Performance Of Photoelectrodes Research Articles

Sulfate-Functionalized Core–Shell ZnO/CdS/Ag2S Nanorod Arrays with Dual-Charge-Transfer Channels for Enhanced Photoelectrochemical Performance

Insufficient light absorption and fast charge recombination seriously restrain the photoelectrochemical (PEC) water splitting performance of semiconductor photoelectrodes. Herein, sulfate ([SO4])-functionalized CdS was decorated on ZnO nanorod arrays by one-step magnetron sputtering to construct a core–shell heterojunction, and then Ag2S nanoparticles were deposited by cation exchange. The in situ formed [SO4] as an active site is helpful to accelerate charge transfer and enhance PEC reaction kinetics. Additionally, Ag2S was modified on ZnO/CdS to suppress the photocorrosion of CdS while constructing two heterojunctions with a gradient energy band configuration for separating and transporting photogenerated charge carriers efficiently. Benefiting from the dual-charge-transfer channels in [SO4] and Ag2S co-modified ZnO/CdS nanorod arrays, the optimized photoanode presents high PEC performance, yielding a maximum photocurrent density of ∼6.82 mA cm–2 at 1.23 V vs reversible hydrogen electrode (RHE) under simulated air mass (AM) 1.5 solar light illumination, which is 7.75 times that of pristine ZnO photoanode. This work provides a synergetic in situ [SO4] modification and heterojunction construction strategy to design photoelectrodes with multicharge-transfer channels for enhanced PEC performance.

Engineering Interfacial Band Bending over ZnIn2S4/SnS2 by Interface Chemical Bond for Efficient Solar‐Driven Photoelectrochemical Water Splitting

AbstractDeveloping a simple and effective strategy to modulate the energy band bending of heterojunction photoelectrodes is pivotal in terms of photoelectrochemical (PEC) water splitting. Herein, it is demonstrated that the introduction of the interfacial InOSn chemical bonds at the ZnIn2S4/SnS2 interface regulates the band bending of ZnIn2S4/SnS2 heterojunction photoanodes, reverses the charge transport direction, and reduces the oxygen evolution reaction (OER) overpotential. Detailed analysis indicates that the interfacial InOSn bond makes band adaptation to promote carrier separation and transfer through ultraviolet photoelectron spectrometry, hydroxyl radical production tests, and surface photovoltage measurements. Due to the special nanosheet morphology with exposed edges of the heterojunction interface, the InOSn bonds are partially exposed, which can reduce the OER overpotential and boost the surface injection efficiency according to the PEC impedance spectroscopy and density functional theory calculations. The synergistic modulation of InOSn bond yields a photocurrent of 4.57 mA cm−2 at 1.23 V (vs reversible hydrogen electrode, AM 1.5 G) and a low onset potential of −0.14 VRHE. This work provides a new solution for energy band regulation to improve the performance of heterojunction photoelectrodes for PEC water splitting.

Water-Induced Fine-Structure Disorder and Its Effect on the Performance of Photoelectrodes in Dye-Sensitized Solar Cells

Water-Induced Fine-Structure Disorder and Its Effect on the Performance of Photoelectrodes in Dye-Sensitized Solar Cells

Rational construction of S-doped FeOOH onto Fe2O3 nanorods for enhanced water oxidation

Hematite-based photoanode (α-Fe2O3) is considered the promising candidate for photoelectrochemical (PEC) water splitting due to its relatively small optical bandgap. However, severe charge recombination in the bulk and poor surface water oxidation kinetics have limited the PEC performance of Fe2O3 photoelectrodes, which is far below the theoretical value. Herein, a new catalyst, S-doped FeOOH (S-FeOOH), has been immobilized onto the surface of the Fe2O3 nanorod (NR) array by a facile chemical bath deposition incorporated thermal sulfuration process. The grown S-FeOOH layer acts not only as an efficient catalyst layer to accelerate the water oxidation on the surface of photoelectrode but also constructs a heterojunction with the light absorption layer to facilitate the interface charge carrier separation and transfer. As expected, the modified S-FeOOH@Fe2O3 photoanode achieves a remarkable increase in PEC performance of 2.30 mA cm−2 at 1.23 V versus the reversible hydrogen electrode (VRHE) andan apparent negative shifted onset potential of 250 mV in comparison with pristine Fe2O3 (0.95 mA cm−2 at 1.23 VRHE). These results provide a simple and effective strategy to coupling oxygen evolution catalysts with photoanodes for practically high-performance PEC applications.

Improved Performance of GaN Photoelectrodes from the Facile Fabrication of a Binder-Free Catalyst: Ni(OH)2 Nanosheets

Improved Performance of GaN Photoelectrodes from the Facile Fabrication of a Binder-Free Catalyst: Ni(OH)₂ Nanosheets

Converting Sewage Water into H2 Fuel Gas Using Cu/CuO Nanoporous Photocatalytic Electrodes.

This work reports on H2 fuel generation from sewage water using Cu/CuO nanoporous (NP) electrodes. This is a novel concept for converting contaminated water into H2 fuel. The preparation of Cu/CuO NP was achieved using a simple thermal combustion process of Cu metallic foil at 550 °C for 1 h. The Cu/CuO surface consists of island-like structures, with an inter-distance of 100 nm. Each island has a highly porous surface with a pore diameter of about 250 nm. X-ray diffraction (XRD) confirmed the formation of monoclinic Cu/CuO NP material with a crystallite size of 89 nm. The prepared Cu/CuO photoelectrode was applied for H2 generation from sewage water achieving an incident to photon conversion efficiency (IPCE) of 14.6%. Further, the effects of light intensity and wavelength on the photoelectrode performance were assessed. The current density (Jph) value increased from 2.17 to 4.7 mA·cm−2 upon raising the light power density from 50 to 100 mW·cm−2. Moreover, the enthalpy (ΔH*) and entropy (ΔS*) values of Cu/CuO electrode were determined as 9.519 KJ mol−1 and 180.4 JK−1·mol−1, respectively. The results obtained in the present study are very promising for solving the problem of energy in far regions by converting sewage water to H2 fuel.

Computation-assisted performance optimization for photoelectrochemical photoelectrodes

The generation rate and collection efficiency of photocarriers fatally determine the photoelectrochemical performance of photoelectrodes. However, it is challenging to simultaneously reach a high generation rate and a high collection efficiency due to their conflictive dependence on the thickness of photocatalytic films, especially for metal oxide photocatalysts. Therefore, it is critical to select an appropriate thickness to reach the highest photocatalytic rate under certain light illustration. Herein, we proposed a physical model to predict the optimal thickness of photocatalytic films by combining computation and experiments. In this model, a photoelectrode was investigated by thoroughly considering the electric potential distribution in the whole photocatalytic film rather than only considering the depletion layer as previously. We solved the continuity equation and got the distribution of minority carriers in photocatalytic films. The used parameters for calculation were obtained through density functional theory calculation and experiments. The optimal thickness of photocatalytic films can be predicted with this model. We have used CuFeO2 films as the model material to verify the accuracy of the proposed model. Compared to the traditional trial-and-error process, our computation-assisted approach is highly efficient and can be broadly employed to other materials.

Machine Learning Guided Dopant Selection for Metal Oxide-Based Photoelectrochemical Water Splitting: The Case Study of Fe2 O3 and CuO.

Doping is an effective strategy for tuning metal oxide-based semiconductors for solar-driven photoelectrochemical (PEC) water splitting. Despite decades of extensive research effort, the dopant selection is still largely dependent on a trial-and-error approach. Machine learning (ML) is promising in providing predictable insights on the dopant selection for high-performing PEC systems because it can uncover correlations from the seemingly ambiguous linkages between vast features of dopants and the PEC performance of doped photoelectrodes. Herein, the authors successfully build ML model to predict the doping effect of 17 metal dopants into hematite (Fe2 O3 ), a prototype photoelectrode material. Their findings disclose the critical parameters from the 10 intrinsic features of each dopant. The model is further experimentally validated by the coherent prediction on Y and La dopants' behaviors. Further interpretation of the ML model suggests that the chemical state is the most significant selection criteria, meanwhile, dopants with higher metal-oxygen bond formation enthalpy and larger ionic radius are favored in improving the charge separation and transfer (CST) in the Fe2 O3 photoanodes. The generic feature of this ML guided selection criteria has been further extended to CuO-based photoelectrodes showing improved CST by alkaline metal ions doping.

Exploring the modulation mechanism of the LSPR effect of Cu periodic nanosphere arrays to promote the performance of TiO2 photoelectrodes

Cu periodic nanosphere arrays can greatly promote the photoelectrochemical performance of TiO2 photoelectrodes by localized surface plasmon resonance effects, multiple scattering and coupling effects.

Prediction of the photoelectrochemical performance of hematite electrodes using analytical data

Machine learning (ML) has been extensively utilized in various fields of chemistry, such as molecular design and optimization of the fabrication parameters of the material. However, there is still a difficulty in applying ML for devices/materials fabricated in a lab because plenty of data for accurate calculation are difficult to obtain due to the limited number of samples. As a promising energy-harvesting material, we have studied hematite electrodes for photocatalytic water splitting. Herein, we have examined the critical factors affecting the photoelectrochemical (PEC) performance by applying ML for a limited number of fabricated electrodes to reveal the origin of poor reproducibility of the performance. To find the dominant factors affecting the PEC performance, the feature values were directly extracted from analytical data such as X-ray diffraction, Raman, UV/vis and photoelectrochemical impedance spectroscopy (PEIS) measurements. The dominant factors for the performance were identified from the prediction analysis of the performance by ML. Two types of descriptors were examined; all the analytical data were included and those without the PEIS data, which had a high correlation with the photocurrent. The determination coefficients (R2) of the prediction accuracy were >0.8 in both cases and the dominant features were identified for the improvement of PEC performance without any prior knowledge.

Inter-facet junction effects on particulate photoelectrodes.

Particulate semiconductor photocatalysts are paramount for many solar energy conversion technologies. In anisotropically shaped photocatalyst particles, the different constituent facets may form inter-facet junctions at their adjoining edges, analogous to lateral two-dimensional (2D) heterojunctions or pseudo-2D junctions made of few-layer 2D materials. Using subfacet-level multimodal functional imaging, we uncover inter-facet junction effects on anisotropically shaped bismuth vanadate (BiVO4) particles and identify the characteristics of near-edge transition zones on the particle surface, which underpin the whole-particle photoelectrochemistry. We further show that chemical doping modulates the widths of such near-edge surface transition zones, consequently altering particles' performance. Decoupled facet-size scaling laws further translate inter-facet junction effects into quantitative particle-size engineering principles, revealing surprising multiphasic size dependences of whole-particle photoelectrode performance. The imaging tools, the analytical framework and the inter-facet junction concept pave new avenues towards understanding, predicting and engineering (opto)electronic and photoelectrochemical properties of faceted semiconducting materials, with broad implications in energy science and semiconductor technology.

On the relevance of understanding and controlling the locations of dopants in hematite photoanodes for low-cost water splitting

Successful large-scale implementation of solar fuel technologies relies on cost, performance, and reliability of materials, devices, and infrastructures. Earth-abundant, low-cost, easily recyclable, and environmentally benign light absorbers are desired for renewable fuel generation technologies, such as solar photoelectrochemical (PEC) water splitting. Hematite is considered an ideal material for PEC oxygen evolution reaction, which is a critical component in the overall water splitting process for hydrogen fuel generation. However, intrinsic and operational limitations have prevented hematite-based PEC devices from reaching their highest theoretical solar-to-hydrogen efficiency of 15%–17%. Literature clearly shows that no single approach can eliminate these limitations. An overall fundamental understanding of the effect of dopant addition as well as their physical locations and functions within the photoelectrode, in both as-synthesized form and under operating conditions, is of critical importance to unleash the tremendous potentials of hematite-based PEC systems. In this short perspective, the concept of effective doping (i.e., increase of charge carrier density) up to the limit of dopant segregation at the grain boundaries to lower the charge recombination is discussed. Based on relevant theoretical and experimental data from the literature on the effects of surface-to-bulk doping as well as dopant segregation at the grain boundaries on hematite photoelectrode performance, we discuss here the views on the necessity of understanding these processes and their individual and synergistic effects to unravel a simple yet powerful approach to design and develop highly efficient hematite photoanodes for clean hydrogen generation using water and sunlight.

Design and Demonstration of Large Scale Cu2O Photocathodes with Metal Grid Structure for Photoelectrochemical Water Splitting

Upscaling of photoelectrode for a practical photoelectrochemical (PEC) water splitting system is still challenging because the PEC performance of large-scale photoelectrode is significantly low, compared to the lab scale photoelectrode. In an effort to overcome this challenge, sputtered gold (Au) and copper (Cu) grid lines were introduced to improve the PEC performance of large-scale cuprous oxide (Cu2O) photocathode in this work. It was demonstrated that Cu grid lines are more effective than Au grid lines to improve the PEC performance of large-scale Cu2O photocathode because its intrinsic conductivity and quality of grid lines are better than ones containing Au grid lines. As a result, the PEC performance of a 25-cm2 scaled Cu2O photocathode with Cu grid lines was almost double than one without grid lines, resulting in an improved charge transport in the large area substrate by Cu grid lines. Finally, a 50-cm2 scaled Cu2O photocathode with Cu grid lines was tested in an outdoor condition under natural sun. This is the first outdoor PEC demonstration of large-scale Cu2O photocathode with Cu grid lines, which gives insight into the development of efficient upscaled PEC photoelectrode.

Investigation and Optimization of Mxene Functionalized Mesoporous Titania Films as Efficient Photoelectrodes.

Three-dimensional mesoporous TiO2 scaffolds of anatase phase possess inherent eximious optical behavior that is beneficial for photoelectrodes used for solar energy conversion applications. In this regard; substantial efforts have been devoted to maximizing the UV and/or visible light absorption efficiency; and suppressing the annihilation of photogenerated charged species; in pristine mesoporous TiO2 structures for improved solar illumination conversion efficiency. This study provides fundamental insights into the use of Mxene functionalized mesoporous TiO2 as a photoelectrode. This novel combination of Mxene functionalized TiO2 electrodes with and without TiCl4 treatment was successfully optimized to intensify the process of photon absorption; charge segregation and photocurrent; resulting in superior photoelectrode performance. The photocurrent measurements of the prepared photoelectrodes were significantly enhanced with increased contents of Mxene due to improved absorption efficiency within the visible region; as verified by UV–Vis absorption spectroscopy. The anatase phase of TiO2 was significantly augmented due to increased contents of Mxene and postdeposition heat treatments; as evidenced by structural analysis. Consequently; an appreciable coverage of well-developed grains on the FTO surface was observed in SEM images. As such; these newly fabricated conductive mesoporous TiO2 photoelectrodes are potential candidates for photoinduced energy conversion and storage applications.

Spinel-Oxide-Integrated BiVO4 Photoanodes with Photothermal Effect for Efficient Solar Water Oxidation.

Spinel oxide materials have been widely used as oxygen evolution catalysts to enhance the photoelectrochemical (PEC) performance of photoelectrodes. Herein, we demonstrate that the water splitting efficiency of a photoanode can be further enhanced by introducing its photothermal effect. Under near-infrared radiation, the temperature of the NiCo2O4/BiVO4 photoanode increases moderately, leading to improved water oxidation kinetics and charge transport simultaneously. With the assistance of the photothermal effect, the obtained photoanode reaches a photocurrent density of 6.20 mA cm-2 at 1.23 V vs reversible hydrogen electrode. A series of spinel-type MCo2O4 oxides (M = Mn, Zn, Cu, and Fe) are deposited on the surface of the BiVO4 photoanode to show similar photothermally enhanced PEC performance. The research discovery provides a way for improving the catalytic activity of photoanode materials with a photothermal effect, which may be applied to various fields of energy conversion, including CO2 reduction, N2 fixation, and pollutant degradation.

Inter-lamellar nanostructures-by-design for high-performance dual-photoelectrode photofuel cell based genosensor

Photofuel cells (PFCs) that integrate “clean-solar-to-electric energy” and “sensing platform” can enable next-generation biosensors for diverse health care and environmental applications. However, the inferior performance of photoelectrodes often results in insufficient solar-to-power conversion for reliable molecular detection. To overcome this problem, we developed a PFC-based genosensor by combining a Ti3C2Tx|CdS photoanode and a CuInS2 photocathode to generate significant output power for the reliable detection of miRNA-21. The innovative photoanode design involves (i) the insertion of CdS nanorods into multi-layered Ti3C2Tx to expand the interlamellar space from ~0.98 to ~1.34 nm for accommodating more biomolecules to improve the sensor sensitivity; (ii) the formation of the nanoscale Schottky junction to enhance photo-generated charge separation and photoelectric conversion rates. The hybridization of capture DNA, assistant DNA and miRNA-21 on the photoanode led to the initial quenching of output signal of prepared PFC. As a mimic enzyme, manganese porphyrin was intercalated into the conjugated DNA double chains to catalyze a precipitation reaction on the photoanode surface, which resulted in a further signal quenching. Due to the combination of specially designed PFC with dual signal quenching, the proposed PFC-based genosensor exhibited a dynamic detection range of 1 fM to 0.01 μM with a LOD of 0.053 fM for detection of miRNA-21.

Multisample Correlation Reveals the Origin of the Photocurrent of an Unstable Cu2O Photocathode during CO2 Reduction.

The reliable characterization of the photoelectrochemical (PEC) performance of unstable photoelectrodes, often the simplest devices used as a baseline, is a huge challenge. By performing a correlation analysis of more than 100 parameters of Cu2O photocathodes electrodeposited under the same conditions, we discovered a strong positive correlation (R = 0.866) between the photocurrent in argon and the deposition current peak magnitude during electrodeposition, while a strong negative correlation (R = -0.787) was found in CO2. In argon, a positive correlation between the photocurrent during PEC tests and the post-PEC dark current suggests the dominance of photodegradation. In CO2, the higher photocurrent in PEC tests correlates well with the lower post-PEC dark current, revealing the dominance of photocatalytic CO2 reduction during the rapid PEC tests. Correlation analysis provides statistically robust insights into the operation of unstable electrodes based on routinely measured parameters and thus constitutes a simple yet previously unexplored methodology for characterizing photoelectrodes within the first minutes of operation.

Performance of Dye Sensitized Solar Cells (DSSCs) with ZnO Nanorod Electrode in Different Seed Solution

Studies of comparing the performance of photoelectrode for dye-sensitized solar cells (DSSCs) continue to be carried out and developed. The ZnO nanorods as an electrode for DSSCs have been shown to have high electron collection due to the capability of electron photoexcitation and increased electron transport. Various methods of making ZnO nanorods have been studied and developed. However, the method requires controlled conditions under high temperature and pressure, thus limiting the commercialization of ZnO nanorods. Therefore, the seed solution-based hydrothermal method was chosen in the ZnO nanorod deposition process because it is an effective method, low-cost and easier fabrication process. The method of growing ZnO nanorod was carried out with three times of growing for 6 hours. ZnO nanorod was synthesized using different seed solutions, namely sample 1 and sample 2 by using methoxy and isopropanol, respectively. In this work, the SEM image shows the growth of ZnO nanorods vertically aligned on the FTO substrate and resulted in a smaller diameter for the isopropanol seed solution. The smaller diameter of the ZnO nanorod provides a larger surface area then increasing the total amount of dye attached to the ZnO nanorod and improve the photovoltaic performance.

Single-atomic-Co cocatalyst on (040) facet of BiVO4 toward efficient photoelectrochemical water splitting

Monoclinic bismuth vanadate (BiVO4) shows promising application prospect in photoelectrochemical (PEC) water splitting on account of its relatively ideal band gap to harvest sunlight. However, the poor charge migrate property and sluggish water oxidation kinetics severely limit the PEC performance of BiVO4 photoelectrodes. In this work, BiVO4 photoanode with highly exposed (040) facets for superior charge transfer was prepared by a seed assisted hydrothermal method. Moreover, cobalt single atoms stabilized in N-doped carbon nanosheet (Co SAs-NC) was well modified on BiVO4 (040) (denoted as BiVO4 (040)/Co SAs-NC) with much improved water oxidation efficiency. The as-prepared BiVO4 (040)/Co SAs-NC photoanode generated 2.2 times higher photocurrent density than that of pristine BiVO4 (040) at 1.23 V vs. RHE, and presented nearly 100% charge injection efficiency. The detail kinetic measurements reveal that the modified Co SAs-NC cocatalyst effectively suppresses the carrier recombination and promotes the surface reaction kinetics. This work provides a promising strategy to fabricate composite photoanodes for solar energy conversion based on facet engineering matched with single-atomic-catalyst.

Improving the photoelectrochemical performance of spin-coated WO3/BiVO4/ZnO photoanodes by maximizing charge transfer using an optimized ZnO decoration layer

The photoelectrochemical (PEC) method has potential for harvesting solar energy to eventually resolve the fossil fuel crisis owing to its green and renewable characteristics and inherently low conversion efficiency. Herein, we introduce a controlled ZnO decoration layer on a WO3/BiVO4 type II heterojunction array using a facile spin-coating method to enhance the PEC performance of photoelectrodes. The ZnO decoration layer plays a crucial role in attaining superior charge transfer, reduced charge recombination, and stable photoactivity in the composite WO3/BiVO4/ZnO systems. An optimally decorated ZnO layer with oxygen vacancies in the WO3/BiVO4/ZnO photoanode allows extended light absorbance in the UV and visible wavelength regions with a narrow band gap and passivates the underlying WO3/BiVO4 type II heterojunction surfaces by covering the defect sites. Thus, the optimized WO3/BiVO4/ZnO-3 photoanode exhibits the highest photocurrent density (190 μA cm−2 at 1.23 VRHE) with the lowest onset potential (0.41 VRHE), reproducible photo-reaction under chopped light, the smallest charge transfer resistance in the Nyquist plot (1755 Ω), the highest quantum efficiencies for ABPE, IPCE, and APCE (0.036% at 0.92 VRHE, 6% at 380 nm at 1.23 VRHE and 11% at 380 nm, respectively), the highest reliability (30% decay after 1500 s), and high charge injection (63%) and charge separation (7.3%) efficiencies. These findings demonstrate that the component optimization in WO3/BiVO4/ZnO-x composite photoelectrodes is crucial in achieving high PEC performance by improving charge separation and reducing charge recombination.