Enhanced Photoelectrochemical Performance Research Articles

Preparation of double-layered Co−Ci/NiFeOOH co-catalyst for highly meliorated PEC performance in water splitting

The cobalt−carbonate (CoCi)/NiFeOOH double-layer co-catalyst was prepared on bismuth vanadate (BiVO 4 ). Compared with the same type of electrode (Co−Pi/NiFeOOH/BiVO 4 and Co−Sil/NiFeOOH/BiVO 4 ), the photoelectrochemical (PEC) performance of the composite electrode presents the most excellent performance. The Co−Ci/NiFeOOH/BiVO 4 electrode prepared by photoelectric deposition (PED) achieves a photocurrent density of 4.1 ​mA/cm 2 at 1.23 ​V vs RHE, and the applied bias photon-current efficiency (ABPE) is up to 0.95%. In addition, with the help of the equivalent circuit fitting in electrochemical impedance spectroscopy (EIS), the charge transfer resistance ( R ct ) of Co−Ci/NiFeOOH/BiVO 4 is only 108.9 ​Ω, which is 16% that of BiVO 4 . The enhanced PEC performance of Co−Ci/NiFeOOH/BiVO 4 in the double-layer cocatalyst system is attributed to the outstanding advantages of Co−Ci cocatalyst in oxygen vacancy defects, superior to other cobalt-based catalysts in promoting charge transfer and improving the kinetics of water oxidation. This makes Co−Ci co-catalyst become one of the favorable competitors in the field of photoelectric catalysis.

Enhanced charge separation and conductivity of hematite enabled by versatile NiSe2 nanoparticles for improved photoelectrochemical water oxidation

The inherent drawbacks of severe charge recombination and poor conductivity of hematite (α-Fe2O3) are still the obstacles for its applications. Herein, we report the integration of NiSe2 nanoparticles on the surface of Fe2O3 films for the photoelectrochemical (PEC) water oxidation. The resulting heterostructure photoanode exhibited significantly enhanced PEC performance with a current density enlarged by 50%. The investigations on mechanism reveals that a built-in electric field was formed to accelerate the charge transfer and separation, the charge carrier concentration was significantly enhanced by the formation of oxygen vacancies induced by NiSe2, the lifetime of photogenerated electrons and holes were substantially prolongated due to the suppression of recombination by the surface passivation and promoted surface kinetics for water oxidation by of Se-O species. This work brings inspiration to integrate multifunctional modifiers on photoelectrodes that allows for addressing several issues simultaneously and consequently improving the PEC performance for hydrogen production via water splitting.

Engineering efficient hole transport layer Ferrihydrite-MXene on BiVO4 photoanodes for photoelectrochemical water splitting: Work function and conductivity regulated

Although great interest is focused on development of semiconductor photoanodes for efficient photoelectrochemical (PEC) water splitting, the pressing bottleneck to address the intrinsic charge transport for enhancement of PEC performance still remains to be resolved. Herein, hole transport layer (Fh-MXene) constructed by doping of MXene (Ti3C2) in Ferrihydrite (Fh) is loaded on BiVO4 photoanode. This novel BiVO4@Fh-MXene photoanode achieves high current density of 4.55 mA cm−2 at 1.23 V versus reversible hydrogen electrode (vs. RHE), exhibiting excellent photostability. From electrochemical analysis and density functional theory calculations, high PEC performance is ascribed to incorporation of Fh-MXene as hole transport layer, enhancing conductivity and water oxidation reaction. Notably, MXene can improve band alignment of BiVO4/Fh-MXene interface by tuning work function, which strengthens the built-in electric field for more efficient hole extraction. This work provides a simple method to design photoanodes with efficient charge transport layers for feasible PEC water splitting application.

Insights into the Enhanced Photoelectrochemical Performance through Construction of the Z-Scheme and Type II Heterojunctions.

Photoelectrochemical (PEC) water splitting technology is a promising strategy toward producing sustainable hydrogen fuel. However, it is an essential bottleneck to reduce severe charge recombination for the improvement of PEC performance. Construction of heterojunction systems, such as Z-scheme and type II heterojunctions, could efficiently boost charge separation, whereas the mechanism of charge separation is still ambiguous. We describe herein a charge transfer system designed with Bi2WO6/Bi2S3 (BWO/BS) as a prototype. In this system, Au nanoparticles act as charge relays to engineer a charge transfer pathway, and the obtained BWO/Au/BS photoanode achieves a remarkable photocurrent density of 0.094 mA cm-2 at 1.23 V versus reversible hydrogen electrode (vs RHE), over approximately 1.2 and 2.3 times larger than those of BWO/BS/Au and BWO, exhibiting long-term photostability. More importantly, scanning photoelectrochemical microscopy (SPECM) and intensity-modulated photocurrent spectroscopy (IMPS) studies are performed to in situ-capture the photogenerated hole during the PEC process. Operando analysis reveals that the Z-scheme BWO/Au/BS system (1.33 × 10-2 cm s-1) exhibits higher charge transfer kinetics compared to the type II BWO/BS/Au heterostructure (0.85 × 10-2 cm s-1) while efficiently suppressing charge recombination for optimized PEC activity. Note that this smart strategy can also be extended to other semiconductor-based photoanodes such as BiVO4. Our study offers an effective pathway for the rational design of highly efficient charge separation for solar conversion based on water splitting.

Mo-doped BiVO4 modified with NH2-MIL-88B(Fe) cocatalyst overlayer for enhanced photoelectrochemical water oxidation

The photoelectrochemical (PEC) performance of BiVO4 is limited by poor charge separation and slow surface water oxidation kinetics. Herein, an simple and effective caffeic acid-assisted solvothermal method was developed to grow Fe-based metal–organic framework (NH2-MIL-88B(Fe)) overlayer onto the Mo-doped BiVO4 for efficient PEC water oxidation. The synergistic role of Fe-MOF cocatalyst and Mo dopant resulted in a 3.5-fold photocurrent density (1.46 mA cm−2) increase in comparison with bare BiVO4 (0.46 mA cm−2) at 1.23 V [vs. reversible hydrogen electrode (RHE)] and showed an obviously negative shift of the onset potential (200 mV). The enhanced PEC performance can be attributed to the improved charge separation and injection efficiency with Mo doping and Fe-MOF coating, the introduction of Fe-MOF also increased the utilization of visible-light and served as an efficient electrocatalyst to accelerate the oxygen evolution reaction (OER) kinetics. This work provides a universal strategy for constructing semiconductor/MOFs photoanodes for enhanced photoelectrochemical water splitting.

Ternary TiO2/Ni–Ni(OH)2/NiPi nanotube arrays with synergetic effect for enhanced photoelectrocatalytic H2-evolution

Dual co-catalysts have an essential effect on improving the photoelectrochemical (PEC) performance of semiconductor materials. In this study, Ni–Ni(OH)2 or/and Nikel phosphate (NiPi) nanocrystals co-catalysts were deposited on the surface of as-prepared TiO2 nanotube arrays (TNTAs) by a simple electrodeposition route for PEC hydrogen production. The TNTAs loading with Ni and NiPi bifunctional co-catalysts exhibited remarkably enhanced PEC performance, with about an 8.3-fold increase in the photocurrent; and an 11.7-fold improvement in H2 evolution rate in comparison to bare TNTAs. The constructed ternary TNTAs/Ni–Ni(OH)2/NiPi comprised the advantage of Ni–Ni(OH)2 and NiPi nanoparticles to enhance visible-light absorption and promote oxygen evolution reaction (OER) kinetics. The internal electric field is generated between supported p-type Ni(OH)2 and n-type TiO2 under light irradiation, which will drive holes to flow to Ni(OH)2 and oxidize it as the OER active layer. Also, the photo-generated holes remaining in the TiO2 valence band can migrate to NiPi co-catalysts to cause OER. Therefore, the photogenerated electron-hole pairs can be successfully separated under the synergetic influence of Ni–Ni(OH)2 and NiPi co-catalyst, leading to a superior PEC water splitting ability.

Eliciting the contribution of TiN to photoelectrochemical performance enhancement of Imma-LaTiO2N at neutral pH

The presence of defects, which act as the recombination hubs for photogenerated charge carriers, hinders the improvement of photocatalytic activity for oxygen evolution reaction of LaTiO2N under visible light irradiation via a four-electron-transfer reaction pathway. Here, we involve titanium nitride (TiN) in a varying content (0–17.8%) to improve the efficiency of charge separation and transport, influencing the photoelectrochemical performance of LaTiO2N. The characterization results confirm the formation of a strong contact between orthorhombic-LaTiO2N and cubic-TiN particles. The photoelectrochemical (PEC) measurements reveal the inverse dependence between electron transfer phenomena and charge carrier recombination, which allows to understand the trend when modifying LaTiO2N with TiN. In fact, the incorporation of 17.8% TiN in the LaTiO2N:TiN material results in a higher photocurrent. Open-circuit potential (OCP) decay and transient absorption spectroscopy (TAS) studies confirm longer lifetimes of charge carriers for increasing amounts of TiN in the synthesized materials. Thus, the main role of TiN is to improve the properties of the semiconductor-electrolyte interface, having verified its impact on the separation and transport of photogenerated charge carriers. Furthermore, computational studies predict that the adsorption of water molecules is favored at the LaTiO2N:TiN surface compared to the individual TiN and LaTiO2N surfaces.

A sensitive photoelectrochemical aptasensor for enrofloxacin detection based on plasmon-sensitized bismuth-rich bismuth oxyhalide

Highly sensitive detection of enrofloxacin (ENR) is crucial for contaminant detection and environmental protection. A sensitive and selective photoelectrochemical (PEC) aptasensor was assembled by Au nanoparticles sensitized Bi24O31Br10 (Au/Bi24O31Br10) composites for detecting ENR. Due to the synergistic effect of bismuth-rich strategy and surface plasmon resonance (SPR) effect, Au/Bi24O31Br10 possessed promoted visible light absorption capacity further enhancing PEC performance and detection sensitivity of the constructed PEC aptasensor. By chemically adsorption effect between the sulfhydryl modified aptamer and Au nanoparticles, the ENR-aptamer was introduced into the PEC sensor to achieve highly selective detection of ENR. The PEC ENR aptasensor based on Au/Bi24O31Br10 composites possessed a broad linear detection scope (0.72–36000 ng L−1), satisfactory limit of detection (0.30 ng L−1, S/N = 3), high selectivity and stability. This work provides a new way for the trace detection of antibiotics in environmental analysis field.

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.

Photoelectrochemical hydrogen generation with nanostructured CdS/Ti–Ni–O composite photoanode

Composite photocatalysts have aroused great interest due to combination of favorable electronic and optical properties. Herein, novel CdS/Ti–Ni–O composite photoanodes were constructed through anodic fabrication of nanostructured Ni-doped TiO2 (Ti–Ni–O) oxide films and CdS deposition by successive ionic layer adsorption and reaction (SILAR). The morphology and composition evolution, optical properties and photoelectrochemical (PEC) performance of the photoanodes were investigated. The composite nanofilms mainly consisted of micropores and nanotubes. The CdS/Ti–Ni–O composite photoanode demonstrated remarkable PEC hydrogen generation properties with a high photocurrent density (6.72 mA·cm−2 at 0 V vs Ag/AgCl) which was 18.2 times to that of the bare Ti–Ni–O photoanode. The synergy of Ni-doping and CdS-coupling on the enhancement of PEC performance offers useful ideas to the exploitation of effective photocatalysts and contributes to the development of solar-driven PEC hydrogen generation.

Fabrication of α-Fe2O3/Ag film by spin coating with enhanced photoelectrochemical activity

Photoelectrochemical (PEC) water oxidation represents one of the biggest scientific challenges in producing solar fuels. As a promising photoanode candidate, hematite (α-Fe2O3) suffers from limited separation of photogenerated charges. In this work, a simple spin coating method is reported to obtain α-Fe2O3/Ag films on FTO glass substrates with accurately controlled thickness and composition. The α-Fe2O3 photoanode with appropriate amount of Ag exhibited superior photoelectrochemical performance with a photocurrent density of 1.33 mA/cm2 at 1.23 V, which is 1.77 times higher than that of the pure α-Fe2O3. By calculating the bulk separation efficiency and surface separation efficiency, the significantly enhanced PEC performance is ascribed to the interfacial effect on separating the photogenerated charges in hematite. The method described herein provides a simple and general method for engineering the interface of metal/oxide interface.

Controlled Synthesis and Photoelectrochemical Performance Enhancement of Cu2−xSe Decorated Porous Au/Bi2Se3 Z-Scheme Plasmonic Photoelectrocatalyst

In this paper, uniform Cu2−xSe-modified Au/Bi2Se3 hybrid nanoparticles with porous shells have been prepared through a cation exchange method. Bi2Se3/Cu2−xSe Z-scheme heterojunction is introduced onto Au nanocube by replacing Bi3+ with Cu2+. Owing to the effective coupling between Au core and semiconductor shells, Au/Bi2Se3/Cu2−xSe hybrids present a broad and strong plasmon resonance absorption in the visible band. More intriguingly, the carrier lifetime of Au/Bi2Se3/Cu2−xSe hybrid photoelectrodes can be further tailored with corresponding Cu2−xSe content. Through parameter optimization, 0.1-Au/Bi2Se3/Cu2−xSe electrode exhibits the longest electron lifetime (86.03 ms) among all the parallel samples, and corresponding photoelectrochemical performance enhancement is also observed in the tests. Compared with that of pure Bi2Se3 (0.016% at 0.90 V vs. RHE) and Au/Bi2Se3 (0.02% at 0.90 V vs. RHE) nanoparticles, the maximum photoconversion efficiency of porous Au/Bi2Se3/Cu2−xSe hybrid photoanodes increased by 5.87 and 4.50 times under simulated sunlight illumination, attributing to the cooperation of Z-scheme heterojunction and plasmon resonance enhancement effects. All the results indicate that Au/Bi2Se3/Cu2−xSe porous hybrids combine eco-friendliness with excellent sunlight harvesting capability and effectively inhibiting the charge recombination, which provide a new idea for efficient solar-driven water splitting.

Fabrication of sensitive photoelectrochemical aptasensor using Ag nanoparticles sensitized bismuth oxyiodide for determination of chloramphenicol

A highly sensitive and selective photoelectrochemical (PEC) aptasensor was constructed by Ag nanoparticles sensitized bismuth oxyiodide (AgNPs/BiOI) composites for detecting trace chloramphenicol (CAP). Because the sufficient light utilization of AgNPs and high photoelectrons transfer efficiency of BiOI, AgNPs/BiOI composites exhibited dramatically enhanced PEC performance, which is in favor of realizing efficient CAP detection. Attributed to the specific recognition of modified CAP aptamer, the PEC CAP aptasensor based on the aptamer/AgNPs/BiOI/ITO electrodes performed a wide linear range (1 pM − 20000 pM), a satisfactory detection limit (0.4 pM, S/N = 3), and superior selectivity. In addition, the CAP aptasensor possessed favorable stability and reproducibility, promoting further application of CAP trace detection and providing a foothold for ultrasensitive antibiotic detection and environmental monitoring.

FeFx and Fe2ZrO5 Co-modified hematite for highly efficient solar water splitting

Hematite is an excellent catalyst for photoelectrochemical (PEC) water splitting but its performance has been highly limited by poor conductivity and high charge recombination. Here by a Zr-based treatment to create bulk Fe2ZrO5 in hematite and a F-based treatment to form an ultrathin surface FeFx layer, the charge transfer can be highly improved and the charge recombination can be significantly suppressed. As a result, the FeFx/Zr-Fe2O3 photoanode presents an enhanced PEC performance with a photocurrent density of 2.43 mA/cm2 at 1.23 V vs. RHE, which is around 3 times higher than that of the pristine Fe2O3. The FeFx/Zr-Fe2O3 photoanode also shows a low onset potential of 0.77 V vs. RHE (100 mV lower than the pristine hematite). The performance is much higher than that of the sample treated by Zr or F alone, suggesting the synergistic effect between bulk Fe2ZrO5 and surface FeFx. By coupling with the FeNiOOH co-catalyst, the final photoanode can achieve a high photocurrent density of 2.81 mA/cm2 at 1.23 V vs. RHE. The novel design of Zr and F co-modified hematite can be used as a promising way to prepare efficient catalysts for solar water splitting.

A Semiconductor-Mediator-Catalyst Artificial Photosynthetic System for Photoelectrochemical Water Oxidation.

In fabricating an artificial photosynthesis (AP) electrode for water oxidation, we have devised a semiconductor-mediator-catalyst structure that mimics photosystem II (PSII). It is based on a surface layer of vertically grown nanorods of Fe2 O3 on fluorine doped tin oxide (FTO) electrodes with a carbazole mediator base and a Ru(II) carbene complex on a nanolayer of TiO2 as a water oxidation co-catalyst. The resulting hybrid assembly, FTO|Fe2 O3 |-carbazole|TiO2 |-Ru(carbene), demonstrates an enhanced photoelectrochemical (PEC) water oxidation performance compared to an electrode without the added carbaozle base with an increase in photocurrent density of 2.2-fold at 0.95 V vs. NHE and a negatively shifted onset potential of 500 mV. The enhanced PEC performance is attributable to carbazole mediator accelerated interfacial hole transfer from Fe2 O3 to the Ru(II) carbene co-catalyst, with an improved effective surface area for the water oxidation reaction and reduced charge transfer resistance.

High-quality CdS quantum dots sensitized ZnO nanotube array films for superior photoelectrochemical performance

The surface characteristics of ZnO were synthetically optimized by a self-designed simultaneous etching and W-doping hydrothermal method utilizing as-prepared ZnO nanorod (NR) array films as the template. Benefiting from the etching and regrowth process and the different structural stabilities of the various faces of ZnO NRs, the uniquely etched and W-doped ZnO (EWZ) nanotube (NT) array films with larger surface area, more active sites and better energy band structure were used to improve the photoelectrochemical (PEC) performance and the loading quality of CdS quantum dots (QDs). On the basis of their better surface characteristics, the CdS QDs were uniformly loaded on EWZ NT array film with a good coverage ratio and interface connection; this effectively improved the light-harvesting ability, charge transportation and separation as well as charge injection efficiency during the PEC reaction. Therefore, all the CdS QD-sensitized EWZ NT array films exhibited significantly enhanced PEC performance. The CdS/EWZ-7 composite films exhibited the optimal photocurrent density with a value of 12 mA⋅cm−2, 2.5 times higher than that of conventional CdS/ZnO-7 composite films under the same sensitization times with CdS QDs. The corresponding etching and optimizing mechanisms were also discussed.

Nanoetching TiO2 nanorod photoanodes to induce high-energy facet exposure for enhanced photoelectrochemical performance.

Crystal facet engineering is considered as an effective way to improve photoelectrochemical (PEC) performance. Here, we have developed a nanoetching technology (TiO2 → TiO2/Bi4Ti3O12 → TiO2/BiVO4 → etching-TiO2) to treat rutile TiO2 nanorod films. Interestingly, the technology can induce the exposure of a large number of high energy (101) faces, and the etching-TiO2 film (E-TiO2) showed a significantly enhanced PEC performance. A dynamic study indicates that charge separation and transfer have been obviously improved by such a nanoetching technology. In particular, the charge transfer efficiency (ηtrans) of E-TiO2 reaches 93.4% at 1.23 V vs. RHE without any loaded cocatalyst. The mechanism of PEC performance enhanced by the strategy is experimentally and theoretically unraveled. The improvement of PEC performance is mainly attributed to the shorter distance between H and the neighboring O-b for the HO* intermediates of the rutile (101) facet, which can reduce the energy barrier for the OER. Besides, the driving force for spatial charge separation between the (110) and (101) facets can promote charge separation. This work offers a new and versatile nanotechnology to induce the exposure of the high energy crystal facets and improve the PEC performance.

Eliciting the Contribution of Tin to Photoelectrochemical Performance Enhancement of Imma-Latio2n at Neutral Ph

Eliciting the Contribution of Tin to Photoelectrochemical Performance Enhancement of Imma-Latio2n at Neutral Ph

Precisely Modulating the Photosensitization Efficiency of Transition-Metal Chalcogenide Quantum Dots toward Solar Water Oxidation.

Precisely modulating the spatial charge migration/separation constitutes the central issue in dictating the solar conversion efficiency of photoelectrochemical (PEC) cells, whereas it still remains a grand challenge. Here, we conceptually demonstrate the construction of hierarchically ordered metal oxide (MO)/transition-metal chalcogenide quantum dots (TMC QDs) multilayered heterostructured photoanodes, that is, MO/[TMC QDs(+)/TMC QDs(-)]n (TMC QDs: CdTe, CdSe, CdS), by a simple and general bottom-up self-assembly route. Tailor-made intrinsically oppositely charged TMC QDs are alternately deposited on the highly ordered MO via a generic ligand-triggered electrostatic interaction to craft heterostructured photoanodes. The charge-transfer pathway stimulated by the photosensitization of TMC QDs is finely tuned by the assembly sequence. The advantageous multilayered nanoarchitecture renders the MO/[TMC QDs(+)/TMC QDs(-)]n photoanodes exhibit substantially enhanced PEC performances under light irradiation, owing to the applicable energy-level configuration and peculiar combination fashion between building blocks and considerably boosted interfacial charge separation resulting from generating spatial tandem charge transport. Furthermore, photosensitization efficiency comparison among TMC QDs is comprehensively performed with PEC mechanisms elucidated.

Influence of ZnO Magnetron Sputtering on Controlled Buildout of Zirconium-Doped ZnFe2O4/Fe2O3 Heterojunction Photoanodes for Photoelectrochemical Water Splitting

The development of efficient photoanodes for solar fuel generation via photoelectrochemical (PEC) water splitting is becoming a bottleneck. These limitations necessitate the design of iron-containing metal oxides, like “ferrites-based electrode materials” with improved oxygen evolution kinetics, light absorptivity, and intrinsic stability, yet at a low cost. Herein, we report the in-situ formation of Zr–ZnFe2O4/Fe2O3 heterojunction (ZZFO/HT) photoelectrodes using a facile magnetron sputtering and hydrothermal processes. First, the ZnO is systematically sputtered on in-situ Zr-doped FeOOH electrodes and then the ZnO-sputtered electrodes are quenched at 800 °C, 13 min to form ZZFO/HT. Furthermore, the effect of ZnO sputtering and roles of Zr–ZnFe2O4 and Fe2O3 in the ZZFO/HT heterojunction as well as their structural and photoelectrochemical properties were studied in detail. The optimum biphasic 25.6 nm ZnO-sputtered ZZFO/HT (ZZFO/HT-2) photoelectrode exhibited a photocurrent density of 0.430 mA/cm2 at 1.23 V vs RHE with an appropriate fraction of Zr–ZnFe2O4 and Fe2O3. The enhanced PEC performance is attributed to the optimum fraction of Zr–ZnFe2O4 and Fe2O3 in ZZFO/HT-2 heterojunction, which provides efficient charge transport across the bulk and at heterojunction interface. Lastly, the integration of Al2O3 passivation layer and Co–Pi cocatalyst on the optimized ZZFO/HT-2 photoelectrode exhibited a high photocurrent density of 0.780 mA/cm2 at 1.23 V vs RHE and generated 11.8 and 6.2 μmol/cm2 of hydrogen and oxygen, respectively during PEC water splitting. Further, it is expected that by fine-tuning of Zr–ZnFe2O4 and Fe2O3 NC ratio, the photocurrent density can be improved for establishing a benchmark for ZnFe2O4-based photoelectrodes.