Applied Bias Photon-to-current Efficiency Research Articles

Modified successive ionic layer adsorption and reaction for interconnected bismuth vanadate nanograins: Highly active visible light harvesting photoanodes

A modified successive ionic layer adsorption and reaction (SILAR) method is developed for depositing interconnected bismuth vanadate (BiVO4) nanoparticles with improved visible light harvesting activity. Facile control of preparative parameters like deposition cycles, anionic precursor, pH and deposition temperature significantly altered BiVO4 surface morphology. BiVO4 thin films prepared with Na3VO4 anionic precursor show dispersed nanoparticles type morphology and that deposited with NaVO3 precursor displays 3D interconnected nanoparticles morphology. The BiVO4 photoanodes with 3D interconnected nanoparticles morphology exhibits an excellent photocurrent density of 5.19 mA cm−2 at 1.23 V vs. RHE with superior photostability and improved applied bias photon to current efficiency (ABPE) (1.50 %) compared to dispersed nanostructured BiVO4 photoanodes. The excellent photoelectrochemical (PEC) characteristics of BiVO4 photoanodes with 3D interconnected nanoparticle morphology can be ascribed to porous morphology, optimum thickness, narrow band gap energy and favorable electronic band structure for water splitting. The current study illustrates the usefulness of the modified SILAR approach for depositing 3D interconnected BiVO4 nanoparticle morphology in a single step that is superior and efficient to previously reported multistep processes.

Solution Processing Silicon Heterojunction Photocathode for Efficient and Stable Hydrogen Production.

Efficient and stable photocathodes are crucial for the development of photoelectrochemical (PEC) water-splitting devices. Silicon heterojunction (SHJ) solar cell is one of the most advanced photovoltaic cells. However, due to the instability of its outermost indium tin oxide (ITO) layers in the electrolyte, a protective layer needs to be introduced on its surface. Previously reported high-quality protective layers almost all involved the use of expensive thin film manufacturing techniques such as atomic layer deposition (ALD). In this work, for the first time, a new strategy is proposed of modifying SHJ-based photocathode with yttrium hydroxide (Y(OH)3) through two-step solution methods to simultaneously improve the stability and activity. The optimized SHJ photocathode exhibits a high applied bias photon-to-current efficiency (ABPE) of 8.4% under simulated 100mWcm-2 (1 Sun) with an AM 1.5G filter in 0.5m KOH. Furthermore, the obtained SHJ photocathode demonstrates excellent stability of at least 110h at 0.3V versus RHE. In this work, combining facile direct current magnetron sputtering with a solution treatment technique provides a novel design strategy, which lowers the threshold for preparing high-quality protective layer, and paves the way for developing economic, efficient, and stable SHJ-based PEC devices.

Boosting photoelectrocatalytic oxygen evolution activity of BiVO4 photoanodes via caffeic acid bridged to NiFeOOH

Bismuth vanadate (BiVO4) is a promising n-type photoanode material for photoelectrochemical (PEC) water splitting. However, its activity is impeded by poor charge carrier transport and sluggish oxygen evolution kinetics. In this study, we reports a Fe doping and caffeic acid (CA)/NiFeOOH (NiFe) modification with BiVO4 photoanode (NiFe/CA/Fe-BiVO4) to enhance the PEC water oxidation performance and stability. The modified BiVO4 demonstrates significant advantages in promoting the PEC performance and stability. Specifically, Fe doping via in-situ electro-deposition results in smaller crystal sizes, larger specific surface areas, and more exposed active sites. Furthermore, co-catalyst NiFe connects with Fe-BiVO4 through CA bridge facilitates a more uniform self-assembly distribution of NiFe on BiVO4 surface. The NiFe/CA/Fe-BiVO4 exhibits an excellent photocurrent density of 6.2 mA/cm2 at 1.23 VRHEand demonstrates good stability at 0.8 VRHE. In addition, the composite photoanode shows a high applied bias photon-to-current efficiency (ABPE) value of 2.15% at 0.65 VRHE. EPR and in-situ FTIR confirm the generation of superoxide active species (O2- and ·O2-) during the PEC water oxidation reaction.

Gamma-irradiated stibnite thin films set a remarkable benchmark performance for photoelectrochemical water splitting.

The study sets out to show the positive impact of sulfur vacancy engineering on the structural, morphological, optical, electrical, and photoelectrochemical (PEC) properties of Sb2S3 films synthesized using the spin coating technique. The produced films were exposed to γ-irradiation with different doses from 0 to 20 kGy. We have demonstrated the formation of sulfur vacancies and loss of oxygen content in the irradiated samples. XRD measurements revealed that all films exhibit a polycrystalline structure, and the crystallite size increases with the rising radiation dose, reaching the highest value of 87.4 nm measured for the Sb2S3 film irradiated with 15 kGy. The surface roughness of the irradiated samples increases with increasing γ-irradiation dose. The increase in surface roughness not only raises the active sites but enhances the conductivity of the Sb2S3 material as well. The wettability properties of the irradiated films were affected by γ-irradiation doses and the sample irradiated with 15 kGy exhibited the lowest hydrophobicity compared to others. The Hall measurements reveal that irradiated samples exhibit p-type semiconductor behavior. The optical band gap decreased progressively from 1.78 eV to 1.60 eV up to the irradiation dose of 15 kGy and slightly increased thereafter. The irradiated sample with 15 kGy showed a maximum photocurrent density of ca. 1.62 mA cm-2 at 0 V vs. reverse hydrogen electrode (RHE) under AM 1.5 G illumination with applied bias photon-to-current efficiency (ABPE) of 0.82% at 0.47 V vs. RHE, suggesting superior PEC water splitting performance compared to other samples. At 0 V vs. RHE and 648 nm, the incident photon current efficiency (IPCE) and absorbed photon current efficiency (APCE) of the photocathode irradiated with 15 kGy are significantly higher than those of the other photocathodes with values of 9.35% and 14.47%, respectively. Finally, Mott-Schottky measurement was also performed on all photocathodes to estimate their acceptor density and flat band potential.

Metal Phthalocyanine Sensitized Photoelectrochemical Cell Assembling with Azide‐Functionalized Reduced Graphene and Quaternary Metal Chalcogenide Composites

AbstractHere, photoelectrodes of photoelectrochemical (PEC) cells consisting of azide functionalized reduced graphene oxide (GO‐N3) and quaternary metal chalcogenide (CdZnNiSSe) composites sensitized with metal phthalocyanines (MPc, M: Co, Zn, Ti) are developed and then tested in hydrogen evolution reaction (HER). CdZnNiSSe/RGO‐N3 composite is deposited on an indium tin oxide (ITO) electrode through a facile electrodeposition technique and ITO/CdZnNiSSe/RGO‐N3 photoelectrode is constructed. Then, MPcs bearing terminal alkyne groups are connected to RGO‐N3 via the copper(I)‐catalyzed azide‐alkyne cycloaddition (click chemistry) technique to produce ITO/CdZnNiSSe/RGO‐N3‐MPc structures. Decoration of ITO/CdZnNiSSe/RGO‐N3 with MPcs is proposed to improve the charge transfer capability of the photoelectrode due to wide light absorption of MPcs from UV toward the IR region of the light spectrum. PECHER responses indicate that among the photoanodes bearing ZnPc, CoPc, and TiOPc, ITO/CdZnNiSSe/RGO‐N3‐ZnPc electrode exhibits the highest PECHER performance owing to the suitability of band structure of ZnPc. Sensitizing ITO/CdZnNiSSe/RGO‐N3 with ZnPc increases the photocurrent density from 5.0 to 7.3 mA cm−2 at 0.8 V vs. RHE and the applied bias photon to current efficiency (ABPE) enhances from 3.18 % to 3.87 %. This study provides a new approach for increasing the performance of photoanodes via sensitization with MPcs in photoelectrochemical hydrogen evolution processes for future applications.

Dissolution-Induced Surface Reconstruction of Ni0.95 Pt0.05 Si/p-Si Photocathode for Efficient Photoelectrochemical H2 Production.

Metal silicide/Si photoelectrodes have demonstrated significant potential for application in photoelectrochemical (PEC) water splitting to produce H2 . To achieve an efficient and economical hydrogen evolution reaction (HER), a paramount consideration lies in attaining exceptional catalytic activity on the metal silicide surface with minimal use of noble metals. Here, this study presents the design and construction of a novel Ni0.95 Pt0.05 Si/p-Si photocathode. Dopant segregation is used to achieve a Schottky barrier height as high as 1.0eV and a high photovoltage of 420mV. To achieve superior electrocatalytic activity for HER, a dissolution-induced surface reconstruction (SR) strategy is proposed to in situ convert surface Ni0.95 Pt0.05 Si to highly active Pt2 Si. The resulting SR Ni0.95 Pt0.05 Si/p-Si photocathode exhibits excellent HER performance with an onset potential of 0.45V (vs RHE) and a high maximum photocurrent density of 40.5mAcm-2 and a remarkable applied bias photon-to-current efficiency (ABPE) of 5.3% under simulated AM 1.5 (100mWcm-2 ) illumination. The anti-corrosion silicide layer effectively protects Si, ensuring excellent stability of the SR Ni0.95 Pt0.05 Si/p-Si photoelectrode. This study highlights the potential for achieving efficient PEC HER using bimetallic silicide/Si photocathodes with reduced Pt consumption, offering an auspicious perspective for the cost-effective conversion of solar energy to chemical energy.

Synergistic Effect of Co3(HPO4)2(OH)2 Cocatalyst and Al2O3 Passivation Layer on BiVO4 Photoanode for Enhanced Photoelectrochemical Water Oxidation

Bismuth vanadate (BVO) is regarded as an exceptional photoanode material for photoelectrochemical (PEC) water splitting, but it is restricted by the severe photocorrosion and slow water oxidation kinetics. Herein, a synergistic strategy combined with a Co3(HPO4)2(OH)2 (CoPH) cocatalyst and an Al2O3 (ALO) passivation layer was proposed for enhanced PEC performance. The CoPH/ALO/BVO photoanode exhibits an impressive photocurrent density of 4.9 mA cm−2 at 1.23 VRHE and an applied bias photon-to-current efficiency (ABPE) of 1.47% at 0.76 VRHE. This outstanding PEC performance can be ascribed to the suppressed surface charge recombination, facilitated interfacial charge transfer, and accelerated water oxidation kinetics with the introduction of the CoPH cocatalyst and ALO passivation layer. This work provides a novel and synergistic approach to design an efficient and stable photoanode for PEC applications by combining an oxygen evolution cocatalyst and a passivation layer.

Statistical Design-Guided Synthesis of Nanoarchitectonics of High-Performance NiFeMoN Electrocatalyst through Facile One-Step Magnetron Sputtering.

This study presents an innovative, statistically-guided magnetron sputtering technique for creating nanoarchitectonics of high-performing, NiFeMoN electrocatalysts for oxygen evolution reaction (OER) in water splitting. Using a central composite face-centered (CCF) design, 13 experimental conditions are identified that enable precise optimization of synthesis parameters through response surface methodology (RSM), confirmed by analysis of variance (ANOVA). The statistical analysis highlighted a interaction between Mo% and N% in the nanostructured NiFeMoN and found optimizing values at 31.35% Mo and 47.12% N. The NiFeMoN catalyst demonstrated superior performance with a low overpotential of 216mV at 10mA cm-2 and remarkable stability over seven days, attributed to the modifications in electronic structure and the creation of new active sites through Mo and N additions. Furthermore, the NiFeMoN coating, when used as a protective layer for a Si photoanode in 1m KOH, achieved an applied-bias photon-to-current efficiency (ABPE) of 5.2%, maintaining stability for 76 h. These advancements underscore the profound potential of employing statistical design for optimizing synthesis parameters of intricate catalyst materials via magnetron sputtering, paving the way for accelerated advancements in water splitting technologies and also in other energy conversion systems, such as nitrogen reduction and CO2 conversion.

High-performance photoelectrochemical cells with MoS2 nanoflakes/TiO2 photoanode on 3D porous carbon spun fabric

A solar-driven photoelectrochemical (PEC) cell is emerging as one of the promising clean hydrogen generation systems. Engineering of semiconductor heterojunctions and surface morphologies of photoelectrodes in a PEC cell has been a primitive approach to boost its performance. This study presents that a molybdenum disulfide (MoS2) nanoflakes photoanode on 3-dimensional (3D) porous carbon spun fabric (CSF) as a substrate effectively enhances hydrogen generations due to sufficiently enlarged surface area. MoS2 is grown on CSFs utilizing a hydrothermal method. Among three different MoS2 coating morphologies depending on the amount of MoS2 precursor and hydrothermal growth time, film shape MoS2 on CSFs had the largest surface area, exhibiting the highest photocurrent density of 26.48 mA/cm2 and the highest applied bias photon-to-current efficiency (ABPE) efficiency of 5.32% at 0.43 VRHE. Furthermore, with a two-step growth method of sputtering and a subsequent hydrothermal coating, continuous TiO2/MoS2 heterojunctions on a porous CSF further promoted the photoelectrochemical performances due to their optimized bandgap alignments. Enlarged surface area, enhanced charge transfer, and utilization of visible light enable a highly efficient MoS2/TiO2/CSF photoanode with a photocurrent density of 33.81 mA/cm2 and an ABPE of 6.97 % at 0.87 VRHE. The hydrogen generation amount of the PEC cell with MoS2/TiO2/CSF photoanode is 225.4 μmol/L after light irradiation of 60 s.

MoO3/BiVO4 heterojunction modified with cobalt-manganese layered double hydroxide cocatalyst for photoelectrochemical water oxidation

To improve the charge recombination and poor oxygen evolution reaction (OER) kinetics of BiVO4, in this paper, a high-performance CoMn-LDH/MoO3/BiVO4 photoanode was synthesized by a simple electrodeposition and calcination method. CoMn-LDH/MoO3/BiVO4 shows a photocurrent density of 3.78 mA cm−2 at 1.23 V vs. RHE, which is 3.78 times higher than that of pure BiVO4 with negative shift onset potentials of 330 mV. The maximum applied bias photon-to-current efficiency (ABPE) and incident photon-to-current conversion efficiency (IPCE) are 1.24 % and 55.5 %, respectively, which are 13.8 and 12.5 times higher than those of pure BiVO4. In-depth studies demonstrate that the MoO3/BiVO4 heterojunction can better drive the transfer of photogenerated carriers and suppress bulk charge recombination, CoMn-LDH improves the OER kinetics and broadens the absorption of visible light, their synergistic effect significantly enhances charge separation and light harvesting of BiVO4. This work provides a facile electrodeposition method to fabricate highly efficient photoanodes for solar-driven water splitting.

Substitutional Cd Dopant as Photohole Transfer Mediator Boosting Photoelectrochemical Solar Energy Conversion of 2D Cd-ZnIn2 S4 Photoanode.

Fast recombination dynamics of photocarriers competing with sluggish surface photohole oxidation kinetics severely restricts the photoelectrochemical (PEC) conversion efficiency of photoanode. Here, a defect engineering strategy is developed to regulate photohole transfer and interfacial injection dynamics of 2DZnIn2 S4 (ZIS). Via selectively introducing substitutional Cd dopant at Zn sites of the ZIS basal plane, energy band structure and surface electrochemical activity are successfully modulated in the Cd-doped ZIS (Cd-ZIS) nanosheet array photoanode. Comprehensive characterizations manifest that a shallow acceptor level induced by Cd doping and superior electrochemical activity make surface Cd dopants simultaneously act as capture centers and active sites to mediate photohole dynamics at the reaction interface. In depth photocarrier dynamics analysis demonstrates that highly efficient photohole capture of Cd dopants brings about effective space separation of photocarriers and acceleration of surface reaction kinetics. Therefore, the optimum 2D Cd-ZIS achieves excellent PEC solar energy conversion efficiency with a photocurrent density of 5.1mA cm-2 at 1.23 VRHE and a record of applied bias photon-to-current efficiency (ABPE) of 3.0%. This work sheds light on a microstructure design strategy to effectively regulate photohole dynamics for the next-generation semiconducting PEC photoanodes.

Enhancing the hydrogen photo-production using zinc oxide films doped with iron, tin, and aluminum

Hydrogen is recognized as the most promising renewable energy source and can be efficiently produced through water photo-electrolysis green process. This study investigates the performance of ZnO nanorods doped with Fe, Al, and Sn at a 2 % molar ratio for hydrogen photo-production. The films were prepared using a combination of successive ionic layer adsorption and reaction (SILAR) and chemical bath deposition (CBD) methods. X-ray diffraction (XRD) analysis confirmed the hexagonal structure of the doped ZnO films with preferential growth along the (002) orientation, while energy-dispersive X-ray spectroscopy (EDX) confirmed their high purity. The doping with Al maintains the ZnO nanorods morphology while Fe, and Sn doping induced changes to overlapped nanoflakes/nanoflowers morphology. Optical analysis revealed a clear trend in the energy band gap, with Fe-ZnO film exhibiting the lowest value (2.95 eV), followed by Al-ZnO (3.03 eV), Sn-ZnO (3.07 eV), and ZnO (3.11 eV). The Fe-ZnO film also demonstrated the best performance as a photoelectrode for hydrogen generation, achieving optimized incident photon-to-current efficiency (IPCE) and applied bias photon-to-current efficiency (ABPE) values of 1.45 % and 0.20 % respectively, under 500 nm monochromatic illumination, with high reproducibility, and durability. These findings represent one step forward to developing ZnO-doped photoanodes for efficient and sustainable hydrogen green production.

Combining heterointerface/surface oxygen vacancies engineering of bismuth oxide to synergistically improve its solar water splitting performance

Solar-powered photoelectrochemical (PEC) water splitting is recognized as a strategy for addressing fossil resource and global warming concerns. The purpose of this paper is to demonstrate for the first time a facile method to fabricate dendritic nanostructured (DN) Bi:Bi2O3 heterointerface engineering junctions that possess abundant surface oxygen vacancies (OVs, DN Bi:Bi2O3-OVs/FTO), with outstanding PEC performance. The surface OVs serve as shallow donors and active reaction sites, whereas the Bi-metal bridges are used for fast electron transport. Furthermore, surface OVs can enhance the surface features of Bi:Bi2O3 heterointerfaces and boost their electrical conductivity and donor density. This greatly enhances electrolyte ion and electron mobility, resulting in rapid water oxidation reactions at the Bi:Bi2O3/electrolyte interfaces. By combining the Bi:Bi2O3 heterointerface junction and surface OVs, we are able to create an effective photoanode with 95 % charge injection efficiency, applied bias photon-to-current efficiency (ABPE) of 0.112 %, and a photocurrent response of 0.334 mA.cm−2 at 1.23 V vs. the reversible hydrogen electrode (RHE), which represents improvements of about 4.5 and 10 folds over that of pure DN Bi2O3 photoanode. It is possible to construct a variety of unique nanostructured electrodes with adjustable optical and electronic properties to be used in solar cells, energy storage, and PEC applications.

Cooperative catalytic behavior of Bi2S3 and ZrO2 nanoparticles on Bi2O3 photoanodes for promoted stability and solar driven photoelectrochemical hydrogen production

Photoelectrochemical water splitting via solar energy consumption is recognized as a strategy to address fossil resources and global warming concerns. Here, we reveal the co-catalytic effect of ZrO2 and Bi2S3 nanoparticles on nanostructured bismuth oxide (Bi2O3) electrodes synthesized by electrochemical deposition and an in-situ photoelectrochemical transformation process to fabricate heterostructured Bi2S3/Zr-Bi2O3 electrodes. The cooperative interaction between ZrO2 and Bi2S3 nanoparticles leads to a 12-fold enrichment in Bi2O3 electrode photocurrent density. The cooperation between the above features has considerably reduced the photocurrent onset potential, and improved the separation of charge carriers and optical features of the Bi2O3:Zr/Bi2S3 electrodes resulting in attaining an applied bias photon-to-current efficiency (ABPE) of 1.22 %. Through these examinations, it is possible to create a variety of nanostructured electrode films with adjustable optical and electronic features for solar cells, electrochemical energy storage, and PEC.

Synthesis of CuInS2 thin film photocathode with variation of sulfurization sources and Pt-In2S3 modification for photoelectrochemical water splitting

CuInS2 thin films have been successfully synthesized from the electrodeposition of copper (Cu), indium (In), and sulfurization on a molybdenum glass substrate as a water splitting photocathode. The effect of various sources of sulfurization with thiourea, sulphur, and H2S and modification with Pt-In2S3 on the character and performance of the material was observed. The success of the synthesis was confirmed by the typical peaks of 28.2, 46.8, and 55.4° on XRD, the presence of Cu, In, S elements on SEM-EDX analysis, the appearance of peaks of 298 cm−1 on Raman analysis, and the detection peaks of Cu 2p, In 3d, and S 2p with XPS analysis. Meanwhile, performance effectiveness and photoelectrochemical properties were analysed with photocurrent linear sweep voltammetry (LSV), applied bias photon-to-current efficiency (ABPE), and incident photon-to-current conversion efficiency (IPCE). Variations of sulfurization sources give different character and photocurrent results due to differences in the existing reaction mechanisms. While the modification treatment with Pt-In2S3 increased the resulting photocurrent. Sulfurization with H2S and modification of Pt-In2S3 gave the best results with a photocurrent of 18 mA cm−2, an efficiency of 3% ABPE, 47.2% IPCE, was evolved 467 μmol H2 and 230,1 μmol O2. This shows good potential as a water splitting material to produce environmentally friendly hydrogen fuel.

Integration of Ag Plasmonic Metal and WO3/InGaN Heterostructure for Photoelectrochemical Water Splitting.

In this study, a Ag/WO3/InGaN hybrid heterostructure was successfully developed by sputtering and molecular beam epitaxy techniques, to obtain unique Ag nanospheres adorned with cauliflower-like WO3 nanostructure over the InGaN nanorods (NRs). Exploiting the localized surface plasmon resonance of Ag, the Ag/WO3/InGaN heterostructure exhibited superior photoabsorption ability in the visible region (400-700 nm) of the solar spectrum, with a surface plasmon resonance band centered around 440 nm. Comprehensive analysis through photoluminescence spectroscopy, photocurrent measurements, and electrochemical impedance spectroscopy revealed that the Ag/WO3/InGaN hybrid heterostructure significantly enhances the charge carrier separation and transfer kinetics leading to improved overall photoelectrochemical (PEC) performance. The photocurrent density of the Ag/WO3/InGaN photoanode is 1.17 mA/cm2, which is about 2.72 times higher than that of pure InGaN NRs under visible light irradiation. The photoanode exhibited excellent stability for about 12 h. From the study, it has been found that the maximum applied bias photon-to-current efficiency (ABPE) is ∼1.67% at the applied bias of 0.6 V. The improved PEC water splitting efficiency of the Ag/WO3/InGaN photoanode is attributed to the synergistic effects of localized surface plasmon resonance (LSPR), efficient charge carrier separation and transport, and the presence of a Schottky junction. Consequently, the plasmonic metal-assisted heterojunction-based semiconductor Ag/WO3/InGaN demonstrates immense potential for practical applications in photoelectrochemical water splitting.

High efficiency Bi2S3/Bi2MoO6/TiO2 photoanode for photoelectrochemical hydrogen generation

The ternary Bi2S3/Bi2MoO6/TiO2 photoanode with waterfall-type energy level structure was engineered firstly for photoelectrochemical (PEC) water-splitting hydrogen generation. The results of XRD, SEM, EDS and TEM illustrated that Bi2MoO6 flakes were self-assembled in flower-ball shape on TiO2 nanoparticles via solvothermal reaction and the “green” Bi2S3 quantum dots (QDs) distributed in Bi2MoO6 flake edge through in-situ anion exchange process. UV-Vis. DRS and PL spectra showed that Bi2S3 QDs broadened the response range in visible and near-infrared region and waterfall-type energy level structure is helpful to inhibit the recombination of photo-generated electrons and holes. EIS spectra proved that Bi2S3 QDs amount and size can affect significantly photoanode/electrolyte interface transfer resistance and the minimum is down to 14.20 kΩ/cm2. The PEC device comprised with Bi2S3/Bi2MoO6/TiO2 photoanode, Ag/AgCl reference electrode, Pt counter electrode and Na2SO4 solution electrolyte exhibited high performance for water splitting: the photocurrent density maximum is 21.42 mA/cm2 and the applied bias photon-to-current efficiency (ABPE) maximum is 20.8%. However, the stability of PEC cell samples is a little poor and ABPE declines to 7.28% after 12 h. The ternary Bi2S3/Bi2MoO6/TiO2 photoanode with waterfall-type energy level structure can be also employed in other photovoltaic devices besides PEC cells.

Investigation of p-type spinel structure as photocathode thin films under neutral pH condition

Owing to the special electronic structure and earth-abundance, spinel structure-based oxides (AB2O4, A = Ni, Cu and B= Co, Fe) have considerable attractive for photo/electro/catalysis. In this work, AB2O4 thin films were synthesized via the spray pyrolysis method on FTO substrates and annealed at 550 °C for 1 h. The structural, morphology, optical and photoelectrochemical properties were studied. The crystalline results show that the thin films have a cubic spinel structure, and the morphology results show a fine grainy surface. The photoelectrochemical measurements in terms of photocurrent density, Incident Photon-to-Current Efficiency (IPCE) and applied bias photon-to-current efficiency (ABPE) were investigated for all samples under neutral pH condition. The results of photocurrent density were (109, 41, 28, 25) μA/cm2 and the IPCE results at 530 nm were 3.05% > 1.52% > 1.42% > 1.32% for CuCo2O4, NiCo2O4, CuFe2O4 and NiFe2O4 respectively under AM 1.5G (100 mW/cm−2) and applied bias −0.5 V. The band structure including the conduction/valence band was determined by Mott-Schottky plot revealing the ability of hydrogen production from neutral water.

Modulating Oxygen Vacancies in Lead Chromate forPhotoelectrocatalytic Water Splitting.

Although modulating oxygen vacancies in semiconductors has attracted broad interest in photocatalysis and photoelectrocatalysis, identifying the intrinsic roles of oxygen vacancies on photoelectrocatalytic properties is often elusive. In this work, the oxygen vacancies in a typical semiconductor lead chromate (PbCrO4 ) are regulated via controlling the oxygen chemical potentials of O-poor and O-rich post-annealing atmospheres. Oxygen vacancies identified in PbCrO4 can introduce electronically shallow energy levels and deep energy levels owing to the symmetry difference of oxygen atoms in the structure. A higher population of deep energy levels created under O-poor atmosphere induces the formation of more surface trapped states, resulting in a higher photovoltage for charge separation. Meanwhile, the existence of surface trapped states can significantly improve the charge injection efficiency of the PbCrO4 photoanode and enhance the water oxidation activity. By modulating oxygen vacancies in the PbCrO4 photoanode, a photocurrent density of 3.43mA cm-2 at 1.23V vs reversible hydrogen electrode (RHE) under simulated AM1.5G is acheived. Further passivation of surface trapped states and introducing the water oxidation cocatalyst CoPi lead to a record applied bias photon-to-current efficiency (ABPE) of 1.12%. This work provides a guide to understand the mechanism of oxygen vacancies in oxide-based semiconductor photocatalysis and photoelectrocatalysis.

Efficient BiVO4-Based Photoanode with Chemically Precipitated Hierarchical Cobalt Borate (Co-Bi) Oxygen Evolution Reaction Catalysts.

The integration of cobalt borate OER catalysts with electrodeposited BiVO4-based photoanodes through a simple drop casting technique was shown to provide an improvement of the photoelectrochemical performance of electrodes under simulated solar light. Catalysts were obtained by chemical precipitation mediated by NaBH4 at room temperature. Scanning electron microscopy (SEM) investigation of precipitates showed a hierarchical structure with globular features covered in nanometric thin sheets providing a large active area, whereas X-ray diffraction (XRD) and Raman spectroscopy highlighted their amorphous structure. The photoelectrochemical behavior of samples was investigated by linear scan voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques. The amount of particles loaded onto BiVO4 absorbers was optimized by variation of the drop cast volume. The enhancement of photocurrent generation by Co-Bi-decorated electrodes with respect to bare BiVO4 was observed with an increase from 1.83 to 3.65 mA/cm2 at 1.23 V vs RHE under AM 1.5 simulated solar light, corresponding to a charge transfer efficiency of 84.6%. The calculated maximum applied bias photon-to-current efficiency (ABPE) value for optimized samples was 1.5% at 0.5 V applied bias. Under constant illumination at 1.23 V vs RHE, a depletion of photoanode performances was observed within an hour, likely due to the detachment of the catalyst from the electrode surface.