Ni(OH)2 quantum dots as a stable cocatalyst modified α-Fe2O3 for enhanced photoelectrochemical water-splitting

Abstract Depositing a cocatalyst has proven to be an important strategy for improving the photoelectrochemical (PEC) water-splitting efficiency of photoanodes. In this study, Ni(OH)2 quantum dots (Ni(OH)2 QDs) were deposited in situ onto an α-Fe2O3 photoanode via a chelation-mediated hydrolysis method. The photocurrent density of the Ni(OH)2 QDs/α-Fe2O3 photoanode reached 1.93 mA(cm−2 at 1.23 V vs. RHE, which is 3.5 times that of α-Fe2O3, and an onset potential with a negative shift of ca. 100 mV was achieved. More importantly, the Ni(OH)2 QDs exhibited excellent stability in maintaining PEC water oxidation at a high current density, which is attributed to the ultra-small crystalline size, allowing for the rapid acceptance of holes from α-Fe2O3 to Ni(OH)2 QDs, formation of active sites for water oxidation, and hole transfer from the active sites to water molecules. Further (photo)electrochemical analysis suggests that Ni(OH)2 QDs not only provide maximal active sites for water oxidation but also suppress charge recombination by passivating the surface states of α-Fe2O3, thereby significantly enhancing the water oxidation kinetics over the α-Fe2O3 surface.