Formation of Mo–Polydopamine Hollow Spheres and Their Conversions to MoO2/C and Mo2C/C for Efficient Electrochemical Energy Storage and Catalyst

Highly uniform hierarchical Mo–polydopamine hollow spheres are synthesized for the first time through a liquid‐phase reaction under ambient temperature. A self‐assembly mechanism of the hollow structure of Mo–polydopamine precursor is discussed in detail, and a determined theory is proposed in a water‐in‐oil system. Via different annealing process, these precursors can be converted into hierarchical hollow MoO 2 /C and Mo 2 C/C composites without any distortion in shape. Owing to the well‐organized structure and nanosize particle embedding, the as‐prepared hollow spheres exhibit appealing performance both as the anode material for lithium‐ion batteries and as the catalyst for hydrogen evolution reaction (HER). Accordingly, MoO 2 /C delivers a high reversible capacity of 940 mAh g −1 at 0.1 A g −1 and 775 mAh g −1 at 1 A g −1 with good rate capability and long cycle performance. Moreover, Mo 2 C/C also exhibits an enhanced electrocatalytic performance with a low overpotential for HER in both acidic and alkaline conditions, as well as remarkable stability.