Tandem Photoelectrochemical Cell Research Articles

TiO2 Photonic Crystal Sensitized with Mn3O4 Nanoparticles and Porphine Manganese(III) as Efficient Photoanode for Photoelectrochemical Water Splitting

We report the synthesis and photoelectrochemical characterization of a novel composite consisting of Mn3O4 nanoparticles, porphine manganese(III) (PMA), and TiO2 photonic crystal (TPC). The prepared composite (Mn3O4/PMA/TPC) was used for fabricating the photoanode of a photoelectrochemical tandem cell. The obtained Mn3O4/PMA/TPC composite was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and UV–vis diffuse reflectance spectroscopy (DRS). The results demonstrated that PMA and Mn3O4 nanoparticles had been loaded in the hole of TPC successfully. The photoelectrochemical characterization of the Mn3O4/PMA/TPC electrode revealed an enhanced light harvesting and effective electron–hole separation. The photoelectrochemical tandem cell, of which Mn3O4/PMA/TPC electrode acted as a photoanode and a Pt plate as counter electrode, was used to evaluate the feasibility for water splitting to produce H2 and O2 under a 300 W solar simulator irradiation. The gases evolved from...

A low-cost photoelectrochemical tandem cell for highly-stable and efficient solar water splitting

The stability and cost of solar-driven water splitting system are still the main bottlenecks for its large-scale implementation. Here, an ingeniously designed low-cost photoelectrochemical tandem cell possessing three performance-superior components, i.e., a front novel photoanode of WO3 nanoplates epitaxially coated with [001]-oriented TiO2 nanoprickles, and a rear Si photovoltaic cell, and a counter-cathode of interlayer-expanded MoS2 nanostructures, is reported for highly-stable and efficient solar water splitting. The tandem cell shows a close-to-unity Coulomb efficiency for water splitting, and a high and sustained-stable solar-to-hydrogen efficiency in a 35 days’ test. The result also reveals that it is versatile in solar-driven wastewater treatment. Most importantly, the composite photoanode that, for the first time, is proposed using epitaxial-growth based on double-match, i.e. lattice match and band match, shows dramatical improvement in stability and photoelectrochemical performance, in which the photocurrent of the WO3/ TiO2 photoanode is improved by 80% without any obvious decay after 100h of continuous testing compared with a 92% decay in photocurrent for the WO3 photoanode. The epitaxial TiO2 layer facilitates interfacial charge transportations and provides a complete sealing of WO3 surfaces at an atomic level. Such efficient interfacial design and system-level integration of high-performance nanomaterials shed a unique light on the potential large-scale implementation of solar water splitting for renewable hydrogen fuel production.

Characterization of opto-electrical enhancement of tandem photoelectrochemical cells by using photoconductive-AFM

Solar-to-hydrogen conversion by water splitting in photoelectrochemical cells (PECs) is a promising approach to alleviate problems associated with intermittency in solar energy supply and demand. Several interfacial resistances in photoelectrodes limit the performance of such cells, while the properties of interfaces are not easy to analyze in situ. We applied photoconductive-AFM to analyze the performance of WO3/p+n Si photoanodes, containing an ultra-thin metal interface of either Au or Pt. The Au interface consisted of Au nanoparticles with well-ordered interspacing, while Pt was present in the form of a continuous film. Photoconductive-AFM data show that upon illumination significantly larger currents are measured for the WO3/p+n Si anode equipped with the Au interface, as compared to the WO3/p+n Si anode with the Pt interface, in agreement with the better performance of the former electrode in a photoelectrochemical cell. The remarkable performance of the Au-containing electrode is proposed to be the result of favorable electron-hole recombination rates induced by the Au nanoparticles in a plasmon resonance excited state.

Spinel Ferrites MFe2O4 (M = Cu, Mg, Zn) As Emerging Photoanodes for Water Oxidation: An in-Depth Analysis of the Photoelectrochemical Properties

The direct energy conversion of sunlight into hydrogen by using photoelectrochemical (PEC) tandem cells has emerged as a leading technology to tackle the growing demand of hydrogen in an environmentally-friendly and potentially cost-effective way. Basically, the device comprises a photocathode and a photoanode wired together, which under illumination delivers an overall photovoltage above 1.23 V, enough to drive the reduction and oxidation of water on the respective surfaces of the electrodes with reasonable currents. Despite the encouraging progress in the development of a wide-variety of low-cost and high-performing photocathodes by solution-based approaches, the rather short family of available photoanodes for water oxidation (Fe2O3, WO3, BiVO4, TaON) and their low-performance is one major bottlenecks in the overall solar-to-hydrogen conversion of these devices. Exploring new materials for water photo-oxidation may help the development of promising photoanodes with favorable optical and electronic properties enlarging the family of photoanodes available to combine with the vast library of photocathodes. The quest for new materials for water photo-oxidation has recently found in the vast family of spinel ferrites (MFe2O4, M = Ba, Ca, Cu, Co, Mg, Mn, Ni, Zn) a promising candidate, leveraging a remarkable chemical stability together with a broad optoelectronic tunability (band gap between 1.4-2.7 eV by selecting the M cation) [1]. However, very little is known about the potential of these materials as photoelectrodes for solar energy conversion or on the main limiting factors on the performance. Herein, thin-film electrodes of three representative spinels, namely CuFe2O4, MgFe2O4 and ZnFe2O4, were fabricated by a solution-based approach and their PEC properties were extensively characterized. Annealing post-treatments together with the deposition of a well-known electrocatalyst (NiFeOx) demonstrated to effectively improve the native n-type response, although a strong bulk recombination (especially in MgFe2O4) limits the saturation photocurrents (below 0.4 mA cm-2 at 1.23 V vs RHE). Apart from the drawbacks related to bulk properties, a strong Fermi level pinning detected at around 0.9 V vs RHE in all the cases appears to dictate the low photovoltages delivered by the electrodes (~ 300 mV for ZnFe2O4), which evidences the presence of a high-density of surface states. Although recent studies support the role of NiFeOx as an effective passivating agent capable of mitigating the Fermi level pinning in Fe2O3 [2], the combination of photocurrent and open circuit potential experiments proved unambiguously that here NiFeOx is incapable to alleviate the pinning, but participates as an electrocatalyst to improve the overall performance. Detailed analysis of the surface energetics by fast-scan cyclic voltammetry, revealed hole accumulation at the potential where Fermi level pinning occurs and next to the turn-on voltage. This provides direct evidence for the location of surface states, inherent to the oxide electrodes, and/or for intermediates involved in the water oxidation reaction. In more general vein, these results draw a complete picture of the PEC behavior of the spinel ferrites evidencing the current intrinsic limitations, and establishes a roadmap for the design of the next generation of photoanodes based on spinel ferrites. [1] Dillert, R.; Taffa, D. H.; Wark, M.; Bredow, T.; Bahnemann, D. W. APL Mater. 2015, 3 (10), 104001. [2] Jang, J.-W.; Du, C.; Ye, Y.; Lin, Y.; Yao, X.; Thorne, J.; Liu, E.; McMahon, G.; Zhu, J.; Javey, A.; Guo, J.; Wang, D. Nat. Commun. 2015, 6, 7447.

GaP/GaNP Heterojunctions for Efficient Solar-Driven Water Oxidation.

The growth and characterization of an n-GaP/i-GaNP/p+ -GaP thin film heterojunction synthesized using a gas-source molecular beam epitaxy (MBE) method, and its application for efficient solar-driven water oxidation is reported. The TiO2 /Ni passivated n-GaP/i-GaNP/p+ -GaP thin film heterojunction provides much higher photoanodic performance in 1 m KOH solution than the TiO2 /Ni-coated n-GaP substrate, leading to much lower onset potential and much higher photocurrent. There is a significant photoanodic potential shift of 764 mV at a photocurrent of 0.34 mA cm-2 , leading to an onset potential of ≈0.4 V versus reversible hydrogen electrode (RHE) at 0.34 mA cm-2 for the heterojunction. The photocurrent at the water oxidation potential (1.23 V vs RHE) is 1.46 and 7.26 mA cm-2 for the coated n-GaP and n-GaP/i-GaNP/p+ -GaP photoanodes, respectively. The passivated heterojunction offers a maximum applied bias photon-to-current efficiency (ABPE) of 1.9% while the ABPE of the coated n-GaP sample is almost zero. Furthermore, the coated n-GaP/i-GaNP/p+ -GaP heterojunction photoanode provides a broad absorption spectrum up to ≈620 nm with incident photon-to-current efficiencies (IPCEs) of over 40% from ≈400 to ≈560 nm. The high low-bias performance and broad absorption of the wide-bandgap GaP/GaNP heterojunctions render them as a promising photoanode material for tandem photoelectrochemical (PEC) cells to carry out overall solar water splitting.

Photoelectrochemical Reduction of Carbon Dioxide to Methanol through a Highly Efficient Enzyme Cascade.

Natural photosynthesis is an effective route for the clean and sustainable conversion of CO2 into high-energy chemicals. Inspired by the natural process, a tandem photoelectrochemical (PEC) cell with an integrated enzyme-cascade (TPIEC) system was designed, which transfers photogenerated electrons to a multienzyme cascade for the biocatalyzed reduction of CO2 to methanol. A hematite photoanode and a bismuth ferrite photocathode were applied to fabricate the iron oxide based tandem PEC cell for visible-light-assisted regeneration of the nicotinamide cofactor (NADH). The cell utilized water as an electron donor and spontaneously regenerated NADH. To complete the TPIEC system, a superior three-dehydrogenase cascade system was employed in the cathodic part of the PEC cell. Under applied bias, the TPIEC system achieved a high methanol conversion output of 220 μm h-1 , 1280 μmol g-1 h-1 using readily available solar energy and water.

Photoelectrochemical Reduction of Carbon Dioxide to Methanol through a Highly Efficient Enzyme Cascade

AbstractNatural photosynthesis is an effective route for the clean and sustainable conversion of CO2 into high‐energy chemicals. Inspired by the natural process, a tandem photoelectrochemical (PEC) cell with an integrated enzyme‐cascade (TPIEC) system was designed, which transfers photogenerated electrons to a multienzyme cascade for the biocatalyzed reduction of CO2 to methanol. A hematite photoanode and a bismuth ferrite photocathode were applied to fabricate the iron oxide based tandem PEC cell for visible‐light‐assisted regeneration of the nicotinamide cofactor (NADH). The cell utilized water as an electron donor and spontaneously regenerated NADH. To complete the TPIEC system, a superior three‐dehydrogenase cascade system was employed in the cathodic part of the PEC cell. Under applied bias, the TPIEC system achieved a high methanol conversion output of 220 μm h−1, 1280 μmol g−1 h−1 using readily available solar energy and water.

CuInGaS2 photocathodes treated with SbX3 (X = Cl, I): the effect of the halide on solar water splitting performance

The realization of photoelectrochemical tandem cells for efficient solar-to-hydrogen energy conversion is currently impeded by the lack of inexpensive, stable, and efficient photocathodes. The family of sulfide chalcopyrites (CuInxGa1−xS2) has recently demonstrated a remarkable stability and performance even when prepared by solution-based routes that potentially lower the cost of fabrication. However, the photovoltage delivered by the photocathodes is still well-below the attainable values, a classical limitation linked to a large density of surface states in these materials. In the present work, we show that the identity of halide present during the growth of the solution-processed CuIn0.3Ga0.7S2 (CIGS) thin-films governs the overall performance by directing the crystal growth and the passivation of surface states. Replacing chlorine by iodine leads to CIGS photocathodes that deliver photocurrents of 5 mA cm−2 (at 0 V versus RHE) and a turn-on voltage of 0.5 V versus RHE without charge extracting overlayer nor any sign of deterioration during stability test.

A Cu2O/Cu2S-ZnO/CdS tandem photoelectrochemical cell for self-driven solar water splitting

A self-driven tandem cell for overall water splitting composed of a p-Cu2O photocathode modified with a thin Cu2S layer connected to a n-ZnO/CdS nanowire photoanode is demonstrated. By calculating the absorbed photon flux, it is proved that the two photoelectrodes are well spectral-matched in the wavelength range of 300–800 nm. Compared with the bare Cu2O photocathode, the Cu2S modified Cu2O counterpart has a higher photocurrent and a more anodic turn-on voltage due to the improved light absorption and the reduced charge transfer resistance. The photoelectrochemical (PEC) properties of the Cu2O/Cu2S photocathode coupled to the ZnO/CdS photoanode were investigated to demonstrate the feasibility of unassisted solar water splitting. An apparent photocurrent was observed for the tandem cell at zero bias, corresponding to a photoconversion efficiency of 0.38%. Our results indicate the tandem PEC cells based on connected semiconductor electrodes made from earth abundant elements have promising application potential in overall solar water splitting.

A Dye-Sensitized Photoelectrochemical Tandem Cell for Light Driven Hydrogen Production from Water.

Tandem junction photoelectrochemical water-splitting devices, whereby two light absorbing electrodes targeting separate portions of the solar spectrum generate the voltage required to convert water to oxygen and hydrogen, enable much higher possible efficiencies than single absorber systems. We report here on the development of a tandem system consisting of a dye-sensitized photoelectrochemical cell (DSPEC) wired in series with a dye-sensitized solar cell (DSC). The DSPEC photoanode incorporates a tris(bipyridine)ruthenium(II)-type chromophore and molecular ruthenium based water oxidation catalyst. The DSPEC was tested with two more-red absorbing DSC variations, one utilizing N719 dye with an I3-/I- redox mediator solution and the other D35 dye with a tris(bipyridine)cobalt ([Co(bpy)3]3+/2+) based mediator. The tandem configuration consisting of the DSPEC and D35/[Co(bpy)3]3+/2+ based DSC gave the best overall performance and demonstrated the production of H2 from H2O with the only energy input from simulated solar illumination.

Enhanced Output from Biohybrid Photoelectrochemical Transparent Tandem Cells Integrating Photosynthetic Proteins Genetically Modified for Expanded Solar Energy Harvesting

A transparent biohybrid photoelectrochemical tandem cell is developed by employing optically-complementary variants of a photosynthetic protein in a stacked tandem architecture that utilizes a conductive polymer, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), as a transparent counter electrode. The tandem design demonstrates the photocurrent enhancement by complementary absorption of two naturally-occurring red and green versions of a bacterial Reaction center/Light Harvesting protein (RC-LH1) that vary in the type of light harvesting carotenoid feeding the central reaction center module with excited state energy. The use of PEDOT:PSS electrode results in a 12-fold improvement in photocurrent compared to that achievable with Platinum.

Investigating Water Splitting with CaFe2O4 Photocathodes by Electrochemical Impedance Spectroscopy

Artificial photosynthesis constitutes one of the most promising alternatives for harvesting solar energy in the form of fuels, such as hydrogen. Among the different devices that could be developed to achieve efficient water photosplitting, tandem photoelectrochemical cells show more flexibility and offer high theoretical conversion efficiency. The development of these cells depends on finding efficient and stable photoanodes and, particularly, photocathodes, which requires having reliable information on the mechanism of charge transfer at the semiconductor/solution interface. In this context, this work deals with the preparation of thin film calcium ferrite electrodes and their photoelectrochemical characterization for hydrogen generation by means of electrochemical impedance spectroscopy (EIS). A fully theoretical model that includes elementary steps for electron transfer to the electrolyte and surface recombination with photogenerated holes is presented. The model also takes into account the complexity of the semiconductor/solution interface by including the capacitances of the space charge region, the surface states and the Helmholtz layer (as a constant phase element). After illustrating the predicted Nyquist plots in a general manner, the experimental results for calcium ferrite electrodes at different applied potentials and under different illumination intensities are fitted to the model. The excellent agreement between the model and the experimental results is illustrated by the simultaneous fit of both Nyquist and Bode plots. The concordance between both theory and experiments allows us to conclude that a direct transfer of electrons from the conduction band to water prevails for hydrogen photogeneration on calcium ferrite electrodes and that most of the carrier recombination occurs in the material bulk. In more general vein, this study illustrates how the use of EIS may provide important clues about the behavior of photoelectrodes and the main strategies for their improvement.

Optimization hydrogen production over visible light-driven titania-supported bimetallic photocatalyst from water photosplitting in tandem photoelectrochemical cell

Solar hydrogen production was investigated over a Cu-Ni doped TiO2 photocatalyst from water photosplitting in a tandem photoelectrochemical cell, which was made up by connecting a modified photoelectrochemical cell to dye solar cell in a series. A mathematical representation for preparation parameters for hydrogen production was successfully generated. Optimization of hydrogen production was conducted with varying preparation parameters of Cu-Ni doped TiO2 photocatalyst including molar ratios of water, acetic acid and Cu to titanium tetraisopropoxide. The optimum preparation parameters of photocatalyst was obtained at molar ratios of water, acetic acid and Cu to titanium tetraisopropoxide of 32, 4.9, and 5.9, respectively. Physical and photoelectrochemical characterization revealed that low content of water and Cu decreased the charge transfer resistance and charge carrier recombination rate on Cu-Ni/TiO2 surface. This is attributed to the better crystallinity and less degree of agglomeration which led to obtain optimum particle size at this condition. Maximum hydrogen production rate of 2.12 mL/cm2. h was achieved under the optimum condition using the tandem photoelectrochemical cell in the aqueous KOH and glycerol solution under visible light irradiation (λ > 400 nm).

P-Type Cu-Doped Zn0.3Cd0.7S/Graphene Photocathode for Efficient Water Splitting in a Photoelectrochemical Tandem Cell

By doping Cu(I) ions in Zn0.3Cd0.7S, a novel p-type Cu doped Zn0.3Cd0.7S modified graphene (Zn0.3Cd0.7S (Cu)/GR) film photocathode was prepared. The as-prepared p-type Zn0.3Cd0.7S (Cu)/GR photocathode and an n-type WO3/graphene (WO3/GR) photoanode were used to assemble a photoelectrochemical tandem cell. Through examination of the optoelectronic and photoelectrochemical properties of Zn0.3Cd0.7S (Cu)/GR and WO3/GR photoelectrode, we evaluate the feasibility of the tandem cell for overall water splitting under UV–vis light irradiation. The optimal Cu doping in Zn0.3Cd0.7S photocathode concentration was found to be 6%. The rates of hydrogen and oxygen evolved from this tandem cell with the optimal electrodes were 65.6 and 12.3 μmol g–1 h–1 (80.5 and 15.1 μmol cm–2 h–1), respectively. This study suggests a promising method for constructing an efficient photoelectrochemical tandem device for overall water splitting.

(Invited) Photoelectrochemical Investigation of Ta3N5 Films on TCO Substrates Synthesized Via Atomic Layer Deposition for Photocatalytic Water Splitting

Solar driven photoelectrochemical (PEC) water splitting is a promising method to store solar energy in chemical bonds. Tantalum nitride (Ta3N5) has recently emerged as a promising candidate for PEC water splitting. Most of the studies on Ta3N5 begin with a similar synthetic route, consisting of an initial oxidation of Ta(0) metal to Ta(IV), followed by ammonolysis at elevated temperatures ( > 850 °C). Despite the simplicity of this method, there are also several drawbacks. Importantly, the high temperature ammonolysis limits the utilization of transparent conductive oxide (TCO) substrates which are necessary for fundamental photoelectrochemical measurements. In addition, lack of viable TCOs thwart use of Ta3N5 as the top electrode in a tandem PEC cell. As a solution to the above problems, we will present the synthesis of Ta-doped TiO2 (TTO) as a TCO substrate via atomic layer deposition (ALD) which we found to be stable in reducing atmospheres. ALD was also used to directly deposit thin films of Ta3N5 on TTO. While initial attempts produced as-deposited films are primarily amorphous TaOxNy, these films can be nitridized to Ta3N5 at far more moderate conditions compared to all previous reports and ALD–deposited tantalum oxide analogue films. The photoelectrochemical properties of the TTO/Ta3N5 films were investigated and the PEC water oxidation performance was analyzed. The excellent material control reported here allowed for a detailed material structure – function relationship to be determined and a path to improved performance elucidated. Initial results of a modified procedure, including ALD precursor and temperature variations, which allowed the direct synthesis of crystalline Ta3N5 on TTO substrates, will also be presented.

ChemInform Abstract: Molecular Catalyst Immobilized Photocathodes for Water/Proton and Carbon Dioxide Reduction

AbstractReview: 74 refs.

Design of a Monolithic Photoelectrochemical Tandem Cell for Solar Water Splitting with a Dye-sensitized Solar Cell and WO3/BiVO4Photoanode

Photoelectrochemical cell (PEC) is one of the attractive ways to produce clean and renewable energy. However, solar to hydrogen production via PEC system generally requires high external bias, because of material`s innate electronic band potential relative to hydrogen reduction potential and/or charge separation issue. For spontaneous photo-water splitting, here, we design dye-sensitized solar cell (DSSC) and their monolithic tandem cell incorporated with a photoanode. has high conduction band edge potential and suitable band gap (2.4eV) to absorb visible light. To achieve efficient photoanode system, electron and hole mobility should be improved, and we demonstrate a tandem cell in which film is connected to cobalt complex based DSSC.

Overall Photoelectrochemical Water Splitting using Tandem Cell under Simulated Sunlight.

A stand-alone photoelectrochemical (PEC) water-splitting system driven only by sunlight was demonstrated with a tandem-scheme of Pt/CdS/CuGa3 Se5 /(Ag,Cu)GaSe2 photocathode and NiOOH/FeOOH/Mo:BiVO4 photoanode in a neutral phosphate buffer solution as an electrolyte. The as-prepared semi-transparent Mo:BiVO4 layer allows sunlight to pass through the top photoanode and reach the bottom photocathode. Consequently, the tandem cell showed stoichiometric hydrogen and oxygen evolution with a solar-to-hydrogen (STH) conversion efficiency of 0.67 % over 2 h without degradation. The stability and STH efficiency are the highest among similar configuration of PEC tandem cells.

Multifunctional Coatings from Scalable Single Source Precursor Chemistry in Tandem Photoelectrochemical Water Splitting

The straightforward and inexpensive fabrication of stabilized and activated photoelectrodes for application to tandem photoelectrochemical (PEC) water splitting is reported. Semiconductors such as Si, WO3, and BiVO4 can be coated with a composite layer formed upon hydrolytic decomposition of hetero­bimetallic single source precursors (SSPs) based on Ti and Ni, or Ti and Co in a simple single‐step process under ambient conditions. The resulting 3d‐transition metal oxide composite films are multifunctional, as they protect the semiconductor electrode from corrosion with an amorphous TiO2 coating and act as bifunctional electrocatalysts for H2 and O2 evolution based on catalytic Ni or Co species. Thus, this approach enables the use of the same precursors for both photoelectrodes in tandem PEC water splitting, and SSP chemistry is thereby established as a highly versatile low‐cost approach to protect and activate photoelectrodes. In an optimized system, SSP coating of a Si photocathode and a BiVO4 photoanode resulted in a benchmark noble metal‐free dual‐photoelectrode tandem PEC cell for overall solar water splitting with an applied bias solar‐to‐hydrogen conversion efficiency of 0.59% and a half‐life photostability of 5 h.

Wireless Solar Water Splitting Device with Robust Cobalt-Catalyzed, Dual-Doped BiVO4 Photoanode and Perovskite Solar Cell in Tandem: A Dual Absorber Artificial Leaf.

A stand-alone, wireless solar water splitting device without external energy supply has been realized by combining in tandem a CH3NH3PbI3 perovskite single junction solar cell with a cobalt carbonate (Co-Ci)-catalyzed, extrinsic/intrinsic dual-doped BiVO4 (hydrogen-treated and 3 at% Mo-doped). The photoanode recorded one of the highest photoelectrochemical water oxidation activity (4.8 mA/cm(2) at 1.23 VRHE) under simulated 1 sun illumination. The oxygen evolution Co-Ci co-catalyst showed similar performance to best known cobalt phosphate (Co-Pi) (5.0 mA/cm(2) at 1.23 VRHE) on the same dual-doped BiVO4 photoanode, but with significantly better stability. A tandem artificial-leaf-type device produced stoichiometric hydrogen and oxygen with an average solar-to-hydrogen efficiency of 4.3% (wired), 3.0% (wireless) under simulated 1 sun illumination. Hence, our device based on a D4 tandem photoelectrochemical cell represents a meaningful advancement in performance and cost over the device based on a triple-junction solar cell-electrocatalyst combination.