bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Charge Carrier Dynamics and Origin of Instability of Organo-Metal Perovskite Films and Quantum Dots
Authors: Zhang Jin Z 
Published: February 2020

Organo-metal perovskites are highly promising materials for photovoltaic applications, yet their degradation due to factors such as light, moisture, and oxygen remains a significant problem and the mechanism behind is not yet well understood. We have studied the degradation mechanism of methylammonium lead iodide (MAPbI3) perovskite films subjected to light in a dry environment from a structural perspective. The effect of mesoporous titanium dioxide (mp-TiO2) layer, commonly used in device applications, on the degradation is also investigated. The perovskite structural change was investigated using XRD, UV-Vis absorption spectroscopy, Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, and Fourier Transform Infrared (FT-IR) spectroscopy. The mp-TiO2 plays a significant role in the degradation rate of the perovskite film. Our results indicate that the first step in the light-induced degradation process is the deprotonation of the methylammonium cations, which results in the evaporation of HI and CH3NH2 molecules leaving unreacted PbI2 behind. This is further supported by ultrafast dynamics studies of charge carriers using femtosecond transient absorption spectroscopy.
In addition, have synthesized various organo-metal perovskite quantum dots (PQDs) and used them as a model system to understand the origin of the materials instability. We have found the photogenerated electrons and holes can cause material degradation through redox reactions that damage the ammonium ions acting as localized trap sites, which is likely the origin of instability from light. We also found that species that are likely to react with or extract the protons from the ammonium ions will cause degradation, such as water or alcoholic solvents. Therefore, a more acidic environment is desired for better stability. Based on this understanding, we have designed new strategy to passivate the surface of PQDs using branched ligands to improve stability. The new insight gained from our studies is also important for developing new perovskite materials for solar cell and other applications such as LEDs and sensors.
(Invited) Insight into Polyoxometalate-Induced Catalysis at Semiconducting Oxides
Authors: Solarska Renata , Augustynski Jan 
Published: February 2020

One of the major limitations in photoelectrochemical water splitting with use of semiconducting oxide is their sluggish surface water oxidation kinetics. Identification of a molecular oxygen evolution catalysts active especially in highly corrosive media is not a trivial case. N-type mesoporous tungsten trioxide, WO3, is one of few stable semiconductor materials able to photo-electrochemically split water under solar light irradiation but it’s operational acidic environment restricts use of any catalyst to the precious metals. In an attempt to overcome this limitation, Keggin‐type polyoxometalate, [PW12O40]3− and [PMo12O40]3−, anions have been employed to act as highly effective oxygen evolution reaction molecular catalysts in photoelectrochemical water splitting devices. This the first example of oxidatively stable in acid media non noble metal water splitting catalyst. Combined with semitransparent Na‐doped nanoporous WO3 film photoanode, they allow achieving under simulated AM 1.5G sunlight exceptionally high water oxidation photocurrent of 4.5 mA cm−2 at 1.1 V versus reversible hydrogen electrode. The surface and structure modifications of a WO3 photoanode which led to this performance, in parallel with the mechanism of the enhancement will be presented and discussed in details.
M. Sarnowska, K. Bienkowski, R. Solarska, P. Barczuk, J.Augustynski; Highly Efficient and Stable Solar Water Splitting at (Na)WO3 Photoanodes in Acidic Electrolyte Assisted by Non-noble Metal Oxygen Evolution Catalyst; Advanced Energy Materials 10.1002/aenm201600526
Structural Design of Graphitic Carbon-Nitride Photocatalysts for Boosting Hydrogen Production from Water Decomposition
Authors: Huang Yu-Jie , Wu Kwun-Han , Teng Hsisheng 
Published: February 2020

Melem-based two-dimensional (2D) conjugated polymer, graphitic carbon nitride (g-C3N4), has been demonstrated to be a promising material for photo-driven water splitting due to its unique electronic band structure and good photochemical stability.1 The search for suitable precursors is an important issue regarding the synthesis of active g-C3N4. Commonly used precursors are nitrogen-rich compounds containing pre-bounded triple or double C-N core structure, such as cyanamide, dicyandiamide, melamine, and urea. 2

g-C3N4 synthesized from urea is active in hydrogen production, which is attributable to the resulting sheet-like structure.3 The 2D carbon nitride polymer offers many technical options to engineer the molecular structure, electronic structure, and texture for promoting the performance of water splitting. Methods that have been applied to modify the carbon-nitride photocatalysts include dye sensitization, copolymerization, hybridization, hard-templating fabrication, loading with cocatalysts (e.g., Pt, RuO2, NiO is effective for hydrogen evolution while PtOx, Co is effective for oxygen evolution), and doping with metal (e.g., Fe, Zn, Cu) or non-metal (e.g., S, B, P, I) atoms.4

The present study develops a novel method to synthesize a melem/g-C3N4 hybrid photocatalyst through temperature-programmed ammonia treatment. This treatment regulates the crystalline phase of g-C3N4 and reproduces melem fragments, which is the building blocks of g-C3N4. The hybridized melem/g-C3N4 structure facilitates separation of photo-generated charges and therefore exhibits excellent performance in hydrogen production from photocatalytic water decomposition. We have evaluated the photocatalytic activities of this melem/g-C3N4 catalyst in an assay of photocatalytic hydrogen evolution from water under visible light irradiation, by using Pt and triethanolamine as the cocatalyst and sacrificial reagent, respectively. The hydrogen evolution quantum yield is unprecedented for photocatalytic reactions using g-C3N4-based catalysts.

References

X. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J. M. Carlsson, K. Domen, M. Antonietti., Nat. Mater. 8 (2009), 76−82.

(a) F. Dong, Y. Sun, L. Wu, M. Fu, Z. Wu., Catal. Sci. Technol. 2 (2012), 1332-1335. (b) J. Liu, T. Zhang, Z. Wang, G. Dawson, W. Chen, J. Master. Chem., 21 (2011), 14398-14401.

G. Zhang, Z. A. Lan, L. Lin, S. Lin, X. Wang, Chem. Sci., 10.1039/c5sc04572j .

G. Zhang, M. Zhang, X. Ye, X. Qiu, S. Lin, X. Wang, Adv. Mater., 26 (2014), 805-809.

Acknowledgments: This research was supported by the Ministry of Science and Technology, Taiwan (104-2221-E-006-231-MY3, 104-2221-E-006-234-MY3, 105-3113-E-006-005, and 104-3113-E-006-011-CC2), and by the Ministry of Education, Taiwan, The Aim for the Top University Project to the National Cheng Kung University.
High Efficiency Photoelectrochemical Water Splitting Using Graphene/GaN Nanowire Photoelectrode
Authors: Ha Jun-Seok , Bae Hyojung , Min Jung-Wook , Seo Dong-Ju , Ryo Hokyun , Lee Hyo-Jong , Lee Dong-Seon , Lee Yong-Tak , Lee Sang Hyun 
Published: February 2020

GaN based photoelectrode with a nanowire structure have been studied due to superior performance of water splitting ability. Self‐organized GaN nano‐rod on silicon has been demonstrated, and a direct growth via vapour–liquid–solid using metal particle as a catalyst has been reported. Nonowire structure has benefit with short minority carrier diffusion lengths and large surface-to-volume ratio. It allows minor carrier to easily reach to surface without recombination, so that water splitting ability could be increased. However, this structure has photocorrosion problem. For solving this problem, we covered graphene material on the tips of nanowires as a passivation layer. Graphene has been known to have excellent mechanical, thermal, optical, and electrical properties.
For these reasons, we studied the photoelectrochemical water splitting properties of graphene coated GaN nanowire (graphene/GaN nanowire) photoelectrode. GaN nanowire sample without graphene was used for the reference. The GaN nanowire structures were grown on n-type Si(111) substrates using radio-frequency plasma-assisted molecular beam epitaxy. The graphene was grown by chemical vapor deposition method and exfoliated to surface of GaN nanowire. As a result, compared with non-coated GaN nanowire sample, the graphene/GaN nanowire phoeoelectrode showed higher photocurrent density. Also, we could know that it has much higher photocurrent stability. We will present the results and the reasons for higher efficiency and stability of this graphene coated GaN nanowire sample at this conference.
Reference
[1] Allon I. Hochbaum, and Peidong Yang, Chem. Rev., 110 (2010) 527–546
[2] B. AlOtaibi, M. Harati, S. Fan, S. Zhao, H. P. T. Nguyer, M. G. Kibiria, and Z. Mi, Nanotechnology, 24 (2013) 175401
Hieratical Cu2SnS3 (CTS) Nanostructure As a Highly Efficient Visible Light Photocatalyst for CO2 Reduction to Solar Fuels
Authors: Shown Indrajit , Chang H. S. , Tai Yian , Chen Li-Chyong , Chen Kuei-Hsien 
Published: February 2020

The conversion of greenhouse CO2 gas into value added chemicals using solar energy or photocurrent derived from visible light is known as artificial photosynthesis. Recently, the production of solar fuel through artificial photosynthesis has been gained tremendous attention due to their fascinating potential in environmental and energy-related application. In CO2 photoreduction technology, the major challenge is the low efficiency of the photocatalyst. Several wide band gap and hybrids carbonaceous materials have been demonstrated as photocatalyst for CO2 reduction. However, in real application these photocatalyst materials are far away from the actual requirement due to the low quantum efficiency and lack of selectivity. Thus, it is a great challenge to develop a potential low-cost photocatalyst for a high CO2 reduction efficiency and produce desire solar fuel under visible light. Last few years several metal sulfides like MoS2, CuS, Cu2S, ZnS and their composite have been attracted considerable attention as a photocatalyst due to their good optical property, high absorption coefficient. However, the application of these perfect semiconductors for photocatalytic CO2 reduction to solar fuels may be limited due to their high interfacial electron-hole recombination process. Recently, Cu-Sn-S ternary semiconductor system has been attracted for its potential contribution as a light absorber layer in photovoltaic application. Cu2SnS3 (CTS) is a ternary p-type semiconductor with a high absorption coefficient. The observed optical band edge of CTS is around 1.4 eV, nearly ideal for solar-energy harvesting. In this study, CTS nanostructure has been demonstrated as a photocatalyst for photocatalytic CO2 reduction to solar fuels under visible light. The ternary CTS nanostructure was obtained from the hydrothermal process and characterized by XRD, Raman spectroscopy, UV-Vis spectroscopy and SEM technique. The photocatalytic activity of the CTS nanostructure hybrid with different S composition was measured in the gas phase CO2 photoreduction under visible-light irradiation. Ethanol has been found to be major product as a high selectivity and efficiency from the photocatalytic CO2 reduction. The observed ethanol formation rate is around 5.6 μmol/g-cat.hr. Detailed investigation on the optimum phase composition, its nanoarchitectures and possible mechanism for the selective solar fuel generation will be discussed.

References

Nanoscale, 5, 262, (2013)
Nano letters, 14, 6097, (2014)
Fabrication of a Monolithic Heterostructured c-Si/BiVO4 Core-Shell Photoanode for Unassisted Solar Water Splitting
Authors: Chakthranont Pongkarn , Hellstern Thomas R , McEnaney Joshua M , Jaramillo Thomas F 
Published: February 2020

Photoelectrochemical (PEC) water splitting is a promising way of storing solar energy in hydrogen, which can be used as a carbon-free fuel or a chemical feed stock. A tandem-junction PEC device offers a high theoretical solar-to-hydrogen (STH) efficiency due to the additive voltages across two photoabsorbers and the better utilization of the solar spectrum. Modeling STH efficiency as a function of band gap for a tandem device shows that over 20% STH can be achieved with band gaps of 1.2 and 1.8 eV.1 One promising photoabsorber material combination is c-Si paired with a metal oxide, especially BiVO4. In addition to the appropriate band structure alignment of both semiconductors, c-Si and BiVO4 are low cost, earth abundant, and industrially scalable. However, the key challenges for these materials are the instability of c-Si in aqueous environment and the poor electronic properties of BiVO4, a common limitation for most metal oxides. Hence, only a very few c-Si/metal oxide systems have been demonstrated for unassisted water splitting.2

In this work, we present the fabrication of a monolithic heterostructured c-Si/BiVO4 core-shell tandem based monolithic device capable of performing spontaneous water splitting without any precious metal. The wafer scaled device architecture was prepared by (1) nanostructuring of the d c-Si substrate to serve as both a bottom absorber and a scaffold to improve the charge separation of BiVO4; (2) tuning the c-Si p-n junction depth to maximize the device photovoltage; (3) engineering the SnO2 interfacial layer to passivate the c-Si/BiVO4 interface and protect the c-Si p-n junction; (4) conformally coating a BiVO4 thin film on the nanostructured Si; and (5) decorating the c-Si and BiVO4surfaces with both oxygen and a hydrogen evolution catalysts.
(1) Seitz, L. C.; Chen, Z.; Forman, A. J.; Pinaud, B. A.; Benck, J. D.; Jaramillo, T. F. ChemSusChem
2014,
7(5), 1372-1385.
(2) (a) Shaner, M. R.; Fountaine, K. T.; Ardo, S.; Coridan, R. H.; Atwater, H. A.; Lewis, N. S. Energy Environ. Sci.
2014,
7 (2), 779-790; (b) Liu, C.; Tang, J.; Chen, H. M.; Liu, B.; Yang, P. Nano Lett.
2013,
13 (6), 2989-2992; (c) Xu, P.; Feng, J.; Fang, T.; Zhao, X.; Li, Z.; Zou, Z. RSC Adv.
2016,
6 (12), 9905-9910.
Electrochemical Modification of Boron-Doped Diamond with Cu2O Nanoparticles for Photocatalytic Applications
Authors: Hasan Maksudul , Mavrokefalos Christos K. , Rohan James F. , Foord John S. 
Published: February 2020

It is generally accepted that one of the main challenges facing our planet today is the human interfered climate change and its inseparable link to our global society’s present and future needs. Solar energy is doubtless one of the most attractive ways to deal with these issues. Water splitting by artificial photosynthesis is a favourable means of converting solar energy into transportable and end user chemical energy. Two of the major issues that remain unresolved in artificial photosynthesis are first to find a visible light absorber earth abundant semiconductor and second a robust substrate. Additionally, photon to current conversion efficiency of the current state-of-the-art semiconductor is far below the theoretical value due to undesirable charge carrier recombination loses. Cuprous oxide (Cu2O) is a naturally occurring p-type metal oxide semiconductor, is abundant and promisingly possesses a suitable band gap (2.0 eV) and energy band position that enable it to absorb solar light in the visible spectrum to produce hydrogen gas without external bias. However, Cu2O suffers from rapid charge carrier recombination losses and self-photocorrosion when comes in contact with water under illumination. The use of bimetallic alloys or core-shell metals in nanoparticle format is beneficial in two ways; protecting semiconductor from self-photo corrosion and providing short diffusion paths for electron-hole pairs enabling fast transfer to the respective redox reaction sites. Boron-doped diamond (BDD) is a potential substrate in the field of electrocatalysis due to its plethora of advantages such as wide potential window, low background current, resistance to fouling and electrocorrosion as well as its availability at a low cost when grown by chemical vapour deposition (CVD).
In this work, the electrochemical modification of oxygen terminated boron doped diamond (OBDD) electrodes decorated with NiO-Cu2O nanoparticles is described. The method involves the electrodeposition of Cu2O nanoparticles on OBDD from a surfactant-free electrolyte followed by a thin coating of NiO onto Cu2O nanoparticles (Fig. 1a). The electrochemical experimental data showed that electronic effects due to the bimetallic catalysts led to higher photocurrent densities in comparison with Cu2O nanoparticles alone (Fig. 1b). In order to understand the morphology, dispersity and size of the nanoparticles, deposits were characterised by high resolution scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).

Figure 1 (a) SEM image of NiO-Cu2O modified OBDD electrode and (b) Linear-sweep voltammograms of the photoelectrochemical response of Cu2O and NiO-Cu2O modified OBDD electrodes, respectively under chopped light (100 mW cm-2 and on-off frequency 0.2 Hz) at a scan rate of 10 mV s-1 in 0.1 M Na2SO4 (pH 6.2).

Figure 1
Carrier Selective Contacts Design for Efficient Photocatalytic Water Reduction
Authors: Bae Dowon , Pedersen Thomas , Seger Brian , Hansen Ole , Vesborg Peter C. K. , Chorkendorff Ib 
Published: February 2020

2-photon tandem device structures that consist of a wide band gap and narrow band gap photoabsorber can maximize photoelectrolysis efficiency since their I-V characteristics match well with that needed for photoelectrolysis [1]. In the case of the narrow band gap (Eg
) material, recent theoretical work has shown that Si has a suitable Eg
for the bottom cell of tandem water splitting device [2]. Since current performance of Si PEC cells lag far behind the theoretical limit [3], the need for a different approach increases. Up to now, tremendous efforts have been made to improve the performance of Si-based photocathodes [4-6]. One approach the solar cells industry uses to increase performance is to use metal-oxide-semiconductor (MOS) carrier-selective contacts due to their efficient carrier transport and low recombination [5,6]. However, very little work has been done studying photocatalytic hydrogen evolution reaction (HER) with the MOS structure. Moreover, there has been no detailed report on energy band level analysis to understand how the carriers can be selectively injected.
In this work we demonstrate μc-Si/SiO2/p-Si structure (see Figure 1) to both front and back contacts which provide interface passivation and selective injection of minority and majority carrier to solid/liquid interface and back contact, respectively. A transparent TiO2 is placed above the highly doped μc-Si thin film as a conducting protection layer, and then Pt nanoparticles were drop-casted on the samples for photocatalytic HER in 1M HClO4. Using thin film degenerately doped Si as a metallic layer has been employed in recent state-of-art MOS based PV cells [7], but combination with TiO2 as a conducting protection layer for PEC hydrogen production has not been shown so far. Moreover, the details working principles based on the band energy analysis are outlined to understand how the carriers can be injected selectively and transferred to solid/liquid interface in PEC system.
1. B. Seger, I.E. Castelli, P.C.K. Vesborg, K.W. Jacobsen, O. Hansen, I. Chorkendorff, Energy Environ. Sci. 7 (2014) 2397–2413.
2. A.B. Laursen, S. Kegnæs, S. Dahl, I. Chorkendorff, Energy Environ. Sci. 5 (2012) 5577.
3. W. Shockley, H.J. Queisser, J. Appl. Phys. 32 (1961) 510–519.
4. D. Bae, T. Pedersen, B. Seger, M. Malizia, A. Kuznetsov, O. Hansen, I. Chorkendorff, P.C.K. Vesborg, Energy Environ. Sci. 8 (2015) 650–660.
5. D. V Esposito, I. Levin, T.P. Moffat, A.A. Talin, Nat. Mater. 12 (2013) 562–8.
6. A.G. Scheuermann, J.P. Lawrence, K.W. Kemp, T. Ito, A. Walsh, C.E.D. Chidsey, P.K. Hurley, P.C. McIntyre, Nat. Mater. (2015) 1–8.
7. F. Feldmann, M. Simon, M. Bivour, C. Reichel, M. Hermle, S.W. Glunz, Sol. Energy Mater. Sol. Cells. 131 (2014) 100–104.

Figure 1
A Biomimetic Redox Flow Battery Based on a Flavin Mononucleotide
Authors: Orita Akihiro , Verde Michael , Sakai Masanori , Meng Shirley 
Published: February 2020

Biological redox reactions inspire us to design sustainable and environmentally safe energy storage systems. Flavins have been demonstrated as solid-state electroactive materials for Li-metal batteries. [1,2] The concentration of flavin in those composite electrodes was no more than 50 wt%, however, due to the high content of conductive carbon necessary to complement the low electronic conductivity of flavin. In nature, flavins are often found dissolved in water or fat, such as in biological systems. As they are commonly more useful in this state, so may it be in batteries as well. Interestingly, flavins have yet to be reported as an active material for any redox flow batteries (RFBs). Here we explore the use of riboflavin-5’-phosphate sodium salt (FMN-Na) for RFBs. A diffusion coefficient and a kinetic rate constant of FMN in a strongly alkaline aqueous solution are determined and shown to be comparable to those of vanadium ions used for industrially utilized RFBs. Nicotinamide (known as vitamin B3) is used as a hydrotropic agent to enhance the water-solubility of FMN-Na, and therefore, its energy density in a RFB by as much as 15 times. A RFB using strongly basic FMN-based anolyte and ferrocyanide/ferricyanide-based catholyte shows highly stable cycling performance over the course of 200 cycles. The oxidized and reduced FMN can be stabilized by a variety of resonance structures, leading to the stable cycling performance. This work shows that biological redox centers are shown to be promising materials for environmentally friendly energy storage systems and warrant future exploration in this field.

References

[1] Hong, J. et al. Biologically inspired pteridine redox centres for rechargeable batteries. Nat. Commun 5, 9, (2014).
[2] Lee, M. et al. Redox Cofactor from Biological Energy Transduction as Molecularly Tunable Energy-Storage Compound. Angew. Chem. Int. Ed. 52, 8322-8328, (2013).