Morphology selective electrodeposition of Cu2O microcrystals on ZnO nanotube arrays as efficient visible-light-driven photo-electrode

ZnO nanotube arrays were synthesized by the electrodeposition method and Cu₂O microcrystals with two kinds of morphologies were deposited on ZnO nanotube arrays successfully. At the deposition potential of −0.5 or −0.7 V, the cubic or spherical Cu₂O microcrystals were selectively deposited on ZnO nanotube arrays. By adjusting the deposition time, Cu₂O microcrystals with different sizes were obtained. The optical properties and photo-electrochemical performance of ZnO/Cu₂O were measured. The results showed that the as-prepared ZnO/Cu₂O heterojunction exhibited improved visible light absorption and enhanced photocurrent due to the excellent ability of Cu₂O microcrystals for harvesting visible light, and the effective separation and transfer of photo-generated electrons and holes owing to p-n junction between ZnO and Cu₂O. The experimental results demonstrate that the photo-electrochemical performance of ZnO/Cu₂O heterojunction nanotube arrays can be manipulated by controlling the morphology and the size of Cu₂O microcrystals.     

Flame-assisted pyrolysis formation of Cu2O/Cu/TiO2 nanotube arrays to boost superior photo-electrochemical response

Herein, a flame-assisted pyrolysis technique is developed for one-step in-situ construction of Cu₂O/Cu/TiO₂ nanotube arrays. The structure and morphology of the obtained samples are systematically characterized. Interestingly, UV–vis absorption spectroscopy reveals that the introduction of Cu₂O and Cu considerably enhance light response of TiO₂ nanotube arrays in the visible region. Moreover, the composited electrode shows enhanced photo-electrochemical activity. Compared with blank TiO₂ nanotube arrays, not only the photocurrent and photo-voltage of composited electrodes are improved but also the stability is also enhanced. And, the maximum photo-conversion efficiency for composited electrode presents 4.71 folds larger than that of blank TiO₂ electrode. This enhancement is due to the faster charge separation/transportation ability of Cu and visible light response of Cu₂O. This research develops a novel and facile method for the in-situ fabrication of Cu₂O/Cu/TiO₂ nanotube arrays and demonstrates their improved utilization of solar energy.     

Cu2O/Cu/TiO2 nanotube Ohmic heterojunction arrays with enhanced photocatalytic hydrogen production activity

Cu₂O/Cu/TiO₂ nanotube heterojunction arrays were prepared by assembling Cu@Cu₂O core-shell nanoparticles on TiO₂ nanotube arrays (NTAs) using a facile impregnation-reduction method. SEM and TEM results show that Cu@Cu₂O plate-like nanoparticles with tens of nanometers in size are confined inside TiO₂ NTAs. Only the outmost several nanometers of the nanoparticles are Cu₂O and the predominant inner of the nanoparticles are Cu metals. Cu L₃VV Auger spectra of Cu₂O/Cu/TiO₂ NTAs suggest that Cu metals are enveloped by at least several nanometers Cu₂O on the surface, which further confirms the Cu@Cu₂O core shell structure of Cu nanoparticles. The ability of light absorption of Cu₂O/Cu/TiO₂ NTAs is enhanced. The range of absorption wavelengths changes from 400 to 700 nm due to the surface plasmon response of Cu metals core and Cu₂O nanoparticles shell. The photocatalytic hydrogen production rate of Cu₂O/Cu/TiO₂ heterojunction arrays is enhanced when compared with those of Cu₂O/TiO₂ NTAs and TiO₂ NTAs under UV light. Moreover, a stable H₂ generation property was obtained under visible light (λ gt; 400 nm). The Cu metal core is believed to play a key role in the enhancement of photocatalytic properties of Cu₂O/Cu/TiO₂ nanotube heterojunction arrays.     

ZnO/Cu2O-decorated rGO: Heterojunction photoelectrode with improved solar water splitting performance

In present work, we report a facile fabrication process to improve the photoelectrochemical (PEC) performance of ZnO-based photoelectrodes. In order to achieve that, the Cu₂O nanocubes are cathodic-deposited on the as-prepared ZnO nanorods. Then rGO nanosheets are electrodeposited on the ZnO/Cu₂O heterostructures. The fabricated photoelectrodes are systematically studied in detail by different characterization techniques such as powder X-ray diffraction, micro-Raman, X-ray photoelectron spectroscopy, ultraviolet diffused reflectance spectroscopy and photoluminescence spectroscopy analysis. Morphologies of the fabricated photoelectrodes are investigated through electron microscopy in scanning and transmission mode. To evaluate the PEC performance of the fabricated photoelectrodes, the line scan voltammetry (LSV) measurement is performed using a three-electrode system in 0.5-M Na₂SO₄ electrolyte solution under stimulated light illumination at 100 mW/cm² from a 300-W Xenon Arc lamp coupled with an AM 1.5G filter using a three-electrode system. The photocurrent measurement demonstrates that the photoelectrodes based on ZnO/Cu₂O/rGO possess enhanced PEC performance compared to the pristine ZnO and ZnO/Cu₂O photoelectrodes. The photocurrent density of ZnO/Cu₂O/rGO-15 photoelectrode (10.11 mA/cm²) is ∼9 and ∼3 times higher than the photoelectrodes based on pristine ZnO (1.06 mA/cm²) and ZnO/Cu₂O (3.22 mA/cm²). The enhanced PEC performance of ZnO/Cu₂O/rGO photoelectrode is attributed to the excellent light absorption properties of Cu₂O and excellent catalytic and charge transport properties of rGO. Experimental results reveal that the proposed functional nanomaterials have a great potential in water splitting applications.     

Structural properties and enhanced photoelectrochemical performance of ZnO films decorated with Cu2O nanocubes

Combination of ZnO and Cu₂O semiconductors is remarkable for efficient photovoltaic cells and enhanced photoelectrochemical (PEC) performance due to the high electronic energy band alignment of these materials and their controllable electronic structure at the interface. This study reports on a systematic analysis of the effects of Cu₂O nanocube doping on the structural properties and PEC performance of ZnO films. ZnO samples doped with Cu₂O were prepared by a practical electrochemical method. Characterization of the materials was performed by XRD, Raman, FTIR spectroscopy and electrochemical techniques. The XRD, Raman, FTIR spectroscopy analyses indicated a single phase of ZnO for the lower Cu₂O deposition time, while a secondary phase of Cu₂O evolved for the 5 min deposition time. This study showed that ZnO doped with Cu₂O grown for 3 min had the best PEC performance. ZnO/Cu₂O photoelectrodes are recommended as an attractive, competitive and alternative candidate for advanced PEC sensing and this may be for the extended field of water splitting into oxygen and hydrogen under sunlight.     

Surface modification of aligned TiO2 nanotubes by Cu2O nanoparticles and their enhanced photo electrochemical properties and hydrogen generation application

In this work, we report the synthesis of cuprous oxide (Cu₂O) nanoparticles modified vertically oriented aligned titanium dioxide (TiO₂) nanotube arrays through wet chemical treatment of TiO₂ nanotubes and their multi-functional application as enhanced photo electrochemical and hydrogen generation. The synthesized samples were characterized by X-ray diffraction, SEM, TEM, and UV–Vis spectroscopy. The structural characterization revealed that the admixed Cu₂O nanoparticles on the TiO₂ surface did not alter its crystalline structure of vertically oriented aligned TiO₂ nanotube. The photocatalytic performance and hydrogen generation of as synthesized Cu₂O nanoparticles modified aligned TiO₂ nanotube was found to highly depend on the Cu₂O content. The optical characterizations reveal that the presence of Cu₂O nanoparticles extends its absorption into the visible region which improves the photocurrent density in comparison to pristine aligned TiO₂ nanotubes electrodes due to enhanced photoactivity and better charge separation. The optimum photocurrent density and hydrogen generation rate has been found to be 3.4 mA cm^?2 and 127.5 μmole cm^?2 h^?1 in 1 M Na₂SO₄ electrolyte solution under 1.5 AM solar irradiance of white light with illumination intensity of 100 mW cm^?2.     

Efficient light harvesting by NiS/CdS/ZnS NPs incorporated in C,N-co-doped-TiO2 nanotube arrays as visible-light sensitive multilayer photoanode for solar applications

Here, we report a significant enhancement in photo-electrochemical activity of co-doped/modified TiO₂ nanotube arrays (TNAs). First, TiO₂ nanostructures were sensitized with nitrogen and carbon via a single step/low cost anodization process and then modified with Nis/CdS/ZnS nano particles (NPs) by the successive ionic layer adsorption and reaction (SILAR) method at room temperature. Photo-electrochemical properties and physical/chemical characteristics of the pure and sensitized/modified TNAs were investigated using field emission scanning electron microscopy (FESEM), XRD, XPS and EDX, comprehensively. Electrochemical measurements and UV–Vis DRS spectroscopy of the photo-electrodes showed that co-doping with anions and modification with different NPs result in the broadening of the absorption region of visible light and the reduction of band gap energy. The mechanism responsible for the enhanced photo-electrochemical activity of the C, N-co-doped/NiS, CdS, ZnS NPs modified TNAs for the water reduction reaction using aqueous solutions of Na₂S/Na₂SO₃ as sacrificial electrolyte under the whole spectrum of simulated solar light irradiation has been presented. The highest photocurrent in presence of sacrificial agent (Na₂S/Na₂SO₃) was obtained as 18.79 mA/cm², for the optimized SILAR loading cycles and dopants concentration. Furthermore, a high incident photon to current efficiency (IPCE) of about 82% for the optimum photo-anode had been achieved. These results confirm that the C, N-co-doped/NiS, CdS, ZnS NPs modified TNAs nanocomposite may offer a promising strategy to attain maximum efficiency in a variety of solar energy conversion systems, along with reduced photo-corrosion in the semiconductor-semiconductor heterojunction.     

Photoelectrochemical and photocatalytic properties of Ag-loaded BaTiO3/TiO2 heterostructure nanotube arrays

BaTiO₃/TiO₂ (BT) heterostructure nanotube arrays were fabricated by in situ hydrothermal method using TiO₂ nanotubes as both template and reactant. Compared with pure TiO₂ nanotube arrays, the BT heterostructures exhibited enhanced photocurrent under UV light irradiation. For further improving the photoelectrochemical performance, Ag nanoparticles were loaded on the surface of BT heterostructure by two different photo-reduction (Ag/BT-P) and chemical reduction (Ag/BT-C) methods. The results showed that the Ag nanoparticles on Ag/BT-C were uniform and dispersed homogeneously, but the Ag nanoparticles on Ag/BT-P were very large, which resulted in the tailored and integrated nanotube structure destroyed. The electrochemical impedance spectra (EIS) indicated that the impedance arc radius of Ag/BT-C was much smaller than Ag/BT-P and the pure BT nanotube arrays, indicating that the enhanced charge carrier separation was achieved on Ag/BT-C. In addition, the Ag/BT-C nanotube arrays exhibited a higher photocatalytic activity for methylene blue (MB) degradation.     

Deposition of heterojunction of ZnO on hydrogenated TiO2 nanotube arrays by atomic layer deposition for enhanced photoelectrochemical water splitting

The heterojunction of ZnO was deposited on hydrogenated TiO₂ nanotube arrays (H–TiO₂) by atomic layer deposition (ALD) with various cycles. The ZnO was uniformly wrapped with the H–TiO₂ samples and the thickness could be accurately controlled by the cycle numbers of ALD. The higher growth rate ~2.7 Å/cycle was obtained due to the surface amorphous layer, compared with the air-treated samples (A-TiO₂), ~2.3 Å/cycle. When the cycle numbers increased to 200, nanowire arrays appeared. Interestingly, the absorption in the visible light region improved more significantly when ALD ZnO was employed for the H–TiO₂ rather than the A-TiO₂ samples. The H–TiO₂ samples with 42 nm of ALD ZnO exhibited enhanced photoelectrochemical water splitting performances, compared with the A-TiO₂ with 42 nm of ALD ZnO. This was related to the higher degree of the electronic band bending and improved photo-response in the UV and visible light region, resulting from the oxygen vacancies.     

Fabrication of dye-sensitized solar cells by transplanting highly ordered TiO2 nanotube arrays

Highly ordered TiO₂ nanotube arrays fabricated by anodization are very attractive to dye-sensitized solar cells (DSCs) due to their superior charge percolation and slower charge recombination. However, the efficiency of TiO₂-nanotube-based DSCs is 6.89%, which is still lower than that of TiO₂-nanoparticle-based DSCs. We have suggested the transplanting the highly ordered TiO₂ nanotube arrays to FTO glass to improve the performance of TiO₂-nanotube-based DSCs. DSCs based on transplanted TiO₂ nanotube arrays and TiO₂ nanoparticles were fabricated by same process and materials to exclude the unexpected factors. In TiO₂ thickness of ca. 15 μm, the efficiency of 2.91% in front-side illuminated DSCs based on TiO₂ nanotube arrays was higher than those in back-side illuminated DSCs based on TiO₂ nanotube arrays and in front-side illuminated DSCs based on TiO₂ nanoparticle. Front-side illuminated DSCs based on TiO₂ nanotube arrays having various thicknesses were successfully fabricated. The efficiency in DSCs having 20.0 μm thick TiO₂ nanotube arrays was improved to 5.36% by TiCl₄ treatment.     

Surface modification of the p-type Cu2ZnSnS4 photocathode with n-type zinc oxide nanorods for photo-driven salt water splitting

The sulfurization of co-sputtering Cu–Zn–Sn metal precursors was employed to prepare the quaternary copper-zinc-tin-sulphide (Cu₂ZnSnS₄, CZTS) photocathodes on substrates. Influence of [Zn]/[Sn] ratios in CZTS photocathodes on their phases, morphologies, and the efficiencies of photo-driven salt-water splitting was examined. Pristine p-type CZTS photocathodes showed the highest photo-driven performance of 0.61 mA cm^?2 in an electrolyte containing 1 M sodium chloride with the external bias kept at ?1.0 V vs. Ag/AgCl. An n-type zinc oxide (ZnO) nanorod arrays layer was then coated on the CZTS photocathode to improve its photo-driven salt-water splitting performance. The CZTS/ZnO photoelectrode had the best photo-driven performance of 1.87 mA cm^?2 in the 1 M NaCl solution under illumination with the external bias set at ?1.0 V vs. Ag/AgCl. From results of electrochemical impedance spectra measurements for the samples in the electrolyte, the CZTS/ZnO sample had good photo-driven salt-water splitting performance due to its lowest charge transfer resistance and p-n junction formed at the sample. Intensity modulated photocurrent spectroscopy and electrochemical impedance spectra results of samples indicated that the surface states at the CZTS/ZnO interface were the recombination centers with the electrons from the CZTS sample and holes from the ZnO and therefore improved its photo-driven salt-water splitting performance.     

Thin film deposition of Cu2O and application for solar cells

Deposition conditions of cuprous oxide (Cu₂O) thin films on glass substrates and nitrogen doping into Cu₂O were studied by using reactive radio-frequency magnetron sputtering method. The effects of defect passivation by crown-ether cyanide treatment, which simply involves immersion in KCN solutions containing 18-crown-6 followed by rinse, were also studied. By the crown-ether cyanide treatment, the luminescence intensity due to the near-band-edge emission of Cu₂O at around 680 nm was enhanced, and the hole density was increased from 10¹⁶ to 10¹⁷ cm⁻³. Finally, polycrystalline p-Cu₂O/n-ZnO heterojunctions were grown for use in solar cells. Two deposition sequences were studied, ZnO deposited on Cu₂O and Cu₂O deposited on ZnO. It was found that the crystallographic orientation and current–voltage characteristics of the heterojunction were significantly influenced by the deposition sequence, both being far superior for the heterojunction with structure Cu₂O on ZnO than for the inverse structure. We successfully obtained a photoresponse for the first time in the deposited thin film of Cu₂O/ZnO.     

Improved photocatalytic efficiency and stability of CdS/ZnO shell/core nanoarrays with high coverage and enhanced interface combination

Photocatalytic hydrogen production of CdS/ZnO shell/core nanoarrays were investigated by combining the sensitization and calcining techniques. Long single crystal ZnO nanoarrays hydrothermally grown on FTO were fully covered with CdS using an optimized chemical bath deposition method. Heating treatment not only improved the interface connection and CdS crystallinity but also formed a (Cd_0.8Zn_0.2)S buffer layer between ZnO and CdS. The CdS/ZnO shell/core arrays showed gradually enhanced photocatalytic activity with raising the calcining temperature. This is predominantly attributed to the improved CdS crystallinity and the resultant (Cd_0.8Zn_0.2)S. The (Cd_0.8Zn_0.2)S buffer layer formed by calcining shows dramatic effect on the photocatalytic activity and stability. The CdS/ZnO shell/core arrays calcined at 550 °C exhibits the optimized photocurrent density of 5.1 mA cm^?2 and a photocatalytic stability over 12 h under visible-light irradiation.     

Bi2S3 anchored ZnS/ZnO nanorod arrays photoanode for enhanced visible light driven photo electrochemical properties

We report on the enhanced photoelectrochemical water splitting of hybrid ZnS/ZnO core-shell nanorod arrays functionalized with Bi₂S₃ nanosheets as photoanode. The ZnO nanorod arrays were prepared by a facile hydrothermal approach and sulphurized to form ZnS shell. Subsequently porous Bi₂S₃ nanosheets were arbitrarily decorated on the nanorod arrays by ionic adsorption and reaction method. Substantial enhancement in photocurrents with twofold increment is observed for hybrid photoanode compared to pristine counterparts. The structural and morphological properties of nano hybrid Bi₂S₃/ZnS/ZnO samples were analyzed by field emission scanning electron microscopy and X-ray diffraction. The higher wavelength shift in the absorption edge of Bi₂S_3/ZnS/ZnO photocatalyst was observed in diffuse reflectance UV–Visible spectra. The low temperature photoluminescence and impedance spectra of Bi₂S₃/ZnS/ZnO photoanode confirm that Bi₂S₃ functionalization reduces the recombination of electron–hole pair and facilitates barrier free charge transfer. The Bi₂S₃/ZnS/ZnO photoanode device exhibits photocurrent density of 220 μA/cm² at 0.2 V vs. Ag/AgCl under the electrolyte solution at pH ~10.8. The resultant hybrid photoanode withhold good stability and maintain the facile charge carrier generation and separation. Bi₂S₃ topological nanosheets are responsible for the absorption of complete visible photons while ZnS/Bi₂S₃ inter-junction provides the robust electron-hole pair separation at their interface due to infiltration pathway. The photoactive hybridization of Bi₂S₃/ZnS/ZnO provokes the enhanced donor charge density for efficient hydrogen evolution reaction.     

Enhanced photoelectrochemical properties of TiO2 nanotube arrays sensitized with energy-band tunable (Cu2Sn)x/3Zn1−xS nanoparticles

In this paper, TiO₂ nanotube (TNT) arrays and (Cu₂Sn)_x/3Zn_1−xS (x = 0.75, 0.24, and 0.09) nanocrystals were prepared, and TiO₂ nanotubes (TNTs) were sensitized with (Cu₂Sn)_x/3Zn_1−xS nanocrystals. Compared with the plain TNTs, (Cu₂Sn)_x/3Zn_1−xS sensitized TNTs present an enhanced photoelectrochemical response. The photocurrent enhancement was characterized with the photocurrent ratio of (Cu₂Sn)_x/3Zn_1−xS sensitized TNTs to plain TNTs, which were 1.50, 1.63, and 2.13 for (Cu₂Sn)_x/3Zn_1−xS with the composition of x = 0.75, 0.24, and 0.09, respectively. To understand this phenomenon, the energy band alignments of TNTs and (Cu₂Sn)_x/3Zn_1−xS were investigated, based on which the conduction band offsets (CBO) between TNTs and (Cu₂Sn)_x/3Zn_1−xS were determined, which were 0.31, 0.47, and 0.63 eV for (Cu₂Sn)_x/3Zn_1−xS with the composition of x = 0.75, 0.24, and 0.09, respectively. These results display that the photocurrent enhancement becomes large with the increase of CBO, which indicates that the enhanced photoelectrochemical response is mainly due to the energy level matching between TNTs and (Cu₂Sn)_x/3Zn_1−xS, and the variation of enhancement is resulting from the change of CBO.     

The influence of the electrodeposition potential on the morphology of Cu2O/TiO2 nanotube arrays and their visible-light-driven photocatalytic activity for hydrogen evolution

The influence of the electrodeposition potential on the morphology of Cu₂O/TiO₂ nanotube arrays (Cu₂O/TNA) and their visible-light-driven photocatalytic activity for hydrogen evolution have been investigated for the first time in this work. The photocatalytic hydrogen evolution rate of the as-prepared Cu₂O/TNA at the deposition potential of −0.8 V was about 42.4 times that of the pure TNA under visible light irradiation. This work demonstrated a feasible and simple electrodeposition method to fabricate an effective and recyclable visible-light-driven photocatalyst for hydrogen evolution.     

Cu2S@NiFe layered double hydroxides nanosheets hollow nanorod arrays self-supported oxygen evolution reaction electrode for efficient anion exchange membrane water electrolyzer

Herein, we prepared highly active self-supported Cu₂S@NiFe layered double hydroxides nanosheets (LDHs) oxygen evolution reaction (OER) electrode (Cu₂S@NiFe LDHs/Cu foam) with three-dimensional (3D) multilayer hollow nanorod arrays structure, which is composed of the outer layer (two-dimensional (2D) NiFe LDHs) and the inner layer (one-dimensional (1D) Cu₂S hollow nanorod arrays). The unique structure of NiFe LDHs and Cu₂S hollow nanorod composites can expose more active sites, and simultaneously promote electrolyte penetration and gas release during the water electrolysis process. Thus, the Cu₂S@NiFe LDHs/Cu foam electrode exhibits a significant OER performance, with the overpotentials of 230 and 286 mV at 50 and 100 mA cm⁻², respectively. Anion exchange membrane water electrolyzer (AEMWE) with the prepared electrode can attain a voltage of 1.56 V at the current density of 0.50 A cm⁻², showing a good performance that is comparable to the-state-of-the-art AEMWE in 1 M KOH. In addition, the AEMWE can be run for 300 h at the current density of 0.50 A cm⁻². The high performance and good stability of AEMWE are attributed to the special structure of the OER electrode, which can prevent the agglomeration of nanosheets and thus expose more active sites at the edge of the nanosheets.     

Hydrogen generation under sunlight by self ordered TiO2 nanotube arrays

Highly ordered TiO₂ nanotube arrays generate a considerable interest for hydrogen generation by an electrochemical photocell, since ordered architecture of nanotube arrays provides a unidirectional electric channel for electron's transport. Here, we report the hydrogen generation by highly ordered TiO₂ nanotube arrays under actual sunlight in KOH electrolyte. The two-electrode electrochemical cell included an adjustable anode compartment capable of tracing the trajectory of the sun and a set of alkaline batteries connected with a rheostat for application of external bias. The results showed that the photocurrent responses of nanotube arrays match well with the intensity of solar irradiance on a clear summer day. Addition of ethylene glycol into KOH electrolyte as a hole scavenger enhanced the rate of hydrogen generation. A maximum photocurrent density of 31 mA/cm² was observed at 13:30 h, by focusing the sunlight with an intensity of 113 mW/cm² on the surface of the TiO₂ nanotube arrays in 1 M KOH electrolyte with 10 vol% ethylene glycol under an applied bias of 0.5 V. The observed hydrogen generation rate was 4.4 mL/h cm² under the focalized solar irradiance with an intensity between 104 mW/cm² and 115 mW/cm² from 10:00 to 14:20 h.     

Nano-structured Cu2O solar cells fabricated on sparse ZnO nanorods

Nano-structured Cu₂O/ZnO nanorod (NR) heterojunction solar cells fabricated on indium tin oxide (ITO)-coated glass are studied. Substrate film and NR density have a strong influence on the preferred growth of the Cu₂O film. The X-ray diffractometer (XRD) analysis results show that highly (2 0 0)-preferred Cu₂O film was formed when plating on plain ITO substrate. However, a highly (1 1 1)-preferred Cu₂O film was obtained when plating on sparse ZnO NRs. SEM, TEM and XRD studies on sparse NR samples indicate that the Cu₂O nano-crystallites mostly initiate its nucleation on the peripheral surfaces of the ZnO NRs, and are also highly (1 1 1)-oriented. Solar cells with ZnO NRs yielded much higher efficiency than those without. In addition, ZnO NRs plated on a ZnO-coated ITO glass significantly improve the shunt resistance and open-circuit voltage (V_oc) of the devices, with consistently much higher efficiency obtained than when ZnO NRs are directly plated on ITO film. However, longer NRs do not improve the efficiency due to low short-circuit current (J_sc) and slightly higher series resistance. The best conversion efficiency of 0.56% was obtained from a Cu₂O/ZnO NRs heterojunction solar cell fabricated on a 80 nm ZnO-coated ITO glass with V_oc=0.514 V, J_sc=2.64 mA/cm² and 41.5% fill factor.     

Preparation of carbon dots/TiO2 electrodes and their photoelectrochemical activities for water splitting

Carbon dots with various functional groups can be employed as the potential sensitizer. In this study, carbon dots are obtained by electrochemical ablation of graphite rods in alkaline electrolyte. The better preparation condition is the applied potential of 40 V and the ablation time of 5 h. TiO₂ nanotube arrays and TiO₂ nanoparticles photoelectrodes are sensitized by the as-prepared carbon dots through using impregnation method. Carbon dots/TiO₂ nanotube arrays electrodes exhibit greater photoelectrochemical hydrogen production activities than carbon dots/TiO₂ nanoparticles electrodes. It is because more carbon dots can be well combined with TiO₂ nanotube arrays. Based on the IPCE values in visible light region, the role of carbon dots on TiO₂ nanotube arrays electrode depends on the up-converted PL behaviors from their surface states and the alkaline electrolyte. The results provide insight into carbon dots that serve as sensitizer of TiO₂ photoelectrode in water splitting system of alkaline solution.