Exclusive Formation of Formic Acid from CO2 Electroreduction by a Tunable Pd-Sn Alloy

Article abstract of DOI:10.1002/anie.201707098

Conversion of carbon dioxide (CO₂) into fuels and chemicals by electroreduction has attracted significant interest, although it suffers from a large overpotential and low selectivity. A Pd-Sn alloy electrocatalyst was developed for the exclusive conversion of CO₂ into formic acid in an aqueous solution. This catalyst showed a nearly perfect faradaic efficiency toward formic acid formation at the very low overpotential of ?0.26 V, where both CO formation and hydrogen evolution were completely suppressed. Density functional theory (DFT) calculations suggested that the formation of the key reaction intermediate HCOO* as well as the product formic acid was the most favorable over the Pd-Sn alloy catalyst surface with an atomic composition of PdSnO₂, consistent with experiments.

Full text of DOI:10.1002/anie.201707098

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: Exclusive formation of formic acid from CO2 electroreduction by
tunable Pd-Sn alloy
Authors: Xiaofang Bai, Wei Chen, Chengcheng Zhao, Shenggang Li,
Yanfang Song, Ruipeng Ge, Wei Wei, and Yuhan Sun
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201707098
Angew. Chem. 10.1002/ange.201707098
Link to VoR: http://dx.doi.org/10.1002/anie.201707098
http://dx.doi.org/10.1002/ange.201707098

10.1002/anie.201707098
Angewandte Chemie International Edition
COMMUNICATION
Exclusive formation of formic acid from CO2 electroreduction by
tunable Pd-Sn alloy
Xiaofang Bai, Wei Chen,* Chengcheng Zhao, Shenggang Li, Yanfang Song, Ruipeng Ge, Wei Wei,*
and Yuhan Sun*
Abstract: Conversion of carbon dioxide (CO2) into fuels and
chemicals via electroreduction has attracted significant interest
derived from renewable energy storage and environmental
sustainability, although it suffered from large overpotential and low
selectivity. Here, we report a Pd-Sn alloy electrocatalyst for the
exclusive conversion of CO2 into formic acid in an aqueous solution.
This catalyst showed a nearly perfect faradaic efficiency toward
formic acid formation at the very low overpotential of -0.26 V, where
both CO formation and hydrogen evolution were completely
suppressed. Density functional theory (DFT) calculations suggested
that the formation of the key reaction intermediate HCOO* as well as
the product formic acid was the most favourable over the Pd-Sn
alloy catalyst surface with an atomic composition of PdSnO2,
consistent with our experiments. This indicates the great potential of
the tunable Pd-Sn alloy catalyst for the efficient conversion of CO2
into valuable products.
of alloy nanoparticles (NPs), which was believed to enhance
their electrocatalytic activities[10,11], and determine the favourable
intermediates and final products. However, it is still a great
challenge to exclusively produce certain product via CO2
electroreduction.[12]
Here, we report that by virtue of tuning surface electronic
structures of Pd-Sn alloy electrocatalysts, CO2 can be
exclusively converted to formic acid with nearly 100% FE at an
overpotential as low as -0.26 V. We demonstrated that
systematically varying the Pd/Sn composition in the alloy NPs
resulted in the valley-shaped curve of Pd(0)/Pd(II), which was
found to be correlated with the CO2 electrocatalytic activity and
selectivity. First principles DFT calculations further suggested
that the optimal surface Pd-Sn-O configuration with the highest
oxygen occupancy facilitated the formation of the key reaction
intermediate HCOO* and the generation of the only product of
formic acid by the second proton-electron transfer, whereas both
CO formation and HER were suppressed. These findings offer
the scenario that alloy surface metal-oxide configurations are
highly sensitive to electrocatalytic performance, which is
unexpected from the previous perception on how alloy NPs[13-15]
should function in electrochemical reactions.
CO2 is widely considered to be responsible for the climate
change, and its utilization as an alternative carbon feedstock
may be a viable approach for its remedy. Consequently, there is
significant interest in the electrochemical conversion of CO2 into
value-added chemicals or fuels driven by low-grade renewable
electricity, which means to store the intermittent electric energy
in high-energy-density fuels.[1-3] Although numerous metallic
electrodes were extensively investigated for catalyzing CO2
electroreduction,[4,5] most of them suffered from large
overpotential, low faradaic efficiency (FE) and poor product
selectivity due to the competitive hydrogen evolution reaction
(HER). An effective strategy is to design bimetallic or multi-
metallic alloy electrocatalysts,[6-9] which can benefit from the
synergy between different metallic components to form
superlattice structures, compressive lattice strains, and/or
Activated carbon (AC) supported Pd-Sn alloy NPs were
synthesized via a modified wetting chemistry reduction method
with sodium citrate as
a stabilizing agent and sodium
borohydride as a reductive agent (See Supporting Information
(SI) for details). The composition of Pd-Sn NPs was controlled
by varying the molar ratio of the precursors PdCl2 and SnCl2,
and their particle sizes were preserved as similar as possible by
maintaining the ratio of the stabilizing/reductive agents. The
obtained samples were denoted as PdxSn/C. The subscript x
represents the molar ratio of Pd/Sn. For comparison, single-
component Pd and Sn catalysts supported on AC were also
prepared, and these samples were denoted as Pd/C and Sn/C,
respectively.
unique
shapes/morphologies,
leading
to
enhanced
electrocatalytic performance. Specially, the exquisite surface
oxide formation would change the surface electronic structures
Transmission electron microscopy (TEM) images reveal that
the NPs in Pd/C, PdxSn/C and Sn/C are homogeneously
dispersed on the AC spherical supports (Figure 1A, B and
Figure S1). Size distribution histograms show that over 90% of
NPs in these catalysts possess a very narrow size range of 1–5
nm. The particle with the d-spacing of 2.24 Å corresponds to the
(111) lattice fringe of metallic Pd (the inset in Figure 1A), while
the spacing of 2.25 Å is consistent with the alloy PdSn (121)
plane (the inset in Figure 1B). A large number of NPs in Pd/C
and PdSn/C were imaged randomly and the results showed that
all particles had very similar lattice spacing. The individual phase
compositions were further confirmed by mapping and X-ray
diffraction (XRD) analyses (vide infra). Figure 1C shows the
formation of PdSn alloy NPs on AC in PdSn/C by scanning TEM
(STEM) mapping. The corresponding elemental maps of Pd, Sn,
[*]
Miss. X. Bai, Prof. W. Chen, Prof. W. Wei, C. Zhao, Prof. S. Li, Dr.
Y. Song, Mr. R. Ge, Prof. Y. Sun
CAS Key Laboratory of Low-Carbon Conversion Science and
Engineering, Shanghai Advanced Research Institute
Chinese Academy of Sciences
100 Haike Road, Shanghai 201203 (People Republic of China)
E-mail: chenw@sari.ac.cn
Prof. S. Li, Prof. W. Wei, Prof. Y. Sun
School of Physical Science and Technology
ShanghaiTech University
393 Middle Huaxia Road, Shanghai 201210 (People Republic of
China)
E-mail: weiwei@sari.ac.cn; sunyh@sari.ac.cn
Supporting information for this article is given via a link at the end of
the document
This article is protected by copyright. All rights reserved.

10.1002/anie.201707098
Angewandte Chemie International Edition
COMMUNICATION
C and their overlap indicate that Pd and Sn elements are evenly
distributed in PdSn NPs supported on AC spheres.
3d5/2 peaks centred at 335.1 and 336.8 eV, corresponding to Pd
(0) and Pd (II), respectively. Oxide species were verified in both
Pd/C and PdxSn/C by XPS spectra (Figure S3 and Tables S3,
S4). However, XRD and HRTEM characterizations show only
metallic Pd and Pd-Sn alloy phases as bulk compositions in
Pd/C and PdxSn/C, implying that the surface oxide layers
evidenced by XPS are too thin to be detectable. The surface of
metal NPs is intrinsically prone to getting oxidized when
exposed to air, while the bulk remains metallic because of the
kinetic limit of surface oxidation.[16] The intense Sn 3d5/2 peaks of
PdSn/C (Figure 2Bb) at 485.0 and 486.7 eV correspond to the
metallic Sn(0) state and the Sn(IV) state in SnO2, respectively.
While for Sn/C (Figure 2Bc), only Sn(IV) is present, and metallic
Figure 1D displays the XRD patterns of monometallic Pd/C,
Sn/C and PdxSn/C alloy catalysts in the range of 15o–85o (2θ).
The diffraction peaks corresponding to metallic Pd (111), (200),
(220), (311) and (222) planes (JCPDS# 050681) were detected
along with the broad characteristic (002) peak of AC in Pd/C
(Figure 1Da). The alloy catalysts PdxSn/C (Figure 1Db-g)
possess broadened diffraction peaks, which exhibit stepwise
broadening and slight shift with decreasing Pd/Sn ratios. The
intense peak around 40o in Pd4Sn/C (Figure 1Db) downshifts by
0.1o and the full width half maximum (FWHM) increases by 0.7o
compared to the Pd (111) peak in Pd/C. With the decrease in Pd
content, such intense peaks continuously downshift and broaden. Sn(0) was not detected, whose existence was confirmed by
Exhaustive analyses for the intense peaks from 35o to 50o in
PdxSn/C (Figure 2B and Table S2) indicate that the apparently
broadened peaks were actually composed of multiple
overlapping peaks from different alloy phases. The PdxSn/C
catalysts have the corresponding alloy phase compositions in
accordance with initial feeding ratios. This shows that bimetallic
alloy phases Pd3Sn, Pd2Sn, PdSn, PdSn2, PdSn4 were formed,
as evidenced by HRTEM investigations (the insets in Figure S1),
implying that the bulk phase compositions of PdxSn NPs were
well controlled to the desired alloy phases through the accurate
wetting chemistry processes. With respect to Sn/C (Figure 1Dh),
the peaks of both metallic Sn and SnO2 phases were detected,
in agreement with the HRTEM image (Figure S1H), where the
Sn NPs were adjacent to the SnO2 ones.
XRD patterns. This implies that the metallic Sn phase was
enwrapped by surface SnO2 layer.
Variation of the relative intensity ratios of Pd(0)/Pd(II) and
Sn(0)/Sn(IV) with respect to the molar ratios of Pd/Sn in Pd, Sn
and alloy PdxSn NPs can also be clearly seen in Figure 2C. The
Pd(0)/Pd(II) ratio in Pd/C is 2.33, comparable of the previously
reported values.[17,18] However, it decreases rapidly when the Pd
content in NPs gradually decreases, and the Pd(0) was
minimum in PdSn/C with the lowest Pd(0)/Pd(II) ratio of 1.47.
Interestingly, the Pd(0)/Pd(II) ratios rise again when further
decreasing the Pd/Sn molar ratios, leading to the valley-shaped
variation of Pd(0)/Pd(II) with bulk Pd/Sn molar ratios. In contrast,
the Sn(0)/Sn(IV) ratios monotonically decrease with decreasing
Pd/Sn molar ratios. It has been known that noble metal Pd has
relatively high electron negativity and low oxygen affinity,[19]
while Sn is considered as an oxophilic metal.[20,21] The
proportions of the low oxidation state Pd(0) and Sn(0) are
relatively higher when Pd is dominant. When more Sn is present,
a substantive amount of SnO2 generate on the surface, which in
turn prevents Pd from being oxidized resulting in the increasing
Pd(0)/Pd(II) ratios again. Therefore, the distinct oxygen affinities
of Pd and Sn combined with the variation of their compositions
in NPs led to the valley-shaped curve with a unique bottom
located at PdSn/C, which comprises the bulk PdSn alloy and the
surface Pd-O-Sn layer with the Pd(0)/Pd(II) ratio of 1.47 and the
Sn(0)/Sn(IV) ratio of 0.18. In contrast to the bulk composition,
the surface electronic states of catalysts can exert significant
influence on the adsorption/desorption capacity as well as the
catalytic performance.[22] The largest amount of CO2 was
observed to desorb at lower temperature on PdSn/C than on
other catalysts in the temperature-programmed desorption
experiments (Figure S4), indicating the distinct interaction of
CO2 with the optimal Pd-O-Sn configuration, which will
significantly influence the adsorption/activation of CO2.
Figure 1. Microstructural analysis and bulk compositions of the catalysts. TEM
images and size distributions of the NPs in (A) Pd/C and (B) PdSn/C. The
insets show the high resolution TEM (HRTEM) images of corresponding NPs.
(C) STEM-EDS element mapping of PdSn/C. Scale bars in the maps
represent 2 nm unless noted otherwise. (D) XRD patterns of the catalysts.
Single-metallic (a) Pd/C, (h) Sn/C and alloy PdxSn/C (b–g): (b) Pd4Sn/C, (c)
Pd3Sn/C, (d) Pd2Sn/C, (e) PdSn/C, (f) Pd0.5Sn/C, and (g) Pd0.25Sn/C.
The surface electronic states of Pd/C, Sn/C and PdxSn/C
alloys were studied by X-ray photoelectron spectroscopy (XPS).
The Pd 3d spectrum in Pd/C (Figure 2Aa) was fitted with two
components, and the 3d5/2 peak located at a binding energy of
335.1 eV was the characteristic of metallic Pd (0) while that at
336.8 eV was assigned to Pd(II) in the PdO state. The catalyst
PdSn/C (Figure 2Ab) also consists of two components with Pd
This article is protected by copyright. All rights reserved.

10.1002/anie.201707098
Angewandte Chemie International Edition
COMMUNICATION
Figure 2. Surface analysis of the electrocatalysts. XPS spectra of (A) the Pd
3d level and (B) the Sn 3d level of the catalysts (a) Pd/C, (b) PdSn/C, (c)
Sn/C. (C) The relatively intensity ratios of Pd(0)/Pd(II) and Sn(0)/Sn(IV) versus
the molar ratios of Pd/Sn.
before the reaction, implying the surface oxide species in these
catalysts were stable.
The potentiostatic CO2 electrolysis was performed in a CO2-
saturated KHCO3 aqueous solution (See SI for details), and the
results are shown in Figure 3. CO2 electroreduction on these
catalysts reproducibly yielded CO and formic acid with a
substantial amount of hydrogen from HER. The reaction on the
non-supported Pd2Sn catalyst was dominated by hydrogen
production (51% FE) with CO and HCOOH as minor products at
an overpotential of -0.86 V. However, it was reversed with
carbon-supported catalysts, indicating that activated carbon
suppress the HER, in agreement with previous findings.[23,24]
Pd/C and Sn/C delivered similar HCOOH FE about 50%. With
respect to the alloy catalysts, it was found that their HCOOH and
CO FEs were highly dependent on the surface configurations at
the respective cathodic peak potentials, where CO2
electroreduction reaction rates were maximum (Figure S5). The
less-Sn substituted catalyst Pd4Sn/C gave relatively low HCOOH
FE (43%), resulting from the metallic Sn on the surface.[25,26]
With increasing Sn content, the HCOOH FE increases to 54%
over Pd3Sn/C and further up to 63% over Pd2Sn/C. Surprisingly,
the highest FE of >99% for producing HCOOH was obtained
over the PdSn/C catalyst at the lowest overpotential of -0.26 V.
We note that negligible H2 (FE less than 0.3%) was produced
from the HER, and CO formation was completely suppressed
over PdSn/C. Subsequently, HCOOH FE decreased gradually to
73% over Pd0.5Sn/C and 42% over Pd0.25Sn/C when further
increasing the Sn content. At the same potential of -0.43 V (vs.
RHE), the HCOOH FEs over all other alloy catalysts were far
lower than that over PdSn/C (Figure S6). In contrast, the CO
FEs followed the opposite variation trend to the HCOOH FEs,
suggesting that the productions of CO and HCOOH are
competing routes during CO2 electroreduction. Note that the
changes in the HCOOH FE and overpotential are synchronous
with those of Pd(0)/Pd(II) in PdxSn NPs, indicating that the
activity of producing HCOOH is sensitive to the surface oxide
species on alloy NPs. Recently, Luc et al. reported that an
optimal SnOx layer in the Ag-Sn bimetallic catalyst was obtained
via tuning the molar ratio of Sn and Ag, exhibiting a high
HCOOH FE of ~80% at −0.8 V (vs. the reversible hydrogen
electrode, RHE).[27] In comparison, the catalyst PdSn/C
delivered the HCOOH FE over 99% at the lower potential of -
0.43 V (vs. RHE). By tuning the electronic state via Sn alloying,
the largest amount of palladium oxide species were formed on
the surface of the catalyst PdSn/C, as indicated by the XPS
results, resulting in superior performance to produce HCOOH in
the electrocatalytic reduction of CO2. The catalysts with Pd/Sn
ratio close to one also resulted in relatively high HCOOH FEs
compared to other alloy catalysts (Table S5). In addition,
PdSn/C delivered rather stable potentiostatic electrolysis at the
potential of -0.43 V (vs. RHE), showing the negligible decay in
the current density after electrolysis for 5 h (Figure S8). The
post-reaction XPS analyses showed that the ratios of
Pd(0)/Pd(II) and Sn(0)/Sn(IV) of the catalysts after the reaction
(Figure S9 and Tables S6, S7) were almost same to those
Figure 3. Faradaic efficiency and overpotential of Pd/C, Sn/C and alloy
PdxSn/C at the applied potentials (0.5 M KHCO3 saturated by CO2). The non-
supported Pd2Sn was compared as reference. The faradaic efficiency is stated
as an average and calculated at the steady-state current and product
concentration.
To further shed light on the origin of the exclusive formation of
formic acid over the PdSn alloy electrocatalyst, we performed
DFT calculations to investigate the energetics of the key reaction
intermediates involved in the different pathways in CO2
electroreduction over characteristic alloy surface configurations
(see SI for details). Starting from bicarbonate (HCO3*) species,
which was demonstrated as the primary carbon source on
electrode surface for CO2 electroreduction,[28-30] we examined
the
possible
pathways
of
stepwise
electrocatalytic
hydrogenations on the surfaces composed of Pd3O, Pd2SnO,
PdSnO2 and Sn2O2. From the energy profiles in Figure 4 and
Figures S11–S13, we can see that the preferred intermediates
and most favourable pathways are highly dependent on the
surface configurations. For Pd3O, Pd2SnO, PdSnO2 and Sn2O2,
the calculated reaction energies for the intermediates HCOO*
and COOH* via the first proton-electron transfer are -0.17 eV/-
0.65 eV, -0.79 eV/-0.41 eV, -1.23 eV/-0.37 eV and -1.52 eV/-
0.88 eV, respectively. The reaction energies for the further
formation of the adsorbed products HCOOH* and CO*/H2O* via
the second proton-electron transfer are -1.68 eV/-1.12 eV, -1.55
eV/-1.69 eV, -1.44 eV/-0.73 eV and -2.10 eV/-1.64 eV,
respectively. Thus, the energy differences between the
intermediates (∆E1) and the adsorbed products (∆E2) are -0.48
eV/0.56 eV, 0.38 eV/-0.14 eV, 0.86 eV/0.71 eV and 0.64 eV/0.46
eV, respectively. Both ∆E1 and ∆E2 reach the maximum over the
surface composed of PdSnO2, where the most favourable
pathway involves the HCOO* intermediate and leads to formic
acid formation. Over surfaces of other Pd-Sn-O compositions,
Pd3O, Pd2SnO and Sn2O2, it is unfavourable to form either
HCOO* or HCOOH*, resulting in reduced formic acid formation.
This article is protected by copyright. All rights reserved.

10.1002/anie.201707098
Angewandte Chemie International Edition
COMMUNICATION
[2]
M. Asadi, K. Kim, C. Liu, A. V. Addepalli, P. Abbasi, P. Yasaei, P.
Phillips, A. Behranginia, J. M. Cerrato, R. Haasch, P. Zapol, B. Kumar,
R. F. Klie, J. Abiade, L. A. Curtiss, A. Salehi-Khojin, Science 2016, 353,
467−470.
[3]
[4]
J. Gong, L. Zhang, Z. J. Zhao, Angew. Chem. Int. Ed. 2017, DOI:
10.1002/anie.201612214;
10.1002/ange.201612214.
Angew.
Chem.
2017,
DOI:
H. Won, H. Shin, J. Koh, J. Chung, H. S. Lee, H. Kim, S. I. Woo, Angew.
Chem. Int. Ed. 2016, 55, 9297−9300; Angew. Chem. 2016, 128,
9443−9446.
[5]
[6]
D. Raciti, K. J. Livi, C. Wang, Nano Lett. 2015, 15, 6829−6835.
D. A. Torelli, S. A. Francis, J. C. Crompton, A. Javier, J. R. Thompson,
B. S. Brunschwig, M. P. Soriaga, N. S. Lewis, ACS Catal. 2016, 16,
2100−2104.
[7]
S. Rasul, D. H. Anjum, A. Jedidi, Y. Minenkov, L. Cavallo, K. Takanabe,
Angew. Chem. Int. Ed. 2015, 54, 2146−2150; Angew. Chem. 2015, 127,
2174−2178.
Figure 4. Calculated reaction energy profiles for CO2 electroreduction to form
CO (top) and HCOOH (bottom) on the PdSnO2 surface. PdSnO2 represents
the configuration with almost half Pd atoms are substituted by Sn atoms, in
which the surface composition of palladium oxide reach the maximum (for
more detials, see SI computational section).
[8]
[9]
D. Kim, J. Resasco, Y. Yu, A. Mohamed, P. Yang, Nat. Comm. 2014, 5,
4948.
S. Sarfraz, A. T. Garcia-Esparza, A. Jedidi, L. Cavallo, K. Takanabe,
ACS Catal. 2016, 6, 2842−2851.
[10] E. J. Coleman, A. C. Co, ACS Catal. 2015, 5, 7299−7311.
[11] A. Stassi, I. Gatto, G. Monforte, V. Baglio, E. Passalacqua, V.
Antonucci, A. S. Arico, J. Power Sources. 2012, 208, 35−45.
[12] J. L. Qiao, Y. Y. Liu, F. Hong, J. J. Zhang, Chem. Soc. Rev. 2014, 43,
631−675.
Our results indicated that the preferred intermediates and
most favourable pathways during CO2 electroreduction reaction
were highly dependent on the surface configurations of alloy
catalysts. The alloy catalyst PdSn/C with a Pd/Sn molar ratio of
one possessed the lowest Pd(0)/Pd(II) ratio, leading to the
exclusive formation of formic acid. On the basis of our DFT
calculations, we concluded that only on the PdSnO2 surface
does HCOO* and HCOOH* remain the most favoured species,
which is consistent with the experimental findings.
In conclusion, a simple strategy is illustrated for selective
synthesis of formic acid from CO2 electroreduction, which is
attributed to the tuning of surface electronic structures of
supported Pd-Sn alloy NPs. The electrocataytic activity and
selectivity are highly dependent on the surface configurations, in
which formic acid with nearly 100% FE at the lowest
overpotential of -0.26 V was produced on the PdSn alloy surface
with optimal surface Pd, Sn and O configuration. Our findings
are important for the further development of low cost, high
activity and high selectivity alloy catalysts for CO2
electrochemical conversion, with the potential for the efficient
utilization of CO2.
[13] P. S. Strasser, S. Koh, T. Anniyev, J. Greeley, K. More, C. Yu, Z. Liu, S.
Kaya, D. Nordlund, H. Ogasawara, M. F. Toney, A. Nilsson, Nat. Chem.
2010, 2, 454−460.
[14] P. He, L. Ma, Z. Shi, G. Y. Guo, S. M. Zhou, Phys. Rev. Lett. 2012, 109,
066402.
[15] C. Zhang, S. Y. Hwang, A. Trout, Z. Peng, J. Am. Chem. Soc. 2014,
136, 7805−7808.
[16] Z. C. Zhang, B. Xu, X. Wang, Chem. Soc. Rev. 2014, 43, 7870−7886.
[17] D. A. Bulushev, M. Zacharska, E. V. Shlyakhova, A. L. Chuvilin, Y. Guo,
S. Beloshapkin, A. V. Okotrub, L. G. Bulusheva, ACS Catal. 2016, 6,
681−691.
[18] Q. L. Zhu, N. Tsumori, Q. Xu, J. Am. Chem. Soc. 2015, 137,
11743−11748.
[19] Q. Fu, F. Yang, X. Bao, Acc. Chem. Res. 2013, 46, 1692−1701.
[20] Jin, S. A.; Kwon, K.; Park, C.; Chang, H. Catal. Today 2011, 164,
176−180.
[21] Puthiyapura, V. K.; Brett, D. J.; Russell, A. E.; Lin, W. F.; Hardacre, C.
ACS Appl. Mater. Interfaces 2016, 8, 12859−12870.
[22] V. R. Stamenkovic, B. Fowler, B. S. Mun, G. Wang, P. N. Ross, C. A.
Lucas, N. M. Markovic, Science 2007, 315, 493−497.
[23] X. Min, M. W. Kanan, J. Am. Chem. Soc. 2015, 137, 4701−4708.
[24] H. Huang, H. Jia, Z. Liu, P. Gao, J. Zhao, Z. Luo, J. Yang, J. Zeng,
Angew. Chem. Int. Ed. 2017, 56, 3594−358; Angew. Chem. 2017, 129,
3648−3652.
Acknowledgements
[25] Y. Chen, M. W. Kanan, J. Am. Chem. Soc. 2012, 134, 1986−1989.
[26] B. Kumar, V. Atla, J. P. Brian, S. Kumari, T. Q. Nguyen, M. Sunkara, J.
M. Spurgeon, Angew. Chem. Int. Ed. 2017, 56, 3645−3649; Angew.
Chem. 2017, 129, 3699−3703.
This work was supported by the Hundred Talents Program of
Chinese Academy of Sciences. We acknowledge the support of
the Ministry of Science and Technology under contract of
2016YFA0202800.
[27]
W. Luc, C. Collins, S. Wang, H. Xin, K. He, Y. Kang, F. Jiao, J. Am.
Chem. Soc. 2017, 139, 1885−1893.
[28] N. Sreekanth, K. L. Phani, Chem. Commun. 2014, 50, 11143−11146.
[29] M. Dunwell, Q. Lu, J. M. Heyes, J. Rosen, J. G. Chen, Y. Yan, F. Jiao, B.
Xu, J. Am. Chem. Soc. 2017, 139, 3774−3783.
Keywords: CO2 conversion • electrochemical reduction • Pd-Sn
alloy • formic acid
[30] C. Cui, J. Han, X. Zhu, X. Liu, H. Wang, D. Mei, Q. Ge, J. Catal. 2016,
343, 257−265.
[1]
S. Gao, Y. Lin, X. Jiao, Y. Sun, Q. Luo, W. Zhang, D. Li, J. Yang, Y. Xie,
Nature 2016, 529, 68−71.
This article is protected by copyright. All rights reserved.

10.1002/anie.201707098
Angewandte Chemie International Edition
COMMUNICATION
Entry for the Table of Contents (Please choose one layout)
Layout 1:
COMMUNICATION
Layout 2:
COMMUNICATION
Xiaofang Bai, Wei Chen,* Chengcheng
Zhao, Shenggang Li, Yanfang Song,
Ruipeng Ge, Wei Wei,* and Yuhan Sun*
Page No. – Page No.
Exclusive formation of formic acid
from CO2 electroreduction by tunable
Pd-Sn alloy
Text for Table of Contents
The Pd-Sn alloy supported electrocatalysts were synthesized for the electrochemical conversion of CO2 in an aqueous solution. A
nearly perfect faradaic efficiency toward formic acid formation at the very low overpotential of -0.26 V was achieved over PdSn/C,
which was attributed to the optimal surface oxide configuration.
This article is protected by copyright. All rights reserved.