Facile Synthesis Route of Various Porous Transition Metal Hydroxides for Pseudocapacitor using Poly(4-vinyl pyridine)

Transition metal hydroxides are widely used in electrochemical fields because of their low cost and many advantages. In particular, porous transition metal hydroxides are attracting attention because their large surface area compensates for the disadvantage of poor electrical conductivity. Herein, we suggest facile synthesis of porous transition metal hydroxide using poly(4-vinyl pyridine) (P4VP) homopolymer by polymer-precursor method. To synthesis the metal hydroxide, we used a cyanide metal precursor present in the form of a metal hydroxide anion in an aqueous solution and coordinated it with P4VP.<b> </b>However, the cyanide precursor prevents the protonation of P4VP because it makes the aqueous solution basic. Therefore, in order to maintain the pH so that P4VP can be sufficiently protonated, a buffer solution that pH is not easily changed by the external environment was used. At the same time, porous transition metal hydroxide can be obtained when P4VP film was immersed in a precursor-buffer solution by inducing a nanoscale phase separation and by selective removing of P4VP through O₂ RIE. Using this prepared porous transition metal hydroxides, we compared pseudocapacitive properties of the fabricated structures depending on pH of solution. As a result, the porous metal hydroxide structure with the best efficiency among them showed satisfactory specific capacitance without optimization.