Synthesis Of Nickel Oxide With Porous Structure And Their Electrochemical Performance

Nickel oxide (NiO) is promising material applied as electro-catalyst of methanol in direct methanol fuel cells and as electrode material in supercapacitors, due to its high electrochemical activity, low cost and ease of synthesis. In order to further improve the electrochemical performance of NiO, several facile and efficient methods, such as ionothermal precipitation method, water vapor template method, and chemical bath deposition, are used to fabricate porous structure and composite with graphene. Moreover, the correlation between NiO microstructure and its electrochemical performance is studied.Porous NiO electrodes are obtained through ionothermal precipitation method using ChCl-urea (CU) based deep eutectic solvent as medium and NaOH-induced direct precipitation method. The CU-based ionothermal precipitation method provides homogeneous nucleation sites, moderate crystal growth process and possible template effect, which could conduce to the production of flower-like NiO with porous structure. However, the NaOH-induced direct precipitation process leads to construction of porous agglomeration comprised of NiO nanoparticles. Compared with the disorderly aggregated NiO nanoparticles, the flower-like NiO with self-supporting mesoporous structure provides larger active surface area, shorter ion and molecule diffusion passage and better strain-mediated capability, which endows it superior electro-catalytic activity and stability for methanol oxidation. A NiO-graphene hybrid film with 3D hierarchically porous structure has been rationally designed and constructed through water vapor template method and chemical bath deposition. The NiO-graphene hybrid film exhibits specific capacitance of 540 F g-1 at 2 A g-1 with 80% capacitance retention after 2000 cycles, which is much higher than that achieved from the bare NiO nanoflakes film (370 F g-1, with 66% capacitance retention). The enhanced electrochemical performance of NiO-graphene hybrid film is attributed to its novel hierarchical porous structure and porous graphene sheet framework, which can provide larger active reaction area, better electron and ion accessibility and good mechanical stability.