MINISTRY OF EDUCATION
AND TRAINING

VIETNAM ACADEMY OF
SCIENCE AND TECHNOLOGY

GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY
------------------------------

Pham Hong Hanh

STUDY AND FABRICATED ELECTROCATALYSTS ON
THE IrO2 BASIS FOR OXYGEN EVOLUTION REACTION
IN PROTON EXCHANGE MEMBRANE WATER
ELECTROLYZER
Major: Theoretical and Physical Chemistry
Code: 9.44.01.19

SUMMARY OF CHEMICAL DOCTORAL THESIS

Ha Noi – 2019


The work was completed at : Graduate University Science and
Technology – Vietnam Academy of Sicence and Technology
Science instructor: Doc. Nguyen Ngoc Phong
Doc. Le Ba Thang

Reviewer 1:
Reviewer 2:
Reviewer 3:

renewable energy. So hydrogen-based economics will gradually replace
the oil economy and will be the most ideal sustainable economy of
mankind.
There are many ways to produce hydrogen, the proton exchange
membrane water electrolysis method (PEMWE) using uses electricity to
split the pure water into hydrogen at cathode and oxygen at anode. It is a
method with many outstanding advantages: high efficiency (possibly
more than 90%), high purity (about 99%), safe, low energy
consumption, can operate with high current density (up to 2 A.cm-2) and
1


ability to combine with renewable energy sources such as wind power,
solar energy…There are a lot of intensive researches and developments
which have been done on PEMWE and commercialized product s(with
hydrogen production capacity of 0,01‒50000 Nm3.h-1) were provided by
globe companies. However, high cost of investment to use precious and
expensive catalysts material has limited their mass commercialization.
In addiction, the overpotential loss on anode of PEMWE for oxygen
evolution reaction (OER) is still relatively high and this reduce the
efficiency of water electrolysis processes. Therefore, in recent PEMWEs
research have been focused on new catalysts material in order to
improve the anode active surface area, catalyst utilization, and stability
by use nanosize powder materials, thereby improving the performance
and capacity of PEMWE.
In Vietnam, studies of hydrogen production electrolysis using
proton exchange membranes have not been given much attention. In
order to continue gradually with the hydrogen economy and keep up
with the research trend of catalytic materials for PEMWE. Stemming
from that reason, the thesis is aimed at: “Study and fabbricated

PEMWE when operating.
CHAPTER 1. INTRODUCTION
- Introduction of development history, structure, operational principles
and application of PEMWE.
- Present the mechanisms and kinetics of oxygen evolution reaction and
hydrogen evolution reaction on the catalytic materials based on IrO2 in
PEMWE.
- Introduction of development history of catalytic materials used in
PEMWE and research & development of catalytic materials at the anode
and cathode electrodes of PEMWE.
3


CHAPTER 2. EXPERIMENTAL AND RESEARCH METHOD
2.3. Fabrication of electrocatalyst materials on the IrO2 basis
Three methods applied to catalyst synthesis are hydrolysis, Adams and
Adams modified method.
- Hydrolysis method: At first, metal precursors were dissolved in
deionization water with the exactly calculated metal precursors. The
aqueous solution was then heated (100°C) under air atmosphere and
magnetically stirred for 1 hour. Afterward, sodium hydroxide (1 M) was
added to the solution in order to obtain the precursor- hydroxide. This
mixture was maintained under stirring and heat (100°C) for 45 minutes.
The given precipitate was then filtered and washed with deionization
water. After washing the precursor-hydroxide was dried for 5 hours at
80°C. Finally, the dryed paste was calcined in air at 450°C for 1 hour
with a heating ramp of 5°C.min-1.
- Adams method: metal precursors were added to isopropanol to obtain
a total metal concentration of 0.01 M, this solution was ultrasonic for 30
minutes and magnetically stirred for 1-2 hours to ensure complete

ink composed of powder catalyst, Nafion solution, isopropanol and
deionised water were homogenized by stirring and ultrasonicing. The
mixture was cast on a cacbon paper surface by sweep method and dried
in air, this process was repeated until enough the loading.
CV

measurements

are

measured

with three

purposes:

determination of catalytic activation and electrochemical processes on
catalytic

surfaces:

examine

the

reversibility

of

the

MEA
Gasket
Separator
plate
Shell
Current
collector
Bolt

Made in section 2.5.1
Silicon

23 × 23
50 × 50 × 1

Graphite AXF- 5Q (Poco)

50 × 50 × 3,2

Acrylic

50 × 50 × 8

Gold plated copper

50 × 50 × 1

Stainless steel plastic wrap

⏀5



Fig. 3.3. XRD patterns of IrO2
fabricated hydrolysis method

Fig. 3.4. XRD patterns of IrO2
fabricated Adams method

Figure 3.3 and 3.4 are X-ray diffraction pattern of IrO2 powder
samples synthesized by hydrolysis and Adams methods at different
furnacing temperatures. At the furnace temperature values lower than
500oC, the peaks on the X-ray diffraction pattern of both synthesized
methods have an unclear peak signal and narrower. This is because the
IrO2 formed at these furnacing temperatures has a very fine structure or
anatas structure. When the furnacing temperature is increased to 500°C
and 600°C, the size of the peaks is smaller and the more peak signals
that represent the crystal structure. The peaks on the X-ray diffraction
pattern have signal peaks at 2θ angle values: 28(110); 35.1(101);
54.3(211) are similar and all peaks match a rutile-structure as indexed.
Thus, at the furnacing temperature of 500oC or more, the IrO2 catalytic
material changes from amorphous structure to rutil crystal structure.

Fig. 3.5. SEM pictures of IrO2 electrocatalytic powers by hydrolysis
method, degree of magnification 80.000 times
8


In order to determine the morphology of the powders, FE-SEM
analysis was carried out on the catalyst oxide powders that synthesized
by hydrolysis (Fig. 3.5). All powder samples are small and uniform in

curve of IrO2 furnaced 400oC according to Adams method. In both
methods, the CV of the furnaced at 400oC has the largest area compared
to the furnaced samples at higher temperatures in the same synthesis
method, this is due to irO2 heating at 400oC with an anatas structure,
particle size is the smallest and smoothest so their electrochemical
activity surface is the largest so the catalytic activity is the largest
compared to other samples of the same method. Because the particle
size is much smaller, the IrO2 sample furnaced at 400oC by Adam
method has a larger catalytic activity than the synthetic sample by
hydrolysis method. The higher the temperature, the lower the CV area
means, the lower the activation rate, however the samples synthesized
by the Adams method still have greater activation than the sample of
hydrolysis method at the same temperature.
From the anode polarization curves of the catalytic powders, the
electrochemical parameters were calculated and summarized in Table
10


3.1. Based on the data in Table 3.1, it is found that IrO2 oxide is
furnased at 500oC by the Adams method has been catalyzed to OER in
the highest due to the lowest Eoer.
Table 3.1. Electrochemical parameters for IrO2 powders furnaced
different temperatures
io
Eoer
Charge total
Mẫu
(µA/cm2)
(mV)
(C.cm-2.mg-1)

synthetic catalysts by hydrolysis method. Furnacing temperature also
greatly affects the structure, activity and durability of the catalyst, at a
furnace temperature of 400oC, the catalysts have a smaller size, better
catalytic activity but less stable more than c furnaced samples at
temperatures of 500oC and 600oC. Optimal catalytic selection is based
on the best combination of specific characteristics of catalysts such as
activity, durability, good catalytic ability for OER as well as production
costs, and furnace temperature of 500°C is the right temperature to
furnace catalyst powder by Adams method.
In order to further optimize the activity surface of the catalytic
powder, melting temperature of NaNO3 at 308oC, so it should be
maintained at this melting temperature for a while so that the melting
NaNO3 will completely react with H2IrCl6 to form IrO2 with high
performance. Applying this improvement, the IrO2 catalyst was
11


synthesized by the Adams method of improvement according to the
two-step heating process, specifically as follows: furnace at 325oC for
30 minutes with a heating ramp of 5 °C min-1 then raising the furnace
level up to 500oC with a heating ramp of 5°C.min-1 and keep at this
temperature for 1 hour.
X-ray diffraction pattern of two IrO2 samples furnaced in one
step and two step modes have the same intensity and peak peaks are
similar and all peaks match a IrO2 rutile-structure as indexed. This
proves that the samples that burn both of these thermal modes form IrO2
rutile structure. However, the furnaced sample in two thermal steps has
a wider peak footprint meaning that the catalytic particles size obtained
are smaller. TEM images of these samples also show that the two stage
samples has smaller (only a few nanometers in size), more uniform


Fig. 3.14. Process of fabrication of IrO2 powder catalytic material
3.2. Fabrication of IrxRu(1-x)O2 electrocatalyst
From the TGA and DTG diagrams when furnaced salt mixtures
(H2IrCl6.nH2O + NaNO3) and (RuCl3.mH2O + NaNO3) in the air, it is
possible to determine the temperature range of 400-600 oC is the
appropriate temperature range for furnaced of a mixture of salt into
IrxRu(1-x)O2, combined with experimental part 3.1 (proved that the
temperature of 500oC is the optimal temperature to synthesize IrO2) we
give the appropriate temperature to synthesize IrO2, Ir0.9Ru0.1O2,
13


Ir0.8Ru0.2O2, Ir0.7Ru0.3O2, Ir0.6Ru0.4O2, Ir0.5Ru0.5O2 and RuO2 are 500°C
following to the improved Adams method of using are two salts
H2IrCl6.nH2O and RuCl3.mH2O precursors.

Fig. 3.17. XRD patterns of IrxRu(1-x)O2
Fig. 3.17 shows XRD patterns of IrxRu1−xO2 powders. As can be
observed that the diffraction patterns of all samples have well-defined
peaks, narrow pics’ width and rutile structures. Diffusion spectra of pure
ruthenium oxide and pure iridium oxide are distributed in nearly
identical 2θ angles due to their similar structures. The diffraction peaks
of the oxide mixture have both all the diffraction angles of the two pure
oxides, however these peaks slowly toward the peaks of the RuO2 oxide
as the gradual increase of the ruthenium concentration. Which may
indicate that when rutheni was added, a lattice was modificated, the
solid phase was formatted and crystal size increases. The average
crystallite sizes for IrxRu1−xO2 powders were estimated using Scherrer
equation, the results are 2.4 nm and 3.1 nm for IrO2 and RuO2,

has the lowest activity, the oxide mixtures have similar shape and
medium activity and the activation area increases as the ruthenium is
added to the mixture.
15


The activity degradation of the catalyst mixtures were shown
by the reduction in the area of CV curves after 1000th cycles in 0.5 M
H2SO4 at a scanning speed of 50 mV s -1, the results also shown in
Figure 6 and Table 2. Results showed that although IrO2 had lower
reactivity, it was more resistant to RuO2, which is consistent with
previous studies. IrO2 was reduced to 4.6 % activity after 1000th cycles
while RuO2 was reduced to 19.8 %. As RuO2 was gradually added,
activity degradations increased but these increases was insignificant
compared to the large reduction of pure RuO2.
EOER ,io parameters from polarisation (table 3.4). Similar to
previous study, RuO2 is the most active, its corresponding starting
potential of oxygen evolution is the lowest (1100 mV) and the catalytic
properties are optimized and IrO2 is the lowest active. For mixture
oxides, the starting potential of oxygen evolution decreases with the
increase of RuO2. There result are similar to the result of the CV
measurements. This imply that the presence of the ruthenium in the
electrocatalyst and it can be insert the latice to the formation of a
common valence band with iridium oxide, thus promotes the oxygen
evolution reaction. However, RuO2 is also known to be less stable than
IrO2, in the acid media RuO2 can corrode to RuO4 so the corrosion of the
mixture oxides increase with increase of ruthenium content. Thus, a
solid solution with a moderate Ru content on the outercatalyst surface
should represent a good compromise between activity and stability. In
this study, the optimun Ru content is 30 % mol, because at this mol ratio

7.8
Ir0.6Ru0.4O2
20
1160
34.6
9.5
Ir0.5Ru0.5O2
24
1150
36.9
10.2
RuO2
42
1100
38.9
19.8

Fig. 3.27. Polarisatiom curves of IrxRu1−xO2 electrocatalytic power in
0.5 molL-1 H2SO4 electrolyte, 1 mV.s-1
Thus, it can be seen that the modified Adams method has
produced IrxRu1−xO2 catalyst mixture with relatively uniform size, small
size of nanometer size and rutile structure, with good activity and
durability for oxygen evolution reaction at anode. The addition of
ruthenium formed a solid solution between Ir and Ru which
significantly improved the surface morphology as well as the size of the
catalytic particles thereby improving the catalytic activity without
significantly reducing the durability for OER. Ir0.7Ru0.3O2 catalyst
mixture has the best crystallization because at this molar ratio the solid
solution formation between Ru and Ir is the highest. Ir0.7Ru0.3O2 particles
have fairly uniform morphology for highest activity and average

listed in Table 3.5. The activity of catalyst also changed with increasing
activity towards Ti
process that will affect the properties of MEA: pressure, temperature
and pressing time. In this thesis, the pressing time and temperature are
fixed at 180 s and 130oC, the pressure is changed from 18-22 kg.cm-2.
Figure 3.43 is a V-I graph of a single PEMWE with MEA
pressed at different pressures. Observing on V-I, it is found that when
the pressure decreases, the polarization curves tend to shift to the left,
indicating that the pressure is reduced, the voltage of PEMWE
increases. During the average current density stage, the slope of line V-I
of MEA fabricated at 20 and 22 kg.cm-2 is lower than that of MEA
manufactured at other pressure values, meaning that the internal
20


resistance of MEA is made at pressures of 18 and 24 kg.cm-2will be
higher than the internal resistance of MEA fabricated at pressures of 20
and 22 kg.cm-2. This may be due to the loose cohesion between the
diaphragm and the catalyst layer at the pressure of 18 kg.cm-2, while at
the pressure of 24 kg.cm-2, this cohesion is much more compact as the
results of SEM photo. At the pressure value of 22 kg.cm-2, the potential
of PEMWE is reached at the lowest current density of 1 A.cm-2,
indicating that the performance of this pressure is the highest in
PEMWE.
Figure 3.44 is a potentiometric graph of PEMWE with MEA
made from four different pressures. On the graph, it can be seen that the
voltage curves over time shift to the left in the direction of reducing
pressure. With MEA fabricated at small pressure of 18 kg.cm-2, the
voltage value increases rapidly and has the greatest value. This may be
due to weak pressure so the bonding is not good enough, causing the
separation of the GDL layer with the nafion membrane after a period of
osmosis of the water molecule through the bonding surface. Therefore,

Ir0.2Ru0.8O2
5
Ir0.7Ru0.3O2
6
Ru0.8Nb0.2O2
7
Ir0.5Ru0.5O2
8
Ru0.9Ir0.1O2
9
Ir
10
Ir0.5Ru0.5O2

Potential at current density
1 A/cm2 (V)
1.567
1.600
1.610
1.617
1.618
1.620
1.710
1.750
2.000
2250

Reference
[35]
[97]

It is a catalytic mixture Ir0.7Ru0.3O2.
4. The IrRuMO2 (M = Ti; Sn; Co) were synthesized. The research
results indicate that the third element is Titan has activity and durability.
The application of IrRuTiO2 catalyst in PEMWE promises to bring
economic efficiency by reducing the cost of using iridium precious.
5. A single PEMWE with a 5 cm2 working area has been designed and
manufactured in the laboratory with self-synthetic Ir0.7Ru0.3O2 catalyst.
The suitable technical parameters for manufacturing MEA used hot
pressing method were pressure: 22kg.cm-2, temperature: 130oC, time:
180 s. The potential of single PEMWE was 1.618 V at 1 A.cm-2. This
voltage equivalent to studies in the world.
NEW DISTRIBUTRIONS OF THESIS
1. The IrO2 và IrxRu(1-x)O2 (x = 0; 0.5; 0.6; 0.7; 0.8; 1) electrocatalysts
has been fabricated based on modified Adams process with correction

23