Laia Francas

Laia Francas
Imperial College London | Imperial · Department of Chemistry

About

78
Publications
10,315
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2,788
Citations
Citations since 2016
63 Research Items
2504 Citations
20162017201820192020202120220100200300400500
20162017201820192020202120220100200300400500
20162017201820192020202120220100200300400500
20162017201820192020202120220100200300400500

Publications

Publications (78)
Article
Electrocatalytic and photoelectrocatalytic technologies are key players in the transition to a circular economy. In order to rationally design the new generation of efficient (photo)electrocatalysts it is critical to establish which performance bottlenecks must be overcome during the complex catalytic transformations. Obtaining such detailed mechan...
Article
Full-text available
Covalent organic frameworks (COFs) are crystalline porous organic polymers built from covalent organic blocks that can be photochemically active when incorporating organic semicon-ducting units, such as triazine rings or diacetylene bridges. The bandgap, charge separation capacity , porosity, wettability, and chemical stability of COFs can be tuned...
Article
Full-text available
In this work, spectroelectrochemical techniques are employed to analyse the catalytic water oxidation performance of a series of three nickel/iron oxyhydroxide electrocatalysts deposited on FTO and BiVO4, at neutral pH. Similar electrochemical water oxidation performance is observed for each of the FeOOH, Ni(Fe)OOH and FeOOHNiOOH electrocatalysts s...
Article
WO3 photoanodes offer rare stability in acidic media, but are limited by their selectivity for oxygen evolution over parasitic side reactions, when employed in photoelectrochemical (PEC) water splitting. Herein, this is remedied via the modification of nanostructured WO3 photoanodes with surface decorated PdO as an oxygen evolution co-catalyst (OEC...
Preprint
In this work, spectroelectrochemical techniques are employed to analyse the catalytic water oxidation performance of a series of three nickel/iron oxyhydroxide electrocatalysts deposited on FTO and BiVO<sub>4</sub>, at neutral pH. Similar electrochemical water oxidation performance is observed for each of the FeOOH, Ni(Fe)OOH and FeOOHNiOOH electro...
Article
Nickel oxide-based catalysts currently represent the state of the art in electrochemical water oxidation in alkaline pH. However, much of their functionality remains poorly understood, particularly regarding catalytically active sites and mechanism. Herein, we conduct a thickness dependent study of sputter deposited NiOx films by electrochemical im...
Preprint
Multi-redox catalysis requires the transfer of more than one charge carrier and is crucial for solar energy conversion into fuels and valuable chemicals. In photo(electro)chemical systems, however, the necessary accumulation of multiple, long-lived charges is challenged by recombination with their counterparts. Herein, we investigate charge accumul...
Article
Operando spectroelectrochemical analysis is used to determine the water oxidation reaction kinetics for hematite photoanodes prepared using four different synthetic procedures. Whilst these photoanodes exhibit very different current / voltage performance, their underlying water oxidation kinetics are found to be almost invariant. Higher temperature...
Article
Semiconducting polymers are versatile materials for solar energy conversion and have gained popularity as photocatalysts for sunlight-driven hydrogen production. Organic polymers often contain residual metal impurities such as palladium (Pd) clusters that are formed during the polymerization reaction, and there is increasing evidence for a catalyti...
Preprint
p> Operando spectroelectrochemical analysis is used to determine the water oxidation reaction kinetics for hematite photoanodes prepared using four different synthetic procedures. Whilst these photoanodes exhibit very different current / voltage performance, their underlying water oxidation kinetics are found to be almost invariant. Lower photoanod...
Preprint
Semiconducting polymers are versatile materials for solar energy conversion and have gained popularity as photo-catalysts for sunlight-driven hydrogen production. Organic polymers often contain residual metal impurities such as palladium (Pd) clusters that are formed during the polymerization reaction, and there is increasing evidence for a cat-aly...
Article
Full-text available
Oxygen vacancies are common to most metal oxides, whether intentionally incorporated or otherwise, and the study of these defects is of increasing interest for solar water splitting. In this work, we examine nanostructured WO3 photoanodes of varying oxygen content to determine how the concentration of bulk oxygen-vacancy states affects the photocat...
Article
Full-text available
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Article
Full-text available
Water oxidation is the key kinetic bottleneck of photoelectrochemical devices for fuel synthesis. Despite advances in the identification of intermediates, elucidating the catalytic mechanism of this multi-redox reaction on metal–oxide photoanodes remains a significant experimental and theoretical challenge. Here, we report an experimental analysis...
Article
Full-text available
Ni/Fe oxyhydroxides are the best performing Earth-abundant electrocatalysts for water oxidation. However, the origin of their remarkable performance is not well understood. Herein, we employ spectroelectrochemical techniques to analyse the kinetics of water oxidation on a series of Ni/Fe oxyhydroxide films: FeOOH, FeOOHNiOOH, and Ni(Fe)OOH (5% Fe)....
Article
Oxygen vacancies are ubiquitous in metal oxides and critical to performance, yet the impact of these states upon charge carrier dynamics important for photoelectrochemical and photocatalytic applications, remains contentious and poorly understood. A key challenge is the unambiguous identification of spectroscopic fingerprints which can be used to t...
Preprint
Oxygen vacancies are common to most metal oxides, whether intentionally incorporated or otherwise, and the study of these defects is of increasing interest for solar water splitting. In this work, we examine nanostructured WO<sub>3</sub> photoanodes of varying oxygen content to determine how the concentration of bulk oxygen-vacancy states affects t...
Article
In metal oxide-based photoelectrochemical devices, the spatial separation of photogenerated electrons and holes is typically attributed to band-bending at the oxide / electrolyte interface. However, direct evidence of such band-bending impacting upon charge carrier lifetimes has been very limited to date. Herein we use ultrafast spectroscopy to tra...
Article
Porous and amorphous materials are typically not employed for photocatalytic purposes, like CO2 photoreduction as their high number of defects can lead to low charge mobility and favour bulk electron-hole recombination. Yet, with a disordered nature can come porosity, which in turns promotes catalyst/reactant interactions and fast charge transfer t...
Article
Full-text available
Oxygen vacancies are widely used to tune the light absorption of semiconducting metal oxides, but a photophysical framework describing the impact of such point defects on the dynamics of photogenerated charges, and ultimately on catalysis, is still missing. We herein use WO3 as a model material and investigate the impact of significantly different...
Article
Here, it is investigated whether an energetic cascade between mixed and pure regions assists in suppressing recombination losses in non‐fullerene acceptor (NFA)‐based organic solar cells. The impact of polymer‐NFA blend composition upon morphology, energetics, charge carrier recombination kinetics, and photocurrent properties are studied. By changi...
Article
Full-text available
The four hole oxidation of water has long been considered the kinetic bottleneck for overall solar-driven water splitting, and thus requires the formation of long-lived photogenerated holes to overcome this kinetic barrier. However, photogenerated charges are prone to recombination unless they can be spatially separated. This can be achieved by cou...
Article
Full-text available
With the emergence of non-fullerene electron acceptors resulting in further breakthroughs in the performance of organic solar cells, there is now an urgent need to understand their degradation mechanisms in order to improve their intrinsic stability through better material design. In this study, we present quantitative evidence for a common root ca...
Article
The reasons for improved photoelectrochemical performance upon catalyst modification are often controversial. When depositing the efficient CoFe Prussian blue (CoFe-PB) water oxidation catalyst on BiVO4, a large photocurrent increase and onset potential shift (up to 0.8 V) is observed, while maintaining staibility for over 50 hours. To elucidate th...
Article
A thorough understanding of the kinetic competition between desired water oxidation/electron extraction processes and any detrimental surface recombination is required to achieve high water oxidation efficiencies in transition metal oxide systems. The kinetics of these processes in high Faradaic efficiency tungsten trioxide (WO3) photoanodes (>85%)...
Article
Graphitic carbon nitride (g-C3N4) is regarded as an attractive photocatalyst for solar fuels production, i.e. H2 evolution and CO2 photo-reduction. Yet, its structural, chemical and optoelectronic properties are very much dependent on the synthesis method and are likely to contribute differently whether H2 evolution or CO2 reduction is considered....
Article
The effect of residual Pd on hydrogen evolution activity in conjugated polymer photocatalytic systems is systematically investigated using colloidal poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (F8BT) nanoparticles as a model system. Residual Pd, originating from the synthesis of F8BT via Pd catalyzed polycondensation polymerization, is observed...
Article
Multiple equilibria are involved in Ru‐bda based complexes in aqueous solutions at low oxidation states. These equilibria are pH‐dependent and are the key for understanding the generation of Ru active species at high oxidation states, which are responsible for water oxidation catalysis. More information can be found in the Full Paper by A. Llobet,...
Article
The Ru complex [RuII(bda‐κ‐N2O2)(N‐NH2)2], 1, (bda2‐ = (2,2'‐bipyridine)‐6,6'‐dicarboxylate; N‐NH2 = 4‐(pyridin‐4‐yl)aniline) is used as a synthetic intermediate to prepare Ru‐bda complexes that contain the NO+, acetonitrile (MeCN) or H2O ligands at oxidation states II and III. Complex 1 reacts with excess NO+ to form a Ru complex where the aryl am...
Article
Full-text available
In this work we lay out design guidelines for catalytically more efficient organic photocathodes achieving stable hydrogen production in neutral pH. We propose an organic photocathode architecture employing a NiO hole selective layer, a PCDTBT:PCBM bulk heterojunction, a compact TiO2 electron selective contact and a RuO2 nanoparticle catalyst. The...
Chapter
In this chapter, we discuss how rate law analyses can shed light into the kinetics and reaction mechanisms of those processes involved in the production of solar fuels. We show that the key data necessary to elucidate rate laws can be easily obtained by combining photo-induced absorbance (PIA) and transient photocurrent (TPC) measurements. The chap...
Article
The kinetics of photoelectrochemical (PEC) oxidation of methanol, as a model organic substrate, on α-Fe2O3 photoanodes are studied using photo-induced absorption spectroscopy and transient photocurrent measurements. Methanol is oxidized on α-Fe2O3 to formaldehyde with near unity Faradaic efficiency. A rate law analysis under quasi-steady state cond...
Article
We report an efficient molecular light-driven system to oxidize water to oxygen and the kinetic analysis of the factors determining the efficiency of the system. The system comprises a highly active molecular catalyst ([RuIV(tda)(py)2(O)]), [RuII(bpy)(bpy-COOEt)2]2+ (RuP) as sensitizer and Na2S2O8 as sacrificial electron acceptor. This combination...
Article
It has been more than 40 years since Fujishima and Honda first demonstrated water splitting using TiO2, yet there is still no clear mechanism by which surface holes on TiO2 oxidize water. In this article, we use a range of complementary techniques to study this reaction and provide new insight into the reaction mechanism. Using transient photocurre...
Article
Solar water splitting is a promising solution for the renewable production of hydrogen as an energy vector. To date, complex or patterned photoelectrodes have shown the highest water splitting efficiencies, but lack scalable routes for commercial scale-up. In this article, we report a direct and scalable chemical vapor deposition (CVD) route at atm...
Article
Full-text available
Multi-electron heterogeneous catalysis is a pivotal element in the (photo)electrochemical generation of solar fuels. However, mechanistic studies of these systems are difficult to elucidate by means of electrochemical methods alone. Here we report a spectroelectrochemical analysis of hydrogen evolution on ruthenium oxide employed as an electrocatal...
Article
Full-text available
A new CNNC carbene-phthalazine tetradentate ligand has been synthesised, which in the reaction with [Ru(T)Cl3] (T = trpy, tpm, bpea; trpy = 2,2';6',2''-terpyridine; tpm = tris(pyrazol-1-yl)methane; bpea = N,N-bis(pyridin-2-ylmethyl)ethanamine) in MeOH or iPrOH undergoes a C-N bond scission due to the nucleophilic attack of a solvent molecule, with...
Article
Efficient catalysts for water oxidation are key to all scenarios for artificial solar water splitting, and in case of molecular catalysts their immobilization on conductive solid supports is considered essential for the construction of a photoelectrochemical cell. In this work, derivatives of the rugged 3,5-bis(bipyridyl)pyrazolate (bbp) based diru...
Article
An end-on superoxido complex with formula {[CoIII(OH2)(trpy)][CoIII(OO·)(trpy)](m-bpp)}4+ , 34+, (bpp- is bis-2-pyridyl-3,5-pyrazolate; trpy is 2,2’;6’:2”-terpyridine) has been characterized by resonance Raman, electron paramagnetic resonance and x-ray absorption spectroscopies. These results together with on-line mass spectrommetry experiments usi...
Article
A Ru(II)-pentadentate polypyridyl complex [Ru(II)(κ-N(5)-bpy2PYMe)Cl](+) (1(+), bpy2PYMe = 1-(2-pyridyl)-1,1-bis(6-2,2'-bipyridyl)ethane) and its aqua derivative [Ru(II)(κ-N(5)-bpy2PYMe)(H2O)](2+) (2(2+)) were synthesized and characterized by experimental and computational methods. In MeOH, 1(+) exists as two isomers in different proportions, cis (...
Article
Spectroelectrochemical studies employing pulsed LED irradiation are used to investigate the kinetics of water oxidation on undoped dense bismuth vanadate (BiVO4) photoanodes under conditions of photoelectrochemical water oxidation, and compared to those obtained for oxidation of a simple redox couple. These measurements are employed to determine th...
Article
Full-text available
A series of symmetric and non-symmetric dinuclear Ru complexes of general formula {[Ru(R2-trpy)(H2O)][Ru(R3-trpy)(H2O)](µ-R1-bpp)}3+ where trpy is 2,2’:6’,2”-terpyridine, bpp- is 3,5-bis(2-pyridyl)-pyrazolate and R1, R2 and R3 are electron donating (ED) and electron withdrawing (EW) groups such as Me, MeO, NH2 and NO2 have been prepared using micro...
Article
Three distinct functionalisation strategies have been applied to the in,in-[{Ru(II) (trpy)}2 (μ-bpp)(H2 O)2 ](3+) (trpy=2,2':6',2''-terpyridine, bpp=bis(pyridine)pyrazolate) water-oxidation catalyst framework to form new derivatives that can adsorb onto titania substrates. Modifications included the addition of sulfonate, carboxylate, and phosphona...
Article
Mastering the light-induced four-electron oxidation of water to molecular oxygen is a key step towards the achievement of overall water splitting to produce alternative solar fuels. In this work, we report two rugged molecular pyrazolate-based diruthenium complexes that efficiently catalyze visible-light-driven water oxidation. These complexes were...
Article
A new bis-facial dinuclear ruthenium complex, {[Ru(II)(bpy)]2(μ-bimp)(μ-Cl)}(2+), 2(2+), containing a hexadentate pyrazolate-bridging ligand (Hbimp) and bpy as auxiliary ligands has been synthesized and fully characterized in solution by spectrometric, spectroscopic, and electrochemical techniques. The new compound has been tested with regard to it...
Article
The Inside Back Cover picture shows the inspiration for water oxidation catalysis (WOC), that is, the light reaction of photosynthesis that produces O2, H+, and e− through the use of solar energy, next to a functional mimic of nature's oxygen-evolving complex: a new dinuclear ruthenium complex that has been designed for high activity in WOC, both c...
Article
Electrochemical reduction of the dizaonium complex, [RuII(bda)(NO)(N-N2)2]3+, 23+, (N-N22+ is 4-(pyridin-4-yl) benzenediazonium and bda2- is 2,2'-bipyridine-6,6'-dicarboxylate) in acetone produces the covalent grafting of this molecular complex onto glassy carbon (GC) electrodes. Multiple cycling voltammetric experiments on the GC electrode generat...
Article
Water splitting is one of the key steps in the conversion of sunlight into a usable renewable energy carrier such as dihydrogen or more complex chemical fuels. Developing rugged and highly efficient catalysts for the oxidative part of water splitting, the water oxidation reaction generating dioxygen, is a major challenge in the field. Herein, we in...
Article
The replacement of fossil fuels by a clean and renewable energy source is one of the most urgent and challenging issues our society is facing today, which is why intense research has been devoted to this topic recently. Nature has been using sunlight as the primary energy input to oxidise water and generate carbohydrates (solar fuel) for over a bil...
Article
Three dinucleating Ru-Cl complexes containing the hexadentate dinucleating ligand [1,1'-(4-methyl-1H-pyrazole-3,5-diyl)bis(1-(pyridin-2-yl)ethanol)] (Hpbl) and the meridional 2,2':6',2″-terpyridine ligand (trpy) have been prepared and isolated. These complexes include {[RuCl(trpy)]2(μ-pbl-κ-N(3)O)}(+) (1a(+)), {[RuCl(trpy)]2(μ-Hpbl-κ-N(3)O)}(2+) (1...
Article
A new tetradentate dinucleating ligand [1,1'-(4-methyl-1H-pyrazole-3,5-diyl)bis(1-(pyridin-2-yl)ethanol)] (Hpbl) containing an O/N mixed donor set of atoms has been synthesized and characterized by analytical and spectroscopic techniques. The Ru-Cl and Ru-aqua complexes containing this ligand of general formula [Ru(II)X(Hpbl)(trpy)](y+) (trpy = 2,2...