The p-Orbital Delocalization of Main-Group Metals to Boost CO2 Electroreduction

Article abstract of DOI:10.1002/anie.201810538

Enhancing the p-orbital delocalization of a Bi catalyst (termed as POD-Bi) via layer coupling of the short inter-layer Bi?Bi bond facilitates the adsorption of intermediate *OCHO of CO₂ and thus boosts the CO₂ reduction reaction (CO₂RR) rate to formate. X-ray absorption fine spectroscopy shows that the POD-Bi catalyst has a shortened inter-layer bond after the catalysts are electrochemically reduced in situ from original BiOCl nanosheets. The catalyst on a glassy carbon electrode exhibits a record current density of 57 mA cm^?2 (twice the state-of-the-art catalyst) at ?1.16 V vs. RHE with an excellent formate Faradic efficiency (FE) of 95 %. The catalyst has a record half-cell formate power conversion efficiency of 79 % at a current density of 100 mA cm^?2 with 93 % formate FE when applied in a flow-cell system. The highest rate of the CO₂RR production reported (391 mg h^?1 cm²) was achieved at a current density of 500 mA cm^?2 with formate FE of 91 % at high CO₂ pressure.

Full text of DOI:10.1002/anie.201810538

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Accepted Article
Title: The p-Orbital Delocalization of Main-Group Metal Boosting CO2
Electroreduction
Authors: Sisi He, Fenglou Ni, Yujin Ji, Lie Wang, Yunzhou Wen,
Haipeng Bai, Gejun Liu, Ye Zhang, Youyong Li, Bo Zhang,
and Huisheng Peng
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201810538
Angew. Chem. 10.1002/ange.201810538
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http://dx.doi.org/10.1002/ange.201810538

10.1002/anie.201810538
Angewandte Chemie International Edition
The p-Orbital Delocalization of Main-Group Metal Boosting CO2
Electroreduction
Sisi He1†, Fenglou Ni1†, Yujin Ji2†, Lie Wang1, Yunzhou Wen1, Haipeng Bai1, Gejun
Liu1, Ye Zhang1, Youyong Li2*, Bo Zhang1* and Huisheng Peng1*
1State Key Laboratory of Molecular Engineering of Polymers, Department of
Macromolecular Science and Laboratory of Advanced Materials, Fudan University,
Shanghai 200438, China
2Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory
for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou,
Jiangsu 215123, China
†These authors contributed equally to this work
*Correspondence and requests for materials should be addressed to Youyong Li
(yyli@suda.edu.cn), Bo Zhang (bozhang@fudan.edu.cn) and Huisheng Peng
(penghs@fudan.edu.cn).
Abstract: Electrochemical reduction of CO2 to valuable chemical products is a
promising strategy to store intermittent renewable energy and mitigate net greenhouse
gas emissions. Among CO2 reduction products, formate has a high product value per
electron, and can potentially be used in fuel cells, hydrogen storage, and
pharmaceuticals synthesis. However, electrocatalysts for formate production have yet
to exhibit the combination of high current density and high power conversion
efficiency required for practical applications - indeed most catalysts are typically
limited to current densities below 10 mA/cm2 and production rates below 30
mg/h×cm2. Further improvements in current density and production rate with
maintained high power conversion efficiency are necessary to increase the
productivity and thus the economic feasibility for large-scale applications. Here we
find, using density functional theory, that enhancing the p-orbital delocalization of a
main-group Bi (p-orbital delocalized Bi, termed as POD-Bi) catalyst via layer
coupling of the short inter-layer Bi-Bi bond length can facilitate the adsorption of
intermediate *OCHO of CO2 and thus, boost the CO2 reduction reaction (CO2RR) rate
to formate. Using X-ray absorption fine spectroscopy, we determine that the
1
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10.1002/anie.201810538
Angewandte Chemie International Edition
engineered POD-Bi catalyst exhibits a shortened inter-layer bond length after the
catalysts are in-situ electrochemically reduced from original BiOCl nanosheets. The
POD-Bi catalyst on glassy carbon electrode exhibits a record current density of 57
mA/cm2 (more than 2 times higher than the state-of-the-art catalyst) at -1.16 V vs.
reversible hydrogen electrode with excellent formate Faradic efficiency (FE) of 95%.
The POD-Bi catalyst shows the record half-cell formate power conversion efficiency
of 79% at a large current density of 100 mA/cm2 with 93% formate FE when applied
in flow cell system. Furthermore, the highest rate of the CO2RR production ever
report, 391 mg/h×cm2 was achieved at a current density of 500 mA/cm2 with formate
FE of 91% at a high CO2 pressure, more than 2 times higher than the state-of-the-art
synthesized catalysts.
Electrochemical reduction of CO2 to useful fuels and chemicals offers a means to
store renewable electricity at high volume and mass density with the ability to utilize
existing infrastructure for transportation and distribution.[1] As an important product
of CO2 reduction reaction (CO2RR), formate has a high product value per electron
(16.1×10−3 $/electron).[2] Moreover, formate has various useful industrial applications
such as a raw material for the pharmaceutical synthesis, a promising chemical for
hydrogen storage, an anode fuel for fuel cells and a raw chemical to be converted to
syngas.[3] Various metal catalysts have been evaluated with a wide range of Faradic
efficiency (FE) and current density for formate production. Abundant main-group
metals such as Bi, Sn and Pb have been found to be good catalysts to produce formate
-
with FE greater than 90% in CO2-saturated aqueous HCO3 solution.[4] Unfortunately,
the reduction activity has been far too low for practical applications, i.e., the current
densities are generally below 10 mA/cm2 and production rates are below 30
mg/h×cm2,[5] which greatly increases electrolyzer capital cost and makes production
uneconomical.[2] In addition, the power conversion efficiency (chemical energy stored
in the desired products versus input electric energy) is also a vital figure of merit,
which is mainly limited by the overpotentials of CO2 to formate reaction and anodic
reaction (water oxidation). Recent technoeconomic analyses have identified formate
as a profitable product only when current densities reach at least 200 mA/cm2, FEs
6]
greater than 90%, and power conversion efficiencies more than 50%.[2,
Improvement in simultaneously achieving high current densities, high production
rates, high selectivity and satisfactory power conversion efficiencies are required to
make formate economically viable and increase its demand, but unfortunately not yet
2
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achieved.[2, 3a]
Transition metals have been widely applied for the electroreduction of CO2 due to the
availability of their versatile d-orbital electron states to participate in adsorption as
described in d-band theory.[7] Numerous strategies such as quantum size tuning of
nanoparticles, [8] heteroatom doping, [9,10] reactive surface modulation[11,12] etc. have
been explored to modulate their versatile d-orbital electron states to obtain a higher
activity. [7] For instance, after introducing Se and S into Mo to synthetize a MoSeS
alloy, the shortened Mo-S and lengthened Mo-Se bonds allow for the modulation of
the d-band electronic structure of Mo atoms. The current density towards CO
production during CO2RR was increased from 16 to 43 mA/cm2.[9c] However, most
transitional metals fail to produce formate effectively due to the intrinsic stronger
binding of the *COOH intermediate, inhibiting further reduction.[13]
In contrast to the easily tunable and delocalized electronic structure of d-orbitals in
transition metals, main-group metals exhibit localized p-orbital electron states.[14] It
has been hypothesized that delocalized d electrons are the origin of the high catalytic
activity of transition metals.[7, 8b] We posit that modulating the electron density of
localized p-orbitals in main-group metals into delocalized states and thus endowing
versatile electronic structures, may impart p-orbital character similar to transition
metals, and thus enhance the reduction activity to produce formate.
Herein, using density functional theory (DFT) simulation, we discovered that the
delocalization degree of the Bi-p orbital can be tuned by compressing the inter-layer
Bi-Bi bond length. Furthermore, the Bi-p orbital delocalization facilitates the
adsorption of intermediate *OCHO of CO2, thus improving the electrocatalytic
activity. Experimentally, we synthesized p-orbital localized Bi (POD-Bi) catalysts that
exhibit a compressed inter-layer bond length by electrochemically reducing BiOCl
nanosheets. The POD-Bi catalyst under high pressure reached a record partial current
density of 500 mA/cm2 and a record production rate of 391 mg/h×cm2 with a FE of
91%, 2 times higher than the previous reports (Table S3).
We first sought to modulate the p-orbital of Bi by tuning the bond length of inter-layer
Bi and then investigated this effect on the thermodynamic energetics of CO2RR. As
shown in Figure 1a, conventional Bi metal exhibits a layered structure with an
3
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10.1002/anie.201810538
Angewandte Chemie International Edition
intra-layer Bi-Bi bond length of 3.07 Å and an inter-layer Bi-Bi bond length of 3.53 Å.
It has been reported that the energetically favoured reaction step after the first
protonation of CO2 is the formation of *OCHO immediate with a Bi-O bond on the
Bi(012) surface.[15] Herein, we modeled a series of Bi (012) surfaces with different
inter-layer Bi-Bi bond lengths to tune the Bi p-orbital delocalization and investigate
its effects on CO2RR activity. Results show that the delocalized degrees of Bi electron
states increase with the decreasing inter-layer Bi-Bi bond length. The electronic
distribution of inter-layer Bi atoms in real space will couple with each other due to the
compressed structure, which is responsible for the delocalization electrons across Bi-p
orbitals (Figure 1b). Furthermore, Figure 1c and d reveal that the projected density
of state (PDOS) of Bi-p electrons tend to delocalize into deeper energy levels and
have a linear relationship with the adsorption free energy G(*OCHO). The p-orbital
delocalization of Bi atoms leads to greater orbital hybridization between the surface
Bi atom and an adsorbed *OCHO, clearly enhancing the interaction energies of
*OCHO. Meanwhile, more electronic states through the Fermi level will facilitate the
electron transfer ability and enhance the reduction of CO2 on the electrode surface.
From DFT simulations, the Bi with short inter-layer bond length tends to exhibit a
better electrocatalytic performance because of delocalized p-electrons and electronic
conductance through the inter-layer coupling.
It was found that the adsorption energy of the intermediate *OCHO increased with the
decrease of inter-layer Bi-Bi bond length. This leads to a decreased activation barrier
in the first protonation of CO2, and correspondingly enhance the performance of
CO2RR towards formate. Interestingly, when the inter-layer Bi-Bi bond length
decreases to 3.36 Å, the overpotential of *OCHO is predicted to be near-zero (0.01 eV)
as shown in Figure 1e. These theoretical simulations suggest that optimizing the
degree of Bi p-orbital delocalization via inter-layer compression may provide an
enhanced electrocatalytic performance.
Inspired by the DFT prediction of valuable p-orbital delocalization, we sought to
synthesize Bi catalysts with short inter-layer bond lengths. It is impressive to find that
Bi catalysts can possess short inter-layer bond lengths, when prepared via
electrochemically reducing bismuth oxychloride (BiOCl) in situ. For comparison,
commercial Bi was chosen as a control sample. We carried out in-situ X-ray
absorption fine spectroscopic (XAFS) method to analyze the electronic structure of
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formed Bi during in-situ electrochemical reducing BiOCl. To make sure the stability
of XAFS measurement during the reduction process, we conducted a
chronamperometry electroreduction at -0.76 V vs. reversible hydrogen electrode
(RHE) in CO2-saturated 0.5 M KHCO3 aqueous solution (see details in Methods and
supplementary). Figure 2a shows the Bi L3-edge normalized absorption spectra of
the BiOCl during the electrochemical reducing process, as well as commercial Bi as a
comparison. During 20-min reduction reaction, a notable feature of the Bi3+ in the
BiOCl at 13.44 keV gradually shifted to higher energy at 13.45 keV which
contributed to the metallic Bi, while the spectra of commercial Bi remained almost
unchanged (Figure S1). The overlapped curves imply that the BiOCl was almost
reduced to metallic Bi after reduction reaction. The k2-weighted XAFS χ versus
reciprocal wave vector indicated good qualities of the data (Figure 2b). The absolute
of measured spectrum i.e., |χ(R)|, was derived from Fourier transformation by
transforming the above measured spectrum to real R-space produced χ(R) (Figure 2c).
The |χ(R)| exhibits the dependence of the density of neighboring atoms on real
distance (R).[16] By fitting the measured spectrum with the window from 1 to 4 Å, we
obtained the bond lengths of POD-Bi and commercial Bi. The measured bond lengths
of commercial Bi are 3.1 Å and 3.7 Å, and the POD-Bi are 3.1 Å and 3.4 Å, which
correspond to intra- and inter-layer spacings, respectively (Figure 2d). We further
conducted X-ray diffraction patterns, and the reduced Bi possessed obvious
characteristic peaks at 27.2o, 38.0o, 39.6o, and 48.8o, corresponding to the (012), (104),
(110), and (202) facets of metallic Bi, respectively (Figure S2), which is almost the
same to the control sample of commercial Bi sample (Figure S3). However, the peak
showed an obviously shift with the control commercial Bi sample with a higher
degree, which accordingly indicates a shorter inter-layer bond length (Figure S4). [17]
These results point towards that a POD-Bi catalyst possesses a shorter inter-layer
bond length than the conventional Bi.
We also conducted X-ray photoelectron spectroscopy (XPS) measurements to further
investigate the chemical nature of the reduced Bi catalyst. In the high resolution XPS
spectra of Bi 4f shown in Figure 2e and Figure S5, two obvious peaks at 161.2 and
166.4 eV that correspond to Bi3+ were found. [5c, 18] After reduction, these two peaks
disappeared and another two predominant peaks at 160.0 eV and 165.3 eV can be
observed which ascribed to metallic Bi0.[19] We then used scanning transmission
electron microscopy to track the morphology and growth of the POD-Bi catalyst after
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the in-situ reduction. The as-prepared BiOCl were single-crystalline nanosheets with a
uniform width of about 500 nm and thickness of about 10 nm (Figure S6). The
nanosheets were electrochemically reduced under cyclic voltammetry method in
CO2-saturated 0.5 M KHCO3 aqueous solution (Figure S7). With potentials scanning
from -0.2 to -1.4 V vs. RHE, an obvious cathodic peak at -1.1 V indicates that BiOCl
was reduced. After two cycles, the cathodic peak disappeared, suggesting that BiOCl
was thoroughly reduced to metallic state. After in-situ electrochemical reduction, the
original nanosheets turned into nanoparticles (Figure S8). Furthermore,
high-resolution transmission electron microscopy showed that the resultant reduced
Bi was consisted of fine nanocrystals. The nanoparticle diameter was found to be
uniform (~5 nm) (Figure 2f). It can be concluded that during in-situ electrochemical
reduction process, BiOCl was reduced to metallic Bi but with compressed inter-layer
Bi-Bi bond length. According to the DFT simulation results, p-orbital delocalization,
i.e., POD-Bi, is formed.
To verify the DFT prediction of the effect of p-orbital delocalization on CO2RR
performance, we conducted chronopotentiometry experiments on POD-Bi and
commercial Bi on glassy carbon electrodes (GCEs) at the range of -0.86 to -1.36 V vs.
RHE for 3600 s at each applied potential in CO2-saturated 0.5 M KHCO3 aqueous
electrolytes in H-cell system, respectively. A maximal formate FE (FEformate) of 95%
was obtained on POD-Bi at the potential of -1.16 V vs. RHE. The corresponding
partial current density reached 57 mA/cm2, which is almost 4 times higher than that of
commercial Bi (15 mA/cm2) under the same condition. Moreover, the maximal
FEformate can be well maintained at a large range of -0.86 to -1.36 V vs. RHE (Figure
3a), with few side-products of CO (FE=2-3%) and H2 (FE=2-5%) (Figure S9). When
the potential was further increased, the FEformate started to decrease due to the
favorable H2 evolution at higher potentials, but the partial current density was still
much higher than those for the reported metal catalysts in aqueous solution. However,
the commercial Bi exhibited only a peak FEformate at the potential of -1.06 V and
decreased at both higher and lower potentials (Figure S10). To evaluate the effect of
Cl element on BiOCl precursor, we conducted the electrocatalytic performance of
POD-Bi in fresh electrolytes, and found that the performance was almost the same as
before, indicating that the leached Cl ions had no influence on the performance.
Generally, the POD-Bi yielded a higher partial current density with a higher
selectivity for formate than that of commercial Bi.
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To further investigate the CO2RR performance, we conducted cyclic voltammograms
of catalysts in CO2-saturated 0.5 M KHCO3 aqueous electrolyte and compared with
the results obtained in the blank Ar-saturated 0.5 M KHCO3 aqueous electrolyte in
H-cell system. The linear sweep voltammetry results in Figure 3b showed that a
cathodic current of POD-Bi quickly increased at potentials more negative than -0.54
V vs. RHE in both electrolytes. The onset potential of POD-Bi was more positive than
that of the commercial Bi. The current densities of catalysts were obviously increased
in CO2-saturated electrolyte in comparison with those in Ar-saturated electrolyte, and
a larger increase for POD-Bi was also observed compared with the commercial Bi,
indicating that the POD-Bi exhibited higher CO2 reduction current. The above results
demonstrate that POD-Bi exhibits higher reduction rate, lower overpotential and
higher catalytic activity.
To better understand the charge transfer at the solid/electrolyte interface of these two
catalysts, we applied electrochemical impendence spectroscopy (EIS) to investigate
them on GCEs at -1.16 V vs. RHE. The obtained Nyquist plots showed that the
high-frequency intercepts on the real axis of two catalysts (Rs) were almost the same,
suggesting the similar series resistances which included the resistances of catalysts
and GCE and the contact resistance (Figure 3c). The charge transfer resistance (Rct)
was directly proportional to the diameter of the semicircle in the spectra, and it
represents the ease of charge exchange between the catalyst and reactants in the
electrolyte. Obviously, the Rct of the reduced Bi was 171 W, which is much lower than
that of the commercial Bi (471 W), indicating that POD-Bi has higher catalytic
activity than the commercial one.[20]
To further explore the experimental mechanistic pathways for the CO2RR in the
POD-Bi catalyst, the Tafel plots were investigated (Figure 3d). At a lower current
density, the slope values of POD-Bi and commercial Bi are 116 and 128 mV/decade,
respectively. The similar values of the two catalysts are close to 118 mV/decade,
pointing towards that an initial electron transfer rate is the determining step for both
catalysts,[21] consistent with the DFT results. The fast electron transfer to CO2 can
Ÿ
-
form a short-lived surface to adsorb CO2 intermediate. Moreover, the Tafel slope of
POD-Bi is smaller than that of commercial Bi, showing an increased CO2 reduction
kinetic.[22]
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To explore the intrinsic performance of these two catalysts and to eliminate the effect
of crystal size and real surface area on the CO2RR performance, we measured the
electrochemical surface area (ECSA) by Pb underpotential deposition (UPD) method
(Figure 3e).[23] These two catalysts were coated on GCEs, and the obtained
Pb-stripping curves demonstrated an obvious peak at -0.32 V vs. Ag/AgCl, which
represents Pb monolayer deposition on Bi catalyst surface. After calculation, from the
consumed charge, the ECSAs of POD-Bi and commercial Bi were 51.6 and 38.7
cm2/mg, respectively. To further confirm these results, we also conducted Cu UPD,
which was in good agreement with that obtained by Pb UPD (Figure S11).[24] It
implied that the ECSA of POD-Bi was 1.3 times larger than that of the commercial Bi,
which may be due to the smaller particle size of POD-Bi. When the current densities
were re-normalized by the ECSA, the partial current density of POD-Bi at -1.16 V vs.
RHE was still 3.2 times higher than that of commercial Bi, indicating a much higher
intrinsic catalytic activity of POD-Bi. The experimental activity of these shortened
inter-layer Bi catalysts suggest that p-orbital delocalization can facilitate the
production of HCOO-, which is good consistent with our DFT calculation results.
To further increase the catalytic current density and production rate towards industrial
applications, we explored methods including a flow cell reactor and a stainless steel
high-pressure reactor with our catalysts.[25] In a flow cell configuration, by using the
gas diffusion electrodes, the mass transport limitation was minimized and the rate of
electrochemical reduction for CO2 can be greatly increased. We first measured Rs via
EIS (Figure S12) and obtained 95% iR corrected polarization curves (Figure S13).
The current density of POD-Bi reached 200 mA/cm2 at -0.61 V vs. RHE, much higher
than the reported best (Figure S14 and 15 and Table S2). Moreover, FE for HCOO-
production was still above 93% at 200 mA/cm2, demonstrating a high catalytic
activity and selectivity of POD-Bi even at such a high current density. In addition, the
half-cell formate power conversion efficiency of POD-Bi reached 79% at 100
mA/cm2 (Table S2). Furthermore, we explored another strategy to increase the current
density by increasing the dissolved amount of CO2 in the electrolyte under high CO2
pressure. We also obtained 95% iR corrected chronopotential curves on GCE in 0.5 M
KHCO3 solution with the applied pressure of 5.6 MPa (Figure S16 and Figure 4a).
The current density further gradually increased to 500 mA/cm2. At the same time, the
selectivity for HCOO- production was still more than 90% (Figure 4b). The
8
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10.1002/anie.201810538
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production rate reached a record value of 391 mg/h×cm2 at the so high current density
with a faradaic efficiency of 91% (Figure 4c), which is more than 2 times higher than
the state-of-the-art synthesized catalysts (Table S3).
In conclusion, we have developed a powerful strategy to achieve a highly efficient Bi
catalyst for electrochemical CO2 reduction by optimizing inter-layer bond length to
tune the electron density of localized p-orbital in a main-group metal into its
delocalized states, combining the DFT simulation and experimental verification. This
work provides a new pathway for further advances to the development of main-group
catalysts along this crucial front via p-orbital delocalization.
Acknowledgements
This work was supported by Ministry of Science and Technology (2016YFA0203302),
National Natural Science Foundation of China (grants 21503079, 21634003,
51573027, 51673043, 21875042 and 21604012), Science and Technology
Commission of Shanghai Municipality (grants 18QA1400800, 16JC1400702,
15XD1500400 and 15JC1490200), SHMEC (2017-01-07-00-07-E00062) and the
Shanghai youth talent support program. The transmission microscopy study in this
work was supported by the Frontier Research Center for Materials Structure, School
of Materials Science and Engineering of Shanghai Jiao Tong University.
Keywords: CO2 electroreduction, delocalization, formate, main-group metal
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Figure 1. DFT calculations of electrocatalytic CO2 into formate on Bi by tuning
Bi-Bi bond length. a) The crystal structure of bulk Bi. b) The electronic distribution
between two neighboring inter-layer Bi atoms. c) PDOS of the external p orbital of Bi
atom. d) The relationship between p-band center and adsorption free energy of
*OCHO. e) The calculated free energy diagrams of electrocatalytic CO2 into formate
without considering the effect of electrode potential (U=0 V).
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Figure 2. Characterization of POD-Bi and commercial Bi. a) Bi L3-edge XAFS
spectra of BiOCl after reduction at -0.76 V vs. RHE in CO2-saturated electrolyte with
the comparison of commercial Bi. b) The k2-weighted XAFS χ(k) of POD-Bi and
commercial Bi. c) Bi L3-edge extended XAFS spectra of POD-Bi and commercial Bi.
d) Bond lengths of the POD-Bi and commercial Bi. e) Bi 4f XPS spectra of BiOCl,
POD-Bi and commercial Bi. f) Scanning transmission electron microscopy image of
POD-Bi (inset, corresponding magnified image showing the lattice and selected area
electron diffraction pattern).
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10.1002/anie.201810538
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Figure 3. CO2 reduction performance of POD-Bi and commercial Bi. a) Potential
dependence of FEs and current densities for electrochemical reduction of CO2 of
POD-Bi and commercial Bi on GCE in CO2-saturated 0.5 M KHCO3 aqueous
electrolyte. b) The electrochemical reduction of CO2 polarization curves of POD-Bi
and commercial Bi in CO2-and Ar-saturated 0.5 M KHCO3 aqueous electrolyte. c)
Nyquist plots for POD-Bi and commercial Bi at -1.16 V vs. RHE (inset,
corresponding magnified image). d) Partial current density Tafel plots for POD-Bi
and commercial Bi. e) Linear sweep voltammetry curves of POD-Bi and commercial
Bi after stripping from underpotential deposited Pb.
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10.1002/anie.201810538
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Figure 4. High current densities of POD-Bi under high pressure. a) Potential
dependence on time during reduction at 100, 200 and 500 mA/cm2 in 0.5 M KHCO3
aqueous electrolyte on the GCE at 5.6 MPa CO2 pressure. b) Corresponding formate
FEs and production rates of POD-Bi and commercial Bi under reduction at 100, 200
and 500 mA/cm2.
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10.1002/anie.201810538
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The Table of Contents
Main-group bismuth catalyst with p-orbital delocalization exhibits the highest rate
of CO2 reduction reaction ever reported, 391 mg/h×cm2 at current density of 500
mA/cm2 with formate Faradic efficiency of 91%, a factor of 2 times over the
state-of-the-art synthesized catalysts. The simulations reveal that the p-orbital
localization facilitates adsorption of intermediate *OCHO of CO2 and hence the
formation of formate.
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