Hollow graphitized carbon nanocage supported Pd catalyst with

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Hollow graphitized carbon nanocage supported Pd catalyst with excellent electrocatalytic activity for ethanol oxidation Qiang Zhang, Liang Jiang, Hua Wang, Jinglei Liu, Junfeng Zhang, Yiqun Zheng, Fengting Li, Chenxue Yao, and Shifeng Hou ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b00208 • Publication Date (Web): 14 May 2018 Downloaded from http://pubs.acs.org on May 15, 2018

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ACS Sustainable Chemistry & Engineering

Revised MS: sc-2018-00208m

Hollow graphitized carbon nanocage supported Pd catalyst with excellent electrocatalytic activity for ethanol oxidation Qiang Zhanga,c, Liang Jiangb, Hua Wangc, Jinglei Liuc, Junfeng Zhangc, Yiqun Zhengc, Fengting Lia,c, Chenxue Yaoa,c, Shifeng Houa,* a

School of Chemistry and Chemical Engineering, Shandong University, 27 Shanda Nanlu,

Jinan 250100, China b

Bio-Nano & Medical Engineering Institute, Jining Medical University, 16 Hehua Road,

Jining, 272067, China c

National Engineering and Technology Research Center for Colloidal Materials, Shandong

University, 27 Shanda Nanlu, Jinan 250100, China *

Corresponding Author: Prof. S. Hou, E-mail: [email protected]

ABSTRACT: Low cost, high activity and reliable stability are significant to the commercialization of fuel cell electrocatalysts. However, the synthesis of non-Pt anode catalysts with low-cost, excellent performance and reliable stability is still a great challenge. Herein, we developed hollow graphitized carbon nanocages for improving the electrocatalytic performance of Pd nanoparticles (NPs) towards ethanol oxidation. A mild method was utilized for the preparation of hollow graphitized carbon nanocages (CN) using magnesium oxide as a sacrificial template without high-temperature processing. The CN can act as high-efficiency support for the distribution of Pd NPs. Pd NPs decorated on CN exhibited high catalytic performance with the current density of 2411.5 mA mg-1 for ethanol oxidation reaction (EOR), which is 1.84 and 4.42 times higher than reduced graphene oxide (RGO) 1

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(1308.5 mA mg-1) and C (545.2 mA mg-1) as supports, respectively. The Pd/CN with excellent catalytic performance can be attributed to the CN, including the large surface area with a mesoporous hollow structure, uniform dispersion of Pd NPs, and excellent electrical conductivity. This study may offer new insights for the development of highly effective carbon-based support for applications in ethanol oxidation. KEYWORDS: hollow carbon nanocage; fuel cell; Pd nanoparticles; electrocatalytic activity; ethanol oxidation INTRODUCTION Direct ethanol fuel cells (DEFCs) have received broad interest mainly due to their much lower cost, environmentally friendly and higher energy efficiency.1-7 However, the main challenges regarding the development of non-Pt-based DEFCs is the low energy conversion efficiency of commercial Pd/C anode catalyst due to its relatively low electrocatalytic activity and stability, limiting their ultimate commercialization.8-11 Until now, many researches have been concentrated on designing of electrocatalytic supports with unique properties, for instance, excellent electrical conductivity, large pore volume, and high surface area.12,13 The performance and durability towards EOR mainly depend on supports and active species of catalysts.13,14 Therefore, it is essential to develop not only the electrocatalysts with high catalytic activity, but also the electrocatalyst supports with specific morphologies and performances. Most efforts centered on exploiting novel catalyst substrates for improving the electrocatalytic activity of catalysts, including inorganic oxides (SnO2, TiO2, WO2, among others)15-17 and novel nanostructured carbon (carbon nanotubes, carbon nanofibers, 2


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mesoporous carbon, graphene, etc.).18-23 Carbon materials are used as the primary catalyst support and inorganic oxides materials are mainly used to modify and promote the primary supports as the secondary support.24 Among these, for instance, mesoporous carbons (MCs), provide a better alternative as electrode materials for highly efficient ethanol oxidation due to their excellent mass transfer, large specific surface area and structural effect on the loaded active sites.25,26 Currently, various strategies, such as hard

27-29

and soft

30,31

templates, have

been reported to obtain MCs of high specific surface areas/pore volumes and controlled pore size. Hu et al. used SBA-15 as the template to prepare Pd-functionalized ordered mesoporous carbons (Pd-OMCs) which showed high electrocatalytic ability in alkaline conditions.32 However, these synthetic routes have some important drawbacks such as high cost, use of environmentally harmful chemicals and the required use of a template, limiting their widespread application. 33 29 Among the various nano-structured MCs materials, mesoporous hollow carbons (MHCs) have inspired great interest because of their particular properties, such as hierarchically three-dimensional porous framework, abundant hollow architecture and large specific surface area.

34-37

In general, MHCs could be fabricated by using core/shell silica as sacrificial

template, and subsequent carbonization, followed by etching of the core.34,38,39 However, synthesis of MHCs commonly involves tedious processes and cost-efficiency problems. Most importantly, most MHCs possess a poorly graphitized structure, leading to poor electrical conductivity and low electron transfer, which is inevitably unfavorable to the EOR. Therefore, a simple but effective strategy for constructing a desirable support with hollow well-graphitized structure, and high surface area is still a great challenge in this field. 3



Herein, we synthesized hollow graphitized carbon nanocage supports for improving the activity of Pd catalysts (denoted as Pd/CN) toward ethanol oxidation in an alkaline solution via a scalable route. The CN was fabricated by igniting magnesium metal in carbon dioxide atmosphere without high-temperature processing and followed by dispersion of Pd NPs, as shown in Scheme 1. The hollow frame, excellent electrical conductivity and large surface area of CN provide more active sites, which promote higher electrocatalytic performance of Pd NPs towards ethanol oxidation compared to RGO and C as supports. Its outstanding catalytic performance suggests that graphitized cubic carbon could act as an excellent support in fuel cell applications. EXPERIMENTAL SECTION Materials. Palladium (II) chloride (PdCl2, 98%), isopropanol, ethanol, potassium hydroxide (KOH) and potassium hydroxide (HCl, 37.5%) were from Sinopharm Chemical Reagent Co., Ltd. Commercial Pd black (containing 20 wt% Pd) was acquired from Shanghai Hesen Electric Co., Ltd. Nafion (5 wt%), magnesium ribbon and dry ice were purchased from Sigma-Aldrich. Ultrapure water (resistance: 18.25 MΩ cm-1) was utilized in all experiments. Preparations of electrocatalysts. CN was prepared according to a procedure developed in a recent previously reported work with slight modification.40,41 Briefly, dry ice was dissolved in 500 mL of ultrapure water equipped with beaker under vigorous magnetic stirring at room temperature, meanwhile, carbon dioxide gas emerged. Then, ignited magnesium ribbon (3.0 g) was put into the atmosphere of carbon dioxide for 2 h to ensure all reactants were completely combusted. After, 200 mL of 3.0 M HCl was mixed with the black products for

4


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dissolving the resultant of MgO and all residual Mg metal. Finally, the products were washed with ultrapure water and dried at 65 °C for further measurement. The Pd/CN catalyst was prepared via a simple reflux procedure, and ethanol served as reductant. The process can be briefly described as follows: 15 mg of the as-synthesized CN dissolved in 30 mL isopropanol-water mixtures (Visopropanol:Vwater = 9:1) was ultrasonicated for 2 h. Then, 1.57 mL of H2PdCl4 (22.5×10-3 mol L-1) was slowly injected into the formed suspension with rapid stirring, followed by the reduction process mixing with a volume of 40 mL ethanol. KOH solution (200 uL, 1 M) was added into the mixture until the pH was reached to 9. Then, the uniform solution was heated by an oil bath (80 °C) while stirring and refluxing for 2 h. Finally, the resulting sample was centrifuged, washed and dried under vacuum overnight to obtain Pd/CN. The catalysts of Pd/CN have a metal of Pd loading of 20 wt %. For the control experiment, Pd/RGO catalyst was fabricated under a similar process except that the CN were replaced by RGO. Briefly, GO was synthesized by the modified Hummers method.42 Then, the GO (0.5 mg mL-1) was dispersed in ultrapure water with an ultrasonic homogenizer for 1 h, followed by dropping the same amount of H2PdCl4 (1.57 mL, 22.5 mM). Afterwards, excess ethanol solution (40 mL) was also poured into the reaction suspension and raised to 80 °C in an oil bath under stirring for 2 h. After cooling to room temperature, the obtained samples was washed with ethanol and water in sequence. And the commercial Pd/C catalyst (20 %) was also used. The palladium content of all the above-described catalysts is 20 wt%.

5



Scheme 1 Schematic illustration of synthesis for CN and Pd/CN Characterization. Scanning electron microscopy (SEM) analyses were measured using a Hitachi SU-8010 instrument. The morphology and structure of the materials were characterized by transmission electron microscopy (TEM, FEI Quanta 200F). High-resolution TEM (HRTEM) and high-angle annular dark field-scanning transmission electron microscopy (HADDF-STEM) measurements were performed using a JEM-2100F with an energy dispersive spectrometer (EDS) attachement. X-ray diffraction (XRD) were investigated with a diffractometer (Bruker D8 Advanced). Nitrogen adsorption and desorption isotherms were conducted using a gas instrument (Kubo X1000). X-ray photoelectron spectroscopy (XPS) analysis was recorded on a photoelectron spectrometer (VGESCALAB MKII). Electrochemical test. The electrochemical measurements of as-prepared samples were performed in a three-electrode system with an electrochemical workstation (CHI 760E, Shanghai CH Instrumental Co.). A platinum wire was used as the counter electrodes, and a KCl -saturated calomel electrode (SCE) served as the reference electrode. The working electrode was fabricated by coating the suspension of catalyst on a glassy carbon electrode (GCE) and dried with nitrogen. Prior to the electrochemical measurements, the electrolytes 6


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were degassed with high-purity nitrogen for 30 min. For estimating the value of electrochemically active surface area (ECSA) of the electrodes, cyclic voltammograms (CV) were carried out in a N2-saturated 1.0 M KOH solution at the potential from -0.7 to 0.2 V (SCE). For the EOR measurement, CV measurements were measured at the scan rate of 50 mV s-1 between -0.7 and 0.2 V in the mixture of 1.0 M methanol + 1.0 M KOH. Chronoamperometry (CA) analysis was performed at -0.4 V (vs. SCE) with the sweep rate of 50 mV s-1. The catalytic durability of all samples for EOR was measured by performing CV of catalysts over 1000 cycles with the scan rate of 0.05 V s-1 and from -0.7 V to 0.2 V. Electrochemical impedance spectroscopy (EIS) tests were measured in the frequency range between 0.1 and 100 kHz at 0.2 V in a mixture of 5.0 mM K3[Fe(CN)6/K4[Fe(CN)6] (1:1). The modified electrodes were produced as follows: 4.0 mg samples were dissolved in a isopropanol, ultrapure water and Nafion solution (0.5 wt%) mixture (Visopropanol:Vwater:V Nafion=

9:1:0.025, 4.0 mL) by ultrasonication to obtain a uniform ink. Then, 10 µL of resultant

catalyst solution was coated and air-dried on the GCE at room temperature. Assuming that Pd2+ is 100% reduced, the theoretical Pd loading mass on the GCE was estimated to be 2.0 µg. For comparison, we kept the same metal loading on the commercial Pd/C and Pd/RGO catalyst. RESULTS AND DISCUSSION Experimentally, the CN was easily obtained directly from CO2 by burning Mg in it. Figures. 1a and 1b show the SEM images of the CN. It is observed that nanocage-like morphology of CN with the size range of 50-150 nm. The white arrows in Figure 1a mark some of the broken products, showing the cubic hollow structure. The use of an in situ MgO template 7



results in the formation of the open nanocage.40 Upon further increase of the magnification (Figure 1b), it is clear that many of the tiny cubic particles assemble into cubic porous hollow structures. Such cubic porous hollow structure is beneficial for the efficient ionic diffusion, facilitating the EOR activity. SEM images of Pd/CN were also investigated, as displayed in Figures. 1c and 1d. Pd/CN possess a rough surface, with almost no shape and size change of CN. TEM analysis was then conducted to investigate the morphological and structural features of CN and Pd/CN in more detail. An overview TEM image of the products displays a cubic hollow structure, consistent with the SEM observations. The difference between the edge and the center demonstrated that the cubic hollow structure has formed.43,44 Using the hollow cubic material as support, Pd nanoparticles with relatively homogeneous sizes were anchored onto the CN skeleton, as presented in Figures. 2c and 2d. The average dimensions of Pd nanoparticles is 3.43 ± 0.99 nm, which conforms to a normal distribution.

Figure 1. SEM images of (a, b) CN and (c, d) Pd/CN. 8


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Figure 2. TEM images of (a, b) CN and (c, d) Pd/CN nanocomposites. The inset in panel (d) is histogram of the Pd particles-size distribution of in Pd/CN nanocomposites. Surprisingly, the high-magnification TEM image (Figure 3a and 3b) shows that the CN has a highly graphitized structure. The selected area electronic diffraction (SAED) patterns (Figure 3d inset) exhibit concentric rings of spots, suggesting that the Pd NPs are polycrystalline. The morphology of the as-prepared catalysts was further studied by HRTEM images. Figure 3e confirms that small NPs (~3.4 nm) are distributed on the surface of CNs. Moreover, clear lattice structures are observed for both CN and metallic NPs. The two clear lattice fringes with an interplanar distances for CN and Pd NPs are measured as 0.34 and 0.22 nm, respectively, consisting with the previous report.45 The elemental mapping images of the composite reveals that C, Pd and O elements are homogeneously distributed throughout the whole nanocage.

9



Figure 3. High-magnification TEM images of (a, b) CN and (c, d) Pd/CN at different magnifications. Inset image in panel d is corresponding SAED pattern. HRTEM image (e), HAADF-STEM image (f) and corresponding elemental mappings of Pd/CN. The inset in panel (e) is the enlarged images obtained from the region labeled by the blue square. The XRD technique was investigated to explore the structural features of the CN and Pd/CN samples. For all samples, the typical C (002) diffraction peak around 26° that originates from the CNs with good graphitization is observed for two samples. For Pd/CN, XRD patterns can be assigned to the (111), (200), (220) and (311) diffractions of crystal planes of Pd [JCPDS no. 46-1043] with four peaks located at 40.6, 46.2, 67.8 and 81.4°, respectively,

46,47

The composition of the Pd/CN composites was further confirmed by EDX 10


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analysis. The results indicates that the as-prepared samples is constituted of C, Pd and O elements, as shown in Figure S1. To explore the surface and pore-size characterization of the CN,

N2

adsorption/desorption

was

measured

(Figure

4b).

The

obtained

N2

adsorption/desorption isotherm is a type-IV isotherms, indicating the existence of a mesoporous structure. A large surface area of 790 m2 g-1 with a pore volume of 1.50 cm3 g-1 was calculated from the Brunauer−Emmett−Teller method, which is similar to the previous report40. The pore size distributions correspond to mesopores of ca. 2-10 nm (inset in Figure 4b), except for the open macropores observed in the SEM images. Such porous structure can endow CN with an enlarged ECSA and increase the supply of active sites available for ethanol oxidation.

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Figure 4. (a) XRD patterns of CN and Pd/CN; (b) N2 adsorption–desorption isotherms of CN. Inset in b: pore size distribution curve of the CN. XPS spectra were investigated to obtain the oxidation state and surface information of CN and Pd/CN. For CN, only C 1s and O 1s peaks appear in the full XPS survey spectrum. Following the introduction of Pd, three elements including Pd 3d, C 1s and O 1s are detected in Pd/CN, in agreement with the elemental mappings measurement. The high-resolution Pd 3d spectrum is shown in Figure 5b and reveals strong peaks arising from Pd 3d5/2 and Pd 3d3/2. The Pd 3d peaks can be further resolved into two doublets, indicating the coexistence of two electronic states of Pd. The binding energies at 335.1 eV (Pd 3d5/2) and 340.4 eV (Pd 3d3/2) correspond to Pd (0), meanwhile, the peaks at 336.0 eV (Pd 3d5/2) and 341.3 eV (Pd 3d3/2) are assigned to Pd (II) species.48 49 Based on the relative integrated intensity values for Pd (0) and Pd (II), suggesting that Pd (0) predominates on the Pd/CN surface.

Figure 5. (a) XPS spectra for Pd/CN, CN samples and (b) deconvoluted Pd 3d peaks for Pd/CN. Prior to electrocatalytic tests, CV and EIS of catalysts were performed in Fe(CN)6 solution. The Fe(CN)6

3-/4-

3-/4-

redox couple can be used for testing due to its sensitivity or

insensitivity to the surface chemistry and microstructure, electronic performances of carbon 12


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electrodes. Pd/CN,

50,51

Figure 6a depicts the CV of the Fe(CN)6

3-/4-

reversible redox couple of

Pd/RGO and Pd/C samples. For Pd/CN, the peak-to-peak potential separation

(Ep=0.09 V) is slightly lower than those for all other catalysts, signifying an improvement of the charge transfer between electrode surface and electrolyte solution.50 Moreover, the higher redox peak current (ip) of the Pd/CN compared to Pd/RGO and JM Pd/C indicates its higher electrochemical activity.52 The value of active surface areas of the samples are obtained by using Randles-Sevcik equation, ip = 269n3/2AD1/2v1/2c

(1)

where ip is expressed in amp, n is the number of electrons during the process of redox, the area A of the electrode in cm2, diffusion coefficient D of the oxidized species in cm2 s-1, v in V s-1 and the bulk concentration C of the oxidized species in mol cm-3.53 Here, for Pd/CN, Pd/RGO and Pd/C, the corresponding active surface areas of was measured to be 2.24 cm2, 1.68 cm2 and 1.12 cm2, respectively. EIS analysis of all catalysts were conducted at 0.2 V in order to evaluate the charge-transfer behavior, as displayed in Figure 6b. The Nyquist plots exhibit a semicircle in the high-frequency range related to the charge transfer resistance (Rct) for the EOR. Generally, a smaller radius indicates a lower charge-transfer resistance with a faster rate for the catalytic reaction.54 It is obvious that Pd/CN exhibited the smallest impedance arc radius among these three samples, showing that Pd/CN exhibits the highest electron transfer rate. This indicates that CNs possess good electrical conductivity, which is benefit for promoting the electron transfer.55,56 And, the result further confirmed that the larger active surface area and good electrical conductivity of the CNs can facilitate electron transport on Pd/CN, making it extremely attractive for ethanol electrooxidation activity. 13



Figure 6. (a) CV curves and (b) Nyquist plots of the as-prepared catalysts in aqueous 5 mM K3[Fe(CN)6]/ K4 [Fe(CN)6] containing 0.1 M KCl solution at a fixed potential of 0.2 V. Motivated by the unique nanostructure (mesoporous hollow carbon, cubic nanocage, large surface area) of the as-prepared CN as a support for distributing Pd catalyst, we then investigated the electrocatalytic oxidation of EOR as a model reaction. In order to evaluate the active sites of the catalysts, the electrochemically active surface area (ECSA) of Pd/CN, Pd/RGO and commercial Pd/C were initially analyzed based on the charge required for oxygen desorption via cyclic voltammetry measurements, and the results obtained for these three systems were compared.57,58 Figure 7a shows CVs of Pd/CN, Pd/RGO, and Pd/C catalysts in the deaerated 1.0 M KOH solution at the scan rate of 50 mV s-1. The ECSA (m2 g-1Pd) is defined as: ECSA=Q/(0.405×WPd)

(2)

where Q corresponds to the reduction charge of PdO (mC), 0.405 is the charge required to reduce a monolayer of PdO (mC cm-2 Pd), and WPd represents the amount of Pd (mg cm-2) loaded on the GCE.59 Here, the calculated ECSA of Pd/CN was 63.6 m2 g-1, which is superior to the values obtained for the Pd/RGO (21.8 m2 g-1) and Pd/C (16.9 m2 g-1) catalysts (inset in Figure 7a). The increased ECSA of Pd/CN may be attributed to good dispersion of Pd 14


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particles on CN. Moreover, the mesoporous hollow graphite carbon structure can allow for a greater degree of Pd catalyst dispersion, which would be responsible to higher ECSA of Pd/CN.26 To evaluate the electrocatalytic performances of the abovementioned three composites towards EOR, the measurements were studied in a solution of 1.0 M CH3CH2OH + 1.0 M KOH at 50 mV s-1 (Figure 7b). The mass and specific activities for the EOR were calculated by normalizing to the Pd mass loading. For Pd/CN, the forward anodic peak current density (jf) reaches 2411.5 mA mg-1, which is 1.84 and 4.42 fold larger than those of Pd/RGO and commercial Pd/C catalysts (1308.5 mA mg-1, 545.2 mA mg-1), further revealing the significant improvement of EOR activity by forming the porous cubic structure of CN. Compared to various previously reported values in the literature on EOR activities and ECSA value of Pd-based catalysts (summarized in Table S1 in the Supporting Information), the electrocatalysis performance our Pd/CN catalysts is higher. In addition, the EOR onset oxidation potential on Pd/CN is slightly more negative than those of any other catalysts, suggesting that EOR is more favorable on the Pd/CN than on the Pd/RGO as well as Pd/C catalyst.60 Based on the above studies, the lower onset potential and higher catalytic performance of Pd/CN indicate the enhanced catalytic activity of Pd/CN for EOR.

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Figure 7. Comparison of electrocatalytic measurements of the Pd/CN, Pd/RGO and Pd/C electrodes. CVs recorded in (a) 1.0 M KOH solution and (b) in 1.0 M KOH electrolyte containing 1.0 M CH3CH2OH at 50 mV s-1. The insets in panels a and b shows the corresponding ECSA values and respective jf of the as-prepared catalysts. To investigate the long-term durability of the Pd/CN, Pd/RGO and Pd/C catalysts, chronoamperometric experiments were further performed in 1.0 M CH3CH2OH + 1.0 M KOH solution at -0.4 V for 4000 s, and the results are depicted in Figure 8a. Clearly, Pd/CN exhibits much higher current density over the entire testing time compared to the Pd/RGO and Pd/C catalysts, confirming its superior electrocatalytic activity and durability. We also carried out CV cycling measurements in 1.0 M CH3CH2OH + 1.0 M KOH solution for 1000 cycles, and the comparison of the peak current density vs. the cycle number was displayed in Figure 8b. The current density of the Pd/CN increased at initial stage and reached the maximum at about the 50th cycle. And then, the current densities decreases gradually with successive scans. However, compared with Pd/RGO and Pd/C, the Pd/CN composite shows superior current density over the whole durability test. As such, the as-obtained porous cubic Pd/CN with high EOR activity and good durability may be promising for use in practical EOR fuel cell systems as an efficient electrocatalyst.

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Figure 8. (a) CA of the Pd/CN, Pd/RGO, commercial Pd/C electrodes in a solution of 1.0 M CH3CH2OH +1.0 M KOH for the EOR at -0.4 V; (b) Peak current density on Pd/CN, Pd/RGO, commercial Pd/C electrodes vs. the cycle number in 1.0 M CH3CH2OH + 1.0 M KOH solution. CONCLUSIONS In conclusion, mesoporous hollow graphitized carbon nanocages can act as a high-efficiency support for the distribution of Pd NPs. The Pd/CN catalysts exhibit high electrocatalytic activity with the current density of 2411.5 mA mg-1 compared to Pd/RGO and Pd/C catalysts towards EOR in basic solution. These results suggest that the enhancement of electrocatalytic activity can be ascribed to the unique structural characteristics of the nanocages, including their large surface area with a mesoporous hollow structure, uniform dispersion of Pd NPs, as well as excellent electrical conductivity. ASSOCIATED CONTENT Supporting Information. Comparison of ethanol oxidation behavior on the Pd/CN composites and recent state-of-the art Pd-based electrocatalysts. This information is available free of charge via the Internet at http://pubs.acs.org/. AUTHOR INFORMATION Corresponding Author *E–mail: [email protected] (S. Hou)

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. 17



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Notes: The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China grant (No. 13450005131401). REFERENCES (1) Xue, J.; Han, G.; Ye, W.; Sang, Y.; Li, H.; Guo, P.; Zhao, X. S. Structural Regulation of PdCu2 Nanoparticles and Their Electrocatalytic Performance for Ethanol Oxidation. ACS Appl. Mater. Interfaces 2016, 8, 34497-34505. DOI 10.1021/acsami.6b13368. (2) Wu, W. P.; Periasamy, A. P.; Lin, G. L.; Shih, Z. Y.; Chang, H. T. Palladium copper nanosponges for electrocatalytic reduction of oxygen and glucose detection. J. Mater. Chem. A 2015, 3, 9675-9681. DOI 10.1039/c5ta00382b. (3) Anu Prathap, M. U.; Srivastava, R. Synthesis of NiCo2O4 and its application in the electrocatalytic oxidation

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Hollow graphitized carbon nanocage as support of Pd shows high electrocatalytic activitity (2411.5 mA mg-1) compared to RGO and C

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Hollow graphitized carbon nanocage as support of Pd shows high electrocatalytic activitity (2411.5 mA mg1) compared to RGO and C 79x33mm (300 x 300 DPI)


Hollow graphitized carbon nanocage supported Pd catalyst with

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