Particle-size effect of nanoscale platinum catalysts in oxygen reduction reaction: an electrochemical and 195Pt EC-NMR study

Abstract

Oxygen reduction reaction (ORR) measurements and (195)Pt electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy were combined to study a series of carbon-supported platinum nanoparticle electrocatalysts (Pt/CB) with average diameters in the range of roughly 1-5 nm. ORR rate constants and H(2)O(2) yields evaluated from hydrodynamic voltammograms did not show any particle size dependency. The apparent activation energy of 37 kJ mol(-1), obtained for the ORR rate constant, was identical to that obtained for bulk platinum electrodes. Pt/CB catalysts on Nafion produced only 0.7-1% of H(2)O(2), confirming that the direct four-electron reduction of O(2) to H(2)O is the predominant reaction. NMR spectral features showed characteristic size dependence, and the line shapes were reproduced by using the layer-deconvolution model. Namely, the variations in the NMR spectra with particle size can be explained as due to the combined effect of the layer-by-layer variation of the s-type and d-type local density of states. However, the surface peak position of (195)Pt NMR spectra and the spin-lattice relaxation time of surface platinum atoms showed practically no change with the particle size variation. We conclude that there is a negligible difference in the surface electronic properties of these Pt/CB catalysts due to size variations and therefore, the ORR activities are not affected by the differences in the particle size.

Research and Development of Highly Active and Durable Electrocatalysts Based on Multilateral Analyses of Fuel Cell Reactions

“…39 We have demonstrated that the ORR rate constant (k app , per unit ECA), its activation energy, and P(H 2 O 2 ) in O 2 -saturated 0.1 M HClO 4 were all independent of d Pt from Pt 1.6nm /CB to bulk-Pt at 30 to 50°C, as well as from Pt 2.6nm /CB to bulk-Pt up to 110°C. 40 It was also found that the smallest (Pt 1.6nm ) particles agglomerated at higher temperatures (² 60°C). This result led our research to the second important issue regarding the Pt particle-size effect on the durability.…”

“…Recently, non-fluorinated hydrocarbon (HC) electrolyte membranes have been developed to reduce cost, to elevate the operating temperature, and to avoid environmental pollution due to fluoride on disposal. Specifically, the elevation of operating temperature (² 100°C) leads to a significant cost reduction by increases in the MA values for the ORR 40 of the cathode catalysts and the CO-tolerant HOR of the anode catalysts, 36,55 together with a down-sizing of the heat exchanger (radiator) in FCVs (due to increased ¦T ).…”

“…40 The use of 0.1 M HClO 4 electrolyte solution, which was purified in advance by a conventional preelectrolysis method, 107,108 allowed us to obtain steady-state ORR voltammograms with neither hysteresis nor interference by impurities at such a low sweep rate. Moreover, Pt/CB was uniformly dispersed on a gold substrate electrode at a constant loading of CB support, 5.5 µg cm ¹2 (corresponding to approximately one monolayer of CB particles) and coated with a thin Nafion film (0.1 µm), in order to minimize the O 2 diffusion resistance within the thin catalyst layer.…”

“…[1][2][3][4] For PEFC anode and cathode catalysts, the activity and its degradation have been analyzed by multilateral techniques such as X-ray photoelectron spectroscopy combined with an electrochemical cell (EC-XPS), 2,[5][6][7][8] in situ Fourier-transform infrared spectroscopy (FTIR), [9][10][11][12][13][14][15][16][17][18][19][20][21][22] electrochemical quartz crystal microbalance (EQCM), [23][24][25][26] in situ scanning tunneling microscopy (STM), [27][28][29][30][31] in addition to conventional electrochemical measurements such as rotating disk electrode (RDE), [32][33][34] channel flow electrode (CFE), 21,35,36 and channel flow double electrode (CFDE) methods. [37][38][39][40][41][42] Based on these results, new practical catalysts have been synthesized. [43][44]…”

Silicon nanograss as micro fuel cell gas diffusion layer

“…The reaction on carbon supported Pt is practically H2O specific in acid conditions [124], although the presence of Nafion can slightly increase H2O2 production to a percent most likely as a result of sulfonate interactions [125]. In alkali, a few percent of H2O2…”