Film Fabrication and Composition Control of Transition Metal Oxide Nanoparticles for Oxygen Evolution Catalysts

Abstract

Development of highly efficient oxygen evolution reaction (OER) catalysts is necessary for commercial implementation of water electrolysis due to overcome slow kinetics of OER. Noble metal based electrocatalysts such as Ir and Ru demonstrate high performance for OER in acidic media. In contrast, the first-row transition metal oxides such as Ni, Co, and Fe oxides show the high catalytic activity and stability in alkaline media. In this work, the composition of bimetallic metal oxide NPs was tuned and their electrochemical performance was analyzed. Furthermore, the electrophoretic deposition (EPD) technique was utilized for the efficient fabrication of NP thin film electrode. The bimetallic transition metal oxide NPs were synthesized by using Ni(acac)2 as Ni precursor and Fe(acac)3 as Fe precursor, leading to the phase control of bimetallic Ni-Fe oxide NPs. As Fe precursor amount was gradually increased compared to that of Ni, the particle size of Ni-Fe oxide NPs was increased, and the shape of NPs was transformed from spherical to irregular shape. The magnetic property of Ni-Fe oxide NPs was also analyzed by vibrating sample magnetometer. The saturation magnetization (Ms) of bimetallic metal oxide was increased and the magnetic coercivity was decreased when the Fe composition was increased. For the electrochemical analysis for OER, the overpotential of bimetallic metal oxide NPs catalysts was highly influenced by the composition of bimetallic metal oxide NPs. Higher Fe contents than Ni in the NPs led to high performance as OER catalysts. The EPD technique was introduced to manufacture the uniform NP films with improved catalytic activity. The catalyst film formed through EPD technique was prepared under the applied voltage of 500 V for 10 minutes. The film of Ni-Fe oxide NPs was well covered on the substrate of the Ti foil. The overpotential of the bimetallic metal oxide NP film fabricated by EPD was decreased from 510 mV to 400 mV at 10 mA/cm2 compared to the films fabricated by drop casting. These results provide useful insights not only for understanding the catalytic activity of bimetallic metal oxide NPs in OER but also for suggesting the film fabrication method for enhancing the catalytic activity.