In Situ Photosynthesis of an MAPbI3/CoP Hybrid Heterojunction for Efficient Photocatalytic Hydrogen Evolution

Article abstract of DOI:10.1002/adfm.202001478

Halide perovskite like methylammonium lead iodide perovskite (MAPbI₃) with its prominent optoelectronic properties has triggered substantial concerns in photocatalytic H₂ evolution. In this work, to attain preferable photocatalytic performance, a MAPbI₃/cobalt phosphide (CoP) hybrid heterojunction is constructed by a facile in situ photosynthesis approach. Systematic investigations reveal that the CoP nanoparticle can work as co-catalyst to not only extract photogenerated electrons effectively from MAPbI₃ to improve the photoinduced charge separation, but also facilitate the interfacial catalytic reaction. As a result, the as-achieved MAPbI₃/CoP hybrid displays a superior H₂ evolution rate of 785.9?μmol?h^?1?g^?1 in hydroiodic acid solution within 3 h, which is ≈8.0 times higher than that of pristine MAPbI₃. Furthermore, the H₂ evolution rate of MAPbI₃/CoP hybrid can reach 2087.5?μmol?h^?1?g^?1 when the photocatalytic reaction time reaches 27 h. This study employs a facile in situ photosynthesis strategy to deposit the metal phosphide co-catalyst on halide perovskite nanocrystals to conduct photocatalytic H₂ evolution reaction, which may stimulate the intensive investigation of perovskite/co-catalyst hybrid systems for future photocatalytic applications.

Full text of DOI:10.1002/adfm.202001478

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In Situ Photosynthesis of an MAPbI /CoP Hybrid
3
Heterojunction for Efficient Photocatalytic Hydrogen
Evolution
Cheng Cai, Yuan Teng,* Jian-Hao Wu, Jun-Yan Li, Hong-Yan Chen,* Jing-Hua Chen,
and Dai-Bin Kuang*
etc. have been put to work as photo-
Halide perovskite like methylammonium lead iodide perovskite (MAPbI ) with
its prominent optoelectronic properties has triggered substantial concerns in
3
catalysts. In particular, lead-based halide
perovskite (LHP) materials have obtained
great interest in photovoltaics and opto-
electronic applications due to their unique
photocatalytic H evolution. In this work, to attain preferable photocatalytic
2
performance, a MAPbI /cobalt phosphide (CoP) hybrid heterojunction
3
[
10–18]
optical and electrical properties.
is constructed by a facile in situ photosynthesis approach. Systematic
investigations reveal that the CoP nanoparticle can work as co-catalyst to not
LHPs with appropriate band structures
have also been developed as the photo-
only extract photogenerated electrons effectively from MAPbI to improve the
[9,19]
3
catalytic materials for CO2 reduction,
[
20]
photoinduced charge separation, but also facilitate the interfacial catalytic
the oxidation of alcohols,
and particu-
[
8,21]
larly hydroiodic acid (HI) splitting.
As
reaction. As a result, the as-achieved MAPbI /CoP hybrid displays a superior
3
−1
−1
a promising example, methylammonium
H evolution rate of 785.9 µmol h
g in hydroiodic acid solution within 3 h,
2
lead iodide perovskite (MAPbI ) with wide
3
which is ≈8.0 times higher than that of pristine MAPbI . Furthermore, the H
3
2
light absorption range and excellent photo-
electronic properties has been proved
to be a good photocatalyst for hydrogen
evolution reaction (HER). In 2016, Park
−1
−1
evolution rate of MAPbI /CoP hybrid can reach 2087.5 µmol h
g
when the
3
photocatalytic reaction time reaches 27 h. This study employs a facile in situ
photosynthesis strategy to deposit the metal phosphide co-catalyst on halide
et al. first reported the MAPbI as a photo-
3
perovskite nanocrystals to conduct photocatalytic H evolution reaction,
2
catalyst for the solar-driven splitting of HI
which may stimulate the intensive investigation of perovskite/co-catalyst
hybrid systems for future photocatalytic applications.
[
8]
solution, which stimulates the photocata-
lytic application of halide perovskite-based
[
21–34]
materials.
structed a MAPbI /rGO composite using
For instance, Wu et al. con-
3
1
. Introduction
facile photoreduction method, and achieved a much higher
photocatalytic HI splitting efficiency than the pristine MAPbI3
due to the efficient extraction of photogenerated electrons by
Hydrogen energy is an important clean source for replacing
fossil fuels. Photocatalytic H evolution from renewable solar
[
21]
rGO. Wang et al. reported a Pt/TiO -MAPbI composite by
2
2 3
energy is denoted as an effective approach to solve the global
environmental and energy issues owing to the merits of uti-
lizing the solar energy directly and the low energy consump-
tion. Designing highly efficient and stable photocatalysts is
hybriding MAPbI with Pt/TiO which can greatly enhance the
3
2
22]
[
charge separation of MAPbI3. Most recently, Ni C-decorated
3
MAPbI3 composite and black phosphorus-anchored MAPbI3
(BP/MAPbI ) heterostructure have been constructed as well,
3
currently vital for effective H generation. On account of this,
and both of them exhibited remarkable photocatalytic H
activity.
2
[3–5]
2
metal oxides,[
1,2]
sulfides,
C N ,
[6,7]
halide perovskites,
[8,9]
[24,25]
3
4
However, most of the reported works were mainly focused
on large size (about tens of microns) LHP microcrystal mate-
rials, which possess limited active sites, and the photogenerated
charge carriers must transport long distance to perform the
photocatalytic reaction. In comparison, halide perovskite
nanocrystals have large specific surface area and short carrier
C. Cai, Dr. Y. Teng, J.-H. Wu, J.-Y. Li, Dr. H.-Y. Chen, J.-H. Chen,
Prof. D.-B. Kuang
MOE Key Laboratory of Bioinorganic and Synthetic Chemistry
Lehn Institute of Functional Materials
School of Chemistry
Sun Yat-sen University
Guangzhou 510275, P. R. China
E-mail: tengy6@mail.sysu.edu.cn; chenhy33@mail.sysu.edu.cn;
kuangdb@mail.sysu.edu.cn
diffusion length, which may exhibit large potential in the field
[9,35–48]
of photocatalysis application.
Encouragingly, in 2017, we
for the first time reported a photocatalytic CO reduction reac-
2
tion by CsPbBr QDs/graphene oxide composite in the non-
3
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adfm.202001478.
[
9]
aqueous ethyl acetate reaction media. Subsequently, various
lead-free perovskite nanocrystals including Cs AgBiBr ,
Cs PdBr , and Cs CuSb Cl
[
19]
2
6
[
39]
[40]
DOI: 10.1002/adfm.202001478
with tunable band gap were
2
6
4
2
12
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synthesized to perform photocatalytic CO reduction/photoelec-
MAPbI /CoP hybrid exhibited a better photocatalytic H evo-
2
3
2
trochemical cell application. Furthermore, various perovskite
lution performance compared with the MAPbI . The H evo-
3 2
nanocrystal-based composite materials such as CsPbBr @
lution rate of the MAPbI /CoP hybrid in 3 h of reaction was
3
3
[41]
[42]
−1 −1
metal oxides, CsPbBr /Pd, CsPbBr @metal-organic frame-
785.9 µmol h g , which is 8.0 times higher than that of
3
3
works,[
43,44]
Cs SnI /SnS
[45]
as well as Fe O /RGO/CsPbBr
MAPbI alone. Photoluminescence (PL), time-resolved photo-
2
6
2
2
3
3
3
[
46]
Z-scheme heterojunction have been designed for improving
photogenerated charge carrier separation and hence enhancing
the photocatalytic performance.
luminescence (TRPL), electrochemical impedance spectro-
scopy (EIS), and Kelvin probe force microscopy (KPFM) were
performed to characterize the photogenerated charge carriers
separation and transportation. The results strongly indicate that
In addition to regulating the size or the composition of cata-
lysts, the introduction of co-catalysts is an another effective
strategy to improve the photocatalytic performance, which can
the current MAPbI /CoP hybrid heterojunction is a promising
3
catalyst for effective photocatalytic H evolution.
2
work as electron sinks and provides effective proton-reduction
reaction sites.[
42,47–53]
As a typical example, cobalt phosphide
(
CoP) is an ideal candidate for constructing advanced hybrid
2
. Results and Discussion
catalysts due to its outstanding intrinsic activity and supe-
rior conductivity; and exciting progress has been obtained in
The fabrication process of the MAPbI /CoP hybrid hetero-
junction is displayed in Scheme 1. Concretely, the MAPbI3
3
the field of electrocatalytic H2 evolution.[
54–61]
Although the
pristine CoP exhibits negligible photocatalytic activity for H
nanocrystal (denoted as pristine MAPbI ) was first prepared by
the microcrystalline-assisted antisolvent method. And then, the
2
3
evolution,[ the integration of CoP as co-catalyst can help accel-
62]
erate the photoelectron transfer and separation, and also reduce
MAPbI /CoP hybrid was synthesized by the in situ photodepo-
3
the reaction energy barrier effectively.[
63–65]
Hence, combining
sition process in which CoCl and NaHPO were dissolved in
2
2
halide perovskite nanocrystals with CoP co-catalyst could signifi-
MAPbI -saturated HI solution to work as the precursor solu-
3
cantly enhance the photocatalytic H generation activity. However,
tion (see Experimental Section for details). Scanning electron
microscopy (SEM) measurement was applied to determine the
micro/nano-morphology of pristine MAPbI and MAPbI /CoP
2
it remains a big challenge to anchor metal phosphide co-catalyst
on the surface of halide perovskite nanocrystal because of the
compatibility and differences in preparation conditions of the
two kinds of materials.
3
3
samples, as displayed in Figure S1, Supporting Information.
It can be clearly seen that both pristine MAPbI and MAPbI /
3
3
Herein, we devised the synthesis of a MAPbI /CoP hybrid
heterostructure by a facile in situ photosynthesis strategy. The
CoP co-catalyst was found to effectively extract the photoinduced
CoP hybrid exhibit a cube-like morphology, but the hybrid
possesses a larger average size of ≈180 nm compared with
pristine sample (≈90 nm), which could be ascribed to the rip-
3
electrons from MAPbI nanocrystals to participate in the photo-
ening growth of MAPbI nanocrystals during the photodeposit
3
3
catalytic reaction, which contributed to a boosted photocatalytic
process of CoP. The powder X-ray diffraction (XRD) patterns
H evolution performance. As a consequence, the as-prepared
2
of samples (Figure 1a) show that the bare MAPbI exhibits a
3
Scheme 1. Schematic diagram of the fabrication and photocatalytic H evolution process of the MAPbI /CoP hybrid heterojunction.
2
3
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Figure 1. a) XRD patterns of pristine MAPbI and MAPbI /CoP hybrid. b,c) The TEM and HRTEM images of MAPbI /CoP. d,e) HAADF-STEM image,
3
3
3
line scan spectrum of MAPbI /CoP and the corresponding elemental mappings of f) Pb, g) I,h) Co, and (h) P.
3
tetragonal crystal structure with a space group of I4/mcm
clearly reveals the lattice fringe spacing of 0.312 nm, cor-
(
ICSD card No. 250739), which matches well with the previous
responding to the (220) plane of MAPbI . After the photo-
3
[20,23,66,67]
reports.
No peaks of CoP are observed in the XRD pat-
deposition of CoP, the morphology of the MAPbI /CoP sample
3
tern of the MAPbI /CoP hybrid, which could be attributed to
is similar to that of pristine MAPbI except for some fine parti-
3
3
its relatively low content. Further transmission electron micro-
scopy (TEM) image also confirms the cube-like morphology of
cles that can be observed on the surface of MAPbI (Figure 1b).
3
HRTEM image (Figure 1c) exhibits two kinds of lattice fringe
with interplanar spacings of 0.313 and 0.234 nm, corresponding
to the (220) plane of MAPbI3 and the (201) plane of CoP,
MAPbI (Figure S2a, Supporting Information). High-resolution
3
TEM (HRTEM) image (Figure S2b, Supporting Information)
Figure 2. a) Photocatalytic HER performance under visible-light illumination (λ ≥ 420 nm) of pristine MAPbI and MAPbI /CoP hybrid. b) Schematic
3
3
illustration of the photocatalytic HER process over the MAPbI /CoP hybrid. c) The corresponding PL and d) PL decay spectra.
3
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respectively. These results indicate that the MAPbI /CoP hybrid
due to its high electron–hole recombination efficiency. After
decorating with CoP, the emission peak almost disappears.
Apparently, the introduction of CoP provides fast transfer paths
3
heterojunction has been constructed successfully. High-angle
annular dark-field scanning TEM (HAADF-STEM) image, ele-
ment mapping, and line scan element analysis of the hybrid
were also measured. As displayed in Figure 1d–i, the Pb, I, Co,
and P elements are homogeneously distributed on the hybrid.
However, the Co and P elements exhibit a sparse point-like
distribution, which also implies the low content. Further proof
comes from the energy-dispersive X-ray spectroscopy (EDX)
result which also shows that the atomic percent of Co and P
is quite low (Figure S3, Supporting Information). Furthermore,
the optical properties of as-prepared samples were studied by
the ultraviolet–visible (UV–vis) diffuse reflectance spectra. As
shown in Figure S4, Supporting Information, the visible-light
for excited-state electrons of MAPbI , which can facilitate the
3
charge separation and inhibit the radiative recombination. To
obtain more details about the decay behavior of photogenerated
carriers of as-prepared catalysts, TRPL spectra was also meas-
[
21,25]
ured and fitted with a biexponential function,
as shown
in Figure 2d and Table S1, Supporting Information. Obviously,
the PL signal of MAPbI /CoP hybrid shows a faster decay
3
rate than that of pristine MAPbI . According to the fitting
3
results, the average PL lifetime (τavg) of MAPbI /CoP (148.1 ns) is
3
much shorter than that of pristine MAPbI (232.6 ns). Specifically,
3
the contribution of τ (fast decay component, related to electron
1
absorption spectrum of the MAPbI /CoP hybrid is slightly
transfer) increases largely from 5.77% for MAPbI to 14.44% for
3
3
broadened than that of pristine MAPbI . This could be attri-
MAPbI /CoP. This result further confirms the conclusion that
3
3
buted to the increased particle size during the photosynthesis
deposition process of CoP, which is in good agreement with the
SEM results.
the introduction of CoP can accelerate the photogenerated elec-
tron transfer from MAPbI to CoP which inhibits the radiative
3
recombination largely.
The photocatalytic HER activity of the as-prepared MAPbI3/
CoP hybrid was investigated in saturated aqueous HI solution
under visible-light illumination. Figure 2a shows the photocata-
lytic HER activities of the MAPbI and MAPbI /CoP samples.
To further clarify the origin of high HER activity of the
MAPbI /CoP hybrid, optoelectrochemical performance of
3
photocatalysts associated with photogenerated charge transfer
and separation were characterized and analyzed by transient
photocurrent responses and EIS measurement. Figure 3a
3
3
It can be seen that pristine MAPbI possesses a photocatalytic
3
HER rate of 97.8 µmol g−
1
h
−1
in 3 h of photocatalytic reaction.
After photodeposition of CoP, the photocatalytic HER rate
785.9 µmol g h ) is ≈8.0 times higher than that of pristine
MAPbI , which is profited from the formation of the MAPbI /
−
1
−1
(
3
3
CoP heterojunction. Figure 2b illustrates the relative energy
band position of MAPbI3 and CoP, which forms a stepped
path for electron transfer. When irradiated by visible light,
the photogenerated electrons in the conduction band (CB) of
MAPbI could be extracted rapidly by the CoP nanoparticles,
3
which can effectively facilitate the charge separation and inhibit
the radiation recombination. Furthermore, the semi-metallic
CoP nanoparticles, as a good electrocatalyst for HER, can
also provide more reaction active sites (Figure S5, Supporting
Information) and help to accelerate the HER. As a result, the
photocatalytic performance of MAPbI /CoP can be largely
3
enhanced. It should be noted that a proper loading amount of
CoP is significant to achieve improved photocatalytic perfor-
mance. As displayed in Figure S6, Supporting Information,
the photocatalytic H evolution performances of the MAPbI /
2
3
CoP hybrids increase at first and then decrease when continu-
ously increasing the loading amount of CoP, and the MAPbI3/
CoP sample prepared at theoretical feeding mass ratio of 1:0.25
exhibits the best performance. This is because proper amount
of CoP nanoparticles can facilitate the transfer and separation
of photoinduced charge carriers, but the excess loading amount
of CoP would also act as the charge recombination centers,
[
68]
which would lead to a decreased catalytic performance.
To further understand the positive effects of CoP on the cata-
lytic performances of hybrid catalyst, the corresponding charge
transfer and separation behaviors in MAPbI /CoP hybrid
3
were investigated in detail. First, the steady-state PL spec-
trum was conducted to monitor the radiative recombination
process of photoexcited charge carriers. Generally, a dramati-
cally quenched PL signal is regarded as an indicator of effec-
tive charge transfer in the composite catalysts. As displayed in
Figure 3. a) The transient photocurrent response curves of the MAPbI3
and MAPbI /CoP hybrid. b) Nyquist plots of pristine MAPbI and
3
3
Figure 2c, the pristine MAPbI shows a strong emission peak
MAPbI /CoP hybrid.
3
3
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Figure 4. KPFM measurement of the pristine MAPbI and MAPbI /CoP hybrid. a,d) AFM images. b,e) SPV images (ΔCPD = CPD − CPDdark). c,f) The
light
3
3
corresponding line profiles of the SPV difference.
exhibits the chopped photocurrent curves of bare MAPbI3
than that of pristine MAPbI (≈6.3 mV). Such a remarkable
3
and MAPbI /CoP photoelectrodes recorded at the open-circuit
difference in SPV signals between the MAPbI and MAPbI /
3
3
3
potential. It can be found that MAPbI /CoP hybrid produces
CoP samples strongly verifies the efficient spatial charge sepa-
3
−2
a photocurrent of ≈2.01 µA cm , approximately fivefold larger
ration in the MAPbI /CoP hybrid.
3
−
2
than that of pristine MAPbI (≈0.40 µA cm ), implying that
In addition, the long-term photocatalytic activity of the
3
the photoexcited charge carrier transfer in MAPbI /CoP hybrid
MAPbI /CoP hybrid was also investigated and shown
3
3
is largely promoted. To further examine the charge transfer
properties of the samples, the EIS plots were measured at 0 V
versus Ag/AgCl electrode under simulated solar illumination
in Figure 5. It is worth noting that the H2 yield rate for
MAPbI /CoP hybrid increases with prolonging the photocata-
3
lytic reaction time. After continuous reaction of 27 h, the H
2
−
2
−1 −1
(100 mW cm , AM 1.5 G with a 420 nm cut-off filter). As shown
yield rate for MAPbI /CoP is 2087.5 µmol h g , which is
3
in Figure 3b, a large semicircle in the testing frequency range is
observed for the pristine MAPbI . By contrast, the MAPbI /CoP
≈2.7 times larger than the value obtained after 3 h of reaction
and is even superior to most of the reported MAPbI -based
3
3
3
hybrid shows a drastically decreased semicircle after coupling
with CoP, implying a more facilitated charge transfer and trans-
portation process. The EIS results strongly confirm that the
charge transfer property is obviously improved with the assis-
tance of CoP co-catalyst, which is expected to obtain a better
catalytic performance.
photocatalysts (Table S2, Supporting Information). Moreover,
the recycling test of MAPbI /CoP hybrid also presents a similar
3
trend with a gradually increased HER activity in five succes-
sive cycles (Figure S7, Supporting Information). To figure out
the origin of this obviously increased H evolution activity with
2
the extension of reaction time, HRTEM images of samples after
photocatalysis reaction were taken. As shown in Figure S8,
Supporting information, both the lattice fringe of (202) face of
To further confirm the effective charge transfer and sepa-
ration process in MAPbI /CoP hybrid, KPFM was performed
3
to directly observe the spatial charge distribution of MAPbI3/
CoP heterojunction, as displayed in Figure 4. Note that this
measurement is based on Au reference to probe the surface
photovoltage (SPV) difference of samples before and after
illumination. It can be found that no significant SPV signal
MAPbI and the lattice fringe of (201) face of CoP can be clearly
3
observed, indicating both MAPbI and CoP nanoparticles can
3
maintain their crystalline structure. Furthermore, XRD patterns
of the MAPbI /CoP hybrid with different photocatalytic reac-
3
tion times were also determined (Figure S9, Supporting Infor-
mation). It could be found that no significant phase structure
changes are observed after long-term photocatalysis reaction
changes are observed in the pristine MAPbI due to the rapid
3
charge carrier recombination. In contrast, a distinct negative
signal is observed in the MAPbI /CoP hybrid, which could
except for a largely enhanced crystallinity of MAPbI , which
3
3
be attributed to the photogenerated electron accumulation on
the surface of CoP particles under illumination. The potential
implies a gradually improved charge transport properties as
the photocatalytic reaction proceeding. Indeed, the EIS test of
samples with different reaction times (Figure S10, Supporting
Information) also confirms this improved charge transport
difference of the MAPbI /CoP hybrid between the illumination
3
and dark condition is ≈38.4 mV, which is significantly larger
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purchased from Aladdin. Lead bromide (PbI ) and NaHPO powders
2
2
were purchased from Sigma-Aldrich. Hydroiodic acid (HI, 57 wt%) and
oleylamine (OAm) were purchased from Macklin. Hexane, chloroform,
absolute ethanol, absolute diethyl ether, and dimethyl formamide (DMF)
were purchased from Guangzhou Chemical Reagent Factory.
Fabrication of the MAPbI3 Nanocrystal: MAPbI3 nanocrystals
were synthesized with modifications to the previously described
method.[
66,69,70]
First, 62.5 mg (0.1 mmol) MAPbI microcrystal powder
3
was dissolved in 3 mL DMF with continuous stirring to form a MAPbI3
precursor solution. Next, 200 µL oleic acid and 35 µL oleylamine were
added into as above precursor solution. Third, 200 µL as-prepared
perovskite precursor solution was added into 10 mL chloroform. After
stirring for 3 h, the reaction mixture was centrifuged for 2 min at
9
000 rpm, and the precipitate was collected. The resulting products were
washed with hexane and chloroform in sequence two times, and then
dried in a vacuum at 50 °C for 3 h.
Figure 5. Long-term stability test of the MAPbI /CoP hybrid for photo-
3
catalytic H evolution in MAPbI -saturated HI solution.
Preparation of the MAPbI /CoP Hybrids, MAPbI Films, and MAPbI /
3
3
3
2
3
CoP Films: 2.5 mg as-prepared MAPbI3 nanocrystal was added into a
0 mL photocatalytic bottle. Then 5 mL MAPbI -saturated HI solution
4
3
in the hybrid. In addition, the EDX analysis (Figure S3, Sup-
porting Information) presents that the atomic percent of Co and
with H PO2 as the stabilizer was added. After that, 0.9 mg absolute
3
cobalt chloride (CoCl ) and 15 mg NaHPO were added into the above
2
2
P in MAPbI /CoP sample after 27 h of photocatalytic reaction is
mixture and sealed well. And then it was evacuated by a vacuum pump
and treated with nitrogen atmosphere for 5 min, respectively. This
process was repeated another time. Furthermore, the above mixture was
illuminated under simulated sunlight without 420 nm cut-off filter for
3
higher than that of the fresh one and the 3 h one, which reveals
that more reaction active sites might be formed during the
photocatalytic reaction process. Based on the aforementioned
results, one can speculate that both the ripening of MAPbI3
nanocrystals and the in situ photodeposition of CoP co-catalyst
can promote the separation of photogenerated charge carriers
and improve the interfacial catalysis kinetics, which may be
responsible for the enhanced photocatalysis performances.
3
0 min. The obtained precipitates were centrifuged, and subsequently
rinsed with hexane. Finally, the product was dried in vacuum conditions
at 50 °C.
The MAPbI and MAPbI /CoP films were prepared by the centrifugally
3
3
cast method. Briefly, FTO glass was cleaned ultrasonically in acetone
for 30 min, rinsed with distilled water and absolute ethanol, and dried
at 70 °C for 24 h. 2.5 mg MAPbI or MAPbI /CoP hybrid was dispersed
3
3
in 2 mL absolute diethyl ether, then ultrasound treated for 5 min. The
suspension was centrifuged onto FTO at 9000 rpm for 2 min, and then
dried at 50 °C under vacuum condition for 30 min to form the MAPbI3
3
. Conclusion
and MAPbI /CoP films.
3
In summary, we reported an in situ photosynthesis of CoP
co-catalyst on MAPbI3 nanocrystal to construct an MAPbI3/
CoP heterojunction for efficient photocatalytic H2 evolu-
Characterization and Measurements: The phase structure of samples
was studied by X-ray powder diffraction (XRD; D-MAX 2200 VPC).
The morphology and micro/nanostructure were investigated by the
field-emission SEM (FE-SEM, Hitachi SU8010), TEM (JEOL-2010 HR),
and aberration-corrected TEM (JEOL, ARM-200F). The thickness and
spatial charge distribution were determined by AFM (DIMENSION
FASTSCAN) and KPFM. The absorption behaviors were studied by the
UV–vis spectrometer (Shimadzu UV-3600). The amount of evolved H2
was qualitatively determined by using a gas chromatograph (GC9790,
Fuli Analytical Instrument Co., Ltd.) equipped with a TDX-01 packed
column and a TCD detector and N2 was used as the carrier gas.
Photoluminescence (PL) spectra were scanned on a photoluminescence
spectrometer (FLS980, Edinburgh Instruments Ltd.), under an excitation
wavelength of 500.0 nm. The PL decay spectra was recorded on the same
instrument under a 472 nm laser extinction with the time-correlated
single-photon counting mode. The decay curves were fitted using a
biexponential decay kinetic function.
tion. The H2 evolution rate of the MAPbI /CoP hybrid was
3
−
1
−1
785.9 µmol h
g
after 3 h of reaction, which was about 8.0
times higher than that of pristine MAPbI . PL, TRPL, EIS,
3
and KPFM results revealed that the transfer and separation
of photogenerated charge carriers were significantly enhanced
for the MAPbI /CoP hybrid sample, which should be respon-
3
sible for the improved photocatalytic HER performance. Con-
tinuous long-term photocatalysis investigation indicated the
photocatalytic HER performance increased with the reaction
−
1
time, for example, H amount of 56362.5 µmol g after 27 h
2
of photocatalysis reaction, which can be probably ascribed to
the improved crystallinity of MAPbI and the more loading of
3
CoP co-catalyst during the continuous photocatalysis reaction.
Overall, this current study offers a facile in situ photosynthesis
strategy to deposit metal phosphide co-catalyst on the surface
of halide perovskite, which can be potentially broadened to var-
ious perovskite/co-catalyst hybrid materials for versatile photo-
t
t
−
−
2
A(t)=K + A1e τ + A2e τ
1
(1)
where A(t), A , and A2 are constants obtained after fitting every
1
decay curve. τ1 and τ2 reflect the fast and sloe decay components,
respectively.[
21,25]
Based on the above decay fitting data, and the average
catalytic applications, such as HER reaction, CO reduction, dye
2
PL life times (τavg) were calculated according to the following equation.
degradation, and organic synthesis.
2
2
2
B τ + B2τ
1
1
(2)
τ avg
=
B τ + B τ
1
1
2
2
4
. Experimental Section
Chemicals and Reagents: Oleic acid (OA), 50% H PO , absolute
Transient photocurrent responses and EIS were determined on the
CHI660E electrochemical workstation and Zennium electrochemical
3
2
cobalt chloride (CoCl ), and 30–33 wt% methylamine (MA) were
workstation (Zahner) in
a
three-electrode configuration using
2
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dichloromethane solution containing 0.1
hexafluorophosphate as the electrolyte, respectively. The MAPbI or the
ꢀ
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Keywords
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