钯纳米晶/还原氧化石墨烯复合材料的可控合成及其增强的电催化性能资源-CSDN文库

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本研究论文的标题“钯纳米晶/还原氧化石墨烯复合材料的可控合成及其增强的电催化性能”，涉及的是材料科学和电化学领域的最新研究进展。研究的核心内容是通过一种简洁的一步法合成钯纳米立方体/还原氧化石墨烯（PdNCs/rGO）复合材料，并且评估这种新材料在电催化反应，特别是乙醇氧化反应中的性能。在详细探讨知识点之前，首先需要解释一下几个关键术语。钯（Palladium, Pd）是一种银白色金属，属于铂族金属，因其优秀的催化性能和化学稳定性而广泛应用于化学工业中的催化剂。氧化石墨烯（Graphene Oxide, GO）是一种单层碳原子以六边形排列形成的二维材料，经过化学还原后可得还原氧化石墨烯（Reduced Graphene Oxide, rGO），其具有良好的导电性和机械强度。电催化性能是指材料在电化学反应中促进反应速率的能力。研究的具体内容包括以下几个关键知识点： 1. 控制合成方法：研究中提出了一种一步法合成方法，利用抗坏血酸（ascorbic acid）作为还原剂，同时使用溴化钾（KBr）作为封端剂。这种方法可实现钯纳米立方体在还原氧化石墨烯表面的均匀分布。这种一步合成法简化了制备过程，易于操作和推广。 2. 可控合成的形成机制：文章系统研究了影响钯纳米颗粒形态和结构的实验因素，探索了钯纳米立方体（PdNCs）的形成机制。通过实验发现，KBr能够通过表面钝化作用选择特定晶面，而抗坏血酸则控制钯前驱体的还原速度，这两者共同决定了钯纳米颗粒的形态变化。 3. 环境友好型还原剂：研究中选用的抗坏血酸是一种环境友好的还原剂，其应用体现了绿色化学的理念，有助于减少环境污染和提高合成过程的安全性。 4. 电催化性能评估：进一步的电化学评估表明，所合成的钯纳米立方体/还原氧化石墨烯复合材料在乙醇氧化反应中表现出优异的电催化活性和稳定性。这一点对于燃料电池等电化学能源装置的研发具有重要意义。 5. 材料的结构与性能关系：文中探讨了钯纳米立方体具有{100}活性晶面的结构特征，并指出了其平均边长约为15纳米。研究指出，这种具有特定活性晶面的钯纳米立方体在乙醇氧化中展现出更好的性能。总结来说，这项研究不仅为开发新型高效的电催化剂提供了科学依据，还展示了通过一步法合成纳米复合材料的可行性和优势。研究在材料的合成、表征以及性能评估等方面提供了丰富信息，对于推动电化学能源转换和存储技术的发展具有重要的理论和实际意义。同时，这项工作还体现了绿色化学原则在材料科学领域中的应用，为实现可持续发展的科学目标提供了积极的示范作用。

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Controllable synthesis of palladium nanocubes/reduced graphene

oxide composites and their enhanced electrocatalytic performance

Yuting Zhang

, Qiwei Huang

, Gang Chang

, Zaoli Zhang

, Tiantian Xia

Honghui Shu

, Yunbin He

Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Ministry-of-Education Key Laboratory for the Green Preparation and

Application of Functional Materials, Faculty of Materials Science and Engineering, Hubei University, No.368 Youyi Avenue, Wuchang, Wuhan 430062, China

Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, A-8700 Leoben, Austria

highlights

 Pd nanocubes/reduced graphene oxide was synthesized within one-step process.

 Environment friendly ascorbic acid was chosen as the reductant.

 Experimental factors have been systematically studied for the formation mechanism.

 The PdNCs/G exhibits superior activity and stability towards ethanol oxidation.

article info

Article history:

Received 24 October 2014

Received in revised form

15 January 2015

Accepted 20 January 2015

Available online 21 January 2015

Keywords:

Pd nanocubes

Graphene

One-step method

Ethanol oxidation

abstract

Homogeneous distribution of cube-shaped Pd nanocrystals on the surface of reduced graphene oxide is

obtained via a facile one-step method by employing AA and KBr as the reductant and capping agent,

respectively. The experimental factors affecting the morphology and structure of Pd nanoparticles have

been systematically investigated to explore the formation mechanism of Pd nanocubes (PdNCs). It is

revealed that PdNCs enclosed by active {100} facets with an average side length of 15 nm were suc-

cessfully synthesized on the surface of reduced graphene oxide. KBr plays the role for facet selection by

surface passivation and AA controls the reduction speed of Pd precursors, both of which govern the

morphology changes of palladium nanoparticles. In the further electrochemical evaluations, the Pd

nanocubes/reduced graphene oxide composites show better electrocatalytic activity and stability to-

wards the electro-oxidation of ethanol than both reduced graphene oxide supported Pd nanoparticles

and free-standing PdNCs. It could be attributed to the high electrocatalytic activity of the dominated

active {100} crystal facets of Pd nanocubes and the enhanced electron transfer of graphene. The

developed approach provide a versatile way for shape-controlled preparation of noble metal nano-

particles, which can work as novel electrocatalysts in the application of direct alcohols fuel cells.

1. Introduction

Novel electronic, thermal, optical, magnetic and catalytical

properties of nanocrystals are proved to be much dependent on

their shape and structure. Therefore, extensive interest in past

decades have been devoted to controllable synthesis of metal

nanocrystals with different shapes and facet orientations, which is

a powerful means to tune the properties of nanomaterials for

various applications [1e3]. As an extremely important nano-

material in catalysis, Pd nanocrystals exhibit efﬁcient electro-

catalytic activities in fuel cell applications [4e7]. In this regard,

controlling the shape and facets of Pd nanocrystals is an effective

way to enhance the performance in catalytic reactions. Among the

Pd nanomaterials, Pd nanocubes have gained exceptional attention

for their superior catalytic ability resulting from the relatively high

surface energy of the surrounding {100} facets among low index

facets. Notably, Zhang et al. applied a one-pot method to fabricate

the cubic Pd nanocrystals with {100} facets showing a higher ac-

tivity than the {110}-facet-enclosed Pd rhombic dodecahedral in

* Corresponding authors.

E-mail addresses: gchanghubei@gmail.com (G. Chang), ybhe@hubu.edu.cn

(Y. He).

Contents lists available at ScienceDirect

Journal of Power Sources

journal homepage: www.elsevier.com/locate/jpowsour

http://dx.doi.org/10.1016/j.jpowsour.2015.01.127

Journal of Power Sources 280 (2015) 422e429

electro-oxidation of ethanol [8]. Moreover, Shao et al. and Yin et al.

demonstrated that the {100}-facet-enclosed Pd nanocrystals also

showed a higher activity than the other types of Pd nanocrystals

towards the methanol electro-oxidation [9,10].

In order to further maximize the catalytic activity of Pd nano-

crystals and minimize the use of precious Pd metal, a combination

of Pd nanocrystals with carbon materials, such as carbon black,

carbon nanotubes and carbon nanoﬁbers, has been considered an

effective way [11,12]. These carbon materials supports can enhance

the dispersity of Pd nanocrystals and increase the utilization and

efﬁciency of Pd-based electrocatalysts [11]. Among the carbon

materials, graphene, with distinctive 2-dimensional sheet structure

consisting of a few layers of sp

-hybridized carbon lattice [13,14],

has received great attention due to its outstanding physicochemical

properties, such as large speciﬁc surface area, superior electrical

conductivity and good mechanical strength [12,15e18]. Thus, it is

expected to be the best candidate for the combination with Pd

nanocrystals to design novel catalyst for direct alcohols fuel cells

(DAFCs) [19e22]. So far, Pd nanostructures supported on graphene

are mostly nanospheres [20,21,23], nanoclusters [24], and nano-

dendrites [11,25]. The study about the preparation of cube-shaped

Pd nanocrystals attached graphene composites and their applica-

tion in the electro-oxidation of alcohols is rarely reported. A com-

plete understanding about the details of the formation mechanism

of PdNCs on the surface of RGO is also lacking, including the

inﬂuencing of substrate and experimental factors, and the rela-

tionship between structure and properties. In anticipation of

fascinating electrochemical properties of Pd nanocubes attached

graphene, it is desirable to develop a facile chemical method for the

synthesis of Pd nanocubes anchoring on graphene and further

investigate their electrocatalytical performance towards ethanol

oxidation.

In the present work, we attempt to synthesize the cube-shaped

Pd nanocrystals/reduced graphene oxide composites via a facile

one-step method, in which the reduction of graphite oxide and

metal precursor was carried out simultaneously by employing

ascorbic acid (AA) and potassium bromide (KBr) as the soft

reducing and capping agents, respectively [23,26,27]. Herein, the

experimental factors affecting the morphology and structure of Pd

nanoparticles on the graphene, such as the role of reduced gra-

phene oxide, concentrations of KBr and AA, the reduction time and

reaction temperature, have been systematically investigated to

explore the formation mechanism of Pd nanocubes. The

morphology and structure of Pd nanocubes/reduced graphene ox-

ide (PdNCs/G) composites were characterized by transmission

electron microscopy (TEM), ﬁeld-emission scanning electron mi-

croscopy (FE-SEM), X-ray diffraction (XRD) and X-ray photoelec-

tron spectroscopy (XPS). Further electrochemical experiments

including cyclic voltammograms and chronoamperometry were

performed toward the electro-oxidation of ethanol. The results

revealed superior electrocatalytic activity and stability of the

PdNCs/G as compared with both reduced graphene oxide sup-

ported Pd nanoparticles (PdNPs/G) and free-standing PdNCs,

showing a great potential as new anode catalysts in DAFCs.

2. Experimental section

2.1. Chemicals and materials

Potassium tetrachloropalladite (II) (K

PdCl

) was purchased

from Aldrich Chem Co. Graphite was obtained from Alfa Aesar and

5wt% naﬁon was purchased from DuPont. Ascorbic acid (AA), Po-

tassium Bromide (KBr), sulfuric Acid, KMnO4, K

and P

were purchased from Sinopharm Chemical Reagent Co and used

without further puriﬁcation. All chemicals were analytically pure

and used as received without further puriﬁcation. The deionized

water for solution preparation was from a Kertone Ultrapure Water

System P60-CY (Kertone Water Treatment Co. Ltd, resistivity

>18 M

cm).

2.2. Synthesis of PdNCs/G, PdNPs/G composites and PdNCs

The graphite oxide (GO) powder were prepared from graphite

powder via a modiﬁed Hummers' method [28]. 12.5 mg GO was

ﬁrst dissolved in 40 mL pure water and exfoliated using ultrasonic

treatment for 1 h to achieve well dispersion. Then, 1 mL of 0.035 M

PdCl

and 1 mL of 0.03 mM KBr were mixed with 48 mL pure

water. Next, the resulting solution was mixed with the above GO

dispersed solution, following the addition of 200 mg AA as the

reductant. The mixture was kept stirring for 1 h at a temperature of



C under reﬂux conditions. Finally, solid powders were collected

via centrifugation, sequentially washed with double-distilled water

and ethanol for several cycles, and dried at 60



C in a vacuum oven

for 12 h. The PdNCs/G composite was then obtained. Similarly, Pd

nanoparticles attached reduced graphene oxide (PdNPs/G) and free

standing Pd nanocubes (PdNCs) were prepared by the same pro-

cedure in the above description without the capping agent and

supporting materials, respectively.

2.3. Electrochemical characterizations of PdNCs/G

The working electrodes were independently fabricated as fol-

lows. First, a glassy carbon (GC) disk (diameter ¼ 3 mm) electrode

was polished with slurry of 1, 0.3 and 0.05

m alumina to mirror

ﬁnish, rinsed with pure water and dried at room temperature in a

vacuum oven for hours. Then, 2 mg of PdNCs/G composite was

dispersed in the mixture of 0.9 mL H

O and 0.1 mL 5 wt% Naﬁon

using ultrasonic treatment to form a homogeneous black suspen-

sion. Finally, 5

L of the catalyst suspension was carefully pipetted

onto the surface of the GC disc and dried at room temperature to

form a layer that prevented the catalyst particles from detaching.

The as-prepared PdNCs/G working electrodes were for electro-

chemical evaluations. PdNPs/G and PdNCs working electrodes were

prepared using the same procedure described above.

All electrochemical measurements including cyclic voltammo-

grams (CV) and chronoamperometry (CA) were conducted using a

550 electrochemical workstation (Gaoss Union Instrument Com-

pany, China) at room temperature in a conventional three-

electrode cell, with PdNCs/G, PdNPs/G or PdNCs modiﬁed glassy

carbon electrode as the working electrode, a Pt wire as the counter

electrode and a Ag/AgCl electrode saturated with KCl as the refer-

ence electrode. Before each experiment, N

gas (99.999%) was used

to remove the dissolved oxygen in the solution to preserve an inert

atmosphere.

2.4. Physicochemical characterizations of PdNCs/G

Pd nanocubes/reduced graphene oxide composites were char-

acterized by XRD using a D8-Advance diffractometer (Bruker, Ger-

many) with Cu K

radiation source (

¼ 0.15418 nm) and glass

plates as a substrate. The morphology and structure of the samples

were characterized using TEM (FEI TECNAI 20, USA, and JEOL 2100F

with an image-corrector, Japan) and FE-SEM (JSM-7100F, Japan).

EDS analysis of chemical composition was taken by the analyzer

coupled to the FE-SEM. XPS were recorded by a SPeCS system

(PHOIBOS 150, Germany) with Al K

radiation (h

¼ 1486.6 eV), and

the vacuum in the analysis chamber was maintained at about

9

mbar. By EDS, the Pd loading amounts were calculated to be

43.2% in PdNCs/G and 48.2% in PdNPs/G.

Y. Zhang et al. / Journal of Power Sources 280 (2015) 422e429 423

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