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Advanced electrochemical reforming of methanol for hydrogen production

University of British Columbia

The issue of efficient, low-cost, sustainable hydrogen (H₂) production is one of the barriers to the adoption of a H₂ economy. In this thesis, the electrochemical production of H₂ from liquid methanol (CH₃OH) in acidic aqueous media was studied in a proton exchange membrane (PEM) electrolyser in the static mode at low temperatures. A baseline study showing the influence of CH₃OH concentration, catalyst, catalyst support, operating temperature and operating mode was established. A theoretical thermodynamic analysis of the system was carried out as a function of temperature, and the limiting current densities, kinetic parameters, including the Tafel slopes and current exchange density, and apparent activation energies were determined. The effect of electrochemical promotion (EP) was investigated to see if it can increase the efficiency and performance of H₂ production through electrochemical processes. The electrochemical promotion of electrocatalysis (EPOE) was investigated by carrying out the electrolysis in triode and tetrode operation. It was shown to improve the PEM electrolysis in the galvanostatic and potentiostatic modes. A decrease in electrolysis voltage or an increase in electrolysis current proportional to the current or potential imposed in the auxiliary circuit was observed when the auxiliary current or potential was opposite to the electrolyser circuit current or potential. The effect was observed using catalytic and non-catalytic non-precious electrolyser electrode materials. It was postulated that triode and tetrode operation enhanced the electro-oxidation rate through electrochemical pumping and spillover of protons. With this novel electrolysis configuration, electrolysis cost reduction may be achieved through the use of non-precious electrolyser anode materials and/or improving electrolyser performance. The electrochemical promotion of catalysis (EPOC) was also investigated for the catalytic reforming of CH₃OH at low temperature with Pt-Ru/C and Pt-Ru/TiO₂. The synthesized Pt-Ru/TiO₂ was characterized physico-chemically and electrochemically. Powder catalytic CH₃OH reforming tests showed that both catalysts can be used to generate H₂. EPOC experiments were conducted on gas diffusion electrodes (GDEs) in galvanostatic control. Under the experimental conditions, only supplying H⁺ to the catalyst working electrode surface resulted only in a Faradaic enhancement of the catalytic activity for the low temperature reforming of CH₃OH, which appears to be a purely electrophilic behaviour.

Text

2012-01-03

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/39857

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/