New routes towards efficient electrocatalyst development
Electrocatalysis is the linchpin of several modern electrochemical applications ranging from energy storage devices over electroanalytical sensors to organic electrosynthesis. Over the past decades electrocatalysis has grown to be a full-fledged part of heterogeneous catalysis, supported by state-of-the-art theoretical insights. Despite its vast possibilities, economical profitability still impedes the widespread implementation of electrocatalysis in several areas. A major topic within modern electrocatalyst research therefore is the tailoring of nanostructures to enhance the surface specific activity and reduce the mass amount of precious metals. Some of the most attractive strategies include directing the particle size, tuning metal support interactions, alloying and controlling catalyst morphology. A general model based activity prediction of catalytic materials is not yet possible to date and might not lie within reach. Certainly more complex catalyst morphologies are difficult to describe theoretically. Future advances in electrocatalysis will thus require a contribution of both theoretical models and experimental techniques.
This work focuses on the latter and aims to develop an innovative measurement approach to contribute to the elucidation of a variety of electrocatalytic activity enhancement strategies. To reach this ambition, a well-considered combination of measurement techniques is applied. Atomic resolution microscopic and spectroscopic analyses are intertwined with macroscopic electrochemical techniques. The proposed approach is validated in two relevant electrocatalytic case-studies: polymer electrolyte membrane fuel cells and organic electrosynthesis. First, the oxygen reduction reaction (ORR) activity of platinum based electrocatalysts is investigated in relation to their composition and morphology. A practical two-step galvanic displacement process is applied to obtain both Cu@Pt and Ni@Pt core-shell nanoparticles relevant for polymer electrolyte membrane fuel cells. Also highly porous, unsupported Pt nanostructures are synthesized using a double pulse electrodeposition procedure. The morphology of the structures is detailed using three dimensional reconstructions gathered from state-of-the-art electron tomography. The high amount of control able to exert on the particle morphology is put to use to augment the ORR activity of these Pt structures. Second, electrochemical hydrogen peroxide formation is studied as step-up to organic electrosynthesis. The selectivity of the oxygen reduction reaction is conducted towards the two-electron mechanism by using a metal free nitrogen doped mesoporous ordered catalyst. Also the organic halide reduction is investigated through the benzyl bromide model reaction. An electrodeposition approach is applied to direct the nanoparticle diameter and study its activity enhancement.
In general, a variety of catalyst synthesis technique are applied successfully in this work with the final goal being to induce activity enhancement effects. Applying acase specific measurement approach ensured adequate catalyst activity augmentation.