Size effects of cocatalysts in photoelectrochemical and photocatalytic water splitting

Abstract

The direct conversion of solar energy into the renewable fuel hydrogen can be carried out either by photocatalytic or by photoelectrochemical water splitting. In order to enhance the efficiency of photocatalytically active materials like the oxynitride LaTiO2N, cocatalysts are often used. Here, four different LaTiO2N particle morphologies are decorated with the oxygen evolution cocatalyst Co3O4. It is shown by transmission electron microscopy characterization that the four morphologies give rise to different Co3O4 cocatalyst particle size distributions. By studying the effect of the cocatalysts on both the photocatalytic and the photoelectrochemical performance, we find that the improvement depends on cocatalyst size, in different ways for both processes. In order to design efficient cocatalysts, not only their chemical composition is decisive, but also their size, as a function of the solar energy conversion process.