Nanorod Array Photoanode Research Articles

Band engineering for building cascading charge transport channels in ternary CdS-based nanorod array photoanode toward efficient photoelectrochemical H2 generation

A novel CdS/CdSe/Cu2O nanorod array (NRA) photoelectrode with cascading charge transport channels was designed for the first time to remarkedly boot photoelectrochemical (PEC) hydrogen generation under visible light illumination with zero bias. This ternary photoelectrode was constructed by modifying CdS nanorod arrays with n-type CdSe and p-type Cu2O nanoparticles, successively. In this novel photoanode, CdSe and Cu2O with small band gap not merely highly heighten the visible light absorption capacity of CdS, but more importantly integrate with CdS to build cascading charge transport channels at the CdS/CdSe and CdSe/Cu2O interfaces, dramatically facilitating the separation and transport efficiency for photoexcited electron and hole pairs. The CdS/CdSe/Cu2O NRA photoelectrode gains an obvious hydrogen generation rate of 193.2 μmol·h−1, 8.2 times higher than that of bare CdS NRA photoelectrode. The remarkably enhanced PEC hydrogen production for the CdS/CdSe/Cu2O NRA photoanode can be ascribed to effective solar energy utilization and charge carrier separation.

Enhancing Iron(III) Oxide Photoelectrochemical Water Splitting Performance Using Defect Engineering and Heterostructure Construction.

Fe2O3 is a promising semiconductor for photoelectrochemical (PEC) water decomposition. However, severe charge recombination problems limit its applications. In this study, a F-Fe2O3-x/MoS2 nanorod array photoanode was designed and prepared to facilitate charge separation. Detailed characterization and experimental results showed that F doping in Fe2O3 regulated the electronic structure to improve the conductivity of Fe2O3 and induced abundant oxygen vacancies to increase the carrier concentration and promote charge separation in bulk. In addition, the internal electric field between F-Fe2O3-x and MoS2 facilitated the qualitative transfer of the photogenerated charge, thus inhibiting their recombination. The synergistic effect between the oxygen vacancy and F-Fe2O3-x/MoS2 heterojunction significantly enhanced the PEC performance of Fe2O3. This study provides a universal strategy for designing other photoanode materials with high-efficiency charge separation.

ZnFe2O4 nanosheets as an electron transport bridge and a hole mediator enhance solar-driven unbiased hydrogen generation of ZnO-based nanorod arrays photoanode

In this study, a novel ternary ZnO-based nanorod arrays (NRAs) photoanode is designed and constructed for the first time for unassisted solar-light-driven water splitting to generate H2 using photoelectrochemical (PEC) cell. The ternary heterojunction photoanode is constructed by modifying ZnO NRAs with ZnFe2O4 nanosheets (NSs) and CdS nanoparticles (NPs), successively. The band alignment study demonstrates that ZnFe2O4 NSs as an interfacial modification layer not only enlarge the contact area with ZnO and CdS respectively to build a stair-step band alignment of conduction band levels for the efficient transport of electrons but also make the valence band of ZnFe2O4 to be as the hole accumulation site in the ternary heterojunction. The electrochemical and photoluminescence measurements demonstrate the efficient separation of the carriers. Consequently, the ternary ZnO-based NRAs photoanode achieves a significant H2 generation rate of 92.9 μmol/h, 6.23 and 2.97 times of ZnO NRAs and ZnO/ZnFe2O4 NRAs/NSs photoanodes, respectively.

Improved aquaculture wastewater treatment and concomitant power generation in a photoelectrocatalytic fuel cell equipped with S-scheme Fe2WO6/ZnO nanorod arrays photoanode and NiFe2O4 cathode

The treatment of aquaculture wastewater involved the elimination of refractory organics and total nitrogen (TN) concurrently was one of the towering challenges in wastewater treatment. In this work, aquaculture wastewater comprised of tetracycline (TC) and TN as well as its energy recovery was recuperated in a visible light responsive photocatalytic fuel cell (PFC) system. The S-scheme Fe2WO6 nanoparticle-anchored on ZnO nanorod array (Fe2WO6/ZNA) photoanode and NiFe2O4 nanoflower-loaded on carbon felt (NiFe2O4/CF) cathode spanned photoelectrocatalysis and catalytic chlorination, conducing both contaminant removal and power production. In the presence of optimized conditions (0.5 M Cl−, dual constructed electrodes, solution pH 7), the system exhibited a maximum power density of 1.820 mW cm−2 and removed 100 % and 88.4 % of TC and TN in 120 min, respectively. The yielded small amount of NH4+ and NO3– can also destroy by NiFe2O4/CF cathode because of its large surface area and rapid charge carrier transport. Moreover, the toxicity results testified that the treated aquaculture organic seemed to have no harmful impact on zebrafish model after PFC-chlorine treatment. The mechanism involving S-scheme Fe2WO6/ZNA-NiFe2O4/CF electrodes and PFC-chlorination enabled the core species Cl and OH partook in the photoelectrocatalytic reaction. Based on the trapping agent, electron spin resonance and liquid chromatography mass spectrometry test outcomes, the degradation pathway of TC and its by-product was also postulated.

Enhanced solar-light-driven photoelectrochemical water splitting performance of type II 1D/0D CdS/In2S3 nanorod arrays

One-dimensional (1D)/zero-dimensional (0D) CdS/In2S3 nanorod arrays (NRAs) have been successfully constructed by depositing In2S3 nanoparticles (NPs) on 1D CdS NRAs via successive ion layer absorption and reaction. The constructed CdS/In2S3 NRAs photoanode with optimized In2S3 loading generates a photocurrent density of 1.15 mA/cm2, which is augmented by 2.6 times to that of unmodified CdS photoanode under simulated solar light irradiation without an external bias. The significantly boosted PEC capability of the constructed CdS/In2S3 NRAs is ascribed to (i) the synergistic actions of CdS and In2S3; (ii) improvement of optical absorption and (iii) efficient charge separation due to type-II band structure.

Treatment of diluted palm oil mill effluent (POME) synchronous with electricity production in a persulfate oxidant-promoted photocatalytic fuel cell.

Attributable to the prosperous production growth of palm oil in Malaysia, the generated palm oil mill effluent (POME) poses a high threat owing to its highly polluted characteristic. Urged by the escalating concern of environmental conservation, POME pollution abatement and potential energy recovery from the effluent are flagged up as a research topic of interest. In this study, a cutting-edge photocatalytic fuel cell (PFC) system with employment of ZnO/Zn nanorod array (NRA) photoanode, CuO/Cu cathode, and persulfate (PS) oxidant was successfully designed to improve the treatment of POME and simultaneous energy production. The photoelectrodes were fabricated and characterized by field emission scanning electron microscopy with energy (FESEM), X-ray diffraction (XRD), energy-dispersive X-ray (EDX), and Brunauer, Emmett, and Teller analysis (BET). Owing to the properties of strong oxidant of PS, the proposed PFC/PS system has exhibited exceptional performance, attaining chemical oxygen demand (COD) removal efficiency of 96.2%, open circuit voltage (Voc) of 740.0mV, short circuit current density (Jsc) of 146.7 μA cm-2, and power density (Pmax) of 35.6μWcm-2. The pre-eminent PFC/PS system performance was yielded under optimal conditions of 2.5mM of persulfate oxidant, POME dilution factor of 1:20, and natural solution pH of 8.51. Subsequently, the postulated photoelectrocatalytic POME treatment mechanism was elucidated by the radical scavenging study and Mott-Schottky (M-S) analysis. The following recycling test affirmed the stability and durability of the photoanode after four continuous repetition usages while the assessed electrical energy efficiency revealed the economic viability of PFC system serving as a post-treatment for abatement of POME. These findings contributed toward enhancing the sustainability criteria and economic viability of palm oil by adopting sustainable and efficient POME post-treatment technology.

Surface Modification of TiO2/g-C3N4 Electrode with N, P Codoped CQDs for Photoelectrocatalytic Degradation of 1,4-Dioxane

The aim of this study was to synthesize N, P codoped CQDs modifying TiO2/g-C3N4 nanorod array (i.e., N, P-CQD/TCN NA) photoanodes for the degradation of 1,4-dioxane (1,4-D) and to explore the possibility of the photoelectrocatalytic (PEC) process in wastewater treatment. With the characterization of N, P-CQD/TCN NA anodes, 1,4-D degradation and pesticide wastewater was tested in the PEC cell, respectively. Under a bias voltage of 1.2 V and visible light, the current density of the N, P-CQD/TCN NAs was much higher than that of the CQD/TCN NAs (0.15 vs. 0.11 mA/cm2). The removal of 1,4-D reached 97% in the PEC cell within 6 h. The high performance of the N, P-CQD/TCN NA anodes could be attributed to the efficient charge separation, narrowed energy gap, and high upconverted PL properties. The C4 and C6 positions of 1,4-D were the preferential sites for the nucleophilic attack to form intermediates. The COD removal in the pesticide wastewater was kept stable at ~80% in a five-cycle operation using the PEC cell with the N, P-CQD/TCN NA photoelectric anodes. The results from this study should provide a promising way to develop novel photoelectric catalysts and to expand PEC application in wastewater treatment.

Cooperative effects of surface plasmon resonance and type-II band alignment to significantly boost photoelectrochemical H2 generation of TiO2/CdS/TiN nanorod array photoanode

Here, we demonstrate for the first time a novel ternary TiO2/CdS/TiN nanorod array (NRA) photoanode for high-efficiency photoelectrochemical H2 generation under bias-free simulated sunlight illumination. The ternary photoanode was constructed through modifying TiO2 nanorod arrays with two-dimensional (2D) CdS nanosheets and nonmetal plasmonic TiN nanoparticles. In this novel photoanode, 2D CdS nanosheets with large surface area not only improve visible light absorption, but also extend the contact area with TiO2 to form type-II band structure favorable for the separation and transfer of photogenerated electron-hole pairs. Moreover, 2D CdS nanosheets provide more sites to absorb TiN nanoparticles to further boost photon energy utilization via surface plasmon resonance-induced hot electron injection. The TiO2/CdS/TiN NRA photoanode achieved an average H2 generation rate of 129.6 μmol cm−2 h−1, 4.2 times that of TiO2 NRA photoanode. Substantially boosted photoelectrochemical H2 generation of the TiO2/CdS/TiN NRA photoanode is attributed to effective hot-electron injection and charge separation.

Nanoscale-based ZnS-GdS shell layer decorated hierarchical ZnO nanorod array photoanode with enhanced photo-electrochemical activity under visible light

We established a nanograined ZnS-GdS shell layer decorated with hierarchical ZnO nanorod (NR) arrays with significantly improved visible light photo-electrochemical performance. The ZnO nanorod surface is decorated with a ZnS-GdS shell layer through the sulfidation. Photoluminescence (PL) spectral study stated that the introduction of a ZnS-GdS shell layer improvises effective charge separation efficiency with the additional influence of surface defect states. The ZnO/ZnS-GdS core-shell NR array shows higher photo-electrochemical performance than the ZnO NR arrays under visible light, with a significant photocurrent density of 2.6 mA/cm2. The highest solar to hydrogen conversion efficiency is reached 3.2%, 14 times higher than pristine ZnO nanorod with a bias potential of 0 V versus Ag/AgCl. The results suggest that the ZnS-GdS shell layer enhances the visible light absorption and makes heterostructure, which helps transfer photogenerated charge carriers and reduces the recombination rate to enhance the photo-electrochemical efficiency of ZnO/ZnS-GdS heterostructure.

Tannic Acid-Fe complex with dual-function modified TiO2 photoanode for enhanced photoelectrochemical water oxidation

TiO2, as a promising photoanode material, has been commonly investigated in recent years, but its poor photoelectric conversion efficiency limits its practical application. Here, we fabricated in-situ a low-cost and eco-friendly tannic acid-Fe modified TiO2 nanorod arrays photoanode (TiO2/Tan-Fe) with improved photoelectric conversion efficiency. Compared with pristine TiO2 nanorod arrays (0.55 mA/cm2 at 1.23 V vs. RHE), the TiO2/Tan-Fe exhibits the enhanced photocurrent density (0.98 mA/cm2 at 1.23 V vs. RHE). The enhancement of photoelectrochemical (PEC) performance is mainly attributed to tannic acid-Fe as a light absorber with a wide absorbance region and increasing charge separation and transport in the composite photoanode, which is testified via ultraviolet–visible absorption, enhanced charge separation efficiency and Motty-Schottky curves, and so on. Importantly, the modification of tannic acid-Fe as a cocatalyst facilitates the water oxidation dynamic, which is confirmed by charge injection efficiency and oxygen evolution reaction (OER). These results indicate that the rationally designed and assembled photoanode has the potential to improve PEC performance and fabricate solar cell for efficient photoelectric conversion.

Design of a novel photoelectrochemical enzymatic biofuel cell with high power output under visible light

• A novel PEBFC with high enough power output under visible light was designed. • GR-CdS QDs/TiO 2 NRAs photoanode could catalyze the oxidation of AA excellently. • The reduction of oxygen was highly efficient at the 3D GR-SWCNTs-laccase biocathode. • Two PEBFCs connected in series could light the red LED successfully. Photoelectrochemical enzymatic biofuel cell (PEBFC) shows the obvious advantages in the renewable energy conversion field. However, because of the low utilization efficiency of solar energy and the unendurable power output, PEBFC cannot satisfy the demand of practical applications. Herein, a novel PEBFC prototype is designed. Taking a TiO 2 nanorod arrays (NRAs) decorated graphene–cadmium sulfide quantum dots (GR–CdS QDs) hybrid at fluorine-doped tin oxide (FTO) glass electrode as the photoanode, it can catalyze the oxidation of ascorbic acid (AA) effectively, with the oxidation current being as high as –137.8 μA cm −2 , and the anodic open circuit potential ( E a O C P ) reaching approximately –0.52 V; using a laccase–bound three–dimensional graphene–single walled carbon nanotubes (3D GR–SWCNTs–laccase) hybrid electrode as the biocathode, along with 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), the biocathode can catalyze the reduction of oxygen remarkably, and the cathodic open circuit potential ( E c OCP ) is as high as 0.54 V. Under optimal conditions, such PEBFC can obtain sufficient high open circuit voltage (V oc ) of 1.05 V and maximum power output density (P max ) of 227.5 μW cm −2 , respectively. Two PEBFCs connected in series can light a red light-emitting diode (LED) successfully.

N-doped graphene quantum dots for boosting the photoelectrochemical and photo-sensing properties of TiO2 nanorod array photoanodes

Nitrogen-doped graphene quantum dots (NGQDs) were successfully synthesized via a solvothermal technique using citric acid as carbon and N, N-dimethylformamide (DMF) acting as a solvent and also a nitrogen source. The as-prepared quantum dots have a diameter of less than 5 nm with a highly crystalline structure resembling graphene. TiO2 nanorods (NRs) were hydrothermally grown on fluorine-doped tin oxide (FTO) coated glass substrate. A photoanode of NGQD decorated TiO2 NRs was studied for its photoelectrochemical performance. Scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and photoelectrochemical characterizations were performed to investigate the photoanode and its performance. The NGQD decorated TiO2 NR (NGQD/TiO2 NR) photoanode recorded an NGQD induced improvement of 36.7% in photocurrent density (at 5 V vs Ag/AgCl) and 58.7% in the photoconversion efficiency (η%).

Feasibility study of municipal wastewater removal synchronized with electricity generation via solar-driven photocatalytic fuel cell with Bi2WO6/ZnO nanorods array photoanode

The reclamation of energy from municipal wastewater treatment process is highly demanded and could resolve the two most formidable dilemmas of water pollution and energy crisis nowadays. In this study, a photocatalytic fuel cell (PFC) utilizing a Z-scheme heterojunction Bi2WO6/ZnO nanorod arrays (NRAs) photoanode was employed for efficient municipal wastewater treatment and electricity generation simultaneously under sunlight irradiation. Various characterization techniques, including energy dispersive X-ray (EDX), field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), transient photoresponse (TPR), and linear sweep voltammetry (LSV) were used to analyze the physical, chemical and photoelectrochemical characteristics of the as-synthesized photoanode. The results indicated that the Z-scheme heterojunction Bi2WO6/ZnO NRAs exhibited the excellent photocatalytic performance under sunlight irradiation as compared to pristine ZnO NRAs. Ergo, the PFC system achieved complete removal of COD and produced 3.30 μW cm−2, 37.10 μA cm−2 and 563 mV of maximum power density (Pmax ), short-current density (Jsc) and open-circuit voltage (Voc) within 4 h of sunlight irradiation, respectively. The boosted photoactivity was ascribed to the successful formation of the Z-scheme hybridization interface betwixt the Bi2WO6 and ZnO NRAs, that not only enhanced the visible light adsorption of ZnO NRAs, concomitantly significantly accelerated the spatial charge separation and restrained the electron-hole pair recombination.

Surface Photo-Voltage (SPV) and Photo electrochemistry (PEC) on TiO2

Hydrothermally grown rutile titanium dioxide (TiO2) nanorod array photoanode with various nanorod lengths were investigated for understanding the charge carrier separation including hole diffusion length using Photoelectrochemistry (PEC) and surface photo voltage (SPV) measurements for their importance in photoconversion as photoelectrode for solar water splitting. Various lengths of TiO2 nanorods with lengths 1.35, 1.85, 2.5 and 4.5 micrometers were prepared and used in the present investigation. Front and back illumination in SPV and PEC Mott-Schottky plots were investigated and found to show significant difference in charge carrier separation. The hole diffusion length calculations using PEC was up to 200 nm and using SPV was in the order of 600-700nm.

Nonmetal plasmonic TiN nanoparticles significantly boost photoelectrochemical performance for hydrogen evolution of CdS nanoroad array photoanode

We report for the first time that nonmetal plasmonic TiN nanoparticles act as hot-electron booster to remarkably enhance photocurrent and hydrogen production of CdS nanoroad arrays (NRAs) via a photoelectrochemical cell. The optimized TiN–CdS NRAs produce a bias-free photocurrent of 2.9 mA cm−2. Furthermore, the highest photoconversion efficiency of the TiN–CdS nanorod array (NRA) photoanode with optimized loading of the TiN NPs is up to 2.2%, 1.6-fold that of the pristine CdS NRA photoanode (1.4%) at 0.22 V versus RHE. Most importantly, TiN–CdS NRAs achieve a hydrogen production rate of 101.5 μmol h−1 cm−2, about 2 times higher than that of the CdS NRAs. Experimental evidences of the photoluminescence emission apparently confirm that hot-electron injection from TiN to CdS plays a crucial role for enhancing photocurrent and hydrogen production. This work demonstrates that nonmetal plasmonic TiN can be integrated into new platforms for efficient solar energy conversion.

Convenient synthesis of highly oriented α-Fe2O3 microcone arrays with efficient photoelectrochemical properties

Highly oriented α-Fe2O3 microcone arrays have been synthesized by an one-step low temperature CVD method. The α-Fe2O3 microcone arrays are found to exhibit superior photocurrent response and can be applied as efficient photoeletrodes for photoelectrochemical water splitting reaction. The prepared microcone arrays photoanode possesses several advantages such as perfect crystal quality, highly preferred orientation, excellent visible light absorption and high electron density, showing excellent PEC performance. The photocurrent density of microcone arrays photoanode reaches a value of 0.20 mA/cm2 under AM 1.5 G illumination, which is much higher than the value of 0.08 mA/cm2 of nanorod arrays photoanode. This one-step CVD method thus can be applied to synthesis α-Fe2O3 nanostructure photoanode with high single crystal quality, highly preferred orientation and excellent photoelectrochemical performance, which has potential application in water splitting.

The co-decorated TiO2 nanorod array photoanodes by CdS/CdSe to promote photoelectrochemical water splitting

A cascade structure of TiO2/CdS/CdSe semiconductor heterojunction is synthesized using a three-step technique of facile hydrothermal growth for the enhancement of the photoelectrochemical performances. The optical and photoelectrochemical properties controlled by the deposition processing parameters have been investigated. It is shown that the patterns of semiconductor heterojunction enlarge the absorption range of solar spectra, and improve the properties of the photogenerated charge carriers describing separation and transportation, and reduce the interface resistance between the photoelectrode and electrolyte comparing with the pure TiO2 and CdS-decorated TiO2 nanorod array photoanodes. The higher photocurrent density and photoconversion efficiency are up to 4.23 mA cm−2 and 4.2%, which are the 4.1 and 25.3 times superior than that of the pure TiO2 photoanode. The hydrothermal growth time increment of CdSe yields greater photoelectrochemical water splitting performances. The underlying physics mechanisms have been discussed based on forming a type-Ⅱ energy band alignment structure.

Cover Feature: Enhanced Photoelectrochemical Water Oxidation Performance in Bilayer TiO2/α‐Fe2O3 Nanorod Arrays Photoanode with Cu : NiOx as Hole Transport Layer and Co−Pi as Cocatalyst (ChemSusChem 11/2021)

Cover Feature: Enhanced Photoelectrochemical Water Oxidation Performance in Bilayer TiO₂/α‐Fe₂O₃ Nanorod Arrays Photoanode with Cu : NiO_<i>x</i> as Hole Transport Layer and Co−Pi as Cocatalyst (ChemSusChem 11/2021)

Optimization of Ag2S Quantum Dots Decorated ZnO Nanorod Array Photoanodes for Enhanced Photoelectrochemical Performances

The synthesis of Ag2S quantum dots (QDs) deposited on the surface of electrodeposited ZnO nanorods (NRs) by a successive ionic-layer adsorption and reaction (SILAR) method is reported. A Box-Behnken response surface factorial design was used to organize the experiments conducted and identify the effects of three electrochemical parameters and their potential interactions. These parameters include zinc precursor concentration in the electrolytic bath, the electrolytic bath temperature and the electrodeposition time on the morphological and structural properties of the electrochemically grown ZnO nanorods. Morphological, structural and optical characterizations of these NRs heterojunctions were done. A direct band gap for Ag2S QDs, tuned between 2.54 and 2.73 eV by varying the SILAR cycle numbers, was determined. The presence of ZnO nanostructures increases the light scattering capability of the samples, allowing an important quantity of diffuse light near the absorption edge of Ag2S. The photoelectrochemical performance of these ZnO NRs decorated with Ag2S QDs based photoanodes has been evaluated. The SILAR parameters related to the growth of the Ag2S QDs that optimize the performance of this photoelectrode are presented. The effect of a ZnS passivation layer has been studied leading to an increase of about 400% in the short-circuit current density after passivation.

Integration of Earth‐Abundant Catalysts on Si Solar Cells for Overall Solar Hydrogen Production

Development of low‐cost and earth‐abundant metal catalysts, as alternative to noble metals, is a promising approach for direct hydrogen production from solar light with integrated photoelectrochemical devices. Herein, a mild electrochemical method is used to directly synthesize two earth‐abundant catalysts, namely, CoP and CoSe, on planar‐junction p+nn+‐Si solar cells. It is observed that the CoP–Si photocathodes achieve the best performance with ≈12 h of stability, a photocurrent density of up to 38 mA cm−2 at 0 V versus the reversible hydrogen electrode (RHE), and an onset potential of 488 mV versus RHE, and one of the most efficient solar‐driven hydrogen generation from earth‐abundant systems to date. Overall solar water splitting is also demonstrated in a tandem device configuration with a top TiO2 nanorod arrays photoanode achieving more than 5 h continuous hydrogen production. These results demonstrate the feasibility of using low‐cost earth‐abundant materials and the established Si solar cells technology for direct water splitting powered from sunlight.