Electrocatalysis under the atomic force microscope

The newly developed method was used to scan the surface of a bimetallic catalyst material in an aqueous medium. The figure shows an overlay of the current signal on a three-dimensional representation of the height image. This clearly shows island-like regions.

The newly developed method was used to scan the surface of a bimetallic catalyst material in an aqueous medium. The figure shows an overlay of the current signal on a three-dimensional representation of the height image. This clearly shows island-like regions. © M. Munz/HZB

The principle of correlative atomic force microscopy in contact mode: a fine tip at the end of a cantilever scans the surface. This allows force interactions between the tip and the sample surface to be measured, including frictional forces. If a voltage is also applied, the electric current flowing through the contact can also be measured.

The principle of correlative atomic force microscopy in contact mode: a fine tip at the end of a cantilever scans the surface. This allows force interactions between the tip and the sample surface to be measured, including frictional forces. If a voltage is also applied, the electric current flowing through the contact can also be measured.

A further development in atomic force microscopy now makes it possible to simultaneously image the height profile of nanometre-fine structures as well as the electric current and the frictional force at solid-liquid interfaces. A team from the Helmholtz-Zentrum Berlin (HZB) and the Fritz Haber Institute (FHI) of the Max Planck Society has succeeded in analysing electrocatalytically active materials and gaining insights that will help optimise catalysts. The method is also potentially suitable for studying processes on battery electrodes, in photocatalysis or on active biomaterials.

To manage the energy transition, it will also be important to rapidly develop cheap and efficient materials that can be used to split water or CO2 by electrocatalysis. In this process, part of the electrical energy is stored in the chemical reaction products. The efficiency of such electrocatalysts depends largely on the nature of the electrode-electrolyte interfaces, i.e. the interfaces between the solid electrodes and the typically aqueous electrolyte. However, spatially resolved physical studies of such solid-liquid interfaces are still relatively scarce.

More insights with AFM

Dr Christopher S. Kley and his team have now developed a new approach to correlative atomic force microscopy (AFM). An extremely sharp tip is scanned across the surface and its height profile is recorded. By attaching the tip to the end of a miniaturised cantilever, the force interactions between the tip and the sample surface, including frictional forces, can be measured with high sensitivity. In addition, the electrical current flowing through the mechanical contact can be measured, provided a voltage is applied. "This allowed us to simultaneously determine the electrical conductivity, the mechanical-chemical friction and the morphological properties in situ (i.e. under the relevant liquid-phase conditions rather than in vacuum or in air)," emphasises Kley.

Copper-gold electrocatalyst

Using this method, the scientists now studied a nanostructured and bimetallic copper-gold electrocatalyst, in collaboration with Prof. Beatriz Roldán Cuenya from the Fritz-Haber-Institute (FHI). Among others, such materials are used in the electrocatalytic conversion of CO2 into energy carriers. "We were able to clearly identify islands of copper oxide with higher electrical resistance, but also grain boundaries and low-conductivity regions in the hydration layer where the catalyst surface comes into contact with the aqueous electrolyte," says Dr Martin Munz, first author of the study.

Such results on catalyst-electrolyte interfaces help to optimise them in a targeted manner. "We can now observe how local electrochemical environments influence charge transfer at the interface," says Kley.

Focus on solid-liquid interfaces

"However, our results are also of general interest to energy research, especially for the study of electrochemical conversion processes, which also play a role in battery systems." Insights into solid-liquid interfaces can also be useful in completely different areas of research, such as understanding corrosion processes, nanosensor systems, and possibly addressing scientific queries in fluidics and environmental sciences, such as dissolution or deposition processes on metal surfaces exposed to water.

Note: This work was carried out within the framework of the CatLab project, where researchers from the HZB and the FHI of the MPG are working together, to develop thin-film catalysts for the energy transition.

arö


You might also be interested in

  • Green Deal Ukraina: HZB launches an Energy & Climate Project
    News
    07.06.2023
    Green Deal Ukraina: HZB launches an Energy & Climate Project
    Green Deal Ukraina, funded by the German Federal Ministry of Education and Research, is working with partner institutions in Ukraine and Poland to establish an energy and climate think tank in the capital, Kiev. The aim is to provide independent and evidence-based advice on rebuilding a sustainable energy system in Ukraine. After all, the implementation of energy and climate legislation is a prerequisite for Ukraine's accession to the EU. The project started on 1 June 2023 and will run for four years.
  • Spintronics at BESSY II: Domain walls in magnetic nanowires
    Science Highlight
    02.06.2023
    Spintronics at BESSY II: Domain walls in magnetic nanowires
    Magnetic domains walls are known to be a source of electrical resistance due to the difficulty for transport electron spins to follow their magnetic texture. This phenomenon holds potential for utilization in spintronic devices, where the electrical resistance can vary based on the presence or absence of a domain wall. A particularly intriguing class of materials are half metals such as La2/3Sr1/3MnO3 (LSMO) which present full spin polarization, allowing their exploitation in spintronic devices. Still the resistance of a single domain wall in half metals remained unknown. Now a team from Spain, France and Germany has generated a single domain wall on a LSMO nanowire and measured resistance changes 20 times larger than for a normal ferromagnet such as Cobalt.
  • Fractons as information storage: Not yet quite tangible, but close
    Science Highlight
    26.05.2023
    Fractons as information storage: Not yet quite tangible, but close
    A new quasiparticle with interesting properties has appeared in solid-state physics - but so far only in the theoretical modelling of solids with certain magnetic properties. An international team from HZB and Freie Universität Berlin has now shown that, contrary to expectations, quantum fluctuations do not make the quasiparticle appear more clearly, but rather blur its signature.