Photoelectrochemical Conversion Efficiency Research Articles

High‐Efficiency Monolithic Photosupercapacitors: Smart Integration of a Perovskite Solar Cell with a Mesoporous Carbon Double‐Layer Capacitor

The integration of solar cells with supercapacitors into hybrid monolithic power packs can provide energy autonomy to smart electronic devices of the Internet of Things (IoT) by mediating between intermittent load and supply. Herein, such a photorechargeable supercapacitor (also called a photosupercapacitor) is developed via a three‐electrode integration of a p–i–n halide perovskite solar cell with a gel electrolyte‐type supercapacitor that uses mesoporous N‐doped carbon nanospheres (MPNC) as the active electrode material. Benefiting from the large surface area, well‐defined mesoporous structure, and homogeneous particle size of the MPNC material, the supercapacitor demonstrates high capacitance, resulting in large energy and power densities with a high charge/discharge efficiency. Its integration with a large‐area (1 cm2) FA0.75Cs0.25Pb(I0.8Br0.2)3 perovskite solar cell, with an optimized layer sequence to minimize degradation, results in a photosupercapacitor exhibiting fast (< 5 s) photocharging up to 1 V. The outstanding peak overall photoelectrochemical energy conversion efficiency of 11.5% is a result of a high solar cell power conversion efficiency of 12.5%, a high supercapacitor storage efficiency of 92%, and low internal energy losses due to monolithic integration. These results underline the high potential of this type of device toward application in the IoT.

Efficient Photoelectrochemical Conversion of Methane into Ethylene Glycol by WO3 Nanobar Arrays

AbstractPhotoelectrochemical (PEC) conversion of methane (CH4) has been extensively explored for the production of value‐added chemicals, yet remains a great challenge in high selectivity toward C2+ products. Herein, we report the optimization of the reactivity of hydroxyl radicals (.OH) on WO3 via facet tuning to achieve efficient ethylene glycol production from PEC CH4 conversion. A combination of materials simulation and radicals trapping test provides insight into the reactivity of .OH on different facets of WO3, showing the highest reactivity of surface‐bound .OH on {010} facets. As such, the WO3 with the highest {010} facet ratio exhibits a superior PEC CH4 conversion efficiency, reaching an ethylene glycol production rate of 0.47 μmol cm−2 h−1. Based on in situ characterization, the methanol, which could be attacked by reactive .OH to form hydroxymethyl radicals, is confirmed to be the main intermediate for the production of ethylene glycol. Our finding is expected to provide new insight for the design of active and selective catalysts toward PEC CH4 conversion.

Efficient Photoelectrochemical Conversion of Methane into Ethylene Glycol by WO3 Nanobar Arrays.

Photoelectrochemical (PEC) conversion of methane (CH4 ) has been extensively explored for the production of value-added chemicals, yet remains a great challenge in high selectivity toward C2+ products. Herein, we report the optimization of the reactivity of hydroxyl radicals (. OH) on WO3 via facet tuning to achieve efficient ethylene glycol production from PEC CH4 conversion. A combination of materials simulation and radicals trapping test provides insight into the reactivity of . OH on different facets of WO3 , showing the highest reactivity of surface-bound . OH on {010} facets. As such, the WO3 with the highest {010} facet ratio exhibits a superior PEC CH4 conversion efficiency, reaching an ethylene glycol production rate of 0.47 μmol cm-2 h-1 . Based on in situ characterization, the methanol, which could be attacked by reactive . OH to form hydroxymethyl radicals, is confirmed to be the main intermediate for the production of ethylene glycol. Our finding is expected to provide new insight for the design of active and selective catalysts toward PEC CH4 conversion.

Efficiency enhancement in a stoichiometrically stable CdS/TiO2 nanotube heterostructure electrode for sunlight-driven hydrogen generation

A stoichiometrically stable CdS/TiO2 heterostructured electrode was developed via electrodeposition for efficient photoelectrochemical conversion.

Efficient photoelectrochemical conversion of CO2 to syngas by photocathode engineering

The synthesis of renewable chemical fuels from CO2 and H2O via photoelectrochemical (PEC) route reprensents a promising room-temperature approach for transforming greenhouse gas into value-added chemicals (e.g., syngas), but to date it has been hampered by the lack of efficient photocathode for CO2 reduction. Herein, we report efficient PEC CO2 reduction into syngas by photocathode engineering. The photocathode is consisting of a planar p-n Si junction for strong light harvesting, GaN nanowires for efficient electron extraction and transfer, and Au/TiO2 for rapid electrocatalytic syngas production. The photocathode yields a record-high solar energy conversion efficiency of 2.3%. Furthermore, desirable syngas compositions with CO/H2 ratios such as 1:2 and 1:1 can be produced by simply varying the size of Au nanoparticle. Theoretical calculations reveal that the active sites for CO and H2 generation are the facet and undercoordinated sites of Au particles, respectively.

Core-shell cadmium sulphide @ silver sulphide nanowires surface architecture: Design towards photoelectrochemical solar cells

Design and development of cadmium sulphide core with silver sulphide shell assembly in nanowire (NWs) surface architecture has been explored through room temperature, simple chemical route towards photoelectrochemical solar cell application. Incorporation of low band gap Ag2S nanoparticles over the outer surface of the chemical bath deposited CdS NWs has been achieved by simple cation exchange route based on negative free energy of formation. Shell optimization has been performed by investigating structure, surface morphologies and optical analyses and correlated with the photovoltaic parameters. Interestingly, core–shell CdS NWs/ Ag2S exhibits 1.5 better performance in terms of linear voltammetry, photocurrent transient response and the photo stability than bare CdS. Furthermore, three-fold enhancement in photoelectrochemical conversion efficiency have been observed for optimized FTO/ CdS NWs/Ag2S compared to bare FTO/CdS NWs due to the augmented light harvesting and condensed charge recombination. External quantum efficiency exhibits 24% for the optimized CdS NWs/ Ag2S core shell structure. Mott-Schottky and electrochemical impedance spectroscopy measurements have been used for better understanding the impact of gradual growth of Ag2S over CdS NWs which directly influences the overall photocurrent density of the devices.

Efficient TiO2/AgInS2/ZnS Nanoarchitecture Photoelectrode for the Photoelectrochemical Cathodic Protection of Copper in NaCl Solution

An environmentally friendly AgInS2/ZnS nanoparticles (NPs) co-sensitized TiO2 ultrafine branched nanolawn photoelectrode was constructed by depositing AgInS2 sensitizer and ZnS passivator on TiO2 ultrafine nanostructure. This architecture significantly improved the photoelectrochemical conversion efficiency and photoelectrochemical cathodic protection performance for pure copper with a more negative self-corrosion potential under simulated sunlight illumination and in NaCl solution containing no additional hole scavengers. Compared with single AgInS2 NPs sensitized TiO2, the design of ZnS passivation layer on TiO2/AgInS2 significantly improves the charge generation and separation efficiency, and promotes the consumption of the photogenerated holes. The three-dimensional TiO2 with porous ultrafine nanobranched structure possesses high-speed electron transmission pathways and facilitates the rapid collection and migration of the photogenerated electrons. Since the conduction band potentials of AgInS2 and ZnS are more negative, the photogenerated electrons generated by TiO2/AgInS2/ZnS will be maintained at a more negative quasi-Fermi level. This ensures that the photogenerated electrons can be transferred to pure copper. The present work provides new ideas for designing nanoheterojunction materials for the protection of pure copper and other metallic materials with more negative self-corrosion potentials exposed in marine environment under simulated sunlight illumination.

Cu(In,Ga)Se2 for selective and efficient photoelectrochemical conversion of CO2 into CO

The performance of photoelectrochemical (PEC) CO2 reduction on a photocathode is determined by the light absorption, charge separation and charge transfer efficiency of the photocathode according toηtotal = ηabs * ηsep * ηtran. Herein, we for the first time establish a photocathode for CO2 reduction on the base of commercially-available p-type Cu(In,Ga)Se2 (CIGS). CIGS has a very high optical absorption coefficient up to 105 cm−1 in wide wavelength region. It reaches an ultrahigh photocurrent density of 4.8 mA cm−2 at −0.2 V vs. RHE and 11.5 mA cm−2 at −0.7 V vs. RHE. Importantly, by fixing the bias at −0.2 V vs. RHE, the CIGS/CdS/ZnO/AZO photocathode selectively converts CO2 into CO with a faradaic efficiency of 99.3%. This is the highest record among the state-of-the-art photocathodes for CO2 to CO. Our work opens new opportunity for CIGS in solar-induced chemical reactions, and is expected to be concerned by researchers who are interested in catalysis and PECs.

Highly efficient 3D-ZnO nanosheet photoelectrodes for solar-driven water splitting: Chalcogenide nanoparticle sensitization and mathematical modeling

Three-dimensional (3D) zinc oxide nanosheets (ZnO-NS), assembled on the FTO coated glass substrates after chemical treatment, have been achieved via a simple yet effective chemical bath deposition technique. The exploration of chalcogenide nanoparticle sensitization on ZnO-NS thin-film photoanodes led us to a spectacular enhancement in the photoelectrochemical conversion efficiency for solar-driven water splitting process as compared to the bare 3D-ZnO-NS. The maximum incident photon-to-charge carrier efficiency of bare 3D-ZnO-NS has been enhanced by approximately four folds as a result of cadmium sulfide (CdS) and cadmium selenide (CdSe) sensitization and the efficiency value have reached to 51% at 550 nm. Besides, the maximum charge injection and charge separation efficiencies of the ZnO–CdSe electrodes have been calculated as 93% and 64%, respectively. Numerical examination of the optical absorption and electrical field distribution has been performed via the finite-difference time-domain (FDTD) method in order to investigate the basis of the enhancement in the photoelectrochemical efficiencies of the 3D-ZnO-NS photoelectrodes. FDTD numerical simulation proved that the accumulation of rectangular 2D-nanosheets of ZnO in 3D-microspherical forms enhanced the light absorption significantly. Moreover, FDTD results also verified that the optical absorption of the ZnO electrodes has been extended from ultraviolet to visible region via CdS and CdSe nanoparticle deposition.

Electrochemically Deposited NiO Films as a Blocking Layer in p-Type Dye-Sensitized Solar Cells with an Impressive 45% Fill Factor.

The enhancement of photoelectrochemical conversion efficiency of p-type dye-sensitized solar cells (p-DSSCs) is necessary to build up effective tandem devices in which both anode and cathode are photoactive. The efficiency of a p-type device (2.5%) is roughly one order of magnitude lower than the n-type counterparts (13.1%), thus limiting the overall efficiency of the tandem cell, especially in terms of powered current density. This is mainly due to the recombination reaction that occurs especially at the photocathode (or Indium-doped Tin Oxide (ITO))/electrolyte interface. To minimize this phenomenon, a widely employed strategy is to deposit a compact film of NiO (acting as a blocking electrode) beneath the porous electrode. Here, we propose electrodeposition as a cheap, easy scalable and environmental-friendly approach to deposit nanometric films directly on ITO glass. The results are compared to a blocking layer made by means of sol-gel technique. Cells embodying a blocking layer substantially outperformed the reference device. Among them, BL_1.10V shows the best photoconversion efficiency (0.166%) and one of the highest values of fill factor (approaching 46%) ever reported. This is mainly due to an optimized surface roughness of the blocking layer assuring a good deposition of the porous layer. The effectiveness of the implementation of the blocking layer is further proved by means of Electrochemical Impedance Spectroscopy.

Facile Fabrication of Plasmonic Enhanced Noble-Metal-Decorated ZnO Nanowire Arrays for Dye-Sensitized Solar Cells

Novel decoration of high aspect ratio zinc oxide nanowires (ZnO NWs) with noble metals such as Ag and Au nanoparticles (NPs) was demonstrated in this work. A facile method of chemical deposition with good controllability, as well as good homogeneity would be a huge advantage towards large scale fabrication. The highlight of this work is the feasibility of multiple component decoration such as a hybrid (co-exist) Ag-Au NPs decorated ZnO NWs formation that could be beneficial towards the development of nanoarchitectured materials with the most desired properties. The local surface plasmon effect (LSPR) of Ag and Au NPs were confirmed using extinction spectra and significant photoelectrochemical conversion efficiency (PCE) enhancement of dye-sensitized solar cells (DSSCs) was achieved. The Ag-NPs and hybrid Ag-Au NPs decorated ZnO NWs marked an impressive 125 and 240% efficiency improvement against pure ZnO NWs. The improved dye light extinction resulted from the LSPR effect that had enabled greater electron generation leading to improved PCE. As the complex design of oxides' nanoarchitectures have reached a point of saturation, this novel method would enable further enhancement in their photoelectrochemical properties through decoration with noble metals via a simple chemical deposition route.

Growth of NiMn layered double hydroxides on nanopyramidal BiVO4 photoanode for enhanced photoelectrochemical performance

Photoelectrochemical water oxidation for hydrogen generation via utilizing sunlight is considered a very promising pathway for generating sustainable energy in an environmental manner. Here, a composite photoanode, consisting of nanopyramidal BiVO4 arrays and one layered double hydroxide (NiMn-LDH) was designed and fabricated via a facile route. The obtained BiVO4/NiMn-LDH composite photoelectrode presented a significant enhancement in the photoelectrochemical (PEC) current density, conversion efficiency and stability for solar water oxidation. With 2D NiMn-LDH decoration, an obvious cathodic shift of ∼480 mV in the onset potential can be observed, and more than two times enhancement in photocurrent performance is achieved. The improvement in photoelectrochemical activity for BiVO4/NiMn-LDH composite photoanode can be attributed to the enhanced water-oxidation kinetics leading to the efficient separation, transfer and collection of charge carriers at the photoanode/electrolyte interface. The result demonstrates NiMn-LDH represents one of the active oxygen evolution catalysts (OECs) to improve the PEC activity of metal oxide photoanode.

Study of TiO2 nanotubes decorated with PbS nanoparticles elaborated by pulsed laser deposition: microstructural, optoelectronic and photoelectrochemical properties

Titanium dioxide nanotube arrays (TiO2 NTAs) have been synthesized using the electrochemical anodization procedure. Lead sulfide nanoparticles (PbS NPs) were deposited on TiO2 NTAs (PbS NPs/TiO2 NTAs) using the pulsed laser deposition (PLD) method. The prepared samples (PbS NPs/TiO2 NTAs) were characterized using scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–Vis spectroscopy and photoluminescence. The size of the PbS NPs was controlled by varying the number of laser pulses (NLP) during the PLD process. TEM observations show that the PbS NPs are in the range of 10–20 nm, consistent with the results obtained from XRD. HRTEM and diffuse reflectivity show that, at NLP ≥ 2500, the growth of the PbS NPs occurs on a previously formed PbS layer. Transmission and absorption spectra show that the PbS-NPs have an indirect optical bandgap which is particle size independent. This optical bandgap corresponds to excitonic transitions, which are greatly affected by oxygen defects, off-stoichiometry and other surface state defects, particularly for smaller NPs (NLP < 2500). The absorption spectra of the TiO2 NTAs show that the PbS NPs extend the absorption range of the TiO2-NTAs from the ultraviolet to the visible region, indicating that the PbS NPs/TiO2 NTAs heterojunction facilitates the separation of the photogenerated charge carriers. Photoelectrochemical analyses show that a maximum photocurrent current density of ~1.05 mA/cm2 and a photoelectrochemical conversion efficiency of 2.5% are reached for NLP = 2500 under an illumination of 100 mW/cm2 in the UV–Vis range.

Interfacial oxygen vacancies yielding long-lived holes in hematite mesocrystal-based photoanodes

Hematite (α-Fe2O3) is one of the most promising candidates as a photoanode materials for solar water splitting. Owing to the difficulty in suppressing the significant charge recombination, however, the photoelectrochemical (PEC) conversion efficiency of hematite is still far below the theoretical limit. Here we report thick hematite films (∼1500 nm) constructed by highly ordered and intimately attached hematite mesocrystals (MCs) for highly efficient PEC water oxidation. Due to the formation of abundant interfacial oxygen vacancies yielding a high carrier density of ∼1020 cm−3 and the resulting extremely large proportion of depletion regions with short depletion widths (<10 nm) in hierarchical structures, charge separation and collection efficiencies could be markedly improved. Moreover, it was found that long-lived charges are generated via excitation by shorter wavelength light (below ∼500 nm), thus enabling long-range hole transfer through the MC network to drive high efficiency of light-to-energy conversion under back illumination.

Tuning charge transfer process of MoS2 photoanode for enhanced photoelectrochemical conversion of ammonia in water into gaseous nitrogen

Charge transfer efficiency of semiconductor photoanode in photoelectrochemical (PEC) system is one of crucial factor determining the overall PEC performance. Previously, we have developed a MoS2-based PEC system that is able to specifically convert ammonia nitrogen in aqueous solution into gaseous nitrogen (e.g. N2) utilizing oxysulfur radicals. Herein, in order to solve the slow charge transfer issue of reported MoS2-based PEC oxidation system, we further improve the PEC conversion efficiency by tuning composition of MoS2/WS2 nanosheets heterojunction photoanode. The hybrid MoS2/WS2(1:1) electrode displays the highest PEC performance and ammonia conversion efficiency compared to the individual MoS2 or WS2 constituent under visible light irradiation, which can be mainly ascribed to the reduced electrode resistance and improved charge transfer efficiency according to the physiochemical, electrochemical and spectroscopic analysis. The results prove that both interfacial and interior charge carrier transfer processes of photoanode are crucial and tailorable in order to efficiently generate reactive radical species for ammonia conversion.

CdO nanonecklace: Effect of air annealing on performance of photo electrochemical cell

Thin film consisting of hierarchical cadmium oxide nanonecklaces has been synthesized through room temperature chemically deposited cadmium hydroxide nanowires as template followed by air annealing. Formation of thin film has been confirmed with aid of structural, surface morphological, valence state and optical, studies performed by X-ray diffraction, Raman analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, and UV–visible spectroscopy. Air annealing at 330 °C has enhanced the photo electrochemical power conversion efficiency of the CdO as photoanode to 0.21% configured through platinum as counter electrode and polyiodide as a liquid electrolyte. Complete device performance have been correlated through rate of recombination, and electron life time. The schematic energy band alignment also has been comprehended herein.

Multinary CdZnIn2(SeTe)5 thin films produced by arrested precipitation technique for photoelectrochemical solar cells

Chemically synthesized multinary CdZnIn2(SeTe)5 thin film used as photoanodes in solar cell have been systematically investigated. The indium ion concentration dependent morphological evolution and its consequent effect on photoelectrochemical properties were studied. The growth mechanism for the morphological evolution of CdZnIn2(SeTe)5 thin films has been proposed. Optical absorption values varied with the indium concentration and the band gap energy is found in the range 1.87eV to 1.72 eV. The X-ray diffraction (XRD) patterns reveal the formation of rhombohedra, cubic and hexagonal CdZnIn2(SeTe)5 thin films with the preferred (110), (138) and (220) orientation for CdZnIn2(SeTe)5 microflower, which is further supported by the analysis of the high resolution transmission electron micrographs (HRTEM). The SEM image revealed that the surface morphology of multinary thin films have been changed to microflower by systematic control of indium ion concentration. Finally, current-voltage measurements at different concentration for solar cell with maximum efficiency were carried out in order to find out the dominant transport mechanisms. The solar cell fabricated shows the best conversion efficiency of 1.28%. The deposition of a certain amount of indium was beneficial to the improvement of photoelectrochemical conversion efficiency. To the best of our knowledge, it is the highest efficiency for CdZnIn2(SeTe)5 based photoanode solar cells fabricated from APT.

Enhanced photoelectrocatalytic water oxidation using CoPi modified GaN/MWCNTs composite photoanodes

GaN is promising material for photoelectrochemical (PEC) water oxidation owing to its adjustable band gap and suitable band edge locations, which straddle the H+/H2 and O2/H2O redox conditions. However, due to its wide band gap and unavoidable surface defects, the PEC conversion efficiency of GaN is insufficient to be used for practical applications. To improve the PEC efficiency of GaN, we report fabrication of a cobalt phosphate (CoPi)-modified GaN/multiwall carbon nanotube (MWCNT) composite photoanode through combination of metal organic chemical vapor deposition, dip and dry methods, and electrodeposition. Here, GaN photoanodes with different MWCNT surface coverages were obtained by cost effective ‘dip and dry’ method. Different deposition cycles were performed to prepare a series of samples, which were evaluated for their photoelectrochemical water oxidation. The highest photocurrent density (Jph) of 2.23 mA/cm2 at (0 V vs. Pt electrode) was achieved in a sample with moderate incorporation of MWCNTs, formed by through three cycles of the dip and dry coating (i.e., GaN/MWCNT 3T). We attribute this result to the MWCNTs facilitating light sensitization. However, excessive MWCNT loading produced a shielding effect, which lowered the photocurrent density, and an undesirable two-plateau photocurrent behavior indicating sluggish reaction kinetics. The maximum photocurrent density Jph of 2.81 mA/cm2, (vs. Pt electrode) with solar to hydrogen conversion efficiency 0.91% was achieved for GaN/MWCNTs 3T/CoPi ternary composite photoanode, which was approximately 2.51 and 1.26 times as high as that of bare GaN and GaN/MWCNTs 3T photoanodes.

Removing Defects in WSe2 via Surface Oxidation and Etching to Improve Solar Conversion Performance

Layered metal dichalcogenide materials (MX2) have great potential for solar energy conversion. However, as-grown MX2 materials often contain edge and terrace defects that degrade semiconducting properties and hinder their solar performance. Herein, we demonstrate a simple approach to removing surface defects and improving the solar performance by using UV-generated ozone to oxidize the surface of WSe2 nanoplates and single crystals, followed by a simple soak in aqueous solutions to remove the oxide. Structural characterizations reveal that defective edges and basal plane defect sites are selectively oxidized and subsequently etched, and the ratio of the nonstoichiometric WSex species is reduced. After this treatment, p-type WSe2 single crystals show increased electron accumulation on the surface and significantly enhanced photoelectrochemical solar conversion efficiency. These results and insights will be useful in the improvement and utilization of layered MX2 materials based on both Se and S for solar energy conversion and other device applications.

Highly oriented SnS2/RGO/Ag heterostructures for boosting photoeletrochemical and photocatalytic performances via schottky and RGO-n dual-heterojunctions interfacial effects

A single semiconductor remains a great challenge for photocatalysis due to highly recombination of charge carriers. However, construction of multiple heterojunctions photocatalysts is an effective way for photocatalysis technique. Herein, two-dimensional sheet-like highly oriented SnS2/RGO/Ag (SRA) nanocomposites with multiple junctions including schottky- and RGO-n junctions designed and synthesized via hydrothermal strategy followed by in situ sequential UV reductions. The as-prepared SRA nanocomposites exhibited superior photoelectrochemical conversion efficiencies and photocatalytic activities for the degradation of typical antibiotics Norfloxacin (NOR) under simulated solar light condition, with the highest removal ratio of 94%. XPS and low temperature EPR technology demonstrates the existence of oxygen vacancies and chemical bond effect among SnS2, Ag and RGO components. Highly oriented crystal facet and efficient spatial charge carrier separations and interfacial transfers in the photo-induced redox reactions are evidenced by various physical techniques. Interestingly, in this paper, RGO was proposed to act as holes trapper to improve photo responsive charge separation in great extent. The mechanism of photoinduced redox reactions including the pathways of interfacial charges transfers and ROS species generations have been proposed in terms of the Density Functional Theory (DFT) quantum calculations and the outcomes of various physicochemical characterizations over SRA nanocomposites.