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Correlating activities and defects in (photo)electrocatalysts using in-situ multi-modal microscopic imaging. Nat Commun 2024; 15:3908. [PMID: 38724495 PMCID: PMC11082147 DOI: 10.1038/s41467-024-47870-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Accepted: 04/09/2024] [Indexed: 05/12/2024] Open
Abstract
Photo(electro)catalysts use sunlight to drive chemical reactions such as water splitting. A major factor limiting photocatalyst development is physicochemical heterogeneity which leads to spatially dependent reactivity. To link structure and function in such systems, simultaneous probing of the electrochemical environment at microscopic length scales and a broad range of timescales (ns to s) is required. Here, we address this challenge by developing and applying in-situ (optical) microscopies to map and correlate local electrochemical activity, with hole lifetimes, oxygen vacancy concentrations and photoelectrode crystal structure. Using this multi-modal approach, we study prototypical hematite (α-Fe2O3) photoelectrodes. We demonstrate that regions of α-Fe2O3, adjacent to microstructural cracks have a better photoelectrochemical response and reduced back electron recombination due to an optimal oxygen vacancy concentration, with the film thickness and extended light exposure also influencing local activity. Our work highlights the importance of microscopic mapping to understand activity, in even seemingly homogeneous photoelectrodes.
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Improved Photoelectrochemical Performance of WO 3/BiVO 4 Heterojunction Photoanodes via WO 3 Nanostructuring. ACS APPLIED MATERIALS & INTERFACES 2023; 15. [PMID: 37921705 PMCID: PMC10658457 DOI: 10.1021/acsami.3c10869] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2023] [Revised: 09/29/2023] [Accepted: 10/19/2023] [Indexed: 11/04/2023]
Abstract
WO3/BiVO4 heterojunction photoanodes can be efficiently employed in photoelectrochemical (PEC) cells for the conversion of water into molecular oxygen, the kinetic bottleneck of water splitting. Composite WO3/BiVO4 photoelectrodes possessing a nanoflake-like morphology have been synthesized through a multistep process and their PEC performance was investigated in comparison to that of WO3/BiVO4 photoelectrodes displaying a planar surface morphology and similar absorption properties and thickness. PEC tests, also in the presence of a sacrificial hole scavenger, electrochemical impedance analysis under simulated solar irradiation, and incident photon to current efficiency measurements highlighted that charge transport and charge recombination issues affecting the performance of the planar composite can be successfully overcome by nanostructuring the WO3 underlayer in nanoflake-like WO3/BiVO4 heterojunction electrodes.
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3
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A Perovskite Photovoltaic Mini-Module-CsPbBr 3 Photoelectrochemical Cell Tandem Device for Solar-Driven Degradation of Organic Compounds. ACS ENERGY LETTERS 2023; 8:4488-4495. [PMID: 37854043 PMCID: PMC10580309 DOI: 10.1021/acsenergylett.3c01361] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/07/2023] [Accepted: 09/27/2023] [Indexed: 10/20/2023]
Abstract
Recently, halide perovskites have been widely explored for high-efficiency photocatalysis or photoelectrochemical (PEC) cells. Here, in order to make an efficient photoanode electrode for the degradation of pollutants, concretely 2-mercaptobenzothiazole (MBT), nanoscale cesium lead bromide (CsPbBr3) perovskite was directly formed on the surface of mesoporous titanium dioxide (meso-TiO2) film using a two-step spin-coating process. This photoelectrode recorded a photocurrent of up to 3.02 ± 0.03 mA/cm2 under standard AM 1.5G (100 mW/cm2) illumination through an optimization process such as introducing a thin aluminum oxide (Al2O3) coating layer. Furthermore, to supply high voltage for efficient oxidation of MBT without an external bias, we developed a new photovoltaic/PEC tandem system using a methylammonium lead iodide (MAPbI3) based mini-module consisting of three solar cells interconnected in series and confirmed its successful operation. This approach looks very promising due to its applicability to various PEC reactions.
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4
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Highly Durable Nanoporous Cu 2-xS Films for Efficient Hydrogen Evolution Electrocatalysis under Mild pH Conditions. ACS Catal 2023; 13:10457-10467. [PMID: 37564127 PMCID: PMC10411506 DOI: 10.1021/acscatal.3c01673] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Revised: 06/30/2023] [Indexed: 08/12/2023]
Abstract
Copper-based hydrogen evolution electrocatalysts are promising materials to scale-up hydrogen production due to their reported high current densities; however, electrode durability remains a challenge. Here, we report a facile, cost-effective, and scalable synthetic route to produce Cu2-xS electrocatalysts, exhibiting hydrogen evolution rates that increase for ∼1 month of operation. Our Cu2-xS electrodes reach a state-of-the-art performance of ∼400 mA cm-2 at -1 V vs RHE under mild conditions (pH 8.6), with almost 100% Faradaic efficiency for hydrogen evolution. The rise in current density was found to scale with the electrode electrochemically active surface area. The increased performance of our Cu2-xS electrodes correlates with a decrease in the Tafel slope, while analyses by X-ray photoemission spectroscopy, operando X-ray diffraction, and in situ spectroelectrochemistry cooperatively revealed the Cu-centered nature of the catalytically active species. These results allowed us to increase fundamental understanding of heterogeneous electrocatalyst transformation and consequent structure-activity relationship. This facile synthesis of highly durable and efficient Cu2-xS electrocatalysts enables the development of competitive electrodes for hydrogen evolution under mild pH conditions.
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Rational Design of Carbon Nitride Photoelectrodes with High Activity Toward Organic Oxidations. Angew Chem Int Ed Engl 2022; 61:e202211587. [PMID: 36224107 PMCID: PMC10099510 DOI: 10.1002/anie.202211587] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2022] [Indexed: 11/16/2022]
Abstract
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 (NCN CNx ) was co-deposited with ITO nanoparticles on a 1.8 Å 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 NCN CNx , whilst the alumina underlayer reduces recombination losses between the ITO and the FTO glass. The Al2 O3 |ITO : NCN CNx film displays a benchmark performance for CNx -based photoanodes with an onset of -0.4 V vs a reversible hydrogen electrode (RHE), and 1.4±0.2 mA cm-2 at 1.23 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.
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The role of crystal facets and disorder on photo-electrosynthesis. NANOSCALE 2022; 14:15596-15606. [PMID: 36148901 DOI: 10.1039/d2nr03609f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Photoelectrochemistry has the potential to play a crucial role in the storage of solar energy and the realisation of a circular economy. From a chemical viewpoint, achieving high conversion efficiencies requires subtle control of the catalyst surface and its interaction with the electrolyte. Traditionally, such control has been hard to achieve in the complex multinary oxides used in PEC devices and consequently the mechanisms by which surface exposed facets influence light-driven catalysts are poorly understood. Yet, this understanding is critical to further improve conversion yields and fine-tune reaction selectivities. Here, we review the impact that crystal facets and disorder have on photoelectrochemical reactivity. In particular, we discuss how the crystal orientation influences the energetics of the surface, the existence of defects and the transport of reactive charges, ultimately dictating the PEC activity. Moreover, we evaluate how facet stability dictates the tendency of the solid to undergo reconstructions during catalytic processes and highlight the experimental and computational challenges that must be overcome to characterise the role of the exposed facets and disorder in catalytic performance.
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Spectroelectrochemistry of Water Oxidation Kinetics in Molecular versus Heterogeneous Oxide Iridium Electrocatalysts. J Am Chem Soc 2022; 144:8454-8459. [PMID: 35511107 PMCID: PMC9121376 DOI: 10.1021/jacs.2c02006] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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Water oxidation is the step limiting
the efficiency of electrocatalytic
hydrogen production from water. Spectroelectrochemical analyses are
employed to make a direct comparison of water oxidation reaction kinetics
between a molecular catalyst, the dimeric iridium catalyst [Ir2(pyalc)2(H2O)4-(μ-O)]2+ (IrMolecular, pyalc
= 2-(2′pyridinyl)-2-propanolate) immobilized on a mesoporous
indium tin oxide (ITO) substrate, with that of an heterogeneous electrocatalyst,
an amorphous hydrous iridium (IrOx) film. For both systems, four analogous redox states were
detected, with the formation of Ir(4+)–Ir(5+) being the potential-determining
step in both cases. However, the two systems exhibit distinct water
oxidation reaction kinetics, with potential-independent first-order
kinetics for IrMolecular contrasting
with potential-dependent kinetics for IrOx. This is attributed to water oxidation on the heterogeneous
catalyst requiring co-operative effects between neighboring oxidized
Ir centers. The ability of IrMolecular to drive water oxidation without such co-operative effects
is explained by the specific coordination environment around its Ir
centers. These distinctions between molecular and heterogeneous reaction
kinetics are shown to explain the differences observed in their water
oxidation electrocatalytic performance under different potential conditions.
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Abstract
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Metal oxides and
oxyhydroxides exhibit state-of-the-art activity
for the oxygen evolution reaction (OER); however, their reaction mechanism,
particularly the relationship between charging of the oxide and OER
kinetics, remains elusive. Here, we investigate a series of Mn-, Co-,
Fe-, and Zn-doped nickel oxides using operando UV–vis
spectroscopy coupled with time-resolved stepped potential spectroelectrochemistry.
The Ni2+/Ni3+ redox peak potential is found
to shift anodically from Mn- < Co- < Fe- < Zn-doped samples,
suggesting a decrease in oxygen binding energetics from Mn- to Zn-doped
samples. At OER-relevant potentials, using optical absorption spectroscopy,
we quantitatively detect the subsequent oxidation of these redox centers.
The OER kinetics was found to have a second-order dependence on the
density of these oxidized species, suggesting a chemical rate-determining
step involving coupling of two oxo species. The intrinsic turnover
frequency per oxidized species exhibits a volcano trend with the binding
energy of oxygen on the Ni site, having a maximum activity of ∼0.05
s–1 at 300 mV overpotential for the Fe-doped sample.
Consequently, we propose that for Ni centers that bind oxygen too
strongly (Mn- and Co-doped oxides), OER kinetics is limited by O–O
coupling and oxygen desorption, while for Ni centers that bind oxygen
too weakly (Zn-doped oxides), OER kinetics is limited by the formation
of oxo groups. This study not only experimentally demonstrates the
relation between electroadsorption free energy and intrinsic kinetics
for OER on this class of materials but also highlights the critical
role of oxidized species in facilitating OER kinetics.
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Redox-State Kinetics in Water-Oxidation IrO x Electrocatalysts Measured by Operando Spectroelectrochemistry. ACS Catal 2021. [DOI: 10.1021/acscatal.1c03290] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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10
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Water oxidation kinetics of nanoporous BiVO 4 photoanodes functionalised with nickel/iron oxyhydroxide electrocatalysts. Chem Sci 2021; 12:7442-7452. [PMID: 34163834 PMCID: PMC8171343 DOI: 10.1039/d0sc06429g] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
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 studied, which is found to result from a balance between degree of charge accumulation and rate of water oxidation. Once added onto BiVO4 photoanodes, a large enhancement in the water oxidation photoelectrochemical performance is observed in comparison to the un-modified BiVO4. To understand the origin of this enhancement, the films were evaluated through time-resolved optical spectroscopic techniques, allowing comparisons between electrochemical and photoelectrochemical water oxidation. For all three catalysts, fast hole transfer from BiVO4 to the catalyst is observed in the transient absorption data. Using operando photoinduced absorption measurements, we find that water oxidation is driven by oxidised states within the catalyst layer, following hole transfer from BiVO4. This charge transfer is correlated with a suppression of recombination losses which result in remarkably enhanced water oxidation performance relative to un-modified BiVO4. Moreover, despite similar electrocatalytic behaviour of all three electrocatalysts, we show that variations in water oxidation performance observed among the BiVO4/MOOH photoanodes stem from differences in photoelectrochemical and electrochemical charge accumulation in the catalyst layers. Under illumination, the amount of accumulated charge in the catalyst is driven by the injection of photogenerated holes from BiVO4, which is further affected by the recombination loss at the BiVO4/MOOH interface, and thus leads to deviations from their behaviour as standalone electrocatalysts. Elucidating the role of charge accumulation and reaction kinetics in governing the performance of Ni/Fe oxyhydroxides as electrocatalysts and as co-catalysts on BiVO4 photoanodes water oxidation.![]()
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11
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Publisher Correction: Spectroelectrochemical study of water oxidation on nickel and iron oxyhydroxide electrocatalysts. Nat Commun 2020; 11:410. [PMID: 31949162 PMCID: PMC6965187 DOI: 10.1038/s41467-020-14297-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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Reply to: Questioning the rate law in the analysis of water oxidation catalysis on haematite photoanodes. Nat Chem 2020; 12:1099-1101. [PMID: 33168963 DOI: 10.1038/s41557-020-00570-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Accepted: 09/25/2020] [Indexed: 11/09/2022]
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Charge accumulation kinetics in multi-redox molecular catalysts immobilised on TiO 2. Chem Sci 2020; 12:946-959. [PMID: 34163861 PMCID: PMC8178996 DOI: 10.1039/d0sc04344c] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Accepted: 11/07/2020] [Indexed: 11/29/2022] Open
Abstract
Multi-redox catalysis requires the accumulation 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 accumulation in two model multi-redox molecular catalysts for proton and CO2 reduction attached onto mesoporous TiO2 electrodes. Transient absorption spectroscopy and spectroelectrochemical techniques have been employed to study the kinetics of photoinduced electron transfer from the TiO2 to the molecular catalysts in acetonitrile, with triethanolamine as the hole scavenger. At high light intensities, we detect charge accumulation in the millisecond timescale in the form of multi-reduced species. The redox potentials of the catalysts and the capacity of TiO2 to accumulate electrons play an essential role in the charge accumulation process at the molecular catalyst. Recombination of reduced species with valence band holes in TiO2 is observed to be faster than microseconds, while electron transfer from multi-reduced species to the conduction band or the electrolyte occurs in the millisecond timescale. Finally, under light irradiation, we show how charge accumulation on the catalyst is regulated as a function of the applied bias and the excitation light intensity.
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Impact of the Synthesis Route on the Water Oxidation Kinetics of Hematite Photoanodes. J Phys Chem Lett 2020; 11:7285-7290. [PMID: 32787321 DOI: 10.1021/acs.jpclett.0c02004] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Operando spectroelectrochemical analysis is used to determine the water oxidation reaction kinetics for hematite photoanodes prepared using four different synthetic procedures. While these photoanodes exhibit very different current/voltage performance, their underlying water oxidation kinetics are found to be almost invariant. Higher temperature thermal annealing was found to correlate with a shift in the photocurrent onset potential toward less positive potentials, assigned to a suppression of both back electron-hole recombination and of charge accumulation in intra-bandgap states, indicating these intra-bandgap states do not contribute directly to water oxidation.
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15
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Impact of Oxygen Vacancy Occupancy on Charge Carrier Dynamics in BiVO4 Photoanodes. J Am Chem Soc 2019; 141:18791-18798. [DOI: 10.1021/jacs.9b09056] [Citation(s) in RCA: 104] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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16
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Multihole water oxidation catalysis on haematite photoanodes revealed by operando spectroelectrochemistry and DFT. Nat Chem 2019; 12:82-89. [DOI: 10.1038/s41557-019-0347-1] [Citation(s) in RCA: 111] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2018] [Accepted: 09/03/2019] [Indexed: 11/09/2022]
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17
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Ultra-thin Al2O3 coatings on BiVO4 photoanodes: Impact on performance and charge carrier dynamics. Catal Today 2019. [DOI: 10.1016/j.cattod.2017.11.014] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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18
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Chapter 5. Rate Law Analysis of Water Splitting Photoelectrodes. ADVANCES IN PHOTOELECTROCHEMICAL WATER SPLITTING 2018. [DOI: 10.1039/9781782629863-00128] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Abstract
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The kinetics of photoelectrochemical
(PEC) oxidation of methanol, as a model organic substrate, on α-Fe2O3 photoanodes are studied using photoinduced 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
conditions of PEC methanol oxidation indicates that rate of reaction
is second order in the density of surface holes on hematite and independent
of the applied potential. Analogous data on anatase TiO2 photoanodes indicate similar second-order kinetics for methanol
oxidation with a second-order rate constant 2 orders of magnitude
higher than that on α-Fe2O3. Kinetic isotope
effect studies determine that the rate constant for methanol oxidation
on α-Fe2O3 is retarded ∼20-fold
by H/D substitution. Employing these data, we propose a mechanism
for methanol oxidation under 1 sun irradiation on these metal oxide
surfaces and discuss the implications for the efficient PEC methanol
oxidation to formaldehyde and concomitant hydrogen evolution.
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Spectroelectrochemical analysis of the mechanism of (photo)electrochemical hydrogen evolution at a catalytic interface. Nat Commun 2017; 8:14280. [PMID: 28233785 PMCID: PMC5333116 DOI: 10.1038/ncomms14280] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Accepted: 12/09/2016] [Indexed: 12/18/2022] Open
Abstract
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 electrocatalyst and as part of a cuprous oxide-based photocathode. We use optical absorbance spectroscopy to quantify the densities of reduced ruthenium oxide species, and correlate these with current densities resulting from proton reduction. This enables us to compare directly the catalytic function of dark and light electrodes. We find that hydrogen evolution is second order in the density of active, doubly reduced species independent of whether these are generated by applied potential or light irradiation. Our observation of a second order rate law allows us to distinguish between the most common reaction paths and propose a mechanism involving the homolytic reductive elimination of hydrogen.
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Abstract
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Water oxidation is a key chemical
reaction, central to both biological
photosynthesis and artificial solar fuel synthesis strategies. Despite
recent progress on the structure of the natural catalytic site, and
on inorganic catalyst function, determining the mechanistic details
of this multiredox reaction remains a significant challenge. We report
herein a rate law analysis of the order of water oxidation as a function
of surface hole density on a hematite photoanode employing photoinduced
absorption spectroscopy. Our study reveals a transition from a slow,
first order reaction at low accumulated hole density to a faster,
third order mechanism once the surface hole density is sufficient
to enable the oxidation of nearest neighbor metal atoms. This study
thus provides direct evidence for the multihole catalysis of water
oxidation by hematite, and demonstrates the hole accumulation level
required to achieve this, leading to key insights both for reaction
mechanism and strategies to enhance function.
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