Enhancement of the hydrogen evolution performance by finely tuning the morphology of Co-based catalyst without changing chemical composition

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.