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Resonance Raman spectra of 1 in CH 3 CN at an excitation wavelength of 413 nm (a); 1 on PS-b-P2VP-templated three-layer NiO film at 413 nm (b) and 476 nm (c) excitation wavelengths; DFT-calculated Raman spectrum of 1 after application of a 0.98 scaling factor (d).
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Moving from homogeneous water-splitting photocatalytic systems to photoelectrochemical devices requires the preparation and evaluation of novel p-type transparent conductive photoelectrode substrates. We report here on the sensitization of polystyrene-block-poly-(2-vinylpyridine) (PS-b-P2VP) diblock copolymer-templated NiO films with an organic pus...
Citations
... 134 The efficiency of the NiOjRuP 3 -Zr 4+ -NiP electrodes may be improved by developing phosphonated push-pull dyes optimized for the photoelectrocatalytic H 2 evolution. 135 Further work may also include the synthesis and investigation of dyes, which are more suitable for injecting holes into the NiO valence band. 135 Thus, the multifunctions of light-harvesting, electron transfer and H 2 evolution catalytic functions can be further optimized. ...
... 135 Further work may also include the synthesis and investigation of dyes, which are more suitable for injecting holes into the NiO valence band. 135 Thus, the multifunctions of light-harvesting, electron transfer and H 2 evolution catalytic functions can be further optimized. ...
Solar fuel production from water has received increasing attention with increasing energy and environmental concerns. Herein we highlight dual- and multi-functional photocatalytic systems, which have both photosensitizing and thermal redox...
... the large number of published D-π-A compounds, I will focus on those based on a triphenylamine (TPA) donor and a cyanovinyl-based acceptor group(Figure 3.2), to which the organic dyes studied in this thesis belong. In general, these dyes show two main absorption bands: one band in the UV caused by a transition localized on the TPA moiety and an intramolecular charge transfer (ICT) band in the visible part of the spectrum (ε = 29,000 to 58,000 M -1 cm -1 ).25,[116][117][118][119][120][121] Upon excitation of the latter, electron density is shifted from the TPA part, where the HOMO is localized, to the cyanovinyl acceptor part, where the LUMO is localized. The absorption, but especially the emission from the ICT state shows a strong solvatochromic effect due to the stabilization of the charge-transfer state in polar solvents.116,122,123 ...
... The films were sensitized by soaking for 24 h in methanolic solutions of the deprotected dyes and dyads. The grafting densities, determined by desorption of the molecules from the surface followed by measuring UV-Vis absorption spectra of the resulting solution, were in the range of 6 to 14 nmol•cm -2 , similar to those observed in literature on other dye-sensitized NiO films.26,79,87,121 As the grafting density varies between films and especially between different batches of prepared NiO, the grafting density was determined for each prepared film individually to accurately determine the TON values of hydrogen production for each film. ...
The summary presented here is only the beginning of that in the thesis since it is longer than the 4000 characters permitted.Dye-sensitized photoelectrochemical cells represent a highly promising technology for the production of solar fuels via light-driven water splitting as an integral part of a carbon-neutral economy. In that context, the design of more performant dye-catalyst assemblies is highly demanded as they should allow to precisely control over the excited state processes, especially ET. However, detailed investigations on the light-induced processes of dyad-sensitized photocathodes under operando conditions are scarce in the literature, and few studies have addressed in depth the degradation processes in those photocathodes.Therefore, this work aimed at providing a comprehensive understanding of the performances of hydrogen-evolving DSPC based on a series of molecular dye-catalyst assemblies varying by the nature of the dye and the catalyst, including the elucidation of the systems’ weak points and bottlenecks for hydrogen production. To this end, a full characterization of the photoelectrochemistry and activity of the photocathodes was combined with the study of the excited state processes both in solution and on films to gain a full understanding of the systems and their performance-limiting factors. Especially important was the determination of the lifetime of the CSS and the kinetics of the ET to the catalyst unit. The mainly studied compounds were a series of four noble-metal free dyads which varied in the nature of the push-pull organic dye (T1 or T2R) and in that of the catalyst for proton reduction (Co or Cat1). Assessing the activity of all four combinations enabled the determination of each part’s contribution to the overall performance and therefore to link the molecular structure to the activity of the system. The elucidation of such a structure-acitivity relationship is important to be able to rationally improve the molecular structure of the dyads. The best-performing system T2R-Cat1 was studied in detail, notably including the excited state processes at applied potential by TA-SEC and post- and in-operando measurements to determine the deactivation pathways and kinetics. In addition, NiO photocathodes sensitized with a Ruthenium-cobalt dyad were studied by TA-SEC for comparison.
... At pH 5, where an acetate buffer was employed, there was a steady decay of photocurrent consistent with degradation or desorption of the photocatalyst. This is in contrast to studies by Massin et al. who found the opposite trend for their dye-sensitised photoelectrocatalytic system with an organic dye, which was found to be stable in acetate buffer but unstable with phosphate buffer (46). In order to address the problems with photocatalyst instability in pH 5 acetate buffer an alternative non coordinating buffer was employed, 2-(N-morpholino)ethanesulfonic acid (MES). ...
Photoelectrocatalysis offers a way to generate hydrogen and oxygen from water under ambient light. Here, a series of hydrogen evolving photocatalysts based on a ruthenium(II) bipyridyl sensitiser covalently linked to Pt or Pd catalytic centres were adsorbed onto mesoporous NiO and tested for hydrogen evolution in a photoelectrochemical half-cell. The electrolyte buffer was varied and certain catalysts performed better at pH 7 than pH 3 (e.g. PC3 with photocurrent density = 8 µA cm-2), which is encouraging for coupling with an oxygen evolving photoanode in tandem water splitting devices. The molecular catalysts were surprisingly robust when integrated into devices, but the overall performance appears to be limited by rapid recombination at the photocatalyst|NiO interface. Our findings provide further insight towards basic design principles for hydrogen evolving photoelectrochemical (PEC) systems and guidelines for further development.
... This procedure has been previously optimized in the group. 79,87 It was observed that soaking for 24 hours is sufficient to achieve maximum grafting of the molecular components onto NiO films. ...
... The dyad loading was estimated by UV-Vis spectroscopy after the desorption of the dyad The estimation of the immobilized compounds was previously made by measuring the UV-Vis absorption spectra of the sensitized NiO films. 79,55 However, scattering could complicate the interpretation of the spectra depending on the NiO film thickness. Thus, the methodology employed here is more accurate. ...
Production of solar fuels in a dye-sensitized hydrogen-evolving photoelectrochemical cell, where splitting of water into H2 and O2 occurs is an attractive method in order to fulfill future energy demands and face the environmental problems arising by the combustion of fossil fuels. The group constructed a functional NiO DS-photocathode for H2 evolution, a counterpart of the tandem device, based on the first noble metal-free covalent dye-catalyst assembly. Here, we report the synthesis and characterization of two novel dye-catalyst assemblies, both relying on the same ruthenium photosensitizer. The first dyad is based on the cobalt diimine-dioxime complex previously employed by the group and the second one on a cobalt tetraazomacrocyclic complex. Photoelectrochemical experiments under identical conditions enabled us to correlate the performance with the choice of the photosensitizer and the catalyst. Ruthenium outperformed in activity photocathodes based on organic dyes. Transient absorption spectroelectrochemistry revealed that one limiting factor for the activity of our systems is the thermal electron transfer from the reduced dye to the catalytic unit. In addition, post-operando analysis showed that desorption of the molecular architecture from the surface and decomposition of the cobalt diimine-dioxime also limits the efficiency. The second dye-catalyst assembly exhibits the higher TON ever reported for dye-sensitized hydrogen-evolving photocathodes, implying that more stable and robust catalysts are of significant importance. Finally, the second dyad was functional for PEC CO2 reduction to CO under aqueous media with promising preliminary results.
... Compared to the two dyads, the ICT band of T2R is slightly red-shifted (∆E ≈ 200 cm −1 ), which might stem from the stronger electron-withdrawing character of the ester terminal group in comparison with the amide, slightly increasing the push-pull character of the dye. As previously reported [23], the presence of the rigid CPDT unit strongly enhances the light-harvesting efficiency in the visible region (ε of 60,300 M −1 •cm −1 ) compared to our previously-studied dyads relying on mono-or bis-thiophene units (ε of 31,800 and 38,600 M −1 •cm −1 , respectively) [12,13,17,27]. ...
... Compared to the two dyads, the ICT band of T2R is slightly red-shifted (∆E ≈ 200 cm −1 ), which might stem from the stronger electron-withdrawing character of the ester terminal group in comparison with the amide, slightly increasing the push-pull character of the dye. As previously reported [23], the presence of the rigid CPDT unit strongly enhances the light-harvesting efficiency in the visible region (ε of 60,300 M −1 ·cm −1 ) compared to our previously-studied dyads relying on mono-or bis-thiophene units (ε of 31,800 and 38,600 M −1 ·cm −1 , respectively) [12,13,17,27]. Figure S1). These results are in full agreement with TD-DFT calculations previously reported for a structural analog of T2R, varying only by the nature of the acceptor group (dicyanovinyl unit instead of cyanoacrylate unit) [23]. ...
The light-induced processes occurring in two dye-catalyst assemblies for light-driven hydrogen production were investigated by ultrafast transient absorption spectroscopy. These dyads consist of a push-pull organic dye based on a cyclopenta[1,2-b:5,4-b’]dithiophene (CPDT) bridge, covalently linked to two different H2-evolving cobalt catalysts. Whatever the nature of the latter, photoinduced intramolecular electron transfer from the excited state of the dye to the catalytic center was never observed. Instead, and in sharp contrast to the reference dye, a fast intersystem crossing (ISC) populates a long-lived triplet excited state, which in turn non-radiatively decays to the ground state. This study thus shows how the interplay of different structures in a dye-catalyst assembly can lead to unexpected excited state behavior and might open up new possibilities in the area of organic triplet sensitizers. More importantly, a reductive quenching mechanism with an external electron donor must be considered to drive hydrogen production with these dye-catalyst assemblies.
... - [67] 800 > λ > templated Cl]Cl 2 (SEA) Ag/AgCl 400 nm three layer NiO films TSB -17 200 ---100 NiO Dissolved co-7 -0.1 V vs. - [66] balt complex Ag/AgCl -Co1 TB -13 200 ---100 NiO Dissolved co-7 -0.1 V vs. - [66] balt complex Ag/AgCl -Co1 BH4 ...
... Artero et al. presented a new nickel oxide photocathode modified with a polystyrene-block-poly-(2-vinylpyridine) (PS-b-P2VP) diblock copolymer and sensitized by a triphenylaminederivative dye with two carboxylic anchor groups and one π-A branch (D-π-A1). [67] In this case the acceptor groups consisted in a cyanoacrylate ester functionality. The performance was optimized using a cobalt-based sacrificial electron acceptor (SEA) with different amounts and in different buffer solutions. ...
The photoelectrochemical approach to photoinduced water splitting is gaining increasing interest for solar fuels generation. Dye‐sensitized photoelectrochemical cells (DS‐PEC) have been studied to improve the collection of the Vis range of solar radiation. Metal complexes have so far been the most investigated dyes but in recent years metal‐free organic dyes have emerged as a new frontier for the evolution of the sector. This Minireview systematically describes the use of organic sensitizers and has been organized in terms of dye‐sensitized photoactive electrode(s): photoanode; photocathode; tandem DS‐PEC with photoanode and photocathode. The main classes of dyes are introduced and described in their key properties, device performance, and water splitting data. Thanks to the increasing number of articles, this review highlights the growing importance of organic sensitizers and their molecular design for a more efficient solar generation of clean fuels.
... Electronic absorption spectroscopy is the most convenient for the organic dye, which is characterized in ACN solution by a charge transfer band at 436 nm with an extinction coefficient ε max = 29 300 M −1 cm −1 . 22 After grafting, a slight red-shift was observed, and the maximum of absorbance (A max ) was measured at 450 nm after subtraction of the spectrum of the bare nano-ITO recorded for each slide before sensitization (see Figure S1). The surface loading (reported versus the geometrical surface area of the electrode) was then calculated for the various substrates using the following equation: 26 ...
... The average value of 1.1 × 10 −8 mol cm −2 is fully consistent with the values previously reported on other structured nickel oxide electrodes. 22,24 (Note that this value is overestimated when compared to grafting onto planar substrates because it does not take into account the real oxide surface available.) For the PS/POM- Yet, wavelength dispersive spectroscopy (WDS), a sensitive technique to perform compositional analysis of the surface, allowed for the quantification of the POM loading. ...
... Photocurrent Assessment. The as-modified nano-ITO slides have been evaluated as photocathodes (active area 0.5 cm 2 ) in a three electrode cell configuration comprising a Pt counter electrode, a Ag/AgCl (KCl saturated) reference electrode, and [Co(NH 3 ) 5 Cl]Cl 2 as an irreversible electron acceptor, 1 mM in a pH 3.75 acetic buffer (0.1 M). 22 The pH value was set at the stability limit of the parent K 4 [PW 11 O 39 {SnC 6 H 4 I}] as monitored by 31 P NMR. Measurements were performed at ∼1 sun. ...
The amplification effect of polyoxometalates (POMs) on the efficiency of dye-sensitized nano-ITO cathodes is disclosed. The use of hybrid polyoxometalates of the type [PW11O39{SnC6H4-≡-C6H4F}]4-, F standing for a carboxylic group (POM-COOH) or a diazonium unit, allows to control the loading of the POMs on the electrode and to investigate key parameters. Even at very low loading, POM-COOH has a substantial effect on the photocurrent response, with up to 25-fold increase. Besides ensuring the stability towards leaching, the anchoring function of the POM hybrids was also found to play an intricate role in the competition between the multiple events involved.
... 5,[28][29][30][31] These defects, which are reected in the absorption spectrum of NiO, create localized electronic states in the band gap and act as trap states which cause charge recombination at the NiO-photosensitizer interface. [37][38][39][40] In order to reduce the defects in NiO, modications of the synthetic routes or post-treatment have been suggested. It has been shown that modifying the structural properties of metal-oxide semiconductor alters the electronic energy levels in semiconductors by modifying interatomic distances and hence, affects its functionality. ...
... 36,37 Photoelectrochemical activity assessment of the NiO photocathodes Photocurrent measurements were performed in a specic electrochemical cell in a three-electrode conguration, using the different NiO lms sensitized with the organic push-pull dye T1 (((E)-4,40-((4-(5-(2-cyano-3-ethoxy-3-oxoprop-1-en-1-yl) thiophen-2-yl)phenyl)aza-nediyl)dibenzoic acid)). 38,39 For comparison, T1-sensitized commercial NiO lms (two layers, screen-printed onto conductive glass) purchased from Dyenamo AB (Stockholm, Sweden) were employed. The surface of the working electrode in contact with the electrolyte was 0.24 cm 2 . ...
We report the wet chemical synthesis of mesoporous NiO nanostars (NS) as photocathode material for dye-sensitized solar cells (DSSCs). The growth mechanism of NiO NS as a new morphology of NiO is assessed by TEM and spectroscopic investigations. The NiO NS are obtained upon annealing of preformed β-Ni(OH)2 into pristine NiO with low defect concentrations and favorable electronic configuration for dye sensitization. The NiO NS consist of fibers self-assembled from nanoparticles yielding a specific surface area of 44.9 m² g⁻¹. They possess a band gap of 3.83 eV and can be sensitized by molecular photosensitizers bearing a range of anchoring groups, e.g. carboxylic acid, phosphonic acid, and pyridine. The performance of NiO NS-based photocathodes in photoelectrochemical application is compared to that of other NiO morphologies, i.e. nanoparticles and nanoflakes, under identical conditions. Sensitization of NiO NS with the benchmark organic dye P1 leads to p-DSSCs with a high photocurrent up to 3.91 mA cm⁻² whilst the photoelectrochemical activity of the NiO NS photocathode in aqueous medium in the presence of an irreversible electron acceptor is reflected by generation of a photocurrent up to 23 μA cm⁻².
... 56 Assuming that the molar absorptivity coefficient (3 Co(I) 601 nm z 8300 L mol À1 cm À1 ) of [Co I (DO)(DOH)pn(CH 3 CN)] (Fig. S13 †) at peak maximum does not vary signicantly when shiing from MeCN to water, this signature allowed us to evaluate the surface coverage in Co C11P ; we determined the surface loading G CoC11P z 4.5 nmol cm À2 from the photoelectrochemically measured absorbance value A NiO|CoC11P (601 nm) ¼ 0.037 ( Fig. 9) using eqn (1). 54 NiO is a p-type semiconductor and should behave as an insulator at applied potentials negative to its valence band edge, usually reported at +0.3 to +0.5 V vs. NHE at pH 7. 57 To better understand how Co I species can be electrochemically generated below À0.37 V vs. NHE, the scan rate dependence of the signal was studied (Fig. 8a) between 10 and 100 mV s À1 . Actually, the peak current linearly depends on the square root of the scan rate (Fig. 8a, inset). ...
Dye-sensitized photo-electrochemical cells (DS-PECs) form an emerging technology for the large-scale storage of solar energy in the form of (solar) fuels because of the low cost and ease to process of their constitutive photoelectrode materials. Preparing such molecular photocathodes requires a well-controlled co-immobilization of molecular dyes and catalysts onto transparent semiconducting materials. Here we used a series of surface analysis techniques to describe the molecular assembly of push-pull organic dyes and cobalt diimine-dioxime catalysts co-grafted on p-type NiO electrode substrate. (Photo)electrochemical measurements allowed to characterize electron transfer processes within such assembly and to demonstrate for the fisrt time that CoI species are formed as the entry into light-driven H2 evolution mechanism.This co-grafted noble-metal free H2-evolving photocathode architecture displays similar performances as its covalent dye-catalyst counterpart based on the same catalytic moiety. Post-operando time-of-flight secondary ion mass spectrometry (Tof-SIMS) analysis of these photoelectrodes suggested decomposition pathways of the dye and triazole linkage used to graft catalyst onto NiO during extensive photoelectrochemical operation, providing grounds for the design of optimized molecular DS-PEC components with increased robustness upon turnover.
... The self-assembly of PS-b-P2VP (Fig. 1a), a binary block copolymer, has been widely utilized in various applications such as templates for synthesize of inorganic materials, 6 high density information storage media, 7 sensors, 8 photo-catalysis, 9 and photosensitive electrodes. 10,11 The phase separation of BCPs is well understood in thermodynamic theory. [12][13][14][15] There are three independent parameters control the phase separation and self-assembly behavior of PS-b-P2VP: the copolymer composition (or the volume fractions of the A and B blocks), f, the total degree of polymerization, N, and the segment-segment interaction energy parameter, . ...
Block copolymers can form various ordered structures by self-assembly, and their composites with inorganic materials may give surprising properties. This review summarizes recent development in preparation, mechanism, and application of various types of self-assembly of polystyrene-block-poly (2-vinylpyridine) (PS-b-P2VP). The focus of the review is put on how to control the self-assembly dynamic and ordered structure of the PS-b-P2VP based materials by applying effective factors such as thermal annealing, solvent annealing, block composition, and blending. Moreover, the combination of the self-assembly of PS-b-P2VP and various nanoparticles, with potentials in drug delivery, sensors, and catalysis, is highlighted.
