Synthesis And Photoelectrochemical Properties Of Cu₂ZnSnS₄?CZTS? Based Nanohybrids

The global energy crisis and environmental issue attract more and more attention on development of novel green energy technologies. Among them, hydrogen generation by photoelectrocatalytic water splitting, and furthermore, the electricity generation by the burning of hydrogen in a fuel cell (FCs), is a new green energy technology. Nevertheless, photoelectrocatalysts play a vital role among all the related factors of the above mention key renewable-energy technologies.Cu2ZnSnS4 nanocrystals (CZTS NCs) are a new type of photoelectric catalytic material, which show good catalytic performance in the photovoltaic and hydrogen production. Herein, CZTS based nanohybrids have been prepared and their photoelectrocatalytic properties toward some challenging reactions have been studied. The main results are as follows:(1) A cation exchange-based route was used to produce Cu2ZnSnS4 (CZTS)-Ag2S nanoparticles with controlled relative composition by using CZTS nanocrystals as substrates. A detailed study of this epitaxy formation at the junction of CZTS and Ag2S has been carried out and reported. Such nanoscale p-n heterostructures as sensitizers exhibited superior photocurrent and photoresponse behavior under visible light illumination when compared to pure CZTS. For example, at 0.5 V vs. RHE, the photocurrent of CZTS-Ag2S was 0.58 mA·cm-2, which is about ten times higher than that of the pure CZTS (0.06 mA·cm-2). We associated this experimental fact to a higher separation efficiency of the photogenerated electron-hole pairs. We proposed that the different photoresponse behaviors of the catalysts can be attributed to their different band structures.(2) Narrow size distribution and controlled crystal phases CZTS nanocrystals were obtained by a high-yield colloidal synthesis route, and their potential as electrocatalysts for ORR in alkaline fuel cells has been studied. By using the commercial carbon as a support, these CZTS/C composites showed the crystal phase-dependent catalytic activities. Most importantly, it is interesting to find that the kesterite CZTS/C composites showed better catalytic activity than wurtzite CZTS/C composites, and a direct four-electron transfer pathway was observed. Furthermore, Kesterite CZTS/C composites exhibited superior stability and resistance to methanol. For example, after 40000s, the catalytic performance of kesterite CZTS/C composites dropped to 90%, whereas that of Pt/C dropped to 72%. Meanwhile, methanol nearly had no influence on the catalytic performance of kesterite CZTS/C composites, whereas that of Pt/C dropped to 80% after methanol was introduced. The mechanism of the ORR for CZTS NCs and the reason for the crystal phase-dependent catalytic activity have been proposed base on the first-principles calculations.