A Study of the Photocatalytic and Photovoltaic Properties of Photocatalysts Based on Carbon Nitride, Cobalt Phosphide, and Cobalt Phosphate

In this study, a cocatalyst is supported on the surface of carbon nitride by the following three different methods: thermal phosphorylation, a hydrothermal method, and photochemical reduction. In the first case, the cocatalyst is a cobalt phosphide–cobalt orthophosphate mixture; the use of the hydrothermal and photochemical synthesis methods provides the formation of cobalt orthophosphate. In addition, a sample is synthesized by a hydrothermal treatment of presynthesized carbon nitride and cobalt phosphide. The synthesized samples are studied using the following set of physicochemical methods: X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectroscopy. All the synthesized photocatalysts are tested in photocatalytic hydrogen evolution from an aqueous alkaline solution of triethanolamine and in a photoelectrochemical cell containing a sodium polysulfide solution. It is shown that, in the case of using a cobalt phosphide–cobalt orthophosphate mixture, the target characteristics are higher than those in the case of cobalt orthophosphate and carbon nitride. The highest catalytic activity is 156 μmol h −1 g −1 ; it is comparable to the activity of platinized carbon nitride. The highest short-circuit current density obtained in the case of using a photoelectrode containing cobalt phosphide and cobalt phosphate is 2.4 mA/cm 2 .