A review on powering energy storage with molybdenum-based oxide quantum dots: from nanoscale design to high-performance electrochemical systems

Molybdenum-based metal oxide quantum dots (MoOx QDs) have caught the eye as viable next-generation electrode materials in energy storage devices because they exhibit novel quantum confinement effects, a large surface-to-volume ratio, and highly diverse multivalent redox chemistry. MoOx QDs, in comparison with bulk molybdenum oxides, surpass inherent drawbacks like poor electrical conductivity, slow ion diffusion, and excessive volume swelling when subjected to electrochemical cycling. This is a systematic review of recent developments in the synthesis, the structural properties, and the charge-storage mechanisms of MoOx QDs, especially focusing on hydrothermal, solvothermal, microwave-assisted, ligand-controlled and laser-based processes. Performance enhancement strategies and future perspectives are also critically debated, highlighting that although oxygen-vacancy engineering, heterostructure formation, and composite design can significantly improve conductivity and electrochemical performance, these approaches may also introduce challenges such as structural instability, synthesis complexity, and difficulties in identifying the true contribution of MoOx QDs to overall device performance. Electrochemical performance of the MoOx QDs is discussed in lithium-ion, sodium-ion, magnesium-ion, and zinc-ion batteries, in supercapacitors and hybrid supercapacitors, and the performances are outstanding because of their high capacities, fast kinetics, and enhanced cycling stability. Although this has made tremendous progress, there are still challenges of low initial coulombic efficiency, structural instability, and scalability. Lastly, the proposed research directions in the future involving interface stabilization, multivalent ion storage, and sustainable synthesis routes are suggested to improve the expedited implementation of MoOx QDs in advanced energy storage systems.