Structure‐Activity Relationship in a Cobalt Aluminate Nanoparticle Cocatalyst with a Graphitic Carbon Nitride Photocatalyst for Visible‐Light Water Oxidation

Abstract

AbstractDevelopment of a visible‐light‐driven water oxidation system utilizing a photocatalyst that consists only of earth‐abundant elements is a challenge in artificial photosynthesis. Here the structure of nanoparticulate cobalt aluminate spinel (CoAl2O4) dispersed on a graphitic carbon nitride (g‐C3N4) photocatalyst was studied by electron microscopy and X‐ray absorption fine‐structure spectroscopy. The CoAl2O4 nanoparticle, which is a good cocatalyst for visible‐light water oxidation on the g‐C3N4 photocatalyst, was loaded onto the photocatalyst by a reverse micelle method using Co(NO3)2 ⋅ 6H2O and Al(NO)3 ⋅ 9H2O as precursors, followed by heating at elevated temperatures in air. The O2 evolution activity was enhanced with increasing the heating temperature, reaching a plateau at 573–673 K, beyond which it decreased. Physicochemical analyses indicated that the formation of CoAl2O4 spinel nanoparticles with a minimal extent of aggregation was the key factor to obtain high water oxidation activity.