Dual-absorber photoelectrodes are attractive candidates for solar water splitting due to their broadened absorption spectrum and improved photovoltage compared to single-absorber systems.

Dual-absorber photoelectrodes have been proved to possess greater potential than the single-absorber systems in the applications of photoelectrochemical (PEC) cells (e.g., solar-driven water splitting); however, the mismatching of the energy bands and substantial carrier recombinations at the two absorber interfaces are normally subsistent. Here, we introduce an intermediate layer of conformal Al2O3 into the silicon/hematite (Si/α-Fe2O3) microwire photoanode for enriching the understanding of the interaction among the interlayer, inner absorber, and outer absorber. Our results show that the Si/Al2O3/α-Fe2O3 microwire photoanode with the thickness-optimized Al2O3 can lead to a substantial increase in the photocurrent from 0.83 to 2.08 mA/cm2 at 1.23 VRHE (under 1 sun irradiation) and an obvious decrease in the onset potential relative to the counterpart without Al2O3. By analyzing the PEC responses under various monochromatic lights, PEC impedance spectroscopy, and intensity-modulated photocurrent spectroscopy, we ascribe the improvements to the fact that the suitable-thickness Al2O3 can passivate the Si microwire surfaces and the bottom surfaces of the α-Fe2O3 film and give rise to Al doping into the post-synthesized α-Fe2O3. These essential causes promote the carrier separation in α-Fe2O3, diminish the photoanode surface recombination rate, and then increase the surface charge-transfer efficiency.

Hematite (α-Fe 2 O 3 ) material is regarded as a promising candidate for solar-driven water splitting because of the low cost, chemical stability, and appropriate bandgap; however, the corresponding system performances are limited by the poor electrical conductivity, short diffusion length of minority carrier, and sluggish oxygen evolution reaction. Here, we introduce the in situ Sn doping into the nanoworm-like α-Fe 2 O 3 film with ultrasonic spray pyrolysis method. We show that the current density at 1.23 V vs. RHE (J ph@1.23V ) under one-sun illumination can be improved from 10 to 130 μA/cm 2 after optimizing the Sn dopant density. Moreover, J ph@1.23V can be further enhanced 25folds compared to the untreated counterpart via the post-rapid thermal process (RTP), which is used to introduce the defect doping of oxygen vacancy. Photoelectrochemical impedance spectrum and Mott-Schottky analysis indicate that the performance improvement can be ascribed to the increased carrier density and the decreased resistances for the charge trapping on the surface states and the surface charge transferring into the electrolyte. Xray photoelectron spectrum and X-ray diffraction confirm the existence of Sn and oxygen vacancy, and the potential influences of varying levels of Sn doping and oxygen vacancy are discussed. Our work points out one universal approach to efficiently improve the photoelectrochemical performances of the metal oxide semiconductors.

Surface engineering, as an efficient strategy, can improve the photoelectrochemical water splitting (PEC-WS) performance for converting inexhaustible sunlight into clean hydrogen fuel. Oxyhydroxides and p–n heterojunctions have been demonstrated as efficient catalysts for the water oxidation reaction. In this work, to address the drawbacks of poor conductivity and sluggish oxidation kinetics of hematite, we introduce a p-type NiOOH overlayer as a surface catalyst onto n-type Sn-doping hematite (Sn@α-Fe2O3) photoanode. The oxygen vacancies (Ov) are reconstructed both in the bulk of Sn@α-Fe2O3 and the surface decoration layer of NiOOH via Ar plasma treatment, effectively reducing unavoidable defects introduced by the NiOOH overlayer. Compared with the original Sn@α-Fe2O3 photoanode, the Sn@α-Fe2O3/NiOOH–Ar photoanode exhibits a significant increase in photocurrent density (at 1.23 VRHE) of ∼3 times and a decrease in the onset potential of ∼200 mV. The performance improvement can be ascribed to the synergistic effect of the p–n junctions formed by NiOOH decoration and improved conductivity through oxygen vacancy reconstruction, which remarkably improves carrier separation in the bulk of α-Fe2O3 and suppresses carrier recombination on the photoanode surface. Moreover, the density functional theory (DFT) calculation proves that the real active sites are farther from (rather than near) the oxygen vacancies.

Hematite (α-Fe2O3) material has outstanding advantages in photoelectrochemical water splitting (PEC-WS) field, while its generally-low photogenerated-carrier separation (ηsep) and transfer (ηtran) efficiencies severely impede its further application. An internal electric...

The effect of extracts from four types of tea made from Camelia sinensis (green, white, black, and oolong) on in vitro amylolysis of gelatinized starch and the underlying mechanisms were studied. Of the four extracts, black tea extract (BTE) gave the strongest inhibition of starch digestion and on α-amylase activity. Fluorescence quenching and surface plasmon resonance (SPR) showed compounds in BTE bound to α-amylase more strongly than those in the green, white, and oolong tea extracts. Individual testing of five phenolic compounds abundant in tea extracts showed that theaflavins had a greater inhibitory effect than catechins on α-amylase. SPR showed that theaflavins had much lower equilibrium dissociation constants and therefore bound more tightly to α-amylase than catechins. We conclude that BTE had a stronger inhibitory effect on in vitro enzymatic starch digestion than the other tea extracts, mainly due to the higher content of theaflavins causing stronger inhibition of α-amylase.

Both the bulk and surface electrical properties of the α-Fe2O3 photoanode are obviously self-improved under continuous irradiation.

Hot electrons from the nonradiative decay of surface plasmons have drawn extensive attention due to the outstanding performance in realizing below-bandgap photodetection. However, the widely employed metallic nanostructures are normally complex and delicate with a great challenge in large-area fabrication, and there is a great limitation to achieve substantial photoresponse at relatively long wavelengths (e.g., 2000nm) with polarization- and incident-angle independence. In this study, we theoretically and experimentally demonstrate a broadband, omnidirectional, and polarization-insensitive absorber based on wafer-scale silicon honeycomb nanobowls with 20-nm-thick gold overlayer. The average absorption across the long wave near infrared band (LW-NIR, i.e., 1100−2500 nm) is higher than 82%, which is contributed from the random nature and multimode localized plasmonic resonances excited on the side walls of nanobowls. Benefitted from the well-connected thin Au film and relatively low Schottky barrier, the generated hot electrons have a high transport probability to reach Schottky interface and participate in the interfacial charge transfer process. As a result, the hot-electron photodetector under no bias realizes a broadband photodetection up to 2000nm wavelength with a responsivity of 0.145 mA/W, and its cutoff wavelength is predicted up to 3300 nm by fitting the experimental result with Fowler theory. Our proposed Au/Si nanobowls photodetector could open a pathway to further extend the detection wavelength of Si-based photodetectors with a large-area and low-cost fabrication process, which promotes practical hot-electron applications.