Supporting Information
A Solution-Phase Bifunctional Catalyst for Lithium-oxygen
Batteries
Dan Sun†, Yue Shen†,*, Wang Zhang†, Ling Yu†, Ziqi Yi†, Wei Yin†, Duo Wang†,
Yunhui Huang†,*, Jie Wang§, Deli Wang§ and John B. Goodenough‡
† State Key Laboratory of Material Processing and Die & Mould Technology, School of Materials Science
and Engi-neering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
§School of Chemistry and Chemical Engineering, Key Laboratory of Large-Format Battery Materials and
System, Ministry of Education, Huazhong University of Science and Technology, Wuhan, Hubei 430074,
China
‡ Texas Materials Institute, ETC 9.102, 1 University Station, C2200, The University of Texas at
Austin, Austin, TX 78712, USA
Table of Contents
1. Calculation of the number of electrons transferred in the (FePc-O2) + e- => (FePc-O2)- transition . S2
2. Calculation of the capacity of FePc itself.......................................................................................... S3
3. Supplementary RDE experiments proving the Li2O2 blocking effect ............................................... S4
4. Characterization of the CFs with & without Fe-N/C ........................................................................ S5
5. A homemade device to depress the DMSO evaporation ................................................................... S7
6. A set-up to fabricate graphene sponge with uniform thickness ......................................................... S7
S1
1. Calculation of the number of electrons transferred in the [(FePc-O2) + e- =>
(FePc-O2)-] transition
In rotating disk electrode experiments, the calculation of the number of electrons transferred is based
on the Levich equation as below (cited from wikipedia):
In traditional fuel cell catalyst studies, it is effective because all of the physical parameters above are
known. However, in our case, it is very difficult to measure the diffusion coefficient of the FePc-O2,
(FePc-O2)- and FePc-LiOOLi compounds in DMSO solution.
We can do a semiquantitative calculation based on an assumption that the FePc-O2 and FePc
molecules have similar diffusion coefficient. And we already know that in inert atmosphere, the
Fe(II)/Fe(I) transition in FePc is a single electron reaction. The Levich current of the first step reaction
in oxygen atmosphere (the current value of the solid blue curve at 2.75 V in Fig. 2b) divided by the
Levich current of the Fe(II)/Fe(I) transition of FePc in inert atmosphere (the current value of the solid
red curve at 2.3 V in Fig. 2b) should equal to the number of electrons transferred in the first step
reaction. The result is 1.14, which is close to one.
S2
So it is reasonable that the [(FePc-O2) + e- => (FePc-O2)-] transition is a single electron reaction,
agreeing with our mechanism.
However, this calculation cannot be applied on the the 2nd step reaction. As shown in Fig. 2c. There is
a recirculation of FePc. LiOOLi may leave the FePc-LiOOLi and FePc may combine with another free
oxygen molecule and catalyze its reduction. In this case, because of these liquid phase reactions, the
Levich equation is not applicable anymore. Besides, the LiOOLi blocking effect (Fig. 2d) passivates
the electrode surface, also makes the Levich equation not applicable.
2. Calculation of the capacity of FePc itself
As shown in Fig. 2e, the dissolved FePc may be oxidized in the charging process; therefore, it is
necessary to determine whether it serves as a catalyst or only as an electrode material. The capacity
contributed from the FePc as an electrode material can be calculated as
This value is two orders of magnitude lower than the cathode capacity of at least 0.05 mAh with only
FePc in the electrolyte. We may conclude, therefore, that the dissolved FePc acts primarily as a
catalyst.
S3
3. Supplementary RDE experiments proving the Li2O2 blocking effect
Figure S1. A reverse scan RDE test proving the Li2O2 blocking effect: The glassy carbon disk working
electrode was put in a DMSO-LiTFSI electrolyte without FePc and was rotating at 1600 rpm. We
scanned the potential from low to high. The ORR current was large at beginning. Because the
produced Li2O2 deposited on the electrode surface blocked further reaction, the current decreased very
fast. The current was close to 0 at 2.6 V. Then, as the potential further increased, the deposited Li2O2 is
oxidized. So we observe an oxidation current. The oxidation current density reached a peak at about
3.2 V, agreeing with the Li2O2 oxidation potential in the CV test (Fig. 2a). After the peak, the current
began to decrease because the Li2O2 on the electrode surface was either oxidized or washed away.
Figure S2. A second RDE scan after the first scan in the ORR potential range. The current was
substantially reduced, it indicates the insoluble deposit on the disk surface.
S4
4. Characterization of the CFs with & without Fe-N/C
Figure S3. SEM images of the synthesized CFs with (a & b) and without (c & d) Fe-N/C solid
catalyst
Figure S4. EDX results of the CFs with and without Fe-N/C solid catalyst. This figure shows that the
weight percentages of Fe and N in the as-synthesized CFs with attached Fe-N/C are, respectively, 1%
S5
and 12%.
Figure S5. (a) XPS results of the CFs with and without Fe-N/C solid catalyst. The Fe and N contents
are 3.7% and 12.9%. The detection depth of XPS (< 20 nm) is less than that of EDX (about 1 µm),
which can account for the difference since C and N are more easily lost from the surface during
carbonization. (b) High resolution N 1s spectrum fitting curves. It shows that 21.3% of the N atoms
are incorporated with Fe atoms. This result is calculated from the peak area of the Fe-pyr N, compared
with the following literature: R. Kothandaraman, V. Nallathambi, et al. Applied Catalysis
B-Environmental 92, 209-216 (2009).
S6
5. A homemade device to depress the DMSO evaporation
Figure S6. Scheme of the device to depress the DMSO evaporation.
6. A set-up to fabricate graphene sponge with uniform thickness
Figure S7. Fabrication of the graphene sponge with uniform thickness = 250 µm. Homogeneous GO
(4−5 mg ml-1) aqueous dispersion and pyrrole were pre-mixed through vigorous stirring with volume
ratio of 95:5. Then the mixture was transferred to a Teflon-lined autoclave with silicon mold inside.
The silicon mold was for the thickness control of the product. After hydrothermal treatment at 180 oC
S7
for 12 h, the graphene hydrogel with uniform thickness = 250 µm was obtained. Then the hydrogel
was treated in ammonia solution (14 vol%) at 90 oC for 1 h and freeze dried. The final graphene
sponge was obtained through heat treatment in Ar at 1050 oC for 3 h.
S8