2. New Nitrogen-Doped Graphene/ZIF-modified catalyst for Fuel Cell Systems
Hello again, everyone. A repeated introduction to someone who was not here at my first presentation. My name is Shiqiang Zhuang. I’m a PhD candidate from Mechanical Engineering of NJIT. My research area is about catalyst for fuel cell systems. This talk is about“New Nitrogen-Doped Graphene/ZIF-modified catalyst for Fuel Cell Systems”. And my first talk is about New nitrogen doped graphene Catalyst Synthesized by Wet Ball Milling, abstract number is 0109.
Shiqiang Zhuang
PI: Eon Soo Lee, Ph.D.
ADVANCED ENERGY SYSTEMS & MICRODEVICES LABORATORY
Mechanical and Industrial Engineering
6/1/2016

3. Content INTRODUCTION OF THE RESEARCH BACKGROUND
REVIEW OF NITROGEN-DOPED GRAPHENE CATALYSTS-LAB SYNTHESIZED, AND ZIF-8
METHODOLOGY OF NITROGEN-DOPED GRAPHENE MODIFIED BY ZIF-8
CHARACTERIZATION ANALYSIS OF LAB SYNTHESIZED N-G/ZIF
NEXT…
My presentation includes five sections: an introduction of research background… and the next research tasks.

4. 1. Introduction of Research Background
Proton Exchange Membrane (PEM) Fuel Cell
Nitrogen-doped Graphene (N-G) catalyst
Platinum (Pt) => non-platinum group metal material (non-PGM)
The catalyst I’m working on is catalysts for electrochemical systems such as the Proton Exchange Membrane, or PEM fuel cell. PEM fuel cell is a promising energy device which can directly convert chemical energy to electrical energy with high efficiency. But the application of PEM fuel cell is limited by the high cost.
Currently people use platinum as catalyst in PEM fuel cells because of the excellent catalytic and electrochemical performance of it. The advantages of Pt catalyst include high activity, high selectivity, and high stability. But the cost of Pt is too high, which is almost 17% of the whole fuel cell system, because of the limited production and wide application requirement. So researchers are trying to reduce the material cost of catalyst by developing non platinum group metal catalyst, or non-PGM catalyst, to replace Pt.
Nitrogen doped-graphene catalyst, which is one of non-PGM catalyst, is our research target. The active sites of N-G includes four nitrogen functional groups: pyridinic-N, graphitic N, pyrrolic-N (N-H) and pyridinic-N-O+. The composition of these four bonds can directly influence the catalytic activity of N-G. Compare to Pt, the N-G catalyst has much less raw material cost. But it still has good catalytic activity for oxygen reduction reaction, good selectivity, and good chemical stability. And it is a support-free catalyst as well.
Q: Platinum group metal includes?
 ruthenium, rhodium, palladium, osmium, iridium, and platinum.
(Ref.:
Pt/Graphene catalyst
Advantages
Disadvantages
Advantages:
Good oxygen reduction reaction (ORR) activity, selectivity, and stability.
The cost of materials is much less than precious metal-based catalyst;
Support-free catalyst.
High Activity
High Cost
High Selectivity
Limited Production
High Stability
(Ref. Seger B, Kamat PV (2009) Electrocatalytically active graphene–platinum nanocomposites. Role of 2-D carbon support in PEM fuel cells. J Phys Chem C 113:7990–7995)

5. 2. Review of N-G Catalysts-Lab Synthesized, and ZIF-8
Synthesis Methodology
Mechanochemical synthesis approach for N-G catalyst — High Energy Ball Milling.
Advantages:
The machine can be used for dry or wet material;
simple operating conditions, and grinding in a closed machine, with no dust flying;
reliable intermittent or continuous operation;
the mill can be filled with inert gas instead of air;
room temperature working condition.
we have investigated a mechanochemical approach-nanoscale high energy wet ball milling as synthesis method in the research of N-G catalysts. Compare to chemical approaches, high energy ball milling has several advantages such as dry or wet grinding environment; simple operation, and room temperature synthesis.
The mechanism of ball milling is that: the materials and grinding media are mixed and moving in the high speed rotating jar. the mechanical energy generated by the impact between grinding media will be used as activation energy for the synthesis reaction. This process in the synthesis of N-G catalysts is: first is the breaking phase. The graphene oxide particles are fractured between grinding media. Some area is activated by this behavior. And then the nitrogen doping reaction can occur on these active area.
The ground resultants were tested by several characterization analysis methods. The results presented in the last talk show that the nitrogen atoms were successfully doped on graphene oxide by this mechanochemical approach..

6. Synthesizing N-G catalysts by using high-energy wet ball milling
N-G Particles
A simple sketch of the experimental process is shown here.
The targeted N-G catalyst sample was prepared by wet ball milling with graphene oxide and melamine as reactants. The mass ratio between GO and melamine is 1:6. The jar size is 12 ml. grinding media is zirconia, which has very high density and hardness to reduce the material loss. We have measure the weight changing of grinding media after ball milling, the weight loss is less than 3%. The one step experimental process is that graphene oxide and melamine are dispersed and ground in the water at 500 rpm grinding speed for 24 hours to form N-G catalyst, which is named BM500N-G-24hr.
Experimental Conditions:
Reactants: Graphene Oxide, Melamine (mass ratio=1:6)
Grinding Jar: 12 mL
Grinding Speed: 500 RPM
Grinding Time: 24 hours
Grinding Environment: water
Grinding Media: Zirconia
Sample name: BM500N-G-24hr

7. Properties of a Lab Synthesized N-G Catalyst
Physical Properties of BM500N-G-24hr
Chysical Properties of BM500N-G-24hr
SEM image
BM500N-G-24hr
Elemental Composition At % (relative ratio between C, N, O)
C: 67.23
N: 16.11
O: 16.67
Nitrogen Bonding Composition At % (relative ratio)
Pyrrolic N-H: 28.4
Pyridinic N: 59.5
Graphitic N: 15.1
Pyridinic N+-O-: 0
Current Density
3.1 mA/cm2
Electron Transfer Number (n)
2.79
(n=4: O2+4e->2O2-
n=2: O2+2e->2O-)
BET Surface area
25 m2/g
The physical and chemical properties of synthesized N-G catalyst sample was analyzed by several characterization analysis methods, include Zetasizer, XPS, SEM, TEM, and RDE test. The particle size of this sample is nm. The nitrogen content is 16%. Current density generated in oxygen reduction reaction is 3.1 mA/cm2
By the way, We have synthesized N-G catalysts with different experimental conditions in the lab. The work of N-G synthesized by high energy wet ball milling is already submitted as journal paper.
The XPS test results of elemental composition and nitrogen bonding composition show that nitrogen atoms were successfully doped on the graphene oxide particles. From the study of synthesis experiment, we found that grinding speed represent the energy intensity in the ball milling. In the previous research, it is found that the formation of pyrrolic N, pyridinic N, graphitic N and pyridinic NO is directly controlled by energy intensity in the ball milling process. The nitrogen bonding composition of N-G synthesized at 500 RPM and 24 hours grinding time is listed in the table. As I mentioned in the last talk, the BET surface area of this N-G sample is 25 m2/g, which is smaller than original graphene oxide. And that is one reason which make the N-G doesn’t have good catalytic performance. The electron transfer number is only 2.79.
It is known that two oxygen reduction reactions can occur on the active sites of N-G catalysts, 4 electrons reaction and 2 electrons reaction. It is always expected that the electron transfer number of catalyst can be close to 4. So that most of oxygen atoms are directly reduced to oxygen ion with negative 2 charges. The electron transfer number of this sample is 2.79, which means the ORR is more close to 2 electrons reaction occurs on the active sites of this catalysts. So the ORR catalytic activity is not high.
Particle size: nm
TEM image

8. Influencing Factors of Catalytic Activity
Relative ratio of N functional groups
Catalytic Activity
BET
Surface Area
Catalytic Performance of Active Sites
Surface Density of Active Sites
Surface Structure
Porosity
Nitrogen At%
Therefore, we studied the influencing factors of catalytic activity in order to investigate some way to enhance the catalytic performance of this N-G sample. The first thing is, What is catalytic activity? Catalytic activity means the amount of reactants reacted on per unit of catalysts in per unit time. It can be affected by specific surface, catalytic properties of active sites, and surface density of active sites. In N-G catalyst, specific surface area is related to surface structure and porosity; Catalytic performance of active sites is related to the composition of Nitrogen functional groups; And the surface density of active sites is related to the nitrogen content. We are trying to enhance the catalytic activity of the N-G sample by changing these three factors.

9. Purpose of Adding ZIF-8 To increase BET surface area of N-G;
It is already reported that the catalytic activity of catalysts can be influenced by specific surface area. Larger surface area can make catalysts have better catalytic activity. Porosity can affect the catalytic activity as well. The component of active sites in N-G includes 4 nitrogen groups. The pyridinic N and graphitic N (edge) are located at the edge of graphene sheet or pores in the sheet. High porosity can increase the possibility of the formation of these two groups. There are some researches show that these two groups may have better catalytic performance than pyrrolic nitrogen and pyridinic N-O.
We are investigating a technology approach to increase the specific surface area of N-G catalysts based on these studies. This approach is modifying N-G catalyst with metal organic framework material.
(Haiwai Liang, Wei Wei, Zhongshuai Wu, Xinliang Feng, Klaus Mullen, Mesoporous Metal–Nitrogen-Doped Carbon Electrocatalysts for Highly Efficient Oxygen Reduction Reaction, J. Am. Chem. Soc., 2013, 135 (43), pp 16002–16005 )
(Qiliang Wei , Xin Tong, Gaixia Zhang, Jinli Qiao, Qiaojuan Gong, and Shuhui Sun, Nitrogen-Doped Carbon Nanotube and Graphene Materials for Oxygen Reduction Reactions, Catalysts 2015, 5, ; doi: /catal )
To increase BET surface area of N-G;
To increase the amount of pores-pyridinic N and graphitic N (edge) groups can be formed at the edges of pores
=> more active sites

10. Introduction of Metal Organic Framework Material
Figure. (a,b) Zeolitic imidazolate framework-8 (ZIF-8, one type of MOF), (c) micrograph of the porous structure of ZIF-8.
(Tayirjan T. Isimjan, Hossein Kazemian, Sohrab Rohani and Ajay K. Ray, Photocatalytic activities of Pt/ZIF-8 loaded highly ordered TiO2 nanotubes, J. Mater. Chem., 2010,20, )
This technical approach is investigated based on the development of metal organic framework material, or MOFs. The structure and elemental composition shown in the figure a,b and c is an example of MOFs. It is named ZIF-8. MOFs are compounds consisting of metal and non-metal elements to form one-, two-, or three-dimensional structures. They are a subclass of coordination polymers, with the special feature that they are often porous. The advantages of MOFs include high porosity, large specific surface area, it can be over 1000 m2/g, and high structural and thermal stability. There is a high possibility that the structure of materials with low surface area and porosity can be adjusted by additional MOF component. Therefore, modifying non-PGM catalysts with MOFs can be an effective approach to enhance the catalytic activity of catalysts.
Q: high pore diffusion rate and high bulk mass transfer rate of reactants, what is the effect to reaction rate?
Higher reactants transfer rate means more reactants can reach catalyst surface at the same time. Therefore more reactions will occur on the surface of catalyst.
Properties of ZIF-8:
high porosity and big surface area (>1000 m2/g);
high nitrogen content;
high structural stability and high thermal stability (up to 550℃);

11. 3. Methodology of N-G Modified by ZIF-8 (N-G/ZIF)
Synthesis Methodology
Mechanochemical synthesis approach for N-G/ZIF catalyst — High Energy Ball Milling.
Based on the recent results showing promising effects by MOF structures and graphene structures doped with nitrogen, graphene structures with the nitrogen elements into the MOF structure (or we call it N-G/MOF)is expected to have enhanced catalytic activities and diffusion mechanism. It is also expected to reduce the metal content in MOF by reacting with N-G particles. The experimental synthesis process of N-G/MOF is shown in the figure here. The reactants are BM500N-G-24hr, which is a lab synthesized nitrogen-doped graphene catalyst by wet ball milling, and ZIF-8, which is mentioned in the previous slide. The mass ratio between them is 1 to 3. The method used to add ZIF-8 into N-G is wet ball milling. The N-G and ZIF-8 are mixed and dispersed in water. The solution is ground with zirconia balls in a 12 ml grinding jar for 24 hours. The grinding speed is 650 RPM. The image of final resultant, which is named N-G/ZIF, is shown in the figure at your right hand side.
Experimental Conditions:
Reactants: BM500N-G-24hr, ZIF-8 (mass ratio=1:3)
Grinding Jar: 12 mL
Grinding Speed: 650 RPM
Grinding Time: 24 hours
Grinding Environment: water
Grinding Media: Zirconia

12. 4. Characterization Analysis of Lab Synthesized N-G/ZIF
XPS
N-G/ZIF
BM500N-G-24hr
Zn bonding composition
Nitrogen bonding composition
Zn2+
Pyridinic N
The influence of adding ZIF-8 on the chemical and physical properties of the N-G sample is studied through several characterization analysis methods include XPS, XRD,SEM, TEM and BET.
Here is the comparison between original N-G and zif-modified N-G. The elemental composition, nitrogen bonding composition and oxygen bonding composition are listed in the table at your right hand side.
The first phenomena can be observed from these XPS results is that oxygen content of N-G/zif is 11.6%, which is lower than the oxygen content of the original N-G catalyst. The result shows that the relative ratio between C-O and C=O bonds is changed. It is already known that these two carbon oxygen bonds do not exist in the zif-8. So it can be concluded that the decomposition of C=O bonds occurred in the modification process of N-G catalysts.
It can be observed that N bonding composition of N-G is changed as well. The relative percentage of Pyridinic N was increased to 72%.This result confirmed that adding ZIF-8 can change the relative ratio of N functional groups. Therefore, it is possible to see some changing on the catalytic activity of N-G catalysts.
In addition, Zinc oxide is found in both ZIF-8 and N-G/ZIF samples. But it is unknown that if all the zinc atoms in this sample is in zinc oxide state. Therefore, this sample will be treated by a acid wash treatment. The zinc content in the treated N-G/ZIF sample will confirm the percentage of zinc atoms moved from ZIF-8 and formed zinc oxide.
Actually the comparison between synthesized N-G/ZIF and another N-G sample, which will be prepared by grinding the same N-G sample without adding ZIF-8 with the same experimental conditions, is included in our research plan. It will be helpful to understand if the changing of N-G is because of the existence of ZIF-8 or the physical ball milling behavior.
BM500N-G-24hr
ZIF-8
N-G/ZIF-500
N & O Content
O: 16.67%
N: 16.11%
O: 18.79%
N: 20.15%
O: 11.6%
N: 18.3%
N bonding composition At%
P-N-H: 28.4%
P-N: 59.5%
G-N: 15.1%
P-N-H: 17.6%
P-N: 72%
G-N: 10.4%
O bonding composition At%
C-O (55%)
C=O (45%)
ZnO
C-O (70%)
C=O (30%)
Oxygen bonding composition
ZnO

13. XRD Test Results of N-G, ZIF-8, and N-G/ZIF
31.7°(ZnO)
This figure is the Crystal phase curve of N-G, ZIF-8 and N-G/ZIF samples. Almost all of the XRD peaks for ZIF-8 were in good agreement with previous reports, confirming the sample in pure crystalline ZIF-8 phase. But the zif-8 crystal phase couldn’t be found in N-G/ZIF sample. This indicates that the framework of ZIF-8 was unstable throughout the 650 RPM ball milling process of catalyst preparation.
A minimal amount of zinc oxide in the impurity phase was found at 31.7°in both ZIF-8 and N-G/ZIF. It is good agreement of the existence of the zinc oxide in the N-G/ZIF sample.
N-G/ZIF
N-G
2 Theta (degree)

14. TEM images of N-G, ZIF and N-G/ZIFc c b
N-G a a b
N-G+ZIF
100 nm +
500 nm
N-G/ZIF
ZIF-8 b d
SEM of N-G/MOF
This page shows the surface structure of N-G, ZIF-8 and N-G/ZIF. The nanoparticle structure of N-G and crystal structure of ZIF-8 can be clearly observed from the TEM image. Figure d shows the structure of N-G modified by ZIF-8. The particle size of new N-G/ZIF material is around 300~500 nm. It can be observed that the crystal structure of ZIF-8 doesn’t exist in this N-G/ZIF sample. Here is a closer view of N-G/ZIF (click). The big particles are N-G/ZIF. The rod shape particles are ZnO. It is already confirmed by EDS mapping test.
We already synthesized some N-G/MOF catalyst by high energy wet ball milling. The surface structure of N-G/MOF is shown in the figure d by TEM and SEM images. Obviously new structure is formed from the reaction between N-G and MOF with ball milling condition. It can be observed that the new sample has 3-D porous structure. Therefore, compared to original N-G catalyst, the structure of ZIF-8-modified N-G is obviously changed.
100 nm
500 nm
400 nm
Figure. TEM images of (a) surface structure of N-G catalyst without ZIF, (b) structure of ZIF without N-G catalyst, (c) mixture of N-G and ZIF-8 before ball milling, and (d) surface structure of N-G/ZIF after high speed wet ball milling.

15. BET tests of N-G, ZIF and N-G/ZIF
Particle size
337.5 nm
Ave. 4.9 μm
300 nm (estimate from TEM)
BET surface area (m2/g) 25
1300~1800 (BASF)
1267~1732 (BET, Micromeritics)
Pore size
1 nm
Ave. 6nm
Max: 150 nm nm
ZIF-modified N-G catalyst, which is generated by 650 RPM and 24 hours grinding time, is expected to have larger BET surface area than N-G. But the final result shows that there is not big change on the BET surface area. N-G is 25, N-G/zif is 26. Considered the previous characterization test result of N-G/ZIF, we found that the reason of this phenomenon is the decomposition of ZIF-8. It is known that ZIF-8 can be decomposed at temperature higher than 550 C. Now it can be concluded that ZIF-8 can be fully decomposed in 650 RPM and 24 hours ball milling process with N-G as well. Actually another ZIF-8 sample will be prepared by grinding ZIF-8 at same experimental conditions but without N-G. The comparison between these samples will help us to understand if the decomposition of ZIF-8 is because of the mechanical ball milling behavior or the reaction between N-G and ZIF-8.
We are still working on the RRDE test of this N-G/ZIF sample to see the changes on the current density and electron transfer number. The study of the influence of grinding speed and grinding time on the BET surface area, pore size, porosity, nitrogen content and nitrogen bonding composition is on going as well.
N-G/ZIF

16. 5. Next … Next objectives:
Task 1: Experimentally synthesize new N-G/ZIF catalysts with superior performance characteristics based on cheap carbon material, nitrogenous substance, transition metal salt and metal organic frameworks (MOF), against state-of-the-art PGM catalysts.
Task 2: Characterize the physical, chemical, electrochemical properties and stability of N- G/ZIF catalyst samples prepared with different grinding speed or grinding time. The relations of grinding speed to BET surface area, pore size, porosity, elemental composition, and chemical bonding composition will be studied. The effect of grinding time on the properties of N-G/ZIF will help us to study the controllability of the resultants.
Task 3:Understand the mechanism of the reaction kinetics between N-G and ZIF-8, and functional mechanism of N-G/ZIF catalysts through the characterization analysis.
The main objective of our research is to develop new low cost and high performance non-PGM ORR catalysts for electrochemical applications. The next Specific objectives of this research include:
First, Experimentally synthesize new non-PGM catalysts with superior performance characteristics based on cheap carbon material, nitrogenous substance, transition metal salt and metal organic frameworks (MOF), against state-of-the-art PGM catalysts.
Second, Characterize the physical, chemical and electrochemical properties, and stability of the new non-PGM catalyst samples by using different methods such as XPS, FTIR, SEM, TEM,EDS, XRD, and rotating ring disk electrode and potentiostat; and
Third, Understand the mechanism of the reaction kinetics and functional mechanism of the new synthesized catalysts through the characterization analysis.

17. Publications ACS2015-2425505[2015] POWERENERGY2015-49602[2015]
S Zhuang, E S Lee, L Lei, B B Nunna, L Kuang, W Zhang
ER Synthesis of NITROGEN-DOPED Graphene catalyst BY high energy WET BALL MILLING for electrochemical systems [IJER Journal]
S Zhuang, Nunna, B, L Lei, E S Lee
ACS [2015]
Shiqiang Zhuang, Xuan Shi, Eon Soo Lee
POWERENERGY [2015]

18. Thanks!
Thank you for your patient. And welcome any questions.