Size dependence of perovskite-type BaNbO2N particles on sunlight-driven photoelectrochemical water splitting

Abstract

The size of particulate semiconductors is a critical factor in photoelectrochemical (PEC) water splitting activity because the surface area determined by the particle size establishes the electrochemical reaction sites as well as the resulting photoactivity. Herein we demonstrate the size dependence of perovskite-type BaNbO2N particles, responsive to intensive-visible-light up to 740 nm, on the PEC water splitting activity. The layered perovskite Ba5Nb4O15 particles in different sizes, as a starting oxide for synthesis of BaNbO2N, were synthesized by polymerized complex method, followed by calcination at different temperatures (1073, 1173, 1273, and 1373 K). The size of Ba5Nb4O15 particles was dependent on the calcination temperature so that low-temperature calcination led to smaller BaNbO2N particles. Although the different Ba5Nb4O15 particles experienced nitridation at 1123 K for 13 h, the sizes of the resulting BaNbO2N particles were nearly unchanged from those of the starting oxides. The sizes and Brunauer-Emmett-Teller surface areas of porous BaNbO2N particles largely influenced the PEC water splitting activity. As a result, photoelectrode employing the small BaNbO2N particles, prepared from the calcination at 1173 K, produced the highest photocurrent of 2.20 mA cm−2 at 1.23 VRHE during the sunlight-driven water splitting, showing the size dependence of oxynitride particles on photoactivity. Therefore, findings from this study support that the size reduction of oxynitride particles largely improved the PEC water splitting activity.