Mesoporous MoO 3– x Material as an Efficient Electrocatalyst for Hydrogen Evolution Reactions

A unique approach for the synthesis of nonstoichiometric, mesoporous molybdenum oxide (MoO 3– x ) with nanosized crystalline walls by using a soft template (PEO‐ b ‐PS) synthesis method is introduced. The as‐synthesized mesoporous MoO 3– x is very active and stable (durability > 12 h) for the electrochemical hydrogen evolution reaction (HER) under both acidic and alkaline conditions. The intrinsic MoO 3 serves as an HER electrocatalyst without the assistance of carbon materials, noble metals, or MoS 2 materials. The results from transmission electron microscopy and N 2 sorption techniques show that the as‐synthesized mesoporous MoO 3– x has large accessible pores (20–40 nm), which are able to facilitate mass transport and charge transfer during HER. In terms of X‐ray diffraction, X‐ray photoelectron spectroscopy, temperature‐programmed oxidation, and diffusive reflectance UV–vis spectroscopy, the mesoporous MoO 3– x exhibits mixed oxidation states (Mo 5+ , Mo 6+ ) and an oxygen‐deficient structure. The as‐synthesized MoO 3– x only requires a low overpotential (≈0.14 V) to achieve a 10 mA cm −2 current density in 0.1 m KOH and the Tafel slope is as low as 56 mV dec −1 . Density functional theory calculations demonstrate a change of electronic structure and the possible reaction pathway of HER. Oxygen vacancies and mesoporosity serve as key factors for excellent performance.