The effects of the thickness of TiO2 films on the performance of dye-sensitized solar cells

Nanocrystalline anatase TiO₂ thin films with different thicknesses (0.5-2.0 μm) have been deposited on ITO-coated glass substrates by a sol-gel method and rapid thermal annealing for application as the work electrode for dye-sensitized solar cells (DSSC). From the results, the increases in thickness of TiO₂ films can increase adsorption of the N3 dye through TiO₂ layers to improve the short-circuit photocurrent (J_sc) and open-circuit voltage (V_oc), respectively. However, the J_sc and V_oc of DSSC with a TiO₂ film thickness of 2.0 μm (8.5 mA/cm² and 0.61 V) are smaller than those of DSSC with a TiO₂ film thickness of 1.5 μm (9.2 mA/cm² and 0.62 V). It could be due to the fact that the increased thickness of TiO₂ thin films also resulted in a decrease in the transmittance of TiO₂ thin films thus reducing the incident light intensity on the N3 dye. An optimum power conversion efficiency (η) of 2.9% was obtained in a DSSC with the TiO₂ film thickness of 1.5 μm.     

Rose bengal-sensitized nanocrystalline ceria photoanode for dye-sensitized solar cell application

For efficient charge injection and transportation, wide bandgap nanostructured metal oxide semiconductors with dye adsorption surface and higher electron mobility are essential properties for photoanode in dye-sensitized solar cells (DSSCs). TiO₂-based DSSCs are well established and so far have demonstrated maximum power conversion efficiency when sensitized with ruthenium-based dyes. Quest for new materials and/or methods is continuous process in scientific investigation, for getting desired comparative results. The conduction band (CB) position of CeO₂ photoanode lies below lowest unoccupied molecular orbital level (LUMO) of rose bengal (RB) dye. Due to this, faster electron transfer from LUMO level of RB dye to CB of CeO₂ is facilitated. Recombination rate of electrons is less in CeO₂ photoanode than that of TiO₂ photoanode. Hence, the lifetime of electrons is more in CeO₂ photoanode. Therefore, we have replaced TiO₂ by ceria (CeO₂) and expensive ruthenium-based dye by a low cost RB dye. In this study, we have synthesized CeO₂ nanoparticles. X-ray diffraction (XRD) analysis confirms the formation of CeO₂ with particle size ～7 nm by Scherrer formula. The bandgap of 2.93 eV is calculated using UV–visible absorption data. The scanning electron microscopy (SEM) images show formation of porous structure of photoanode, which is useful for dye adsorption. The energy dispersive spectroscopy is in confirmation with XRD results, confirming the presence of Ce and O in the ratio of 1:2. UV–visible absorption under diffused reflectance spectra of dye-loaded photoanode confirms the successful dye loading. UV–visible transmission spectrum of CeO₂ photoanode confirms the transparency of photoanode in visible region. The electrochemical impedance spectroscopy analysis confirms less recombination rate and more electron lifetime in RB-sensitized CeO₂ than TiO₂ photoanode. We found that CeO₂ also showed with considerable difference between dark and light DSSCs performance, when loaded with RB dye. The working mechanism of solar cells with fluorine-doped tin oxide (FTO)/CeO₂/RB dye/carbon-coated FTO is discussed. These solar cells show V _OC ～360 mV, J _SC ～0.25 mA cm ^?2 and fill factor ～63% with efficiency of 0.23%. These results are better as compared to costly ruthenium dye-sensitized CeO₂ photoanode.     

Synthesis of anatase TiO2 microspheres and their efficient performance in dye-sensitized solar cell

Nanomaterials play important role in performance of dye-sensitized solar cells. In this paper, highly phase pure anatase TiO₂ microspheres were synthesized using a low-cost hydrothermal route. Initially, X-ray diffraction studies and Raman spectroscopic analysis were carried out, and the formation of tetragonal structure of TiO₂ with the anatase phase was confirmed. The UV–Vis DRS studies showed the excellent reflectance and optical band-gap energy of 3.29 eV. The well-interconnected spherical nanoparticles with different sizes were examined by Field Emission Scanning Electron Microscopic analysis. The fabricated dye-sensitized solar cell (DSSC) composed of prepared TiO₂ microspheres as photoanode exhibited a higher power conversion efficiency (PCE) (η) of 5.4% as compared to commercial P25 with PCE of 3.6%. The higher J_sc (12.03 mA/cm²) in the fabricated DSSC due to efficient dye loading capacity and high light-scattering property was also observed.

     

Hydroxyapatite-Derived Heterogeneous Ru-Ru2P Electrocatalyst and Environmentally-Friendly Membrane Electrode toward Efficient Alkaline Electrolyzer

Alkaline membrane water electrolysis is a promising production technology, and advanced electrocatalyst and membrane electrode design have always been the core technology. Herein, an ion-exchange method and an environmentally friendly in situ green phosphating strategy are successively employed to fabricate Ru-Ru₂P heterogeneous nanoparticles by using hydroxyapatite (HAP) as a phosphorus source, which is an exceptionally active electrocatalyst for hydrogen evolution reaction (HER). Density functional theory calculation results reveal that strong electronic redistribution occurs at the heterointerface of Ru-Ru₂P, which modulates the electronic structure to achieve an optimized hydrogen adsorption strength. The obtained Ru-Ru₂P possesses excellent HER performance (24 mV at 10 mA cm⁻²) and robust stability (1000 mA cm⁻² for 120 h) in alkaline media. Furthermore, an environmentally friendly membrane electrode with a sandwich structure is assembled by HAP nanowires as an alkaline membrane, Ru-Ru₂P as a cathodic catalyst, and NiFe-LDH as an anodic catalyst, respectively. The voltage of (−) Ru-Ru₂P || NiFe-LDH/CNTs (+) (1.53 V at 10 mA cm⁻²) is lower than that of (−) 20 wt% Pt/C || RuO₂ (+) (1.60 V at 10 mA cm⁻²) for overall water splitting. Overall, the studies not only design an efficient catalyst but also provide a new route to achieve a high-stability electrolyzer for industrial H₂ production.     

Surface Self-Transforming FeTi-LDH Overlayer in Fe2O3/Fe2TiO5 Photoanode for Improved Water Oxidation

Integrating hematite nanostructures with efficient layer double hydroxides (LDHs) is highly desirable to improve the photoelectrochemical (PEC) water oxidation performance. Here, an innovative and facile strategy is developed to fabricate the FeTi-LDH overlayer decorated Fe₂O₃/Fe₂TiO₅ photoanode via a surface self-transformation induced by the co-treatment of hydrazine and NaOH at room temperature. Electrochemical measurements find that this favorable structure can not only facilitate the charge transfer/separation at the electrode/electrolyte interface but also accelerate the surface water oxidation kinetics. Consequently, the as-obtained Fe₂O₃/Fe₂TiO₅/LDH photoanode exhibits a remarkably increased photocurrent density of 3.54 mA cm⁻² at 1.23 V versus reversible hydrogen electrode (RHE) accompanied by an obvious cathodic shift (≈140 mV) in the onset potential. This work opens up a new and effective pathway for the design of high-performance hematite photoanodes toward efficient PEC water oxidation.     

Enhanced conversion efficiency of quasi solid state dye sensitized solar cells based on functionalized multi-walled carbon nanotubes incorporated TiO<Subscript>2</Subscript> photoanode

A series of quasi solid state dye sensitized solar cells were fabricated based on the different weight% of MWCNT@TiO₂ photoanode. The MWCNT@TiO₂ nanocomposites were synthesized by simple wet impregation method. The incorporation of MWCNT into the TiO₂ was confirmed by X-ray diffraction, energy dispersive X-ray spectrum and UV–visible spectroscopy. The morphological properties of the nanocomposites were analyzed by transmission electron microscopic analysis. The performance of the quasi solid state dye sensitized solar cell depends solely on the MWCNT content of the photoanode, as the same PVA polymer gel electrolyte has been used. Compared to the conventional TiO₂ photoanode based DSSCs 0.05 wt% MWCNT containing photoanode provide the maximum short circuit current density and the photo conversion efficiency of 9.811 mA/cm^?2 and 3.59 %. The introduction of MWCNT into the TiO₂ results in the rapid electron transport in the photoanode by forming a conductive network due to which improvement in the short circuit current was observed.     

Design of XS2 (X = W or Mo)-Decorated VS2 Hybrid Nano-Architectures with Abundant Active Edge Sites for High-Rate Asymmetric Supercapacitors and Hydrogen Evolution Reactions

Two-dimensional layered transition metal dichalcogenides have emerged as promising materials for supercapacitors and hydrogen evolution reaction (HER) applications. Herein, the molybdenum sulfide (MoS₂)@vanadium sulfide (VS₂) and tungsten sulfide (WS₂)@VS₂ hybrid nano-architectures prepared via a facile one-step hydrothermal approach is reported. Hierarchical hybrids lead to rich exposed active edge sites, tuned porous nanopetals-decorated morphologies, and high intrinsic activity owing to the strong interfacial interaction between the two materials. Fabricated supercapacitors using MoS₂@VS₂ and WS₂@VS₂ electrodes exhibit high specific capacitances of 513 and 615 F g⁻¹, respectively, at an applied current of 2.5 A g⁻¹ by the three-electrode configuration. The asymmetric device fabricated using WS₂@VS₂ electrode exhibits a high specific capacitance of 222 F g⁻¹ at an applied current of 2.5 A g⁻¹ with the specific energy of 52 Wh kg⁻¹ at a specific power of 1 kW kg⁻¹. For HER, the WS₂@VS₂ catalyst shows noble characteristics with an overpotential of 56 mV to yield 10 mA cm⁻², a Tafel slope of 39 mV dec⁻¹, and an exchange current density of 1.73 mA cm⁻². In addition, density functional theory calculations are used to evaluate the durable heterostructure formation and adsorption of hydrogen atom on the various accessible sites of MoS₂@VS₂ and WS₂@VS₂ heterostructures.     

Preparation of TiO2 paste using poly(vinylpyrrolidone) for dye sensitized solar cells

The surface morphology of titanium oxide (TiO₂) films as a photoanode in dye sensitized solar cells plays a vital role in converting light to electricity. Therefore, TiO₂ films were prepared using TiO₂ paste with different compositions of poly(vinylpyrrolidone) (PVP) as a binder to optimize their physico-chemical properties. The paste was prepared with commercial TiO₂ powder mixed with acetylacetone, PVP, 4-octylphenol polyethoxylate, acetic acid and ethanol. The chemical composition remains the same for all pastes except PVP. The quantity of the PVP was optimized in such a way that it provides a thick film with a good network connection. The impact of the quantity of PVP in the TiO₂ paste was analyzed. The prepared TiO₂ film structure was characterized by X-ray diffraction. The surface morphology was analyzed by scanning electron microscopy. The electrochemical performance of the prepared TiO₂ as a photoanode was also investigated. Among the four different photoanodes, the cells fabricated with a TiO₂ film prepared with 0.4 g of PVP exhibited the highest power conversion efficiency of 6.77%, short-circuit photocurrent density and open circuit voltage of 12.38 mA/cm² and 0.77 V, respectively.     

Matching CP@NCOH/NF Cathode and GH/FNP/NF Anode for High-Performance Asymmetric Supercapacitor

It is extremely crucial to design and match high-quality cathode and anode for achieving high-performance asymmetric supercapacitors (ASCs). Herein, Co₃(PO₄)₂@NiCo-LDH/Ni foam (CP@NCOH/NF) cathode with hierarchical morphology and graphene hydrogel/Fe–Ni phosphide/Ni foam (GH/FNP/NF) anode with the robust and porous structure are elaborately designed and prepared, respectively. Owing to their unique and profitable structures, both CP@NCOH/NF and GH/FNP/NF electrodes yield the superior capacity (10760 and 2236 mC cm⁻² at 2 mA cm⁻², respectively), good rate capability (63% retention at 200 mA cm⁻² and 52% retention at 50 mA cm⁻², respectively), and excellent cycling stability (72% and 74% retention after 10 000 cycles, respectively). Benefiting from their matchable electrochemical performances, the configured solid-state CP@NCOH/NF//GH/FNP/NF ASC outputs both competitive energy density (80.2 Wh kg⁻¹/4.1 mWh cm⁻³) and power density (14563 W kg⁻¹/750 mW cm⁻³), companied by remarkable cyclability (71% retention after 10 000 cycles), manifesting its great promise for large-scale integrated energy-storage system.     

The effects of electronic structure of non-metallic doped TiO<Subscript>2</Subscript> anode and co-sensitization on the performance of dye-sensitized solar cells

N/TiO₂, S/TiO₂, and N S/TiO₂ nanocrystalline films anode were obtained by doping non-metallic element N and S which could change the LUMO of anode, leading to the easy injection of electron from the excited state of dye molecule to the conduction band of semiconductor, and thus improving the photoelectric conversion efficiency and reducing the impedance of solar cells. The anode films treated by titanium tetrachloride and co-sensitized by P3HT/N719 were also studied. The absorption region of P3HT/N719 covered the entire visible region in the solar cells. The solar cell based on N/TiO₂ anode film treated by titanium tetrachloride and P3HT/N719 showed a short-circuit current density of 10.20 mA/cm², open-circuit voltage of 0.557 V, and photoelectric conversion efficiency of 2.55%.     

Dynamic Reconstructed RuO2/NiFeOOH with Coherent Interface for Efficient Seawater Oxidation

Developing efficient oxygen evolution reaction (OER) electrocatalysts for seawater electrolysis is still a big challenge. Herein, a facile one-pot approach is reported to synthesize RuO₂-incorporated NiFe-metal organic framework (RuO₂/NiFe-MOF) with unique nanobrick-nanosheet heterostructure as precatalyst. Driven by electric field, the RuO₂/NiFe-MOF dynamically reconstructs into RuO₂ nanoparticles-anchored NiFe oxy/hydroxide nanosheets (RuO₂/NiFeOOH) with coherent interface, during which the dissolution and redeposition of RuO₂ are witnessed. Owing to the synergistic interaction between RuO₂ and NiFeOOH, the as-reconstructed RuO₂/NiFeOOH exhibits outstanding alkaline OER activity with an ultralow overpotential of 187.6 mV at 10 mA cm⁻² and a small Tafel slope of 31.9 mV dec⁻¹ and excellent durability at high current densities of 840 and 1040 mA cm⁻² in 1 m  potassium hydroxide (KOH). When evaluated for seawater oxidation, the RuO₂/NiFeOOH only needs a low overpotential of 326.2 mV to achieve 500 mA cm⁻² and can continuously catalyze OER at 500 mA cm⁻² for 100 h with negligible activity degradation. Density function theory calculations reveal that the presence of strong interaction and enhanced charge transfer along the coherent interface between RuO₂ and NiFeOOH ensures improved OER activity and stability.     

Fabrication of partially crystalline TiO2 nanotube arrays using 1, 2-propanediol electrolytes and application in dye-sensitized solar cells

We report the fabrication of self-organized partial crystalline TiO₂ nanotube arrays in 1, 2-propanediol containing fluoride ion. The influence of anodization parameters including NH₄F concentration, water content, anodization voltage and time on the morphology, diameter and length of TiO₂ nanotube were investigated in detail. The prepared TiO₂ nanotube has diameter in 30–120 nm and length in 0.6–3 μm. TiO₂ nanotube arrays are used as photoanode for the application in dye-sensitized solar cell and the photovoltaic performance of 1.91% is achieved with a TiO₂ nanotube sample of 2.2 μm in length combining with N719 dye, and the corresponding photovoltaic parameters of 3.6 mA cm^?2 in short circuit photocurrent density, 840 mV in open circuit potential, and 63.2% in fill factor.     

Rear-side passivation characteristics of Si-rich SiNx for various Local Back Contact solar cells

This paper focuses on two main challenges: (i) to achieve a low surface recombination velocity and (ii) the quantitative control of the positive charges contained in the rear SiN_x by varying the refractive index (n). We adopted a Si-rich SiN_x film with a relatively thin thickness to control the fixed charge density (Q_f) from 2.74 × 10¹² to 1.63 × 10¹²/cm² and flat-band voltage (V_FB) is shifted from −2.53 to −1.41 V. A rear side recombination velocity (S_rear) and implied open circuit voltage (iV_oc) was achieved 30 cm/s and 630 mV respectively after forming gas anneal (FGA) treatment. The low temperature processed LBC solar cell fabricated with photolithographic contacts exhibits V_oc of 647 mV, and efficiency of 19.3%. The laser fired cell exhibits V_oc of 637 mV, and efficiency of 19.0%.     

Ce Site in Amorphous Iron Oxyhydroxide Nanosheet toward Enhanced Electrochemical Water Oxidation

Iron oxyhydroxide has been considered an auspicious electrocatalyst for the oxygen evolution reaction (OER) in alkaline water electrolysis due to its suitable electronic structure and abundant reserves. However, Fe-based materials seriously suffer from the tradeoff between activity and stability at a high current density above 100 mA cm⁻². In this work, the Ce atom is introduced into the amorphous iron oxyhydroxide (i.e., CeFeO_xH_y) nanosheet to simultaneously improve the intrinsic electrocatalytic activity and stability for OER through regulating the redox property of iron oxyhydroxide. In particular, the Ce substitution leads to the distorted octahedral crystal structure of CeFeO_xH_y, along with a regulated coordination site. The CeFeO_xH_y electrode exhibits a low overpotential of 250 mV at 100 mA cm⁻² with a small Tafel slope of 35.1 mVdec⁻¹. Moreover, the CeFeO_xH_y electrode can continuously work for 300 h at 100 mA cm⁻². When applying the CeFeO_xH_y nanosheet electrode as the anode and coupling it with the platinum mesh cathode, the cell voltage for overall water splitting can be lowered to 1.47 V at 10 mA cm⁻². This work offers a design strategy for highly active, low-cost, and durable material through interfacing high valent metals with earth-abundant oxides/hydroxides.     

Pyreno-chalcone dendrimers as an additive in the redox couple of dye-sensitized solar cells

Novel pyreno-chalcone dendrimers 1, 2, and 3 were synthesized and their ability to act as an additive in the redox couple (I⁻/I₃ ⁻) of dye-sensitized nanocrystalline TiO₂ solar cell has been tested. The redox couple doped with pyreno-chalcone dendrimer 3 gave a short circuit photocurrent density (J _sc) of 7.40 mA/cm², open circuit voltage (V _oc) of 820 mV, and a fill factor of 0.51, corresponding to an overall conversion efficiency (η) of 7.89% under 40 mW/cm² irradiation.     

Architecting the High-Entropy Oxides on 2D MXene Nanosheets by Rapid Microwave-Heating Strategy with Robust Photoelectrochemical Oxygen Evolution Performance

High-entropy oxides (HEO) have recently concerned interest as the most promising electrocatalytic materials for oxygen evolution reactions (OER). In this work, a new strategy to the synthesis of HEO nanostructures on Ti₃C₂T_x MXene via rapid microwave heating and subsequent calcination at a low temperature is reported. Furthermore, the influence of HEO loading on Ti₃C₂T_x MXene is investigated toward OER performance with and without visible-light illumination in an alkaline medium. The obtained HEO/Ti₃C₂T_x-0.5 hybrid exhibited an outstanding photoelectrochemical OER ability with a low overpotential of 331 mV at 10 mA cm⁻² and a small Tafel slope of 71 mV dec⁻¹, which exceeded that of a commercial IrO₂ catalyst (340 mV at 10 mA cm⁻²). In particular, the fabricated water electrolyzer with the HEO/Ti₃C₂T_x-0.5 hybrid as anode required a less potential of 1.62 V at 10 mA cm⁻² under visible-light illumination. Owing to the strong synergistic interaction between the HEO and Ti₃C₂T_x MXene, the HEO/Ti₃C₂T_x hybrid has a great electrochemical surface area, many metal active sites, high conductivity, and fast reaction kinetics, resulting in an excellent OER performance. This study offers an efficient strategy for synthesizing HEO-based materials with high OER performance to produce high-value hydrogen fuel.     

An efficient dye-sensitized solar cell based on a functionalized-triarylamine dye

A new functionalized-triarylamine dye (MXD10) has been designed, synthesized, and characterized. Two CH₃(CH₂)₄CH=CH- units were introduced into triphenylamine for improvement of light harvesting, suppression of dye aggregation and retardation of charge recombination. Photophysical, electrochemical and photovoltaic measurements are in accord with the molecular design. Device based on MXD10 gave a maximum power conversion efficiency of 6.47% under simulated AM 1.5 irradiation (100 mW cm⁻²) with J_SC = 15 mA/cm², V_OC = 635 mV, and ff = 0.68.     

Construction of Nitrogen-Doped Biphasic Transition-Metal Sulfide Nanosheet Electrode for Energy-Efficient Hydrogen Production via Urea Electrolysis

Urea-assisted hybrid water splitting is a promising technology for hydrogen (H₂) production, but the lack of cost-effective electrocatalysts hinders its extensive application. Herein, it is reported that Nitrogen-doped Co₉S₈/Ni₃S₂ hybrid nanosheet arrays on nickel foam (N-Co₉S₈/Ni₃S₂/NF) can act as an active and robust bifunctional catalyst for both urea oxidation reaction (UOR) and hydrogen evolution reaction (HER), which could drive an ultrahigh current density of 400 mA cm⁻² at a low working potential of 1.47 V versus RHE for UOR, and gives a low overpotential of 111 mV to reach 10 mA cm⁻² toward HER. Further, a hybrid water electrolysis cell utilizing the synthesized N-Co₉S₈/Ni₃S₂/NF electrode as both the cathode and anode displays a low cell voltage of 1.40 V to reach 10 mA cm⁻², which can be powered by an AA battery with a nominal voltage of 1.5 V. The density functional theory (DFT) calculations decipher that N-doped heterointerfaces can synergistically optimize Gibbs free energy of hydrogen and urea, thus accelerating the catalytic kinetics of HER and UOR. This work significantly advances the development of the promising cobalt–nickel-based sulfide as a bifunctional electrocatalyst for energy-saving electrolytic H₂ production and urea-rich innocent wastewater treatment.     

Introducing High-Valence Iridium Single Atoms into Bimetal Phosphides toward High-Efficiency Oxygen Evolution and Overall Water Splitting

Single atoms are superior electrocatalysts having high atomic utilization and amazing activity for water oxidation and splitting. Herein, this work reports a thermal reduction method to introduce high-valence iridium (Ir) single atoms into bimetal phosphide (FeNiP) nanoparticles toward high-efficiency oxygen evolution reaction (OER) and overall water splitting. The presence of high-valence single Ir atoms (Ir⁴⁺) and their synergistic interaction with Ni³⁺ species as well as the disproportionation of Ni³⁺ assisted by Fe collectively contribute to the exceptional OER performance. In specific, at appropriate Ir/Ni and Fe/Ni ratios, the as-prepared Ir-doped FeNiP (Ir₂₅-Fe₁₆Ni₁₀₀P₆₄) nanoparticles at a mass loading of only 35 µg cm⁻² show the overpotential as low as 232 mV at 10 mA cm⁻² and activity as high as 1.86 A mg⁻¹ at 1.5 V versus RHE for OER in 1.0 m KOH. Computational simulations confirm the vital role of high-valence Ir to weaken the adsorption of OER intermediates, favorable for accelerating OER kinetics. Impressively, a Pt/C||Ir₂₅-Fe₁₆Ni₁₀₀P₆₄ two-electrode alkaline electrolyzer affords a current density of 10 mA cm⁻² at a low cell voltage of 1.42 V, along with satisfied stability. An AA battery with a nominal voltage of 1.5 V can drive overall water splitting with obvious bubbles released.     

Dense-Packed RuO2 Nanorods with In Situ Generated Metal Vacancies Loaded on SnO2 Nanocubes for Proton Exchange Membrane Water Electrolyzer with Ultra-Low Noble Metal Loading

Proton exchange membrane water electrolyzer (PEMWE) is a green hydrogen production technology that can be coupled with intermittent power sources such as wind and photoelectric power. To achieve cost-effective operations, low noble metal loading on the anode catalyst layer is desired. In this study, a catalyst with RuO₂ nanorods coated outside SnO₂ nanocubes is designed, which forms continuous networks and provides high conductivity. This allows for the reduction of Ru contents in catalysts. Furthermore, the structure evolutions on the RuO₂ surface are carefully investigated. The etched RuO₂ surfaces are seen as the consequence of Co leaching, and theoretical calculations demonstrate that it is more effective in driving oxygen evolution. For electrochemical tests, the catalysts with 23 wt% Ru exhibit an overpotential of 178 mV at 10 mA cm⁻², which is much higher than most state-of-art oxygen evolution catalysts. In a practical PEMWE, the noble metal Ru loading on the anode side is only 0.3 mg cm⁻². The cell achieves 1.61 V at 1 A cm⁻² and proper stability at 500 mA cm⁻², demonstrating the effectiveness of the designed catalyst.