Light-Harvesting Property from Self-Assembly of Cobalt Nanocluster Aggregates for Efficient Hydrogen Evolution

Herein, we report the light-harvesting property (LHP) from a self-assembled cobalt nanoaggregate (S-CoNA) for an efficient hydrogen evolution. The syntheses of S-CoNAs were achieved using 3-mercaptopropylsulfonate (MPS) as the stabilizer, and the as-formed compound exhibits broad absorption at 407 and 496 nm which appears in the visible region that prompts us to investigate the photo-electrochemical studies. Interestingly, the as-prepared S-CoNAs achieved enhanced hydrogen energy production in the visible region. To know the mechanism of LHP from S-CoNAs and to examine the (M/L) ratios and varying the M/L contribution in detail, we further synthesized S-CoNAs in different metal to ligand ratios (M/L). Out of the five different ratios, the M/L (1:4) ratio resulted in a maximum response of 15 mA cm –2 at 0.3 V applied potential (vs Ag/AgCl). Further, we performed electrochemical studies by tuning the potentials (0, 0.3 V) followed by illumination in the presence and absence of visible light. Furthermore, Fourier-transform infrared spectroscopy analysis before and after photo-electrochemical reaction resulted in a notable peak at 998 and 2115 cm –1, respectively, which is attributed to a metal sulfur linkage via both the thiol (−SH) and sulfonate (−SO 3 H) terminals of MPS. The photo-electrochemical reaction which is observed after this effective stabilization for S-CoNAs via Co–S linkages was responsible for the hydrogen energy production.