Supplementary Materials:

Superior Activity of Pd Nanoparticles Confined in Carbon

Nanotubes for Hydrogen Production from Formic Acid

Decomposition at Ambient Temperature

Tian-Yi Ding, Zhi-Gang Zhao, Mao-Fei Ran,* Yao-Yue Yang*

College of Chemistry and Environmental Protection Engineering, Southwest Minzu University, Chengdu 610041, Sichuan, China.*Corresponding author: YYY: E-mail: yaoyueyoung@swun.edu.cn, ORCID ID: 0000-0002-4573-9437; RMF: E-mail: murphy_ran@foxmail.com

1. Extra TEM images

Figure S1. TEM images of Pd-CNTs-out sample (A) and (B), Pd-CNTs-in sample (C) and (D).

2. The calculation of TOF values

Here TOF is defined as the apparent hydrogen production rate calibrated with the surface active sites number, thus

TOF = mole of hydrogen gas production per hourmole of surface active sites

As the equilibrium shapes of fcc metals are cuboctahedra, the cuboctahedron model has been widely used to estimate the surface areas of Pd and Pt nanoparticles in literatures.[1-2] Along this lien, the modelled cuboctahedra made up of concentric shells of atoms were adopted here to simulate the actual Pd nanoparticles. The mole of surface active sites may be calculated as follows,[3-4]

mole of surface active sites=N s

N t× ntotal

Where ntotal means the total moles of Pd metal, Ns is the number of surface atoms of nanoparticles, expressed as Ns = 10m2 -20m+12; Nt is the total number of atoms, expressed as Nt = 0.33(2m-1)(5m2-5m+3). Where m is the number of atomic layers and equals to 2.2d (here d is the average particle diameter).

References:[1]. Sun, Y.; Dai, Y.; Liu, Y.; Chen, S., Phys. Chem. Chem. Phys. 2012, 14, 2278-2285.[2]. Henry, C. R., Surf. Sci. Rep. 1998, 31, 231-325.[3]. Benfield, R. E., J. Chem. Soc. Faraday Trans. 1992, 88, 1107-1110.[4]. Zhang, Y.; Hsieh, Y. C.; Volkov, V.; Su, D.; An, W.; Si, R.; Zhu, Y.; Liu, P.; Wang, J. X.; Adzic, R. R., ACS Catal. 2014, 4, 738-742.

3. TOF Comparison with previous workDue to different definitions adopted for TOF in literatures, thus here we estimated

their TOF values according to the following equation to facilitate comparison.

TOF=

Patm VH 2

RTnmetal t

Where Patm is the ambient pressure (normally 100 Kpa), VH2 is the generated

hydrogen volume within 10 min , R is the gas constant with its value of 8.314 Pa m3

mol-1 K-1, T is the reaction temperature, nmetal is the mole number of noble metal, and t

is the reaction time (here we used 10 min except specific description).

Table S1. The comparison of TOF between our results with that in literatures.

CatalystsFA

(mmol)Additive

Tem.

(K)

H2

(mL)

nCatalyst

(mmol)

TOF

(molH2

molCatalyst-1 h-1)

Ref.

Pd-CNTs-in 11.0 HCOONa 303 60 0.045 323.1 This work

Pd-CNTs-out 11.0 HCOONa 303 41 0.043 230.1 This work

Pd/C 5.3 HCOONa 298 25.2 0.047 131.5 [1]

Pd@CN 10.0 None (150 W Xe lamp) 288 4.0 0.015 67.7 [2]

Pd- poly(allyl-amine) 15.2 None 295 10.0 0.040 62.0 [3]

Pd/mpg-C3N4 10.0 None 288 4.0 0.045 143.3 [4]

Pd/S-1-in-K(1.7nm) 3.0 HCOONa 298 72 0.030 852.5 [5]

Pd/S-1-im(2.7nm) 3.0 HCOONa 298 35.5 0.030 294.2 [5]

Pd/C(2.2nm) 11.0 HCOONa 303 120 0.047 617.4 [6]

Pd/C(3.6nm) 11.0 HCOONa 303 40 0.047 205.8 [6]

Pd/C(5.2nm) 11.0 HCOONa 303 25 0.047 128.6 [6]

Pd/C-m(1.4nm) 3.0 HCOONa 303 220a 0.056 1255.3 [7]

Pd-B/C 11.0 HCOONa 303 75 0.047 385.0 [8]

NiPd@Pd/GNs-CB 5.0 HCOONa 298 112.5 0.200 138.0 [9]

Pd0.6Ni0.4/NH2-N-rGO 0.5 None 298 24.5b 0.100 954.0 [10]

PdAu/ED-MIL-101 3.0 HCOONa 363 38.0 0.026 294.3 [11]

PdAu/C-CeO2 49.7 HCOONa 365 75.0 0.113 132.9 [12]

PdAg/C-CeO2 49.7 HCOONa 365 40.0 0.113 70.9 [12]

PdAu@Au/C 33.2 HCOONa 365 55.0 0.227 48.5 [13]

AuPd-MnOx/ZIF-8-

rGO5.0 None 298 101.0 0.065 381.2 [14]

a The TOF value of initial 7.5min process b The TOF value of initial 0.63 min process. Others are the

TOF value of initial 10 min process.

References：[1]. Z.-L. Wang, J.-M. Yan, H.-L. Wang, Y. Ping, Q. Jiang, Sci. Rep. 2012, 2, 598.[2]. Y. Y. Cai, X. H. Li, Y. N. Zhang, X. Wei, K. X. Wang, J. S. Chen, Angew. Chem., Int. Ed. 2013, 125, 12038.[3]. S. Jones, J. Qu, K. Tedsree, X.-Q. Gong, S. C. E. Tsang, Angew. Chem. Int. Ed. 2012, 124, 11437.[4]. Z.-L. Wang, H.-L. Wang, J.-M. Yan, Y. Ping, S.-I. O, S.-J. Li, Q. Jiang, Chem. Commun. 2014, 50, 2732.[5]. N Wang, Q-M Sun, R-S Bai, X Li, G-Q Guo J-H Yu. J. Am. Chem. Soc. 138, 24, 7484.[6]. S Zhang, B Jiang, K Jiang, W-B Cai, ACS Appl. Mater. Interfaces. 9, 29, 24678.[7]. Q.-L. Zhu, N Tsumori, Q. Xu, J. Am. Chem. Soc. 2015, 137, 11743.[8]. K. Jiang, K. Xu, S. Zou, W.-B. Cai, J. Am. Chem. Soc. 2014, 136, 4861.[9]. Y.-L. Qin, J. Wang, F.-Z. Meng, L.-M. Wang, X.-B. Zhang, Chem. Commun. 2013, 49, 10028.[10]. J.-M. Yan, S.-J. Li, S.-S. Yi, B.-R. Wulan, W.-T. Zheng, Q. Jiang, Adv. Mater. 2018, 1703038.[11]. X. Gu, Z.-H. Lu, H.-L. Jiang, T. Akita, Q. Xu, J. Am. Chem. Soc. 2011, 133, 11822.[12]. X. Zhou , Y. Huang , W. Xing , C. Liu , J. Liao , T. Lu , Chem. Commun. 2008, 3540.[13]. Y. Huang, X. Zhou, M. Yin, C. Liu, W. Xing, Chem. Mater. 2010, 22, 5122.[14]. J.-M. Yan, Z.-L. Wang, L. Gu, S.-J. Li, H.-L. Wang, W.-T. Zheng, Q. Jiang, Adv. Energy Mater. 2015, 1500107.

4. Calculation of apparent activation energy (Ea) of FAD

Figure S2 (A) Time-dependent hydrogen generation process at different reaction temperatures, with 100 mg catalysts in 1.1 M FA + 0.8M SF solution. (B) the corresponding TOF values under different reaction temperatures.(C) and (D) are the linearly fitted correlation of ln(TOF-10 min) vs 1/T for Pd-CNTs-in and Pd-CNTs-out, respectively. (E) and (F) are the variations of ln(CFA) versus time for Pd-CNT-in and Pd-CNT-out sample, respectively.

Ea has been calculated through previously described method. (refer to ACS Appl. Mater. Interfaces, 2017, 9, 24678) It is adopted the temperature-dependent FA decoposition on catalysts to obtain the plot of ln(TOF) vs 1/T, whose slope could be used to estmated the Ea value according to Arrhenius equation. Therefore, hydrogen production volume as a function of time was measured at different temperatures with

Pd-CNTs-in and Pd-CNTs-out catalysts in 1.1 M FA + 0.8 M SF (see Figure S2). The as-obtained TOF values over initial 10 min and 20 min (see table S2) are used to plot the fitted line of ln(TOF) vs 1/T, which gives the apparent activation energy values and list in Table S3 below.

Table S2 The TOF value of two catalysts at different temperatures.

Catalysts10 min TOF (h-1) 20 min TOF (h-1)

298 K 303 K 313 K 318 K 298 K 303 K 313 K 318 K

Pd-CNTs-in 881.3 1135.8 1348.1 1828.9 732.1 993.8 1196.9 1593.1

Pd-CNTs-out 496.0 580.8 778.0 794.1 384.0 471.0 625.2 623.9

Table S3. The as-calculated activation energy on two catalysts.

CatalystsEa（kJ mol-1）

10 min 20 min

Pd-CNTs-in 36.60 ± 2.88 39.07 ± 2.41

Pd-CNTs-out 26.50 ± 5.43 27.07 ± 6.23

5. The FA and CO electro-oxidation measurement A CHI 605B electrochemistry workstation with a three-electrode system was used

to perform the electrochemical measurements. A Pt sheet and a saturated calomel electrode (SCE) were employed as the counter and reference electrodes, respectively. The working electrode (WE) was prepared by pipetted a 10 μL catalyst ink that contains 2 mg catalyst, 1 mL C2H5OH and 120 μL Nafion (5 wt%, Aldrich) onto a freshly polished glassy carbon (GC) electrode. As for the CO stripping voltammograms, firstly CO (> 99.99% purity) was bubbled and adsorbed onto WE that is immersed in 0.5 M H2SO4 for 20 min and then dissolved CO was removed by high purity N2 flow for at least 1 h. The WE potential was controlled at -0.1 V (SCE) throughout the whole pretreatment process. At last, CO stripping voltammograms were collected at a scan rate of 10 mV s −1. All electrolytes were performed deaeration by bubbling high-purity N2 before use, and all electrochemical measurements proceed at room temperature.

Figure S3. Linear sweep voltammograms for two catalysts in 0.5 M H2SO4 + 0.5 M HCOOH with a sweep rate of 50 mV s-1.

Figure S4. CO stripping voltammograms for two catalysts in 0.5 M H2SO4 with a sweep rate of 10 mV s-1.