Photoelectrodes For Photoelectrochemical Water Splitting Research Articles

Zr-Doped β-In2S3 Ultrathin Nanoflakes as Photoanodes: Enhanced Visible-Light-Driven Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting via semiconductor is a promising approach to the scalable generation of renewable H2 fuels. Several characteristics are crucial for efficient water splitting in PEC cell systems, including low onset potential for the photoanode, high photocurrent, and long-term stability. In this study, we investigated metal ion doping application to prepare 2, 5, and 8 mol % Zr-doped β-In2S3 two-dimensional nanoflakes; we then used the material to create improved photoelectrodes for PEC water splitting. That Zr4+ doping in the crystal lattice of β-In2S3 led to red-shift absorption of the 40 nm wavelength, which benefits visible-light utilization. Three nanoflake samples were tested for use as PEC water splitting electrodes and compared to pure β-In2S3 nanoflakes. We found that the photocurrent density of 2 mol % Zr-doped β-In2S3 nanoflakes was nearly 10 times higher than that of pure β-In2S3 nanoflakes at 1.2 V versus a reversible hydrogen electrode (RHE). In addition, the anodi...

High-efficiency p-n junction oxide photoelectrodes for photoelectrochemical water splitting.

Development of all oxide p-n junctions makes a significant advancement in photoelectrode catalysis functional materials. In this article, we report the preparation of TiO2 nanorod (NR)/Cu2O photoanodes via a simple hydrothermal method followed by an electrochemical deposition process. This facile synthesis route can simultaneously achieve uniform TiO2 NR/Cu2O composite nanostructures and obtain varied amounts of Cu2O by controlling the deposition time. The photocurrent density of TiO2 NR/Cu2O heterojunction photoanodes enhanced the photocatalytic activity with a photocurrent density of 5.25 mA cm-2 at 1.23 V versus RHE compared to pristine TiO2 NR photoanodes under the same conditions. It is demonstrated that the presence of Cu2O has played an important role in expanding the spectral response region and reducing the photogenerated charge recombination rate. More importantly, the results provide new insights into the performance of all oxide p-n junctions as photoanodes for PEC water splitting.

CdS/Cu2S co-sensitized TiO2 branched nanorod arrays of enhanced photoelectrochemical properties by forming nanoscale heterostructure

This paper described a facile method for the design and utilization of three-dimensional TiO2 branched nanorod arrays with CdS and Cu2S quantum dots co-sensitized photoelectrode for photoelectrochemical water splitting. CdS and Cu2S quantum dots were attached on the surface of TiO2 BNRs by successive ionic layer adsorption and reaction (SILAR). The morphology and element composition of the fabricated samples were characterized by field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and the optical features were measured by UV–vis diffuse reflection spectroscopy (UV–vis DRS) and photocurrent density–voltage (I–V) curves. The photocurrent value can be significantly enhanced due to the introduction of CdS and Cu2S quantum dots on the TiO2 BNRs surface. The 9 cycles of CdS and 6 cycles of Cu2S presented the best performance and reached a high photocurrent density to 13.65 mA at 0 V versus Ag/AgCl and hydrogen generation efficiency of 7.74% at −0.467 V versus Ag/AgCl. This enhancement can be attributed to the improved light absorption and the heterojunction formed between CdS and Cu2S, which can greatly promote the introduction and transportation of the photo electrons. This work provided a facile way for the synthesis of high performance photoelectrode for photoelectrochemical water splitting.

In situ measurement of photostability of CdSe/CdS/ZnO nanowires photoelectrode for photoelectrochemical water splitting

Quantum dot sensitized photoanodes have drawn much attention due to their high potential as efficient anodes for photoelectrochemical (PEC) water splitting or solar cells. However the photocorrosion of QDs is the crucial barrier for applications in these devices. The in situ analysis of photocorrosion is important in understanding its mechanism and also developing the possible solution for photocorrosion. In this study we have developed a novel, integrated analysis system for in situ measurements of photocorrosion and PEC performances. We have fabricated the CdSe/CdS/ZnO nanowire (NW) arrays on quartz crystal microbalance (QCM) as a platform for usage as PEC photoanodes and also mass analysis at the same time. The in situ measuring of photocurrents and mass changes were performed with continuous operation of PEC cells for CdSe/CdS/ZnO NWs photoanode. The study exhibited highly correlated tendency in photocurrent decrease and mass reduction, due to photocorrosion of CdSe/CdS/ZnO NWs. Also to improve the photostability of CdSe/CdS/ZnO NWs, applications of passivation and catalysts were studied and their effects were discussed. Our integrated in situ analysis system is highly applicable to various semiconductor sensitized systems.

Nanostructured carbon substrate improves the photoelectrochemical water splitting activity of cluster-assembled TiO2 thin films

The supersonic cluster beam deposition (SCBD) of titanium oxide nanoparticles is a versatile and effective bottom-up approach for the fabrication of nanostructured titanium dioxide (ns-TiO2) thin films; here we report on its application to the production of photoelectrodes for photoelectrochemical water splitting. The use of a cluster-assembled carbon (ns-C) thin film deposited by SCBD as a substrate layer for the titania nanoparticles deposition is also investigated and demonstrated to originate C:TiO2 nanocomposite photoelectrodes with increased surface roughness and more than four-fold enhanced IPCE (ca. 4.5% under monochromatic illumination at 330 nm employing KOH 1 M as aqueous electrolyte solution and without any external bias) compared to pure TiO2 photoelectrodes deposited by the same technique and featuring the same TiO2 thickness (ca. 250 nm). Electrochemical impedance spectroscopy (EIS) has been used to correlate the increase of the IPCE to an optimized electrode structure, electrolyte accessibility and electric conductivity. These results are promising towards the practical use of nanoparticle-assembled materials and the improving of their properties.

Quantum dot-decorated silicon nanowires as efficient photoelectrodes for photoelectrochemical hydrogen generation

Quantum dot-decorated wide band gap semiconductors, such as TiO2, ZnO, SnO2, etc., which have electron mobilities of less than 200 cm2 V−1 S−1 have been well studied as the photoelectrodes for photovoltaics and photoelectrochemical water splitting. Herein, we report CdSe quantum dot decorated-silicon nanowires (SiNWs) as photoelectrodes for photoelectrochemical water splitting. SiNWs have a comparatively higher electron mobility than metal oxides. A photocurrent density of around 6.1 mA cm−2 was obtained for the CdSe/SiNWs photoelectrode, which is nearly five times higher than that for SiNWs alone and which also shows a good transient photocurrent response. The band energy level alignment was also studied between Si and CdSe by observing the corresponding flat band potentials from a Mott–Schottky analysis.

Oxide semiconductors for solar to chemical energy conversion: nanotechnology approach

The present work considers the application of oxide semiconductors in the conversion of solar energy into the chemical energy required for water purification (removal of microbial cells and toxic organic compounds from water) and the generation of solar hydrogen fuel by photoelectrochemical water splitting. The first part of this work considers the concept of solar energy conversion by oxide semiconductors and the key performance-related properties, including electronic structure, charge transport, flat band potential and surface properties, which are responsible to the reactivity and photoreactivity of oxides with water. The performance of oxide systems for solar energy conversion is briefly considered in terms of an electronic factor. The progress of research in the formation of systems with high performance is considered in terms of specific aspects of nanotechnology, leading to the formation of systems with high performance. The nanotechnology approach in the development of high-performance photocatalysts is considered in terms of the effect of surface energy associated with the formation of nanostructured system on the formation of surface structures that exhibit outstanding properties. The unresolved problems that should be tackled in better understanding of the effect of nanostructures on properties and performance of oxide semiconductors in solar energy conversion are discussed. This part is summarised by a list of unresolved problems of crucial importance in the formation of systems with enhanced performance. This work also formulates the questions that must be addressed in order to overcome the hurdles in the formation of oxide semiconductors with high performance in water purification and the generation of solar fuel. The research strategy in the development of oxide systems with high performance, including photocatalysts for solar water purification and photoelectrodes for photoelectrochemical water splitting, is considered. The considerations are focused on the systems based on titanium dioxide of different defect disorder as well as its solid solutions and composites.

Si/PEDOT hybrid core/shell nanowire arrays as photoelectrodes for photoelectrochemical water-splitting

Si/poly(3,4-ethylenedioxythiophene) (PEDOT) core/shell nanowire arrays have been prepared by chemical etching of Si nanowires followed by vapor-phase polymerization of PEDOT as hybrid photoanodes for photoelectrochemical water-splitting. The PEDOT layer is employed as a multi-functional coating to prevent photocorrosion of Si nanowires, collect photogenerated holes and catalyze the water oxidation reaction. The amino silane modified Si nanowire surface improves PEDOT layer adhesion, and the resulting photoanode exhibits better photoresponse and improved stability. By tuning the length of the nanowires, we identify that the competition between the carrier recombination and catalytic water oxidation reaction is the primary factor determining the photoelectrocatalytic activity of the hybrid photoanode.

One-Dimensional Core/Shell Structured TiO2/ZnO Heterojunction for Improved Photoelectrochemical Performance

One-dimensional array grown on optically transparent electrode holds a promise as a photoelectrode for photoelectrochemical water splitting; however, its crystal structure is rutile, imposing constraints on the potent use of this nanostructure. To address this issue, a heterojunction with type-II band alignment was fabricated using atomic layer deposition (ALD) technique. One-dimensional core/shell structured /ZnO heterojunction was superior to in the photoelectrochemical water splitting because of better charge separation and more favorable Fermi level. The heterojunction also possesses better light scattering property, which turned out to be beneficial even for improving the photoelectrochemical performance of semiconductor-sensitized solar cell.

Photoresponse and stability improvement of ZnO nanorod array thin film as a single layer of photoelectrode for photoelectrochemical water splitting

ZnO nanorod array thin film with Al-doping and hydrogen treatment was developed as a photoelectrode combining the functions of transparent conducting oxide thin film and photoactive 1-dimensional nanostructured semiconductor into a single layer for photoelectrochemical water splitting. It was demonstrated that hydrogen treatment and Al-doping enhanced the dark currents, photocurrents, and hydrogen generation efficiencies largely and the enhancement by hydrogen treatment was more significant. The maximum photoinduced hydrogen generation efficiency was about 0.020%. Furthermore, hydrogen treatment also improved the photosensitivity and the stability under illumination significantly. The minimum decay time constant and rise time constant were 1.71 and 1.22 s, respectively. And after current–voltage scanning upon illumination for 50 cycles, the 1-dimensional morphology still remained unchanged but those without Al-doping and/or hydrogen treatment were altered seriously. The good photoresponse and stability made the Al-doped ZnO nanorod array thin film with hydrogen treatment have wide applications in the photoelectrochemical field.