The grand challenge in electrochemistry is to link electronic properties, surface structure, chemistry and topography, interfacial properties and exposure conditions to predict the electrochemical properties of materials. Such fundamental research underpins development in fuel cells and battery technology, electrocatalysis, electrochemical sensors, solar energy, colloid science, and electrodeposition, and involves the integration of measurement and modelling at different length scales.

Whilst measurement techniques to characterise surface morphology, mechanical properties and chemistry at the micro to nano-scale are comparatively well established, measurement of surface reactivity, kinetics of dynamic processes, and mass transport on a highly localised scale remains challenging. Scanning electrochemical microscopy (SECM) offers a unique and poweful approach to such local characterisation and is becoming increasingly prevailent as a chemical imaging tool. At NPL we are developing related state-of-the-art electrochemical scanning probe techniques for a variety of materials-based applications, including:

• Fuel cells
• Dye-sensitised solar cells
• Heterogeneous catalysis

Scanning Electrochemical Microscopy

In SECM, the sample of interest is immersed in an electrolyte solution and a microelectrode tip is positioned in close proximity to the surface, allowing the chemical and electrochemical properties of the surface to be probed by measurement of the tip current or potential. Scanning the probe laterally above the surface allows one to generate an activity map, yielding detailed information about local processes, typically with micron scale resolution.

At NPL we have used the remarkable chemical sensitivity of SECM to address problems in industry, such as mapping the activity of model fuel cell catalyst films and membrane electrode assemblies. We are currently developing innovative approaches to catalyst, electrocatalyst and photoelectrochemical screening using related techniques.

Imaging at the Nanoscale

Nanoelectrochemistry is an area at the frontier of materials research. A key challenge in electrochemical imaging therefore is to drive the spatial resolution down to the nanoscale. An elegant approach to doing so is to combine SECM with atomic force microscopy (SECM-AFM) through the fabrication of dual function cantilevers with:

• Nanometre dimensions:
  - High spatial resolution

• Atomic force feedback:
  - Topographical imaging
  - Working distance control

At NPL we are developing innovative probes for SECM-AFM with the aim to undertake novel, nanoscale measurement of chemical and electrochemical activity of nanostructured materials. Target applications include fuel cell electrocatalysis, photoelectrochemical phenomenon and heterogeneous catalysis.

People

• Andy Wain
• William Kylberg

Publications

• Screening of Photoactive Dyes on TiO2 Surfaces Using Scanning Electrochemical Microscopy
  W. Kylberg, A. J. Wain, and F. A. Castro
  Journal of Physical Chemistry C, 116, pp 17384−17392 (2012)
• High-aspect ratio needle probes for combined scanning electrochemical microscopy-Atomic force microscopy
  A. J. Wain, D. Cox, S. Zhou, A. Turnbull
  Electrochemistry Communications, 13, 78 (2011)
• Electrocatalytic activity mapping of model fuel cell catalyst films using scanning electrochemical microscopy
  P. G. Nicholson, S. Zhou, G. Hinds, A. J. Wain, A. Turnbull
  Electrochimica Acta, 54, 4525 (2009)
• Fabrication of Probes for In-situ Mapping of Electrocatalytic Activity at the Nanoscale
  A. J. Wain, D. Cox, S. Zhou, A. Turnbull
  Materials Challenges and Testing for Supply of Energy and Resources (eds. T. Bollinghaus, J. Lexow, T, Kishi, M. Kitagawa, Springer, 2012) pp 129-141

NPL Reports

• Scanning electrochemical microscopy activity mapping of model fuel cell catalyst films
• On the fabrication of model proton exchange membrance fuel cell catalyst films
• Electrochemical scanning probe microscopy - an overview
• Novel focused ion beam-milled probes for combined scanning electrochemical microscopy - atomic force microscopy

Presentations

• SECM for the Characterisation of Surface Activity
  Electrochem 2011, September 2011, Bath University, UK (oral, keynote)
• Electrochemical SPM for Micro- and Nanoscale Characterisation of Electrocatalyst Activity
  ISE 62nd Annual Meeting, September 2011, Niigata, Japan (oral)
• Development of Novel Probes for Combined SECM-AFM
  6th SECM Workshop, October 2010, Fréjus, France (oral)
• Electrochemical Imaging of Novel Fuel Cell Catalyst Films
  ECS 216th Meeting, October 2009, Vienna, Austria (oral)

External Collaborators

Pat Unwin (Warwick University)

Julie MacPherson (Warwick University)

Petra Cameron (Bath University)