带电子结构（类似于Pt），被认为是用于氢释放反应（HER）的一种优先使用的不含贵金属的电催化剂。特别地，可以通过元素掺杂来进一步调节此类材料的电子结构以改善其电催化活性。在这里，我们选择了安德森型多金属氧酸盐（POMs）（NH ₄）_n [TMMo ₆ O ₂₄ H ₆ ]·5H ₂ O（TM = Ni 2 ⁺，Co 2 ⁺，n = 4; TM = Fe ³⁺， Cr ³⁺，n = 3）作为前体以制备新的过渡金属掺杂的Mo₂ C材料。当将这些POM与双氰胺（DCA）进行固体研磨混合并在高温下碳化时，一系列的Ni，Co，Fe和Cr掺杂的Mo ₂ C复合纳米颗粒被几层石墨碳壳覆盖获得（缩写为TM-Mo ₂ C @ C）。所有这些纳米颗粒具有相似的尺寸，形态和TM / Mo组分比，因此系统研究不同的TM掺杂剂对Mo ₂ C对HER的电催化活性的影响是可行的。电催化实验和DFT计算均表明TM掺杂剂对氢键能（ ΔG _{H *}）和Mo ₂的催化活性具有显着影响。C. HER电催化活性的序列如下：Ni-Mo系₂ C> Co-Mo系₂ C>铁钼₂ C>铬钼₂ C.其结果是，Ni-Mo系₂ Ç@ C_具有最好HER性能，在10 mA cm ^-2的电流密度下需要72 mV的超电势，并且Tafel斜率为65.8 mV dec ^-1。这项工作提出了捷径，可以合理地研究元素掺杂对碳化钼的影响，并探索用于HER的新型高效，低成本电催化剂。