Design and Fabrication of Pt-Au Nanocatalyst with High Performance

Abstract

Design and Fabrication of Pt-Au Nanocatalyst with High Performance Fanpeng Kong[a], Chunyu Du[a]*, Jinyu Ye[b], Lei Du[a], Guangyu Chen[a], Geping Yin[a]* [a] MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, Harbin Institute of Technology. Email: cydu@hit.edu.cn, yingphit@hit.edu.cn. [b] State Key Lab of Physical Chemistry of Solid Surfaces, Xiamen University. : Direct formic acid fuel cell (DFAFC), as a promising power source, can greatly improve energy conversion efficiency of small organic molecules and dramatically reduce the environment pollution.[1-2] Pt is a key catalytic component at both anode and cathode in DFAFC. However, the scarcity and high cost of Pt require the design and fabrication of Pt-based nanostructure with high performance and reduced usage of Pt. Here, we found that the formic acid oxidation (FAO) activity of Pt and Au nanoparticles supported on carbon (Pt1-Au1/C) increases more than 40 fold relative to that of Pt/C. Generally, ensemble and electronic effects are proposed to explain the enhanced FAO performance.[3-4] However, we have to exclude the ensemble effect since there is no Au adatoms on Pt. From X-ray photoelectron spectroscopy (XPS) patterns, the binding energy of Pt4f and Au4f peak in Pt1-Au1/C shifts positively and negatively compared to that in Pt/C and Au/C, respectively, indicating that Au modifies the electronic structure of adjacent Pt. This electronic modification is further confirmed by the higher onset potential of CO oxidation on Pt1-Au1/C than that on Pt/C in the CO stripping voltammetry, demonstrating stronger binding of CO on Pt1-Au1/C. Unfortunately, the pathway of formic acid oxidation on Pt-Au system is ambiguous because Pt and Au are closely coupled together, so that the in-situ information on the respective role of Au and Pt is difficult to obtain. To this end, a novel selective surface engineering method is proposed to probe the main active sites. We separately employed CO adsorption and selective under potential deposition to engineer respectively Pt and Au surfaces. However, the activity of Pt1-Au1/C with engineered surfaces is obviously lower than that of Pt1-Au1/C. Therefore, the coexistence of Pt and Au, rather than electronic effect, is indispensable for the high FAO activity. In-situ FTIR measurement of Pt/C, Au/C and Pt1-Au1/C is carried out to probe more detailed molecular information. Formate on Pt1-Au1/C is more than that on Pt/C and Au/C, which should result from the coverage of CO on Au, instead of Pt, at low potentials. Since Pt has higher affinity to H than Au, the increased formate is attributed to the accelerated rupture of O-H bond in formic acid on Au by Pt. However, formate is not an active intermediate but a spectator species, so that it cannot account for the increased activity. Recently, it is proved that –COOH is the active species during FAO. In view of strong affinity between Pt and H, we can rationally assume that Pt ruptures the C-H bond of formic acid on Au to produce –COOH, which decomposes to CO2 quickly, so that Pt1-Au1/C possesses a remarkable FAO activity. Reference: J. V. Perales-Rondon, A. Ferre-Vilaplana, J. M. Feliu, E. Herrero, J. Am. Chem. Soc. 2014, 136, 13110-13113.M. E. Scofield, C. Koenigsmann, L. Wang, H. Liu, S. S. Wong, Energy Environ. Sci. 2015, 8, 350-363.Q. S. Chen, Z. Y. Zhou, F. J. Vidal-Iglesias, J. Solla-Gullon, J. M. Feliu, S. G. Sun, J. Am. Chem. Soc. 2011, 133, 12930-12933.G. R. Zhang, D. Zhao, Y. Y. Feng, B. S. Zhang, D. S. Su, G. Liu, B. Q. Xu, ACS Nano 2012, 6, 2226-2236.