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

Abstract

Development 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 (CoAl 2 O 4) dispersed on a graphitic carbon nitride (g-C 3 N 4) photocatalyst was studied by electron microscopy and X-ray absorption finestructure spectroscopy. The CoAl 2 O 4 nanoparticle, which is a good cocatalyst for visible-light water oxidation on the g-C 3 N 4 photocatalyst, was loaded onto the photocatalyst by a reverse micelle method using Co(NO 3) 2 • 6H 2 O and Al(NO) 3 • 9H 2 O as precursors, followed by heating at elevated temperatures in air. The O 2 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 CoAl 2 O 4 spinel nanoparticles with a minimal extent of aggregation was the key factor to obtain high water oxidation activity.