Incident Photon-to-current Efficiency Research Articles

Photo-assisted charge/discharge of a secondary cell of α-Fe2O3/Prussian blue–based electrodes

In this work, an assembly of FTO/α-Fe2O3/PB|M+ electrolyte|PB/α-Fe2O3/FTO (M+ = Li+, Na+, K+) secondary photocell was done to improve the charge capacity in the presence of illumination. Our previous results with these electrodes demonstrated the possibility of transferring photogenerated carriers from hematite to Prussian blue. This cell was characterized by incident photon-to-current efficiency (IPCE) and galvanostatic charge/discharge measurements under illumination and compared in darkness. A higher IPCE when potassium ions are employed in the cell was founded, which suggests an easy insertion/desertion of these ions inside/outside of the hexacyanometallate framework, related to the more compact water coordination sphere for this ion. The voltage cell increased when the system was charged under illumination, indicating an increase in the oxidation/reduction of iron centers in the hexacyanometallate structure due to the increase of photogenerated carriers in hematite. The cell’s specific capacity reaches around 12% of the theoretical capacity, with a voltage close to the theoretical (1.5 V) and about 95% of coulombic efficiency when the cell was charged and discharged at longer times (8 h).

Flexible polypyrrole activated micro-porous paper-based photoanode for photoelectrochemical water splitting

We herein demonstrate polypyrrole decorated micro-porous laboratory filter paper (PFP) as photoanode (PA) for efficient and stable water splitting. The straddling band position with water redox and the measured band gap of ~1.98 eV, make these PFP-PAs effective for water splitting reactions. The results manifest excellent photo-anodic PEC activity of these PFP-PAs, yielding a photocurrent density of ~9.5 mA/cm2 (at 1.23 V vs. RHE) in a three-electrode configuration. The incident photon-to-current efficiency (IPCE) and applied bias photon-to-current efficiency (ABPE) was measured to be 43.19% and ~1%, respectively. Moreover, the robustness of these flexible PFP-PAs was visualized by the provided stability for more than ~160 min in alkaline conditions. The current study provides a proof-of-concept for the realization of a cost-effective, flexible, and efficient paper-based artificial catalyst (like a natural leaf) for solar-driven water splitting.

Function of Porous Carbon Electrode during the Fabrication of Multiporous-Layered-Electrode Perovskite Solar Cells

We demonstrate the effect of sheet conductivity and infiltration using the example of two graphite types, showing that, in general, the graphite type is very important. Amorphous and pyrolytic graphite were applied to carbon electrodes in fully printable carbon-based multiporous-layered-electrode perovskite solar cells (MPLE-PSCs): <glass/F-doped SnO2/compact-TiO2/porous-TiO2+perovskite/porous-ZrO2+perovskite/porous-carbon+perovskite>. The power conversion efficiency (PCE) using amorphous graphite-based carbon (AGC) electrode was only 5.97% due to the low short-circuit photocurrent density (Jsc) value, which was due to the low incident photon-to-current efficiency (IPCE) in the short wavelength region caused by the poor perovskite filling into the porous TiO2-ZrO2 layers. Conversely, using pyrolytic graphite-based carbon (PGC) electrode, Jsc, open-circuit photovoltage (Voc), fill factors (FF), and PCE values of 21.09 mA cm−2, 0.952 V, 0.670, and 13.45%, respectively, were achieved in the champion device. PGC had poorer wettability and a small specific surface area as compared with AGC, but it had better permeability of the perovskite precursor solution into the porous TiO2/ZrO2 layers, and therefore a denser filling and crystallization of the perovskite within the porous TiO2/ZrO2 layers than AGC. It is confirmed that the permeability of the precursor solution depends on the morphology and structure of the graphite employed in the carbon electrode.

Efficient photoselectrochemical hydrogen production utilizing of APbI 3 (A = Na, Cs, and Li) perovskites nanorods

This study investigated the structural, morphological, and optical absorption of three separate perovskites (NaPbI3, CsPbI3, and LiPbI3) developed by a low-cost and massive hydrothermal production technique. For all samples, X-ray diffraction (XRD) measurement demonstrated the growth of perovskites in the hexagonal phase along (002) orientation. From the scanning electron microscope (SEM) analyses, the perovskites have mixed morphologies between nano/micro rods and nano/microdiscs. In the visible field, NaPbI3 demonstrated stronger light absorption than CsPbI3 and LiPbI3. The prepared perovskites were tested under visible light as working electrodes for water splitting reactions using Na2S2O3 electrolyte. With 2.76% at 405 nm, the NaPbI3 perovskite photoelectrode in accordance with its optical properties showed the highest incident photon-to-current efficiency (IPCE) among the studied perovskites. Also, the NaPbI3 perovskite demonstrated higher PEC performance with an H2 production rate of 38 μmolh−1 cm−2 than many other reported perovskites. The studied perovskites have high stability and reproductivity for the photoelectrochemical H2 production.

Metal-Doped Bipyridine-Linked Covalent Organic Framework Nanosheets As a Novel Platform for Photoelectrocatalysts

Light-driven conversion of chemical substances has attracted much attention with respect to the photogeneration of valuable chemicals and the photodegradation of pollutants. Covalent organic frameworks (COFs), which are crystalline porous polymers, have attracted much attention as novel platforms for photo-energy conversion materials because of their unique physiological properties, including their nano-porous structure, high design flexibility and visible light absorption. In addition, as COFs possess abundant hetero atoms with a lone electron pair, such as N, O and S, they can support metal atoms via coordination bonds and exhibit various functions originated from supported metals. For example, our group has recently demonstrated metal-doped COFs (M-COFs) exhibited various unique elctrocatalytic functions depending on the metal species. Cu- and Ni-doped COFs serve as the electrocatalysts for oxygen reduction reaction (ORR) [1] and carbon dioxide reduction (CRR) [2], respectively. In this study, we newly synthesized various metal-doped bipyridine-linked COFs (bpy-COF) and evaluated their photoelectrocatalytic activity. First, the details in the photo-induced charge transfer process were investigated using photoelectrochemical action spectrum, photoluminescence and in situ spectroscopy by employing the ORR mediated by Cu sites doped in bpy-COF (Cu-bpy-COF) as a model system. We subsequently attempted to expand metal-doped COFs as the photo electrocatalysts for CRR toward the application in artificial photosynthesis.First, we physically characterized our Cu-bpy-COF using various X-ray technics. The X-ray diffraction (XRD) pattern of Cu-bpy-COF exhibited a peak at 2q = 3.5° and 26.5°, which are assignable to (100) and (001), respectively. These XRD patterns indicated that the COFs have the microporous structure. The surface elemental composites calculated by X-ray photoelectron spectroscopy (XPS) shows that the atomic ratio of Cu atom was 1.8 %, and Cu/N ratio was 0.13. Then, we analyzed Cu-2p XPs and XANES spectra to determine the oxidation state of Cu atoms. The Cu 2p3/2 XPS peaks generated by Cu-bpy-COF at 932.7 eV corresponded to the Cu(II). The Cu K-edge XANES spectra show that the absorption edges of the Cu-bpy-COF were 8980 eV, which is similar to that of CuO. These results indicate that that the Cu(II) oxidation state was dominant in Cu-bpy-COF.Then, we investigated the photoelectrochemical ORR property of Cu-bpy-COF. The photocurrent was measured under the monochromated light. Interestingly, the value of the cathodic photocurrent corresponded with ORR was drastically increased by the deposition of Cu in bpy-COF. The incident-photon-to-current-efficiency (IPCE) was also calculated. The resulting IPCE for Cu-bpy-COF clearly corresponded to the absorption spectrum of Cu-bpy-COF. These results clearly indicate that the photocurrent was originated due to the photo absorption of Cu-bpy-COF. Then, we investigated the detailed electron transfer mechanism of Cu-bpy-COF in the presence of O2. Photoluminescence and gas-phase in situ X-ray absorption spectra show that the photo-excited electrons in the bpy-COF film were transferred to oxygen via the Cu atom. The remained holes in the valence band reached to the ITO electrode, generating the cathodic photocurrent. At the conference, we will also present the photoelectrocatalytic CO2 reduction reactions (CRR) using M-COF for the application toward artificial photosynthesis.Reference:[1] K.Iwase, T.Yoshioka, S.Nakanishi, K.Hashimoto, K.Kamiya, Angew. Chem. Int. Ed. 2015, 54, 11068-11702.[2] P.Su, K Iwase, T.Harada, K.Kamiya, S.Nakanishi., Chemical Science. 2018, 9, 3941-3947.[3] K.Dey, M.Pal, K.C.Rout, S.Kunjattu, A.Das, R.Mukherjee, U.K.Kharul, R. Banerjee. J. Am. Chem. Soc. 2017, 139, 13083-13091.

Near-Infrared Phosphorescence Emission of Binuclear Mn(II) Based Metal-Organic Framework for Efficient Photoelectric Conversion.

The development of metal-organic framework (MOF) based room-temperature phosphorescence (RTP) materials has raised extensive concern owing to their widespread applications in the field of anti-counterfeiting, photovoltaics, photocatalytic reactions, and bio-imaging. Herein, one new binuclear Mn(II) based 3D MOF [Mn2(L)(BMIB)·(H2O)] (1) (H5L = 3,5-bis(3,5-dicarboxylphenxoy) benzoic acid, BMIB = tran-4-bis(2-methylimidazolyl)butylene) has been synthesized by a facile hydrothermal process. In 1, the protonated BMIB cations show infinite π-stacking arrangement, residing in the channels of the 3D network extended by L ligand and binuclear Mn(II) units. The orderly and uniform host-guest system at molecular level emits intense white light fluorescence and long-lived near infrared phosphorescence under ambient conditions. These photophysical processes were well-studied by density functional theory (DFT) calculations. Photoelectron measurements reveal high photoelectron response behavior and incident photon-to-current efficiency (IPCE).

Y-shaped organic dyes with D2–π–A configuration as efficient co-sensitizers for ruthenium-based dye sensitized solar cells

Three new Y-shaped organic dyes, coded CD1–3, have been synthesized for dye-sensitized solar cells (DSSCs). They have a D2–π–A configuration and been molecularly engineered to modulate the spectral properties and energy levels. For comparison, a D–π–A type sensitizer with one donor group (CD4) is synthesized as well. We have performed a combined experimental and theoretical investigation of their optical, electrochemical, photovoltaic, geometrical and electronic characteristics. These new Y-shaped dyes display intensive UV–vis absorption with high molar extinction coefficients. So their roles as co-sensitizers for ruthenium-based DSSCs are further evaluated. As a consequence, the co-sensitized devices exhibit improved power conversion efficiencies (PCEs) in the range of 7.24–7.96% due to the enhanced short-circuit photocurrents (Jsc) and open-circuit voltages (Voc), which are higher than the DSSCs sensitized with N719 (PCE = 6.75%) or Z907 (PCE = 6.55%) alone. In addition, the mechanisms of these improvements have been elucidated by incident photon to current efficiency (IPCE) and electrochemical impedance spectroscopy (EIS) studies. The Jsc is improved because CD1–3 can compensate for the photocurrent loss by I−/I3−; while the Voc is enhanced because the electron recombination process is retarded by these Y-shaped dyes upon co-sensitization.

Zn0.5Cd0.5S nanoparticles modified TiO2 nanotube arrays with efficient charge separation and enhanced light harvesting for boosting visible-light-driven photoelectrochemical performance

Vertically aligned TiO2 nanotube arrays (TiO2 NTAs) modified with uniformly dispersed Zn0.5Cd0.5S (ZCS) nanoparticles as novel heterojunction photoanodes have been prepared for the first time through a typical two-step anodization followed by successive ionic layer adsorption and reaction (SILAR) process. The photoelectrochemical (PEC) performance of ZCS nanoparticles modified TiO2 NTAs (TiO2 NTAs/ZCS) photoanodes strongly depends on the loading amount of ZCS. By optimizing the amount of ZCS in TiO2 NTAs/ZCS photoanodes, the highest photocurrent density of 10.95 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE) under visible-light illumination is obtained. The optimum photoconversion efficiency is up to 4.54% at 0.49 V vs. RHE, while it is only 0.04% at 0.67 V vs. RHE for bare TiO2 NTAs photoanode. The maximum incident photon-to-current efficiency (IPCE) value in TiO2 NTAs/ZCS photoanodes is 65.0% at 390 nm, which is 2.3-fold as high as that of bare TiO2 NTAs photoanode (28.1% at 340 nm). The formed heterostructure structure between TiO2 NTAs and ZCS possesses a typical type-II band alignment, which is beneficial to drastically promote the improvement of PEC performance due to the efficient charge separation and increased light harvesting.

Heteroleptic Tin-Antimony Sulfoiodide for Stable and Lead-free Solar Cells

Summary The quaternary chalcogenide halides of group IV and V elements have attracted much attention due to their interesting semiconducting properties as well as a suitable band gap for solar cells. Here, for the first time, we report on solar cells using tin-antimony sulfoiodide (Sn2SbS2I3). Sn2SbS2I3 solar cells were fabricated using a chemical single-step deposition process with a solution containing a SbCl3-thiourea complex and SnI2 with the configuration of TiO2 and poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-enzothiadiazole)] as the electron- and hole-transporting layers, respectively. The best-performing cell exhibits a power conversion efficiency of 4.04% under the illumination of standard AM 1.5G conditions (100 mW cm−2). These unencapsulated cells exhibited good stabilities at 80% relative humidity, 85°C in air, and under illumination, respectively. These results provide guidelines for fabrication of lead-free heteroleptic perovskite solar cells by hosting divalent or combinations of monovalent and trivalent metal cations.

Activation of Weak Monochromic Photocurrents by White Light Irradiation for Accurate IPCE Measurements of Carbon-Based Multi-Porous-Layered-Electrode Perovskite Solar Cells

Variations in the time courses of the activation of fully-printable carbon-based multi-porous-layered-electrode perovskite solar cells (MPLE-PSCs) can lead to differences between the photocurrent density (Jsc) values obtained from one-sun photocurrent density-voltage (J–V) measurements and from incident-photon-to-current efficiency (IPCE) integration when using monochromic light. In the present work, the Jsc calculated from IPCE data was initially equal to half that obtained from one-sun J–V measurements. However, equivalent values were obtained when the J–V measurements were performed after 10 min of irradiation by a white light LED from the side of the device. This finding will be very important with regard to permitting accurate photovoltaic evaluation of MPLE-PSCs in the future.

Mixed zinc–cobalt oxide coatings for photocatalytic applications

In this paper, zinc–cobalt oxide coatings on fluorine-doped tin-oxide (FTO) coated glass substrate were synthesized by a simple three-step process including chemical precipitation, thermal decomposition at 773 K for 2 h, and spin-coating techniques. The aim of this work was to synthesize mixed Zn–Co oxides coatings that form a p–n heterostructure and explore the influence of morphology on its photoelectrochemical properties. Four different coatings were formed varying the rotation speed (1000, 1200 RPM) and Zn:Co ratio (1:2 and 1:1). The structure and morphology were investigated by X-ray diffraction (XRD) technique, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The analysis revealed that due to higher Co amount ZnCoO1 (Zn:Co 1:2, 1000 RPM) and ZnCoO2 (Zn:Co 1:2, 1200 RPM) coatings which consist of spinel-type oxides ZnCo2O4, Co3O4, they are more uniform, ~ 442 nm thick and contain lamellar morphology. Meanwhile, changing Zn:Co ratio to 1:1 in ZnCoO3 (1000 RPM) and ZnCoO4 (1200 RPM) leads to spinel (ZnCo2O4) formation, alters the morphology to granular, more rough, porous, uneven with 'hills' and 'valleys', and results in ~ 650 nm thick coatings. Photoelectrochemical activity tests proved high activity of deposited coatings at anodic potentials. The highest active surface area of 0.26 cm2 and the highest activity were reached for ZnCoO3 coating: at 0.85 V vs. Ag,AgCl|KCl(sat) the incident-photon-to-current efficiency (IPCE) was 37% and the applied bias photon-to-current (ABPE) efficiency was − 5.91%. Thus, synthesized ZnCo2O4 coating can be used as a future material for oxygen evolving reaction (OER).

Drop-cast tungsten trioxide semiconducting films in Photoelectrocatalysis

Polycrystalline, monoclinic, uniform WO 3 films of up to 2.5 μm thickness were prepared by drop casting onto F:SnO 2 /glass using as precursor peroxo-tungstic acid and polyethylene glycol in water, and firing in air at 520 °C. The n-type WO 3 layers produced photocurrents in junctions with aqueous electrolytes. Under depletion conditions, IPCEs (incident photon to current efficiencies) of up to 0.7 at 365 nm and 0.2 at 405 nm were obtained. The photosensitivity of WO 3 thin films extended into the visible range up to 470 nm. The photoelectrocatalytic activity of such layers was examined using the azo-dye “acid orange 7” (AO7) as a model pollutant. Degradation of AO7 was carried out under backside UVA broadband illumination of electrodes of 62 cm 2 active surface area, in a parallel plate flow-through reactor equipped with a stainless steel counter electrode under electrical bias of 1.1–1.3 V. Rapid recirculation of the electrolyte was maintained in order to derive true kinetic parameters. During illumination, the concentration of AO7 (initial value 1 mM) decreased exponentially. At the beginning of a degradation experiment the Faradaic efficiency, f 0 , was 0.48. • Polycrystalline WO 3 films of up to 2.5 μm thickness were prepared by drop casting onto F:SnO 2 /glass peroxo-tungstic acid and polyethylene glycol in water, and firing in air at 520 °C. • The n-type WO 3 layers produced photocurrents up to 470 nm in junctions with aqueous electrolytes. • Photoelectrocatalytic activity of such layers was examined using the azo-dye “acid orange 7” (AO7) under backside UVA illumination of electrodes of 62 cm 2 active surface area, in a parallel plate flow-through reactor under electrical bias of 1.1–1.3 V. • During UVA illumination, the concentration of AO7 (initial value 1 mM) decreased exponentially. The initial Faradaic efficiency, f 0 , was 0.48.

Cobalt-Doped ZnO Nanorods Coated with Nanoscale Metal-Organic Framework Shells for Water-Splitting Photoanodes.

Developing highly efficient and stable photoelectrochemical (PEC) water-splitting electrodes via inexpensive, liquid phase processing is one of the key challenges for the conversion of solar energy into hydrogen for sustainable energy production. ZnO represents one the most suitable semiconductor metal oxide alternatives because of its high electron mobility, abundance, and low cost, although its performance is limited by its lack of absorption in the visible spectrum and reduced charge separation and charge transfer efficiency. Here, we present a solution-processed water-splitting photoanode based on Co-doped ZnO nanorods (NRs) coated with a transparent functionalizing metal–organic framework (MOF). The light absorption of the ZnO NRs is engineered toward the visible region by Co-doping, while the MOF significantly improves the stability and charge separation and transfer properties of the NRs. This synergetic combination of doping and nanoscale surface functionalization boosts the current density and functional lifetime of the photoanodes while achieving an unprecedented incident photon to current efficiency (IPCE) of 75% at 350 nm, which is over 2 times that of pristine ZnO. A theoretical model and band structure for the core–shell nanostructure is provided, highlighting how this nanomaterial combination provides an attractive pathway for the design of robust and highly efficient semiconductor-based photoanodes that can be translated to other semiconducting oxide systems.

Improving Photoelectrochemical Properties of Anodic WO3 Layers by Optimizing Electrosynthesis Conditions.

Although anodic tungsten oxide has attracted increasing attention in recent years, there is still a lack of detailed studies on the photoelectrochemical (PEC) properties of such kind of materials grown in different electrolytes under various sets of conditions. In addition, the morphology of photoanode is not a single factor responsible for its PEC performance. Therefore, the attempt was to correlate different anodizing conditions (especially electrolyte composition) with the surface morphology, oxide thickness, semiconducting, and photoelectrochemical properties of anodized oxide layers. As expected, the surface morphology of WO3 depends strongly on anodizing conditions. Annealing of as-synthesized tungsten oxide layers at 500 °C for 2 h leads to obtaining a monoclinic WO3 phase in all cases. From the Mott-Schottky analysis, it has been confirmed that all as prepared anodic oxide samples are n-type semiconductors. Band gap energy values estimated from incident photon−to−current efficiency (IPCE) measurements neither differ significantly for as−synthesized WO3 layers nor depend on anodizing conditions such as electrolyte composition, time and applied potential. Although the estimated band gaps are similar, photoelectrochemical properties are different because of many different reasons, including the layer morphology (homogeneity, porosity, pore size, active surface area), oxide layer thickness, and semiconducting properties of the material, which depend on the electrolyte composition used for anodization.

Tailoring the properties of g-C3N4 with CuO for enhanced photoelectrocatalytic CO2 reduction to methanol

In the present work, the physico-chemical and photoelectrocatalytic (PEC) carbon dioxide (CO2) reduction to methanol properties of graphitic carbon nitride (g-C3N4) were enhanced by the incorporation of CuO. The XRD, XPS, TEM, FESEM, UV–vis and photoluminescence (PL) spectroscopy techniques were used to characterize the synthesized g-C3N4 and CuO/g-C3N4 photocatalysts. The fabricated CuO/g-C3N4/carbon paper photocathode showed ∼10.0 times enhanced photocurrent response and 5.3 times enhanced incident photon to current efficiency (IPCE) than the g-C3N4/carbon paper photocathode under CO2 atmosphere in aqueous NaHCO3 electrolyte solution on 470 nm light irradiation. The higher IPCE of CuO/g-C3N4/carbon paper photocathode was attributed to the higher absorption of the incident visible light which results in efficient electron (e−-hole (h+) pair generation and charge transfer for the PEC conversion of CO2. The production of methanol in aqueous phases was analysed and found to be 4.1 and 2.6 times higher by CuO/g-C3N4/carbon paper photocathode than g-C3N4/carbon paper and CuO/carbon paper photocathodes, respectively. The CuO/g-C3N4/carbon paper photocathode showed Faradaic efficiency and quantum efficiency of 75 % and 8.9 %, respectively for the production of methanol. The plausible mechanism for the production of methanol by CuO/g-C3N4/carbon paper photocathode by PEC reaction was also discussed.

Photoelectrocatalytic reduction of CO2 to methanol over CuFe2O4@PANI photocathode

The present study was aimed to convert CO2 into methanol which not only addresses the potential solution for controlling the CO2 concentration level in the atmosphere but also offers an alternative approach for the production of renewable energy source. In this perspective, a hybrid photocatalyst, PANI@CuFe2O4 was synthesized, characterized and used as a photocathode for photoelectrocatalytic (PEC) reduction of CO2 to methanol in aqueous medium at an applied potential of −0.4 V vs NHE under visible light irradiation. The combination of PANI with CuFe2O4 greatly increased the PEC CO2 reduction to methanol owing to enhance the CO2 chemisorption capacity by the photocathode surface and at the same time facilitated the separation of photogenerated electron-hole (e−/h+) pairs. The incident photon to current efficiency (IPCE) and quantum efficiency (QE) for methanol formation in PEC CO2 reduction could be achieved as 7.1 and 24.0% respectively. The rate of formation of methanol in PEC CO2 reduction was found as 49.3 μmol g−1h−1 with 73% Faradaic efficiency. Compared to photocatalytic reaction, the PEC results demonstrated that the applied potential could effectively separate the photogenerated e−/h+ pairs and therefore, enhanced the PEC CO2 reduction activity of the hybrid photocatalyst.

Exploiting Direct Current Plasma Electrolytic Oxidation to Boost Photoelectrocatalysis

In this study, we report an investigation of the photoelectrochemical activity of TiO2 films formed by DC plasma electrolytic oxidation (PEO) at a variable potential in a sulfuric acid electrolyte at 0 and 25 °C. The surface morphology was mainly determined by the oxide-forming potential. X-Ray Diffraction and Raman analyses showed that the relative amount of the anatase and rutile phases varied from 100% anatase at low potential (110–130 V) to 100% rutile at high potential (180–200 V), while mixed-phase oxide films formed at intermediate potential. Correspondingly, the band gap of the TiO2 films decreased from about 3.20 eV (pure anatase) to 2.94 eV (pure rutile) and was red-shifted about 0.1 eV by reducing the electrolyte temperature from 25 °C to 0 °C. Glow-Discharge Optical Emission Spectroscopy (GD-OES) and X-ray Photoelectron Spectroscopy (XPS) analyses evidenced S-containing species located preferentially close to the TiO2/Ti interface. The photoelectrochemical activity was assessed by measuring the incident photon-to-current efficiency (IPCE) under Ultraviolet C (UV-C) irradiation, which showed a non-gaussian normal trend as a function of the PEO cell potential, with maximum values exceeding 80%. Photoelectrocatalytic activity was assessed by decolorization of model solutions containing methylene blue. Photoanodes having higher IPCE values showed faster decolorization kinetics.

Multilayer WO3/BiVO4 Photoanodes for Solar-Driven Water Splitting Prepared by RF-Plasma Sputtering

A series of WO3, BiVO4 and WO3/BiVO4 heterojunction coatings were deposited on fluorine-doped tin oxide (FTO), by means of reactive radio frequency (RF) plasma (co)sputtering, and tested as photoanodes for water splitting under simulated AM 1.5 G solar light in a three-electrode photoelectrochemical (PEC) cell in a 0.5 M NaSO4 electrolyte solution. The PEC performance and time stability of the heterojunction increases with an increase of the WO3 innermost layer up to 1000 nm. A two-step calcination treatment (600 °C after WO3 deposition followed by 400 °C after BiVO4 deposition) led to a most performing photoanode under back-side irradiation, generating a photocurrent density of 1.7 mA cm−2 at 1.4 V vs. SCE (i.e., two-fold and five-fold higher than that generated by individual WO3 and BiVO4 photoanodes, respectively). The incident photon to current efficiency (IPCE) measurements reveal the presence of two activity regions over the heterojunction with respect to WO3 alone: The PEC efficiency increases due to improved charge carrier separation above 450 nm (i.e., below the WO3 excitation energy), while it decreases below 450 nm (i.e., when both semiconductors are excited) due to electron–hole recombination at the interface of the two semiconductors.

Graphdiyne Coupled with g‐C3N4/NiFe‐Layered Double Hydroxide, a Layered Nanohybrid for Highly Efficient Photoelectrochemical Water Oxidation

AbstractRecently discovered graphdiyne (GDY) is a unique two‐dimensional (2D) planar structure with a high‐degree π‐conjunction network composed of sp and sp2 hybridized carbon bonds. GDY has high carrier mobility, rich chemical bond properties, and having a bandgap of ≈2.1 eV. In this study, for the first time, g‐C3N4/NiFe‐layered double hydroxide (LDH) is decorated by GDY to obtain a new strongly coupled ternary nanocomposite g‐C3N4/GDY/NiFe‐LDH, which has hierarchical mesoporous layered structure, large surface area, and broad visible spectrum absorption. These properties make g‐C3N4/GDY/NiFe‐LDH nanocomposite an outstanding candidate for photoelectrochemical water oxidation. Therefore, the new architecture is analyzed and achieve a high photocurrent density of 178.66 µA cm−2 by applying 1.4 V, a maximum incident photon‐to‐current efficiency (IPCE) of 3.59% at wavelength of 350 nm and 2.05% at 420 nm under standard AM 1.5G condition, which are also the best reported values in the literature. More interestingly, the proposed nanocomposite indicates a great durability, where there is nearly no dropping on the photocurrent under continuous illumination after 3600 s. This work suggests that additive engineering using GDY is an effective approach for the fabrication of efficient photoelectrochemical water oxidation devices.

New organic dyes with varied arylamine donors as effective co-sensitizers for ruthenium complex N719 in dye sensitized solar cells

Three new organic dyes (TD1–TD3) featured with donor–π–acceptor architecture are synthesized and applied to dye-sensitized solar cells (DSSCs). In these sensitizers, an alkyl oligothiophene π-spacer is used to link the 2-cyanoacrylic acid acceptor with varied arylamines donors, i.e. carbazole (TD1), phenothiazine (TD2) or triphenylamine (TD3). The effects of different donor units on the photophysical, electrochemical, and photovoltaic properties of sensitizers are investigated in detail. They all show intensive UV–vis absorption around 400 nm with rod-like molecular structures. The co-sensitizations of TD1–TD3 with ruthenium complex N719 are further evaluated. Consequently, the co-sensitized DSSCs demonstrate superior photovoltaic performances with power conversion efficiencies (PCEs) ranging from 7.60% to 8.02% in relation to the cell with N719 (PCE = 7.29%) alone, which is mainly ascribed to the higher short-circuit photocurrents (Jsc) in combination with larger open-circuit voltages (Voc). Moreover, the origins of these improvements are examined by incident photon to current efficiency (IPCE) spectra and electrochemical impedance spectroscopy (EIS) investigations. The Jsc is improved because TD1–TD3 could compensate for the photocurrent loss induced by I−/I3−; whereas, the Voc is enhanced owing to the fact that the electron recombination process is retarded upon co-sensitization.