关键词: 碳纸, 铂纳米粒子, 高指数晶面, 电沉积, 直接甲酸燃料电池

Abstract:

Direct formic acid fuel fuels (DFAFCs) are promising energy source for portable electronic devices. Palladium (Pd) is more active than platinum (Pt) for the formic acid electrooxidation. However, the stability of Pd is much poorer than that of Pt. Unfortunately, the ultra-low natural abundance of the Pt makes it extremely expensive and limits its application as a fuel cell catalyst. Boosting both the activity and stability of Pt nanoparticles to enhance their efficiency is urgent. As previous works illustrated, nanoparticles enclosed with high-index facets usually bare a higher activity toward fuel cell related reactions than those nanoparticles with low-index facet. We adopted in this study the square-wave potential (SWP) method to electrochemically synthesize high-index faceted Pt nanoparticles on carbon paper support (HIF-Pt/C-paper). By carefully tuning the deposition conditions such as upper potential limit (EU) and lower potential limit (EL) of the SWP, we successfully synthesized the tetrahexahedral Pt nanoparticles and trapezohedral Pt nanoparticles with different sizes ranging from 40 ~ 200 nm. Furthermore, when the electrodeposition was carried out on the XC-72 modified carbon paper, the high-index faceted Pt nanoparticles of ~ 10 nm in size with high density can be synthesize by delicately adjusting the electrodeposition conditions, the Pt loading on this electrode was determined to be 0.069 mg•cm^-2 by ICP-MS. Using the HIF-Pt/C-paper as the anode of DFAFCs and 3 mol•L^-1 formic acid as the fuel, the maximum power density of single cell was 10.6 mW•cm^-2 under 30 °C, and 95% of the cell voltage had been maintained after 50 h test with current density equal to 20 mA•cm^-2, which demonstrates a reasonable stability under the test condition. The Pt mass normalized maximum power density was 153.5 mW•mg-1Pt, which is 8.4 times as high as that of the DFAFCs using commercial 60% (by mass) Pt/C as the anode catalyst (Pt loading of 1 mg•cm^-2). The enhanced mass activity of the as-synthesized HIF-Pt/C-paper is mainly attributed to the ultralow loading of the Pt and the unique distribution of Pt nanoparticles, and to the electrodeposition method that generates the Pt nanoparticles mainly locating at the boundary site between the carbon support and the Nafion membrane.

Key words: carbon paper, Pt nanoparticles, high-index facet, electrodeposition, Direct formic acid fuel cells.