Three-Dimensional Cobalt Hydroxide Hollow Cube/Vertical Nanosheets with High Desalination Capacity and Long-Term Performance Stability

Faradaic electrode materials have significantly improved the performance of membrane capacitive deionization, which offers an opportunity to produce freshwater from seawater or brackish water in an energy-efficient way. However, Faradaic materials hold the drawbacks of slow desalination rate due to the intrinsic low ion diffusion kinetics and inferior stability arising from the volume expansion during ion intercalation, impeding the engineering application of capacitive deionization. Herein, a pseudocapacitive material with hollow architecture was prepared via template-etching method, namely, cuboid cobalt hydroxide, with fast desalination rate (3.3 mg (NaCl)·g-1 (h-Co(OH)2)·min-1 at 100 mA·g-1) and outstanding stability (90% capacity retention after 100 cycles). The hollow structure enables swift ion transport inside the material and keeps the electrode intact by alleviating the stress induced from volume expansion during the ion capture process, which is corroborated well by in situ electrochemical dilatometry and finite element simulation. Additionally, benefiting from the elimination of unreacted bulk material and vertical cobalt hydroxide nanosheets on the exterior surface, the synthesized material provides a high desalination capacity (117±6 mg (NaCl)·g-1 (h-Co(OH)2) at 30 mA·g-1). This work provides a new strategy, constructing microscale hollow faradic configuration, to further boost the desalination performance of Faradaic materials.

Synthesis of Samarium Cobalt Oxide Nanosheets and Nanoflowers on Nickel Foam via Electrochemical Route

Cobalt oxide (Co3O4) nanosheets were successfully synthesized and deposited onto the nickel foam substrate via electrochemical route. The chronoamperograms during the deposition revealed electrochemical activity resulting to the nucleation of the cobalt ions forming cobalt hydroxide and transformation to cobalt oxide. Energy dispersive xray (EDX) results elucidates the presence of samarium, cobalt and oxygen in the sample. The formation of nanosheets was confirmed by scanning electron microscopy. It was found that adding more samarium in the electrochemical bath changes the morphology of the final product from nanosheets to nanoflowers. The evolution of nanosheets to nanoflowers of the synthesized material could pave way for its potential application in the field of electrochemical energy storage devices and electrochemical sensors.