Prof. Dr. Hubert Gasteiger
Academic Research Focus
- Materials for Li-ion batteries, PEM fuel cells and electrolysers
- Material aging mechanisms using ex-situ and operando characterization
- Material aging mechanisms using ex-situ and operando characterization
Fields of Application
Batteries, Electrolysers, Fuel Cells, Hydrogen, Photo-(electro)catalysis
Publications
11.
S M Qian, A T S Freiberg, F Friedrich, C Grön, H A Gasteiger
Simulating Electrochemical Aging in NCM111 Materials Through Controlled Chemical Delithiation Journal Article
In: Journal of the Electrochemical Society, vol. 172, no. 8, 2025, ISSN: 0013-4651.
@article{nokey,
title = {Simulating Electrochemical Aging in NCM111 Materials Through Controlled Chemical Delithiation},
author = {S M Qian and A T S Freiberg and F Friedrich and C Gr\"{o}n and H A Gasteiger},
url = {\<Go to ISI\>://WOS:001559898400001},
doi = {10.1149/1945-7111/adfca2},
issn = {0013-4651},
year = {2025},
date = {2025-08-28},
journal = {Journal of the Electrochemical Society},
volume = {172},
number = {8},
abstract = {To meet the cycle life requirements and to guarantee the safe operation of lithium-ion batteries, the upper cutoff potential of cathode active materials based on mixed transition metal layered oxides like NCM (LiMO2, with M = Ni, Co, Mn) must be restricted, thereby limiting the available specific capacity. A significant degradation mechanism in NCM materials involves the harmful release of lattice oxygen at high degrees of delithiation (reached at high cathode potentials), forming an oxygen-depleted surface phase on the active material particles accompanied by electrolyte oxidation. To mimic the electrochemically-induced lattice oxygen release, NCM materials can be subjected to chemical delithiation and subsequent heat-treatment. We thus investigated the chemical delithiation of NCM111 (Li1.0(Ni1/3Co1/3Mn1/3)O2) with NO2BF4, followed by a heat-treatment. The resulting materials are characterized with regards to their electrochemical characteristics as well as by thermogravimetric analysis-mass spectrometry, X-ray diffraction, scanning electron microscopy, and gas adsorption analysis. We discovered that chemical delithiation initially produces a disordered layered phase that is electrochemically less active. Upon heat-treatment, this phase restructures into a fully-lithiated and well-ordered layered phase and an electrochemically inactive spinel phase. This study enhances our understanding of the phases that form when NCM materials undergo extensive delithiation.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
To meet the cycle life requirements and to guarantee the safe operation of lithium-ion batteries, the upper cutoff potential of cathode active materials based on mixed transition metal layered oxides like NCM (LiMO2, with M = Ni, Co, Mn) must be restricted, thereby limiting the available specific capacity. A significant degradation mechanism in NCM materials involves the harmful release of lattice oxygen at high degrees of delithiation (reached at high cathode potentials), forming an oxygen-depleted surface phase on the active material particles accompanied by electrolyte oxidation. To mimic the electrochemically-induced lattice oxygen release, NCM materials can be subjected to chemical delithiation and subsequent heat-treatment. We thus investigated the chemical delithiation of NCM111 (Li1.0(Ni1/3Co1/3Mn1/3)O2) with NO2BF4, followed by a heat-treatment. The resulting materials are characterized with regards to their electrochemical characteristics as well as by thermogravimetric analysis-mass spectrometry, X-ray diffraction, scanning electron microscopy, and gas adsorption analysis. We discovered that chemical delithiation initially produces a disordered layered phase that is electrochemically less active. Upon heat-treatment, this phase restructures into a fully-lithiated and well-ordered layered phase and an electrochemically inactive spinel phase. This study enhances our understanding of the phases that form when NCM materials undergo extensive delithiation.
10.
R Wilhelm, R Schuster, T Kutsch, S M Qian, J Mahl, T Kratky, J Wandt, E J Crumlin, H A Gasteiger
Exploring the Electrochemical Stability Window of an All-Solid-State Composite Cathode via a Novel Operando Tender XPS Setup Journal Article
In: Acs Applied Materials & Interfaces, 2025, ISSN: 1944-8244.
@article{nokey,
title = {Exploring the Electrochemical Stability Window of an All-Solid-State Composite Cathode via a Novel Operando Tender XPS Setup},
author = {R Wilhelm and R Schuster and T Kutsch and S M Qian and J Mahl and T Kratky and J Wandt and E J Crumlin and H A Gasteiger},
url = {\<Go to ISI\>://WOS:001514153300001},
doi = {10.1021/acsami.5c01672},
issn = {1944-8244},
year = {2025},
date = {2025-06-18},
journal = {Acs Applied Materials \& Interfaces},
abstract = {All-solid-state batteries (ASSBs) have the potential to provide greater energy density than conventional batteries based on liquid electrolytes. Here, an operando ASSB cell setup for tender X-ray photoelectron spectroscopy (XPS) was developed, and the interface of a Ni-rich layered transition metal oxide cathode active material (CAM) and an Li6PS5Cl (LPSCl) solid electrolyte (SE) was evaluated during initial charge/discharge cycles. After validating the cell performance against a conventional pouch cell operated at high compression, intermittent galvanostatic cycling was performed, and XPS data were recorded as a function of state of charge (SOC). Upon the initial charge of the cell to approximate to 3.3 V-Li, the LPSCl appears to decompose into LiCl, Li3PS4, and polysulfides, whose amount gradually increases with potential. Upon further charge, at a potential higher than approximate to 3.8 V-Li, initially, present sulfate and sulfite impurities decompose, and at approximate to 74% SOC (corresponding to a cathode potential of approximate to 4.10 V-Li), surface reconstruction of the CAM particles due to lattice oxygen release is detected. In addition, at potentials beyond approximate to 4.6 V-Li, a decrease of the S 1s counts of the sum of the LPSCl, the thiophosphate, and polysulfide species suggests the formation of elemental sulfur that is lost via sublimation into the vacuum chamber.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
All-solid-state batteries (ASSBs) have the potential to provide greater energy density than conventional batteries based on liquid electrolytes. Here, an operando ASSB cell setup for tender X-ray photoelectron spectroscopy (XPS) was developed, and the interface of a Ni-rich layered transition metal oxide cathode active material (CAM) and an Li6PS5Cl (LPSCl) solid electrolyte (SE) was evaluated during initial charge/discharge cycles. After validating the cell performance against a conventional pouch cell operated at high compression, intermittent galvanostatic cycling was performed, and XPS data were recorded as a function of state of charge (SOC). Upon the initial charge of the cell to approximate to 3.3 V-Li, the LPSCl appears to decompose into LiCl, Li3PS4, and polysulfides, whose amount gradually increases with potential. Upon further charge, at a potential higher than approximate to 3.8 V-Li, initially, present sulfate and sulfite impurities decompose, and at approximate to 74% SOC (corresponding to a cathode potential of approximate to 4.10 V-Li), surface reconstruction of the CAM particles due to lattice oxygen release is detected. In addition, at potentials beyond approximate to 4.6 V-Li, a decrease of the S 1s counts of the sum of the LPSCl, the thiophosphate, and polysulfide species suggests the formation of elemental sulfur that is lost via sublimation into the vacuum chamber.
9.
M Graf, L Reuter, S Qian, T Calmus, R Bernhard, S Haufe, H A Gasteiger
Understanding the Effect of Lithium Nitrate as Additive in Carbonate-Based Electrolytes for Silicon Anodes Journal Article
In: Journal of The Electrochemical Society, vol. 171, no. 9, pp. 090514, 2024, ISSN: 1945-7111 0013-4651.
@article{nokey,
title = {Understanding the Effect of Lithium Nitrate as Additive in Carbonate-Based Electrolytes for Silicon Anodes},
author = {M Graf and L Reuter and S Qian and T Calmus and R Bernhard and S Haufe and H A Gasteiger},
url = {https://dx.doi.org/10.1149/1945-7111/ad71f7},
doi = {10.1149/1945-7111/ad71f7},
issn = {1945-7111
0013-4651},
year = {2024},
date = {2024-09-19},
journal = {Journal of The Electrochemical Society},
volume = {171},
number = {9},
pages = {090514},
abstract = {Due to its high specific capacity, silicon is one of the most promising anode materials for next-generation lithium-ion batteries. However, its large volumetric changes upon (de)lithiation of ∼300% lead to a rupture/re-formation of the solid-electrolyte interphase (SEI) upon cycling, resulting in continuous electrolyte consumption and irreversible loss of lithium. Therefore, it is crucial to use electrolyte systems that form a more stable SEI that can withstand large volume changes. Here, we investigate lithium nitrate (LiNO3) and lithium nitrite (LiNO2) as electrolyte additives. Linear scan voltammetry on carbon black working electrodes in a half-cell configuration with LiNO3-containing 1 M LiPF6 in EC/DEC (1/2 v/v) revealed a two-step reduction mechanism, whereby the first reduction peak could be attributed to the conversion of LiNO3 to LiNO2, while X-ray photoelectron spectroscopy on harvested electrodes suggests the formation of Li3N during the second reduction peak. On-line electrochemical mass spectrometry (OEMS) on carbon black electrodes showed that N2O gas is evolved upon the reduction of LiNO3- and LiNO2-containing electrolytes but that the gassing associated with EC reduction is significantly reduced. Furthermore, OEMS and voltammetry were used to examine the redox chemistry of LiNO2 additive. Finally, LiNO3 and LiNO2 additives significantly improved the cycle-life of Si||NCM622 full-cells.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Due to its high specific capacity, silicon is one of the most promising anode materials for next-generation lithium-ion batteries. However, its large volumetric changes upon (de)lithiation of ∼300% lead to a rupture/re-formation of the solid-electrolyte interphase (SEI) upon cycling, resulting in continuous electrolyte consumption and irreversible loss of lithium. Therefore, it is crucial to use electrolyte systems that form a more stable SEI that can withstand large volume changes. Here, we investigate lithium nitrate (LiNO3) and lithium nitrite (LiNO2) as electrolyte additives. Linear scan voltammetry on carbon black working electrodes in a half-cell configuration with LiNO3-containing 1 M LiPF6 in EC/DEC (1/2 v/v) revealed a two-step reduction mechanism, whereby the first reduction peak could be attributed to the conversion of LiNO3 to LiNO2, while X-ray photoelectron spectroscopy on harvested electrodes suggests the formation of Li3N during the second reduction peak. On-line electrochemical mass spectrometry (OEMS) on carbon black electrodes showed that N2O gas is evolved upon the reduction of LiNO3- and LiNO2-containing electrolytes but that the gassing associated with EC reduction is significantly reduced. Furthermore, OEMS and voltammetry were used to examine the redox chemistry of LiNO2 additive. Finally, LiNO3 and LiNO2 additives significantly improved the cycle-life of Si||NCM622 full-cells.
8.
M Kost, M Kornherr, P Zehetmaier, H Illner, D S Jeon, H A Gasteiger, M Döblinger, D Fattakhova-Rohlfing, T Bein
Chemical Epitaxy of Iridium Oxide on Tin Oxide Enhances Stability of Supported OER Catalyst Journal Article
In: Small, vol. 20, no. 42, pp. 2404118, 2024, ISSN: 1613-6810.
@article{nokey,
title = {Chemical Epitaxy of Iridium Oxide on Tin Oxide Enhances Stability of Supported OER Catalyst},
author = {M Kost and M Kornherr and P Zehetmaier and H Illner and D S Jeon and H A Gasteiger and M D\"{o}blinger and D Fattakhova-Rohlfing and T Bein},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/smll.202404118},
doi = {https://doi.org/10.1002/smll.202404118},
issn = {1613-6810},
year = {2024},
date = {2024-08-21},
urldate = {2024-08-21},
journal = {Small},
volume = {20},
number = {42},
pages = {2404118},
abstract = {Abstract Significantly reducing the iridium content in oxygen evolution reaction (OER) catalysts while maintaining high electrocatalytic activity and stability is a key priority in the development of large-scale proton exchange membrane (PEM) electrolyzers. In practical catalysts, this is usually achieved by depositing thin layers of iridium oxide on a dimensionally stable metal oxide support material that reduces the volumetric packing density of iridium in the electrode assembly. By comparing two support materials with different structure types, it is shown that the chemical nature of the metal oxide support can have a strong influence on the crystallization of the iridium oxide phase and the direction of crystal growth. Epitaxial growth of crystalline IrO2 is achieved on the isostructural support material SnO2, both of which have a rutile structure with very similar lattice constants. Crystallization of amorphous IrOx on an SnO2 substrate results in interconnected, ultrasmall IrO2 crystallites that grow along the surface and are firmly anchored to the substrate. Thereby, the IrO2 phase enables excellent conductivity and remarkable stability of the catalyst at higher overpotentials and current densities at a very low Ir content of only 14 at%. The chemical epitaxy described here opens new horizons for the optimization of conductivity, activity and stability of electrocatalysts and the development of other epitaxial materials systems.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Significantly reducing the iridium content in oxygen evolution reaction (OER) catalysts while maintaining high electrocatalytic activity and stability is a key priority in the development of large-scale proton exchange membrane (PEM) electrolyzers. In practical catalysts, this is usually achieved by depositing thin layers of iridium oxide on a dimensionally stable metal oxide support material that reduces the volumetric packing density of iridium in the electrode assembly. By comparing two support materials with different structure types, it is shown that the chemical nature of the metal oxide support can have a strong influence on the crystallization of the iridium oxide phase and the direction of crystal growth. Epitaxial growth of crystalline IrO2 is achieved on the isostructural support material SnO2, both of which have a rutile structure with very similar lattice constants. Crystallization of amorphous IrOx on an SnO2 substrate results in interconnected, ultrasmall IrO2 crystallites that grow along the surface and are firmly anchored to the substrate. Thereby, the IrO2 phase enables excellent conductivity and remarkable stability of the catalyst at higher overpotentials and current densities at a very low Ir content of only 14 at%. The chemical epitaxy described here opens new horizons for the optimization of conductivity, activity and stability of electrocatalysts and the development of other epitaxial materials systems.
7.
B M Stühmeier, A M Damjanović, K Rodewald, H A Gasteiger
Selective anode catalyst for the mitigation of start-up/shut-down induced cathode degradation in proton exchange membrane fuel cells Journal Article
In: Journal of Power Sources, vol. 558, pp. 232572, 2023, ISSN: 0378-7753.
@article{nokey,
title = {Selective anode catalyst for the mitigation of start-up/shut-down induced cathode degradation in proton exchange membrane fuel cells},
author = {B M St\"{u}hmeier and A M Damjanovi\'{c} and K Rodewald and H A Gasteiger},
url = {https://www.sciencedirect.com/science/article/pii/S037877532201549X},
doi = {https://doi.org/10.1016/j.jpowsour.2022.232572},
issn = {0378-7753},
year = {2023},
date = {2023-02-28},
journal = {Journal of Power Sources},
volume = {558},
pages = {232572},
abstract = {Reducing cathode degradation during start-up and shut-down (SUSD) events is one of the remaining challenges for the widespread application of proton exchange membrane fuel cells (PEMFC). An anode catalyst that is selective for the hydrogen oxidation reaction (HOR) while its activity for the oxygen reduction reaction (ORR) is severely reduced, could substantially prolong the SUSD lifetime of the cathode. Herein, we report on single-cell measurements with a Pt/TiOx/C (x ≤ 2) catalyst that has been shown to be HOR selective by rotating disk electrode (RDE) measurements. The HOR activity of the catalyst was compared to conventional Pt/C by H2-pump measurements at ultra-low loadings. The ORR activity of Pt/TiOx/C was compared to Pt/C anodes with high and low Pt loadings, showing a diminished selectivity in MEA compared to RDE measurements. Unfortunately, the PEMFC performance with the Pt/TiOx/C catalyst was compromised by TiOx dissolution, deduced from voltage loss analysis of the H2/O2 performance curves and by ex-situ SEM/EDX of the MEAs. Finally, the successful mitigation of cathode carbon corrosion was shown over the course of 3200 SUSD cycles, whereby the retention of Pt surface area when using a Pt/TiOx/C anode by far exceeded the improvements expected from the reduced ORR kinetics.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Reducing cathode degradation during start-up and shut-down (SUSD) events is one of the remaining challenges for the widespread application of proton exchange membrane fuel cells (PEMFC). An anode catalyst that is selective for the hydrogen oxidation reaction (HOR) while its activity for the oxygen reduction reaction (ORR) is severely reduced, could substantially prolong the SUSD lifetime of the cathode. Herein, we report on single-cell measurements with a Pt/TiOx/C (x ≤ 2) catalyst that has been shown to be HOR selective by rotating disk electrode (RDE) measurements. The HOR activity of the catalyst was compared to conventional Pt/C by H2-pump measurements at ultra-low loadings. The ORR activity of Pt/TiOx/C was compared to Pt/C anodes with high and low Pt loadings, showing a diminished selectivity in MEA compared to RDE measurements. Unfortunately, the PEMFC performance with the Pt/TiOx/C catalyst was compromised by TiOx dissolution, deduced from voltage loss analysis of the H2/O2 performance curves and by ex-situ SEM/EDX of the MEAs. Finally, the successful mitigation of cathode carbon corrosion was shown over the course of 3200 SUSD cycles, whereby the retention of Pt surface area when using a Pt/TiOx/C anode by far exceeded the improvements expected from the reduced ORR kinetics.
6.
A T S Freiberg, S Qian, J Wandt, H A Gasteiger, E J Crumlin
In: ACS Applied Materials & Interfaces, vol. 15, no. 3, pp. 4743-4754, 2023, ISSN: 1944-8244.
@article{nokey,
title = {Surface Oxygen Depletion of Layered Transition Metal Oxides in Li-Ion Batteries Studied by Operando Ambient Pressure X-ray Photoelectron Spectroscopy},
author = {A T S Freiberg and S Qian and J Wandt and H A Gasteiger and E J Crumlin},
url = {https://doi.org/10.1021/acsami.2c19008},
doi = {10.1021/acsami.2c19008},
issn = {1944-8244},
year = {2023},
date = {2023-01-09},
journal = {ACS Applied Materials \& Interfaces},
volume = {15},
number = {3},
pages = {4743-4754},
abstract = {A new operando spectro-electrochemical setup was developed to study oxygen depletion from the surface of layered transition metal oxide particles at high degrees of delithiation. An NCM111 working electrode was paired with a chemically delithiated LiFePO4 counter electrode in a fuel cell-inspired membrane electrode assembly (MEA). A propylene carbonate-soaked Li-ion conducting ionomer served as an electrolyte, providing both good electrochemical performance and direct probing of the NCM111 particles during cycling by ambient pressure X-ray photoelectron spectroscopy. The irreversible emergence of an oxygen-depleted phase in the O 1s spectra of the layered oxide particles was observed upon the first delithiation to high state-of-charge, which is in excellent agreement with oxygen release analysis via mass spectrometry analysis of such MEAs. By comparing the metal oxide-based O 1s spectral features to the Ni 2p3/2 intensity, we can calculate the transition metal-to-oxygen ratio of the metal oxide close to the particle surface, which shows good agreement with the formation of a spinel-like stoichiometry as an oxygen-depleted phase. This new setup enables a deeper understanding of interfacial changes of layered oxide-based cathode active materials for Li-ion batteries upon cycling.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
A new operando spectro-electrochemical setup was developed to study oxygen depletion from the surface of layered transition metal oxide particles at high degrees of delithiation. An NCM111 working electrode was paired with a chemically delithiated LiFePO4 counter electrode in a fuel cell-inspired membrane electrode assembly (MEA). A propylene carbonate-soaked Li-ion conducting ionomer served as an electrolyte, providing both good electrochemical performance and direct probing of the NCM111 particles during cycling by ambient pressure X-ray photoelectron spectroscopy. The irreversible emergence of an oxygen-depleted phase in the O 1s spectra of the layered oxide particles was observed upon the first delithiation to high state-of-charge, which is in excellent agreement with oxygen release analysis via mass spectrometry analysis of such MEAs. By comparing the metal oxide-based O 1s spectral features to the Ni 2p3/2 intensity, we can calculate the transition metal-to-oxygen ratio of the metal oxide close to the particle surface, which shows good agreement with the formation of a spinel-like stoichiometry as an oxygen-depleted phase. This new setup enables a deeper understanding of interfacial changes of layered oxide-based cathode active materials for Li-ion batteries upon cycling.
5.
T Lazaridis, B M Stühmeier, H A Gasteiger, H A El-Sayed
Capabilities and limitations of rotating disk electrodes versus membrane electrode assemblies in the investigation of electrocatalysts Journal Article
In: Nature Catalysis, vol. 5, no. 5, pp. 363-373, 2022, ISSN: 2520-1158.
@article{nokey,
title = {Capabilities and limitations of rotating disk electrodes versus membrane electrode assemblies in the investigation of electrocatalysts},
author = {T Lazaridis and B M St\"{u}hmeier and H A Gasteiger and H A El-Sayed},
url = {https://doi.org/10.1038/s41929-022-00776-5},
doi = {10.1038/s41929-022-00776-5},
issn = {2520-1158},
year = {2022},
date = {2022-05-23},
journal = {Nature Catalysis},
volume = {5},
number = {5},
pages = {363-373},
abstract = {Cost-competitive fuel cells and water electrolysers require highly efficient electrocatalysts for the respective reactions of hydrogen oxidation and evolution, and oxygen evolution and reduction. Electrocatalyst activity and durability are commonly assessed using rotating disk electrodes (RDEs) or membrane electrode assemblies (MEAs). RDEs provide a quick and widely accessible testing tool, whereas MEA testing is more complex but closely resembles the actual application. Although both experimental set-ups allow investigation of the same reactions, there are scientific questions that cannot be answered by the RDE technique. In this Perspective, we scrutinize protocols widely used to determine the activity and durability of electrocatalysts, and highlight discrepancies in the results obtained using RDEs and MEAs. We discuss where the use of RDEs is appropriate and, conversely, where it leads to erroneous interpretations. Ultimately, we show that many of the current challenges for hydrogen and oxygen electrocatalysts require MEA testing and advocate for its greater adoption in the early stages of electrocatalyst development.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Cost-competitive fuel cells and water electrolysers require highly efficient electrocatalysts for the respective reactions of hydrogen oxidation and evolution, and oxygen evolution and reduction. Electrocatalyst activity and durability are commonly assessed using rotating disk electrodes (RDEs) or membrane electrode assemblies (MEAs). RDEs provide a quick and widely accessible testing tool, whereas MEA testing is more complex but closely resembles the actual application. Although both experimental set-ups allow investigation of the same reactions, there are scientific questions that cannot be answered by the RDE technique. In this Perspective, we scrutinize protocols widely used to determine the activity and durability of electrocatalysts, and highlight discrepancies in the results obtained using RDEs and MEAs. We discuss where the use of RDEs is appropriate and, conversely, where it leads to erroneous interpretations. Ultimately, we show that many of the current challenges for hydrogen and oxygen electrocatalysts require MEA testing and advocate for its greater adoption in the early stages of electrocatalyst development.
4.
B M Stühmeier, R J Schuster, L Hartmann, S Selve, H A El-Sayed, H A Gasteiger
In: Journal of The Electrochemical Society, 2022, ISSN: 1945-7111.
@article{nokey,
title = {Modification of the Electrochemical Surface Oxide Formation and the Hydrogen Oxidation Activity of Ruthenium by Strong Metal Support Interactions},
author = {B M St\"{u}hmeier and R J Schuster and L Hartmann and S Selve and H A El-Sayed and H A Gasteiger },
url = {http://iopscience.iop.org/article/10.1149/1945-7111/ac58c9},
doi = {https://doi.org/10.1149/1945-7111/ac58c9},
issn = {1945-7111},
year = {2022},
date = {2022-02-25},
urldate = {2022-02-25},
journal = {Journal of The Electrochemical Society},
abstract = {A major hurdle for the wide spread commercialization of proton exchange membrane based fuel cells (PEMFCs) and water electrolyzers are the durability and high cost of noble metal catalysts. Here, alternative support materials might offer advantages, as they can alter the properties of a catalyst by means of a strong metal support interaction (SMSI) that has been shown to prevent platinum oxidation and suppress the oxygen reduction reaction on titanium oxide supported platinum nanoparticles deposited on a carbon support (Pt/TiOx/C). Herein, we report a novel Ru/TiOx/C catalyst that according to tomographic transmission electron microscopy analysis consists of partially encapsulated Ru particles in a Ru/TiOx-composite matrix supported on a carbon support. It is shown by cyclic voltammetry and X-ray photoelectron spectroscopy that ruthenium oxidation is mitigated by an SMSI between Ru and TiOx after reductive heat-treatment (Ru/TiOx/C400°C,H2 ). As a result, the catalyst is capable of oxidizing hydrogen up to the onset of oxygen evolution reaction, in stark contrast to a Ru/C reference catalyst. PEMFC-based hydrogen pump measurements confirmed the stabilization of the hydrogen oxidation reaction (HOR) activity on Ru/TiOx/C400°C,H2 and showed a ≈3 fold higher HOR activity compared to Ru/C, albeit roughly two orders of magnitude less active than Pt/C.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
A major hurdle for the wide spread commercialization of proton exchange membrane based fuel cells (PEMFCs) and water electrolyzers are the durability and high cost of noble metal catalysts. Here, alternative support materials might offer advantages, as they can alter the properties of a catalyst by means of a strong metal support interaction (SMSI) that has been shown to prevent platinum oxidation and suppress the oxygen reduction reaction on titanium oxide supported platinum nanoparticles deposited on a carbon support (Pt/TiOx/C). Herein, we report a novel Ru/TiOx/C catalyst that according to tomographic transmission electron microscopy analysis consists of partially encapsulated Ru particles in a Ru/TiOx-composite matrix supported on a carbon support. It is shown by cyclic voltammetry and X-ray photoelectron spectroscopy that ruthenium oxidation is mitigated by an SMSI between Ru and TiOx after reductive heat-treatment (Ru/TiOx/C400°C,H2 ). As a result, the catalyst is capable of oxidizing hydrogen up to the onset of oxygen evolution reaction, in stark contrast to a Ru/C reference catalyst. PEMFC-based hydrogen pump measurements confirmed the stabilization of the hydrogen oxidation reaction (HOR) activity on Ru/TiOx/C400°C,H2 and showed a ≈3 fold higher HOR activity compared to Ru/C, albeit roughly two orders of magnitude less active than Pt/C.
3.
G C Tok, S Reiter, A T S Freiberg, L Reinschlüssel, H A Gasteiger, R De Vivie-Riedle, C R Hess
H2 Evolution from Electrocatalysts with Redox-Active Ligands: Mechanistic Insights from Theory and Experiment vis-à-vis Co-Mabiq Journal Article
In: Inorganic Chemistry, 2021, ISSN: 0020-1669.
@article{,
title = {H2 Evolution from Electrocatalysts with Redox-Active Ligands: Mechanistic Insights from Theory and Experiment vis-\`{a}-vis Co-Mabiq},
author = {G C Tok and S Reiter and A T S Freiberg and L Reinschl\"{u}ssel and H A Gasteiger and R De Vivie-Riedle and C R Hess},
url = {https://doi.org/10.1021/acs.inorgchem.1c01157},
doi = {10.1021/acs.inorgchem.1c01157},
issn = {0020-1669},
year = {2021},
date = {2021-07-23},
urldate = {2021-07-23},
journal = {Inorganic Chemistry},
abstract = {Electrocatalytic hydrogen production via transition metal complexes offers a promising approach for chemical energy storage. Optimal platforms to effectively control the proton and electron transfer steps en route to H2 evolution still need to be established, and redox-active ligands could play an important role in this context. In this study, we explore the role of the redox-active Mabiq (Mabiq = 2\textendash4:6\textendash8-bis(3,3,4,4-tetramethlyldihydropyrrolo)-10\textendash15-(2,2-biquinazolino)-[15]-1,3,5,8,10,14-hexaene1,3,7,9,11,14-N6) ligand in the hydrogen evolution reaction (HER). Using spectro-electrochemical studies in conjunction with quantum chemical calculations, we identified two precatalytic intermediates formed upon the addition of two electrons and one proton to [CoII(Mabiq)(THF)](PF6) (CoMbq). We further examined the acid strength effect on the generation of the intermediates. The generation of the first intermediate, CoMbq-H1, involves proton addition to the bridging imine-nitrogen atom of the ligand and requires strong proton activity. The second intermediate, CoMbq-H2, acquires a proton at the diketiminate carbon for which a weaker proton activity is sufficient. We propose two decoupled H2 evolution pathways based on these two intermediates, which operate at different overpotentials. Our results show how the various protonation sites of the redox-active Mabiq ligand affect the energies and activities of HER intermediates.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Electrocatalytic hydrogen production via transition metal complexes offers a promising approach for chemical energy storage. Optimal platforms to effectively control the proton and electron transfer steps en route to H2 evolution still need to be established, and redox-active ligands could play an important role in this context. In this study, we explore the role of the redox-active Mabiq (Mabiq = 2–4:6–8-bis(3,3,4,4-tetramethlyldihydropyrrolo)-10–15-(2,2-biquinazolino)-[15]-1,3,5,8,10,14-hexaene1,3,7,9,11,14-N6) ligand in the hydrogen evolution reaction (HER). Using spectro-electrochemical studies in conjunction with quantum chemical calculations, we identified two precatalytic intermediates formed upon the addition of two electrons and one proton to [CoII(Mabiq)(THF)](PF6) (CoMbq). We further examined the acid strength effect on the generation of the intermediates. The generation of the first intermediate, CoMbq-H1, involves proton addition to the bridging imine-nitrogen atom of the ligand and requires strong proton activity. The second intermediate, CoMbq-H2, acquires a proton at the diketiminate carbon for which a weaker proton activity is sufficient. We propose two decoupled H2 evolution pathways based on these two intermediates, which operate at different overpotentials. Our results show how the various protonation sites of the redox-active Mabiq ligand affect the energies and activities of HER intermediates.
2.
Q He, A T S Freiberg, M U M Patel, S Qian, H A Gasteiger
Operando Identification of Liquid Intermediates in Lithium–Sulfur Batteries via Transmission UV–vis Spectroscopy Journal Article
In: Journal of The Electrochemical Society, vol. 167, no. 8, pp. 080508, 2020, ISSN: 0013-4651 1945-7111.
@article{nokey,
title = {Operando Identification of Liquid Intermediates in Lithium\textendashSulfur Batteries via Transmission UV\textendashvis Spectroscopy},
author = {Q He and A T S Freiberg and M U M Patel and S Qian and H A Gasteiger},
url = {http://dx.doi.org/10.1149/1945-7111/ab8645},
doi = {10.1149/1945-7111/ab8645},
issn = {0013-4651 1945-7111},
year = {2020},
date = {2020-01-05},
urldate = {2020-01-05},
journal = {Journal of The Electrochemical Society},
volume = {167},
number = {8},
pages = {080508},
abstract = {Lithium-sulfur (Li-S) batteries are facing various challenges with regards to performance and durability, and further improvements require a better understanding of the fundamental working mechanisms, including an identification of the reaction intermediates in an operating Li-S battery. In this study, we present an operando transmission UV\textendashvis spectro-electrochemical cell design that employs a conventional sulfur/carbon composite electrode, propose a comprehensive peak assignment for polysulfides in DOL:DME-based electrolyte, and finally identify the liquid intermediates in the discharging process of an operating Li-S cell. Here, we propose for the first time a meta-stable polysulfide species (S32−) that is present at substantial concentrations during the 2nd discharge plateau in a Li-S battery. We identify the S32− species that are the reduction product of S42−, as deducted from the analysis of the obtained operando UV\textendashvis spectra along with the transferred charge, and confirmed by rotating ring disk electrode measurements for the reduction of a solution with a nominal Li2S4 stoichiometry. Furthermore, our operando results provide insight into the potential-dependent stability of different S-species and the rate-limiting (electro)chemical steps during discharging. Finally, we propose a viable reaction pathway of how S8 is electrochemically reduced to Li2S2/Li2S based on our operando results as well as that reported in the literature.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Lithium-sulfur (Li-S) batteries are facing various challenges with regards to performance and durability, and further improvements require a better understanding of the fundamental working mechanisms, including an identification of the reaction intermediates in an operating Li-S battery. In this study, we present an operando transmission UV–vis spectro-electrochemical cell design that employs a conventional sulfur/carbon composite electrode, propose a comprehensive peak assignment for polysulfides in DOL:DME-based electrolyte, and finally identify the liquid intermediates in the discharging process of an operating Li-S cell. Here, we propose for the first time a meta-stable polysulfide species (S32−) that is present at substantial concentrations during the 2nd discharge plateau in a Li-S battery. We identify the S32− species that are the reduction product of S42−, as deducted from the analysis of the obtained operando UV–vis spectra along with the transferred charge, and confirmed by rotating ring disk electrode measurements for the reduction of a solution with a nominal Li2S4 stoichiometry. Furthermore, our operando results provide insight into the potential-dependent stability of different S-species and the rate-limiting (electro)chemical steps during discharging. Finally, we propose a viable reaction pathway of how S8 is electrochemically reduced to Li2S2/Li2S based on our operando results as well as that reported in the literature.
1.
B M Stühmeier, S Selve, M U M Patel, T N Geppert, H A Gasteiger, H A El-Sayed
Highly Selective Pt/TiOx Catalysts for the Hydrogen Oxidation Reaction Journal Article
In: ACS Applied Energy Materials, vol. 2, no. 8, pp. 5534-5539, 2019.
@article{nokey,
title = {Highly Selective Pt/TiOx Catalysts for the Hydrogen Oxidation Reaction},
author = {B M St\"{u}hmeier and S Selve and M U M Patel and T N Geppert and H A Gasteiger and H A El-Sayed},
url = {https://doi.org/10.1021/acsaem.9b00718},
doi = {10.1021/acsaem.9b00718},
year = {2019},
date = {2019-08-05},
journal = {ACS Applied Energy Materials},
volume = {2},
number = {8},
pages = {5534-5539},
abstract = {Reducing the cathode degradation in proton exchange membrane fuel cells during start-up and shut-down events (where the anode is filled with H2 and air) is crucial for its widespread automotive implementation. The use of selective catalysts for the hydrogen oxidation reaction (HOR) that sparingly reduce oxygen on the anode could significantly reduce the carbon corrosion on the cathode. Herein, we report a novel system of carbon supported Pt/TiOx catalysts that combines the unique properties of a strong metal\textendashsupport interaction (SMSI) with the known advantages of a carbon support. High-resolution transmission electron microscopy of the selective catalyst shows the encapsulation of the Pt nanoparticles (NPs) by a TiOx layer resulting from the SMSI. Rotating disk electrode experiments confirmed that Pt oxidation and oxygen reduction are hindered due to the TiOx layer. Furthermore, a high HOR activity that is retained even at high potentials proved the superior HOR selectivity of the catalyst.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Reducing the cathode degradation in proton exchange membrane fuel cells during start-up and shut-down events (where the anode is filled with H2 and air) is crucial for its widespread automotive implementation. The use of selective catalysts for the hydrogen oxidation reaction (HOR) that sparingly reduce oxygen on the anode could significantly reduce the carbon corrosion on the cathode. Herein, we report a novel system of carbon supported Pt/TiOx catalysts that combines the unique properties of a strong metal–support interaction (SMSI) with the known advantages of a carbon support. High-resolution transmission electron microscopy of the selective catalyst shows the encapsulation of the Pt nanoparticles (NPs) by a TiOx layer resulting from the SMSI. Rotating disk electrode experiments confirmed that Pt oxidation and oxygen reduction are hindered due to the TiOx layer. Furthermore, a high HOR activity that is retained even at high potentials proved the superior HOR selectivity of the catalyst.