Effect of potassium on the mechanisms of biomass pyrolysis studied using complementary analytical techniques

Complementary analytical methods have been used to study the effect of potassium on the pyrolysis mechanisms of cellulose and lignocellulosic biomasses. Thermogravimetry, calorimetry, high-temperature 1H NMR spectroscopy (in situ and real-time analysis of the fluid phase formed during pyrolysis), and water extraction of quenched char followed by size-exclusion chromatography coupled with mass spectrometry have been combined. Potassium impregnated in cellulose suppresses the formation of anhydrosugars, reduces the formation of mobile protons, and gives rise to a mainly exothermic signal. The evolution of mobile protons formed from K-impregnated cellulose has a very similar pattern to the evolution of the mass loss rate. This methodology has been also applied to analyze miscanthus, demineralized miscanthus, miscanthus re-impregnated with potassium after demineralization, raw oak, and Douglas fir. Hydrogen mobility and transfer are of high importance in the mechanisms of biomass pyrolysis

The effect of ruthenium crossover in polymer electrolyte fuel cells operating with platinum-ruthenium anode

Verkefnið er unnið í tengslum við Háskóla Íslands og Háskólann á AkureyriProton exchange membrane fuel cells with PtRu anode catalyst and Pt cathode suffer from severe performance degradation due to ruthenium dissolution from the anode, migration through Nafion® membrane, and deposition on the surface of cathode catalyst where it inhibits ORR. A detailed analysis of ruthenium crossover mechanism for a 5 cm2 active area direct methanol fuel cell was performed to quantify the contamination rate and degree starting from contamination during manufacturing process, through initial humidification and ending with severe degradation due to operation. The change of ruthenium content on the cathode was defined with the use of CO stripping voltammetry and X-ray fluorescence. The fuel cell performance loss due to severe cathode contamination with ruthenium was measured to be 0.1 A/cm2 at 0.5 V cell voltage for methanol-air operating mode. The air cathode performance loss was determined to be 80 mV. The ORR kinetics degradation was investigated by using platinum RDE contaminated with ruthenium via spontaneous deposition from 1.0 mM RuCl3 in 0.1M HClO4. The half-wave potential showed a negative shift by 20 mV just after 10 seconds deposition time. The CO stripping results obtained from RDE experiments show great similarity to results obtained from fuel cell tests. Initial anode cleaning was found out to greatly decrease the ruthenium contamination rate and thus enhance DMFC durability.The Master Thesis was supported by a grant from Iceland, Liechtenstein and Norway through the EEA Financial Mechanism - Project PL046