UBC Theses and Dissertations
Colloidal electrodesposition of Pt-Ru and Pd nanostructires on three-dimensional substrates : application for direct methanol and direct formic acid fuel cell anodes Cheng, Tsz Hang Tommy
Direct liquid fuel cells (DLFC’s) including the direct methanol (DMFC) and formic acid systems (DFAFC) are promising alternatives to hydrogen fuel cells. However, DLFC’s are challenged by slow anodic kinetics, fuel crossover, and CO₂ disengagement. In the present work, new colloidal catalyst preparation methods were studied with the aim to electrodeposit Pt-Ru and Pd nanoparticles onto three-dimensional (3-D) substrates: reticulated vitreous carbon, graphite felt (GF), and titanium mesh. The electrodes were investigated as 3-D anodes to mitigate the above-mentioned issues to improve power output, while reducing the catalyst load. The novel catalyst preparation technique involved electrodeposition from various colloidal media including Triton X-100 and Triton X-102-based microemulsion and micellar solutions. Compared to conventional aqueous-based media, using colloidal media resulted in catalysts with more desirable Pt-Ru atomic ratio for CH₃OH oxidation and higher specific surface area. In the absence of surfactants, large catalyst particles (>500nm) were deposited on mostly the exterior surfaces of the 3-D substrates. Employing colloidal media led to more uniform deposition of nanoparticles (5—40nm, depending on conditions) throughout the substrate thickness. In DMFC experiments at 333K with 1M CH₃OH and 0.5M H₂S0₄, the Pt-Ru/GF anode (10g m−²) generated a peak power density of 741W m−² compared to 703W m−² obtained with a commercial catalyst-coated membrane (CCM) with four-times higher Pt- Ru load. In DFAFC experiments at 333K with 1M HCOOH and 0.5M H₂S0₄,the peak power density using the Pt-Ru/GF anode reached 860W m−², compared to 526W m−² with CCM (Pt-Ru load: 10g m−²). However, increasing the HCOOH concentration to 3 and 10M led to lower protonic conductivity and resulted in lower peak power density of 727 and 468W m−², respectively. The electrodeposition of Pd on GF was investigated for a comparative study with Pt-Ru/GF for HCOOH electro-oxidation. Pd/GF was found to have better HCOOH oxidation kinetics and poorer stability than Pt-Ru/GF. In DFAFC experiments at 333K with 1M HCOOH and 0.5M H₂S0₄, the peak power density using Pd/GF anode (57g m−²) reached 852W m−², compared to 392W m−² with 40g m−² commercial Pd CCM.
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