Light intensity responsive changes of products in photocatalytic reduction of nitrous acid on a Cu-doped covalent triazine framework/TiO2 hybrid.

In the design of solar-energy conversion electrochemical systems, it is important to consider that natural sunlight fluctuates. By taking nitrous acid photoreduction as an example, the present work has shown that the reaction pathway, and hence the reaction products, dynamically responded to the variation of light intensity. Under irradiation, the photooxidation of methanol (as sacrificial agent) on TiO 2 and the reduction of HNO 2 on Cu-modified covalent triazine framework (Cu-CTF) were electrically coupled, which led to the photoreduction of HNO 2 without an external bias. The dominant reaction product changes from N 2 O to NH 4 + with an increase in the light intensity. The operating potential also shifted negatively (or positively) when the light intensity was increased (or decreased). These results indicate that a change of the reaction pathway was triggered by a change of the operating potential of the Cu-CTF catalysts under varying light intensity. Such a light-intensity dependent change of the reaction pathway is particularly important in systems that use photoresponsive electrodes and where multiple products can be obtained, such as the solar-driven reduction of carbon dioxide and nitrogen oxides.