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Supercapacitors often deliver a significantly high-power density with a long cycling life but low energy density. An exceedingly promising approach is to construct asymmetric supercapacitors (ASCs) reconciling the compromise between power density and energy density. However, ASCs combining transition metal oxides (TMOs) and activated carbon (AC) struggle to improve energy density due to a vast difference in their specific capacitance. To cross this hurdle, we first proposed a new strategy to construct the ASCs with α-MoO3 as the anode and conductive polymer polypyrrole (PPy) as the cathode. The remarkable features of α-MoO3, including its layered structure and ultra-high specific capacitance, along with the stability and fast charge–discharge ability of PPy, have contributed significantly to the augmentation of power density and energy density in ASCs. Taking advantage of these bright features, the operation voltage for α-MoO3//PPy is effectively expanded to 2.0 V, exhibiting a high energy density of 25.9 W h kg−1 at 1538 W kg−1. Furthermore, the energy density presented a remarkable recovery rate, reaching 91.04% of its initial state after undergoing full rate tests. These conclusions reveal that the construction of α-MoO3//PPy can effectively enhance the energy density and power density of supercapacitors. [ABSTRACT FROM AUTHOR]

The development of photoelectrochemical (PEC) water splitting is hindered by the slow kinetics of four-electron processes for the oxygen evolution reaction (OER) and severe charge recombination. Amorphous carbon was chosen as a carrier for the active sites due to its exceptional conductivity and strong loading capacity. In addition, this enhanced performance was attributed to the loading of oxides of cobalt. Here, amorphous carbon-covered cobalt oxides chosen as a co-catalyst loaded on α-Fe2O3 (noted as CoOx@C/Ti-Fe2O3) have been synthesized, and they show a high current density (2.86 mA cm−2 under 1.23 V vs. RHE), and a low onset potential (0.611 V vs. RHE). Experimental analysis demonstrates that the charge transfer and separation leading to accelerated OER dynamics and improved PEC performance are enhanced by CoOx@C effectively. This study provides new ideas for designing high-performance photoelectrochemical electrodes based on amorphous carbon co-catalysts. [ABSTRACT FROM AUTHOR]

Constructing a high-efficiency and low-cost cocatalyst on g-C3N4 is of great significance for realizing efficient photocatalytic hydrogen production. However, balancing the active center and mass transport is still a great challenge in the design of a cocatalyst. Herein, a Ni@Ni2P cocatalyst with a core–shell structure was rationally fabricated on g-C3N4 such that photogenerated electrons could transfer to Ni2P through Ni directionally and orderly, as their amount can strongly influence photocatalytic H2 evolution performance. The optimal H2 evolution rate of 50P-Ni reaches 2.9 mmol h−1 g−1, which is about 3.5-fold and 137-fold higher than that of g-C3N4 and Ni/g-C3N4, respectively. Systematic investigations reveal that the Ni@Ni2P cocatalyst with a unique core–shell structure not only endows Ni metal with stability from corrosion but also prolongs the recombination time of photoinduced electrons and holes, which results in better separation efficiency. This work provides useful inspiration for rationally designing a robust and efficient core–shell cocatalyst for photocatalytic H2 evolution. [ABSTRACT FROM AUTHOR]

Photogenerated carrier behavior at a CO2/Cs2AgBiBr6 quantum dot (QD) interface is investigated. In situ photovoltage spectra reveal electron transfer from the Cs2AgBiBr6 QDs to CO2. Moreover, this carrier transfer prefers Bi3+ sites (over Ca+ and Ag+ sites) due to them exhibiting the lowest adsorption energy (Eads = −0.125 eV) and CO2–Bi3+ interactions being more stable. [ABSTRACT FROM AUTHOR]

Interface modification is an important means to enhance the photovoltaic performance of quantum dot sensitized solar cells (QDSCs). The TiO2/CdS/CdSe solar cells are sensitized with CdS QDs and CdSe QDs, which inevitably introduces a new interface to form a recombination center. Therefore, it is necessary to coat a passivation layer in order to effectively inhibit charge recombination at the CdS/CdSe interface. In this work, CuInS2 (CIS) has been introduced into the CdS/CdSe QD system as an inner passivation layer and the CdS/CIS/CdSe photoanode structure has been fabricated in an environmentally friendly manner. The extracted charge amount (Q) is used to express the charge separation efficiency, indicating that we have obtained outstanding charge extraction efficiency in CIS based CdS/CdSe QDSCs. As a result, the photocurrent density of the TiO2/CdS/CIS/CdSe photoanode significantly has increased from 19.01 mA cm−2 to 22.74 mA cm−2 (TiO2/CdS/CdSe photoanode), which demonstrates a higher photoconversion efficiency of 4.52% in comparison with that of TiO2/CdS/CdSe photoanode. [ABSTRACT FROM AUTHOR]

One of the key objectives for the hematite photoanode is to accelerate the kinetics of oxidative water splitting and inhibit the recombination of electron and hole. Here, we report a titanium boride (TiB2)-modified hematite (α-Fe2O3) photoanode produced by spin coating and subsequent calcination; a surface oxidized layer is formed during this process. The photocurrent density of the surface-oxidized TiB2 on α-Fe2O3 (α-Fe2O3/SO-TiB2) photoanode [at 1.23 V versus reversible hydrogen electrode (vs. RHE), 2.0 mA cm−2] is observably increased compared to α-Fe2O3 (at 1.23 vs. RHE, 0.57 mA cm−2). In addition, the SO-TiB2-decorated heterogeneous junction hematite (HJ-Fe2O3/SO-TiB2) has greater photocurrent activity (at 1.23 vs. RHE, 2.5 mA cm−2). This improvement of the photoelectrochemical (PEC) property is due to the formation of a surface oxide layer, which regulates the direction of the interface electric field, improving improves the separation and injection efficiency of photogenerated charges, as proved by photophysical characterization and PEC measurements. Thereby, the water oxidation kinetics for the α-Fe2O3-based photoanode are significantly accelerated. [ABSTRACT FROM AUTHOR]

Decorating a high-efficiency oxygen evolution reaction (OER) electrocatalyst as a cocatalyst on an α-Fe2O3 photoanode is known to be one of the most efficient methods to improve the photoelectrochemical (PEC) water oxidation activity. In our work, different from traditional methods of transition metal sulfide cocatalyst synthesis, an NiFeSx–decorated Ti-Fe2O3 photoanode is synthesized through a simple one-step electrodeposition method, which benefits the interface between Ti-Fe2O3 and NiFeSx. With the help of this excellent OER electrocatalyst, the photocurrent density of the NiFeSx–Ti-Fe2O3 photoanode rises to 3 mA cm−2 at 1.23 V vs. RHE, which is 2.5 times greater than the photocurrent of Ti-Fe2O3. Moreover, the onset potential of NiFeSx–Ti-Fe2O3 shifts negatively by 170 mV compared with that of pure Ti-Fe2O3. Furthermore, surface photovoltage spectroscopy (SPV) and transient photovoltage (TPV) techniques and photoelectrochemical impedance spectroscopy (PEIS) were used to analyze the true effects of NiFeSx as an efficient cocatalyst for enhancing the PEC performance of the NiFeSx–Ti-Fe2O3 photoanode. This work provides a simple method for loading a low-cost and efficient cocatalyst to modify a Ti-Fe2O3 photoanode for the PEC water oxidation reaction. [ABSTRACT FROM AUTHOR]

Doping graphitic carbon nitride (g-C3N4) with metal ions has been developed as a facile approach to improve its visible light photocatalytic performance towards hydrogen evolution via water splitting. In this work, a series of In3+ doped g-C3N4 (In-g-C3N4) photocatalysts were prepared via in situ thermal copolymerization by using a mixture of dicyanamide and InCl3 as precursors. It was proposed, for the first time, that the In3+ ions were doped into g-C3N4 in a unique quasi-interlayer fashion, which contributed to tunable separation efficiency and migration ability of the photogenerated carriers by simply adjusting the amount of In3+ doping without changing the band edge of g-C3N4. The In-g-C3N4 photocatalyst doped with an optimal amount of indium ions, i.e., 2.18 wt%, exhibited a hydrogen evolution rate of 1.35 mmol h−1 g−1, 17 times that of pristine g-C3N4 (0.08 mmol h−1 g−1), attributed to the synergistically promoted separation and migration of the photogenerated charge carriers. [ABSTRACT FROM AUTHOR]

Nickel phosphide (Ni2P) was used as an excellent water oxidation cocatalyst for photoelectrochemical (PEC) water splitting, which could significantly promote the hole injection efficiency and suppress the back reaction of water oxidation over a Ti4+ doped Fe2O3 photoanode. [ABSTRACT FROM AUTHOR]

Anatase TiO2 nanowire (NW) films modified with inverted type-I CdS/CdSe core/shell structure QDs have been successfully prepared by the post synthesis ligand-assisted technique. Surface photovoltage (SPV), transient photovoltage (TPV) and transient photocurrent (TPC) measurements demonstrate that CdS/CdSe core/shell structure QD-sensitized TiO2 NWs electrodes favor photoexicited electron injection and charge transfer due to the special photo-electronic features of CdS/CdSe core/shell structure QDs. With a polysulfide electrolyte, the maximum conversion efficiency was 2.18% for CdS/CdSe QDs with the CdSe shell being 4.4 nanometers thick; a PCE of 0.07% for CdS QDs and a PCE of 0.63% for CdSe QDs were obtained under illumination at 100 mW cm−2. The results reveal that the CdS/CdSe core/shell structure QDs sensitized TiO2 NW electrodes have promising applications in solar cells. [ABSTRACT FROM AUTHOR]

Nickel, a non-noble metal, is one of the most promising candidates for photocatalysis because it is inexpensive and an earth-abundant metal. Herein, Ni/CM-C3N4 nanocomposites with Ni as a cocatalyst were synthesized by a simple solvothermal method. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed that Ni nanoparticles were loaded onto the surface of CM-C3N4. The prepared Ni/CM-C3N4 nanocomposites exhibited an enhanced hydrogen evolution activity. The most active catalyst contained 10% Ni and produced H2 at a rate of 313.2 μmol h−1 g−1, which was obviously higher than that of pure CM-C3N4. The results of photoluminescence (PL) and photoacoustics (PA) studies indicated that the recombination efficiency of photo-induced electron–hole pairs was decreased for CM-Ni10 as compared to that for unmodified CM-C3N4. The transient photovoltage (TPV) measurements directly demonstrated that the recombination time of electron–hole pairs in CM-Ni10 was prolonged. More importantly, the reversed surface photovoltage (SPV) and the declined surface photocurrent (SPC) response of CM-Ni10 revealed that the photogenerated electrons could be trapped by Ni, leading to a better separation efficiency and a superior hydrogen production. Finally, the possible mechanism is proposed to illuminate the photogenerated charge behavior between CM-C3N4 and Ni, which might provide a theoretical basis to develop efficient cocatalysts for photocatalytic water splitting. [ABSTRACT FROM AUTHOR]

Cocatalysts are one essential factor for promoting the photoelectrochemical water oxidation efficiency of photoanodes, but the influence of interface charge transfer between the semiconductor and cocatalyst has been rarely addressed. Due to their poor charge conductivity, the application of many metal oxides as cocatalysts has been limited. In this work, using photoanode Ti/Fe2O3 and cocatalyst CoOx as a model system, we elaborately design a charge transfer channel of metal Co between the photoanode and cocatalyst. Such a ternary nanostructure has proved to possess several advantageous features, including effective charge separation efficiency, long lifetime of photogenerated holes, and fast charge transport from the photoanode to the surface of the cocatalyst. Benefiting from these desirable nanostructures, the photoanode, containing a charge transfer channel of metal Co, exhibited a remarkable photoelectrochemical performance for water oxidation, with an almost 7-fold enhancement in the photocurrent density at 1.23 V vs. RHE under visible light illumination and about a 0.15 V water oxidation onset potential negative shift compared to the Ti/Fe2O3 photoanode. These findings demonstrate that the successful construction of a metallic charge transfer channel between the photoanode and cocatalyst should be employed as a general strategy for photoconversion applications. [ABSTRACT FROM AUTHOR]

Enhancing the efficiency of semiconductor photocatalysts is still a challenging issue for photocatalytic hydrogen evolution. In this work, a synergistic strategy of surface defects and spatial bandgap engineering was realized for constructing a Zn1−xCdxS/SiO2 photocatalyst. A quantum efficiency of 48.6% (at 420 nm) for hydrogen evolution was obtained without the use of a cocatalyst. The molar ratio of Cd : Zn in Zn1−xCdxS particles could be gradually tuned from 0.305 : 1 (inside) to 0.490 : 1 (outside). At least a 0.17 eV potential difference is present between the inside and outside of Zn1−xCdxS particles. Experimental and theoretical analyses showed that photogenerated electrons and holes could vectorially transfer along the spatial bandgap to reach the surface, and be trapped by the surface defects. In situ formed surface Cd species act as the active sites accelerating the surface hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

Three dimensional (3D) center-hollow ZnO architectures assembled by nanoparticles have been successfully fabricated on a large scale via a template-free method using an oil bath. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller specific surface area, surface photocurrent and UV-Vis diffuse reflectance spectroscopy. The photoelectric gas-sensing results demonstrated that the 3D porous, center-hollow ZnO structures exhibited excellent sensitivity and good selectivity to formaldehyde under 365 nm light irradiation at room temperature. The gas response to 1 ppm formaldehyde can reach 70%, which is superior to the results reported in the literature, indicating that the 3D center-hollow ZnO architectures are ideal candidate materials for photoelectric gas sensors. The underlying mechanisms responsible for the high sensitivity and selectivity to formaldehyde are discussed, which provide a new pathway for designing novel VOC sensors. Moreover, the facile method presented in this paper has the advantage of low-cost and high-yield, which is suitable for the practical production processes. [ABSTRACT FROM AUTHOR]

A series of Ni@g-C3N4 composites were synthesized by a simple solvent thermal method using melamine and acetylacetone nickel as precursors. The results of X-ray diffraction, transmission electron microscopy and high resolution transmission electron microscopy indicate that Ni was successfully loaded on g-C3N4. And the Ni loaded greatly enhances the photocatalytic H2 evolution activity of g-C3N4 compared to the pure g-C3N4. In order to study the role of Ni, the surface photovoltage, the surface photocurrent and photoluminescence measurements were used to investigate the photogenerated charge properties of g-C3N4. What is more, Mott–Schottky plots and work function measurements confirmed the surface band bending change of g-C3N4 contacting with Ni. Those results demonstrate that Ni coating deepens surface band bending of g-C3N4, resulting in higher separation efficiency of photogenerated charge carriers, which is contributed to the enhanced photocatalytic H2 evolution activity. [ABSTRACT FROM AUTHOR]

The formation of heterojunctions between two crystals with different band gap structures, acting as a tunnel for the unidirectional transfer of photogenerated charges, is an efficient strategy to enhance the photocatalytic performance of semiconductor photocatalysts. Considering that surface complex photocatalysts also exhibit charge separation and recombination processes, the heterojunctions may also promote the visible-light-response photoactivity of any surface complex catalysts by influencing the transfer of photogenerated electrons. Herein, Nb2O5 microfibers, with a high surface area of interfaces between an amorphous phase and a crystalline phase, were designed and synthesised by the calcination of hydrogen-form niobate while controlling the crystallisation. The photoactivity of these microfibres towards selective aerobic oxidation reactions was investigated. As predicted, the Nb2O5 microfibres containing heterojunctions exhibited the highest photoactivity. This could be due to the band gap difference between the amorphous phase and the crystalline phase that allows electron transfer unidirectionally, which decreased the recombination rate and improved the efficiency. [ABSTRACT FROM AUTHOR]

The true effect of a cocatalyst on photocatalytic reactions is one of the major issues to resolve in photocatalysis research. Herein, the efficient hole collection role of the CoOx cocatalyst grown on TiO2-nanotubes has been directly proved by surface photovoltage (SPV) spectroscopy. Transient SPV measurements provide evidence that the CoOx cocatalyst could significantly prolong the life-time of photogenerated holes. Furthermore, it is proposed that the hole collection effect can be attributed to the work function difference between the TiO2 and CoOx interface. These findings demonstrate that the development of a cocatalyst with a suitable work function can be a general strategy for photoconversion applications. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) BiVO4/Bi2WO6 composite microspheres with enhanced visible-light (λ ＞ 420 nm) photodegradation activity of methylene blue (MB) were synthesized by a simple, one-pot, template-free solvothermal method. A mixture of ethylene glycol (EG) and H2O (volume ratio of EG-H2O was 1 : 1) was used as the solvent. To investigate the relationship between structure and photocatalytic performance, the as-synthesized samples were characterized by XRD, FESEM, HRTEM, UV-vis DRS, SPS and TPV. Structural characterizations indicated that the composite nanostructure mainly consisted of two single-crystal phases, which were BiVO4 and Bi2WO6. In addition, a possible growth mechanism of this microsphere composite and the separation process of photoinduced charge carriers in the heterojunction are discussed. [ABSTRACT FROM AUTHOR]

We report novel hierarchical three-dimensional (3D) TiO2 nanotube-branched rutile TiO2 nanorod arrays (H-TiO2 NRAs) on FTO substrates that serve as model architecture for efficient quantum dot-sensitized solar cells (QDSCs). The newly designed H-TiO2 NRA photoanode offers a large surface area for high QD loading with high light scattering properties. In the meantime, the presence of anatase–rutile heterojunction at the interface helps the rutile nanorods to efficiently collect photo-injected electrons from the anatase nanotubes, reducing electron recombination with the electrolyte and QDs. As a result, the H-TiO2 NRA photoanode with a thickness of only 1 μm, exhibits a solar energy conversion efficiency of 1.04%, which is 2.7 times higher than that found in the pristine nanorod array-based QDSCs, demonstrating the synergistic effect of rutile nanorods and anatase nanotubes for photoelectrochemical solar energy conversion. [ABSTRACT FROM AUTHOR]

In this paper, we present the fabrication of Ti-doped á-Fe2O3 and surface treatment with Al3+ for application as a photoanode in photoelectrochemical water splitting. The Ti-doped a-Fe2O3 with Al3+ treatment shows a 100 mV cathodic shift of the onset potential and a notable improvement of the photocurrent density. The samples were characterized by SEM, TEM, HRTEM, XRD, Raman, UV-vis and XPS to obtain the information after surface treatment. Based on electrochemistry and photoelectrochemistry techniques, it appears that surface treatment with Al[sup 3+] passivates the surface states and decreases the accumulation of charge at the surface of Ti-Fe2O3. The results show that Ti-doped Fe2O3 with Al3+ surface treatment can be used as an efficient photoanode for photoelectrochemical water splitting. [ABSTRACT FROM AUTHOR]

CuS/Zn0.8Cd0.2S composites have been successfully prepared by simple hydrothermal and cation exchange method. The Cu species loaded on Zn0.8Cd0.2S, together with the intimate contact formed between CuS and Zn0.8Cd0.2S, was clearly demonstrated with X-ray photoelectron spectroscopy and transmission electron microscopy. The optimized CuS/Zn0.8Cd0.2S photocatalyst has a high H2 evolution rate of 2792 μmol g−1 h−1 at CuS content of 3 wt% and the apparent quantum efficiency of 36.7% at 420 nm. The photophysical mechanism of the photocatalytic activity was investigated with the help of surface photovoltage spectroscopy (SPS) and transient photovoltage (TPV) techniques. The results revealed that photogenerated charge separation efficiency in Zn0.8Cd0.2S was enhanced and the photogenerated electrons were trapped by the loaded CuS, which benefits photo-reduction. Those were the reasons for significant enhancement in the photocatalytic H2 evolution from water splitting. [ABSTRACT FROM AUTHOR]

The transfer properties of the photogenerated charge carriers in TiO2 nanotube arrays (TNAs) and ZnFe2O4 modified TiO2 nanotube arrays (ZFO–TNAs) were investigated by surface photovoltage phase spectra. The modification of ZnFe2O4 on TNAs will lead to a new process of photogeneration of charge carriers. When irradiated with UV or visible light, before ZnFe2O4 modification photogenerated holes can transfer to the surface of TNAs; while after ZnFe2O4 modification, a process of photogenerated electrons transferring to the surface occurred. The different detected photogenerated charge transfer processes agree well with the photocatalytic reduction of Cr(vi) and the degradation of methyl orange experiments, which confirmed that the photogenerated holes transferring to the surface of the TNAs or ZFO–TNAs were beneficial for the reactions of photocatalytic reduction and electrons transferring to the surface were beneficial for photocatalytic degradation. [ABSTRACT FROM AUTHOR]

The TiO2-B nanobelt (NB)/TiO2nanoparticle (NP) sandwich-type structure photoelectrode, with controllable nanobelt length, has been used to fabricate high-efficiency dye-sensitized solar cells (DSSCs), which combine the advantages of the rapid electron transport in TiO2-B NBs and the high surface area of TiO2NPs. The results indicate that the sandwich-type photoelectrode achieves higher photoelectrical conversion efficiency when compared with the TiO2nanoparticulate electrode. Increasing the length of TiO2-B NBs has been demonstrated to improve the photoelectric conversion efficiency (η). DSSCs with the longest (10 μm) TiO2-B NBs yield the highest ηof 7.94%. The interfacial electron transport of DSSCs with different lengths of TiO2-B NBs has been quantitatively investigated using the photovoltage transient and the electrochemical impedance spectra, which demonstrates that the DSSCs with longest TiO2-B NBs display the highest electron collection efficiency and the fastest interfacial electron transfer. [ABSTRACT FROM AUTHOR]

ZnO/Cu2O heterostructure films were prepared by a two-step electrodeposition method in aqueous solution on fluorine-doped tin oxide (FTO) substrates. Scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and UV-vis transmission measurements were utilized to characterize the films. Surface photovoltage (SPV) technique was used to investigate the process of photoinduced charge transfer. The results show that there is an electric field located at the interface between ZnO and Cu2O film and the photoinduced electrons in Cu2O film inject into ZnO under the effect of interfacial electric field with visible light irradiation. While under ultraviolet light illumination, the photoinduced electrons in Cu2O film accumulate at the surface of Cu2O film instead of injecting into ZnO under the action of surface built-in electric field of Cu2O film. The work function measurements confirm that the direction of interfacial electric field is from ZnO to Cu2O. These results are help to future design of high performance heterostructure photovoltaic devices. [ABSTRACT FROM AUTHOR]

Fe2O3/TiO2heterogeneous photocatalysts with different mass ratios of Fe2O3vs.TiO2were synthesized by impregnation of Fe3+on the surface of TiO2microrods and calcination at 300 °C. Scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), photoluminescence spectra and X-ray diffraction (XRD) have been used to characterize the samples. The photocatalytic activities of Fe2O3/TiO2heterocomposites, pure Fe2O3and pure TiO2were evaluated by the photodegrading efficiency of Orange II under visible light (λ> 420 nm). The experiments demonstrated that Orange II in aqueous solution was more efficiently photodegraded using Fe2O3/TiO2heterogeneous photocatalysts than either pure Fe2O3or TiO2under visible light irradiation. With an optimal mass ratio of 7 : 3 in Fe2O3/TiO2the highest rate of Orange II photodegradation was achieved under the experimental conditions. We have also compared the photoelectric properties of Fe2O3/TiO2heterogeneous photocatalysts with that of pure Fe2O3by surface photovoltage (SPV) and transient photovoltage (TPV) techniques. Based on the photovoltage responses, we discussed the influence of the hetero-interface between Fe2O3and TiO2on transfer characteristics of photogenerated charge carriers. We demonstrated that the formation of heterojunctions between Fe2O3and TiO2for Fe2O3/TiO2composites was pivotal for improving the separation and thus restraining the recombination of photogenerated electrons and holes, which accounts for the enhancement of photocatalytic activity. [ABSTRACT FROM AUTHOR]

The development of photoelectrochemical (PEC) water splitting is hindered by the slow kinetics of four-electron processes for the oxygen evolution reaction (OER) and severe charge recombination. Amorphous carbon was chosen as a carrier for the active sites due to its exceptional conductivity and strong loading capacity. In addition, this enhanced performance was attributed to the loading of oxides of cobalt. Here, amorphous carbon-covered cobalt oxides chosen as a co-catalyst loaded on α-Fe 2 O 3 (noted as CoO x @C/Ti-Fe 2 O 3 ) have been synthesized, and they show a high current density (2.86 mA cm -2 under 1.23 V vs. RHE), and a low onset potential (0.611 V vs. RHE). Experimental analysis demonstrates that the charge transfer and separation leading to accelerated OER dynamics and improved PEC performance are enhanced by CoO x @C effectively. This study provides new ideas for designing high-performance photoelectrochemical electrodes based on amorphous carbon co-catalysts.

Photogenerated carrier behavior at a CO 2 /Cs 2 AgBiBr 6 quantum dot (QD) interface is investigated. In situ photovoltage spectra reveal electron transfer from the Cs 2 AgBiBr 6 QDs to CO 2 . Moreover, this carrier transfer prefers Bi 3+ sites (over Ca + and Ag + sites) due to them exhibiting the lowest adsorption energy ( E ads = -0.125 eV) and CO 2 -Bi 3+ interactions being more stable.

Interface modification is an important means to enhance the photovoltaic performance of quantum dot sensitized solar cells (QDSCs). The TiO 2 /CdS/CdSe solar cells are sensitized with CdS QDs and CdSe QDs, which inevitably introduces a new interface to form a recombination center. Therefore, it is necessary to coat a passivation layer in order to effectively inhibit charge recombination at the CdS/CdSe interface. In this work, CuInS 2 (CIS) has been introduced into the CdS/CdSe QD system as an inner passivation layer and the CdS/CIS/CdSe photoanode structure has been fabricated in an environmentally friendly manner. The extracted charge amount ( Q ) is used to express the charge separation efficiency, indicating that we have obtained outstanding charge extraction efficiency in CIS based CdS/CdSe QDSCs. As a result, the photocurrent density of the TiO 2 /CdS/CIS/CdSe photoanode significantly has increased from 19.01 mA cm -2 to 22.74 mA cm -2 (TiO 2 /CdS/CdSe photoanode), which demonstrates a higher photoconversion efficiency of 4.52% in comparison with that of TiO 2 /CdS/CdSe photoanode.

Decorating a high-efficiency oxygen evolution reaction (OER) electrocatalyst as a cocatalyst on an α-Fe 2 O 3 photoanode is known to be one of the most efficient methods to improve the photoelectrochemical (PEC) water oxidation activity. In our work, different from traditional methods of transition metal sulfide cocatalyst synthesis, an NiFeS x -decorated Ti-Fe 2 O 3 photoanode is synthesized through a simple one-step electrodeposition method, which benefits the interface between Ti-Fe 2 O 3 and NiFeS x . With the help of this excellent OER electrocatalyst, the photocurrent density of the NiFeS x -Ti-Fe 2 O 3 photoanode rises to 3 mA cm -2 at 1.23 V vs. RHE, which is 2.5 times greater than the photocurrent of Ti-Fe 2 O 3 . Moreover, the onset potential of NiFeS x -Ti-Fe 2 O 3 shifts negatively by 170 mV compared with that of pure Ti-Fe 2 O 3 . Furthermore, surface photovoltage spectroscopy (SPV) and transient photovoltage (TPV) techniques and photoelectrochemical impedance spectroscopy (PEIS) were used to analyze the true effects of NiFeS x as an efficient cocatalyst for enhancing the PEC performance of the NiFeS x -Ti-Fe 2 O 3 photoanode. This work provides a simple method for loading a low-cost and efficient cocatalyst to modify a Ti-Fe 2 O 3 photoanode for the PEC water oxidation reaction.

A Z-scheme system In 2 S 3 /WO 3 heterojunction was fabricated via a mild hydrothermal method and further applied for photocatalytic degradation of tetracycline (TCH) and Rhodamine B (Rh B) under visible light irradiation. The morphological structure, chemical composition and optical properties were studied by XRD, SEM, HRTEM and UV-visible absorption spectra. The results revealed that In 2 S 3 /WO 3 hierarchical structures were successfully constructed, and the prepared In 2 S 3 /WO 3 photocatalysts exhibited enhanced visible-light absorption compared to pure WO 3 nanorods, which are essential to improve the photocatalytic performance. The degradation rate of TCH using the In 2 S 3 (40 wt%)/WO 3 heterostructure (WI40) photocatalyst was about 212 times and 22 times as high as that for pure WO 3 and pure In 2 S 3 , respectively. The degradation rate of Rh B with the WI40 photocatalyst was about 56 times the efficiency of pure WO 3 and 7.6 times that of pure In 2 S 3 . The results of the surface photovoltage (SPV), transient photovoltage (TPV) and reactive oxidation species (ROS) scavenger experiments indicated that the Z-scheme system of In 2 S 3 /WO 3 is favorable for photoexcited charge transfer at the contact interface of In 2 S 3 and WO 3 , which benefits the charge separation efficiency and depresses the recombination of photoexcited charge, resulting in favorable photocatalytic pollutant degradation efficiency under visible light irradiation., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Solar-driven H 2 generation from water splitting with semiconductor materials is considered an effective solution to solve the problems of energy shortage and environmental pollution at a low cost. In this study, a highly efficient photocatalyst Ni@NiO/CdS for H 2 evolution was synthesised using a simple solvothermal method and calcination. The HRTEM results and elemental mapping tests confirmed that Ni@NiO was successfully loaded on the surface of CdS. For Ni@NiO loaded, Ni@NiO/CdS exhibited remarkable photocatalytic H 2 evolution activity of 87.6 μmol h -1 , which was about 104 times higher than that of pure CdS. The enhanced H 2 evolution activity of Ni@NiO/CdS was ascribed to the prolonged lifetime of the photogenerated charges and the reduced surface overpotential for H 2 evolution., Competing Interests: There are no conflict to declare., (This journal is © The Royal Society of Chemistry.)

Nickel phosphide (Ni 2 P) was used as an excellent water oxidation cocatalyst for photoelectrochemical (PEC) water splitting, which could significantly promote the hole injection efficiency and suppress the back reaction of water oxidation over a Ti 4+ doped Fe 2 O 3 photoanode.

Anatase TiO 2 nanowire (NW) films modified with inverted type-I CdS/CdSe core/shell structure QDs have been successfully prepared by the post synthesis ligand-assisted technique. Surface photovoltage (SPV), transient photovoltage (TPV) and transient photocurrent (TPC) measurements demonstrate that CdS/CdSe core/shell structure QD-sensitized TiO 2 NWs electrodes favor photoexicited electron injection and charge transfer due to the special photo-electronic features of CdS/CdSe core/shell structure QDs. With a polysulfide electrolyte, the maximum conversion efficiency was 2.18% for CdS/CdSe QDs with the CdSe shell being 4.4 nanometers thick; a PCE of 0.07% for CdS QDs and a PCE of 0.63% for CdSe QDs were obtained under illumination at 100 mW cm -2 . The results reveal that the CdS/CdSe core/shell structure QDs sensitized TiO 2 NW electrodes have promising applications in solar cells.

A series of Ni@g-C3N4 composites were synthesized by a simple solvent thermal method using melamine and acetylacetone nickel as precursors. The results of X-ray diffraction, transmission electron microscopy and high resolution transmission electron microscopy indicate that Ni was successfully loaded on g-C3N4. And the Ni loaded greatly enhances the photocatalytic H2 evolution activity of g-C3N4 compared to the pure g-C3N4. In order to study the role of Ni, the surface photovoltage, the surface photocurrent and photoluminescence measurements were used to investigate the photogenerated charge properties of g-C3N4. What is more, Mott-Schottky plots and work function measurements confirmed the surface band bending change of g-C3N4 contacting with Ni. Those results demonstrate that Ni coating deepens surface band bending of g-C3N4, resulting in higher separation efficiency of photogenerated charge carriers, which is contributed to the enhanced photocatalytic H2 evolution activity.

Three-dimensional (3D) BiVO4/Bi2WO6 composite microspheres with enhanced visible-light (λ > 420 nm) photodegradation activity of methylene blue (MB) were synthesized by a simple, one-pot, template-free solvothermal method. A mixture of ethylene glycol (EG) and H2O (volume ratio of EG-H2O was 1 : 1) was used as the solvent. To investigate the relationship between structure and photocatalytic performance, the as-synthesized samples were characterized by XRD, FESEM, HRTEM, UV-vis DRS, SPS and TPV. Structural characterizations indicated that the composite nanostructure mainly consisted of two single-crystal phases, which were BiVO4 and Bi2WO6. In addition, a possible growth mechanism of this microsphere composite and the separation process of photoinduced charge carriers in the heterojunction are discussed.

CuS/Zn(0.8)Cd(0.2)S composites have been successfully prepared by simple hydrothermal and cation exchange method. The Cu species loaded on Zn(0.8)Cd(0.2)S, together with the intimate contact formed between CuS and Zn(0.8)Cd(0.2)S, was clearly demonstrated with X-ray photoelectron spectroscopy and transmission electron microscopy. The optimized CuS/Zn(0.8)Cd(0.2)S photocatalyst has a high H2 evolution rate of 2792 μmol g(-1) h(-1) at CuS content of 3 wt% and the apparent quantum efficiency of 36.7% at 420 nm. The photophysical mechanism of the photocatalytic activity was investigated with the help of surface photovoltage spectroscopy (SPS) and transient photovoltage (TPV) techniques. The results revealed that photogenerated charge separation efficiency in Zn(0.8)Cd(0.2)S was enhanced and the photogenerated electrons were trapped by the loaded CuS, which benefits photo-reduction. Those were the reasons for significant enhancement in the photocatalytic H2 evolution from water splitting.

The transfer properties of the photogenerated charge carriers in TiO2 nanotube arrays (TNAs) and ZnFe2O4 modified TiO2 nanotube arrays (ZFO-TNAs) were investigated by surface photovoltage phase spectra. The modification of ZnFe2O4 on TNAs will lead to a new process of photogeneration of charge carriers. When irradiated with UV or visible light, before ZnFe2O4 modification photogenerated holes can transfer to the surface of TNAs; while after ZnFe2O4 modification, a process of photogenerated electrons transferring to the surface occurred. The different detected photogenerated charge transfer processes agree well with the photocatalytic reduction of Cr(VI) and the degradation of methyl orange experiments, which confirmed that the photogenerated holes transferring to the surface of the TNAs or ZFO-TNAs were beneficial for the reactions of photocatalytic reduction and electrons transferring to the surface were beneficial for photocatalytic degradation.