Chinese Business Review, March 2015, Vol. 14, No. 3, 159-167
doi: 10.17265/1537-1506/2015.03.005
D
DAVID
PUBLISHING
Possibility of Using Ni-Co Alloy As Catalyst for Oxygen
Electrode of Fuel Cell
Paweł Piotr Włodarczyk, Barbara Włodarczyk
Opole University, Opole, Poland
In recent years, the scale of use of fuel cells (FCs) has been increasing continuously. One of the essential elements
that affect their work is a catalyst. Precious metals (mainly platinum) are known for their high efficiency as FC
catalysts. However, their high cost holds back the FCs from application on a large scale. Therefore, catalysts that do
not contain precious metals are sought. Studies are focused mainly on the search for fuel electrode catalysts, but for
the efficiency of FCs also the oxygen electrode catalyst is of great significance. The paper presents an analysis of
the possibilities of using Ni-Co alloy as a catalyst for the oxygen electrode of the FC.
Keywords: fuel cell (FC), renewable energy sources, Ni-Co alloy, catalyst, electroreduction, oxygen electrode
Introduction 
One of ecological and high efficiency sources of electric energy is a fuel cell (FC). FCs are successfully
used in aerospace, power engineering, cogeneration aggregates, as power supply for FC cars and buses, boats,
submarines, emergency power systems, and more (Hoogers, 2004; O’Hayre, Cha, Colella, & Prinz, 2005;
Stolten, 2010). Furthermore, FCs can power mobile energy sources for laptops and cell phones (Kakaç,
Pramuanjaroenkij, & Vasilev, 2007). The FCs transformed the chemical fuel into the electricity without
intermediate stages. Therefore, the real efficiency is even 80%. Moreover, FCs have no moving parts and are
noiseless (O’Hayre et al., 2005; Stolten, 2010). The major barriers for use of FCs are currently used catalysts.
Due to the excellent catalytic properties, platinum is most commonly used as the catalyst. Nickel is also quite
common. But due to the high price of platinum and problems with the use of nickel, there is a need for finding
other catalysts. Replacement of platinum will contribute to the fast development of green energy sources.
In addition to the catalysts for fuel electrodes, an important issue is also to search for new Pt-free catalysts
for oxygen electrodes (Anastasijevic, Dimitrijevic, & Adzic, 1986; Strbac & Adzic, 1996). Overall efficiency
of the FC depends on the performance of both the fuel electrode and the oxygen electrode. Thus, the quality of
the FC is directly dependent on the oxygen electrode. Therefore, the search for a catalyst of the oxygen
electrode is a very important issue. Selection of an appropriate catalyst for both the fuel electrode and the
oxygen electrode will allow to develop a highly efficient energy source, which is a FC.
Besides platinum, also nickel is frequently used as the catalyst of electrodes for FCs. But problems with
the use of Ni impede its use. Nickel is mostly used as Raney Ni, but Raney nickel is not very easy to use.
Paweł Piotr Włodarczyk, Ph.D., Department of Process Engineering, Opole University, Opole, Poland.
Barbara Włodarczyk, Ph.D., Department of Process Engineering, Opole University, Opole, Poland.
Correspondence concerning this article should be addressed to Paweł Piotr Włodarczyk, Department of Process Engineering,
Opole University, Dmowskiego Street 7-9, 45-365 Opole, Poland. E-mail: [email protected].
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OXYGEN ELECTRODE OF FUEL CELL
Raney nickel is typically supplied as 50% slurry in water. It is essential not to expose Raney nickel to air. Even
after reaction, Raney nickel contains significant amounts of hydrogen gas and may spontaneously ignite when
exposed to air (Armour, 2003). The new catalysts allow for the elimination of costly platinum and difficulties
with the use of nickel (Rolison, Hagans, Swider, & Long, 1999; Twigg, 1989; P. P. Włodarczyk & B.
Włodarczyk, 2014a, 2015).
Theory
One of the major advantages of FCs is their high efficiency. Moreover, the FCs combine the high
efficiency with low influence on environment. Solving problems related to disadvantages of FCs will contribute
to the fast development of green energy sources.
One of the major problems slowing down the fast development of FCs is the catalyst. Most often the
catalyst is platinum, mostly due to the excellent catalytic properties (Bockris & Reddy, 2000; Guo & Le, 2004;
He et al., 2004). However, because of platinum prices, other catalysts are researched. The efficiency of the FC
not only depends on the fuel electrode, but also on the oxygen electrode (Bockris & Reddy, 2000). Thus, the
quality of the FC is also directly dependent on the oxygen electrode. So the search for a catalyst of the oxygen
electrode is a very important issue.
Efficiency Comparison of Heat Engines and FCs
The efficiency of heat engines results from Carnot cycle (Feynman, Leighton, & Sands, 1964). The
efficiency relates how much useful work is output for a given amount of heat energy input. The amount of
energy transferred as work W is:
𝑊 = 𝑝𝑑𝑉 = 𝑇ℎ − 𝑇𝑐 𝑆𝐵 − 𝑆𝐴
(1)
3
where p is pressure (Pa); V is volume (m ); Th is absolute temperature of the hot reservoir (K); Tc is absolute
temperature of the cold reservoir (K); SA is minimum system entropy (J/K); and SB is maximum system entropy
(J/K).
The efficiency of heat engines HE is defined to be:
𝜂𝐻𝐸 =
𝑊
𝑄ℎ
= 1−
𝑇𝑐
𝑇ℎ
(2)
where W is work (J); Qh is total amount of thermal energy transferred between the hot reservoir and the system (J);
Th is absolute temperature of the hot reservoir (K); and Tc is absolute temperature of the cold reservoir (K).
So the efficiency of heat engines depends on the temperature. Therefore, the efficiency is low.
In a FC, the maximum energy of chemical conversion of energy into work is equal to the free energy
reaction (Bockris & Reddy, 2000; Fetter, 1961):
Δ𝐺 = Δ𝐻 − 𝑇Δ𝑆
(3)
where ΔG is change in Gibbs free energy (KJ/mol); ΔH is change in enthalpy (J/kg); T is absolute temperature
(K); ΔS is change in entropy (J/K).
The efficiency of FC (FC) is defined to be:
𝜂FC = 1 −
𝑇∆𝐺
∆𝐻
(4)
The equation (4) shows that the efficiency of the cell depends on the magnitude and sign of entropy. In the
equation, it can be seen that if for the reaction in a FC, ΔH > 0 and ΔS > 0, then the thermodynamic factor of
OXYGEN ELECTRODE OF FUEL CELL
161
efficiency η < 1 and it decreases with the increase of temperature (Bockris & Reddy, 2000; Springer, Wilson, &
Gottesfield, 1993). So, the efficiency of FC is significantly higher than efficiency of heat engines. It is therefore
necessary to focus on the development of FCs, as high efficiency green energy sources.
Electroreduction of Oxygen
The oxygen reduction reaction (ORR) has become one of the most extensively studied electrochemical
reactions. It has become apparent that the ability of current and future researchers to truly understand the
kinetics of the ORR may influence the fate of several fields, most notably polymer electrolyte membrane FCs
(PEM-FC). It is well known that the ORR at the cathode is the performance-limiting reaction due to its
extremely poor reaction kinetics (Damjanovic, Genshaw, & Bockris, 1967; Newman, 1991). Much
experimental work has been done on Pt or Pt alloys (Anderson et al., 2005; Chen & Kucernak, 2004; Markovic,
Gasteiger, Grgur, & Ross, 1999; Stamenkovic, Schmidt, Ross, & Markovic, 2002; Toda, Igarashi, Uchida, &
Watanabe, 1999; Mukerjee & Srinivasan, 1993), as well as many other transition metals and their oxides
(Anastasijevic et al., 1986; Imaizumi, Shimanoe, Teraoka, Miura, & Yamazoe, 2004; Prakash, Tryk, & Yeager,
1999; Strbac & Adzic, 1996).
Depending on the interaction of O2 with the catalyst surface, the oxygen reduction proceeds via a two-site
adsorption leading to the direct four-electron reduction of oxygen to water or end-on adsorption for the
peroxide route, which may rearrange over the threefold hollow site yielding a dual-bond single site adsorption.
A view of the adsorbed oxygen reduction precursors is shown in Figure 1 (Mustain & Prakash, 2007; Wang &
Balbuena, 2004).
Figure 1. The adsorption sites for molecular oxygen on the face of face-centered cubic transition metals.
The schematic diagram of the adsorption sites labelled for the Yager, Pauling, and Griffiths models is
shown in Figure 2.

The adsorption sites are labelled for the: (a) Yeager, (b) Pauling, and (c) Griffiths models.
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OXYGEN ELECTRODE OF FUEL CELL
For each adsorption type, the resultant product is an adsorbed M–OOH (where M is the catalyst site and m
is either one or two depending on the number of sites required for the adsorption) species (Sidik & Anderson,
2002; Wang & Balbuena, 2004):
𝑚M + O2 + 𝑒 − + H + → 𝑚MOOHads
(5)
If the mechanism proceeds via the direct route, the first electron transfer is followed by (Mustain &
Prakash, 2007):
MOMOHads → MOads + MOHads
(6)
Figure 2. Schematic diagram of the adsorption sites are labelled for the (a) Yeager, (b) Pauling, and (c) Griffiths
models.
For the peroxide route, the second electron and proton transfers may follow two alternative processes. The
second proton and electron transfers may lead to the formation of water and an adsorbed oxygen atom or a
hydrogen peroxide-like intermediate, depending on which O the proton attacks shown in equation (7) and
equation (8), respectively (Wang & Balbuena, 2004):
MOOHads + M + 𝑒 − + H + → MOads + MOH2ads
MOOHads + M + 𝑒 − + H+ → MOHOHads
(7)
(8)
The peroxide intermediate from equation (8) is then either desorbed to complete the stunted two-electron
mechanism or further decomposed. The possible 3rd and 4th electron and proton transfer steps involve electron
transfer and protonation to M–O and M–OH2 adsorbed species, leading to water formation.
The Butler-Volmer equation gives the rate expression for electrochemical reaction ri (Bard & Faulkner,
2001; Damjanovic et al., 1967):
𝑟𝑖 =
𝑖𝑖
𝑛 𝑖 𝐹𝐴
= 𝑘𝑖 exp
−𝐹𝑛 𝑖
𝑅𝑇
𝛼𝑖 𝜂𝑖
(9)
where i is electrode current density (A/m2); n is number of electrons involved in the electrode reaction; F is
Faraday constant; A is electrode active surface area (m2); R is universal gas constant; T is absolute temperature
(K);  is the so-called cathodic charge transfer coefficient; and  is efficiency.
The ki is defined by the equation (Mustain & Prakash, 2007):
𝑘𝑖 = 𝑣𝑖 𝜏𝐸 𝜏𝑇
(10)
where vi is reaction frequency factor; E is reaction energy; andT is electron transfer.
Activation barriers impede the conversion of reactants to products. So part of the cell voltage is used for
the reduction in the activation barrier. These losses are called the overpotential act. The correlation between
current density and overpotential describes the Butler-Volmer exponential function (Guo & Le, 2004):
𝑖 = 𝑖0  𝑒 𝑘𝜂 act
(11)
OXYGEN ELECTRODE OF FUEL CELL
163
where i is current density (A/m2); i0 is exchange current density (A/m2); k is factor of dependence of activation
overpotential on reaction speed; andact is activation efficiency.
Material and Methods
The alloys was obtained on copper electrode from a mixture of NiSO4  7H2O and CoSO4  7H2O (P. P.
Włodarczyk & B. Włodarczyk, 2014b).
Ni-Co alloy was obtained by the method of electrochemical deposition. The alloy was deposited on
smooth surface of copper electrode.
Before the deposition of the alloy, copper electrode was prepared in several steps (P. P. Włodarczyk & B.
Włodarczyk, 2014a):
 Surface was mechanically purified to a shine;
 Surface was degreased in 25% aqueous solution of KOH (after degreasing, the surface shall be completely
wettable with water);
 Electrode was digested in acetic acid;
 Electrode was washed with alcohol.
The deposit was obtained at temperature 293K, at current density of deposition id equal to 300 A/m2. The
time of the deposition was equal to 60 minutes.
The chemical composition of Ni-Co alloys was determined with the XRD method. The chemical
composition of alloy was equal to 50% of Co and 50% Ni.
To assess the Ni-Co alloy oxygen activity, first the oxidation of the alloy was carried out—the
measurements of stationary potential of oxidized electrode.
The Ni-Co alloy was oxidized at temperature equal to 673K. Oxidation time was equal to one, three, six,
eight, and 10 hours. Before oxidation all samples of Ni-Co alloy were gray. The samples oxidised for three and
six hours changed their colour into multicolour. The samples oxidised for eight and 10 hours changed their
colour into black.
Researches were done in glass vessel, on a copper electrode with Ni-Co alloy as a catalyst. An aqueous
solution of KOH was used as the electrolyte. Measurements were done in a glass cell with the use potentiostat.
Researches were done in alkaline electrolyte for concentration of KOH equal to 30%, which is presented in this
paper.
Results
Figure 3 shows the change of electroless potential in time in alkaline electrolyte (KOH), for Ni-Co alloy
oxidized for one, three, six, eight, and 10 hours.
Figure 4 shows the influence of electric charge on the electrode potential during the anode polarization in
alkaline medium (KOH), for Ni-Co alloy was oxidized for one, three, six, eight, and 10 hours.
Subsequently, measurements were performed for anodic charge of oxidized samples. Current was
increased to the point of oxygen bubbles formation. Next, the current was disconnected and the measurement of
electroless potential was started. In this process, only the oxidation of surface layer (which was earlier oxidized
in thermal process) takes place.
Figure 5 shows the influence of anodic charge on catalytic activity of Ni-Co catalyst (oxidized for eight
hours).
OXYGEN ELECTRODE OF FUEL CELL
164
0
5
10
15
20
25
30
-0.02
-0.07
Cell voltage (V)
-0.12
-0.17
-0.22
-0.27
1h
-0.32
3h
6h
8h
10h
 (min)
Figure 3. Change of electroless potential in time, for Ni-Co alloy oxidized for one, three, six, eight, and 10 hours.
1.2
1.0
Cell voltage (V)
0.8
0.6
0.4
0.2
1h
3h
6h
8h
10h
0.0
0
5
10
15
Q (C)
20
25
 6  10-2
Figure 4. Influence of electric charge on the electrode potential during the anode polarization.
OXYGEN ELECTRODE OF FUEL CELL
165
0.8
Cell voltage (V)
0.6
0.4
0.2
1
2
3
0.0
0
-0.2
2
4
6
8
Q (C)
10
 6  10-2
Figure 5. Influence of anodic charge on catalytic activity of Ni-Co alloy.
Discussion
Ni-Co alloy was obtained by method electrochemical deposition on smooth surface of copper electrode.
Measurements were conducted change of electroless potential in time in alkaline medium, for Ni-Co alloy
being oxidized for one, three, six, eight, and 10 hours. Analysis of data (Figure 3) allows to assess which time
of oxidation is adequate to the catalyst made of Ni-Co alloy.
The Ni-Co alloy oxidized for eight hours showed high electroless potential. This potential was determined
within about 30 minutes (Figure 3).
Next, measurements were conducted of electric charge on the electrode potential during the anode
polarization in alkaline medium (KOH), for Ni-Co alloy was oxidized for one, three, six, eight, and 10 hours.
Data analysis (Figure 4) allows to assess influence of electric charge on the electrode potential during the anode
polarization. Potential was analysed during the anode polarization of Ni-Co catalyst, which was earlier
oxidizing in thermal process.
Figure 5 shows that after the third anodic charge of the electrode, the parameters which allow to use this
Ni-Co alloy as catalyst for oxygen electrode in FCs, were obtained.
Conclusions
The cost of platinum as an electrode catalyst greatly restricts the use of FCs on a larger scale. Therefore, it
is essential to find an alternative that would allow to replace it. In order to reduce costs, it is highly desirable to
seek catalysts that do not contain precious metals. Eliminating platinum would allow for a rapid increase in the
share of renewable energy sources.
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OXYGEN ELECTRODE OF FUEL CELL
One of the main issues is to find a catalyst, not only for the fuel electrode, but also for the oxygen
electrode. This study demonstrates the basic possibility of using a Ni-Co alloy as a catalyst for the oxygen
electrode. Nonetheless, in order to be efficient, the catalyst should be properly prepared. The first step is to
perform the thermal oxidation and then anodic oxidation. Measurements have shown that the thermal oxidation
should be carried out for eight hours at the temperature of 673K. The next step, necessary to obtain adequate
catalytic properties, is the anodic oxidation. Measurements have shown that the best catalytic properties were
obtained after anodic oxidation repeated three times. Preparing the electrodes in this way allows to use the
Ni-Co alloy as the catalyst for the oxygen electrode of the FC.
The study demonstrated the catalytic properties of the Ni-Co alloy, but in order to evaluate the actual
performance of the catalyst, it is, however, necessary to continue the measurements for a long time. It is
therefore necessary to conduct the tests in a functioning (charged) FC in operating conditions, as there is a risk
of excessive oxidation of the catalyst surface during operation. This condition can cause a sudden drop in the
oxygen electrode catalytic properties and, consequently, decrease the efficiency of the entire FC.
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