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Fast transport of charge carriers in semiconductor photoelectrodes are a major determinant of the solar-to-hydrogen efficiency for photoelectrochemical (PEC) water slitting. While doping metal ions as single atoms/clusters in photoelectrodes has been popularly used to regulate their charge transport, PEC performances are often low due to the limited charge mobility and severe charge recombination. Here, we disperse Ru and P diatomic sites onto hematite (DASs Ru-P:Fe2O3) to construct an efficient photoelectrode inspired by the concept of correlated single-atom engineering. The resultant photoanode shows superior photocurrent densities of 4.55 and 6.5 mA cm-2 at 1.23 and 1.50 VRHE, a low-onset potential of 0.58 VRHE, and a high applied bias photon-to-current conversion efficiency of 1.00% under one sun illumination, which are much better than the pristine Fe2O3. A detailed dynamic analysis reveals that a remarkable synergetic ineraction of the reduced recombination by a low Ru doping concentration with substitution of Fe site as well as the construction of Ru-P bonds in the material increases the carrier separation and fast charge transportation dynamics. A systematic simulation study further proves the superiority of the Ru-P bonds compared to the Ru-O bonds, which allows more long-lived carriers to participate in the water oxidation reaction. This work offers an effective strategy for enhancing charge carrier transportation dynamics by constructing pair sites into semiconductors, which may be extended to other photoelectrodes for solar water splitting.
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Manipulating the interfacial/surface structure of ligand-stabilized atomically precise metal nanoclusters (NCs) is one of the central tasks in nanoscience because surface motifs are directly related to key properties of nanomaterials. Although great progress has been made in engineering the surface of gold and silver nanoclusters, parallel studies on lighter copper analogues hitherto remain unexplored. In this work, we report the design, synthesis, and structure of a new class of copper nanoclusters featuring virtually identical kernels but different surface motifs. The four Cu29 nanoclusters share the same Cu13 kernel with unprecedented anticuboctahedral architecture. Finely modulating synthetic parameters endows the Cu13 core with diverse surface structures, thus affording the Cu29 series with labile surface coatings. More interestingly, the slight surface modification results in distinct optical and catalytic properties of the cluster compounds, highlighting the importance of the surface structure in shaping the behaviors of copper nanomolecules. This work not only exemplifies the efficiency of surface engineering for controlling properties of well-defined copper nanoclusters but also provides a new family of Cu materials with a clear molecular structure and controlled surface motifs that hold great promise in studying structure-property relationships.
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Monoclinic bismuth vanadate (BiVO4) has emerged as an excellent optically active photoanode material due to its unique physical and chemical properties. Experiments reported that the low concentration of oxygen vacancies enhances the photoelectrochemical (PEC) activity of BiVO4, but the high concentration of oxygen vacancies decreases the charge carrier lifetime. Using time-domain density functional theory and molecular dynamics, we have demonstrated that the distribution of oxygen vacancies has strong effects on the static electronic structure and nonadiabatic (NA) coupling of the BiVO4 photoanode. The localized oxygen vacancies create charge recombination centers within the band gap and enhance the NA coupling between the VBM and the CBM, resulting in fast charge and energy losses. By contrast, the discrete oxygen vacancies can eliminate the charge recombination centers and decrease the NA coupling between the VBM and the CBM, enhancing the PEC activity of monoclinic BiVO4. Our study suggests that the PEC performance of a photoanode can be improved by changing the distribution of oxygen vacancies.
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By performing nonadiabatic molecular dynamics combined with ab initio time-domain density functional theory, we have explored the effects of the charge density of a sulfur vacancy on charge trapping and recombination in antimony trisulfide (Sb2S3). The simulations demonstrate that, compared to an antimony vacancy, the sulfur vacancy generates a high charge density trap state within the band gap. This state acts as the recombination center and provides new channels for charge carrier relaxation. Filling the sulfur vacancy with electron donors elevates the defect state to the Fermi level due to the introduced extra electrons. In contrast, the electron acceptor lowers the charge density of the sulfur vacancy by capturing its local electrons, eliminating the charge recombination center and extending the photo-generated charge carrier lifetime. Additionally, compared with electron injection, hole injection can also decrease the charge density of the trap state via neutralizing its local electronic states, eliminate the trap state within the band gap, and suppress nonradiative electron-hole recombination. This study is expected to shed new light on the blocking recombination centers and provide valuable insights into the design of high-performance solar cells.
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Aqueous-phase oxygen evolution reaction (OER) is the bottleneck of water splitting. The formation of the O-O bond involves the generation of paramagnetic oxygen molecules from the diamagnetic hydroxides. The spin configurations might play an important role in aqueous-phase molecular electrocatalysis. However, spintronic electrocatalysis is almost an uncultivated land for the exploration of the oxygen molecular catalysis process. Herein, we present a novel magnetic FeIII site spin-splitting strategy, wherein the electronic structure and spin states of the FeIII sites are effectively induced and optimized by the Jahn-Teller effect of Cu2+. The theoretical calculations and operando attenuated total reflectance-infrared Fourier transform infrared (ATR FT-IR) reveal the facilitation for the O-O bond formation, which accelerates the production of O2 from OH- and improves the OER activity. The Cu1-Ni6Fe2-LDH catalyst exhibits a low overpotential of 210 mV at 10 mA cm-2 and a low Tafel slope (33.7 mV dec-1), better than those of the initial Cu0-Ni6Fe2-LDHs (278 mV, 101.6 mV dec-1). With the Cu2+ regulation, we have realized the transformation of NiFe-LDHs from ferrimagnets to ferromagnets and showcase that the OER performance of Cu-NiFe-LDHs significantly increases compared with that of NiFe-LDHs under the effect of a magnetic field for the first time. The magnetic-field-assisted Cu1-Ni6Fe2-LDHs provide an ultralow overpotential of 180 mV at 10 mA cm-2, which is currently one of the best OER performances. The combination of the magnetic field and spin configuration provides new principles for the development of high-performance catalysts and understandings of the catalytic mechanism from the spintronic level.
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Highly dispersed Pt, such as Pt single atoms and atomic clusters, has great potential in the electrocatalytic hydrogen evolution reaction (HER) due to the high atomic efficiency and unique electronic configuration. Rationally regrating the electronic structure of Pt catalysts is desirable for promoting the HER performance. Herein, a 3D self-supported monolithic electrode consisting of Pt single atoms (PtSAs ) and Pt atomic clusters (PtACs ) anchored on sulfur-doped titanium nitride nanotubes (S-TiN NTs) encapsulated in polyaniline (PANI) on Ti mesh (PANI@Pt/S-TiN NTs/Ti) via a facile electrochemical strategy for efficient HER is designed and synthesized. Contributed by the unique structure and composition and the synergy of PtSAs , PtACs and S-TiN NTs, the PANI@Pt/S-TiN NTs/Ti electrode exhibits ultrahigh HER activities with only 12, 25 and 39 mV overpotentials at -10 mA cm-2 in acidic, alkaline and neutral media, respectively, and can maintain a stable performance for 25 h. Impressively, the mass activities are respectively up to 26.1, 22.4, and 17.7 times as that of Pt/C/CC electrode. Theoretical calculation results show that the synergistic effect of PtSAs , PtACs , and S-TiN NTs can optimize the electronic structure of Pt and generate multiple active sites with a thermodynamically favorable hydrogen adsorption free energy (ΔGH* ), thereby resulting in an enhanced HER activity.
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A photocharge/discharge strategy is proposed to initiate the WO3 photoelectrode and suppress the main charge recombination, which remarkably improves the photoelectrochemical (PEC) performance. The photocharged WO3 surrounded by a 8-10â nm overlayer and oxygen vacancies could be operated more than 25â cycles with 50â h durability without significant decay on PEC activity. A photocharged WO3 /CuO photoanode exhibits an outstanding photocurrent of 3.2â mA cm-2 at 1.23â VRHE with a low onset potential of 0.6â VRHE , which is one of the best performances of p-n heterojunction structure. Using nonadiabatic molecular dynamics combined with time-domain DFT, we clarify the prolonged charge carrier lifetime of photocharged WO3 , as well as how electronic systems of photocharged WO3 /CuO semiconductors enable the effective photoinduced electrons transfer from WO3 into CuO. This work provides a feasible route to address excessive defects existed in photoelectrodes without causing extra recombination.
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Exposure to oxygen and light undermines chemical stability of metal halide perovskites, while it surprisingly improves their optical properties. Focusing on CH3NH3PbI3, we demonstrate that material degradation and charge carrier lifetimes depend strongly on the oxidation state of the oxygen species. Nonadiabatic molecular dynamics simulations combined with time-domain density functional theory show that a neutral oxygen molecule has little influence on the perovskite stability, while the superoxide and the peroxide accelerate degradation by breaking Pb-I chemical bonds and enhancing atomic fluctuations. Creating electron and/or hole traps, the neutral oxygen and the superoxide decrease charge carrier lifetimes by over 1 and 2 orders of magnitude, respectively. Importantly, photoinduced reduction of oxygen to the peroxide eliminates trap states and extends carrier lifetimes by more than a factor of 2 because it decreases the nonadiabatic coupling and shortens quantum coherence. The simulations indicate that the superoxide should be strongly avoided, for example, by full reduction to the peroxide because it causes simultaneous degradation of perovskite stability and optical properties. The detailed simulations rationalize the complex interplay between the influence of atmosphere and light on perovskite performance, apply to other solar cell materials exposed to natural elements, and provide valuable insights into design of high-performance solar cells.
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Hybrid organic-inorganic perovskites have emerged as very successful optically active materials due to their unique electronic and chemical properties. Experiments have shown that oxygen undermines perovskite chemical stability, but enhances charge carrier lifetimes. Focusing on CH3NH3PbI3, which has become the classic material, we demonstrate how and why charge carrier lifetimes change in the presence of oxygen, by carrying out nonadiabatic molecular dynamics simulations combined with time-domain ab initio density functional theory. Calculations have shown that superoxide and peroxide are the common forms of oxygen interacting with CH3NH3PbI3 and that oxygen most readily interacts with iodine vacancies on the perovskite surface. We establish that the iodine vacancy decreases charge carrier lifetimes, because it localizes both electrons and holes, increasing their overlap. By passivating the vacancy, the oxygen species separate electrons and holes and increase the lifetimes by more than an order of magnitude. Passivating the vacancy by water and Lewis bases, such as pyridine and thiophene, also leads to electron-hole separation. The energy gap changes only by a few percent; however, the nonadiabatic coupling becomes much weaker, and the quantum coherence time decreases significantly. The detailed time-domain atomistic analysis of the excited state dynamics rationalizes why the photogenerated charge carriers in perovskites are robust to defects and interactions with chemical species present in air, such as water and oxygen, even though they undermine perovskite chemical stability. The results can apply to other solar energy materials, which are exposed to atmospheric gases and the performance of which often depends on such exposure.
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Carbonyl-modified solid-state carbon nitrogen quantum dots (m-OâCNQDs) have emerged as promising room-temperature phosphorescent (RTP) materials close to commercialization. However, high-crystallinity m-OâCNQDs are insensitive to external stimuli such as water and heat due to strong stacking interactions between layers, restricting their applications in stimulus responsive fields. Here, a polymer template space-confined growth strategy is established for the large-scale synthesis of water stimulus responsive polyvinylpyrrolidone-functionalized m-OâCNQDs with ultralong room-temperature phosphorescence (181 ms) using urea and PVP as precursors. Theoretical and experimental results indicate that the PVP template linked at the rim of m-OâCNQDs formed by in situ self-polymerization of urea inhibits interactions between layers and increases their affinity for water, which is the key to increasing their sensitivity with water. This strategy offers a new path for developing commercial stimulus responsive RTP materials.
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Developing carbon-supported Pt-based electrocatalysts with high activity and long-durability for the oxygen reduction reaction (ORR) is an enormous challenge for their commercial applications due to the corrosion of carbon supports in acid/alkaline solution at high potential. In this work, a Janus structural TaON/graphene-like carbon (GLC) was synthesized via an in-situ molecular selfassembly strategy, which was used as a dual-carrier for platinum (Pt). The as-obtained Pt/TaON/GLC presents high half-wave potential (0.94 V vs. RHE), excellent mass (1.48 A mgPt-1) and specific (1.75 mA cmPt-2) activities at 0.9 V, and superior long-term durability with a minimal loss (8.0 %) of mass activity after 10,000 cycles in alkaline solution, outperforming those of Pt/C and other catalysts. The structural characterizations and density functional theory (DFT) calculations indicate that the Pt/TaON/GLC catalyst exhibits the maximum synergies, including enhanced interfacial electron density, improved charge transfer, enhanced O2 adsorption, andsuperimposed OO cleavage. This work shows a potential strategy for preparing the high-active and long-durable Pt-based electrocatalyst by synergism-promoted interface engineering.
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Constructing nanoreactors with multiple active sites in well-defined crystalline mesoporous frameworks is an effective strategy for tailoring photocatalysts to address the challenging of CO2 reduction. Herein, one-dimensional (1-D) mesoporous single-crystal TiO2 nanorod (MS-TiO2-NRs, ≈110 nm in length, high surface area of 117 m2 g-1, and uniform mesopores of ≈7.0 nm) based nanoreactors are prepared via a droplet interface directed-assembly strategy under mild condition. By regulating the interfacial energy, the 1-D mesoporous single-crystal TiO2 can be further tuned to polycrystalline fan- and flower-like morphologies with different oxygen vacancies (Ov). The integration of single-crystal nature and mesopores with exposed oxygen vacancies make the rod-like TiO2 nanoreactors exhibit a high-photocatalytic CO2 reduction selectivity to CO (95.1%). Furthermore, photocatalytic cascade nanoreactors by in situ incorporation of CuW6O24 (W-Cu) clusters onto MS-TiO2-NRs via Ov are designed and synthesized, which improved the CO2 adsorption capacity and achieved two-step CO2-CO-CH4 photoreduction. The second step CO-to-CH4 reaction induced by W-Cu sites ensures a high generation rate of CH4 (420.4 µmol g-1 h-1), along with an enhanced CH4 selectivity (≈94.3% electron selectivity). This research provides a platform for the design of mesoporous single-crystal materials, which potentially extends to a range of functional ceramics and semiconductors for various applications.
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Focusing on LaFeO3, we investigated the effects of magnetic ordering on carrier relaxation using time-domain density functional theory and nonadiabatic molecular dynamics. The results show that the hot energy and carrier relaxation occur on a sub-2 ps time scale due to the strong intraband nonadiabatic coupling, and the corresponding time scales are distinct depending on the magnetic ordering of LaFeO3. Importantly, the energy relaxation is slower than hot carrier relaxation, guaranteeing photogenerated hot carriers can be effectively relaxed to the band edge before cooling. Following hot carrier relaxation, the charge recombination occurs on the nanosecond scale due to the small interband nonadiabatic coupling and short pure-dephasing times. In addition, the A-AFM system has the longest carrier lifetimes because of its weakest nonadiabatic coupling. Our study suggests that the carrier lifetime can be controlled by changing the magnetic ordering of perovskite oxides and provides valuable principles for the design of high-performance photoelectrodes.
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Photoelectrochemical (PEC) water splitting that functions in pH-neutral electrolyte attracts increasing attention to energy demand sustainability. Here, we propose a strategy to in situ form a NiB layer by tuning the composition of the neutral electrolyte with the additions of nickel and borate species, which improves the PEC performance of the BiVO4 photoanode. The NiB/BiVO4 exhibits a photocurrent density of 6.0 mA cm-2 at 1.23 VRHE with an onset potential of 0.2 VRHE under 1 sun illumination. The photoanode displays a photostability of over 600 hours in a neutral electrolyte. The additive of Ni2+ in the electrolyte, which efficiently inhibits the dissolution of NiB, can accelerate the photogenerated charge transfer and enhance the water oxidation kinetics. The borate species with BâO bonds act as a promoter of catalyst activity by accelerating proton-coupled electron transfer. The synergy effect of both species suppresses the surface charge recombination and inhibits the photocorrosion of BiVO4.
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An effective strategy is developed to synthesize a novel and stable layered Cu nanocluster using a one-pot reduction method. The cluster, with a molecular formula of [Cu14(tBuS)3(PPh3)7H10]BF4 which has been unambiguously characterized by single crystal X-ray diffraction analysis, exhibits different structures from previously reported analogues with core-shell geometries. In the absence of chiral ligands, the cluster displays intrinsic chirality owing to the non-covalent ligand-ligand interactions (e.g., C-Hâ¯Cu interactions and C-Hâ¯π interactions) to lock the central copper core. The interlacing of chiral-cluster enantiomers forms a large cavity, which lays the foundation for a series of potential applications such as drug filling and gas adsorption. Moreover, the C-Hâ¯H-C interactions of phenyl groups between different cluster moieties promote the formation of a dextral helix and realization of the self-assembly of nanostructures.
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Although much effort has been devoted to improving photoelectrochemical water splitting of hematite (α-Fe2O3) due to its high theoretical solar-to-hydrogen conversion efficiency of 15.5%, the low applied bias photon-to-current efficiency remains a huge challenge for practical applications. Herein, we introduce single platinum atom sites coordination with oxygen atom (Pt-O/Pt-O-Fe) sites into single crystalline α-Fe2O3 nanoflakes photoanodes (SAs Pt:Fe2O3-Ov). The single-atom Pt doping of α-Fe2O3 can induce few electron trapping sites, enhance carrier separation capability, and boost charge transfer lifetime in the bulk structure as well as improve charge carrier injection efficiency at the semiconductor/electrolyte interface. Further introduction of surface oxygen vacancies can suppress charge carrier recombination and promote surface reaction kinetics, especially at low potential. Accordingly, the optimum SAs Pt:Fe2O3-Ov photoanode exhibits the photoelectrochemical performance of 3.65 and 5.30 mA cm-2 at 1.23 and 1.5 VRHE, respectively, with an applied bias photon-to-current efficiency of 0.68% for the hematite-based photoanodes. This study opens an avenue for designing highly efficient atomic-level engineering on single crystalline semiconductors for feasible photoelectrochemical applications.
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The atomically precise metal electrocatalysts for driving CO2 reduction reactions are eagerly pursued as they are model systems to identify the active sites, understand the reaction mechanism, and further guide the exploration of efficient and practical metal nanocatalysts. Reported herein is a nanocluster-based electrocatalyst for CO2 reduction, which features a clear geometric and electronic structure, and more importantly excellent performance. The nanocatalysts with the molecular formula of [Ag17Cu10(dppm)4(PhC≡C)20H4]3+ have been obtained in a facile way. The unique metal framework of the cluster, with silver, copper, and hydride included, and dedicated surface structure, with strong (dppm) and labile (alkynyl) ligands coordinated, endow the cluster with excellent performance in electrochemical CO2 reduction reaction to CO. With the atomically precise electrocatalysts in hand, not only high reactivity and selectivity (Faradaic efficiency for CO up to 91.6%) but also long-term stability (24 h), are achieved.
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Interstitial halogens are detrimental to the optoelectronic properties of metal halide perovskites. Using nonadiabatic (NA) molecular dynamics, we demonstrate that the valence state of interstitial bromine strongly changes the carrier lifetimes of MAPbBr3 (MA = CH3NH3+). Both neutral and negatively charged interstitial bromine create no midgap states, and they decrease the bandgap, weaken the NA coupling, and accelerate decoherence in a different extent with respect to pristine MAPbBr3, making free charge recombination either slow down about a 3-fold or remain largely unchanged. In contrast, a positively charged interstitial bromine forms a Br trimer and introduces a deep electron trap state, causing a 1.4-fold increase of charge recombination followed by a rapid electron trapping or across the bandgap because of an enhanced NA coupling. The simulations uncover the influence of different charged interstitial bromine defects on MAPbBr3 carrier lifetimes and provide rational guidelines for optimizing perovskite solar cells.
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In this study, the levels of airborne bacteria and fungi were tested in a female dormitory room; the effects of heating, relative humidity and number of occupants on indoor microorganisms were analyzed and the dose rate of exposure to microbes was assessed. The bacterial and fungal concentrations in the room ranged from 100 to several thousand CFU/m3, and the highest counts were observed in the morning (930 ± 1681 CFU/m3). Staphylococcus spp. and Micrococcus spp. were found in the dormitory. When the heating was on, the total bacterial and fungal counts were lower than when there was no heating. Moreover, statistically significant differences were observed for bacterial concentrations during the morning periods between the times when there was no heating and the times when there was heating. The number of occupants had an obvious positive effect on the total bacterial counts. Moreover, RH had no correlation with the airborne fungi in the dormitory, statistically. Furthermore, the highest dose rate from exposure to bacteria and fungi was observed during sleeping hours. The dose rate from exposure to airborne microorganisms in the dormitory was associated with the activity level in the room. These results helped to elucidate the threat of bioaerosols to the health of female occupants and provide guidance for protective measures.
Assuntos
Microbiologia do Ar , Poluição do Ar em Ambientes Fechados , Poluição do Ar em Ambientes Fechados/análise , Bactérias , Monitoramento Ambiental/métodos , Fungos , HabitaçãoRESUMO
Metal halide perovskites are promising materials for photovoltaics and optoelectronics. However, transfer of an electron from perovskite to oxygen leads to the formation of superoxide that significantly decreases the stability and charge carrier lifetime of perovskites, which constitutes major issues for real applications. Using nonadiabatic (NA) molecule dynamics simulations, we demonstrate that the introduction of a perylene diimide (PDI) molecule into the CH3NH3PbI3 system adsorbed with an oxygen molecule creates a midgap state above the trap state generated by the oxygen molecule, and thus the PDI midgap state can rapidly capture the photogenerated electron of perovskite at about 100 ps prior to the O2-related trap state, which takes about double the time. The route simultaneously avoids the formation of superoxide and enhances the stability of perovskites. The fast electron trapping originates from the strong NA coupling and small energy gap between the PDI midgap state and the CH3NH3PbI3 conduction band minimum. Our simulations suggest that a rational choice an electron-accepting molecule can improve the stability and performance of perovskite solar cells and photoelectric devices.