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 MoO₂ /C and Mo₂ 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, MoO₂ /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, Mo₂ 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.