This document summarizes an electrochemistry workshop presentation on electrocatalyst characterization. It introduces common electrochemical characterization methods like cyclic voltammetry and discusses key figures of merit for evaluating electrocatalyst activity. Examples are provided of electrocatalyst development for important reactions like hydrogen evolution, oxygen evolution, and oxygen reduction. These include developing non-precious metal catalysts and improving catalyst stability and performance through methods like decreasing platinum loading or synthesizing metal phosphides and metal oxides on supports.

1. The 2019 ESRC Workshop on Electrochemistry
FEB 27, 2019
Electrochemical Characterization of Electrocatalysts
Mabrook S. Amer
Electrochemical Science Research Chair (ESRC)
College of Science, king saud university, Chemistry Department,

2. Outline for this Presentation
Introduction and Overview of Electrode Processes
Methods of Electroatalysts Preparation and Modification
Examples of Electrocatalyst Development , characterizations and Applications
Electrochemical Methods for Characterization of Electrocatalysts
RDE and RRDE equation and applications

3. Introduction and Overview of Electrode Processes
What is Electrocatalyst?
An electrocatalyst is a catalyst that increases the rate of the
oxidation and reduction reactions in an electrochemical cell.
Solution‐phase Electrocatalysts
Metallic Or Metal oxides
Metal
Complexes
H.I. Karunadasa et. al. Science (2012)
K.P. Kuhl et. al. Energy & Environmental Science (2012)

4. Introduction and Overview of Electrode Processes
Electrochemical reactions take place at the electrode surface
As in any reaction, the system can
be affected by:
The reactivity of the reactants
The applied voltage at the electrode.
The structure of the interfacial region where the electron
transfer takes place.
•The nature of the electrode surface

5. Electron transfer + mass transport
Faradaic process
Introduction and Overview of Electrode Processes
Mechanism of electrode process
Descriptor for electrocatalysis!
(Inner-sphere e– transfer)
O + ne- ↔ R
Non-faradaic process

6. - Electrode reactions may be controlled by mass transport or
electron transfer depending on the following conditions
 Electrode material
 Potential region
 Media (type of solvent: aqueous or non-aqueous)
Introduction and Overview of Electrode Processes
Mechanism of electrode process

7. metal oxides, such
as TiO2 , SiO2
Typical precursors
are metal alkoxides.
Thin films of metals, metallic
alloys and compounds
Methods of Electrocatalysts Synthesis
Sol-gel methods Electrodeposition methods Hydro/solvo-thermal methods
Thin films of metal
oxides/hydroxides and
campsites compound
Bolla G.Rao et al. Micro and Nano Technologies, 2017, 1-36.

8. Better control on particles size
and shape
Microwave assisted synthesis
Methods of Electrocatalysts Synthesis
Wet-chemical synthesis
Hydrolysis of metal precursors
: for metal oxides
Reduction metal precursors
: for Metals NPs

9. Methods of electrocatalysts synthesis
Electrode Fabrication
 Thin film  Ink paste method
Catalyst + 5 wt% Nafionin 1m distilled water
↓Ultrasonicated for 15 min
↓10 μl pipetted on to Glassy carbon
↓dried at RT or at an C
GC/Catalyst-Nafion (metal loaded or unloaded)
using Ni foam , carbon paper or glassy
carbon as electrode substrate

10. Electrochemical Methods for Characterization of Electrocatalysts
Illustration of a three-electrode cell and an idealized
example of a cyclic voltammogram
Measurement of electrode polarization
Working electrode (W. E.)
Counter electrode (auxiliary electrode) (C. E.)
Reference electrode (R. E.)
1) Three-electrode system/cell:
Cyclic Voltammetry (CV)

11. Electrochemical Methods for Characterization of Electrocatalysts
Linear potential sweep (LSV) Potential step chronoamperometry
current as a function of time and
applied potential
Electrochemical Impedance Spectroscopy (EIS)

12. Four primary figures of merit for electrocatalyst activity:
 Exchange current density, io (mA/cm2)
 Tafel slope, b (mV/decade)
 Current density at a given overpotential:
iE (V vs. RHE) (mA/cm2)
 Overpotential needed to reach a given
current density: ηi = 10mA/cm^2 (mV)
Three ways to report current densities:
 Per geometric area (cm2 geo)
 Per surface area (cm2 real)
 Per electrochemically active surface area (cm2 ECSA)
 Turnover Frequency (TOF =
𝑗𝑆𝑔𝑒𝑜
𝑛𝐹.𝑚
)
Electrocatalyst activity: Figures of merit

13. Electrocatalytic Conversions Related to Energy
Schematic of a sustainable energy
landscape based on electrocatalysis.
Seh et al., Science 355, 146 (2017) 13 January 2017
Thermodynamic Considerations

14. E (vs.RHE)
current
density
0 1.23
2 H+ + 2 e- → H2
H2 → 2 H+ + 2 e-
diffusion-
limited
current
2 H2O → O2 + 4 H+ + 4 e-
O2 + 4 H+ + 4 e- → 2 H2O
diffusion-
limited
current
PtNi
RuO2
platinum
hydrogenase
overpotential
Reaction kinetics involving H2O‐H2‐O2
Redox reactions of water

15. Some Examples of Electrocatalyst Development and Applications
Hydrogen Evolution Reaction (HER)
A noble metal catalyst (such as platinum) as well as
commercial HER Pt-C (20% wt) catalyst are well
recognized as the best catalyst for the HER.
 These elements are expensive
 Less abundant
 Poor chemical stability in alkaline
and acidic media
 Unsuitable to use on a commercial
scale
Strategies
Drawbacks !!
Decrease the Pt loading amount
Explore efficient non-precious
(earth abundant ) catalysts
Seh et al., Science 355, eaad4998 (2017)

16. Some Examples of Electrocatalyst Development and Applications
Decrease the Pt loading amount
-0.4 -0.2 0.0 0.2
-80
-60
-40
-20
0
Potential vs. RHE/ V
Current
density/
mA
cm
–2
Carbon Paper
Pt0.5
/bulk-TiO2
Pt0.5
/meso-TiO2
10 wt. % Pt/C
(b)
-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2
-140
-120
-100
-80
-60
-40
-20
0
Current
density,
mA
cm
–2
Potential vs. RHE/ V
First cycle in 2.0 M H2
SO4
after 500 cycles
after 1000 cycles
(c)
0 0.1 0.3 0.5 1 2 3
0
20
40
60
80
100
120
140
Pt content [wt. %]
Overoptential/
mV
(c)
Low-loading of oxidized Pt NPts into meso-TiO2
Mabrook S Amer, et al. A. J. Chemistry, 2018.
linear sweep voltammetry
(LSV) of the Ptx/meso-TiO2
and pure meso-TiO2
catalysts loaded on CP
electrode in 0.5 M H2SO4 at
a scan rate of 10 mVs-1.
0 4 8 12 16 20 24
-140
-120
-100
-80
-60
Potential
vs.
RHE/
mV
Time, hour
(ii)
(i)
(d)
Chronopotentiometric curves at 20 and -40 mA cm-2

17. Some Examples of Electrocatalyst Development and Applications
Earth Abundant HER catalysts
 Tafel plots
 long-term stability
 Current density
 Onset and overpotential
Metal phosphide
Chun Tang et al. Adv. Mater. 2016,
Fe‐doped CoP nanoarray

18. Some Examples of Electrocatalyst Development and Applications
Self-Supported (HER ) Electrode
Angew. Chem. Int. Ed. 2015, 54, 8188 –8192 All measurements were performed in N2 -saturated 0.5 M
H2SO4 solution at room temperature.
SEM images of Ni5P4 - Ni2P-NS array cathode

19. Oxygen Evolution Reaction (OER)
Low-Symmetry Mesoporous Titanium Dioxide (lsm-TiO2) Electrocatalyst
for Efficient and Durable Oxygen Evolution in Aqueous Alkali
Some Examples of Electrocatalyst Development and Applications
1.4 1.6 1.8 2.0
0
10
20
30
40
50
60
70
80
bare-TiO2
lsm-TiO2
@1
lsm-TiO2
@1.5
lsm-TiO2
@2
hm-TiO2
Current,
mA
cm
-2
Potential vs. RHE/ V
(a)
Onst potential 1.55 V
75 mA cm-2
1.5
1.6
1.7
1.8
1.9
0.1 1 10
Lsm-TiO2
@1.5 (5.0 M KOH) = 45 mV/dec
Lsm-TiO2
@1.5 (1.0 M KOH) = 51 mV/dec
Lsm-TiO2
@1.0 =87 mV/dec
Lsm-TiO 2
@2.0
=98 mV/dec
log(Current/ mA cm
-2
)
Potential
vs.
RHE/
V
Hm-TiO 2
, =112 mV/dec
(a)
OER catalyst stability
Tafel plot for the all catalysts
Linear sweep voltammograms
at 10 mV s-1, 1.0 M KOH
1.0 M KOH, 12h
Mabrook S. Amer, Mohamed A. Ghanem, Abdullah M. Al-Mayouf, and Prabhakarn Arunachalam Low-Symmetry Mesoporous Titanium Dioxide (lsm-
TiO2) Electrocatalyst for Efficient and Durable Oxygen Evolution in Aqueous Alkali Journal of the Electrochemical Society 2018 165: H300-H309.
lsm-TiO2@1.5
hm-TiO2
BET surface area ( 218 m2/g)
BET surface area ( 200 m2/g)

20. Impedance lsm-TiO2@1.0 lsm-TiO2@1.5 lsm-TiO2@2.0 hm-TiO2
Rs (Ω) 27 25 18 33
Rc (Ω) 465 269 10489 171030
C (µF) 76 60 18 17
EIS impedance parameters of low-symmetry
mesoporous TiO2 (lsm-TiO2) catalysts obtained
by fitting the experimental data.
0 40 80 120 160
0
20
40
60
80
100
120
lsm-TiO2
@1.5
lsm-TiO2
@2.0
lsm-TiO2
@1.0
hm-TiO2
off
Concentration
of
O
2
(

mol/L)
Time/ mint.
on
(b)
Electrochemical impedance
spectroscopy (EIS) and O2
evolution rate
O2 evolution as measured by the O2-
oxysense sensor for lsm-TiO2 and hm-
TiO2 electrodes
Some Examples of Electrocatalyst Development and Applications

21. Oxygen Reduction Reaction (ORR)
Some Examples of Electrocatalyst Development and Applications
Energy Environ. Sci., 2014, 7, 3135-3191
Reaction pathways for oxygen reduction reaction
Path A – direct pathway, involves four-electron reduction
O2 + 4 H+ + 4 e-  2 H2O ; Eo = 1.229 V
Path B – indirect pathway, involves two-electron reduction followed
by further two-electron reduction
O2 + 2 H+ + 2 e-  H2O2 ; Eo = 0.695 V
H2O2 + 2 H+ + 2 e-  2 H2O ; Eo = 1.77 V

22. Some Examples of Electrocatalyst Development and Applications
Rotating Disk Electrode (RDE)
A rotating disk electrode (RDE) is a hydrodynamic
working electrode used in a three electrode system.

23. Some Examples of Electrocatalyst Development and Applications
Oxygen Reduction in Acid
Mass transport limiting current density at 3000 rpm
Linear Sweep Under Rotation
Kinetic current >> mass transport limit
MASS TRANSPORT LIMITED
Current estimated by Levich Equation
Dependence on ω
Kinetic current << mass transport limit
KINETIC LIMIT
Current estimated by BUTLER-VOLMER
No dependence on ω

24. Levich Equation
*
6
/
1
2
/
1
3
/
2
, 62
.
0 O
O
Disc
l C
nFAD
i 
 

Some Examples of Electrocatalyst Development and Applications
To Calculation of the numbers of electrons:
= 𝚪 𝑛𝜔1/2 (𝚪 : Levich constant)
Limiting
current
(plateau)
Mass transport control
*
6
/
1
3
/
2
62
.
0 O
O C
nFAD
slope 
 
Mixed control
as kinetic limitations
set in at high ω

25. Koutecky-Levich equation
lim
1
1
1
i
i
i K


*
6
/
1
2
/
1
3
/
2
62
.
0
1
1
1
O
O
K C
nFAD
i
i 




Some Examples of Electrocatalyst Development and Applications
Plotting Mixed Control – f (E) Oxygen Reduction
E
(-)
1/iK
*
6
/
1
3
/
2
62
.
0
1
O
O C
nFAD
slope 



26. R(R)DE (rotation (ring) disk electrode) system
RRDE system : measurement of intermediates
ORR proceeds either to
H2O2 (2-electron path) or
H2O (4-electron path):
http://www.hnei.hawaii.edu/facilities/hiserf/equipment
Ring and disc are both WORKING
ELECTRODES and
are INDEPENDENTLY CONTROLLED

27. Operation
One can measure the extent a specific product is
made at the disc by
reversing the reaction at the ring
R(R)DE (rotation (ring) disk electrode) system
DISC RING r
O2
O2 + 2H+ + 2e- H2O2
Scanning E  (-)
O2 + 4H+ + 2e- H2O H2O2  O2 + 2H+ + 2e-
Constant E (+)

28. RRDE Collection Efficiency
R(R)DE (rotation (ring) disk electrode) system
disc
l
ring
l
i
i
N



Collection Efficiency N : depends on dring, ddisk, gapring-disk
Fraction of H2O2 formed
𝒙 H2O2 = 𝟐𝑰r ⁄ 𝑵 (𝑰d + 𝑰r) ⁄ 𝑵
( 10m M of K3[Fe(CN)6]., 1M, KNO3, )
(at the disk electrode)
(at the ring electrode)

29. Example of ORR catalysts
LSV curves for ORR on CNTs, Co3O4/CNTs and Pt/C catalyst in O2-saturated
0.1 M KOH solution at a scan rate of 5 mV s−1 and at a rotating speed of 1600
rpm
Young-Bae kim et al, Scientific Reports (2018) – 2543 VL - 8IS - 1AB
TEM (a and b), HRTEM of f Co3O4/CNTs ORR electrode
Co3O4 on Carbon Nanotubes (CNTs) for
Oxygen Reduction Reaction.