369 research outputs found
Operational electrochemical stability of thiophene-thiazole copolymers probed by resonant Raman spectroscopy.
Subpicosecond Interfacial Charge Separation in Dye-Sensitized Nanocrystalline Titanium Dioxide Films
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Dye-sensitised semiconductors modified with molecular catalysts for light-driven H2 production.
The development of synthetic systems for the conversion of solar energy into chemical fuels is a research goal that continues to attract growing interest owing to its potential to provide renewable and storable energy in the form of a 'solar fuel'. Dye-sensitised photocatalysis (DSP) with molecular catalysts is a relatively new approach to convert sunlight into a fuel such as H2 and is based on the self-assembly of a molecular dye and electrocatalyst on a semiconductor nanoparticle. DSP systems combine advantages of both homogenous and heterogeneous photocatalysis, with the molecular components providing an excellent platform for tuning activity and understanding performance at defined catalytic sites, whereas the semiconductor bridge ensures favourable multi-electron transfer kinetics between the dye and the fuel-forming electrocatalyst. In this tutorial review, strategies and challenges for the assembly of functional molecular DSP systems and experimental techniques for their evaluation are explained. Current understanding of the factors governing electron transfer across inorganic-molecular interfaces is described and future directions and challenges for this field are outlined.This work was supported by the EPSRC (EP/H00338X/2 to E.R.; DTG scholarship to E.P.), the Christian Doppler Research Association (Austrian Federal Ministry of Science, Research and Economy and National Foundation for Research, Technology and Development; E.R. and J.W.), the OMV Group (E.R. and J.W.), the Advanced Institute for Materials ResearchCambridge Joint Research Centre (K.O.), European Commission Marie Curie CIG (303650 to A.R.) and the ERC (291482 to J.D.).This is the final version of the article. It was first available from RSC via http://dx.doi.org/10.1039/C5CS00733
Nanocrystalline Anatase Tio2/reduced Graphene Oxide Composite Films As Photoanodes For Photoelectrochemical Water Splitting Studies: The Role Of Reduced Graphene Oxide.
Nanocrystalline TiO2 and reduced graphene oxide (TiO2/RGO) composite films were prepared by combining a sol-gel method with hydrothermal treatment, employing titanium isopropoxide (Ti(O(i)Pr)4) and graphene oxide (GO) as starting materials. Although several reports in the literature have explored the benefits of RGO addition in titania films for photocatalysis and water splitting reactions, the role of RGO in the composite is always described as that of a material that is able to act as an electron acceptor and transport electrons more efficiently. However, in most of these reports, no clear evidence for this role is presented, and the main focus is deviated to the improved efficiency and not to the reasons for said efficiency. In this study, we employed several techniques to definitively present our understanding of the role of RGO in titania composite films. The TiO2/RGO composite films were characterized by X ray diffraction, Raman spectroscopy, microscopy and electrochemical techniques. In photoelectrochemical water splitting studies, the TiO2/RGO(0.1%) photoelectrodes showed the highest photocurrent density values (0.20 mA cm(-2) at 1.23 VRHE) compared to other electrodes, with an increase of 78% in relation to pristine TiO2 film (0.11 mA cm(-2) at 1.23 VRHE). The transient absorption spectroscopy (TAS) results indicated increases in the lifetime and yield of both the photogenerated holes and electrons. Interestingly, the TiO2/RGO(0.1%) film exhibited the best charge generation upon excitation, corroborating the photoelectrochemical data. We proposed that in films with lower concentrations (<0.1 wt%), the RGO sheets are electron acceptors, and a decrease in the charge recombination processes is the immediate consequence. Thus, both holes and electrons live longer and contribute more effectively to the photocurrent density.182608-261
Opportunities for mesoporous nanocrystalline SnO2 electrodes in kinetic and catalytic analyses of redox proteins
PFV (protein film voltammetry) allows kinetic analysis of redox and coupled-chemical events. However, the voltammograms report on the electron transfer through a flow of electrical current such that simultaneous spectroscopy is required for chemical insights into the species involved. Mesoporous nanocrystalline SnO2 electrodes provide opportunities for such âspectroelectrochemicalâ analyses through their high surface area and optical transparency at visible wavelengths. Here, we illustrate kinetic and mechanistic insights that may be afforded by working with such electrodes through studies of Escherichia coli NrfA, a pentahaem cytochrome with nitrite and nitric oxide reductase activities. In addition, we demonstrate that the ability to characterize electrocatalytically active protein films by MCD (magnetic circular dichroism) spectroscopy is an advance that should ultimately assist our efforts to resolve catalytic intermediates in many redox enzymes
Rational Design of Carbon Nitride Photoelectrodes with High Activity Toward Organic Oxidations
Carbon nitride (CNx) is a light-absorber with excellent performance in photocatalytic suspension systems, but the activity of CNx photoelectrodes has remained low. Here, cyanamide-functionalized CNx (NCNCNx) was co-deposited with ITO nanoparticles on a 1.8â
Ă
thick alumina-coated FTO electrode. Transient absorption spectroscopy and impedance measurements support that ITO acts as a conductive binder and improves electron extraction from the NCNCNx, whilst the alumina underlayer reduces recombination losses between the ITO and the FTO glass. The Al2O3|ITOâ:âNCNCNx film displays a benchmark performance for CNx-based photoanodes with an onset of â0.4â
V vs a reversible hydrogen electrode (RHE), and 1.4±0.2â
mAâcmâ2 at 1.23â
V vs RHE during AM1.5G irradiation for the selective oxidation of 4-methylbenzyl alcohol. This assembly strategy will improve the exploration of CNx in fundamental and applied photoelectrochemical (PEC) studies.The authors thank Dr. Carla Casadevall, Dr. Motiar Rahaman, and Dr. Mark Bajada (University of Cambridge) for helpful discussions. This work was funded by the European Union's Horizon 2020 project SOLAR2CHEM (Marie SkĆodowska-Curie Actions with Grant Agreement No. 861151, C.P., E.R.) and Methasol (Grant Agreement No. 101022649, S.A.J.H., J.D.), the EPSRC (NanoDTC, EP/L015978/1, and EP/S022953, T.U., E.R.), Generalitat Valenciana (APOSTD/2021/251 fellowship, C.A.M.), and the project PID2020-116093RB-C41 by MCIN/AEI/10.13039/501100011033/ (S.G.). The authors acknowledge the use of the Cambridge XPS System, which is part of Sir Henry Royce Institute - Cambridge Equipment, EPSRC grant EP/P024947/1, and the EPSRC Underpinning Multi-User Equipment Call (EP/P030467/1) for the Talos F200X G2 TEM
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Photodoping and Fast Charge Extraction in Ionic Carbon Nitride Photoanodes
Ionic carbon nitrides based on poly(heptazine imides) (PHI) represent a vigorously studied class of materials with possible applications in photocatalysis and energy storage. Herein, for the first time, the photogenerated charge dynamics in highly stable and binder-free PHI photoanodes using in operando transient photocurrents and spectroelectrochemical photoinduced absorption measurements is studied. It is discovered that light-induced accumulation of long-lived trapped electrons within the PHI film leads to effective photodoping of the PHI film, resulting in a significant improvement of photocurrent response due to more efficient electron transport. While photodoping is previously reported for various semiconductors, it has not been shown before for carbon nitride materials. Furthermore, it is found that the extraction kinetics of untrapped electrons are remarkably fast in these PHI photoanodes, with electron extraction times (ms) comparable to those measured for commonly employed metal oxide semiconductors. These results shed light on the excellent performance of PHI photoanodes in alcohol photoreforming, including very negative photocurrent onset, outstanding fill factor, and the possibility to operate under zero-bias conditions. More generally, the here reported photodoping effect and fast electron extraction in PHI photoanodes establish a strong rationale for the use of PHI films in various applications, such as bias-free photoelectrochemistry or photobatteries. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH Gmb
Photodoping and fast charge extraction in ionic carbon nitride photoanodes
Ionic carbon nitrides based on poly(heptazine imides) (PHI) represent a vigorously studied class of materials with possible applications in photocatalysis and energy storage. Herein, for the first time, the photogenerated charge dynamics in highly stable and binderâfree PHI photoanodes using in operando transient photocurrents and spectroelectrochemical photoinduced absorption measurements is studied. It is discovered that lightâinduced accumulation of longâlived trapped electrons within the PHI film leads to effective photodoping of the PHI film, resulting in a significant improvement of photocurrent response due to more efficient electron transport. While photodoping is previously reported for various semiconductors, it has not been shown before for carbon nitride materials. Furthermore, it is found that the extraction kinetics of untrapped electrons are remarkably fast in these PHI photoanodes, with electron extraction times (ms) comparable to those measured for commonly employed metal oxide semiconductors. These results shed light on the excellent performance of PHI photoanodes in alcohol photoreforming, including very negative photocurrent onset, outstanding fill factor, and the possibility to operate under zeroâbias conditions. More generally, the here reported photodoping effect and fast electron extraction in PHI photoanodes establish a strong rationale for the use of PHI films in various applications, such as biasâfree photoelectrochemistry or photobatteries
Understanding the effect of unintentional doping on transport optimization and analysis in efficient organic bulk-heterojunction solar cells
In this paper, we provide experimental evidence of the effects of unintentional p-type doping on the performance and the apparent recombination dynamics of bulk-heterojunction solar cells. By supporting these experimental observations with drift-diffusion simulations on two batches of the same efficient polymer-fullerene solar cells with substantially different doping levels and at different thicknesses, we investigate the way the presence of doping affects the interpretation of optoelectronic measurements of recombination and charge transport in organic solar cells. We also present experimental evidence on how unintentional doping can lead to excessively high apparent reaction orders. Our work suggests first that the knowledge of the level of dopants is essential in the studies of recombination dynamics and carrier transport and that unintentional doping levels need to be reduced below approximately 7 Ă 1015 cm-3 for full optimization around the second interference maximum of highly efficient polymer-fullerene solar cells.F. D. and J. R. D. are thankful of the support from the
EPSRC APEX Grant No. EP/H040218/2 and SPECIFIC
Grant No. EP/1019278. T. K. acknowledges funding by
an Imperial College Junior Research Fellowship. We are
grateful to the Ministerio de Economa y Competitividad for
funding through the project PHOTOCOMB, Reference
No. MAT2012-37776.Peer Reviewe
Kinetic Analysis of an Efficient Molecular Light-Driven Water Oxidation System
We
report an efficient molecular light-driven system to oxidize
water to oxygen and a kinetic analysis of the factors determining
the efficiency of the system. The system comprises a highly active
molecular catalyst ([Ru<sup>IV</sup>(tda)Â(py)<sub>2</sub>(O)]), [Ru<sup>II</sup>(bpy)Â(bpy-COOEt)<sub>2</sub>]<sup>2+</sup> (<b>RuP</b>), as sensitizer and Na<sub>2</sub>S<sub>2</sub>O<sub>8</sub> as
sacrificial electron acceptor. This combination exhibits a high quantum
yield (25%) and chemical yield (93%) for photodriven oxygen evolution
from water. The processes underlying this performance are identified
using optical techniques, including transient absorption spectroscopy
and photoluminescence quenching. A high catalyst concentration is
found to be required to optimize the efficiency of electron transfer
between the oxidized sensitizer and the catalyst, which also has the
effect of improving sensitizer stability. The main limitation of the
quantum yield is the relatively low efficiency of S<sub>2</sub>O<sub>8</sub><sup>2â</sup> as an electron scavenger to oxidize the
photoexcited ruthenium sensitizer <b>RuP*</b> to 2 <b>RuP</b><sup><b>+</b></sup>, mainly due to competing back electron
transfers to the <b>RuP</b> ground state. The overall rate of
light-driven oxygen generation is determined primarily by the rate
of photon absorption by the molecular sensitizer under the incident
photon flux. As such, the performance of this efficient light-driven
system is limited not by the properties of the molecular water oxidation
catalyst, which exhibits both good kinetics and stability, but rather
by the light absorption and quantum efficiency properties of the sensitizer
and electron scavenger. We conclude by discussing the implications
of these results for further optimization of molecular light-driven
systems for water oxidation
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