Photoelectrochemical overall water splitting has been considered as a promising approach for producing chemical energy from solar energy. Although many photoelectrochemical cells have been developed for overall water splitting by coupling two semiconductor photoelectrodes, inefficient charge transfer between the light-harvesters and electron acceptor/donor severely restricts the solar energy conversion efficiency. Inspired by natural photosynthesis, we assembled a photoelectrochemical platform with multimediator modulation to achieve unassisted overall water splitting. Photogenerated electrons are transferred in order through multimediators driven by the electrochemical potential gradient, resulting in efficient charge separation and transportation with enhanced charge transfer rate and reduced charge recombination rate. The integrated system composed of inorganic oxide-based photoanode (BiVO4) and organic polymer-based photocathode (PBDB-T:ITIC:PC71BM) with complementary light absorption, exhibits a solar-to-hydrogen conversion efficiency as high as 4.3%. This work makes a rational design possible by constructing an efficient charge-transfer chain in artificial photosynthesis systems for solar fuel production.
Photoelectrocatalytic (PEC) degradation of organic pollutants into CO2 and H2O is a promising strategy for addressing ever-growing environmental problems. Titanium dioxide (TiO2) has been widely studied because of its good performance and environmental benignancy; however, the PEC activity of TiO2 catalyst is substantially limited due to its fast electron–hole recombination. Herein, we report a TiO2 nanocone-based photoelectrocatalyst with superior degradation performance and outstanding durability. The unique conical catalyst can boost the PEC degradation of 4-chlorophenol (4-CP) with 99% degradation efficiency and higher than 55% mineralization efficiency at a concentration of 20 ppm. The normalized apparent rate constant of a nanocone catalyst is 5.05 h–1 g–1 m2, which is 3 times that of a nanorod catalyst and 6 times that of an aggregated particle catalyst, respectively. Further characterizations reveal that the conical morphology of TiO2 can make photogenerated charges separate and transfer more efficiently, resulting in outstanding PEC activity. Moreover, computational fluid dynamics simulations indicate that a three-dimensional conical structure is beneficial for mass transfer. This work highlights that tuning the morphology of a photoelectrocatalyst at the nanometer scale not only promotes the charge transfer but also facilitates the mass transportation, which jointly enhance the PEC performance in the degradation of persistent pollutants.
Ferrihydrite (Fh) has been demonstrated acting as a hole‐storage layer (HSL) in photoelectrocatalysis system. However, the intrinsic structure responsible for the hole storage function for Fh remains unclear. Herein, by dehydrating the Fh via a careful calcination, the essential relation between the HSL function and the structure evolution of Fh material is unraveled. The irreversible and gradual loss of crystal water molecules in Fh leads to the weakening of the HSL function, accompanied with the arrangement of inner structure units. A structure evolution of the dehydration process is proposed and the primary active structure of Fh for HSL is identified as the [FeO6] polyhedral units bonding with two or three molecules of crystal water. With the successive loss of chemical crystal water, the coordination symmetry of [FeO6] hydration units undergoes mutation and a more ordered structure is formed, causing the difficulty for accepting photogenerated holes as a consequence.
Understanding the structure–activity relationship of an active site is of great significance toward the rational design of highly active catalysts. Herein, we present a combined experimental and theoretical study on water oxidation catalysis of mononuclear Co catalysts with CoN4Cl, CoCN3Cl, and CoC4Cl motifs incorporated into a graphene matrix. We found that the catalyst with the CoCN3Cl structure exhibits an overpotential of 359 mV at 10 mA/cm2 for the oxygen evolution reaction (OER), much lower than those of catalysts with CoC4Cl (396 mV) and CoN4Cl structure (>500 mV). By introducing the binding strength between the Co site and reaction intermediates (OH*, O* and OOH*) as the reaction descriptor, we revealed that the binding strength for CoO* in these structures is getting stronger when N is replaced by the C atom, which plays a crucial role in the rate-determining step (RDS) and water oxidation performance. The Co site distinctively coordinated with the CN3Cl structure gives rise to the most suitable binding strength of CoO* and consequently the highest OER performance (RDS: Co–OH* → CoO*), much better than that coordinated by C4Cl with a strong binding strength (RDS: CoO* → Co-OOH*) and N4Cl with a weak binding strength (RDS: Co–OH* → CoO*). This work further demonstrates the importance of the coordination environment of the metal nucleus in catalysts for RDS manipulation and activity optimization in OER through modulating the binding strength between active site and reaction intermediates.
Plasmon-induced chemical reaction is an emerging field but its development faces huge challenges because of low quantum efficiency. Herein, we report that the solar energy conversion efficiency of Au/TiO 2 in plasmon-induced water oxidation is greatly enhanced by intercalating Li + into TiO 2 . An incident photon-to-current efficiency as high as 2.0 %@520 nm is achieved by Au/Li 0.2 TiO 2 in photoelectrocatalytic water oxidation, realizing a 33-fold enhancement in photocurrent density compared with Au/TiO 2 . The superior photoelectrocatalytic performance is mainly ascribed to the enhanced electric conductivity and higher catalytic activity of Li 0.2 TiO 2 . Furthermore, the ultrafast transient absorption spectroscopy suggests that lithium intercalation into TiO 2 could change the dynamics of hot electron relaxation in Au nanoparticles. This work demonstrates that intercalation of alkaline ions into semiconductors can promote the charge separation efficiency of the plasmonic effect of Au/TiO 2 .
A critical bottleneck for realizing an efficient Schottky type Si photoelectrode is minimizing the charge extraction losses across the heterointerface via reducing the unfavorite defects. This requires a clear microscopic insight into the correlation between interfacial features and photoconversion. Herein, by taking the n-Si/oxide (MO x )/Ni as the prototype, the heterointerface with the different characteristics and its effects on charge transportation and the corresponding photoelectric/photoelectrochemical (PEC) behaviors were clarified. An ultra-thin AlO x layer can effectively diminish the interfacial pinning of n-Si/Ni and significantly facilitate the photoconversion; meanwhile, it results in some unexpected donor-like deep defects at around 0.59 eV below the conduction band of n-Si, which could be ionized under a reverse bias and cause about 10% photogenerated charge recombination. Fortunately, these deep defects can be further eliminated by cooperating AlO x with a thin Au layer. The AlO x /Au dual-interlayer can remove almost all unexpected defects and maximize the efficiency of the electric field for charge extraction from semiconductor Si for the surface catalytic reaction. Eventually, the n-Si/SiO x /AlO x /Au/Ni/NiFeO x photoanode exhibited a record fill factor of 0.75 for the corresponding photoelectric device and an applied bias photon-to-current efficiency of 3.71% for PEC water oxidation. This study provides definite insights into interfacial electronic states and elaborates their crucial role in solar photoelectric conversion.
Bismuth‐based halide perovskite materials have attracted extensive attention for optoelectronic applications due to nontoxicity and ambient stability. However, limited by low‐dimensional structure and isolate octahedron arrangement, the undesirable photophysical properties of bismuth‐based perovskites are still not well modulated. Here, the rational design and synthesis of Cs3SbBiI9 with improved optoelectronic performance via premeditatedly incorporating antimony atoms with a similar electronic structure to bismuth into the host lattice of Cs3Bi2I9 is reported. Compared with Cs3Bi2I9, the absorption spectrum of Cs3SbBiI9 is broadened from ≈640 to ≈700 nm, the photoluminescence intensity enhances by two orders of magnitude indicating the extremely suppressed carrier nonradiative recombination, and the charge carrier lifetime is further increased from 1.3 to 207.6 ns. Taking representative applications in perovskite solar cells, the Cs3SbBiI9 exhibits a higher photovoltaic performance benefiting from the improved intrinsic optoelectronic properties. Further structure analysis reveals that the introduced Sb atoms regulate the interlayer spacing between dimers in c‐axis direction and the micro‐octahedral configuration, which correlate well with the improvement of optoelectronic properties of Cs3SbBiI9. It is anticipated that this work will benefit the design and fabrication of lead‐free perovskite semiconductors for optoelectronic applications.
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