Plasmon-induced hole-depletion layer on hematite nanoflake photoanodes for highly efficient solar water splitting

The efficiency of photoelectrochemical (PEC) water splitting of semiconductors is mainly restricted by the sluggish kinetics of the oxygen evolution reaction dominated by photogenerated holes. Herein, we demonstrate that with the assistance of photon-induced surface plasmon resonance excitation of Au nanoparticles, the iron oxyhydroxides (FeOOH) cocatalysts could serve as a unique “hole-depletion” layer for significantly promoting the PEC performance of single crystalline α-Fe2O3 photoanodes. The photogenerated holes can be efficiently extracted from α-Fe2O3 nanoflake to FeOOH layer, and promptly depleted by the injected hot-electrons from Au nanoparticles, while the hot-holes left behind on Au participate in the oxygen evolution reaction. Accordingly, the synergy of charge separation and hole transfer could be efficiently improved by the surface plasmon excitation on Au nanoparticles. As a result, the photocurrent density for the Fe2O3/FeOOH/Au photoelectrode without additional doping reaches up to 3.2 mA cm−2 at 1.23 VRHE, and 6.5 mA cm−2 at 1.6 VRHE, with a low onset potential of 0.6 VRHE under AM 1.5 G simulated sunlight, which is 2.5 and 5 times higher than for FeOOH modified and pristine α-Fe2O3 photoanodes, respectively. These results thus provide the basic of a new concept and strategy toward the design of more efficient PEC water splitting systems.