Three-dimensionally co-stabilized metal catalysts towards oxygen reduction reaction Kun Cheng, Min Jiang, Bei Ye, Ibrahim Saana Amiinu, Xiaobo Liu, Zongkui Kou, Wenqiang Li and Shichun Mu* State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, 430070, China. To whom correspondence should be addressed: *Corresponding author. Tel: +86 27 87651837. E-mail: msc@whut.edu.cn (SC Mu). 1
Table S1 Content of Pt in catalysts, determined by ICP-AES. Sample Pt/C Pt-PFSA/GNS Pt-TiO 2 /GNS Pt-PFSA-TiO 2 /GNS Pt content 19.8% 19.3% 18.8% 19.2% The mineralization procedure for ICP analysis is that, firstly, a certain amount of catalyst powder was annealed at 700-800 at air till the carboneous materials converted into CO 2, and then the Pt element in the residual was resolved with boiled aqua regia, followed by diluted with certain amount of pure water, which can be then sent for ICP test. 2
The reference electrode was calibrated before test, using a method similar like the reported. 1 It is performed in a standard three-electrode system with Pt black electrode as both the working and counter electrodes, and the SCE as the reference electrode, and the electrolyte is saturated with high purity H 2. Linear scanning voltammetry (LSV) is then conducted, and the potential at which the current equal to zero is taken to be the thermodynamic potential (vs. SCE) for the hydrogen electrode reaction. Here, in 0.1 M HClO 4, the zero current point is at -0.309 V, so E (RHE) = E (SCE) + 0.309 V. Fig. S1 Linear scanning voltammetry (LSV) conducted to calibrate the SCE reference electrode with and the SCE as the reference electrode and Pt black electrode as both the working and counter electrodes, The electrolyte are saturated with high purity H 2 and the scan rate is 1 mv s 1. 3
a) d) c) b) e) c) f) Fig. S2 TEM images of Pt-TiO 2 /GNS (a-c) and Pt-PFSA-TiO 2 /GNS (d-f), which show TiO 2 nano-flakes dispersed well on the GNS support for both samples. 4
a) d) g) b) e) h) c) f) i) Fig. S3 (a) Normalized current-time (i-t) curves of 0, 3, 10 and 30 wt.% TiO 2 contained Pt-PFSA-TiO 2 /GNS catalysts by chronoamperometric technique at 0.7 V in 0.1 mol L -1 HClO 4. (b) Polarization curves of ORR for 0, 3, 10 and 30 wt.% TiO 2 contained Pt-PFSA-TiO 2 /GNS catalysts with comparison of mass activity shown in the insets. (c) The change of mass activity and the change of current retained rate during the i-t test above after 6000 seconds for those catalysts. TEM images of Pt-TiO 2 /GNS catalyst with TiO 2 content of 3 (d), 10 (e) and 30 (f) wt.% with enlarged images of the box section shown in g, h and i, respectively. 5
a b c d Fig. S4 (a) Normalized current-time (i-t) curves of Pt/GNS, Pt-TiO 2 /GNS and Pt-PFSA/GNS by chronoamperometric technique at 0.7 V in 0.1 mol L -1 HClO 4. Polarization curves of ORR for Pt/GNS, Pt-TiO 2 /GNS and Pt-PFSA/GNS before and after 6,000 potential cycles with the comparison of mass activity shown in the insets. It was tested at a rotating speed of 1600 rpm in an O 2 -saturated 0.1 mol L -1 HClO 4 solution with a sweep rate of 10 mv/s. 6
Fig. S5 Normalized current-time (i-t) curves by chronoamperometric technique at 0.7 V in 0.1 mol L -1 HClO 4. 7
Fig. S6 CV curves as a function of potential cycling numbers for (b) Pt/C, (c) Pt-PFSA/GNS, (d) Pt-TiO 2 /GNS and (e) Pt-PFSA-TiO 2 /GNS using the ADT method, which are used to calculate the change of ECSA valuse. 8
Figure S7 TEM image of commercial Pt/C. It shows Pt NPs dispersed uniformly on carbon surface and the predominant particle size is 2.0 ~ 4.0 nm. 9
It is performed using chronoamperometry technique. It can be seen that, after a long time of electrochemical oxidation, CV curves of TiO 2 displays a negligible electrochemical oxidation peak. In contrast, CV curves of commercial carbon black shows a strong increment on the peaks in the redox region (marked by dashed rectangle), which corresponds to the formation of surface oxides (hydroquinone quinone redox couple) on the carbon surface. 2 a b Figure S8 CV curves of (a) TiO 2 and (b) commercial carbon black with respect to time of electrochemical oxidation at a constant potential of 1.5 V vs. RHE. 10
a) b) c) d) Fig. S9 TEM images of Pt-PFSA-TiO 2 /GNS after ADT. Reference 1. Li Y, Zhou W, Wang H, et al. An oxygen reduction electrocatalyst based on carbon nanotube-graphene complexes[j]. Nature nanotechnology, 2012, 7(6): 394-400. 2. Kinoshita, K.; Bett, J., Potentiodynamic analysis of surface oxides on carbon blacks. Carbon 1973, 11, 403-411. 11