Supporting Information for

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1 Supporting Information for Can Boron and Nitrogen Codoping Improve Oxygen Reduction Reaction Activity of Carbon Nanotubes? ** Yu Zhao, Lijun Yang*,, Sheng Chen, Xizhang Wang, Yanwen Ma, Qiang Wu, Yufei Jiang, Weijin Qian, and Zheng Hu*, Key Laboratory of Mesoscopic Chemistry of MOE and Jiangsu Provincial Lab for Nanotechnology, Institute of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, , Nanjing, P. R. China Jiangsu Key Lab for Organic Electronics and Information Displays, Institute of Advanced Materials, Nanjing University of Posts and Telecommunications, , Nanjing, P. R. China S. No. Content S1 Experimental section S2 TEM images of the products S3 BET measurements for B 3 CNTs-NH 3 and B 3 CNTs-BA samples S4 XPS characterizations on the products S5 Control experiments S6 S7 S8 Stability tests for B 3 CNTs-NH 3 Electron transfer number determination for B 3 CNTs-NH 3 Natural bond orbital (NBO) analysis for the bonded B&N codoped CNT(5,5) References S1

2 S1 Experimental Section B x CNTs-BA (x=1, 2, 3) were prepared by CVD method, and B and N were doped into the CNTs simultaneously. Briefly, a mixture solution of triphenylborane (TPB, as B source), benzylamine (BA, as N source, 2.0 ml), and ferrocene (0.20 g, as catalyst) was introduced into a tubular furnace by an injection pump and carried to the reaction zone (850 ) by flowing Ar of 1400 sccm for 20 min. The TPB concentration in the solution was 0.05, 0.10 and 0.20 g ml -1 for B 1 CNTs-BA, B 2 CNTs-BA and B 3 CNTs-BA, respectively. The products were collected after the reactor cooled down to room temperature under Ar ambient. NCNTs-BA was synthesized by the similar process without the addition of TPB. In this route, TPB (a Lewis acid) could be complexed by BA (a Lewis base) with a stable B-N bonding configuration (see equation I below), [S1] which favors forming the bonded B and N in the final product. (equation I) B x CNTs-NH 3 (x=1, 2, 3) were obtained by post-treating the pre-synthesized B-doped CNTs (BCNTs), and B and N were doped into the CNTs sequentially. Specifically, the BCNTs with different B contents and the pristine CNTs were first synthesized by CVD method using the mixture solution of TPB (as B source), benzene and ferrocene as precursor and catalyst, and the preparation details were reported in our previous paper. [S2] And then the BCNTs were treated in NH 3 gas flow (99 %, 10 sccm) at 400 for 3 h to dope N. To obtain CNTs-NH 3, the CNTs was firstly treated by HNO 3 in 85 for 3 h for activation (otherwise little N could be doped into CNTs [S3] ) followed by the NH 3 treatment. The exposed Fe residue in the products was removed by HCl solution (1:1) at 85 for 6 h. In this route, i.e. by NH 3 post-treatment, the N dopant usually occupies the defective sites, [S3] hence the pre-formed B-doping configuration could be preserved, which favors forming the separated B and N in the final product. The products were characterized by transmission electron microscopy (TEM) (JEM2010 at 200 kv), XPS (VG ESCALAB MKII), surface area and porosimetry analyzer (Micromeritics ASAP 2010) and electrochemical workstation (CHI 760C). The electrochemical measurements including CV, RDE and RRDE voltammetries were carried out at 25, and the saturated calomel electrode (SCE) and platinum wire served as reference and counter electrodes, respectively. The RDE and RRDE voltammetry experiments were performed on a MSR electrode rotator (Pine Instrument Co.). CV and RDE curves were collected with a glassy carbon (GC) electrode (5 mm diameter), while RRDE curves using a GC disk electrode (5 mm diameter) surrounded by a Pt ring (6.5 mm inside diameter). The GC electrode was modified as following. Simply, 1 mg sample was dispersed into 1 ml mixture of water, ethanol and Nafion (DuPont, 5 wt%) with the volume ratio of 3.85 : 1 : 0.15 by ultrasonication, and a catalyst ink of 1.0 mg ml -1 was obtained. Then 20 μl of this ink was dropped onto the GC disk intermittently and dried thoroughly in air for 12 h. ORR evaluation was performed in 1 mol L -1 NaOH electrolyte saturated and protected by bubbling O 2 with a flow of 30 sccm. For comparison, commercial Pt/C catalyst with Pt loading of 20 wt% (Johnson Matthey) was also used in the RDE electrochemical test. The steady-state chronoamperometric response was tested at the polarizing potential of -0.4 V in the O 2 -saturated electrolyte, and 10 % (v/v) CO or 2 % (V/V) methanol was introduced into the electrolyte at 600 or 1200 s to examine the CO poisoning and methanol crossover, respectively. Taking account of the requirement of conductivity for electrocatalysts, theoretical calculations were carried out for the metallic armchair CNT(5,5) with the length of 5.5 unit cells. A B-N pair was S2

3 placed at the center of the CNT(5,5) to model the bonded case. Gaussian09 package [S4] was adopted to execute the calculations for the spin multiplicity corresponding to the lowest energy state. The geometrical optimizations were performed using the unrestricted DFT method with Becke s hybrid three parameter nonlocal exchange functional combined with the Lee-Yang-Parr gradient corrected correlation functional (B3LYP). [S5] The 6-31G (d,p) basis set was employed for all the elements. NBO [S6, S7] charge analysis was done at the same theoretical level with NBO 3.1 embedded in Gaussian 09. For the bonded B&N codoped CNT(5,5) without O 2 adsorption at the spin singlet state, the restricted DFT method was adopted in the geometrical optimization and NBO bond analysis to eliminate spin contamination. S2 TEM images of the products Figure S1. Typical TEM images. a) B 3 CNTs-BA; b) B 2 CNTs-BA; c) B 1 CNTs-BA; d) NCNTs-BA; e) B 3 CNTs-NH 3 ; f) B 2 CNTs-NH 3 ; g) B 1 CNTs-NH 3 ; h) CNTs-NH 3. The Fe residue encapsulated in the nanotubes survived after the HCl treatment as marked by the arrows. Apparent morphological differences are observed between B x CNTs-BA and B x CNTs-NH 3 (x=1, 2, 3). B x CNTs-BA (x=1, 2, 3) from direct CVD synthesis present the straight and bamboo-like structures (Fig.S1a-c), i.e. the typical structures of the N-doped CNTs from CVD growth with benzylamine/ferrocene as precursor and catalyst. [S8] The B x CNTs-NH 3 (x=1, 2, 3) from NH 3 post-treatment route show twisted tubular structures with many knots similar to the case for B x CNTs (Fig.S1e-g), [S2] since the NH 3 post-treatment could introduce N dopant but couldn t change the morphology of B x CNTs. The morphological discrepancy suggests the different microstructures of these two kinds of codoped CNTs. Even after long time (6 hours) HCl treatment, there is still a little survival Fe encapsulated inside the nanotubes as arrowed in Fig. S1f,h. The contribution of the survival Fe to the ORR performance is negligible in comparison with that of the metal-free part, which was thoroughly evaluated in our previous study. [S2] S3

4 S3 BET measurements for B 3 CNTs-NH 3 and B 3 CNTs-BA samples Figure S2. N 2 adsorption/desorption isotherm plot for B 3 CNTs-NH 3 and B 3 CNTs-BA. The specific surface area (SSA) was measured with N 2 as absorbate at 77 K for the B 3 CNTs-NH 3 and B 3 CNTs-BA samples, which present the best and the worst ORR performances in all the codoped CNTs in this study. Before measurement, the sample was degassed at 150 C for 8 h. SSA was obtained by the Brunauer Emmett Teller (BET) equation. N 2 adsorption/desorption isotherm plots are shown in Fig. S2. The SSA was measured to be 83.5 m 2 /g and m 2 /g for B 3 CNTs-NH 3 and B 3 CNTs-BA, respectively. This means that the SSA of B 3 CNTs-NH 3 with the best ORR activity is on the same level as (actually slightly smaller than) that of B 3 CNTs-BA with the worst ORR activity. Hence, the ORR performance of the B&N codoped CNTs is dominated by the doping microstructures rather than SSA or morphology. S4

5 S4 XPS characterizations on the products a) B 3 CNTs-NH 3 Intensity (a.u.) B 2 CNTs-NH 3 B 1 CNTs-NH 3 CNTs-NH Binding Energy (ev) b) B 3 CNTs-BA B 2 CNTs-BA Intensity (a.u.) B 1 CNTs-BA NCNTs-BA Binding Energy (ev) Figure S3. Full XPS spectra. a) B x CNTs-NH 3 (x=1, 2, 3) and CNTs-NH 3 ; b) B x CNTs-BA (x=1, 2, 3) and NCNTs-BA. XPS survey spectra indicate the presence of B and N elements in both B x CNTs-NH 3 and B x CNTs-BA (x=1, 2, 3). The contents for all the samples from XPS are summarized in Table S1. Note: The B-doping into CNTs will introduce the defects leading to the twisted tubular structures, [S2] which facilitate the N incorporation by the NH 3 post treatment route. Thus the N content increases with the B content for the B x CNTs-NH 3 samples in the order of B 1 CNT-NH 3, B 2 CNT-NH 3, B 3 CNT-NH 3. S5

6 Table S1. The atomic concentrations (at%) from XPS for all the samples in this study Sample B 3 CNTs-NH 3 B 2 CNTs-NH 3 B 1 CNTs-NH 3 B 3 CNTs-BA B 2 CNTs-BA B 1 CNTs-BA NCNTs-BA CNTs-NH 3 B N O C a) c) b) Figure S4. XPS subspectra for B x CNTs-NH 3 (x=1, 2, 3) and CNTs-NH 3 prepared by post NH 3 treatment. a) B 1s; b) N 1s. Note: B 1s spectra for B x CNTs (x=1, 2, 3) taken from Ref. S2 (i.e., Ref. 21 in the manuscript) are also presented here as c) for convenient visual comparison with a). S6

7 It is seen that B 1s spectra for B x CNTs-NH 3 (x=1, 2, 3) in Fig. S4a are highly similar to the corresponding ones for B x CNTs (x=1, 2, 3) in Fig. S4c. This similarity suggests that the NH 3 post treatment doesn t significantly change the B doping configuration, and the later doped N atoms mainly bond with C. The B 1s spectra are comprised of two regions of and ev, mainly corresponding to the characteristic signals of B-C and O-B-C species. [S2,S9] The B 1s spectrum for B 3 CNTs-NH 3 could be deconvoluted into five peaks with binding energies of 186.6, 187.6, 189.5, and ev. The former three peaks are ascribed to B cluster, B 4 C, and BC 3, while the latter two to the oxide species of BC 2 O, and BCO 2. [S2,S10,S11] The N 1s spectrum for B 3 CNTs-NH 3 is comprised of the typical pyridinic and pyrrolic N species peaked at and ev respectively, with little quaternary N at ev, [S3] which also suggests the later doped N atoms mainly bond with C defective sites. The results indicate that the B and N dopants are separated apart in B x CNTs-NH 3. a) b) N-B-C Figure S5. XPS subspectra for B x CNTs-BA (x=1, 2, 3) and NCNTs-BA prepared by in situ growth route. a) B 1s; b) N 1s. For B x CNTs-BA (x=1, 2, 3) and NCNTs-BA, the B content arises from 0 to 1.68 at% while the nitrogen contents are at the same level (1.20~1.57 at%). As shown in Fig. S5, the peak intensity of N 1s at ev increases gradually with increasing B content. This clearly indicates that the N 1s peak at ev and the major B 1s peak at ev can be attributed to the N-B-C moieties. The minor peak of B 1s at ev corresponds to BCO 2, [S2,S10,S11] and the N 1s peaks at and ev are assigned to pyridinic and quaternary nitrogen respectively. [S3] The results indicate that the B dopant is mainly bonded with N in B x CNTs-BA. Note 1: Different N doping methods result in different N existing forms. For NCNTs-BA, N mainly exists as quaternary N peaked at ev with a little pyridinic N at ev (Fig. S5b). For S7

8 CNTs-NH 3, N mainly exists as pyridinic and pyrrolic N species peaked at and ev (Fig. S4b). Hence their XPS spectra are quite different. The different N species in the N-doped CNTs have different ORR performances. It was reported that quaternary N presented better ORR activities than pyridinic N [S12,S13]. The more N content in NCNTs-BA (1.20 at%) than CNTs-NH 3 (0.92 at%) is also a influence factor. Note 2: For the group of B x CNTs-BA (x=1,2,3), the oxygen contents are very close (3.40, 3.64 and 3.83 at.%, respectively). Their contributions to the ORR should be on the same level, hence the changing behavior of the ORR performances for this group is not affected by the oxygen, i.e. the conclusion deduced from the changing behavior remains valid. For the group of B x CNTs-NH 3 (x=1,2,3), the samples were obtained by NH 3 post-treatment to the corresponding B x CNTs (x=1,2,3). Thus, the oxygen status in B x CNTs-NH 3 should be similar to that in B x CNTs, which is supported by their similar B1s XPS profiles (Fig. S4a,c) and close oxygen contents (Table S1). [S2] The possible effects of the O-containing groups on the ORR performance were discussed in detail in our previous paper. [S2] S5 Control experiments Table S2. The atomic concentrations (at%) from XPS Sample B 2 CNTs-NH 3 B 3 CNTs (new batch) B 3 CNTs-20min B 3 CNTs-1h B 3 CNTs-6h B N O C a) b) Figure S6. RDE curves at a scan rate of 10 mv s -1 and rotation speed of 2500 rpm. a) four samples with the fixed B and increasing N in the order of B 3 CNTs, B 3 CNTs-20min, B 3 CNTs-1h, B 3 CNTs-6h; b) two samples with the fixed N and increasing B in the order of B 2 CNTs-NH 3, B 3 CNTs-20min. By NH 3 post-treating the new batch of B 3 CNTs for 20min, 1 hour and 6 hours, a set of samples (noted as B 3 CNTs-20min, B 3 CNTs-1h, and B 3 CNTs-6h, respectively) with fixed B and increasing N was obtained as shown in Table S2. Meanwhile, it is noticed that the B 3 CNTs-20min sample has the very close N but higher B content in comparison with the B 2 CNTs-NH 3, which could be used to evaluate the B influence with the fixed N. As shown in Fig. S6, in both cases, the ORR performances get improved with increasing the doping contents, and the N doping is more efficient. This is S8

9 understandable since the mono-n doped CNTs usually possess the better onset and half-wave potentials than the mono-b doped ones at the same doping level. [S2,S14] Current density (ma/mg) B 3 CNTs-NH 3 B 2 CNTs-NH 3 B 1 CNTs-NH 3 B 3 CNTs NCNTs-BA B 2 CNTs B 1 CNTs E(V) vs. SCE Fig. S7. RDE curves at a scan rate of 10 mv s -1 and rotation speed of 2500 rpm for the samples of B x CNTs (x=1, 2, 3), B x CNTs-NH 3 (x=1, 2, 3), and NCNTs-BA. Fig. S7 contains the ORR performances of B x CNTs (x=1, 2, 3), B x CNTs-NH 3 (x=1, 2, 3) as well as NCNTs-BA for comparison. It is seen that, after the NH 3 post-treatment, the ORR performances of B x CNTs (x=1, 2, 3) get improved correspondingly. The NCNTs-BA sets a common standard for the performance comparison between the groups of B x CNTs-NH 3 and B x CNTs-BA. Together with Fig. 2 in the main text, we can see that the ORR performances of B x CNTs-BA group are all worse than that of NCNTs-BA, while those of B x CNTs-NH 3 group could be better than that of NCNTs-BA as the case for B 3 CNTs-NH 3. To certain degree, this phenomenon also supports the main conclusions in this study that the bonded B&N cannot, while the separated one can, turn the inert CNTs into ORR electrocatalysts. Note: 1, B x CNTs-NH 3 (x=1, 2, 3) were obtained by NH 3 post-treatment of B x CNTs (x=1, 2, 3). 2,The data for B x CNTs (x=1, 2, 3) are taken from Ref. S2. 3, NCNTs-BA has 1.20 at.% N, and B 2 CNTs has 1.33 at.% B. The two samples have the close doping level but NCNTs-BA has better ORR performance than B 2 CNTs, which suggests the more efficient doping effect of N that than B. S9

10 S6 Stability tests for B 3 CNTs-NH 3 Relative Current /% a) methanol B 3 CNTs-NH 3 Pt-C Time (second) Relative Current /% b) CO B 3 CNTs-NH 3 Pt-C Time (second) Figure S8. Chronoamperometric responses in the O 2 -saturated electrolyte for Pt/C (black) and B 3 CNTs-NH 3 (red) catalysts. a) Methanol crossover test by introducing methanol into the electrolyte at 1200 s; b) CO poisoning test by introducing additional CO into the electrolyte at 600 s. B3CNTs-NH3 catalyst presents excellent stability and immunity towards methanol crossover and CO poisoning, which overcomes a main challenge faced by the metal-based catalysts in fuel cells. When 2% (v/v) methanol was added to the solution, the ORR current for B3CNTs-NH3 catalyst does not show obvious change while that for Pt/C catalyst suffers a sharp decrease and even changes to a negative current as a result of the mixed potential (Fig.S8a). [S15,S16] When a mixture of CO with oxygen (10% CO v/v) was introduced into the electrolyte, B3CNTs-NH3 electrode was insensitive whereas Pt/C electrode was rapidly poisoned under the same condition (Fig.S8b). Note: Usually platinum is used as electrocatalysts on both anode and cathode in the direct methanol fuel cells (DMFCs). If appreciable amount of methanol leaks into the cathode chamber, it will be oxidized on the cathodic Pt catalyst and cause the loss of cell voltage. It is so called methanol crossover. In addition, CO could easily get chemisorbed on Pt surface, forming the stable bond with the σ donation, π back donation mechanism. [S17,S18] The Pt electrocatalys would soon get covered and deactivated if CO is presented in the incoming gas (H 2 gas usually contains trace CO). This problem is also called CO poising. [S19] Since the carbon based metal-free electrocatalysts are naturally inert to methanol and CO, they are totally free from these issues. S10

11 S7 Electron transfer number determination for B 3 CNTs-NH 3 Current ( ) Ring Disk B 3 CNTs-NH CNTs E(V) vs. SCE Figure S9. RRDE voltammetries of ORR for B 3 CNTs-NH 3 and CNTs in O 2 -saturated 1 mol L -1 NaOH electrolyte at a rotation rate of 2500 rpm and a scan rate of 10 mv s -1. During the tests, Pt ring electrode was polarized at 0.5 V. The transferred electron number (n) per oxygen molecule in ORR was calculated from RRDE voltammetries of B3CNTs-NH 3 and CNTs using the equation of n=4i D / (I D +I R /N), [S20] where I D and I R is the faradic disk and faradic ring currents respectively, and N with the value of 0.27 is the collection efficiency. At V, n is calculated to be 2.5 for B 3 CNTs-NH 3 and 2.2 for CNTs, the same values as the corresponding one for B 3 CNTs and CNTs in our recent study. [S2] This result indicates that the ORR on B 3 CNTs-NH 3 is mainly a two-electron process. This also indicates that the NH 3 post treatment to B 3 CNTs could effectively improve the steady-state diffusion currents and the onset potentials (see Figure 3 in the main text), but has little influence on the O 2 reduction pathway. [S2] S11

12 S8 Natural bond orbital (NBO) analysis for the bonded B&N codoped CNT(5,5) Figure S10. The bonded B&N codoped CNT(5,5). N: blue, B: pink, C: dark, H: gray. Bonded B&N codoped CNT(5,5) was firstly optimized for the spin singlet and triplet states with the unrestricted DFT method. The results show that the singlet state is the ground state with the total energy of 0.73 ev lower than that of the triplet state. This singlet state configuration was further analyzed with the restricted DFT method to eliminate the spin contamination. The natural bonds of B and N dopant are listed in Table S3. Both B and N have the well-defined sp 2 σ bonding feature with the neighboring C (Row 1~4 in Table S3). The remained hybridized orbitals form the B LP* (Row 5 in Table S3) and N LP orbitals (Row 6 in Table S3). The stabilization energy (E2) between these two orbitals, which is the energetic rewarding after superposition, is as high as kcal/mol (Row 3 in Table S4). Such a strong interaction indicates a σ-bond-like interaction between N and B dopants. Row 7 in Table S3 indicates a π bonding feature between the B and N. The hybridization analysis shows that this bond is mainly constituted by the p orbitals of B and N, which should originate from the B vacant orbital and the N LP orbital. This means that the neutralization between the N LP orbital and B vacant orbital indeed happens, leading to the formation of a π bond. Table S3. Bond orbitals of B and N dopants in the bonded B&N codoped CNT(5,5) sp-hybridization for B58 sp-hybridization for N61 Row No Bond orbital Occupancy (e) s(%) p(%) s(%) p(%) 1 BD(1)C39-B BD(1)B58-C BD(1)C42-N BD(1)N61-C LP*(1)B LP(1)N BD(1)B58-N BD*(1)B58-N S12

13 Note: BD bonding orbital; BD* anti-bonding orbital; LP 1-center valence lone pair; LP* the valence non-lewis lone pair. The atoms are marked in Fig.S10. There is no foreign orbital for electron accepting or donating associated with the B and N orbitals, as shown in Table S4. This indicates that the LP electrons of N and the vacant orbital of B are mostly localized within the B-N moiety, thus cannot activate the carbon π electrons for ORR. Table S4. Second order perturbation theory analysis on the bonded B&N codoped CNT(5,5) for the B and N orbitals with E2 > kcal/mol. Donor (i) Acceptor (j) E2(kcal/mol) LP*(1)B58 BD*(1)B58-N LP(1)N61 BD*(1)B58-N LP(1)N61 LP*(1)B Note: E2 the stabilization energy; LP 1-center valence lone pair; LP* the valence non-lewis lone pair. Items with the stabilization energy higher than kcal/mol were selected and the atoms are marked in Fig.S10. References [S1] Vos, M.; Broek, A. EP A1, [S2] Yang, L.; Jiang, S.; Zhao, Y.; Zhu, L.; Chen, S.; Wang, X.; Wu, Q.; Ma, J.; Ma, Y.; Hu, Z. Angew. Chem. Int. Ed. 2011, 50, [S3] Kundu, S.; Xia, W.; Busser, W.; Becker, M.; Schmidt, D. A.; Havenith, M.; Muhler, M. Phys. Chem. Chem. Phys. 2010, 12, [S4] Frisch, M. J. et al. Gaussian 09. Revision A.02 (Gaussian, Inc., Wallingford CT, 2009) [S5] Becke, A. D. J. Chem. Phys. 1993, 98, [S6] Glendening, E. D.; Landis, C. R.; Weinhold, F. WIREs Comput. Mol. Sci. 2012, 2, 1. [S7] Glendening, E. D.; Reed, A. E.; Carrpenter, J. E.; Weinhold, F. NBO, Version 3.1 (Theoretical Chemistry Institute, Univ. Wisconsin, Madison WI, 2001). [S8] Sumpter, B. G.; Meunier, V.; Romo-Herrera, J. M.; Cruz-Silva, E.; Culler, D. A.; Terrones, H.; Smith, D. J.; Terrones, M. ACS Nano, 2007, 1, 369 [S9] Jacobsohn, L. G.; Schulze, R. K.; Maia da Costa, M. E. H.; Nastasi, M. Surf. Sci. 2004, 572, 418. [S10] Shirasaki, T.; Derré, A.; Ménétrier, M.; Tressaud, A.; Flandrois, S. Carbon 2000, 38, [S11] Cermignani, W.; Paulson, T. E.; Onneby, C.; Pantano, C. G. Carbon 1995, 33, 367. [S12] Niwa, H.; Horiba, K.; Harada, Y.; Oshima, M.; Ikeda, T.; Terakura, K.; Ozaki, J-i.; Miyata, S. J. Power Sources, 2009, 187, 93. [S13] Ni, S.; Li, Z.; Yang, J. J. Nanoscale, 2012, 4, [S14] Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L. Science 2009, 323, 760. [S15] Paganin, V. A.; Sitta, E.; Iwasita, T.; Vielstich, W. J. J. Appl. Electrochem. 2005, 35, [S16] Liu, F. Q.; Wang, C. Y. J. Electrochem. Soc. 2007, 154, B514. [S17] Illas, F.; Zurita, S.; Rubio, J.; Marquez, A. M. Phys. Rev. B, 1995, 52, 12372; [S18] Blyholder, G., J. Phys. Chem., 1964, 68, 2772 [S19] Winter, M.; Brodd, R. J. Chem. Rev. 2004, 104, 4245 [S20] Geng, D.; Liu, H.; Chen, Y.; Li, R.; Sun, X.; Ye, S.; Knights, S. J. Power Sources 2011, 196, S13