Development of catalysis and processes for electrochemical energy technologies

• Κύριος συγγραφέας: Shroti, Nivedita
• Γλώσσα: English
• Έκδοση: 2022
• Θέματα: Electrocatalysts; Bimetallic catalysts; Ηλεκτροκαταλύτες; Διμεταλλικοί καταλύτες

The objective of this study is to study new electrocatalyst for high temperature water electrolysis and well as high temperature proton exchange membrane fuel cell. More specifically, to understand and improve the electrochemical interface of anodic electrode in HT electrolysis, as well as optimize the catalyst layer structure for operation under high temperature electrolysis conditions. For that reason the effect of catalyst layer, effect of the catalyst’s substrate and alternative membrane material were investigated on performance of water electrolysis for high temperature application. Initially IrO2 and RuO2 and there different compositions investigated for anodic electrode. Stability of electrocatalyst material were evaluated as anodic material for acid doped TPS® membrane provided by Advent Technologies for high temperature water electrolysis. It was observed that IrxRu1-xO2 gives better performance compare to pure IrO2 but is not stable for high temperature water electrolysis condition. More specifically, under electrolysis conditions in presence of acid, oxidative environment IrOx and RuOx undergoes changes in oxidation state and new formed species that are not stable under electrolysis condition. Pin hole formation is observed for different MEA’s. This can be attributed to catalyst and membrane interaction in presence of acid at high temperature. RuO2 is converting to RuO4, newly formed species may be reacting with pyridine present in membrane making unstable interface. A new concept double layer electrolyte introduce where two membranes, acid doped and solid acid based works as electrolyte for water electrolysis system. By introducing double layer of membranes extra resistance added to system, which doesn’t contribute towards better performance for water electrolysis. For fuel cell Pt based catalyst till now gives better performance. In order to reduce cost of catalyst and to enhance catalytic activity for fuel cell system Pt alloyed catalyst synthesized and tested for high temperature fuel cell. Alloyed catalyst attributed to structure (change in Pt-Pt bond distance) as well as changing Pt d-electron valance. In order to increase the performance and increase the three phase boundary, a newly synthesized electrocatalyst was evaluated, and compared to the commercial 30wt%Pt/C. The new catalyst is based on Pt alloy with Cobalt (Co) on oxidized carbon nanotubes, ox.MWCNT and pyridine functionalized carbon nanotubes (ox.MWCNT)-Py more specifically Pt3Co/f-MWCNT. The aim of studied catalyst is to achieve fine dispersion, quantitative deposition and alloy formation on functional carbon nanotubes. CL employing the new catalyst were formulated and tested at the cathode. Initially different reaction conditions were studied for deposition of Pt and Co on ox.MWCNT as well as for (ox.MWCNT)-Py. It was found that the better Pt deposition and dispersion found on both substrate in acidic pH, while Co deposition takes place in basic pH. To deposits Pt-Co as alloy different parameters varied during reaction like pH, temperature etc. It was found that basic pH conditions favours Pt-Co alloy formation but have negative influence on dispersion. By varying reaction time at basic pH favours alloy formation as well as good dispersion. Prepared catalyst tested in-situ for fuel cell performance in comparison with commercial Pt/C, also optimization of the in-situ ECSA evaluation procedure at the using CO as a probe molecule, without damaging the catalyst distribution was studied. Effect of H3PO4, temperature and different CO stripping methods were studied for ECSA measurements. Low PA amounts in the catalyst layer (<2gPA/gPt) corresponds to low ESCA, while (>2 gPA/gPt) have poisoning effect on catalyst layer which also effect ECSA measurement. ECSA measurements were carried out for Pt3CO/functionalize MWCNT in comparison with commercial Pt/C catalyst. It was found that Pt3CO alloyed catalyst have similar performance compare to Pt/C and Pt/functionalize MWCNT in terms of I-V performance but shows less ECSA values at all studied conditions that may attributed to presence of Co on surface.