Periodic Reporting for period 4 - ME4OER (Mechanism Engineering of the Oxygen Evolution Reaction)
Reporting period: 2023-09-01 to 2024-05-31
The oxygen evolution reaction (OER) is a limiting step on the way to generating molecular oxygen and green hydrogen in numerous processes, particularly in the context of the European Green Deal. It has gained considerable attention recently due to its importance to sustainable industrial processes and particularly renewable energy in metal refining, batteries and production of fuels by electrolysis of water into oxygen and hydrogen. The aim of the project is a better understanding of the mechanisms of catalysis and corrosion on earth-abundant materials while they catalyze the OER. The desired insight is enabled by dynamic synchrotron operando spectroscopy to study the electronic properties of the metal sites during operation and by microkinetic simulations of likely reaction mechanisms. These insights provide guidelines for materials design to engineer the reaction mechanisms of multiple steps in a reaction sequence rather than finding a better catalyst for a single step. It enables a more comprehensive picture of the steps contributing to either catalysis or corrosion. Two grand challenges are thereby addressed: (i) resolving the anticorrelation between catalysis and corrosion based on mechanistic insight and (ii) enhancing the activity for the OER or other electrocatalytic reactions exponentially. Anticorrelation between catalysis and corrosions is discussed in several works arising from the project. As a highlight, we identified requirements to turn corrosion into a process for improving the electrode activity and demonstrated design of the active state (doi: 10.1002/aenm.202101737). Our mechanistic simulations (doi: 10.1002/elsa.202100213) provide clear guidelines how to maximize the activity of the most frequently postulated mechanism, namely by allowing a metal-terminated surface to exist under reaction conditions at high overpotential. Our insights provide guidelines for longer lasting electrocatalysts with consistent performance.
Suitable epitaxial perovskite materials were selected at the start of the project and the analysis published as a review article that included the definition of prototypical mechanisms (doi: 10.1088/2515-7655/ab812f). Clear benchmark criteria for one of the prototypical mechanisms were enabled by calculation of Tafel slope and reaction order (doi: 10.1002/elsa.202100213). We clearly demonstrated a reduction of the Tafel slope by Co addition to a Mn oxide and thereby activated additional mechanistic steps (doi: 10.1002/celc.202200482); our analysis relates the change in metal redox to the change in Tafel slope.
We identified the requirements for beneficial restructuring from the erythrite crystal structure of a layered hydroxide and thereby turned corrosion in a beneficial process (doi: 10.1002/aenm.202101737). This opens the door to engineer the corrosion mechanism to improve other catalysts and ultimately to find repair mechanisms as an attractive alternative to the design of robust but usually less active electrocatalysts. Furthermore, we gained a better understanding of the formation of layered Ni hydroxide on LaNiO3 in collaborative work (doi: 10.1038/s41467-023-43901-z). In both cases, the restructured surface, i.e. a distinct active state that formed during operation, was beneficial for performance. Further information may be found in the press releases (https://www.helmholtz-berlin.de/pubbin/news_seite?nid=23123;sprache=en;seitenid=1(opens in new window) https://www.helmholtz-berlin.de/pubbin/news_seite?nid=25906&sprache=en&seitenid=50901(opens in new window)). The reaction enthalpy of a layered Co oxide was obtained by analyzing the Eyring Polanyi equation where we innovated the treatment as three-dimensional data (doi: 10.1002/cctc.202301578). The precise experimental determination of reaction enthalpies is an important bridge to mechanistic work in the theory community.
X-ray absorption spectroscopy (XAS) was a key method to achieving the goals of the project. We reviewed combining electrochemistry and XAS, proposed a clear definition of operando for electrocatalysis and highlighted the importance of tracking states with sufficient time resolution (doi: 10.1002/anie.202211949). After the flow cell with a unique optical O2 detector had been commissioned, we jointly detected the evolved oxygen and spectral changes in XAS and UV-vis spectroscopy (doi: 10.26434/chemrxiv-2024-srmwb). The electronic structure of limiting states was elucidated by XAS and UV-Vis (doi: 10.26434/chemrxiv-2024-srmwb) which revealed that the availability of Co(IV) becomes important for the mechanism at high current density and pH, i.e. more applied electrochemical conditions.
Overall, results were disseminated to divers audiences at conferences, by peer-reviewed journal publications (Nat. Commun, Angewandte Chemie, Adv. Energy Mater, etc), press releases on publication highlights, public outreach activities (e.g. Berlin Science Week) and on social media.
We identified the requirements for beneficial restructuring from the erythrite crystal structure of a layered hydroxide and thereby turned corrosion in a beneficial process (doi: 10.1002/aenm.202101737). This opens the door to engineer the corrosion mechanism to improve other catalysts and ultimately to find repair mechanisms as an attractive alternative to the design of robust but usually less active electrocatalysts. Furthermore, we gained a better understanding of the formation of layered Ni hydroxide on LaNiO3 in collaborative work (doi: 10.1038/s41467-023-43901-z). In both cases, the restructured surface, i.e. a distinct active state that formed during operation, was beneficial for performance. Further information may be found in the press releases (https://www.helmholtz-berlin.de/pubbin/news_seite?nid=23123;sprache=en;seitenid=1(opens in new window) https://www.helmholtz-berlin.de/pubbin/news_seite?nid=25906&sprache=en&seitenid=50901(opens in new window)). The reaction enthalpy of a layered Co oxide was obtained by analyzing the Eyring Polanyi equation where we innovated the treatment as three-dimensional data (doi: 10.1002/cctc.202301578). The precise experimental determination of reaction enthalpies is an important bridge to mechanistic work in the theory community.
X-ray absorption spectroscopy (XAS) was a key method to achieving the goals of the project. We reviewed combining electrochemistry and XAS, proposed a clear definition of operando for electrocatalysis and highlighted the importance of tracking states with sufficient time resolution (doi: 10.1002/anie.202211949). After the flow cell with a unique optical O2 detector had been commissioned, we jointly detected the evolved oxygen and spectral changes in XAS and UV-vis spectroscopy (doi: 10.26434/chemrxiv-2024-srmwb). The electronic structure of limiting states was elucidated by XAS and UV-Vis (doi: 10.26434/chemrxiv-2024-srmwb) which revealed that the availability of Co(IV) becomes important for the mechanism at high current density and pH, i.e. more applied electrochemical conditions.
Overall, results were disseminated to divers audiences at conferences, by peer-reviewed journal publications (Nat. Commun, Angewandte Chemie, Adv. Energy Mater, etc), press releases on publication highlights, public outreach activities (e.g. Berlin Science Week) and on social media.
The project's results went beyond the state-of-the-art in the following aspects
* We calculated Tafel slope and reaction order, which allows uniquely assigning the rate-determining step of a typical mechanism for the oxygen evolution reaction (doi: 10.1002/elsa.202100213)
* We identified the requirements for beneficial restructuring which turns corrosion into a beneficial effect and allows designing the active state that forms during oxygen evolution (doi: 10.1002/aenm.202101737)
* The reaction enthalpy of a layered Co oxide was obtained by analyzing the Eyring Polanyi equation where we innovated the treatment as three-dimensional data (doi: 10.1002/cctc.202301578)
* We developed an measurement setup for operando XAS where oxygen is measured jointly with the electrochemical and X-ray signals for true operando spectroscopy. We defined the latter term concisely in a review article (doi: 10.1002/anie.202211949)
* Our operando XAS and UV-Vis study revealed that Co(IV) becomes important at high current density and pH, which can be used to control the reaction path (doi: 10.26434/chemrxiv-2024-srmwb)
* We calculated Tafel slope and reaction order, which allows uniquely assigning the rate-determining step of a typical mechanism for the oxygen evolution reaction (doi: 10.1002/elsa.202100213)
* We identified the requirements for beneficial restructuring which turns corrosion into a beneficial effect and allows designing the active state that forms during oxygen evolution (doi: 10.1002/aenm.202101737)
* The reaction enthalpy of a layered Co oxide was obtained by analyzing the Eyring Polanyi equation where we innovated the treatment as three-dimensional data (doi: 10.1002/cctc.202301578)
* We developed an measurement setup for operando XAS where oxygen is measured jointly with the electrochemical and X-ray signals for true operando spectroscopy. We defined the latter term concisely in a review article (doi: 10.1002/anie.202211949)
* Our operando XAS and UV-Vis study revealed that Co(IV) becomes important at high current density and pH, which can be used to control the reaction path (doi: 10.26434/chemrxiv-2024-srmwb)