Periodic Reporting for period 2 - MITICAT (Microfluidic Tuning of Individual Nanoparticles to Understand and Improve Electrocatalysis)
Reporting period: 2023-01-01 to 2024-06-30
Transition metal based nanoparticles (NPs) are envisioned as viable alternatives to the scarce precious metal based catalysts used today for renewable energy conversion. Yet, probing their intrinsic activity to establish property-activity relations and so to smartly design superior catalysts, is impeded by two limitations of existing electrocatalytic techniques. First, the integral assessment of ensembles of non-identical NPs prohibits the identification of intrinsic activity differences. Second, the unknown effects of additives required analyzing the activity of often poorly conductive transition metal oxides, e.g. during the oxygen evolution reaction (OER), prohibit the access to quantitative data and comparable benchmarks. Very recently, we have proposed single NP electrochemistry to overcome both limitations. We demonstrated that the electrocatalytic OER response of individual CoFe2O4 NPs can be assessed in the absence of additives. However, we have not been able to extract property-activity relations, as NP characterization was limited to ex situ data. The groundbreaking strategy of this work is to combine intrinsic activity and physical property measurements of individual NPs. Physical characterization will comprise different online and ex situ methods to gain comprehensive property information. Numerical simulations will allow us to extract quantitative kinetic data from the electrochemical studies, allowing us to provide quantitative benchmarks of intrinsic catalyst performance. Cycling of NPs in a microfluidic platform will enable degradation studies and systematic modification “on the fly”. Moving towards application conditions, catalyst-support interactions will be studied by stepwise immobilization of catalysts on substrates. As a result of revealing intrinsic property-activity relations in electrocatalysis and of elucidating catalyst-support interactions, we will gain the understanding urgently needed to disruptively change electrocatalyst devolopment.
In this first half of the funding period we have successfully hired a team of researchers with the expertise to successfully realize the MITICAT project. The main outcome has been:
A) We have successfully developed a microfluidic platform that enabled in situ characterization (size and composition analysis) of individual nanoparticles by hyperspectral dark field microscopy (DFM) under external flow control. This proof-of concept is a major step that has been published in ACS Phys. Chem. Au.
We also studied the effect of size and shape of transition metal oxide catalyst nanoparticles on their catalytic properties. Thus, we revealed the significant shape-dependency of catalytic activity for the oxygen evolution reaction (OER) of cobalt oxide nanocatalysts. We showed that nanocubes of 9 nm in size, are more catalytically active than nanospheroids of the same size and composition, solving a huge controversy about facet-dependent activity of cobalt oxide spinel catalysts reported in the literature. This achievement has been published in the Journal Adv. Funct. Mat.
B) In line with the project plan we have purchased and successfully set up a Raman microscope in a new laboratory fully dedicated to MITICAT. Hence, we characterized chemical changes of nanoparticles and their surface-adsorbed ligands under operation conditions, which we published in Nano Res.. Additionally, we were able to develop a new approach to characterize surface properties of nanocatalysts at the level of single particles: capacitive nanoimpacts, which is an entirely new methodology to explore properties of the solid/liquid interface and the electrical double layer formed at a nanoparticle. This has been published in Angew. Chem. Int. Ed.
C) We have achieved another major goal of MITICAT: the systematic electrochemical modification of nanoparticles by dealloying. This was published in Electrochim. Acta.
D) Last but not least, we identified and rationalized catalyst-support interactions for transition metal oxide OER catalysts. This major finding enabled us to improve the basic understanding of catalyst-support interactions. We achieved this by applying one of the core methodologies of MITICAT - single-particle electrochemistry combined with finite element-based numerical simulation. This allowed us to reveal the origin of greatly enhanced OER activity of cobalt oxide nanocubes when supported on platinum instead of carbon (published in the Int. J. Mol. Sci.)
A) We have successfully developed a microfluidic platform that enabled in situ characterization (size and composition analysis) of individual nanoparticles by hyperspectral dark field microscopy (DFM) under external flow control. This proof-of concept is a major step that has been published in ACS Phys. Chem. Au.
We also studied the effect of size and shape of transition metal oxide catalyst nanoparticles on their catalytic properties. Thus, we revealed the significant shape-dependency of catalytic activity for the oxygen evolution reaction (OER) of cobalt oxide nanocatalysts. We showed that nanocubes of 9 nm in size, are more catalytically active than nanospheroids of the same size and composition, solving a huge controversy about facet-dependent activity of cobalt oxide spinel catalysts reported in the literature. This achievement has been published in the Journal Adv. Funct. Mat.
B) In line with the project plan we have purchased and successfully set up a Raman microscope in a new laboratory fully dedicated to MITICAT. Hence, we characterized chemical changes of nanoparticles and their surface-adsorbed ligands under operation conditions, which we published in Nano Res.. Additionally, we were able to develop a new approach to characterize surface properties of nanocatalysts at the level of single particles: capacitive nanoimpacts, which is an entirely new methodology to explore properties of the solid/liquid interface and the electrical double layer formed at a nanoparticle. This has been published in Angew. Chem. Int. Ed.
C) We have achieved another major goal of MITICAT: the systematic electrochemical modification of nanoparticles by dealloying. This was published in Electrochim. Acta.
D) Last but not least, we identified and rationalized catalyst-support interactions for transition metal oxide OER catalysts. This major finding enabled us to improve the basic understanding of catalyst-support interactions. We achieved this by applying one of the core methodologies of MITICAT - single-particle electrochemistry combined with finite element-based numerical simulation. This allowed us to reveal the origin of greatly enhanced OER activity of cobalt oxide nanocubes when supported on platinum instead of carbon (published in the Int. J. Mol. Sci.)
The fact that the structure-activity relations and catalysts-support interactions can be probed with the methods developed and showcased in the MITICAT project is a major breakthrough in catalysts research. Given that it avoids binders and other additives, unambiguous identification of the structure/support – activity correlations can be derived in a comparably small system size (for electrochemical experiments).
This is a major step towards achieving a long-requested direct link of experimental electrochemistry at nanocatalysts with high quality theoretical simulations (e.g. by DFT or ab initio MD methods) of the occurring reactions and brings the long desired close interaction of experimentalists and theoreticians in electrocatalysis in reach. Up until now making this link has been strongly limited due to the small size scales high level theory can cover in the presence of liquid water, a solid electrocatalyst and an applied potential – when compared to the trillions of catalyst nanoparticles binder molecules and other additives contained in the usually used porous composite films with hard-to-control local gradients of reactants, intermediates and products. Single nanoparticle electrochemistry overcomes these hurdles and steps the experimental sizes down by several orders of magnitude while keeping the intrinsic properties of the nanocatalyst material. Accordingly, we expect that at the end of the project truly meaningful interlinks between experimental and theoretical electrochemistry can be achieved, providing us the urgently needed insights into reaction mechnisms and active sites for electrochemical reactions relevant in sustainable energy conversion, such as electrochemical water splitting to produce green hydrogen.
This is a major step towards achieving a long-requested direct link of experimental electrochemistry at nanocatalysts with high quality theoretical simulations (e.g. by DFT or ab initio MD methods) of the occurring reactions and brings the long desired close interaction of experimentalists and theoreticians in electrocatalysis in reach. Up until now making this link has been strongly limited due to the small size scales high level theory can cover in the presence of liquid water, a solid electrocatalyst and an applied potential – when compared to the trillions of catalyst nanoparticles binder molecules and other additives contained in the usually used porous composite films with hard-to-control local gradients of reactants, intermediates and products. Single nanoparticle electrochemistry overcomes these hurdles and steps the experimental sizes down by several orders of magnitude while keeping the intrinsic properties of the nanocatalyst material. Accordingly, we expect that at the end of the project truly meaningful interlinks between experimental and theoretical electrochemistry can be achieved, providing us the urgently needed insights into reaction mechnisms and active sites for electrochemical reactions relevant in sustainable energy conversion, such as electrochemical water splitting to produce green hydrogen.