Synthesis And Electrocatalytic Performance Of AgPt Alloy Nanocatalysts

Proton exchange membrane fuel cell (PEMFC) is a kind of potentially clean energy conversion device with high efficiency. However, the key factor restricting the industrialization of PEMFC is the high cost of anode catalyst. Currently, precious metal platinum is the most common catalyst for PEMFC. However, high cost, poor activity and stability of platinum have been important factors inhibiting the performance of PEMFC. Regulating chemical composition and adjusting surface structure to improve the utilization of Pt is the current research hotspots of fuel cells.It has been reported that preparation of Pt-based composite alloy catalysts is a feasible strategy. Among transition metal elements, doping of the Ag atoms can effectively ameliorate the electronic structure and geometrical configuration of Pt nanoparticles,which can improve the stability and catalytic activity of the catalysts. In this thesis,using polymer amine with different molecular chain structure as morphology control agent and dispersant, we designed and manufactured AgPt alloy bimetallic catalysts with different morphologies and constitutions by hydrothermal and selective oxidation etching method for methanol and formic acid oxidation.The main contents are as follows:1. The uniform and high-quality AgPt alloy nanooctahedra are synthesized via one-pot hydrothermal method. The catalytic growth of Ag0 atoms on Pt nuclei and selective oxidative etching on the Ag0 atoms contribute to the formation of alloy nanooctahedra. The mass-normalized cyclic voltammograms show the oxidation peak current of methanol on the Pt-Ag alloy nanooctahedra (350.13 mA mgPt-1) is 1.06 times higher than that on the commercial Pt black (172.43 mA mgPt-1). After the chronoamperometric experiments of 3000s, the stable current density of the Pt-Ag alloy nanooctahedra is 0.72 mA cm-2, which is about 3.8 times higher than that of Pt black (0.15 mA cm-2). Pt-Ag alloy nanooctahedra show better activity and stability towards formic acid oxidation than commercial Pt black.2. For direct formic acid fuel cells (DFAFCs),the dehydrogenation pathway is a desired reaction pathway, to suppress the generation of CO intermediate and boost the overall cell efficiency. On the basis of the above work, we present a facile synthesis of porous AgPt bimetallic nanooctahedra with enriched Pt surface (denoted as AgPt@Pt nanooctahedra) by removing superficial Ag atoms of the AgPt alloy nanooctahedra via a selective etching strategy. Under the potential of 0.60 V(vs. RHE), the mass-normalized current density on porous PtAg@Pt nanooctahedra reaches 282.6 mA mg-1, which is ca. 1.7-fold, 3.6-fold and 10.8-fold as large as that on solid PtAg nanooctahedra (162.8 mA mg-1), pure Pt nanooctahedra (77.9 mA mg-1) and Pt black(26.1 mA mg -1). The ratio (Areadehydrogenation pathway / Areaco pathway) of the porous octahedral AgPt@Pt is about 2.77, which is much higher than the value of 1.22 for the solid PtAg nanooctahedra and commercial Pt black (0.31). The smart integration of geometric and electronic effect between Ag and Pt atoms confers a substantial enhancement of desired dehydrogenation pathway for the formic acid oxidation reaction (FAOR).3. We herein demonstrate a facile hydrothermal synthesis of ultrathin AgPt alloy nanowires using amine terminated-poly(N-isopropyl acrylamide) (PNIPAM-NH2) as a structure-directing agent. The initial generation of AgCl precipitates, subsequent formation of AgPt nanoparticles and later oriented attachment account for the formation of ultrathin AgPt alloy nanowires. The electrochemical test shows that the Pt mass-normalized current density of the dehydrogenation way (Peak I) on the AgPt alloy nanowires is around 2.65 times of that on the Pt black catalyst (151.9 mA mg-1 vs. 57.9 mA mg-1).Meanwhile, the ratio (R) of the dehydrogenation way peak (Peak I)area to the dehydration way (Peak II) area of AgPt alloy wavy nanowires is calculated to be 2.55, which is much larger than that of AgPt nanoparticles (1.9) or commmercial Pt black catalyst (1.21).