The global warming crisis calls for urgent development of high-performance renewable energy devices for decarbonization. Supercapacitors offering a high power density and a long life cycle may fulfill the requirement. However, the relatively low energy densities of such devices compared to those of ion batteries have limited the application and impact of supercapacitors in various industries. To overcome the limitation, we herein introduce a strategy to boost the energy density of the electrochemical capacitors by engineering the morphologies of electrodes. We prepared the electrodes with three distinct molybdenum disulfide (MoS2) structures which served as an ion-accumulation and faradaic-active layer in the energy storage device. The diverse morphologies of MoS2 include fluffy-ball-like (fMoS2), stacked-slabs (sMoS2), and exfoliated-plate (eMoS2) structures. The MoS2 layers were hierarchically synthesized on top of carbon nanotubes (CNT) and zeolitic imidazolate framework (a type of metal organic frameworks). The hybrid composites exhibit high conductivity due to CNT and ion diffusivity due to the MOF, together enhancing the energy storage for the supercapacitors. Among the three morphologies, the fMoS2-embedded sample demonstrated the highest energy and power densities, approximately two times greater than the others. This may be attributed to the unique structural features of fMoS2. It consists of nanometer-thick and micrometer-wide MoS2 flakes, providing a large surface area to accumulate ions. Our structural and electrochemical analyses revealed that the ball-like structure presented many sulfur vacancies. Such vacancy sites are advantageous for the faradaic reaction between ions and electrodes to yield high electrochemical currents. The results strongly indicate that the electrode structure may dominate the energy storage performance. The proposed approach may offer critical insights and novel platforms for developing future supercapacitors.

Morphology-dependent electrochemical behaviors of MoS2-MOF-carbon frameworks

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