Active Site Engineering in Electrocatalysis

The overall goal of this thesis has been to design better catalysts for electrochemical reactions through a fundamental understanding of the materials at atomic scale. This has been achieved by combining electrochemical measurements with a variety of characterization techniques, often in ultra high vacuum, as well as theory calculations.

The thesis falls in three different parts: firstly, study of model systems for oxygen reduction to water; secondly, oxygen reduction to hydrogen peroxide on both model systems and commercially relevant nanoparticles and thirdly CO2 and CO electroreduction studies on nanostructured electrodes.• Oxygen reduction to water has been carried out on Pt-rare earth alloys, which outperformed the activity of Pt by as much as a factor of five while showing promising stability.

The increase in activity can be attributed to compressive strain of the Pt overlayer formed under reaction conditions, which is ultimately controlled by the crystal structure of the underlying alloy.• Oxygen reduction to hydrogen peroxide has been investigated on single site catalysts, mainly alloys of noble metals with Hg.

This resulted in a very special structure with isolated atoms of Pt or Pd surrounded by Hg, which greatly enhanced selectivity to H2O2 during oxygen reduction. Compared to state-of-theart Au-based catalysts, Pt-Hg and Pd-Hg alloys present over 20 and 100 times increase in mass activity respectively.

It was proven that activity for this reaction is controlled by the binding energy of the sole reaction intermediate. • CO2 and CO electroreduction studies have attempted to understand the unprecedented activity of oxide-derived Cu recently reported in the literature. Temperature programmed desorption measurements reveal very strong CO binding at these surfaces, inexistent in other forms of Cu.

The presence of strong CO binding sites correlates well with electrochemical activity, which paves the way for the rational development of even better electrocatalysts.