| Environmental polution and Energy crisis are the two major challenges people all over the world have to face in the 21st century.Solar energy is clean and rich,and therefore exploration of the utilization of solar energy has never stopped.Conversion of solar energy into chemical energy in the form of hydrogen through water splitting is probably the ultimate strategy to solve today's energy and environmental crises.Hematite??-Fe2O3?core-cocatalyst shell nanoarchitectures are promising to maximize the photoelectrochemical?PEC?water oxidation performance of the hematite,but their fabrication presents great challenges and the promotion effect of the cocatalysts needs to be significantly enhanced.For these problems,we report the direct assembly of an ultrathin,uniform,and dense layer of Co3O4 on hematite??-Fe2O3?to form a large-area and high-density?-Fe2O3@Co3O4 core-shell nanoarray via in-situ hydrothermal growth followed by calcination,in which the electrostatic force between?-Fe2O3 and the reactants,pH-and temperature-controlled structures of?-Fe2O3,and ultralow nucleation rate of Co3O4 precursors all play critical roles.The obtained heteronanostructure array shows a photocurrent density of 3.48 mA cm-2,which is 4.01 times higher than that of pristine?-Fe2O3(0.86 mA cm-2),an onset potential of0.62 V,60 mV lower than that of?-Fe2O3?0.68 V?,and a photoconversion efficiency of 0.55%,3.93 times that of?-Fe2O3?0.14%?.It is discovered that the Co3O4 shells can significantly enhance the charge separation,accelerate the charge transport and transfer,and reduce the charge transfer resistance from the photoelectrode to electrolyte for fast water oxidation reaction,therefore greatly promoting the PEC water oxidation performance of pristine?-Fe2O3.This work not only creates a novel low-cost and earth-abundant?-Fe2O3@Co3O4 photoelectrode with superior PEC water oxidation performance and provides scientific insights into the enhancement mechanism,but also offers a general strategy for the in-situ growth of water oxidation catalysts on various photoelectrodes with 3-D complex geometries for PEC water splitting.Further,for the first time,we report the direct growth of an ultrathin,uniform,and dense layer of Co3O4/GQD hybrid cocatalysts on wormlike nanostructured hematite?WN-?-Fe2O3?to form a large-area and high-density WN-?-Fe2O3@Co3O4/GQD core–hybrid shell nanoarray via self-assembly followed by heat treatment.The obtained heteronanostructure array shows a photocurrent density of 3.631 mA cm-2,which is 4.19,1.78,and 1.69 times higher than those of WN-?-Fe2O3,WN-?-Fe2O3@Co3O4,and WN-?-Fe2O3@GQD,respectively,and an onset potential of?0.63 V,90,110,and 30 mV lower than those of WN-?-Fe2O3,WN-?-Fe2O3@Co3O4,and WN-?-Fe2O3@GQD,and a photoconversion efficiency of 0.59%,4.10,2.36,and1.92 times those of WN-?-Fe2O3,WN-?-Fe2O3@Co3O4,and WN-?-Fe2O3@GQD.This is among the highest performances reported for Fe2O3-based photoanodes for water splitting.It is discovered that the Co3O4/GQD shell significantly enhances the charge separation,reduces the charge transfer resistance through both the depletion and the Helmholtz layer,and increases the efficiency of hole injection from the photoanode to the electrolyte,thereby greatly promoting the PEC water oxidation activity of WN-?-Fe2O3,and the GQDs can significantly increase the dispersion of Co2+for conformal assembly of the Co3O4/GQD hybrid and improve the water oxidation activity of Co3O4 for great synergistic effects between Co3O4 and GQDs,thus enhancing the promotion effect of the Co3O4/GQD hybrid.This work not only creates a novel low-cost and earth-abundant WN-?-Fe2O3@Co3O4/GQD photo-electrode with superior PEC water oxidation performance and provides scientific insights into the enhancement mechanism,but also offers a general strategy for the growth of hybrid WOC shells on various photoelectrodes with 3-D complex geometries for PEC water splitting. |
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