Increase In Photocurrent Density Research Articles

Synthesis of SrTiO3-TiO2-CaTiO3/Cu2O composite for stable and efficient H2 generation in deionized water and river water

Herein, the SrTiO3-TiO2-CaTiO3/Cu2O quaternary composite has been designed and prepared via one-step hydrothermal process followed by a NaBH4 reduction treatment. By comparing the H2 production rate (HPR) of Sr-Ti-Ca/Cu samples prepared by different Cu sources, it is found that Sr-Ti-Ca/Cu has the best H2 production performance when CuCl2 is as Cu source. As expected, the highest HPR of Sr-Ti-Ca/Cu sample is up to 5.088 mmol g−1 h−1, which is 195.7 times as higher as that of the Sr-Ti-Ca sample (0.026 mmol g−1 h−1) under the same conditions. Moreover, the HPR reached 0.692, 0.530 and 0.647 mmol g−1 h−1 in tap water, lake water and river water, indicating that the photocatalyst has high practicability in natural water sources. In addition, the experiment of the tap water composition effect on H2 production performance shows that NO3− and SO42− ions have great negative influence on the HPR. Compared with Sr-Ti-Ca, the light absorption of Sr-Ti-Ca/Cu extends over the entire visible region, the interface resistance decreases, and the photocurrent density increases. These results suggest that the well-designed dual p-n heterojunctions and dual type-II heterojunctions in Sr-Ti-Ca/Cu sample can enhance the light absorption in the ultraviolet region and realize the rapid separation and migration of photogenerated charge, thereby accelerating the production of H2. This work shows the strong advantage and potential of non-precious metal efficient photocatalyst system for producing H2 from deionized water and natural fresh water.

Harnessing intrinsic defect complexes for visible-light-driven photocatalytic activity in Delafossite CuAlO2

This study significantly enhances the photo(electro)catalytic capabilities of CuAlO2, a wide bandgap semiconductor, through targeted defect engineering. By employing a tailored solid-state reaction under a mixed oxygen-argon atmosphere, an intrinsic defect complex of [Oi+CuAl] into has been successfully integrated into CuAlO2, thereby expanding its light absorption to the visible spectrum. The optimized CuAlO2 sample, containing the [Oi+CuAl] complex, demonstrates a remarkable 2.13-fold increase in photocatalytic degradation of tetracycline hydrochloride under visible-light irradiation. The maximum incident photon-to-current conversion efficiency value is elevated from 0 to 3.27 %, and the photocatalytic water splitting hydrogen production rate is increased by 10.78-fold. Density functional theory calculations, in conjunction with experimental data, elucidate the role of the [Oi+CuAl] complex in facilitating visible-light absorption and improving the separation of photogenerated electron-hole pairs. Under simulated sunlight, the modified CuAlO2 sample exhibits a substantial 2.26-fold enhancement in photocatalytic degradation of tetracycline hydrochloride, a photocurrent density increase from 0.80 to 8.20 µA·cm−2, and a 1.13-fold increase in photocatalytic hydrogen production rate compared to defect-free CuAlO2. This research underscores the potential of strategic defect engineering to enhance visible-light-driven photo(electro)catalysis in wide bandgap semiconductors.

Cocatalyst Modified Polymeric Carbon Nitride Photoanode for Enhanced Photoelectrochemical Properties.

As a new organic photocatalyst, polymeric carbon nitride (CN) has shown good application potential in the field of photoelectrochemistry due to its unique physical and chemical properties, but its application has been seriously hindered due to its inherent characteristics such as the difficulty in charge separation. In this study, FeOOH modified CN photoanode (CN-Fe) was constructed to investigate the effect of the cocatalyst on the charge injection capacity of organic semiconductor photoelectrodes. The experimental results demonstrate significant improvement in the charge injection efficiency of the photoanode due to the introduction of FeOOH cocatalyst, leading to enhanced photoelectrochemical performance with approximately 2.4 times increase in photocurrent density. By thoroughly investigating the mechanism behind the loading of FeOOH on the polymeric carbon nitride photoanode, we gained profound insights into the behavior of charge carriers and reaction kinetics during the photoelectrocatalytic process.

Nano multi-layered HfO2/α-Fe2O3 nanocomposite photoelectrodes for photoelectrochemical water splitting

This study marks a significant stride in enhancing photoelectrochemical (PEC) water splitting applications through the development of a type II nano-heterojunction comprising HfO2 and α - Fe2O3. Fabricated via Physical Vapor Deposition/Radio Frequency (PVD/RF) sputtering, this nano-heterojunction effectively addresses the efficiency limitations inherent in traditional α - Fe2O3photoanodes. The integration of HfO2 leads to a substantial increase in photocurrent density, soaring from 62 μA/cm2 for pure α - Fe2O3 to 1.46 mA cm−2 at 1.23 V versus the Reversible Hydrogen Electrode (RHE). This enhancement, a 23-fold increase, is primarily attributed to the improved absorption of photons in the visible range and the facilitation of more efficient charge transfer. The enhanced performance and long-term stability of the HfO2/α - Fe2O3 nano-heterojunction, validated through XRD, XPS, Raman Spectroscopy, EDS, SEM, EIS, and UPS analyses, demonstrate its potential as a promising and cost-effective solution for PEC water splitting applications, leveraging renewable energy sources.

Ca-doped birnessite for enhanced photocatalysis of water oxidation

Birnessite is an affordable and high-efficiency catalyst for water oxidation. In this study, we attempted to doping Ca into birnessite to investigate the influence on its photocatalytic oxidation activity. The study was carried out through a combination of experimental investigations and DFT calculations of the relevant crystal and electronic structures. The analysis of Raman spectra using 2T2D correlation and DFT indicates that Ca contributes more to the high frequency regions (400–600 cm−1) than K. DFT further reveals that the introduction of Ca leads to an increase in the number of localized electrons at the Fermi energy level and in the conduction band. Photo-electrochemical experiments demonstrate a significant reduction of 100 mV/dec in the Tafel slope, along with a 1.48-fold increase in photo-current density for Ca-birnessite when compared to K-birnessite. In general, the results demonstrate that Ca-birnessite can effectively heighten visible light absorption, reduce the band gap, and enhance water oxidation activity.

Optimal Selection for Redox Couples and Enhanced Performance through Magnetic Nanofluid Electrolyte in Solar Flow Batteries

The limited photoelectric conversion efficiency poses one of the critical constraints on commercializing solar flow batteries (SFBs). This study compares the chemical and photoelectrochemical properties of three commonly used redox couples. Additionally, magnetic Fe3O4 nanoparticles, for the first time, are introduced to optimize the electrolyte, and they are compared with the original electrolyte. Across different redox couples, the variations in semiconductor flat-band potentials and carrier concentrations result in changes in photoelectric current density. Notably, FeCl2/FeCl3 redox coupled with TiO2 photoelectrodes exhibits the highest photoelectric current density, reaching 75.7 µA cm−2. However, the trade-off of this electrolyte, i.e., providing high photocurrent while being unable to supply sufficient open-circuit voltage, imposes limitations on the practical application of SFBs. Alternatively, for TEMPO and 4-OH-TEMPO electrolytes, which can provide a higher open-circuit voltage, the electrochemical activity is enhanced, and the solution ohmic resistance is reduced by introducing magnetic nanoparticles to form a magnetic nanofluid. As a result, the photoanode’s photocurrent density increases by 36.6% and 17.0%, respectively, in the two electrolytes. The work reported here effectively addresses the current issue of low photocurrent density in SFBs and presents new optimization strategies for SFBs.

Gas-phase self-assembly: Converting 2D graphitic carbon nitride into 1D nanotubes for improved photocatalytic tetracycline degradation

Achieving precise control and optimization of structure and composition is paramount for advancing photocatalyst performance. In this study, we successfully synthesized nitrogen-defect and boron-doped one-dimensional g-C3N4 nanotubes (BCNNT) with a tube diameter of approximately 100 nm using a one-step gas-phase self-assembly strategy. Intriguingly, the introduction of boric acid induced a transformation from a two-dimensional g-C3N4 structure to a one-dimensional tubular form. The physicochemical properties and photocatalytic performance of BCNNT were found to be influenced by the quantity of boric acid employed. The as-synthesized BCNNT exhibited notable advantages, including enhanced visible light absorption, a 0.1 eV reduction in the band gap, 5.1 times increase in photocurrent density, effective suppression of electron-hole recombination, and significant improvement in mass transfer compared to pure g-C3N4. Consequently, the first-order kinetic constant of BCNNT increased by 73.7 %, resulting in nearly 80 % degradation of tetracycline (TC) within half an hour. The boron doping played a crucial role in reducing the surface energy required for nanotube formation during synthesis, a key factor in their structural development. Both density functional theory (DFT) calculations and experimental studies confirmed that the Lewis acid site B enhanced tetracycline adsorption, while nitrogen-deficient sites suppressed electron-hole recombination, thus accelerating photocatalytic degradation rate. This research provides a novel perspective on fabricating tubular g-C3N4 structures and compositions, offering insights for improving the kinetics of photocatalytic reactions.

TiO2 nanorod arrays/Ti3C2T x MXene nanosheet composites with efficient photocatalytic activity

Semiconductor photocatalysis holds significant promise in addressing both environmental and energy challenges. However, a major hurdle in photocatalytic processes remains the efficient separation of photoinduced charge carriers. In this study, TiO2 nanorod arrays were employed by glancing angle deposition technique, onto which Ti3C2T x MXene was deposited through a spin-coating process. This hybrid approach aims to amplify the photocatalytic efficacy of TiO2 nanorod arrays. Through photocurrent efficiency characterization testing, an optimal loading of TiO2/Ti3C2T x composites is identified. Remarkably, this composite exhibits a 40% increase in photocurrent density in comparison to pristine TiO2. This enhancement is attributed to the exceptional electrical conductivity and expansive specific surface area inherent to Ti3C2T x MXene. These attributes facilitate swift transport of photoinduced electrons, consequently refining the separation and migration of electron–hole pairs. The synergistic TiO2/Ti3C2T x composite showcases its potential across various domains including photoelectrochemical water splitting and diverse photocatalytic devices. As such, this composite material stands as a novel and promising entity for advancing photocatalytic applications. This study can offer an innovative approach for designing simple and efficient photocatalytic materials composed of MXene co-catalysts and TiO2 for efficient water electrolysis on semiconductors.

Enhanced Photoelectrochemical Performance Using Cobalt-Catalyst-Loaded PVD/RF-Engineered WO3 Photoelectrodes

Critical to boosting photoelectrochemical (PEC) performance is improving visible light absorption, accelerating carrier separation, and reducing electron–hole pair recombination. In this investigation, the PVD/RF method was employed to fabricate WO3 thin films that were subsequently treated using the surface treatment process, and the film surface was modified by introducing varying concentrations of cobalt nanoparticles, a non-noble metal, as an effective Co catalyst. The results show that the impact of loaded cobalt nanoparticles on the film surface can explain the extended absorption spectrum of visible light, efficiently capturing photogenerated electrons. This leads to an increased concentration of charge carriers, promoting a faster rate of carrier separation and enhancing interface charge transfer efficiency. Compared with a pristine WO3 thin film photoanode, the photocurrent of the as-prepared Co/WO3 films shows a higher PEC activity, with more than a one-fold increase in photocurrent density from 1.020 mA/cm2 to 1.485 mA/cm2 under simulated solar radiation. The phase, crystallinity, and surface of the prepared films were analysed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The PVD/RF method, scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM) were employed to assess the surface morphology of the fabricated film electrode. Optical properties were studied using UV–vis absorbance spectroscopy. Simultaneously, the photoelectrochemical properties of both films were evaluated using linear sweep voltammetry and electrochemical impedance spectroscopy (EIS). These results offer a valuable reference for designing high-performance photoanodes on a large scale for photoelectrochemical (PEC) applications.

Interfacial Charge Transfer Bridge Prolongs Carrier Recombination Lifetimes of CoFe Metal‐Thiolate Framework/Hematite Photoanode for Water Oxidation

AbstractConstructing heterostructural photoanodes is attractive for elevating the photoelectrochemical (PEC) performance, however, it is a long‐standing challenge to achieve highly efficient interfacial charge transfer. Herein, a CoFe metal‐thiolate framework (CoFe MTF)/Fe2O3 photoanode connected by an interfacial Fe─O─N/S bond is designed to modulate the behavior of charge carriers and improve water oxidation performance. It is disclosed that this interfacial bond functions as a direct charge transfer bridge between shallow trap states of Fe2O3 and CoFe MTF, leading to prolonged carrier recombination lifetimes (85 ns for CoFe MTF/Fe2O3 compared to 37 ns for Fe2O3) and enhanced charge transfer efficiency. Alternatively, a robust interfacial electric field is established in the CoFe MTF/Fe2O3 p–n heterojunction, facilitating efficient charge transfer. As expected, the CoFe MTF/Fe2O3 photoanode exhibits significant enhancement in water oxidation, resulting in a three‐fold increase in photocurrent density compared to pristine Fe2O3. This study highlights the significance of designing interfacially bonded heterostructural photoelectrodes to regulate the transfer characters of charge carriers.

Flower-like 3D MoS2/Cu2O hybrids with enhanced photoelectrochemical performance

Molybdenum disulfide (MoS2) is widely employed as a photoanode in photoelectrochemical (PEC) tests due to its energy gap in the visible region and strong interaction with light. In this work, three-dimensional (3D) flower-like MoS2 heterostructures have been introduced by the CVD method and decorated with copper (I) oxide (Cu2O) nanoparticles synthesized by electrodeposition. SEM, XRD, Raman, UV-Visible, current-potential and EIS analyses have been performed to evaluate the heterostructure. The results show that the MoS2/Cu2O heterostructure is not only well-formed but associated with a 61% increase in photocurrent density compared to MoS2. This is due to the smaller charge transfer resistance and effective charge separation in the heterostructure compared to MoS2, based on the EIS analysis and corresponding band energy diagram. A cyclic test of the electrode also shows its excellent stability, making it suitable for practical applications.

A novel p-type CoSe2 co-catalyst cooperated with hematite for boosting photoelectrochemical water splitting

Fe2O3-based photoelectrodes hold promise for photoelectrochemical water splitting due to their cost-effectiveness and stable chemical properties. However, Fe2O3-based photoelectrodes face limitations including low bulk conductivity and severe surface recombination of photo-generated charge carriers, which adversely affect their performance. To address these challenges, a novel p-type CoSe2 surface co-catalyst was developed to establish a Ti-Fe2O3/CoSe2 p-n heterojunction. By incorporating a Ti4+ doping strategy, the resulting Ti-Fe2O3/CoSe2 p-n heterojunction demonstrated a significant increase in photocurrent density, reaching 2.85 mA/cm2 at 1.23 VRHE under 100 mW/cm2 illumination. The corresponding IPCE achieved 60.14 % under 365 nm light irradiation, nearly 5 times higher than that observed on pristine Fe2O3. Besides Ti4+ dopant, the improvement can be attributed to the p-type CoSe2 surface co-catalyst, which created a built-in electric field at the interface between CoSe2 and Ti-Fe2O3, effectively suppressing electron tunneling from the photoelectrode to the electrolyte and reducing surface carrier recombination. This study improves our understanding of the water splitting catalytic reaction on CoSe2-derived heterojunctions and provides insights for the rational design of photoelectrodes used in photoelectrochemical water splitting.

Spin polarized electron dynamics enhance water splitting efficiency by yttrium iron garnet photoanodes: a new platform for spin selective photocatalysis.

This work presents a spectroscopic and photocatalytic comparison of water splitting using yttrium iron garnet (Y3Fe5O12, YIG) and hematite (α-Fe2O3) photoanodes. Despite similar electronic structures, YIG significantly outperforms widely studied hematite, displaying more than an order of magnitude increase in photocurrent density. Probing the charge and spin dynamics by ultrafast, surface-sensitive XUV spectroscopy reveals that the enhanced performance arises from (1) reduced polaron formation in YIG compared to hematite and (2) an intrinsic spin polarization of catalytic photocurrents in YIG. Ultrafast XUV measurements show a reduction in the formation of surface electron polarons compared to hematite due to site-dependent electron-phonon coupling. This leads to spin polarized photocurrents in YIG where efficient charge separation occurs on the Td sub-lattice compared to fast trapping and electron/hole pair recombination on the Oh sub-lattice. These lattice-dependent dynamics result in a long-lived spin aligned hole population at the YIG surface, which is directly observed using XUV magnetic circular dichroism. Comparison of the Fe M2,3 and O L1-edges show that spin aligned holes are hybridized between O 2p and Fe 3d valence band states, and these holes are responsible for highly efficient, spin selective water oxidation by YIG. Together, these results point to YIG as a new platform for highly efficient, spin selective photocatalysis.

Development of a Simple Ink Coating Procedure for BiVO4 Photoanodes for Oxygen Evolution

Photoelectrodes can be implemented in electrochemical cells to accelerate the reaction kinetics of the intended reactions, utilizing the support of visible light. Especially, photoanodes for the oxygen evolution reaction (OER) are of great interest for energy storage and conversion, since the OER is the anodic half-cell reaction of many Power-to-X technologies such as water splitting, CO2 electroreduction and metal-air battery recharge. However, the OER still limits their potential by being a kinetically hindered 4-electron transfer process. In previous research, bismuth vanadate (BiVO4) has shown significant advances for the onset potential and increase in current density of the OER under illumination. Additionally, BiVO4 is a low-cost material, making it favorable over commonly used noble metal electrocatalysts, leading to its rise as one of the most suitable photoelectrocatalysts for OER photoanodes. However, BiVO4 still does not match practical requirements, demanding for further research and development.In this work, we focus on the implementation of a simple ink coating procedure for BiVO4 photoanodes. Ink coating demonstrates a versatile and adaptable preparation procedure for photoelectrodes, since photoelectrocatalyst synthesis and catalyst deposition are decoupled, providing a large degree of preparative freedom. On the one hand, the catalyst synthesis can be modified and adjusted separately. On the other hand, the catalyst deposition can be performed via various techniques using an ink. Thus, the photoelectrode preparation is not restricted to a certain substrate and specific synthesis conditions.In the proposed ink coating procedure, first neat and (Mo or W)-doped BiVO4 photoelectrocatalysts are prepared via hydrothermal synthesis also including Co-Pi as a post-deposited co-catalyst. Afterwards, the resulting catalysts are deposited onto FTO glass for further physico-chemical characterization. Moreover, the photoelectrochemical (PEC) performance under illumination and in the dark is investigated for the prepared electrodes. Finally, the ink coated electrodes are compared to BiVO4 photoanodes, which are prepared via solution-based methods, as reported in literature.[1-4] For the physico-chemical analysis, the ink coated photoanodes are characterized by various microscopic and spectroscopic techniques. SEM images reveal that homogeneous catalyst layers are prepared. Additionally, LSM measurements show that ink coating leads to a catalyst layer with a high surface roughness. XRD and Raman measurements reveal crystalline and pure BiVO4 structures. Furthermore, for the investigation of the PEC performance, an H-cell which is equipped with an LED light source is utilized, allowing for rapid and flexible data acquisition at constant temperatures. In the photoelectrochemical measurements, a significant reduction of the OER onset potential as well as a significant increase in photocurrent density in comparison to dark scans is achieved for neat BiVO4 photoanodes. For now, the ink coated BiVO4 could lower the onset potential by up to 0.6 V under illumination and increase the current density by up to 10 mA/cm² in comparison to the dark scans. In addition, modification of the ink coated BiVO4 by doping and co-catalyst deposition results in an even higher enhancement of the PEC performance for the OER. At this, the ink coated catalyst layers show an excellent stability even after several hours of PEC measurements. Moreover, it is shown that the ink coated BiVO4 photoanodes perform well in comparison to the solution coated electrodes. Overall, the ink coating procedure was successfully established for BiVO4 photoanodes, opening the door for the adaptation to the electrode preparation for different Power-to-X technologies. Literature: [1] B. Pattengale, J. Ludwig, J. Huang, J. Phys. Chem. C 2016, 120, 1421.; [2] S. K. Choi, W. Choi, H. Park, Phys. Chem. Chem. Phys. 2013, 15, 6499.; [3] J. A. Seabold, K.-S. Choi, J. Am. Chem. Soc. 2012, 134, 2186.; [4] K. J. McDonald, K.-S. Choi, Energy Environ. Sci. 2012, 5, 8553.

Interface and Structural Engineering of Cr Doped Zinc Oxide/Graphene Photoanode with Enhanced Photoelectrochemical Water Splitting

The low-cost hydrogen (H2) generation from solar energy is one of the attractive and promising methods for clean and sustainable energy. It is challenging to boost global, renewable H2 energy mission. Until now, no catalytic system has been realized with viable efficiency and stability with reasonable manufacturing cost. Herein, we demonstrate a facile synthesis of chromium doped zinc oxide/graphene (Cr-doped ZnO@Graphene) as multicomponent photoanode using simple, inexpensive hydrothermal method. We investigated that graphene layer beneath ZnO can act in a different way, while salient features of controllable graphene concentration and appropriate Cr doping clearly displayed profound influence on photoelectrochemical water splitting reaction which is due to promoted electron transfer at interface. The detailed computational study was done by density functional theory (DFT) calculations. A photoelectrochemical cell was assembled with optimized photoanode displayed 4-fold increase in photocurrent density as compared to pristine ZnO. The improved PEC performance is attributed to the synergistic effects, where the presence of Cr dopant improves the charge carrier density and enhanced electronic conductivity, and graphene has increased the carrier transport and collection efficiency. Overall, this study provides valuable insights into the development of (Cr-doped ZnO@Graphene) as a highly efficient and stable photoelectrode for practical applications in solar water splitting and renewable energy conversion.

Highly efficient visible-light-driven CdS-loaded ZnO-GaN nanowire photoanode fabricated on Si for H2 evolution

GaN nanowires (NWs) are considered promising photoelectrode materials owing to their direct bandgap, which a high-efficiency photon absorption. Additionally, their conduction and valence bands straddle the water redox level, making them ideal candidates for solar water splitting without external biasing. Moreover, they have a large reactive surface area, which promotes charge separation. However, their practical applicability is limited because of their poor stability and low solar-to-hydrogen conversion efficiency, which can be mitigated by loading a passivation layer and cocatalyst onto the GaN NW surfaces. In this study, CdS/ZnO/GaN NW photoanodes were fabricated on Si substrates for photoelectrochemical water splitting. Vapor–liquid–solid GaN NWs were used as the core material on a Si substrate passivated with a ZnO conformal layer, and CdS was adopted as a cocatalyst. Compared to a ZnO/GaN NW photoanode, the CdS/ZnO/GaN NW photoanode showed a 10-fold increase in photocurrent density and a 47-fold increase in photoconversion efficiency under 1-Sun illumination. We propose that ZnO and CdS inhibit the photocorrosion of bare GaN NWs and thus reduce the surface defects, thereby lowering the photogenerated charge recombination rate. As a result, the stability of GaN NWs in a high pH electrolyte increases, leading to an efficient H2 evolution.

Highly efficient Bi2O2CO3 coupled with interlayer expanded MoS2 photocatalyst with oxygen vacancy mediated direct Z-scheme charge transfer for photocatalytic degradation of organic pollutant

The development of photocatalysts to degrade organic pollutants from wastewater under visible light has attracted a lot of interest. Herein, a series of Bi2O2CO3 (BOC) coupled with interlayer expanded MoS2 (IEM) photocatalysts were synthesized via a facile two-pot hydrothermal technique. Among all the samples, 5 % of BOC with IEM (5 % BOC-IEM) nanocomposite exhibited the highest photodegradation with 94 % (4.97 × 10−2 min−1) for Methylene Blue (MB) dye removal under 1 W LED visible light. The performance by 5 % BOC-IEM is 1.5 times and 13.4 times higher than the parent IEM and BOC, respectively. Increased photocurrent density, lowest PL intensity, and smallest EIS arc further evidenced the lowered charge carrier’s recombination rate in the optimized 5 % BOC-IEM heterostructure. Moreover, the outstanding photocatalytic performance of 5% BOC-IEM was due to the presence of oxygen vacancies, enhanced light absorption, and improved migration and separation of charge carriers. An Ohmic contact formed on the interfaces of BOC and IEM boosts the Z-scheme charge transfer mechanism, which greatly improves the photocatalytic activity of 5% BOC-IEM.

Insights into Chemical Bonds for Eliminating the Depletion Region and Accelerating the Photo-Induced Charge Efficient Separation toward Ultrasensitive Photoelectrochemical Sensing.

The empty-space-induced depletion region in photoelectrodes severely exacerbates the recombination of electron-hole pairs, thereby reducing the photoelectrochemical (PEC) analytical performance. Herein, the chemical bond that can suppress the potential barrier and overcome the high energy barrier of out-of-plane Ohmic or Schottky contact is introduced into the PEC sensor to eliminate the depletion region and dramatically promote the separation of electron-hole pairs. Specifically, three-dimensional (3D) hierarchically wheatear-like TiO2 (HWT) nanostructures featuring a large surface area to absorb incident light are crafted as the substrate. The facile carbonized strategy is further employed to engineer the Ti-C chemical bond, serving as the touchstone. The average PL lifetime of HWT-C (4.14 ns) is much shorter than that of the 3D HWT (8.57 ns) due to the promoting effect of the chemically bonded structure on carrier separation. Consequently, the 3D HWT-C covalent photoelectrode (600 μA/cm2) exhibits a 3.6-fold increase in photocurrent density compared with the 3D HWT (167 μA/cm2). Ultimately, the model analyte of the tumor marker is detected, and the linear range is 0.02 ng/mL-100 ng/mL with a detection limitation of 0.007 ng/mL. This work provides a basic understanding of chemical bonds in tuning charge separation and insights on strategies for designing high-performance PEC sensors.

Enhanced photoelectrochemical water splitting performance of GaN nanowires on textured Si (100) platforms: The role of texturing in 3.69 % STH conversion efficiency

Nanostructured GaN semiconductors, including 0D quantum wells and 1D nanowires (NWs), as well as 3D nanoporous structures, have the potential to enhance the efficiency of photoelectrochemical (PEC) cells due to their shorter charge carrier transfer paths, accelerated separation of photogenerated carriers, and enhanced sunlight absorption. However, their practical applicability is limited due to poor stability and low solar-to-hydrogen conversion efficiency. To address these issues, one approach is to load a passivation layer and cocatalyst onto the GaN surfaces to protect against oxidation and corrosion and promote the oxidation of water, respectively. Another strategy is to design these structures on textured platforms to enhance light management, resulting in broader absorption of wavelengths and reduced sensitivity to incident angle and light polarization. In this study, we present a novel comparison of PEC-WS performance among 120 CdS/ZnO/GaN nanowires fabricated on different substrates, including planar Si (120 CdS/ZnO/GaN NWs-Si), textured 3D pyramids (120 CdS/ZnO/GaN-Si PNWs), and NWs Si (120 CdS/ZnO/GaN-Si HNWS). Compared to the other substrates, 120 CdS/ZnO/GaN-Si HNWS photoanode showed a 1.14 and 1.26-fold increase in photocurrent density and 3.69 % solar to hydrogen conversion efficiency under 1-Sun illumination. Our Si texturing approach, in-depth understanding of charge transportation, and demonstration of a co-catalyst-loaded core-shell passivated structure offer promising opportunities for achieving highly efficient PEC-WS performance in GaN-based photoanodes.

Boosting the photocathode performances of protected Cu2O inverse opals using photonic-crystal heterostructures

Cuprous oxide (Cu2O) is a highly efficient p-type semiconductor photocatalytic material with the capability for visible light absorption. In this work, three-dimensional Cu2O inverse opals with different diameters were prepared using the electrochemical deposition method. The photocathode performances were enhanced by adjusting the wavelength of photonic band gap, being co-modified by Au and Ag nanoparticles, applying the protective layers, and fabricating a photonic-crystal heterostructure with another p-type semiconductor. The slow-light effect leads a 23.9 % increase in photocurrent density. The co-modification of Au and Ag nanoparticles achieves a 77 % average increase in photocurrent density compared with pure Cu2O inverse opals. Conformal protective layers, consisting of ZnO and Al2O3 and deposited using atomic layer deposition, prevent the photocorrosion of the Cu2O photocathode while preserving its photocatalytic activity. After one hour of illumination, the photo-generated current density of protected Cu2O inverse opals is nearly three times higher than that of their uncoated counterparts. By fabricating Ag-doped ZnO with p-type characteristics and combining it with Cu2O into a heterostructure, the saturated photocurrent density of the Ag-doped ZnO/Cu2O heterostructure reaches −3.78 mA/cm2, which is almost 3.2 times higher than that of pristine Cu2O inverse opal at −0.12 V vs RHE.