Nanoconical active structures prepared by anodization and deoxidation of molybdenum foil and their activity origin

Abstract To improve the surface activity of molybdenum (Mo), a method combining anodizing and deoxidizing annealing in a H2 atmosphere has been proposed to prepare nanocone-structured active Mo foils (NCSAMFs) in this paper. The morphology, composition and catalytic properties of the as-prepared NCSAMF were characterized by field-emission scanning electron microscopy (FESEM), energy dispersive spectrometry (EDS) and electrochemical measurements. Nanoconical structures were generated under a voltage of 20 V for 15 min in the optimized electrolyte, and all the oxygen atoms in the nanoconical structure layer were removed under deoxidation at 650 °C for 3 h in a H2 atmosphere while retaining the nanoconical structure and activity. Compared with the Mo foils treated under different conditions, the NCSAMFs exhibit superior hydrogen evolution reaction (HER) activity with a low onset overpotential of 123 mV and a Tafel slope of 96 mV dec−1, indicating that the NCSAMFs possess high activity and outstanding long-term stability in acidic media. Therefore, the NCSAMFs prepared in this paper are promising transition metal HER electrocatalysts and serve as active matrix materials for Mo-based materials. In addition, the surface energies of the NCSAMF and the Mo foils without nanotreatment were calculated at the atomic and mesoscopic scales, respectively, to provide more insights into the origin of the studied process, and the calculation results demonstrate that the high activity of NCSAMFs is mainly derived from the increase in Mo crystal surface area with high surface energy caused by the nanotreatment and the corresponding increase in the amount of active sites.