Evaluation of operating conditions on DBFC (direct borohydride fuel
cell) performance with PtRu anode catalyst by response surface
method
Fatma Gül Boyacı San
*
, Osman Okur, Çi
gdem
_
Iyigün Karada
g, Isil Isik-Gulsac,
Emin Okumus ¸
Energy Institute, TÜB
_
ITAK Marmara Research Center, P.O. Box 21, 41470 Gebze, Kocaeli, Turkey
article info
Article history:
Received 20 June 2013
Received in revised form
26 March 2014
Accepted 14 April 2014
Available online xxx
Keywords:
Direct borohydride fuel cell
Oxidation
Hydrolysis
Operating parameters
Response surface methodology
abstract
Borohydride has been considered as a potential fuel for the fuel cell application due to its high energy
density. A DBFC (direct borohydride fuel cell) is an electrochemical device that converts chemical energy
stored in borohydride and oxidant directly to electrical energy as long as the fuel and oxidant is supplied.
One of the main problems encountered in a DBFC is the simultaneous hydrolysis of BH
4
at the anode
surface. The hydrolysis decreases the fuel utilization and fuel cell performance, since hydrogen bubbles
hinder the contact of catalyst with reactant. This study investigates the effect of operating conditions
(cell temperature, borohydride concentration, flow rates of fuel and oxidant) on DBFC performance by
RSM (response surface methodology). PtRu/C is used as the anode catalyst to systematically investigate
the effect of hydrogen evolution rate on the fuel cell performance. The maximum power density is
obtained at 80
C fuel cell temperature, 0.5 M NaBH
4
concentration, 5 cm
3
min
1
flow of anolyte and
100 cm
3
min
1
flow of oxygen.
© 2014 Elsevier Ltd. All rights reserved.
1. Introduction
In recent years, there has been a considerable interest in a direct
borohydride fuel cell (DBFC) due to its high theoretical cell voltage
and power density [1,2]. DBFCs are good candidates for portable
and mobile applications since they eliminate hydrogen storage
problems and can be used safely due to liquid fuel usage. Sodium
borohydride (NaBH
4
) is a well known, stable and non-toxic
reducing agent. It is the most attractive material due to its high
energy density (9.3 Wh g
1
), its ability is not only to release 8e
per
borohydride ion at a low electrode potential but also to generate a
high power output per unit fuel quantity [1]. In a DBFC, NaBH
4
solution is directly fed to the anode part of the fuel cell as a fuel.
DBFC employs oxygen, air or hydrogen peroxide as an oxidant in the
cathode part. The only byproduct is non-toxic sodium metaborate
(NaBO
2
), which can be converted to NaBH
4
easily without any
pollution.
The reaction at the anode part of the DBFC is the oxidation of the
borohydride ion, BH
4
to metaborate (BO
2
) and water according to
Eq. (1). This reaction should take place in strongly alkaline media
(pH > 12), since BH
4
is unstable in acidic or neutral environment.
BH
4
þ8OH
/ BO
2
þ 6H
2
O þ8e
(E
0
anode
¼1.24 V, vs SHE) (1)
Reaction at the cathode part of the DBFC is the reduction of
oxygen or air according to Eq. (2).
2O
2
þ 4H
2
O þ 8e
/ 8OH
(E
0
cathode
¼ 0.40 V, vs SHE) (2)
The overall reaction is written as:
BH
4
þ 2O
2
/ BO
2
þ 2H
2
O (E
0
cell
¼ 1.64 V) (3)
One of the main problems encountered in a DBFC is the simul-
taneous hydrolysis of BH
4
at the anode surface according to the
reaction in Eq. (4).
BH
4
þ 2H
2
O / BO
2
þ 4H
2
(0.86 V) (4)
Hydrogen gas evolved during the hydrolysis reaction decreases
the anodic potential. Hence, the fuel efficiency is decreased.
Moreover, it causes problems in mass transport and system design
[1e3]. Hydrogen bubbles aggregate easily between the anode
* Corresponding author. Tel.: þ90 262 677 27 03; fax: þ90 262 642 35 53.
E-mail addresses: fatmagul.boyaci@tubitak.gov.tr, fgbs37@gmail.com
(F.G. Boyacı San).
Contents lists available at ScienceDirect
Energy
journal homepage: www.elsevier.com/locate/energy
http://dx.doi.org/10.1016/j.energy.2014.04.037
0360-5442/© 2014 Elsevier Ltd. All rights reserved.
Energy xxx (2014) 1e10
Please cite this article in press as: Boyacı San FG, et al., Evaluation of operating conditions on DBFC (direct borohydride fuel cell) performance
with PtRuanode catalyst by response surface method, Energy (2014), http://dx.doi.org/10.1016/j.energy.2014.04.037