Synthesis Of Cobalt Salen And Porphyrin Complexes For Catalytic Water Splitting

In recent years, inexpensive non-precious metals have attracted much attention to prepare highly active electrocatalysts or photocatalysts for water splitting. In order to improve the catalytic efficiency and stability, catalyst materials with different morphologies and structures were designed and synthesized. In this thesis, cobalt complexes were chosen to study the properties of water splitting:(1) Co-salen complexes can be used as catalyst precursors to deposit CoOx nanoparticles on the surface of working electrode FTO, exhibiting a high catalytic water oxidation performance; (2) Photocatalytic water reduction rate was greatly improved by mixing a Co-salen complex and CdS nanorods photocatalyst; (3) Co-porphyrin complexes can also enhance the photocatalytic performance of CdS nanorods for hydrogen production.Oxygen evolution reaction is an important step in water splitting, which involves a four-electron transfer process and always requires a large overpotential. Therefore, an efficient catalyst is highly desirable to reduce the overpotential of water oxidation. As a precursor, Co-salen complex can be electrodeposited on the surface of FTO substrate to form nanostructured CoOx particles which are in close contact with the surface of the electrode and can significantly improve the catalytic performance. In addition, SEM, XPS, EDX techniques were performed to characterize the nanoparticles. The results showed the catalyst thin films were more stable and active than the films that directly grown from a simple cobalt salt. The catalytic material obtained by this method showed excellent catalytic properties with a Faraday efficiency of more than 90% for oxygen evolution.In the presence of Na2S and Na2SO3 as sacrificial agents, Co-salen complex was used as the cocatalyst to combine with CdS nanorods photocatalyst for photocatalytic hydrogen production. Under the optimum conditions, hydrogen production rate reached 106μmol·h-1·mg-1, with a quantum efficiency of ～29%. In addition, based on the results of the steady-state photoluminescence spectra and time-resolved photoluminescence spectra, it was found that this system allows electron transfer from CdS to Co-salen complexes. Similarly, Co-porphyrin in ascorbic acid solution at pH 4 also showed good photocatalytic hydrogen production properties.