Figure 6 . (a) Comparison of hydrogen evolution of CuP, CoP and Cu-Cu-2P-2 catalyst samples; (b) Comparison of hydrogen production activities of catalysts with different phosphating degrees; (c) Comparison of hydrogen production activities of different Cu-MOFs catalysts; (d) Effect of triethanolamine aqueous solution with different pH on the photocatalytic activity of Cu-Co-2P-2.
The cyclic stability of photocatalysts is very important for their applications. As shown in Figure 7, there is Cu-Co-2P-2 composite photocatalytic activity test comparison for four cycles in consecutive 20 h. The catalyst and sacrificial reagent were not re-added during the entire experiment. 10 mg of EY is added to the reaction flask again at each regassing. Stability tests show that the total amount of produced hydrogen is only slightly reduced at the end of each cycle. This is mainly because the adsorbed EY dye is easily desorbed and diffused into the solution, and the catalyst has slight photo-induced corrosion [38, 40, 41]. Compared with the first cycle, the fourth cycle is only down by 13.7%, which indicates that the Cu-Co-2P-2 photocatalyst has excellent cycle stability and certain application prospects.