Nghiên cứu vật liệu nano siêu mỏng MoS2 pha tạp nitơ và vật liệu tổng hợp graphene/MoS2 chế tạo bằng phương pháp điện hóa plasma ứng dụng cho phản ứng sản sinh hydrô

國立交通大學

材料科學與工程學系

博士論文

電漿電化學法製備氮摻雜二硫化鉬奈米片及石墨烯-二硫

化鉬複合材料及其產氫應用

Nitrogen Doped MoS2 Nanosheets and Graphene/MoS2

Composite Prepared by Electrolysis Plasma-Induced Process

for Hydrogen Evolution Reaction

研究生: 阮文長

指導教授：韋光華 博士

中華民國一零九年四月

電漿電化學法製備氮摻雜二硫化鉬奈米片及石墨烯-二硫化鉬複合

材料及其產氫應用

Nitrogen Doped MoS2 Nanosheets and Graphene/MoS2 Composite

Prepared by Electrolysis Plasma-Induced Process for Hydrogen

Evolution Reaction

研究生：阮文長

指導教授：韋光華 博士

Student: Nguyen Van Truong

Advisor: Dr. Kung-Hwa Wei

A Dissertation

Submitted to Department of Materials Science and Engineering

College of Engineering

National Chiao Tung University

in partial Fulfillment of the Requirements

for the Degree of

Doctor of Philosophy

in

Materials Science and Engineering

March 2020

Hsinchu, Taiwan, Republic of China

中華民國一零九年四月

國立交通大學

材料科學與工程學系

博士論文

i

摘要

為了獲得可持續的富含地球的電催化劑材料，在氫析出反應（HER）中顯示出高性能，

在這裡我們提出了一種簡便的一鍋電漿電化學工藝，用於製造氮摻雜的二硫化鉬奈米

片和石墨烯/ 二硫化鉬複合材料。已經開發出一種有效的一步法，該方法涉及在短時間

內且在低溫（約 80°C）下同時進行二硫化鉬奈米片的電漿摻雜和剝落。特別地，可以

在浸沒的陰極尖端處產生有效的電漿區，以實現將氮原子摻雜到半導體性 2H-二硫化鉬

結構中。在二硫化鉬結構中氮摻雜和剝落的協同作用下調節電子和輸運性質，以增強

其催化活化作用。研究發現，在摻氮的二硫化鉬奈米片上，氮原子濃度為 5.2 at％時，

具有出色的催化氫析出反應，在 10 mA cm–2的電流密度下，低過電位為 164 mV，Tafel

斜率較小，為 71 mV dec-1 –遠低於剝落的二硫化鉬奈米片（207 mV，82 mV dec-1）和塊

狀二硫化鉬（602 mV，198 mV dec-1），達到在 0.5 M 硫酸水溶液 25 小時內的長期穩定

性。有趣的是，在批量反應中通過簡單選擇陰極材料則可獲得兩種不同形態的石墨烯

片，其中可得到洋蔥狀的二硫化鉬奈米片（OGNs @ 二硫化鉬）和片狀的石墨烯包裹的

二硫化鉬複合物（GNs @ 二硫化鉬）。我們發現石墨烯片的存在似乎是增強 HER 能力

的關鍵。因此，我們得出的結論是，石墨烯-二硫化鉬奈米片界面上的電子耦合在增強

二硫化鉬奈米片界面上的電子耦合在增強 HER 活性方面也起著重要作用。我們的 OGNs

@ 二硫化鉬複合材料表現出較高的 HER 性能，在 10 mA cm-2的電流密度下具有 118 mV

的低過電位，Tafel 斜率在 dec-1 的 Tafel 斜率，以及長期的穩定性而不會降解。該性能

比片狀石墨烯包裹的二硫化鉬複合材料 GNs @ 二硫化鉬（182 mV，82 mV dec-1）要好得

多。這種方法似乎是一種有效且簡單的策略，不僅可以調節摻氮過渡金屬硫化物

（TMDCs）材料，還可以調節石墨烯和 TMDCs 複合材料的形貌，從而適用於廣泛的能

源應用。

ii

Nitrogen Doped MoS2 Nanosheets and Graphene/MoS2 Composite Prepared by

Electrolysis Plasma-Induced Process for Hydrogen Evolution Reaction

Student: Nguyen Van Truong Advisor: Prof. Kung-Hwa Wei

Department of Materials Science and Engineering

National Chiao Tung University

Abstract

With the goal of obtaining sustainable earth-abundant electrocatalyst materials displaying high

performance in the hydrogen evolution reaction (HER), here we propose a facile one-pot

plasma-induced electrochemical process for the fabrication of both nitrogen-doped MoS2

nanosheets and graphene/MoS2 composite. An efficient one-step approach that involves

simultaneous plasma-induced doping and exfoliating of MoS2 nanosheets within a short time

and at a low temperature (ca. 80 °C) has been developed. Particularly, an active plasma zone

can be generated at the submerged cathode tip to achieve doping of nitrogen atoms into the

semiconducting 2H-MoS2 structure. The electronic and transport properties were modulated

under the synergy of the nitrogen doping and exfoliation in the MoS2 structure to enhance their

catalytic activation. It is found that the N concentration of 5.2 at % at N-doped MoS2 nanosheets

have excellent catalytic hydrogen evolution reaction where a low over-potential of 164 mV at

a current density of 10 mA cm–2

and a small Tafel slope of 71 mV dec–1—much lower than

those of exfoliated MoS2 nanosheets (207 mV, 82 mV dec–1

) and bulk MoS2 (602 mV, 198 mV

dec–1

)—as well as an extraordinary long-term stability of >25 h in 0.5MH2SO4 can be achieved.

Interestingly, through a simple selection of cathode materials in one-batch process, two

different morphologies of graphene sheets were obtained, resulting in both onion-like covered

MoS2 nanosheets (OGNs@MoS2) and sheets-like graphene wrapped MoS2 composites

(GNs@MoS2). We found that the presence of the graphene sheets appeared to be a key aspect

of the enhanced HER ability. Therefore, we conclude that electronic coupling at the graphene–

iii

MoS2 nanosheet interfaces also played an important role in enhancing the HER activity. Our

OGNs@MoS2 composites exhibited high HER performance, characterized by a low

overpotential of 118 mV at a current density of 10 mA cm–2

, a Tafel slope of 73 mV dec–1

, and

long-time stability without degradation; this performance is much better than that of the sheet￾like graphene-wrapped MoS2 composite GNs@MoS2 (182 mV, 82 mV dec–1

). This approach

appears to be an effective and simple strategy for tuning not only nitrogen-doped transition

metal dichalcogenide (TMDCs) materials but also the morphologies of composites of graphene

and TMDCs materials for a broad range of energy applications.

KEYWORDS: MoS2, Nitrogen doped MoS2, Onion-like graphene, Graphene/MoS2 composite,

One-pot Plasma-Induced exfoliation, Hydrogen evolution reaction, electrocatalyst.

iv

ACKNOWLEDGMENTS

This dissertation presents a summary of my research work which has done in the Department

of Materials Science and Engineering (MSE), National Chiao Tung University (NCTU). It is a

pleasure to express my sincere gratitude to all the people who helped and supported me during

my Ph.D. study.

From bottom of my heart I express my deep sense of gratitude and profound respect to my

supervisor Prof. Kung-Hwa Wei. He continually and convincingly conveyed a spirit of

adventure in regard to research and scholarship, and an excitement in regard to teaching.

Without his generous encouragement and brief advice for those years, this dissertation would

not have been completed. My sincere thanks Prof. Yu-Lun Chueh for his kind guidance and

persistent help.

I would like to thank Dr. Yen Po-Jen, Dr. Cheng Hao-Wen, Dr. Chen Hsiu-Cheng, Dr. Van￾Qui Le, Mr. Phuoc Anh Le, Mr. Chung-Hao Chen, Mr. Tzu-Yi Yang, Mr. Yung-Chi Hsu, Mr.

Bo-Hsien Lin for their kind supporting in my research. Many thanks to all participants in Prof.

Kung-Hwa Wei’s lab who took part in the study and enabled this dissertation to be possible. In

addition, I would like to thank all members of Vietnamese Student Association-NCTU who

made my life in Taiwan really pleasurable and joyful.

Finally, special thanks for my parent, my wife and my two angels who always standing by my

side. Thank you for always encouraging me to pursue my dreams. I love you all so much, thanks

for loving me too!

Nguyen Van Truong

Hsinchu, Taiwan

April 2020

v

Table of Content

摘要.............................................................................................................................................i

Abstract .....................................................................................................................................ii

Acknowledgment .....................................................................................................................iv

Table of Content .......................................................................................................................v

Figures list...............................................................................................................................vii

Tables list..................................................................................................................................xi

Chapter 1. Introduction ...........................................................................................................1

1.1. Introduction of Transition metal dichalcogenides......................................................1

1.2. Production of Transition Metal Dichalcogenides materials. ......................................3

1.3. Introduction of cathodic plasma exfoliation method..................................................6

1.4. Introduction of Electrocatalytic Hydrogen Evolution Reaction .................................9

1.5. Introduction of nitrogen doped MoS2 .......................................................................12

1.6. Introduction of graphene/MoS2 composite...............................................................14

1.7. Strategies to enhancing MoS2 catalytic activity .......................................................16

1.8. Thesis outline............................................................................................................20

Chapter 2. Production Nitrogen-Doped Molybdenum Disulfide nanosheets through

Plasma-Induced process and their electrocatalyst performance .......................................21

2.1. Introduction ..............................................................................................................21

2.2. Experimental section ................................................................................................24

2.3. Results and discussion..............................................................................................27

2.4. Conclusions ..............................................................................................................50

vi

Chapter 3. Production Graphene/MoS2 composite through One-Pot Plasma-Induced

process and their Electrocatalyst performance ...................................................................51

3.1. Introduction ..............................................................................................................51

3.2. Experimental section ................................................................................................54

3.3. Results and discussion..............................................................................................58

3.4. Conclusions ..............................................................................................................83

Chapter 4. Conclusions..........................................................................................................84

References ...............................................................................................................................87

Vita...........................................................................................................................................99

Publications list.....................................................................................................................101

vii

Figures list

Figure 1.1 The periodic table with highlighted transition metal and chalcogenide elements that

form layered TMDCs materials..................................................................................................1

Figure 1.2 The crystal struture of TMDCs with Octahedral (1T), Trigonal prismatic (2H) and

(3R) coordination........................................................................................................................2

Figure 1.3 Six main production methods of TMDCs and their content ....................................3

Figure 1.4 Several TMDCs nanosheets production methods ....................................................5

Figure 1.5 Typical of plasma electrolysis and its applications..................................................6

Figure 1.6 Experimental setup and mechanism of cathodic plasma exfoliation .......................7

Figure 1.7 Schematic representation of the proposed mechanism of plasma exfoliation and

nitrogen-doping ..........................................................................................................................8

Figure 1.8 I-V curve of overall water splitting........................................................................10

Figure 1.9 Schematic of the covalent nitrogen doping in MoS2 upon N2 plasma surface

treatment. ..................................................................................................................................13

Figure 1.10 (a) Schematic illustration of the electrochemical deposition set-up; (b) Comparison

of MoS2-3D graphene hybrid in solution and solid state supercapacitor .................................15

Figure 1.11 Synthesis procedure and structural model for mesoporous MoS2 with a double￾gyroid morphology ...................................................................................................................17

Figure 1.12 the schematic preparation process of MoS2/N-RGO nanocomposite ..................19

Figure 2.1 (a) Experimental setup for plasma-induced exfoliation and (b) proposed mechanism

of exfoliation and nitrogen-doping process. .............................................................................27

Figure 2.2 FE-SEM images of bulk commercial samples of (a) MoS2, (b) MoSe2, (c) WS2 and

(d) WSe2, respectively. .............................................................................................................29

viii

Figure 2.3 SEM images of exfoliated (a) MoS2, (b) MoSe2, (c) WS2 and (d) WSe2 nanosheets.

AFM images of exfoliated (e) MoS2, (f) MoSe2 and (h) WSe2 nanosheets. Raman spectra of

exfoliated (i) MoS2, (j) MoSe2, (k) WS2 and (l) WSe2 nanosheets. .........................................31

Figure 2.4 UV–Vis spectra of (a) MoS2, (b) MoSe2, (c) WS2 and (d) WSe2 nanosheets........32

Figure 2.5 Low-magnification TEM images of (a) MoS2, (b) MoSe2, (c) WSe2 and (d) WS2

nanosheets. Insets show the corresponding SAED patterns. HRTEM images recorded along the

[001] zone axis. Insets: their filtered of (e) MoS2 (f) MoSe2, (g) WSe2, and (h) WS2. STEM

bright-field images of (i) MoS2, (j) MoSe2, (k)WS2 and (l) WSe2 nanosheets, and their element

mapping images, respectively...................................................................................................33

Figure 2.6 (a) Difference in frequency between E1

2g and A1g in Raman spectra and (b) the

lateral size of exfoliated MoS2 using different applied biases..................................................35

Figure 2.7 (a) Mechanism of the N-doped MoS2 nanosheets. (b-f) Dark-field STEM images of

undoped MoS2 and N-doped MoS2 nanosheets and the corresponding EELS elemental mapping

images of Mo, S and N with different electrolytes and/or plasma-induced time, respectively 36

Figure 2.8 The statistical distribution of the lateral size of (a) undoped MoS2, (b) N-doped

MoS2 and (c) the thickness of MoS2 nanosheets......................................................................38

Figure 2.0.21. XPS spectra (a) survey, (b) S 2p and (c) Mo 3d of Undoped MoS2 and N-doped

MoS2 nanosheets, respectively. ................................................................................................39

Figure 2.9 SEM images of N-doped MoS2 after the plasma-induced exfoliation at (a) 200 oC,

(b) 300 oC (c) 500 oC and their BF-STEM images(d-f), respectively, correspond with EDS

mapping of Mo, S and N elements. ..........................................................................................41

Figure 2.10 Raman spectra of N-doped MoS2 nanosheets after the thermal annealing at (a) 200,

(b)300, and (c)500 oC, respectively. .........................................................................................42

Figure 2.11 (a) LSV curves (recorded on a glassy-carbon electrode) of bulk MoS2, undoped

MoS2 and N-doped MoS2 (b) Corresponding Tafel plots derived from (a). (c) Nyquist plots

acquired at –200 mV vs. RHE of the bulk MoS2, undoped MoS2 and N-doped MoS2. (d)

Durability test of the N-doped MoS2 catalyst, performed at an overpotential of 165mV vs. RHE

..................................................................................................................................................45

ix

Figure 3.1 (a) Procedure and setup for the preparation of MoS2 nanosheets covered by onion￾like graphene sheets (OGNs@MoS2) and MoS2 nanosheets decorated on sheet-like graphene

(GNs@MoS2); (b) Schematic representation of the proposed mechanism of OGNs@MoS2 and

GNs@MoS2 ..............................................................................................................................58

Figure 3.2 Digital images of plasma-induced experiments of fabricating MoS2 nanosheets

wrapped with graphene nanosheets: (a) step 1: making MoS2 nanosheets, (b) step 2: making

graphene nanosheets on MoS2 nanosheets ...............................................................................59

Figure 3.3 a–c) SEM and (d–f) TEM images of (a, d) MoS2 nanosheets, (b, e) OGNs@MoS2,

and (c, f) GNs@MoS2 sample prepared through plasma-induced exfoliation. ........................60

Figure 3.4 (a) SEM and (b) low magnification TEM image of OGNs....................................60

Figure 3.5 EDS spectra of MoS2, GNs@MoS2 and [email protected]

Figure 3.6 High resolution TEM image and insets SEAD of (a) MoS2 nanosheets and (b) OGNs

..................................................................................................................................................63

Figure 3.7 AFM images of MoS2 nanosheets and corresponding height profile.....................63

Figure 3.8 (a) HR-TEM image and SAED pattern (inset) of the OGNs@MoS2 sample; (b)

expanded view; and (c) HR-TEM image of the same sample recorded from another position.

(d) STEM bright-field image of the OGNs@MoS2 sample and corresponding elemental

mapping of C, Mo, and S atoms. ..............................................................................................65

Figure 3.9 (a) HR-TEM image of the GNs@MoS2 sample and expanded views of its (b) MoS2

and (c) GNs region; insets: corresponding SAED patterns. (d) STEM dark-field image of the

GNs@MoS2 structure and corresponding elemental mapping of C, Mo, and S atoms............67

Figure 3.10 (a, b) Raman spectra and (c) XRD patterns of the OGN, MoS2, and OGNs@MoS2

samples. ....................................................................................................................................68

Figure 3.11 (a) XPS survey spectra of the OGN and OGNs@MoS2 samples. (b–d) High￾resolution XPS spectra of the (b) C 1s, (c) Mo 3d, and (d) S 2p core levels............................70

Figure 3.12 High resolution XPS spectra of O1s of (a) OGNs@MoS2 and (b) MoS2 nanosheets.

..................................................................................................................................................71