Logotyp: till Uppsala universitets webbplats

As a consequence of the transition from fossil fuels to renewable biofuels and in particular biodiesel, glycerol has shifted from being a commodity chemical to a by-product. Currently, glycerol is often either discarded or further oxidised into value-added 3-carbon products. Electrochemical oxidation also offers the potential to produce clean hydrogen gas. The main challenge from both the industrial and scientific viewpoints is in understanding the reaction mechanisms in order to develop effective and selective catalysts.

This thesis focuses on the development, characterization, and optimization of Pt- (and Pd-) based catalysts for the glycerol electrooxidation reaction (GEOR), with a particular emphasis on the effectiveness, the reaction mechanism, and the selectivity of the reaction. In the first part, the enhancement of the catalytic surface area of Pt is achieved through the use of different porogens where Pt is electrodeposited to fabricate mesoporous catalysts with linear, hierarchical or cubic pore structures. The mass diffusion of the reactant and products in the pores was the critical step where hierarchical pores allowed for an increased electrochemically available surface area without hindering out the diffusion of oxidation products. To tackle some of the drawbacks of pure platinum and to increase the catalytic activity, a Cu-Pt alloy with varying relative compositions was studied. Incorporating Cu into Pt improves the catalytic performance by straining and introduction of vacancies into the valence band of Pt atoms. An enhanced current density, catalytic activity, and stability enhanced activity was found close to the composition Cu₃Pt, which was also theoretically predicted. The composition of these alloys also had an influence on the product selectivity where the composition and potential-dependent mechanism was matched with DFT calculations. The performance and stability of the Cu-Pt catalysts was studied under operando conditions using grazing incidence diffraction with synchrotron radiation, for which a dual-chamber flow cell was specifically designed to mimic normal laboratory conditions. Analysis of the angle- and time-dependent data provided insights into the real-time structural dynamics as function of probing depth as well as the degradation of the electrocatalysts particularly under the first few “activation” cycles but also upon prolonged cycling. The results show that the activation of catalysts with an excess copper resulted unequivocally on the surface leaching of copper species and consequent surface dealloying towards Pt rich surface compositions. The last part of the thesis focused on the characterization of Pd_0.9Ni_0.1 and Pd electrocatalyst electrodeposited on a Ni rotating disk electrode for the GEOR to understand the structural and morphological changes of PdNi catalysts after electrolysis.

Experimental and theoretical results show that Pt- (and Pd-) based alloys are promising catalysts for the industrial GEOR although there is still work to do.