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UBC Theses and Dissertations

Anode catalyst layer engineering for the direct formic acid fuel cell Sanii, Sanam


Direct formic acid fuel cells (DFAFC) are promising alternatives to hydrogen proton exchange membrane fuel cells for microelectronic applications. Compared to direct methanol fuel cell (DMFC), the main advantages of direct formic acid fuel cell (DFAFC) are higher theoretical open circuit voltage (1.45 V at 298 K), lower fuel cross over towards cathode and reasonable power densities at room temperature that make DFAFCs a viable alternative for micropower applications. The operation of DFAFCs on Pd-based catalysts at ambient temperature showed lower fuel permeation from anode to cathode that resulted in better fuel utilization when running on high formic acid concentrations (~10M). However, Pd suffers an unacceptable loss of performance with time that decreases the cell power density by about 50% in a few hours. The aim of the present work is to create an extended reaction zone anode structure to improve the utilization of the catalyst and to modify the electrode surface characteristics in order to reduce performance losses. The novel catalyst deposition technique involved electroless (chemical) deposition of Pd particles directly onto the carbon paper substrate (AvCarbTM P50) in the presence of Nafion® solution. It was found that the use of 4.66 g L⁻¹ of pure Nafion® as an additive to the electroless bath and Shipley pre-treatment resulted in 1.6 mg cm⁻² and 0.07 mg cm⁻² Pd and Sn mass loadings respectively with Pd average particle size of 0.45 to 0.55 μm. When pre-treating in nitric acid solution, the surface coverage was found to be uniform with dense particulate-like structure. The surface nitric acid pre-treatment method in conjunction with 2.46 g L⁻¹ Nafion® additive in the electroless solution were resulted in 4.5 mg cm⁻² Pd mass loading on AvCarbTM P50 and enhanced electrochemical performance at current densities larger than 500 A m⁻² at 333 K . Comparing the Pd/C and PdSn/C performances in DFAFC tests, the Pd/C anode with higher Pd mass loading (4.5 mg cm⁻²) and OCV stayed fairly stable on ~ 0.55 V up to 3.5 hours of constant current draw(100 A m⁻² at 333 K).

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