CoFe prussian blue coordination compounds incorporating metallopolymers: Investigation of electrocatalytic water oxidation activities

Abstract

Hydrogen economy, which depends on water and sunlight as energy source, needs to be implemented as an alternative to carbon based economy. For the development of a technology that incorporates hydrogen energy to our daily lives, it is required to split the water with the help of an efficient water oxidation catalyst. CoFe Prussian Blue analogues have recently been investigated as heterogeneous water oxidation catalysts. Even though they exhibit they exhibit high electrocatalytic activity in addition to superior stability in both acidic and neutral media low current densities were obtained with CoFe PB modified FTO electrodes due to their low surface coverage. This challenge could be overcome by developing novel synthetic methods that will enforce the formation of amorphous CoFe Prussian Blue analogues. Herein this thesis, pentacyanoferrate based metallopolymers were used as precursors to prepare amorphous Co-Fe analogues. The project focuses on the improving surface concentration by using Poly 4-vinyl pyridine (P4VP) not only as a capping ligand connected to pentacyanoferrate complexes but also as a surfactant to prevent the formation of long-range ordering between Co-Fe networks. Surface concentration was improved approximately seven fold, which resulted in an increase in the catalytic activity. A current density of 1 mA.cm-2 was obtained only at η = 510 mV while the same current density could be obtained only at higher overpotentials (>600 mV) with the previously studied Prussian Blue analogues. The stability of CoFe-PVP coated FTO electrodes were investigated before and after the electrocatalytic process using Infrared, XPS, and EDX studies. The results of this study indicate that the rich and diverse chemistry of pentacyanoferrates make them potential candidates for application in heterogeneous water oxidation catalysis.