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Photocatalytic hydrogen production by overall water solar-splitting is a prospective strategy to solve energy crisis. However, the rapid recombination of photogenerated electron-hole pairs deeply restricts photocatalytic activity of catalysts. Here, the in-situ transient photovoltage (TPV) technique was developed to investigate the interfacial photogenerated carrier extraction, photogenerated carrier recombination and the interfacial electron delivery kinetics of the photocatalyst. The carbon dots/NiCo 2 O 4 (CDs/NiCo 2 O 4 ) composite shows weakened recombination rate of photogenerated carriers due to charge storage of CDs, which enhances the photocatalytic water decomposition activity without any scavenger. CDs can accelerate the interface electron extraction about 0.09 ms, while the maximum electron storage time by CDs is up to 0.7 ms. The optimal CDs/NiCo 2 O 4 composite (5 wt.% CDs) displays the hydrogen production of 62 µmol·h −1 g −1 and oxygen production of 29 µmol·h −1 g −1 at normal atmosphere, which is about 4 times greater than that of pristine NiCo 2 O 4 . This work provides sufficient evidence on the charge storage of CDs and the interfacial charge kinetics of photocatalysts on the basis of in-situ TPV tests.

Artificial photosynthesis of H 2 O 2 from H 2 O and O 2 , as a spotless method, has aroused widespread interest. Up to date, most photocatalysts still suffer from serious salt-deactivated effects with huge consumption of photogenerated charges, which severely limit their wide application. Herein, by using a phenolic condensation approach, carbon dots, organic dye molecule procyanidins and 4-methoxybenzaldehyde are composed into a metal-free photocatalyst for the photosynthetic production of H 2 O 2 in seawater. This catalyst exhibits high photocatalytic ability to produce H 2 O 2 with the yield of 1776 μmol g −1 h −1 ( λ  ≥ 420 nm; 34.8 mW cm −2 ) in real seawater, about 4.8 times higher than the pure polymer. Combining with in-situ photoelectrochemical and transient photovoltage analysis, the active site and the catalytic mechanism of this composite catalyst in seawater are also clearly clarified. This work opens up an avenue for a highly efficient and practical, available catalyst for H 2 O 2 photoproduction in real seawater. It is a challenge to produce hydrogen peroxide in seawater by photocatalysis. Here, the authors design and synthesize a metal-free photocatalyst based on carbon dots with a salt-protective electron sink effect, which exhibits enhanced hydrogen peroxide photoproduction in real seawater.

We present an overview of opto-electronic characterization techniques for solar cells including light-induced charge extraction by linearly increasing voltage, impedance spectroscopy, transient photovoltage, charge extraction and more. Guidelines for the interpretation of experimental results are derived based on charge drift-diffusion simulations of solar cells with common performance limitations. It is investigated how nonidealities like charge injection barriers, traps and low mobilities among others manifest themselves in each of the studied cell characterization techniques. Moreover, comprehensive parameter extraction for an organic bulk-heterojunction solar cell comprising PCDTBT:PC 70 BM is demonstrated. The simulations reproduce measured results of 9 different experimental techniques. Parameter correlation is minimized due to the combination of various techniques. Thereby a route to comprehensive and accurate parameter extraction is identified.

Ammonia plays a vital role in the development of modern agriculture and industry. Compared to the conventional Haber—Bosch ammonia synthesis in industry, electrocatalytic nitrogen reduction reaction (NRR) is considered as a promising and environmental friendly strategy to synthesize ammonia. Here, inspired by biological nitrogenase, we designed iron doped tin oxide (Fe-doped SnO 2 ) for nitrogen reduction. In this work, iron can optimize the interface electron transfer and improve the poor conductivity of the pure SnO 2 , meanwhile, the synergistic effect between iron and Sn ions improves the catalyst activity. In the electrocatalytic NRR test, Fe-doped SnO 2 exhibits a NH 3 yield of 28.45 μg·h −1 mg cat −1 , which is 2.1 times that of pure SnO 2 , and Faradaic efficiency of 6.54% at −0.8 V vs. RHE in 0.1 M Na 2 SO 4 . It also shows good stability during a 12-h long-term stability test. Density functional theory calculations show that doped Fe atoms in SnO 2 enhance catalysis performance of some Sn sites by strengthening N—Sn interaction and lowering the energy barrier of the rate-limiting step of NRR. The transient photovoltage test reveals that electrons in the low-frequency region are the key to determining the electron transfer ability of Fe-doped SnO 2 .

The energy crisis has always been a widely concerned problem. It is an urgent need for green and renewable energy technologies to achieve sustainable development, and the photo-assisted charging energy storage devices provide a new way to realize the sustainable utilization of solar energy. Here, we fabricated a photo-assisted charging fibrous supercapacitor (NM 2 P 1 ) with Ti 3 C 2 T x -based hybrid fibre modified by nitrogen-doped carbon dots (NCDs). The NM 2 P 1 fibre provides a volumetric capacitance of 1,445 F·cm −3 (630 F·g −1 ) at 10 A·cm −3 under photo-assisted charging, which increases by 35.9% than that of dark condition (1,063 F·cm −3 /464 F·g −1 ). Furthermore, the NM 2 P 1 fibrous supercapacitor device shows that the maximum volumetric energy density and volumetric power density are 18.75 mWh·cm −3 and 8,382 mW·cm −3 . Notably, the transient photovoltage (TPV) test was used to further confirm that NCDs as a photosensitizer enhance the light absorption capacity and faster charge transfer kinetics of NM 2 P 1 fibre. This work directly exploits solar energy to improve the overall performance of supercapacitor, which opens up opportunities for the utilization of renewable energy and the development of photosensitive energy equipment.

Great attention has been paid to green procedures and technologies for the design of environmental catalytic systems. Biomass-derived catalysts represent one of the greener alternatives for green catalysis. Photocatalytic production of hydrogen peroxide (H 2 O 2 ) from O 2 and H 2 O is an ideal green way and has attracted widespread attention. Here, we show a metal-free photocatalyst from cellulose, which has a high photocatalytic activity for the photoproduction of H 2 O 2 with the reaction rate up to 2,093 µmol/(h·g) and the apparent quantum efficiency of 2.33%. Importantly, a machine learning model was constructed to guide the synthesis of this metal-free photocatalyst. With the help of transient photovoltage (TPV) tests, we optimized their fabrication and catalytic activity, and clearly showed that the formation of carbon dots (CDs) facilitates the generation, separation, and transfer of photo-induced charges on the catalyst surface. This work provides a green way for the highly efficient metal-free photocatalyst design and study from biomass materials with the machine learning and TPV technology.

Photocatalytic reduction of carbon dioxide into valuable chemicals is a sustainable and promising technology that alleviates the greenhouse effect and energy crisis. In this study, the Mn 3 O 4 /FeNbO 4 type II heterojunction photocatalyst with a core-satellite structure was synthesized by the facile soft chemical method. The formation of a nano-heterojunction is supposed to effectively improve light capture, charge transfer, and interfacial charge separation in the photochemical reaction. Meanwhile, the heterojunction has a good ability to capture and activate CO 2 . Our results show that the prepared Mn 3 O 4 /FeNbO 4 photocatalyst exhibit obvious enhanced catalytic properties in the photocatalytic CO 2 reduction reaction, where the CH 4 yielding rate is 1.96 and 9.81 times those of FeNbO 4 and Mn 3 O 4 , respectively. The transient photovoltage test (TPV) shows that the low frequency electrons are crucial to the effective transfer of photogenerated electrons and holes in the Mn 3 O 4 /FeNbO 4 nano heterojunctions. Analysis of in situ Fourier transform infrared spectroscopy (FTIR) verifies the effective CO 2 adsorption on the Mn 3 O 4 /FeNbO 4 surface and the high selectivity of CH 4 products. These properties of the Mn 3 O 4 /FeNbO 4 photocatalyst infer its broad prospects in the fields of carbon fixation and energy conservation.

In recent years, many semiconductor materials have been applied to the photocatalysis technology. As a semiconductor with wide band gap (3.37 eV), ZnO has received extensive attention in the photocatalytic degradation of organic pollutants due to its rich morphology, low cost and other advantages. However, due to the wide band gap of ZnO, it can only absorb ultraviolet light (accounting for about 4% of the whole solar spectrum), which has greatly limited the application of ZnO semiconductor materials. BiOI/ZnO binary complexes were synthesized by simple hydrothermal and solvothermal methods. Their phenol degradation activities were tested under different light sources. The mechanism of photocatalytic degradation of phenol was reasonably explained by free radical trapping experiment, surface photovoltage, transient photovoltage, fluorescence and other tests.

Implementing sensitive and fast formaldehyde (HCHO) sensing at room temperature is still in extreme demand for practical indoor air quality monitoring. Herein, we synthesized P25/ZnO sensing materials for detecting low-concentration HCHO at room temperature. The sensing mechanism based on the P25/ZnO heterojunction was analyzed by the surface photovoltage (SPV), transient photovoltage (TPV), and X-ray photoelectron spectroscopy (XPS) results. Based on the P25/ZnO heterojunction, the obtained 1% P25/ZnO has the highest response among the synthesized sensing materials. The response of 1% P25/ZnO sensor materials to 0.9ppm and 19.1ppm HCHO reaches 44.85% and 255.42%, respectively, which is 21 and 20 times that of ZnO sensor materials (0.9ppm ~ 2.16%, 19.1ppm ~ 12.64%). Furthermore, the detection limit can be as low as 82 ppb under 360 nm light at room temperature. The selectivity, long-term stability, and repeatability of the obtained sensors at room temperature were also revealed. Graphical abstract

The photovoltaic properties of a monocrystalline silicon solar cell were investigated under dark and various illuminations and were modeled by MATLAB programs. According to AM1.5, the studied solar cell has an efficiency rate of 41–58.2% relative to industry standards. The electrical characteristics (capacitance, current–voltage, power-voltage, transient photovoltage, transient photocurrent, and impedance) of a silicon solar cell device were examined. Under complete darkness and light intensity of 100 mW/cm 2 , respectively, we have noticed that the light of the AM1.5 spectrum changes all PV-cell parameters such as short current, open circuit voltage, maximum power, maximum voltage, and power conversion efficiency. An electrical equivalent circuit (R 1 //C 1  + R 2 //C 2 ) was used by the Zview software to fit the experimental data of the Nyquist representations (-Z'' vs. Z'). By analyzing the peak of the conductance G p versus frequency, the density of interface states and the interface trap time constant were calculated. By using MATLAB programs, we have modeled the current versus voltage and power versus voltage properties of equivalent solar cell circuits, ensuring a good agreement between the experimental and theoretical curves.