Incident Photo-to-current Efficiency Research Articles

Unveiling Enhanced PEC Water Oxidation: Morphology Tuning and Interfacial Phase Change in α-Fe2O3@K-OMS-2 Branched Core-Shell Nanoarrays.

A simple fabrication method that involves two steps of hydrothermal reaction has been demonstrated for the growth of α-Fe2O3@K-OMS-2 branched core-shell nanoarrays. Different reactant concentrations in the shell-forming step led to different morphologies in the resultant composites, denoted as 0.25 OC, 0.5 OC, and 1.0 OC. Both 0.25 OC and 0.5 OC formed perfect branched core-shell structures, with 0.5 OC possessing longer branches, which were observed by SEM and TEM. The core K-OMS-2 and shell α-Fe2O3 were confirmed by grazing incidence X-ray diffraction (GIXRD), EDS mapping, and atomic alignment from high-resolution STEM images. Further investigation with high-resolution HAADF-STEM, EELS, and XPS indicated the existence of an ultrathin layer of Mn3O4 sandwiched at the interface. All composite materials offered greatly enhanced photocurrent density at 1.23 VRHE, compared to the pristine Fe2O3 photoanode (0.33 mA/cm2), and sample 0.5 OC showed the highest photocurrent density of 2.81 mA/cm2. Photoelectrochemical (PEC) performance was evaluated for the samples by conducting linear sweep voltammetry (LSV), applied bias photo-to-current efficiency (ABPE), electrochemical impedance spectroscopy (EIS), incident-photo-to-current efficiency (IPCE), transient photocurrent responses, and stability tests. The charge separation and transfer efficiencies, together with the electrochemically active surface area, were also investigated. The significant enhancement in sample 0.5 OC is ascribed to the synergetic effect brought by the longer branches in the core-shell structure, the conductive K-OMS-2 core, and the formation of the Mn3O4 thin layer formed between the core and shell.

Investigation of p-CuNb2O6 for use as photocathodes for photoelectrochemical water splitting

P-type copper niobate (CuNb2O6) was prepared for the first time by a two-step spray pyrolysis method on FTO glass substrates. Its feasibility in photoelectrochemical (PEC) decomposition water was systematically evaluated. The physical and photophysical properties of the thin film, including band edge position, bandgap energy, carrier lifetime, and incident photo-to-current efficiency (IPCE), were characterized and analyzed. The optical band gap of the prepared gray CuNb2O6 film is ∼1.41 eV, which indicates that it can absorb visible light and achieve sunlight-driven water splitting. The photocurrent density under simulated sunlight at AM1.5 was 0.25 mA/cm2, and the IPCE value could reach up to 3% at 400 nm in an aqueous solution (pH = 6.8) when applying a bias of 0.4 V vs. RHE. Despite exhibiting a good optical band gap and photocurrent density, the fabricated p-CuNb2O6 thin films remained unstable under illumination in aqueous solutions due to the reduction reaction of copper. Based on these findings, this study provides a new opinion on the applicability of CuNb2O6 as a photocathode material for PEC water splitting.

The oxidation enhancement photocurrent response in WSe1.95Te0.05 nanosheets

The photocurrent was detected in the WSe1.95Te0.05 with and without surface oxidation. The linear current–voltage relation reveal the WSe1.95Te0.05 nanosheet/Pt ohmic contact. The XPS spectrum reveals the WO3 was formed during the oxidation. The photo responsivity increase from 173 A/W to 442 A/W at 0.5 V after air exposuring in ambient conditions over half year. This value is the highest observed values in two-dimensional transition metal dichalcogenides without artificial treatments. The greatly photocurrent enhancement originated from the incident photo-to-current efficiency (IPCE) enhancement of WO3 at the wavelength of 405 nm.

In situ constructing Ni foam supported ZnO-CdS nanorod arrays for enhanced photocatalytic and photoelectrochemical activity

Abstract Constructing sustainable and efficient photocatalyst for solar hydrogen evolution via photocatalytic (PC) or photoelectrocatalytic (PEC) water splitting is considered as one of the most potential solutions for the contemporary energy crisis. In this study, we synthesized a film-like photocatalyst ZnO-CdS(Ar)@Ni with one-dimensional (1D) nanorod arrays of ZnO-CdS heterojunction anchoring on three-dimensional (3D) Ni foam. The ZnO-CdS(Ar)@Ni photocatalyst not only exhibited higher PC hydrogen generation rate (16.31 µmol cm−2 h−1) than that of precursor samples, but could also be used as a photoelectrode to achieve efficient PEC water splitting on the basis of the applied bias photo-to-current conversion efficiency (ABPE) of 2.0% (at −0.6 V vs. Ag/AgCl) and the incident photo-to-current efficiency (IPCE) of 35% (at 450 nm), respectively. Such enhanced performances relate to the cohesive combination of ZnO-CdS heterojunction via calcination, more active areas in the 1D nanorod structure combining with 3D Ni foam substrate, and the collection and rapid transfer of electrons within Ni foam. This study demonstrates such a strategy of film-like photocatalyst construction has great potential for practical utilization in both PC and PEC systems for renewable energy generation.

Enhanced photocatalytic activity of all-solid-state g-C3N4/Au/P25 Z-scheme system for visible-light-driven H2 evolution

We constructed an all-solid-state g-C3N4/Au/P25 Z-scheme system combining graphitic carbon nitride (g-C3N4) and P25 with Au nanoparticles, as an electron mediator, for hydrogen production under visible-light irradiation (λ > 400 nm). The g-C3N4/Au/P25 system was characterized by X-ray diffraction (XRD), transmission electronic microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–Vis diffuse reflection spectroscopy (UV–Vis DRS), photoluminescence (PL), time-resolved photoluminescence (TRPL), and electrochemical measurements. TEM and high-resolution transmission electron microscopy (HRTEM) clearly reveal the morphology and structure of g-C3N4/Au/P25, implying the existence of the all-solid-state Z-scheme system. The results of electrochemical impedance spectroscopy (EIS) and TRPL indicate that the Z-scheme system can effectively promote the electron transfer rate and the separation of photogenerated electron–hole pairs for the vectorial electron transfer of P25→Au→g-C3N4. The Z-scheme system can also extend the visible light absorption wavelength from 460 to 700 nm due to the surface plasmon resonance (SPR) effect of Au nanoparticles, which is confirmed by UV–Vis DRS and incident photo-to-current efficiency (IPCE) measurements. The synergistic effect of the all-solid-state g-C3N4/Au/P25 Z-scheme system and the Au-induced SPR results in a highly efficient photocatalytic performance with a turnover frequency (TOF) of 259 μmol h−1 g−1, which is 30 times higher than that of pristine g-C3N4.

Surface modification of InVO4 nanoparticles on WO3 plate array films for improved photoelectrochemical performance

Surface modification of InVO4 nanoparticles on WO3 plates array films using a dipping–annealing method.

Sea-Urchin-Like ZnO Nanoparticle Film for Dye-Sensitized Solar Cells

We present novel sea-urchin-like ZnO nanoparticles synthesized using a chemical solution method. Solution approaches to synthesizing ZnO nanostructures have several advantages including low growth temperatures and high potential for scaling up. We investigated the influence of reaction times on the thickness and morphology of sea-urchin-like ZnO nanoparticles, and XRD patterns show strong intensity in every direction. Dye-sensitized solar cells (DSSCs) were developed using the synthesized ZnO nanostructures as photoanodes. The DSSCs comprised a fluorine-doped tin oxide (FTO) glass with dense ZnO nanostructures as the working electrode, a platinized FTO glass as the counter electrode, N719-based dye, and I-/I3-liquid electrolyte. The DSSC fabricated using such nanostructures yielded a high power conversion efficiency of 1.16% with an incident photo-to-current efficiency (IPCE) as high as 15.32%. Electrochemical impedance spectroscopy was applied to investigate the characteristics of DSSCs. An improvement in the electron transport in the ZnO photoanode was also observed.

Improved performance of dye-sensitized solar cell with a specially tailored TiO2 compact layer prepared by RF magnetron sputtering

We demonstrate that a graded index TiO2 antireflective compact layer (arc-TiO2) employed by RF sputtering can modulate the optical transmittance and reduce the electron recombination in dye-sensitized solar cell (DSSC). The spectral response of the DSSC is improved, due to higher and red-shifted transmittance spectra in a specific region that favours the sensitization effect of the dye. The effects of arc-TiO2 prepared at various RF sputtering powers to the performances of DSSC were investigated by means of the incident photo to current efficiency (IPCE), open-circuit voltage decay (OCVD) and electrochemical impedance spectroscopy (EIS). The slow decay of the photo-voltage attributed to the desirable merits of the arc-TiO2 compact layer has been evidenced by the OCVD measurement. Meanwhile, the improvement of adhesion between an arc-TiO2 film and porous-TiO2 has decreased the interfacial-charge resistance, R1 in the EIS measurement. This lower R1 then facilitates the charge-transfer process of the electron in the DSSC. At 100W of RF power, these blended effects improved the overall conversion efficiency of the DSSC by an increase of 42% compared to the cell without the compact layer.

Molecular design of TPD-based organic A-π-D-π-A dyes for dye-sensitized solar cells

An interesitng class of organic A-π-D-π-A dyes based on an N,N,N′,N′-tetraphenylbenzidine(TPD) unit as donor was designed and synthesized for dye-sensitized solar cells(DSSCs). TPD-4-based DSSCs gave a short circuit photocurrent density(Jsc) of 16.67 mA/cm2, a open circuit voltage(Voc) of 0.635 V and a fill factor(ff) of 0.68, achieving a solar-to-electricity conversion efficiency(η) of 7.22% in preliminary tests. The N3-sensitized device gave an η value of 8.02% with a Jsc of 18.81 mA/cm2, a Voc of 0.630 V and an ff of 0.68 under the same conditions. The incident photo-to-current efficiency(IPCE) values above 70% observed in a range of 460 to 600 nm with a maximum value of 80% at 500 nm indicate that the TPD-4-based DSSC shows a high performance. Under the same conditions, the DSSC based on N3 provided the IPCE values above 70% in a range of 490 to 580 nm with a maximum value of 76% at 500 nm. Both further optimization of the device processing and structural modification of these dyes are anticipated to make the device give even better performances.

Natural Chlorophyll-Sensitized Nanocrystalline TiO<sub>2</sub> as Photoanode of a Hybrid Photoelectrochemical Biofuel Cell

A photoelectrochemical biofuel cell (PEBFC) generating electrical energy directly from sunlight and biomass was investigated. In this paper, the PEBFC had a natural chlorophyll-sensitized titanium dioxide (TiO2) film photoanode and Pt black cathode. The electron transport process of the PEBFC was described. The performances of the PEBFC were obtained by photocurrent-photovoltage characteristic curves. The open-circuit photovoltage (Voc), the short-circuit photocurrent (Isc) and the maximum power density (Pmax) is 0.53V, 1.000 μAcm-2 and1.1520 μWcm-2 at 0.37 V, respectively. The incident photo-to-current efficiency (IPCE) is 8.4% at 380 nm.

Photoelectrochemical biofuel cell using porphyrin-sensitized nanocrystalline titanium dioxide mesoporous film as photoanode

Electrical energy generated directly from sunlight and biomass solution with a Photoelectrochemical Biofuel Cell (PEBFC) was investigated. The PEBFC consisted of a meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP)-sensitized nanocrystalline titanium dioxide (TiO 2) mesoporous film (NTDMF) as the photoanode and platinum black as the cathode. The interaction between TCPP sensitizer and NTDMF was evaluated by X-ray photoelectron spectra and FT-IR absorption spectra, indicating that the TCPP sensitizer was adsorbed on the NTDMF by bridging or bidentate coordinate bonds. The spectroscopic properties of pure TCPP ethanol solution and TCPP-sensitized NTDMF were obtained by UV–vis absorption spectra, demonstrating that the characteristic absorption peaks of TCPP on NTDMF displayed slight red shift compared with pure TCPP ethanol solution. The performances of the PEBFC were obtained by photocurrent–photovoltage characteristic curves. The open-circuit photovoltage ( V oc), the short-circuit photocurrent ( I sc) and the maximum power density ( P max) was 0.74 V, 69.96 μA and 33.94 μW cm −2 at 0.45 V, respectively. The fill factor (FF) was 0.19 and the incident photo-to-current efficiency (IPCE) was 36.0% at 436 nm. The results demonstrated that the TCPP was an appropriate photosensitizer for PEBFC.

Photoelectrochemical Biofuel Cell Using Triarylamine Dye-Sensitized Titanium Dioxide Film as Photoanode

A Photoelectrochemical Biofuel Cell (PEBFC) generating electrical energy directly from sunlight and biomass was investigated. In this paper,the PEBFC had a triarylamine dye-sensitized titanium dioxide(TiO2) film photoanode and Pt black cathode. The electron transport process of the PEBFC was also described. The performances of the PEBFC were obtained by photocurrent–photovoltage characteristic curves.The open-circuit photovoltage(Voc), the short-circuit photocurrent (Isc) and the maximum power density (Pmax) was 0.82V, 69.00 μAcm-2 and14.00μWcm-2 at 0.27 V, respectively. The fill factor (FF) was 0.25 and the incident photo-to-current efficiency (IPCE) was 3.5% at 441 nm.

Titanium flexible photoanode consisting of an array of TiO 2 nanotubes filled with a nanocomposite of TiO 2 and graphite for dye-sensitized solar cells

A flexible dye-sensitized solar cell (DSSC) was fabricated using a photoanode consisting of an array of TiO 2 nanotubes (TNT) filled with a nanocomposite of TiO 2 (P90) and nanographite. The array of TNT was obtained by anodic oxidation of Ti foil, and this Ti foil with TNT was used as the photoanode of the DSSC. Each tube in the array has an average diameter of 100 nm. The morphologies of the array of TNT were obtained both after and before filling them with the TiO 2/graphite nanocomposite, using a field-emission scanning electron microscopy (FE-SEM). DSSC with photoanode consisting of the nanocomposite (photoanode designated as Graphite/P90-TNT) rendered a light-to-electricity conversion efficiency ( η) of 5.75%. In contrast, the cells with photoanodes consisting of only TNT (photoanode designated as TNT) and TNT filled with P90-TiO 2 (photoanode designated as P90-TNT) exhibited efficiencies ( η) of 4.44% and 5.14%, respectively. The enhancements in the η’s in favor of the cells with P90-TNT and Graphite/P90-TNT were attributed to the filled P90 and nanocomposite, respectively. The filled particles were assumed to provide more conductive pathways for electron transfer and prolonged lifetime for electrons in the film of TNT. The results were substantiated by light-absorption values, incident-photo-to-current efficiency (IPCE) curves, Nyquist and Bode plots of electrochemical impedance spectroscopy (EIS), and photopotential transient curves.

Dye sensitization of nanocrystalline TiO 2 by perylene derivatives

New sensitizing dye–semiconductor system comprised of 3,4,9,10-perylene tetracarboxylic acid (PTCA) or perylene 3,4-dicarboxylic-9,10-( n-butylamine) carboximide (PNDCA) on titanium dioxide (TiO 2) had been prepared and characterized. Good energy conversion efficiency was obtained. The film of PTCA on TiO 2 yielded an incident photo-to-current efficiency (IPCE) of approximately 40% in the wavelength region of 440 to 530 nm, while that for PNDCA was approximately 14% at the wavelength region from 460 to 510 nm. Further studies concentrated on the doping of this system with bromine (Br 2). The results indicated that the sensitizing wavelength region was red shifted, which was advantageous for solar light harvesting. Furthermore, the doped films gave lower quantum conversion efficiency than the non-doped films.