Tridecaboron diphosphide: a new infrared light active photocatalyst for efficient CO2photoreduction under mild reaction conditions

Article abstract of DOI:10.1039/d0ta10804a

The search for efficient infrared (IR) light responsive photocatalysts for photocatalytic CO₂reduction is highly desirable but remains a huge challenge. Herein, tridecaboron diphosphide (B₁₃P₂) is demonstrated as an effect

Full text of DOI:10.1039/d0ta10804a

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Tridecaboron Diphosphide: A New Infrared Light Active Photocatalyst for
DOI: 10.1039/D0TA10804A
Efficient CO2 Photoreduction under Mild Reaction Conditions
Li Shi a, Xiaohui Ren a,b, Qi Wang a,b, Wei Zhou d, Jinhua Ye a,b,c
*
a
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for
Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki, 305-0044, Japan.
b Graduate School of Chemical Sciences and Engineering, Hokkaido University, Sapporo, 060-
0814, Japan.
c
TJU-NIMS International Collaboration Laboratory, School of Material Science and
Engineering, Tianjin University; Collaborative Innovation Center of Chemical Science and
Engineering (Tianjin), Tianjin 300072, P. R. China.
d
Department of Applied Physics, Tianjin Key Laboratory of Low Dimensional Materials
Physics and Preparing Technology, Faculty of Science, Tianjin University, Tianjin 300072, P.
R. China.
E-mail: Jinhua.YE@nims.go.jp
Abstract
The search for efficient infrared (IR) light responsive photocatalysts for photocatalytic CO2
reduction is highly desirable but remains a huge challenge. Herein, tridecaboron diphosphide
(B13P2) is demonstrated as an effective IR light active photocatalyst for photocatalytic CO2
reduction reaction. Specifically, B13P2 exhibits efficient IR light driven photocatalytic CO2
reduction with a CO evolution rate of 0.13 µmol h-1 and an apparent quantum efficiency (AQE)
2+
of 0.07% at the monochromatic light of 810 nm in the presence of Co(bpy)3 (bpy = 2′2-
bipyridine) as cocatalyst, representing the state-of-the-art IR light active photocatalyst. Both
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the theoretical and experimental investigations indicate that B13P2 is a zero bandgap material
DOI: 10.1039/D0TA10804A
displaying strong light absorption ranging from the ultraviolet to the IR region, and the electron-
hole pairs can be generated by the interband transitions between energy orbitals after absorbing
photons to participate in the photocatalytic reactions.
Key words: infrared light; tridecaboron diphosphide; novel photocatalyst; photocatalytic CO2
reduction
1. Introduction
Photocatalysis can directly convert abundant and renewable solar energy into chemical fuels,
representing one of the most sustainable and economical strategies to solve the environmental
problems and energy crisis.1 Searching appropriate photocatalytic materials has guided the
research of photocatalysis, and numerous semiconductors such as metal sulfides, oxides,
phosphides, nitrides and oxynitrides have been demonstrated as effective photocatalysts for
various photocatalytic applications.2-9 Broadening the light absorption range of photocatalysts
to infrared (IR) light is a feasible strategy to enhance the photo-conversion efficiency.10-12 For
a semiconductor photocatalyst to absorb more light, its bandgap should be as small as
possible.13 However, it is very hard for the traditional semiconductor photocatalysts to trigger
effective photocatalytic reactions under IR light irradiation, because narrowing the bandgaps of
semiconductors via up-shifting the valence band position or down-shifting the conduction band
position would inevitably result in the weak driving force for the charge transfer from band
edges position to reactants.14 As such, exploring new photocatalysts via breaking through this
limitation on basic principle is highly desirable, with efforts to realize effective IR light driven
photocatalysis.
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Up to now, a few unconventional photocatalysts, such as up-conversion materials and
DOI: 10.1039/D0TA10804A
plasmonic materials have been investigated as IR active photocatalysts.15,16 Metallic materials
emerge as another type of IR active photocatalysts that have received much attention.17,18
Unlike semiconductors, there is almost no energy band gap in metallic materials separating the
occupied and unoccupied levels, which endows them the ability to absorb a very wide range of
light.18 Metallic materials can also generate electron–hole pairs via interband transitions after
absorbing photons, which can be evidenced by their strong colored features.18 This indicates
that the metallic materials can potentially realize the IR light driven photocatalytic reactions as
long as the photogenerated electrons and holes can satisfy the redox potentials of target
reactions. On the other hand, another important feature of metallic materials is that they often
have much higher carrier density than the conventional semiconductors, which makes them
promising application in photocatalysis.17 Despite the above interesting features, to the best of
our knowledge, very few metallic materials were found to possess photocatalytic performances
to date, especially for photocatalytic CO2 reduction under IR light irradiation, largely due to the
fact that for most of the metallic materials the redox potential of IR generated electron-hole
pairs cannot overcome the activation barriers for photocatalytic CO2 reduction reaction, and
meanwhile the high carrier density in the metallic materials would result in a serious
recombination of charges, which inevitably lower the photocatalytic efficiency.14,19 Therefore,
the search for an appropriate metallic material as an IR active photocatalyst is indispensable
while challengeable.
Tridecaboron diphosphide (B13P2) is a metal-free compound constructed from boron and
phosphorus elements through strong covalent bonding, displaying rhombohedral crystal
structure.20 B13P2 possesses excellent chemical stability, which endows it as a promising
material for practical applications.21 Even though B13P2 has been discovered for decades, to the
best of our knowledge, its electronic structure as well as the catalytic properties have never been
investigated. In this work, we discover that B13P2 can be applied as a promising photocatalyst
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for photocatalytic CO2 reduction and H2 evolution, even under IR light. The stabiDliOtyI: 1o0.f10B391/D3P0T2A10804A
in various atmospheres was tested, and the results indicated its highly chemical stability, which
was inert to concentrated HNO3, HCl, H2SO4, aqua regia and alkali solution. The valence band
X-ray photoelectron spectroscopy (VB-XPS) measurement and theoretical calculations
revealed that the B13P2 posessed continuous electronic occupied states without bandgap. As
such, B13P2 displayed excellent absorption features from the ultraviolet (UV) region to the IR
region, and electron-hole pairs could be generated under light irradiation. The photocatalytic
performance evaluation indicated that B13P2 was able to photosplit CO2 with a CO evolution
rate of 0.13 µmol h-1 under IR light and an apparent quantum efficiency (AQE) of 0.07% at the
2+
monochromatic light of 810 nm in the presence of Co(bpy)3 (bpy = 2′2-bipyridine) as
cocatalyst, representing a record high value for IR light driven photocatalytic CO2 reduction.
The photocatalytic CO2 reduction performances of B13P2 under full arc and λ>400 nm light
could be further promoted, reaching the CO evolution rates of 10.12 µmol h-1 and 1.35 µmol
h-1, respectively.
2. Experimental section
2.1 Stability test of tridecaboron diphosphide (B13P2). B13P2 was commercially obtained
from Mitsuwa Chemicals Co., Ltd (purity >99%). 0.05 g of the B13P2 powder was immersed
into 50 ml concentrated HNO3, concentrated H2SO4, concentrated HCl, aqua regia and 5 M
NaOH solution, respectively. The above five suspensions were stirred vigorously for 4 hours,
and then thoroughly washed with water and collected by centrifugation, and dried for XRD
analysis.
2.2 Photocatalytic CO2 reduction. The photocatalytic CO2 reduction performance of B13P2
was evaluated in a liquid-solid reaction system at ambient temperature and atmospheric
pressure. The experimental setup is shown in Figure S4. Typically, 15 mg of 2′2-bipyridine
(bpy) and 1 μmol of CoCl2 were firstly added into 35 ml of dimethylformamide (DMF) in a 100
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ml quartz reactor. After stirring for 5 min, a homogeneous solution was formed. Then, 20 mg
DOI: 10.1039/D0TA10804A
of B13P2 photocatalyst and 7 ml of triethanolamine (TEOA) were added in above solution. The
reactor was sonicated for a while to obtain well-dispersed solution, and then was connected to
the gas-closed system. Before photocatalytic reactions, the system was evacuated for 10 min to
remove air, then the system was filled with about 1 bar pure CO2 gas. A 300 W xenon arc lamp
equipped with a UV cutoff filter (λ> 400 nm) or UV-Vis cutoff filter (λ> 780 nm) combined
with cooling water filter was applied as the light sources. The produced H2 and CO were
detected and quantified by gas chromatography (GC-8A, Shimadzu Co., Japan) and (GC-14B,
Shimadzu Co., Japan), respectively. The isotope-labeled experiment was performed by using
13CO2 as reactant and keeping other reaction conditions unchanged, and the product was
investigated by GC-mass spectrum (JEOL-GCQMS, JMS-K9 and 6890N Network GC system,
Agilent Technologies). The cycling photocatalytic experiment was conducted as follows. The
used B13P2 photocatalyst was collected by centrifugation followed with washing with DMF for
two times, then was re-dispersed in a fresh reaction solution (15 mg of bpy, 1 μmol of CoCl2,
35 ml of DMF and 7 ml of TEOA) for the next activity test until a total of 6 cycles. The AQE
of CO evolution was calculated by the below equation:
AQE (%) =
100%
×
=
100%
×
2.3 Photocatalytic H2 evolution. The photocatalytic H2 performances were evaluated with 50
mg B13P2 photocatalyst dispersing in a solution (50 ml H2O solution containing 20 vol.%
methanol as a sacrificial agent, and 2 wt% Pt as cocatalyst) in a 100 ml quartz reactor. The
reactor was connected to a glass-closed system, and then was evacuated for 10 min to remove
air completely. A 300 W xenon arc lamp with a UV cutoff filter (λ> 400 nm) or UV-Vis cutoff
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filter (λ> 780 nm) combined with cooling water filter was applied as the light sources. The
DOI: 10.1039/D0TA10804A
produced H2 was detected and quantified by gas chromatography (GC-8A, Shimadzu Co.,
Japan).
2.4 Photoelectrochemical measurement. The B13P2 photoelectrode was firstly prepared as
follows. 2 mg B13P2 powder was added into 1 ml of ethanol. A well-dispersed solution was
obtained after sonication. The 2 mg/ml B13P2 solution was drop by drop uniformly coated onto
a ITO substrate surface with an exposed area of 1.0 × 1.0 cm2 by spin coating. To improve
adhesion, the prepared photoelectrode was further annealed at 300℃ in Ar for 2 hours. The
linear-sweep-voltammetry (LSV) sweeps were measured in an electrochemical machine
(ALS/CH model 650A, Japan) using the B13P2 photoanode as the working electrode, a Ag/AgCl
electrode as the reference electrode and a Pt foil as the counter electrode. The electrolyte is 0.5
M Na2SO4 solution.
2.5 Characterization. The XRD patterns of the B13P2 were measured by X’Pert PRO
diffractometer (PANalytical). The UV-vis-near-IR absorbance spectrum of the B13P2 was
obtained on SHIMADZU UV-2600. The SEM image and elemental mapping image of B13P2
powders were obtained on a scanning electron microscope (FE-SEM, JSM-6701F). TEM and
HRTEM images of the B13P2 sample were obtained from a transmission electron microscope
(TEM, 2100F, JEOL Co., Japan). The chemical states of B13P2 were measured on X-ray
photoelectron spectroscopy (XPS, VG-ESCA Mark II).
2.6 Computational details. The density functional theory (DFT) calculations in this work were
performed using the Vienna Ab initio Simulation Package (VASP). When doing the calculation,
the projector augmented wave (PAW) pseudopotentials were considered, and meanwhile the
generalized gradient approximation (GGA) combined with the Perdew-Burke-Ernzerhof (PBE)
functional was utilized for the exchange-correlation functional. We expanded the wave-
functions by plane-wave and a cutoff energy of 450 eV was used. We set the energy to 10−6 eV,
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and force convergence threshold to 10−2 eV Å−1. The 6 × 6 ×3 Monkhorst–Pack k-points mesh
DOI: 10.1039/D0TA10804A
was adopted in the 45 atoms model.
3. Results and discussion
In this work, commercial B13P2 powder was purchased and used as starting material. The unit
cell of B13P2 is shown in Figure 1a. The B13P2 has a rhombohedral crystal structure with space
group R_ m.20 The X-ray diffraction (XRD) pattern of B13P2 powder reveals its good crystal
3
structure (Figure S1). The BN was confirmed as the impurity in commercial B13P2 powder
(Figure S1 and S2). Scanning electron microscopy (SEM) was then employed to investigate the
morphology of B13P2. As shown in Figure 1b, B13P2 is a bulk material with particle size ranging
from hundreds of nanometers to several micrometers. The elemental mapping images in Figure
1b confirm the uniform distribution of B and P elements. Figure 1c displays the transmission
electron microscopy (TEM) and high-resolution TEM (HRTEM) images of B13P2. The lattice
fringe with a d-spacing of 0.30 nm is observed, which corresponds to the (110) crystal plane
distance of B13P2.20 The chemical states of B13P2 were investigated by XPS. As shown in Figure
1d, the B1s spectrum of B13P2 can be successfully fitted to two peaks at 188.2 eV and 191.2
eV, attributed to B-P bond and B-O bond, respectively.4,22 The P2p spectrum of B13P2 can be
fitted to a sole peak at 130.4 eV, which is ascribed to B-P bond.4 The stability properties of the
B13P2 powder were investigated by dispersing the B13P2 powder in concentrated HNO3, HCl,
H2SO4, aqua regia and aqueous alkali solution (5 M NaOH) for 4 hours, respectively. It was
found that the B13P2 powder was insoluble in aqueous alkali solution or concentrated mineral
acids. After acids and aqueous alkali solution treatment, the B13P2 powder was collected and
charaterized by XRD. As shown in Figure S1, the crystal structure of B13P2 remains almost
unchanged after acid and alkali solution treatment, which indicates that B13P2 exhibits excellent
chemical stability and is inert to aqueous alkali solution and concentrated mineral acids.
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The optical property of B13P2 was then investigated. B13P2 possesses strong gray color (Figure
DOI: 10.1039/D0TA10804A
2a), indicating its intense light absorption ability. According to the UV-vis-near-IR absorbance
spectrum in Figure 2a, B13P2 displays excellent absorption features ranging from the UV to the
IR region. In strong contrast to conventional semiconductors, no band edge absorption feature
can be observed from B13P2. This is probably due to the fact that B13P2 displays metallic feature
rather than semiconducting properties, which can be proved by its VB-XPS spectrum and
density functional theory (DFT) calculations. As shown in Figure 2b, the Fermi level (Ef) of
B13P2 is occupied by continuous electronic occupied states, revealing its metallic feature. The
calculated density of states (DOS) of B13P2 are displayed in Figure 2c, which indicate that the
total DOS of B13P2 are mainly attributed to the contribution from the p orbitals of B atom, and
the values of DOS around the Fermi level (from -10 eV to 10 eV) are continuous without
bandgap, demonstrating the metallic nature of B13P2. The energy band diagram in Figure 2d
further reveals the absence of bandgap in B13P2, and the optical absorption of B13P2 from UV
to IR probably originates from the electron transfer between each orbital. To reveal whether the
charge carriers could be generated over B13P2 under light irradiation, photoelectrochemical
properties were evaluated. Figure S3 shows the linear-sweep-voltammetry (LSV) sweeps for
the B13P2 photoanode, which produce apparent photocurrents response to light on-off switching
with the bias applied under light irradiation. Even under IR light irradiation, an obvious
photocurrent response can also be observed and the generated photocurrent density is even
comparable to that from visible light irradiated g-C3N4 photoanodes.23-25 These results reveal
that B13P2 is able to produce electron-hole pairs under UV, visible and even IR light irradiation.
Based on the above results, it is interesting to investigate whether the photogenerated
electron-hole pairs could participate in photocatalytic reactions. Photocatalytic CO2 reduction
performance was evaluated over B13P2 under IR light. Compared with the intensively
investigated systems of UV and visible light driven photocatalytic CO2 reduction, IR-induced
CO2 reduction to chemical fuels on a photocatalyst has rarely been investigated.14,19 This is
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mainly due to the fact that a semiconductor photocatalyst that enables photocatalytic CO2
DOI: 10.1039/D0TA10804A
reduction generally has to possess a large band gap to reach the rather negative CO2 reduction
potential and simultaneously satisfy the requirement of the positive potential for hole
consumption (the oxidation of H2O or sacrificial electron donor), which significantly limits the
IR light absorption efficiency.19 The photocatalytic CO2 reduction reaction was performed in a
2+
dimethylformamide (DMF) solution with triethanolamine (TEOA) and Co(bpy)3 as the
sacrificial agent and cocatalyst, respectively, under IR light irradiation (λ > 780 nm, Figure S4),
and ambient temperature and pressure. The experimental device is shown in Figure S5. CO and
H2 were generated as the products from this photocatalytic system, while no liquid products
evolutions (e.g., HCOOH and CH3OH) were observed, consistent with results of previous
works in a similar liquid-solid reaction system when using TEOA as sacrificial agent and
2+
Co(bpy)3 as cocatalyst.26-28 Figure 3a shows the time-dependent CO evolution over B13P2
from photocatalytic CO2 reduction under IR light. It can be seen that the CO yield increases
almost lineally with light illumination time, and an evolution rate of 0.13 µmol h-1 (6.5 µmol
g-1 h-1) is obtained. After 6 hours, 0.78 µmol CO and 0.18 µmol H2 were generated, referring to
the CO selectivity of 81.3%. The achieved IR light driven photocatalytic CO2 reduction
performance over B13P2 is superior to those of the reported IR light active photocatalysts, and
is also comparable to those of some UV and visible light responsive photocatalysts, as shown
in Table S1.14,19,29-32 To verify the light-responsive activity of B13P2 for CO2 reduction, the
wavelength dependent AQE were measured. As shown in Figure 3b, the AQE decreases along
with the increasing of light wavelength, demonstrating the CO2 reduction is driven by the
interband transitions related electrons of B13P2. The longest monochromatic light is chosen at
810 nm due to the instrument limitation. The measured AQE at the monochromatic light of 810
nm over B13P2 reaches up to 0.07%, representing a record high value for IR light driven
photocatalytic CO2 reduction.5 Under IR light irradiation, the temperature in the reaction
solution is measured at around 25 oC. In a controlled experiment performed under 25 oC without
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light irradiation, no CO product is detected, which excludes the thermal effect DfOoIr: 1t0h.1e039C/DO0T2A10804A
reduction performance (Figure S6). We further tested the effects of the reaction solvent on the
photocatalytic CO2 reduction performance of B13P2 (Figure S7). It shows that both the DMF
and acetonitrile solvents are favorable for the photocatalytic CO2 reduction reaction mainly
because of their excellent solubility of CO2 molecular.33 However, the photocatalytic CO2
reduction reaction performance greatly decreases when water is used as solvent, largely
ascribed to the weak chemical affinity of water towards CO2 molecules.33
The stability of B13P2 photocatalyst was then examined by repeatedly conducting the
photocatalytic CO2 reduction reactions under IR light. As shown in Figure 3a, no obvious
deactivation of CO evolution rate is found during 6 cycles tests. Moreover, XRD
characterization of the used B13P2 after photocatalytic reaction also proves its high stability
feature (Figure S8). Figure 3c shows the photocatalytic CO2 reduction activities under different
2+
conditions. The evolution of CO is greatly suppressed without Co(bpy)3 , indicating the
significant role of Co(bpy)32+ as cocatalyst for promoting photocatalytic CO2 reduction (Figure
3c, column 2). No products are detected in the dark or in the absence of B13P2, suggesting CO
is produced through a photocatalytic pathway over B13P2 photocatalyst (Figure 3c, column 4,
5). When TEOA is removed from the photocatalytic system under otherwise identical
conditions, no products are generated, indicating TEOA is both the proton source and electron
donor in the photocatalytic CO2 reduction reaction (Figure 3c, column 6), since the CO and H2
evolutions are proton and electron involved reactions (CO2 + 2H+ + 2e-
+ 2e-
CO + H2O; 2H+
H2). Only H2 is produced under Ar, indicating the produced CO originates from
CO2 (Figure 3c, column 3). In order to directly reveal the carbon source of the produced CO,
isotopic experiment was conducted in the presence of 13CO2. The gas chromatogram (GC) and
mass spectra (MS) were used to analyze the generated gas products. As shown in Figure 3d, a
peak at the retention time of 6.1 min in GC spectrum refers to the CO product, and other two
peaks before CO are demonstrated to be the O2 and N2 in the sampling needle. The m/z= 29 in
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MS is observed by analyzing the CO product, which is ascribed to the 13CO. This result directly
DOI: 10.1039/D0TA10804A
demonstrates that the carbon source of CO originates from CO2. The photocatalytic
performances were further evaluated under full arc (UV+ Vis + IR) and λ>400 nm (Vis+ IR)
light irradiation. As shown in Figure 4, the photocatalytic CO2 reduction performances under
full arc and λ>400 nm light are dramatically improved compared with that under IR light,
reaching the CO evolution rates of 10.12 µmol h-1 and 1.35 µmol h-1, respectively. Only trace
amount of CO and H2 can be detected when using BN as catalyst, which demonstrates that the
high yield of CO and H2 under full arc originates from the photoexcitation of B13P2 (Figure S9).
Not only limited to the photocatalytic CO2 reaction, B13P2 also exhibits photocatalytic H2
evolution performance in water using methanol as a sacrificial agent and in-situ photo-deposited
Pt as cocatalyst under visible light and IR light. As shown in Figure S10, steady H2 evolution
is observed over B13P2 under both visible light and IR light, which further demonstrates the
applicability of B13P2 in photocatalysis.
To understand the mechanism of B13P2 in photocatalysis, the work function value (φ) of
B13P2 was calculated using first-principle methods, and the bulk model of B13P2 crystal with the
surface of (110) was selected on the basis of the XRD and the HR-TEM micrographs results.
As shown in Figure 5a, the work function value (φ) of B13P2 is calculated to be 4.98 eV. In
other words, the Fermi level (Ef) can be estimated as 4.98 eV relative to the vacuum level. The
Ef value is then converted to electrochemical energy potential on the basis of the reference
standard that 0 V versus RHE (reversible hydrogen electrode) corresponds to –4.44 eV versus
evac (vacuum level), which is +0.54 V vs. RHE.34 Charge density distribution of B13P2 is shown
in Figure 5b, which shows that there exists the charge transfer from P to B site through the B-
P bonding in B13P2, and the electrons are finally accumulated on the B atoms. The electrons on
2+
the B atoms of B13P2 could be then transferred to cocatalytic materials (Pt or Co(bpy)3 ) under
light irradiation. Previous studies have revealed that Co (I) generated by in-situ photoreduction
of Co (II) bipyridine is the active site for photocatalytic CO2 reduction reaction, and the redox
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potential of Co (II)/Co (I) locates at around -0.44 V vs NHE.35 The energy difference between
DOI: 10.1039/D0TA10804A
the Ef value and the redox potential of Co (II)/Co (I) is 0.92 V, which indicates that the IR light
irradiation on B13P2 is theoretically possible to reduce Co (II), as the photonic energy of IR light
can reach 1.55 eV.5 To give the direct evidence of the generation of Co (I), electron spin
resonance (ESR) measurement was performed. As shown in Figure S11, under IR light
irradiation, the ESR signal is weakened, indicating the high-spin-state Co (II) is reduced to low-
spin-state Co (I).36 The proposed photocatalytic CO2 reduction process over B13P2 is shown in
Figure 5c and Figure S12. Under light irradiation, electron-hole pairs are generated over B13P2
through interband transition between different orbitals, and electrons will leap over the Fermi
level to a higher energy level. The electrons with energy level above the redox potential of Co
(II)/Co (I) can be injected into Co(bpy)32+ to produce Co (I), which is responsible for the CO2
reduction.
4. Conclusion
In summary, this study provides strong evidence for the potential application of B13P2 as a
novel IR active photocatalyst in photocatalytic CO2 reduction. The photocatalytic performance
evaluation shows that B13P2 is able to stably photosplit CO2 under IR light with a CO evolution
rate of 0.13 µmol h-1 in the presence of Co(bpy)32+ as cocatalyst, and the measured AQE at the
monochromatic light of 810 nm reaches up to 0.07%, representing a record high value for IR
light driven photocatalytic CO2 reduction. The photocatalytic CO2 reduction performances of
B13P2 under full arc and λ>400 nm light can be further promoted, reaching the CO evolution
rates of 10.12 µmol h-1 and 1.35 µmol h-1, respectively. Not only limited to the photocatalytic
CO2 reaction, B13P2 also exhibits photocatalytic H2 evolution performance in water under both
visible light and IR light. Both the theoretical and experimental evidences indicate the zero
bandgap feature of B13P2, which displays intensive and broad light absorption ranging from the
UV to the IR region, and electron-hole pairs are generated in B13P2 by the interband transitions
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between energy orbitals after absorbing photons to participate in the photocatalytDicOI:r1e0a.1c0t3i9o/Dn0sT.A10804A
B13P2 shows highly chemical stability, inert to concentrated HNO3, HCl, H2SO4, aqua regia and
alkali solution, which endows it as a promising material for practical applications. It is expected
that B13P2 will provide new opportunities for the development of IR responsive photocatalysts,
photodetectors, solar cells and many other solar energy conversion systems.
Acknowledgements
This work received financial support from the World Premier International Research Center
Initiative (WPI Initiative) on Materials Nanoarchitectonics (MANA), MEXT (Japan), JSPS
KAKENHI (JP18H02065), the Photo-excitonix Project at Hokkaido University, National
Natural Science Foundation of China (21633004), Fundamental Research Funds for the Central
Universities (No. NE2019103).
Declaration of interests
The authors declare no competing financial interests.
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DOI: 10.1039/D0TA10804A
Figure 1. (a) Unit cell of B13P2. (b) SEM image of B13P2 and the corresponding elemental
mapping images of B and P. (c) TEM and HRTEM images of B13P2. (d) B 1s and P 2p XPS
spectra of B13P2.
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DOI: 10.1039/D0TA10804A
Figure 2. (a) UV-vis-near-IR absorbance spectrum and photograph of B13P2. (b) VB-XPS
spectrum of B13P2. (c) Calculated DOS and (d) energy band diagram of B13P2.
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DOI: 10.1039/D0TA10804A
Figure 3. (a) CO evolution as a function of reaction time under IR light over B13P2. (b) AQE
as a function of incident light wavelength over B13P2. (c) CO and H2 evolution amount in 6
hours under various reaction conditions. (d) GC-MS spectra of CO obtained from 13CO2 isotope
experiment over B13P2 under IR light.
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DOI: 10.1039/D0TA10804A
Figure 4. (a) CO evolution from photocatalytic CO2 reduction over B13P2 in the presence of
Co(bpy)32+ as cocatalyst under full arc and λ>400 nm (Vis+ IR) light irradiation in DMF/TEOA
solution. (b) Comparison of photocatalytic CO2 reduction performances under full arc and
λ>400 nm (Vis+ IR) light after 6 hours reaction.
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DOI: 10.1039/D0TA10804A
Figure 5. (a) Work function calculation for B13P2(110). (b) Charge density distributions of
B13P2, and the value of isosurface is 0.01 e/A3. Green ball and purple ball refer to B and P,
respectively. (c) The mechanism of photocatalytic CO2 reduction over B13P2 in the presence of
Co(bpy)32+ as cocatalyst.
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DOI: 10.1039/D0TA10804A
TOC figure
Tridecaboron diphosphide (B13P2) is demonstrated as a novel and effective IR light active
photocatalyst for photocatalytic CO2 reduction reaction. B13P2 displays intensive and broad
light absorption ability, and the electron-hole pairs generated by the interband transitions
between energy orbitals can participate in the photocatalytic reactions.
22