Photocatalytic activities of potassium-doped lead niobates and the effect of poling

Abstract

Lead niobates with tungsten bronze-type crystal structure have been employed as photocatalysts, and the additive effects of potassium upon the photocatalytic activity for the production of hydrogen from water and upon the photovoltaic properties have been studied. With the addition of K, the photocatalytic activity increased considerably, passed through a maximum and then decreased. The surface photocurrent similarly varied as a function of K content, which indicates that the added K is effective for charge separation. Decreases in catalytic activity in the case of excess K were associated with the structural transition from a rhombohedral to an orthorhombic phase. Such a transition was also found to take place, even for the oxides containing small amounts of K, when subjected to a treatment of poling. Charge-integration measurements demonstrated that poling led to the formation of oppositely polarized surfaces, and it was revealed that the photocatalytic activity was moderately higher for the (+) polar surface than for the (–) one, although both activities were considerably lower than those of non-polar surfaces.