Sonoelectrochemical synthesis of nanostructured of p-Cu2O and n-Fe2O3 and their application for photoelectrochemical splitting of water

Abstract

In the present work, a p-Cu2O nanostructured electrode and n-Fe2O3 nanotubes electrode, were used as photocathode and photoanode, respectively, for study the splitting of water. In this photoelectrochemical cell (PEC) the oxygen evolution reaction takes place in the photoanode and the hydrogen evolution reaction in the photocathode, both from the water decomposition reaction. In this case, the two electrodes were synthesized by ultrasound-assisted anodization (37 kHz, 60 W) in corresponding sheet metallic. The experimental conditions for the formation of p-Cu2O nanostructures were: 75 V, 75°C and 900 s of polarization in a solution of ethylene glycol with 5% wt of water and 0.5% wt of NH4Cl [1]. On the other hand, the Fe2O3 nanotubes were synthesized at 50 V, 50°C and 180 s of polarization in an ethylene glycol solution containing 3% wt of water and 0.5% wt of NH4F [2]. In both cases, after the anodization, the sheets were thermally treated at 190°C for 90 min in an argon atmosphere for p-Cu2O and for n-Fe2O3 at 500°C for 180 min in an oxygen atmosphere. Subsequently, the electrodes were characterized by DRS, EIE by Mott-Schottky plots obtaining the diagrams of respective bands. Finally, electrochemical measurements were performed with the system Fe|nanotubes n-Fe2O3|0.1 M Na2SO4 (pH 10)|p-Cu2O nanostructured|Cu, where the two electrodes were illuminated. In this context, the system required a bias potential of 0.36 V. This value corresponds to 69.5 kJ/mol, for a current density of 0.3 mAcm-2. On the other hand, in equal conditions of current density, but using platinum electrodes, a bias potential of 1.50 V (289.5 kJ/mol) was required. In this context, a decrease in the energy cost for the decomposition reaction of water, in an alkaline solution was evidenced.