Transition-metal phosphides, as the promising alternatives to noble metal catalysts, have been widely used as efficient electrocatalysts for hydrogen evolution reaction (HER). In this work, three kinds of cobalt-8-hydroxyquinoline (Coq_x) with different size and nanostructures are synthesized by varying the hydrothermal conditions, which was named as Coq_x-L, Coq_x-M and Coq_x-S according to the decreased size. Accordingly, the Co_xP/NC with three different size nanostructures (Co_xP/NC-L, Co_xP/NC-M and Co_xP/NC-S) are obtained by the sequential carbonization and phosphidation of Coq_x. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results imply the identical chemical composition in these catalysts with different morphologies. Thus, systematic study is carried out to reveal the relationship between catalytic performance and morphologies of materials with the same chemical composition. The experimental result indicates that the morphology of Co_xP/NC plays a crucial role on the surface area and electron transfer. Finally, the catalyst of Co_xP/NC-S with the smallest size nanostructrue exhibits the best HER performance with a low overpotential at current density of 10 mA/cm² (η = 56.9 and 115.6 mV) and a small Tafel slope (52.3 and 69.3 mV/dec) in both 0.1 M HClO₄ and 1.0 M KOH as well as long-term stability.

中文翻译：

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通过在不改变化学成分的情况下微调Co基催化剂的形貌来提高析氢性能

过渡金属磷化物作为贵金属催化剂的有希望的替代品，已被广泛用作氢释放反应（HER）的有效电催化剂。通过改变水热条件，合成了三种不同尺寸和纳米结构的钴8-羟基喹啉（Coq _x），分别命名为Coq _x -L，Coq _x -M和Coq _x -S。尺寸减小。因此，将Co _X P / NC具有三个不同尺寸的纳米结构（联合_X P / NC-L，钴_X P / NC-M和Co _X P / NC-S）由Coq的的连续碳化和phosphidation获得_X。X射线衍射（XRD）和X射线光电子能谱（XPS）结果表明，这些催化剂具有相同的形态，但具有相同的化学组成。因此，进行了系统的研究以揭示具有相同化学组成的材料的催化性能与形态之间的关系。实验结果表明，Co _x P / NC的形貌对表面积和电子传递起着至关重要的作用。最后，具有最小尺寸纳米结构的Co _x P / NC-S催化剂表现出最好的HER性能，在10 mA / cm ^2的电流密度下（η = 56.9和115.6 mV）具有低的过电势和小的Tafel斜率（52.3）和69.3 mV / dec）在0.1 M HClO _4中 和1.0 M KOH以及长期稳定性。