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Stability of Bimetallic Pt xRu y - From Model Surfaces to Nanoparticulate Electrocatalysts. ACS MATERIALS AU 2024; 4:286-299. [PMID: 38737117 PMCID: PMC11083114 DOI: 10.1021/acsmaterialsau.3c00092] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/26/2023] [Revised: 12/27/2023] [Accepted: 12/27/2023] [Indexed: 05/14/2024]
Abstract
Fundamental research campaigns in electrocatalysis often involve the use of model systems, such as single crystals or magnetron-sputtered thin films (single metals or metal alloys). The downsides of these approaches are that oftentimes only a limited number of compositions are picked and tested (guided by chemical intuition) and that the validity of trends is not verified under operating conditions typically present in real devices. These together can lead to deficient conclusions, hampering the direct application of newly discovered systems in real devices. In this contribution, the stability of magnetron-sputtered bimetallic PtxRuy thin film electrocatalysts (0 at. % to 100 at. % Ru content) along with three commercially available carbon-supported counterparts (50-67 at. % Ru content) was mapped under electrocatalytic conditions in acidic electrolytes using online ICP-MS. We found several differences between the two systems in the amount of metals dissolved along with the development of the morphology and composition. While the Pt-rich PtxRuy compositions remained unchanged, 30-50 nm diameter surface pits were detected in the case of the Ru-rich sputtered thin films. Contrastingly, the surface of the carbon-supported NPs enriched in Pt accompanied by the leaching of a significant amount of Ru from the alloy structure was observed. Change in morphology was accompanied by a mass loss reaching around 1-2 wt % in the case of the sputtered samples and almost 10 wt % for the NPs. Since PtxRuy has prime importance in driving alcohol oxidation reactions, the stability of all investigated alloys was screened in the presence of isopropanol. While Pt dissolution was marginally affected by the presence of isopropanol, several times higher Ru dissolution was detected, especially in the case of the Ru-rich compositions. Our results underline that trends in terms of electrocatalytic activity and stability cannot always be transferred from model samples to systems that are closer to the ones applied in real devices.
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2
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Allotrope-dependent activity-stability relationships of molybdenum sulfide hydrogen evolution electrocatalysts. Nat Commun 2024; 15:3601. [PMID: 38684654 PMCID: PMC11058198 DOI: 10.1038/s41467-024-47524-w] [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: 07/08/2023] [Accepted: 04/03/2024] [Indexed: 05/02/2024] Open
Abstract
Molybdenum disulfide (MoS2) is widely regarded as a competitive hydrogen evolution reaction (HER) catalyst to replace platinum in proton exchange membrane water electrolysers (PEMWEs). Despite the extensive knowledge of its HER activity, stability insights under HER operation are scarce. This is paramount to ensure long-term operation of Pt-free PEMWEs, and gain full understanding on the electrocatalytically-induced processes responsible for HER active site generation. The latter are highly dependent on the MoS2 allotropic phase, and still under debate. We rigorously assess these by simultaneously monitoring Mo and S dissolution products using a dedicated scanning flow cell coupled with downstream analytics (ICP-MS), besides an electrochemical mass spectrometry setup for volatile species analysis. We observe that MoS2 stability is allotrope-dependent: lamellar-like MoS2 is highly unstable under open circuit conditions, whereas cluster-like amorphous MoS3-x instability is induced by a severe S loss during the HER and undercoordinated Mo site generation. Guidelines to operate non-noble PEMWEs are therefore provided based on the stability number metrics, and an HER mechanism which accounts for Mo and S dissolution pathways is proposed.
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3
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Applicability of Single-Layer Graphene as a Hydrogen-Blocking Interlayer in Low-Temperature PEMFCs. ACS APPLIED MATERIALS & INTERFACES 2024; 16. [PMID: 38676629 PMCID: PMC11082842 DOI: 10.1021/acsami.4c01254] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2024] [Revised: 03/21/2024] [Accepted: 04/18/2024] [Indexed: 04/29/2024]
Abstract
Gas crossover is critical in proton exchange membrane (PEM)-based electrochemical systems. Recently, single-layer graphene (SLG) has gained great research interest due to its outstanding properties as a barrier layer for small molecules like hydrogen. However, the applicability of SLG as a gas-blocking interlayer in PEMs has yet to be fully understood. In this work, two different approaches for transferring SLG from a copper or a polymeric substrate onto PEMs are compared regarding their application in low-temperature PEM fuel cells. The SLG is sandwiched between two Nafion XL membranes to form a stable composite membrane. The successful transfer is confirmed by Raman spectroscopy and in ex situ hydrogen permeation experiments in the dry state, where a reduction of 50% upon SLG incorporation is achieved. The SLG composite membranes are characterized by their performance and hydrogen-blocking ability in a fuel cell setup at typical operating conditions of 80 °C and with fully humidified gases. The performance of the fuel cell incorporating an SLG composite membrane is equal to that of the reference cell when avoiding the direct etching process from a copper substrate, as remnants from copper etching deteriorate the performance of the fuel cell. For both transfer processes, the hydrogen crossover reduction of SLG composite membranes is only 15-19% (1.5 barabs) in the operating fuel cell. Further, hydrogen pumping experiments suggest that the barrier function of SLG impairs the water transport through the membrane, which may affect water management in electrochemical applications. In summary, this work shows the successful transfer of SLG into a PEM and confirms the effective hydrogen-blocking capability of the SLG interlayer. However, the hydrogen-blocking ability is significantly reduced when running the cell at the typical humidified operating conditions of PEM fuel cells, which follows from a combination of reversible interlayer alteration upon humidification and irreversible defect formation upon PEM fuel cell operation.
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Toward High-Energy-Density Fuels for Direct Liquid Organic Hydrogen Carrier Fuel Cells: Electrooxidation of 1-Cyclohexylethanol. J Phys Chem Lett 2024; 15:2529-2536. [PMID: 38412511 DOI: 10.1021/acs.jpclett.3c03331] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/29/2024]
Abstract
Electrochemically active liquid organic hydrogen carriers (EC-LOHCs) can be used directly in fuel cells; so far, however, they have rather low hydrogen storage capacities. In this work, we study the electrooxidation of a potential EC-LOHC with increased energy density, 1-cyclohexylethanol, which consists of two storage functionalities (a secondary alcohol and a cyclohexyl group). We investigated the product spectrum on low-index Pt single-crystal surfaces in an acidic environment by combining cyclic voltammetry, chronoamperometry, and in situ infrared spectroscopy, supported by density functional theory. We show that the electrooxidation of 1-cyclohexylethanol is a highly structure-sensitive reaction with activities Pt(111) ≫ Pt(100) > Pt(110). Most importantly, we demonstrate that 1-cyclohexylethanol can be directly converted to acetophenone, which desorbs from the electrode surface. However, decomposition products are formed, which lead to poisoning. If the latter side reactions could be suppressed, the electrooxidation of 1-cyclohexylethanol would enable the development of EC-LOHCs with greatly increased hydrogen storage capacities.
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Stability of Carbon Supported Silver Electrocatalysts for Alkaline Oxygen Reduction and Evolution Reactions. ACS APPLIED ENERGY MATERIALS 2023; 6:11497-11509. [PMID: 38037630 PMCID: PMC10685861 DOI: 10.1021/acsaem.3c01717] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/10/2023] [Revised: 09/15/2023] [Accepted: 10/20/2023] [Indexed: 12/02/2023]
Abstract
Ag-based electrocatalysts are promising candidates to catalyze the sluggish oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFC) and oxygen evolution reaction (OER) in unitized regenerative fuel cells. However, to be competitive with existing technologies, the AEMFC with Ag electrocatalyst must demonstrate superior performance and long-term durability. The latter implies that the catalyst must be stable, withstanding harsh oxidizing conditions. Moreover, since Ag is typically supported by carbon, the strict stability requirements extend to the whole Ag/C catalyst. In this work, Ag supported on Vulcan carbon (Ag/VC) and mesoporous carbon (Ag/MC) materials is synthesized, and their electrochemical stability is studied using a family of complementary techniques. We first employ an online scanning flow cell combined with inductively coupled plasma mass spectrometry (SFC-ICP-MS) to estimate the kinetic dissolution stability window of Ag. Strong correlations between voltammetric features and the dissolution processes are discovered. Very high silver dissolution during the OER renders this material impractical for regenerative fuel cell applications. To address Ag stability during AEMFC load cycles, accelerated stress tests (ASTs) in O2-saturated solutions are carried out in rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) setups. Besides tracking the ORR performance evolution, an ex situ long-term Ag dissolution study is performed. Moreover, morphological changes in the catalyst/support are tracked by identical-location transmission electron microscopy (RDE-IL-TEM). Voltammetry analysis before and after AST reveals a smaller change in ORR activity for Ag/MC, confirming its higher stability. RRDE results reveal a higher increase in the H2O2 yield for Ag/VC after the ASTs. The RDE-IL-TEM measurements demonstrate different degradation processes that can explain the changes in the long term performance. The results in this work point out that the stability of carbon-supported Ag catalysts depends strongly on the morphology of the Ag nanoparticles, which, in turn, can be tuned depending on the chosen carbon support and synthesis method.
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Stability of high-entropy alloys under electrocatalytic conditions. iScience 2023; 26:107775. [PMID: 37736046 PMCID: PMC10509299 DOI: 10.1016/j.isci.2023.107775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Revised: 08/16/2023] [Accepted: 08/28/2023] [Indexed: 09/23/2023] Open
Abstract
High-entropy alloys are claimed to possess superior stability due to thermodynamic contributions. However, this statement mostly lies on a hypothetical basis. In this study, we use on-line inductively coupled plasma mass spectrometer to investigate the dissolution of five representative electrocatalysts in acidic and alkaline media and a wide potential window targeting the most important applications. To address both model and applied systems, we synthesized thin films and carbon-supported nanoparticles ranging from an elemental (Pt) sample to binary (PtRu), ternary (PtRuIr), quaternary (PtRuIrRh), and quinary (PtRuIrRhPd) alloy samples. For certain metals in the high-entropy alloy under alkaline conditions, lower dissolution was observed. Still, the improvement was not striking and can be rather explained by the lowered concentration of elements in the multinary alloys instead of the synergistic effects of thermodynamics. We postulate that this is because of dissolution kinetic effects, which are always present under electrocatalytic conditions, overcompensating thermodynamic contributions.
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7
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Anodic and Cathodic Platinum Dissolution Processes Involve Different Oxide Species. Angew Chem Int Ed Engl 2023; 62:e202304293. [PMID: 37341165 DOI: 10.1002/anie.202304293] [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: 03/24/2023] [Revised: 06/02/2023] [Accepted: 06/20/2023] [Indexed: 06/22/2023]
Abstract
The degradation of Pt-containing oxygen reduction catalysts for fuel cell applications is strongly linked to the electrochemical surface oxidation and reduction of Pt. Here, we study the surface restructuring and Pt dissolution mechanisms during oxidation/reduction for the case of Pt(100) in 0.1 M HClO4 by combining operando high-energy surface X-ray diffraction, online mass spectrometry, and density functional theory. Our atomic-scale structural studies reveal that anodic dissolution, detected during oxidation, and cathodic dissolution, observed during the subsequent reduction, are linked to two different oxide phases. Anodic dissolution occurs predominantly during nucleation and growth of the first, stripe-like oxide. Cathodic dissolution is linked to a second, amorphous Pt oxide phase that resembles bulk PtO2 and starts to grow when the coverage of the stripe-like oxide saturates. In addition, we find the amount of surface restructuring after an oxidation/reduction cycle to be potential-independent after the stripe-like oxide has reached its saturation coverage.
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Effects of Iron Species on Low Temperature CO 2 Electrolyzers. Angew Chem Int Ed Engl 2023:e202306503. [PMID: 37466922 DOI: 10.1002/anie.202306503] [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: 05/09/2023] [Revised: 07/15/2023] [Accepted: 07/17/2023] [Indexed: 07/20/2023]
Abstract
Electrochemical energy conversion devices are considered key in reducing CO2 emissions and significant efforts are being applied to accelerate device development. Unlike other technologies, low temperature electrolyzers have the ability to directly convert CO2 into a range of value-added chemicals. To make them commercially viable, however, device efficiency and durability must be increased. Although their design is similar to more mature water electrolyzers and fuel cells, new cell concepts and components are needed. Due to the complexity of the system, singular component optimization is common. As a result, the component interplay is often overlooked. The influence of Fe-species clearly shows that the cell must be considered holistically during optimization, to avoid future issues due to component interference or cross-contamination. Fe-impurities are ubiquitous, and their influence on single components is well-researched. The activity of non-noble anodes has been increased through the deliberate addition of iron. At the same time, however, Fe-species accelerate cathode and membrane degradation. Here, we interpret literature on single components to gain an understanding of how Fe-species influence low temperature CO2 electrolyzers holistically. The role of Fe-species serves to highlight the need for considerations regarding component interplay in general.
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9
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Abstract
The first step of electrochemical surface oxidation is extraction of a metal atom from its lattice site to a location in a growing oxide. Here we show by fast simultaneous electrochemical and in situ high-energy surface X-ray diffraction measurements that the initial extraction of Pt atoms from Pt(111) is a fast, potential-driven process, whereas charge transfer for the related formation of adsorbed oxygen-containing species occurs on a much slower time scale and is evidently uncoupled from the extraction process. It is concluded that potential plays a key independent role in electrochemical surface oxidation.
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Electrolyte Engineering Stabilizes Photoanodes Decorated with Molecular Catalysts. CHEMSUSCHEM 2023; 16:e202300406. [PMID: 36960909 DOI: 10.1002/cssc.202300406] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Invited for this month's cover is the group of Dunwei Wang from Boston College and Serhiy Cherevko from the Helmholtz Institute Erlangen-Nürnberg for Renewable Energy. The image illustrates the impact of different electrolyte environments on the stability of hematite decorated with an iridium molecular catalyst used for solar water splitting. The Research Article itself is available at 10.1002/cssc.202202319.
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11
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Electrolyte Engineering Stabilizes Photoanodes Decorated with Molecular Catalysts. CHEMSUSCHEM 2023; 16:e202202319. [PMID: 36602840 DOI: 10.1002/cssc.202202319] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Revised: 01/04/2023] [Indexed: 06/17/2023]
Abstract
Molecular catalysts are promising oxygen evolution promoters in conjunction with photoanodes for solar water splitting. Maintaining the stability of both photoabsorber and cocatalyst is still a prime challenge, with many efforts tackling this issue through sophisticated material designs. Such approaches often mask the importance of the electrode-electrolyte interface and overlook easily tunable system parameters, such as the electrolyte environment, to improve efficiency. We provide a systematic study on the activity-stability relationship of a prominent Fe2 O3 photoanode modified with Ir molecular catalysts using in situ mass spectroscopy. After gaining detailed insights into the dissolution behavior of the Ir cocatalyst, a comprehensive pH study is conducted to probe the impact of the electrolyte on the performance. An inverse trend in Fe and Ir stability is found, with the best activity-stability synergy obtained at pH 9.7. The results bring awareness to the overall photostability and electrolyte engineering when advancing catalysts for solar water splitting.
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12
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Towards electrochemical iridium recycling in acidic media: effect of the presence of organic molecules and chloride ions. RSC Adv 2023; 13:7980-7987. [PMID: 36909751 PMCID: PMC9997448 DOI: 10.1039/d2ra07142h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2022] [Accepted: 03/04/2023] [Indexed: 03/12/2023] Open
Abstract
The utilization of iridium is expected to surge in the next few years, notably due to the rising implementation of water electrolyzer devices in the energy transition. However, the natural resources of this noble metal are extremely limited and thus its recycling will become of high importance. Unfortunately, iridium is also the most corrosion resistant platinum group metal, making its recovery from waste a difficult and energy-demanding process. Hereby, we study the impact of organics and chloride ions on the electrochemical dissolution of iridium in order to pave the way towards green recycling of this precious metal. We present a 40 times increased dissolution when cycling iridium in presence of HCl and 1 M ethanol compared to HClO4. Our results point towards the direction of destabilizing Ir at relatively mild conditions in acidic media.
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13
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Isopropanol Electro-Oxidation on Pt-Ru-Ir: A Journey from Model Thin-Film Libraries Towards Real Electrocatalysts. Electrochim Acta 2023. [DOI: 10.1016/j.electacta.2023.142032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
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14
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Optimal Pt-Au Alloying for Efficient and Stable Oxygen Reduction Reaction Catalysts. ACS APPLIED MATERIALS & INTERFACES 2023; 15:1192-1200. [PMID: 36578102 DOI: 10.1021/acsami.2c18655] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Stabilization of cathode catalysts in hydrogen-fueled proton-exchange membrane fuel cells (PEMFCs) is paramount to their widespread commercialization. Targeting that aim, Pt-Au alloy catalysts with various compositions (Pt95Au5, Pt90Au10, and Pt80Au20) prepared by magnetron sputtering were investigated. The promising stability improvement of the Pt-Au catalyst, manifested in suppressed platinum dissolution with increasing Au content, was documented over an extended potential range up to 1.5 VRHE. On the other hand, at elevated concentrations, Au showed a detrimental effect on oxygen reduction reaction activity. A systematic study involving complementary characterization techniques, electrochemistry, and Monte Carlo simulations based on density functional theory data enabled us to gain a comprehensive understanding of the composition-activity-stability relationship to find optimal Pt-Au alloying for maintaining the activity of platinum and improving its resistance to dissolution. According to the results, Pt-Au alloy with 10% gold represent the most promising composition retaining the activity of monometallic Pt while suppressing Pt dissolution by 50% at the upper potential limit of 1.2 VRHE and by 20% at devastating 1.5 VRHE.
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Oxygen Evolution Electrocatalysis in Acids: Atomic Tuning of the Stability Number for Submonolayer IrO x on Conductive Oxides from Molecular Precursors. ACS Catal 2022. [DOI: 10.1021/acscatal.2c04439] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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16
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High-throughput exploration of activity and stability for identifying photoelectrochemical water splitting materials. Chem Sci 2022; 13:13774-13781. [PMID: 36544729 PMCID: PMC9710305 DOI: 10.1039/d2sc05115j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Accepted: 11/05/2022] [Indexed: 11/09/2022] Open
Abstract
The experimental high-throughput (HT) exploration for a suitable solar water splitting photoanode has greatly relied on photoactivity as the sole descriptor to identify a promising region within the searched composition space. Although activity is essential, it is not sufficient for describing the overall performance and excludes other pertinent criteria for photoelectrochemical (PEC) water splitting. Photostability in the form of (photo)electrocatalyst dissolution must be tracked to illustrate the intricate relation between activity and stability for multinary photoelectrocatalysts. To access these two important metrics simultaneously, an automated PEC scanning flow cell coupled to an inductively coupled plasma mass spectrometer (PEC-ICP-MS) was used to study an Fe-Ti-W-O thin film materials library. The results reveal an interrelation between composition, photocurrent density, and element-specific dissolution. These structure-activity-stability correlations can be represented using data science tools like principal component analysis (PCA) in addition to common data visualization approaches. This study demonstrates the importance of addressing two of the most important catalyst metrics (activity and stability) in a rapid and parallel fashion during HT experiments to adequately discover high-performing compositions in the multidimensional search space.
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Atomistic Insights into Activation and Degradation of La 0.6Sr 0.4CoO 3-δ Electrocatalysts under Oxygen Evolution Conditions. J Am Chem Soc 2022; 144:17966-17979. [PMID: 36130265 PMCID: PMC9545157 DOI: 10.1021/jacs.2c07226] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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The
stability of perovskite oxide catalysts for the oxygen
evolution
reaction (OER) plays a critical role in their applicability in water
splitting concepts. Decomposition of perovskite oxides under applied
potential is typically linked to cation leaching and amorphization
of the material. However, structural changes and phase transformations
at the catalyst surface were also shown to govern the activity of
several perovskite electrocatalysts under applied potential. Hence,
it is crucial for the rational design of durable perovskite catalysts
to understand the interplay between the formation of active surface
phases and stability limitations under OER conditions. In the present
study, we reveal a surface-dominated activation and deactivation mechanism
of the prominent electrocatalyst La0.6Sr0.4CoO3−δ under steady-state OER conditions. Using a
multiscale microscopy and spectroscopy approach, we identify the evolving
Co-oxyhydroxide as catalytically active surface species and La-hydroxide
as inactive species involved in the transient degradation behavior
of the catalyst. While the leaching of Sr results in the formation
of mixed surface phases, which can be considered as a part of the
active surface, the gradual depletion of Co from a self-assembled
active CoO(OH) phase and the relative enrichment of passivating La(OH)3 at the electrode surface result in the failure of the perovskite
catalyst under applied potential.
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18
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Heating up the OER: Investigation of IrO2 OER catalysts as function of potential and temperature. ChemElectroChem 2022. [DOI: 10.1002/celc.202200514] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Graphene-Derived Carbon Support Boosts Proton Exchange Membrane Fuel Cell Catalyst Stability. ACS Catal 2022; 12:9540-9548. [PMID: 35966603 PMCID: PMC9361283 DOI: 10.1021/acscatal.2c01753] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2022] [Revised: 06/24/2022] [Indexed: 11/30/2022]
Abstract
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The lack of efficient and durable proton exchange membrane
fuel
cell electrocatalysts for the oxygen reduction reaction is still restraining
the present hydrogen technology. Graphene-based carbon materials have
emerged as a potential solution to replace the existing carbon black
(CB) supports; however, their potential was never fully exploited
as a commercial solution because of their more demanding properties.
Here, a unique and industrially scalable synthesis of platinum-based
electrocatalysts on graphene derivative (GD) supports is presented.
With an innovative approach, highly homogeneous as well as high metal
loaded platinum-alloy (up to 60 wt %) intermetallic catalysts on GDs
are achieved. Accelerated degradation tests show enhanced durability
when compared to the CB-supported analogues including the commercial
benchmark. Additionally, in combination with X-ray photoelectron spectroscopy
Auger characterization and Raman spectroscopy, a clear connection
between the sp2 content and structural
defects in carbon materials with the catalyst durability is observed.
Advanced gas diffusion electrode results show that the GD-supported
catalysts exhibit excellent mass activities and possess the properties
necessary to reach high currents if utilized correctly. We show record-high
peak power densities in comparison to the prior best literature on
platinum-based GD-supported materials which is promising information
for future application.
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Microkinetic Analysis of the Oxygen Evolution Performance at Different Stages of Iridium Oxide Degradation. J Am Chem Soc 2022; 144:13205-13217. [PMID: 35850525 PMCID: PMC9335572 DOI: 10.1021/jacs.2c03561] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
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The microkinetics
of the electrocatalytic oxygen evolution reaction
substantially determines the performance in proton-exchange membrane
water electrolysis. State-of-the-art nanoparticulated rutile IrO2 electrocatalysts present an excellent trade-off between activity
and stability due to the efficient formation of intermediate surface
species. To reveal and analyze the interaction of individual surface
processes, a detailed dynamic microkinetic model approach is established
and validated using cyclic voltammetry. We show that the interaction
of three different processes, which are the adsorption of water, one
potential-driven deprotonation step, and the detachment of oxygen,
limits the overall reaction turnover. During the reaction, the active
IrO2 surface is covered mainly by *O, *OOH, and *OO adsorbed
species with a share dependent on the applied potential and of 44,
28, and 20% at an overpotential of 350 mV, respectively. In contrast
to state-of-the-art calculations of ideal catalyst surfaces, this
novel model-based methodology allows for experimental identification
of the microkinetics as well as thermodynamic energy values of real
pristine and degraded nanoparticles. We show that the loss in electrocatalytic
activity during degradation is correlated to an increase in the activation
energy of deprotonation processes, whereas reaction energies were
marginally affected. As the effect of electrolyte-related parameters
does not cause such a decrease, the model-based analysis demonstrates
that material changes trigger the performance loss. These insights
into the degradation of IrO2 and its effect on the surface
processes provide the basis for a deeper understanding of degrading
active sites for the optimization of the oxygen evolution performance.
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Oxygen Reduction Reaction in Alkaline Media Causes Iron Leaching from Fe-N-C Electrocatalysts. J Am Chem Soc 2022; 144:9753-9763. [PMID: 35609284 DOI: 10.1021/jacs.2c02088] [Citation(s) in RCA: 22] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The electrochemical activity of modern Fe-N-C electrocatalysts in alkaline media is on par with that of platinum. For successful application in fuel cells (FCs), however, also high durability and longevity must be demonstrated. Currently, a limited understanding of degradation pathways, especially under operando conditions, hinders the design and synthesis of simultaneously active and stable Fe-N-C electrocatalysts. In this work, using a gas diffusion electrode half-cell coupled with inductively coupled plasma mass spectrometry setup, Fe dissolution is studied under conditions close to those in FCs, that is, with a porous catalyst layer (CL) and at current densities up to -125 mA·cm-2. Varying the rate of the oxygen reduction reaction (ORR), we show a remarkable linear correlation between the Faradaic charge passed through the electrode and the amount of Fe dissolved from the electrode. This finding is rationalized assuming that oxygen reduction and Fe dissolution reactions are interlinked, likely through a common intermediate formed during the Fe redox transitions in Fe species involved in the ORR, such as FeNxCy and Fe3C@N-C. Moreover, such a linear correlation allows the application of a simple metric─S-number─to report the material's stability. Hence, in the current work, a powerful tool for a more applied stability screening of different electrocatalysts is introduced, which allows on the one hand fast performance investigations under more realistic conditions, and on the other hand a more advanced mechanistic understanding of Fe-N-C degradation in CLs.
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22
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Inter‐relationships between Oxygen Evolution and Iridium Dissolution Mechanisms. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202114437] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Electrolyte Effects on the Stabilization of Prussian Blue Analogue Electrodes in Aqueous Sodium-Ion Batteries. ACS APPLIED MATERIALS & INTERFACES 2022; 14:3515-3525. [PMID: 34990115 DOI: 10.1021/acsami.1c21219] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Aqueous sodium-ion batteries based on Prussian Blue Analogues (PBA) are considered as promising and scalable candidates for stationary energy storage systems, where longevity and cycling stability are assigned utmost importance to maintain economic viability. Although degradation due to active material dissolution is a common issue of battery electrodes, it is hardly observable directly due to a lack of in operando techniques, making it challenging to optimize the performance of electrodes. By operating Na2Ni[Fe(CN)6] and Na2Co[Fe(CN)6] model electrodes in a flow-cell setup connected to an inductively coupled plasma mass spectrometer, in this work, the dynamics of constituent transition-metal dissolution during the charge-discharge cycles was monitored in real time. At neutral pHs, the extraction of nickel and cobalt was found to drive the degradation process during charge-discharge cycles. It was also found that the nature of anions present in the electrolytes has a significant impact on the degradation rate, determining the order ClO4- > NO3- > Cl- > SO42- with decreasing stability from the perchlorate to sulfate electrolytes. It is proposed that the dissolution process is initiated by detrimental specific adsorption of anions during the electrode oxidation, therefore scaling with their respective chemisorption affinity. This study involves an entire comparison of the effectiveness of common stabilization strategies for PBAs under very fast (dis)charging conditions at 300C, emphasizing the superiority of highly concentrated NaClO4 with almost no capacity loss after 10 000 cycles for Na2Ni[Fe(CN)6].
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On the electrocatalytical oxygen reduction reaction activity and stability of quaternary RhMo-doped PtNi/C octahedral nanocrystals. Chem Sci 2022; 13:9295-9304. [PMID: 36093024 PMCID: PMC9384817 DOI: 10.1039/d2sc01585d] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2022] [Accepted: 07/01/2022] [Indexed: 12/01/2022] Open
Abstract
Recently proposed bimetallic octahedral Pt–Ni electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cell (PEMFC) cathodes suffer from particle instabilities in the form of Ni corrosion and shape degradation. Advanced trimetallic Pt-based electrocatalysts have contributed to their catalytic performance and stability. In this work, we propose and analyse a novel quaternary octahedral (oh-)Pt nanoalloy concept with two distinct metals serving as stabilizing surface dopants. An efficient solvothermal one-pot strategy was developed for the preparation of shape-controlled oh-PtNi catalysts doped with Rh and Mo in its surface. The as-prepared quaternary octahedral PtNi(RhMo) catalysts showed exceptionally high ORR performance accompanied by improved activity and shape integrity after stability tests compared to previously reported bi- and tri-metallic systems. Synthesis, performance characteristics and degradation behaviour are investigated targeting deeper understanding for catalyst system improvement strategies. A number of different operando and on-line analysis techniques were employed to monitor the structural and elemental evolution, including identical location scanning transmission electron microscopy and energy dispersive X-ray analysis (IL-STEM-EDX), operando wide angle X-ray spectroscopy (WAXS), and on-line scanning flow cell inductively coupled plasma mass spectrometry (SFC-ICP-MS). Our studies show that doping PtNi octahedral catalysts with small amounts of Rh and Mo suppresses detrimental Pt diffusion and thus offers an attractive new family of shaped Pt alloy catalysts for deployment in PEMFC cathode layers. PtNi nano-octahedra with Rh and Mo dopants are highly active catalysts for the oxygen reduction reaction with excellent stability and shape integrity. We investigate the morphological, structural, and compositional evolution during stability testing.![]()
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Toward the Continuous Production of Multigram Quantities of Highly Uniform Supported Metallic Nanoparticles and Their Application for Synthesis of Superior Intermetallic Pt-Alloy ORR Electrocatalysts. ACS APPLIED ENERGY MATERIALS 2021; 4:13819-13829. [PMID: 34977474 PMCID: PMC8715446 DOI: 10.1021/acsaem.1c02570] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2021] [Accepted: 11/15/2021] [Indexed: 05/27/2023]
Abstract
A fast and facile pulse combustion (PC) method that allows for the continuous production of multigram quantities of high-metal-loaded and highly uniform supported metallic nanoparticles (SMNPs) is presented. Namely, various metal on carbon (M/C) composites have been prepared by using only three feedstock components: water, metal-salt, and the supporting material. The present approach can be elegantly utilized also for numerous other applications in electrocatalysis, heterogeneous catalysis, and sensors. In this study, the PC-prepared M/C composites were used as metal precursors for the Pt NPs deposition using double passivation with the galvanic displacement method (DP method). Lastly, by using thin-film rotating disc electrode (TF-RDE) and gas-diffusion electrode (GDE) methodologies, we show that the synergistic effects of combining PC technology with the DP method enable production of superior intermetallic Pt-M electrocatalysts with an improved oxygen reduction reaction (ORR) performance when compared to a commercial Pt-Co electrocatalyst for proton exchange membrane fuel cells (PEMFCs) application.
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Abstract
The widespread utilization of proton exchange membrane (PEM) electrolyzers currently remains uncertain, as they rely on the use of highly scarce iridium as the only viable catalyst for the oxygen evolution reaction (OER), which is known to present the major energy losses of the process. Understanding the mechanistic origin of the different activities and stabilities of Ir‐based catalysts is, therefore, crucial for a scale‐up of green hydrogen production. It is known that structure influences the dissolution, which is the main degradation mechanism and shares common intermediates with the OER. In this Minireview, the state‐of‐the‐art understanding of dissolution and its relationship with the structure of different iridium catalysts is gathered and correlated to different mechanisms of the OER. A perspective on future directions of investigation is also given.
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Performance of Quaternized Polybenzimidazole-Cross-Linked Poly(vinylbenzyl chloride) Membranes in HT-PEMFCs. ACS APPLIED MATERIALS & INTERFACES 2021; 13:56584-56596. [PMID: 34784464 DOI: 10.1021/acsami.1c17154] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
High-temperature proton-exchange membrane fuel cells (HT-PEMFCs) are mostly based on acid-doped membranes composed of polybenzimidazole (PBI). A severe drawback of acid-doped membranes is the deterioration of mechanical properties upon increasing acid-doping levels. Cross-linking of different polymers is a way to mitigate stability issues. In this study, a new ion-pair-coordinated membrane (IPM) system with quaternary ammonium groups for the application in HT-PEMFCs is introduced. PBI cross-linked with poly(vinylbenzyl chloride) and quaternized with three amines (DABCO, quinuclidine, and quinuclidinol) are manufactured and compared to the state-of-the-art commercial Dapazol PBI membrane ex situ as well as by evaluating their HT-PEMFC performance. The IPMs show reduced swelling and better mechanical properties upon doping, which enables a reduction in membrane thickness while maintaining a comparably low gas crossover and mechanical stability. The HT-PEMFC based on the best-performing IPM reaches up to 530 mW cm-2 at 180 °C under H2/air conditions at ambient pressure, while Dapazol is limited to less than 430 mW cm-2 at equal parameters. This new IPM system requires less acid doping than conventional PBI membranes while outperforming conventional PBI membranes, which renders these new membranes promising candidates for application in HT-PEMFCs.
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Local Chemical Environment Governs Anode Processes in CO 2 Electrolyzers. ACS ENERGY LETTERS 2021; 6:3801-3808. [PMID: 34796265 PMCID: PMC8593866 DOI: 10.1021/acsenergylett.1c01937] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2021] [Accepted: 10/01/2021] [Indexed: 05/20/2023]
Abstract
A major goal within the CO2 electrolysis community is to replace the generally used Ir anode catalyst with a more abundant material, which is stable and active for water oxidation under process conditions. Ni is widely applied in alkaline water electrolysis, and it has been considered as a potential anode catalyst in CO2 electrolysis. Here we compare the operation of electrolyzer cells with Ir and Ni anodes and demonstrate that, while Ir is stable under process conditions, the degradation of Ni leads to a rapid cell failure. This is caused by two parallel mechanisms: (i) a pH decrease of the anolyte to a near neutral value and (ii) the local chemical environment developing at the anode (i.e., high carbonate concentration). The latter is detrimental for zero-gap electrolyzer cells only, but the first mechanism is universal, occurring in any kind of CO2 electrolyzer after prolonged operation with recirculated anolyte.
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Accessing In Situ Photocorrosion under Realistic Light Conditions: Photoelectrochemical Scanning Flow Cell Coupled to Online ICP-MS. ACS MEASUREMENT SCIENCE AU 2021; 1:74-81. [PMID: 36785747 PMCID: PMC9838614 DOI: 10.1021/acsmeasuresciau.1c00016] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
High-impact photoelectrode materials for photoelectrochemical (PEC) water splitting are distinguished by synergistically attaining high photoactivity and stability at the same time. With numerous efforts toward optimizing the activity, the bigger challenge of tailoring the durability of photoelectrodes to meet industrially relevant levels remains. In situ photostability measurements hold great promise in understanding stability-related properties. Although different flow systems coupled to light-emitting diodes were introduced recently to measure time-resolved photocorrosion, none of the measurements were performed under realistic light conditions. In this paper, a photoelectrochemical scanning flow cell connected to an inductively coupled plasma mass spectrometer (PEC-ICP-MS) and equipped with a solar simulator, Air Mass 1.5 G filter, and monochromator was developed. The established system is capable of independently assessing basic PEC metrics, such as photopotential, photocurrent, incident photon to current efficiency (IPCE), and band gap in a high-throughput manner as well as the in situ photocorrosion behavior of photoelectrodes under standardized and realistic light conditions by coupling it to an ICP-MS. Polycrystalline platinum and tungsten trioxide (WO3) were used as model systems to demonstrate the operation under dark and light conditions, respectively. Photocorrosion measurements conducted with the present PEC-ICP-MS setup revealed that WO3 starts dissolving at 0.8 VRHE with the dissolution rate rapidly increasing past 1.2 VRHE, coinciding with the onset of the saturation photocurrent. The most detrimental damage to the photoelectrode is caused when subjecting it to a prolonged high potential hold, e.g., at 1.5 VRHE. By using standardized illumination conditions such as Air Mass 1.5 Global under 1 Sun, the obtained dissolution characteristics are translatable to actual devices under realistic light conditions. The gained insights can then be utilized to advance synthesis and design approaches of novel PEC materials with improved photostability.
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Sacrificial Cu Layer Mediated the Formation of an Active and Stable Supported Iridium Oxygen Evolution Reaction Electrocatalyst. ACS Catal 2021; 11:12510-12519. [PMID: 34676130 PMCID: PMC8524421 DOI: 10.1021/acscatal.1c02968] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Revised: 09/03/2021] [Indexed: 02/03/2023]
Abstract
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The production of
hydrogen via a proton-exchange membrane water
electrolyzer (PEM-WE) is directly dependent on the rational design
of electrocatalysts for the anodic oxygen evolution reaction (OER),
which is the bottleneck of the process. Here, we present a smart design
strategy for enhancing Ir utilization and stabilization. We showcase
it on a catalyst, where Ir nanoparticles are efficiently anchored
on a conductive support titanium oxynitride (TiONx) dispersed over carbon-based Ketjen Black and covered by
a thin layer of copper (Ir/CuTiONx/C),
which gets removed in the preconditioning step. Electrochemical OER
activity, stability, and structural changes were compared to the Ir-based
catalyst, where Ir nanoparticles without Cu are deposited on the same
support (Ir/TiONx/C). To study the effect
of the sacrificial less-noble metal layer on the catalytic performance
of the synthesized material, characterization methods, namely X-ray
powder diffraction, X-ray photoemission spectroscopy, and identical
location transmission electron microscopy were employed and complemented
with scanning flow cell coupled to an inductively coupled plasma mass
spectrometer, which allowed studying the online dissolution during
the catalytic reaction. Utilization of these advanced methods revealed
that the sacrificial Cu layer positively affects both Ir OER mass
activity and its durability, which was assessed via S-number, a recently
reported stability metric. Improved activity of Cu analogue was ascribed
to the higher surface area of smaller Ir nanoparticles, which are
better stabilized through a strong metal–support interaction
(SMSI) effect.
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31
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Operando Stability Studies of Ultrathin Single-Crystalline IrO 2(110) Films under Acidic Oxygen Evolution Reaction Conditions. ACS Catal 2021. [DOI: 10.1021/acscatal.1c03599] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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32
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CrO x-Mediated Performance Enhancement of Ni/NiO-Mg:SrTiO 3 in Photocatalytic Water Splitting. ACS Catal 2021; 11:11049-11058. [PMID: 34513203 PMCID: PMC8422963 DOI: 10.1021/acscatal.1c03104] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2021] [Revised: 08/07/2021] [Indexed: 01/17/2023]
Abstract
![]()
By photodeposition
of CrOx on SrTiO3-based
semiconductors doped with aliovalent Mg(II) and functionalized with
Ni/NiOx catalytic nanoparticles (economically significantly
more viable than commonly used Rh catalysts), an increase in apparent
quantum yield (AQYs) from ∼10 to 26% in overall water splitting
was obtained. More importantly, deposition of CrOx also
significantly enhances the stability of Ni/NiO nanoparticles in the
production of hydrogen, allowing sustained operation, even in intermittent
cycles of illumination. In situ elemental analysis
of the water constituents during or after photocatalysis by inductively
coupled plasma mass spectrometry/optical emission spectrometry shows
that after CrOx deposition, dissolution of Ni ions from
Ni/NiOx-Mg:SrTiO3 is significantly suppressed,
in agreement with the stabilizing effect observed, when both Mg dopant
and CrOx are present. State-of-the-art electron microscopy
and energy-dispersive X-ray spectroscopy (EDX) and electron energy-loss
spectroscopy (EELS) analyses demonstrate that upon preparation, CrOx is photodeposited in the vicinity of several, but not all,
Ni/NiOx particles. This implies the formation of a Ni–Cr
mixed metal oxide, which is highly effective in water reduction. Inhomogeneities
in the interfacial contact, evident from differences in contact angles
between Ni/NiOx particles and the Mg:SrTiO3 semiconductor,
likely affect the probability of reduction of Cr(VI) species during
synthesis by photodeposition, explaining the observed inhomogeneity
in the spatial CrOx distribution. Furthermore, by comparison
with undoped SrTiO3, Mg-doping appears essential to provide
such favorable interfacial contact and to establish the beneficial
effect of CrOx. This study suggests that the performance
of semiconductors can be significantly improved if inhomogeneities
in interfacial contact between semiconductors and highly effective
catalytic nanoparticles can be resolved by (surface) doping and improved
synthesis protocols.
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33
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Model electrocatalysts for the oxidation of rechargeable electrofuels - carbon supported Pt nanoparticles prepared in UHV. Electrochim Acta 2021. [DOI: 10.1016/j.electacta.2021.138716] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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34
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Size and Composition Dependence of Oxygen Reduction Reaction Catalytic Activities of Mo-Doped PtNi/C Octahedral Nanocrystals. ACS Catal 2021. [DOI: 10.1021/acscatal.1c01761] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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35
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Interplay Among Dealloying, Ostwald Ripening, and Coalescence in Pt XNi 100–X Bimetallic Alloys under Fuel-Cell-Related Conditions. ACS Catal 2021. [DOI: 10.1021/acscatal.1c01111] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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36
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Single-Atom Catalysts: A Perspective toward Application in Electrochemical Energy Conversion. JACS AU 2021; 1:1086-1100. [PMID: 34467351 PMCID: PMC8397360 DOI: 10.1021/jacsau.1c00121] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Indexed: 05/29/2023]
Abstract
Single-atom catalysts (SACs) hold great promise for maximized metal utilization, exceptional tunability of the catalytic site, and selectivity. Moreover, they can substantially contribute to lower the cost and abundancy challenges associated with raw materials. Significant breakthroughs have been achieved over the past decade, for instance, in terms of synthesis methods for SACs, their catalytic activity, and the mechanistic understanding of their functionality. Still, great challenges lie ahead in order to render them viable for application in important fields such as electrochemical energy conversion of renewable electrical energy. We have identified three particular development fields for advanced SACs that we consider crucial, namely, the scale-up of the synthesis, the understanding of their performance in real devices such as fuel cells and electrolyzers, and the understanding and mitigation of their degradation. In this Perspective, we review recent activities of the community and provide our outlook with respect to the aspects required to bring SACs toward application.
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37
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Increased Ir–Ir Interaction in Iridium Oxide during the Oxygen Evolution Reaction at High Potentials Probed by Operando Spectroscopy. ACS Catal 2021. [DOI: 10.1021/acscatal.1c02074] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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38
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Phase- and Surface Composition-Dependent Electrochemical Stability of Ir-Ru Nanoparticles during Oxygen Evolution Reaction. ACS Catal 2021. [DOI: 10.1021/acscatal.1c01682] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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40
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Abstract
Photocorrosion of an n-type semiconductor is anticipated to be unfavorable if its decomposition potential is situated below its valence band-edge position. Tungsten trioxide (WO3) is generally considered as a stable photoanode for different photoelectrochemical (PEC) applications. Such oversimplified considerations ignore reactions with electrolytes added to the solvent. Moreover, kinetic effects are neglected. The fallacy of such approaches has been demonstrated in our previous study dealing with WO3 instability in H2SO4. In this work, in order to understand parameters influencing WO3 photocorrosion and to identify more suitable reaction environments, H2SO4, HClO4, HNO3, CH3O3SH, as electrolytes are considered. Model WO3 thin films are fabricated with a spray-coating process. Photoactivity of the samples is determined with a photoelectrochemical scanning flow cell. Photostability is measured in real time by coupling an inductively coupled plasma mass spectrometer to the scanning flow cell to determine the photoanode dissolution products. It is found that the photoactivity of the WO3 films increases as HNO3 < HClO4 ≈ H2SO4 < CH3O3SH, whereas the photostability exhibits the opposite trend. The differences observed in photocorrosion are explained considering stability of the electrolytes toward decomposition. This work demonstrates that electrolytes and their reactive intermediates clearly influence the photostability of photoelectrodes. Thus, the careful selection of the photoelectrode/electrolyte combination is of crucial importance in the design of a stable photoelectrochemical water-splitting device.
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Periodicity in the Electrochemical Dissolution of Transition Metals. Angew Chem Int Ed Engl 2021; 60:13343-13349. [PMID: 33687762 PMCID: PMC8252536 DOI: 10.1002/anie.202100337] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Indexed: 12/18/2022]
Abstract
Extensive research efforts are currently dedicated to the search for new electrocatalyst materials in which expensive and rare noble metals are replaced with cheaper and more abundant transition metals. Recently, numerous alloys, oxides, and composites with such metals have been identified as highly active electrocatalysts through the use of high‐throughput screening methods with the help of activity descriptors. Up to this point, stability has lacked such descriptors. Hence, we elucidate the role of intrinsic metal/oxide properties on the corrosion behavior of representative 3d, 4d, and 5d transition metals. Electrochemical dissolution of nine transition metals is quantified using online inductively coupled plasma mass spectrometry (ICP‐MS). Based on the obtained dissolution data in alkaline and acidic media, we establish clear periodic correlations between the amount of dissolved metal, the cohesive energy of the metal atoms (Ecoh), and the energy of oxygen adsorption on the metal (ΔHO,ads). Such correlations can support the knowledge‐driven search for more stable electrocatalysts.
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43
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Platinum Dissolution in Realistic Fuel Cell Catalyst Layers. Angew Chem Int Ed Engl 2021; 60:8882-8888. [PMID: 33410273 PMCID: PMC8048487 DOI: 10.1002/anie.202014711] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2020] [Revised: 12/15/2020] [Indexed: 11/12/2022]
Abstract
Pt dissolution has already been intensively studied in aqueous model systems and many mechanistic insights have been gained. Nevertheless, transfer of new knowledge to real‐world fuel cell systems is still a significant challenge. To close this gap, we present a novel in situ method combining a gas diffusion electrode (GDE) half‐cell with inductively coupled plasma mass spectrometry (ICP‐MS). With this setup, Pt dissolution in realistic catalyst layers and the transport of dissolved Pt species through Nafion membranes were evaluated directly. We observed that 1) specific Pt dissolution increased significantly with decreasing Pt loading, 2) in comparison to experiments on aqueous model systems with flow cells, the measured dissolution in GDE experiments was considerably lower, and 3) by adding a membrane onto the catalyst layer, Pt dissolution was reduced even further. All these phenomena are attributed to the varying mass transport conditions of dissolved Pt species, influencing re‐deposition and equilibrium potential.
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45
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Different Photostability of BiVO 4 in Near-pH-Neutral Electrolytes. ACS APPLIED ENERGY MATERIALS 2020; 3:9523-9527. [PMID: 33134878 PMCID: PMC7592387 DOI: 10.1021/acsaem.0c01904] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Accepted: 10/02/2020] [Indexed: 05/09/2023]
Abstract
Photoelectrochemical water splitting is a promising route to produce hydrogen from solar energy. However, corrosion of photoelectrodes remains a fundamental challenge for their implementation. Here, we reveal different dissolution behaviors of BiVO4 photoanode in pH-buffered borate, phosphate, and citrate (hole-scavenger) electrolytes, studied in operando employing an illuminated scanning flow cell. We demonstrate that decrease in photocurrents alone does not reflect the degradation of photoelectrodes. Changes in dissolution rates correlate to the evolution of surface chemistry and morphology. The correlative measurements on both sides of the liquid-semiconductor junction provide quantitative comparison and mechanistic insights into the degradation processes.
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46
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Anisotropy of Pt nanoparticles on carbon- and oxide-support and their structural response to electrochemical oxidation probed by in situ techniques. Phys Chem Chem Phys 2020; 22:22260-22270. [PMID: 33001131 DOI: 10.1039/d0cp03233f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Identifying the structural response of nanoparticle-support ensembles to the reaction conditions is essential to determine their structure in the catalytically active state as well as to unravel the possible degradation pathways. In this work, we investigate the (electronic) structure of carbon- and oxide-supported Pt nanoparticles during electrochemical oxidation by in situ X-ray diffraction, absorption spectroscopy as well as the Pt dissolution rate by in situ mass spectrometry. We prepared ellipsoidal Pt nanoparticles by impregnation of the carbon and titanium-based oxide support as well as spherical Pt nanoparticles on an indium-based oxide support by a surfactant-assisted synthesis route. During electrochemical oxidation, we show that the oxide-supported Pt nanoparticles resist (bulk) oxide formation and Pt dissolution. The lattice of smaller Pt nanoparticles exhibits a size-induced lattice contraction in the as-prepared state with respect to bulk Pt but it expands reversibly during electrochemical oxidation. This expansion is suppressed for the Pt nanoparticles with a bulk-like relaxed lattice. We could correlate the formation of d-band vacancies in the metallic Pt with Pt lattice expansion. PtOx formation is strongest for platelet-like nanoparticles and we explain this with a higher fraction of exposed Pt(100) facets. Of all investigated nanoparticle-support ensembles, the structural response of RuO2/TiO2-supported Pt nanoparticles is the most promising with respect to their morphological and structural integrity under electrochemical reaction conditions.
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47
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Cobalt Oxide-Supported Pt Electrocatalysts: Intimate Correlation between Particle Size, Electronic Metal-Support Interaction and Stability. J Phys Chem Lett 2020; 11:8365-8371. [PMID: 32909431 DOI: 10.1021/acs.jpclett.0c02233] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Oxide supports can modify and stabilize platinum nanoparticles (NPs) in electrocatalytic materials. We studied related phenomena on model systems consisting of Pt NPs on atomically defined Co3O4(111) thin films. Chemical states and dissolution behavior of model catalysts were investigated as a function of the particle size and the electrochemical potential by ex situ emersion synchrotron radiation photoelectron spectroscopy and by online inductively coupled plasma mass spectrometry. Electronic metal-support interaction (EMSI) yields partially oxidized Ptδ+ species at the metal/support interface of metallic nanometer-sized Pt NPs. In contrast, subnanometer particles form Ptδ+ aggregates that are exclusively accompanied by subsurface Pt4+ species. Dissolution of Cox+ ions is strongly coupled to the presence of Ptδ+ and the reduction of subsurface Pt4+ species. Our findings suggest that EMSI directly affects the integrity of oxide-based electrocatalysts and may be employed to stabilize Pt NPs against sintering and dissolution.
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48
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Abstract
Single-atom catalysts (SACs) have quickly emerged as a new class of catalytic materials. When confronted with classical carbon-supported nanoparticulated catalysts (Pt/C), SACs are often claimed to have superior electrocatalytic properties, e.g., stability. In this study, we critically assess this statement by investigating S-doped carbon-supported Pt SACs as a representative example of noble-metal-based SACs. We use a set of complementary techniques, which includes online inductively coupled plasma mass spectrometry (online ICP-MS), identical location transmission electron microscopy (IL-TEM), and X-ray photoelectron spectroscopy (XPS). It is shown by online ICP-MS that the dissolution behavior of as-synthesized Pt SACs is significantly different from that of metallic Pt/C. Moreover, Pt SACs are, indeed, confirmed to be more stable toward Pt dissolution. When cycled to potentials of up to 1.5 VRHE, however, the dissolution profiles of Pt SACs and Pt/C become similar. IL-TEM and XPS show that this transition is due to morphological and chemical changes caused by cycling. The latter, in turn, is a consequence of the relatively poor stability of S ligands. As monitored by online ICP-MS and XPS, significant amounts of sulfur leave the catalyst during oxidation. Hence, in case catalysts with improved stability in the anodic potential region are desired, more robust supports and ligands must be developed.
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Fabrication of a Robust PEM Water Electrolyzer Based on Non-Noble Metal Cathode Catalyst: [Mo 3 S 13 ] 2- Clusters Anchored to N-Doped Carbon Nanotubes. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2020; 16:e2003161. [PMID: 32803861 DOI: 10.1002/smll.202003161] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Revised: 07/02/2020] [Indexed: 06/11/2023]
Abstract
High investment costs and a dependence on noble metal catalysts currently obstruct the large-scale implementation of proton exchange membrane water electrolyzers (PEMWEs) for converting fluctuating green electricity into chemical energy via water splitting. In this context, this work presents a high-performing and stable non-noble metal catalyst for the hydrogen evolution reaction (HER), consisting of [Mo3 S13 ]2- clusters supported on nitrogen doped carbon nanotubes (NCNTs). Strikingly, a significant electrochemically induced activation of the Mo3 S13 -NCNT catalyst at high current densities is observed in full cell configuration, enabling a remarkable current density of 4 A cm-2 at a cell voltage of 2.36 V. To the authors' knowledge, this is the highest reported value to date for a PEMWE full cell using a non-noble metal HER catalyst. Furthermore, only a minor degradation of 83 µV h-1 is observed during a stability test of 100 h constant current at 1 A cm-2 , with a nearly unchanged polarization behavior after the current hold. Catalyst stability and activity are additionally analyzed via online dissolution measurements. X-ray photoelectron spectroscopy examination of the catalyst before and after electrochemical application reveals a correlation between the electrochemical activation occurring via electrodissolution with changes in the molecular structure of the Mo3 S13 -NCNT catalyst.
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Influence of Fuels and pH on the Dissolution Stability of Bifunctional PtRu/C Alloy Electrocatalysts. ACS Catal 2020. [DOI: 10.1021/acscatal.0c02094] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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