Cu2ZnSnS4âAuAg Heterodimers and Their Enhanced Catalysis for

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CuZnSnS-AuAg Heterodimers and Their Enhanced Catalysis for Oxygen Reduction Reaction Xuelian Yu, Ruifeng Du, Baoying Li, Lei Liu, and Yihe Zhang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b12868 • Publication Date (Web): 28 Feb 2017 Downloaded from http://pubs.acs.org on March 1, 2017

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The Journal of Physical Chemistry

Cu2ZnSnS4-AuAg Heterodimers and Their Enhanced Catalysis for Oxygen Reduction Reaction

Xuelian Yu,*,† Ruifeng Du,† Baoying Li,† Lei Liu,† Yihe Zhang *,†

†

Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes,

National Laboratory of Mineral Materials, School of Materials Science and Technology, China University of Geosciences, 100083 Beijing, China [email protected], [email protected]

ACS Paragon Plus Environment

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ABSTRACT

Cu2ZnSnS4 (CZTS) and AuAg alloy are important functional materials that have received considerable research interest. In this work, we develop a solution based synthetic method to combine these two materials into CZTS-AuAg heterodimers at low temperature. These CZTSAuAg heterodimers demonstrate prominent catalytic activities toward oxygen reduction reaction (ORR) in alkaline medium and it shows a 20-fold increase in mass activity compared to the single component of AuAg nanocrystals. Meanwhile,

compared to the CZTS-Au

heterostructures, the addition of Ag has remarkably increased the four-electron selectivity of the catalysts. X-ray photoelectron spectroscopy (XPS) analysis reveals that the promising properties are mainly attributed to the electronic coupling between semiconductor and noble metal domain in the heterostructure and alloying effect of Au-Ag. The work proves that it is possible to maximize the catalytic activity through not only alloying method but also of its interaction with semiconductor using metal alloy-semiconductor heterostructure.

1. INTRODUCTION The oxygen reduction reaction (ORR) is a crucial step in several energy conversion and storage electrochemical devices, such as fuel cells, metal-air batteries and some industrial process like chloralkali electrolysis.1,2 Platinum (Pt)-based materials are known to be the most active catalysts for ORR in both acidic and alkaline conditions.3,4 However, the high cost, limited reserves and poor durability still hinder the widespread implementation of Pt-based catalysts. Exploring cost-effective electrocatalysts while maintaining the high performance of Pt is one of the most active and competitive fields for ORR in fuel cells.5-7 In this occasion, a wide range of non-noble metal and metal free electrocatalysts have been explored, such as transition metal


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carbides, nitrides, oxides, sulfide and doped carbon, etc.8-12 Even so, due to the low conductivity of transition metal compound, there is still a clear gap in the ORR activities between these materials and Pt, in terms of the half-wave potential or diffusion-limited current density. Therefore, it is still highly desirable to design and develop earth-abundant materials with new structure for enhanced ORR activity. Multinary chalcogenides, in particular I2−II−IV−VI4 quaternary chalcogenides with tailored morphology, phase and composition, provide outstanding opportunities for the design and engineering of materials with tuned fundamental chemical and physical properties.13,14 The ample chemical and structural freedom permit optimizing this class of materials in multiple applications, including photovoltaics, thermoelectrics and catalysis.15,16 Among them, Cu2ZnSnS4 (CZTS), one fantastic Cu-based chalcogenides excited our research interests. It is composed of four earth-abundant and non-toxic elements, which meets the requirements of lowcost and robust.17,18 Besides, the structural and valence variability in CZTS yields it with large densities of defects and charge carrier concentrations, which makes it possess excellent and tunable photocatalytic properties.19-21 Moreover, recently, CZTS NCs also show good catalytic properties toward ORR, and therefore provide a potential electrocatalyst based on non-noble metal multinary chalcogenides.22 To further improve its electrocatalytic activity, CZTS-metal hybrid nanostructure was investigated. Colloidal hybrid nanoparticles, which compose of multiple functional components, have attracted considerable interest in recent years.23-27 That is because integration of functional materials into a single one unit can not only retain the properties of both components but also exhibit new properties through the electronic coupling between components. For instance, in Ag2S-noble metal nanocomposites, the electron flow from Ag2S to Pt was proved to improve the


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performance and stability in CO-stripping and methanol oxidation reaction.28 Moreover, it is well established that metal alloys with optimal metal ratio often express enhanced catalytic activity than their constituent metals.29 So, in this work, we select AuAg alloy, which not only is relatively inexpensive but also have shown high potential as electrocatalyst.30 Thus, combining the advantages of efficient materials and useful structure, it is expected that colloidal hybrid nanoparticles composed of AuAg alloy and CZTS would exhibit higher electrocatalytic activity toward the ORR. However, for the growth of hybrid nanoparticles, it depends sensitively on the growth conditions and properties of both component, which need to suppress the undesired homogeneous nucleation.31,32 So, up to now, it is still challenging to synthesize high quality hybrid nanoparticles containing alloy domains.33,34 Now, in this work, monodispersed CZTS nanocrystals (NCs) are synthesized and used as seeds for the following nucleation and growth of AuAg nanodomains on the surfaces to form CZTS-AuAg heterodimers. Such hybrid nanoparticles can not only overcome the low conductivity of sulfide and high price of noble metals, but also enhance the catalytic activity toward the ORR in the alkaline media. Electrochemical characterizations show that commercial carbon supported CZTS-AuAg heterodimers show an outstanding oxygen reduction activity with a limiting current density of 5.5 mA cm-2, which is far better than the performance of the single component of CZTS and AuAg alloy nanocrystals. Furthermore, compared to the CZTS-Au heterostructures, the addition of Ag has remarkably increased the four-electron selectivity of the catalysts. X-ray photoelectron spectroscopy reveals the covalent coupling between CZTS and AuAg NCs, suggesting that strongly coupled hybrid materials offer a promising strategy for advanced electrocatalysts. With optimal molar ratio of Au/Ag (1:1), the CZTS-AuAg


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heterodimers show not only a 20-fold higher in mass activity than the AuAg alloy nanocrystals, but also better tolerance to methanol crossover than the commercial Pt nanoparticles catalyst. 2. EXPERIMENTAL SECTION Synthesis of CZTS NCs: CZTS NCs were prepared according to our previous report.19 In a typical synthesis, 1.8 mmol of CuCl2•2H2O, 1.6 mmol of ZnO and 0.6 mmol of SnCl4•5H2O were dissolved in tetrahydrofuran (THF). Following, 8 mmol of oleylamine and 6.5 g 1octadecene were added to the reaction mixture. Then the solution was heated under flow of argon to 175 °C and maintained for 1 hour. After cooling to 100 °C, 1.6 mmol of dodecanethiol and 16 mmol of tertdodecylmercaptan were injected. Finally, the solution was reacted at 250 °C for 1 hour. After reaction, the NCs were purified by multiple precipitation steps. Synthesis of CZTS-AuAg heterostructures: CZTS-AuAg heterostructures were prepared by the nucleation of AuAg on the surface of the CZTS NCs. In a typical synthesis, first, a precursor solution was made by dissolving 16.9 mg AgNO3 (0.1 mmol), 34 mg HAuCl4 (0.1 mmol), 140 mg dodecylamine (DDA), 80 mg didecyldimethylammonium bromide (DDAB) in 3 mL toluene under sonication at 60 °C for 30 min. In another flask, the toluene solution of CZTS NCs was purged with nitrogen and heated to 100 °C for 10 min. Then the metal precursor solution was quickly injected and the reaction was lasted for different time before rapid cooling to room temperature. The final products were washed by multiple precipitation and redispersion steps using toluene and ethanol. For comparison, heterostructures were also synthesized by the same procedure but with the addition of different amount of AgNO3 and HAuCl4. CZTS-Au was prepared by only adding the


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HAuCl4 without AgNO3. AuAg nanocrystals were prepared without the addition of CZTS nanocrystals. Characterization: The morphological, chemical and structural characterizations of the products were carried out by transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). Carbon-coated TEM grids from Ted-Pella were used as substrates. HRTEM images were obtained using a Jeol 2010F field emission gun microscope with a 0.19 nm point-to-point resolution at 200 keV with an embedded Gatan image filter for EELS analyses. Images were analyzed by means of Gatan Digital micrograph software. Powder X-ray diffraction (XRD) patterns were obtained with Cu Kα1 (λ=1.5406 Å) radiation in a reflection geometry on a Bruker D8 operating at 40 kV and 40 mA. Raman scattering measurements were performed in backscattering configuration with a LabRam Model HR800-UV Horiba−Jobin Yvon spectrometer, using the 532 nm line from a Nd:YAG solid-state laser. X-ray Photoelectron Spectroscopy (XPS) was carried out using the XPS spectrometers (ESCALab220I-XL). Electrochemistry Experiments: To study the electrocatalysis toward ORR, the nanoparticles were loaded on carbon black (Ketjen carbon, C) with a weight ratio of 3:7 (nanoparticles/C). The composites were firstly activated via thermal annealing under Ar atmosphere at 400 °C for 1 h and then dispersed in the mixture of 0.5 mL isopropanol, 0.5 mL deionized water and 8.75 µL Nafion (10 wt%). Finally, 10 µL of solution was deposited on the glassy carbon (GC, 4 mm in diameter) rotating disk electrode (RDE) for electrochemical characterization. Cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometric experiments were performed on a CHI760e electrochemical workstation (CHI Instrument Inc.). The prepared thin-film GC electrodes were used as the working electrodes. Platinum foil and


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Ag/AgCl were used as the counter and reference electrodes, respectively. The Ag/AgCl electrode was calibrated with respect to the reversible hydrogen electrode (RHE) in all measurements (+0.949 V vs. RHE). The electrolyte is 0.1 M KOH solution, which was saturated with ultrahighpurity Ar for 30 min before measurements. The oxygen reduction experiments were performed by saturating with ultrahigh-purity O2 for 30 min before the measurements. For comparison, Pt/C (20 wt% Pt on Vulcan XC-72, purchased from Alfa Aesar) electrode was also fabricated with the same procedure. 3. RESULTS AND DISCUSSION To confirm the crystal phase, powder X-ray diffraction (XRD) of the CZTS is checked and the observed patterns for the CZTS shown in Figure S1a match well with the (100), (002), (101), (102) and (110) planes of wurtzite CZTS.35 The Raman spectrum in Figure S1b obtained with a 532 nm excitation shows the band at 326 cm−1, which agrees well with the reported spectrum of CZTS. Thus, the presence of SnS, SnS2, SnS3, Cu2SnS3 or CuS, is ruled out in the final material.36 For the CZTS-AuAg heterostructure, no characteristic diffraction peak corresponding to AuAg alloy is observed in Figure S2, which may be due to the relatively low diffraction intensity for the AuAg alloy and CZTS NCs. A transmission electron microscopy (TEM) image of the prepared CZTS NCs is shown in Figure 1a. The NCs are highly monodisperse with an average diameter of 15±2 nm. Then these CZTS NCs were used as seeds and DDA was used as a reducing agent for the formation of heterostructures. Figure 1b and figure 1c show the representative transmission electron microscopy (TEM) images with different magnification of the CZTS-AuAg heterodimers with the darker dots being metal nanoparticles. The epitaxial relation between AuAg and CZTS is


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seen in a high resolution TEM (HRTEM) image shown in Figure 1d. The distance between two lattice fringes in CZTS part measured from the HRTEM image is 0.32 nm, close to (002) plane spacing in wurtzite structured CZTS. The interfringe distance in AuAg part is 0.24 nm, corresponding to (111) plane spacing in face-centered cubic (fcc) AuAg.37 Furthermore, the HRTEM studies on the metal part show the multitwinned icosahedral structure, which is often observed in fcc metallic nanocrystals at small sizes.38

Figure 1. (a) TEM image of the CZTS NCs, (b, c) TEM and (d) HRTEM images of the CZTSAuAg heterodimers. The existence and chemical state of AuAg in CZTS-AuAg heterodimers was further analyzed by X-ray photoelectron spectroscopy (XPS). Besides the existence of Cu, Zn, Sn, and S (Figure S3), the peaks at 367.9 and 373.9 eV shown in Figure 2a can be assigned to the binding energies


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of Ag 3d5/2 and Ag 3d3/2 of the zero-valent Ag. And in Figure 2b, the peaks at 84.2 and 87.9 eV can be assigned to the Au 4f7/2 and Au 4f5/2 of the zero-valent Au.39 Quantitative analysis shows the presence of both Au and Ag with the molar ratio Au/Ag=1, which is consistent with the EDS results shown in Figure S4.

Figure 2. XPS spectra of Ag 3d (a) and Au 4f (b) spectra for CZTS−AuAg heterodimers. The growth process was investigated by controlling the reaction time. As shown in Figure 3a, after the injection of 5 s, the fast reduction of noble metals leads to the formation of multiple small AuAg NCs on the surface of each CZTS seed. Figure 3b shows the TEM image of the sample after injection of 60 s, we can see the size of the AuAg NCs increased from 2 nm to 3 nm. In Figure 3c, when the reaction time is further extended to 180 s, the AuAg NCs continuously enlarged to 4 nm. When the reaction time is 300 s, the product is dominated by heterodimers (ca. 75%), as shown in Figure 1. When the ripening time is as long as 1 h, flower-like CZTS-AuAg heterostructures are formed with the 6 nm AuAg NCs surrounded by multiple CZTS NCs (Figure 3d). Scheme 1 shows the process in the seeded growth of CZTS-AuAg heterostructures. The process is initiated from a fast nucleation event followed by the subsequent growth of larger particles with the consumption of the smaller ones.40


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Figure 3. TEM images of nanoparticles obtained at different reaction times after the injection of metal precursor. (a) 5 s, (b) 60 s, (c) 180 s and (d) 1 h.


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Scheme 1. Schematic illustration of the formation of CZTS-AuAg heterodimers. To study the electrocatalysis toward ORR, we loaded the CZTS-AuAg heterodimers on carbon black. The representative TEM image and XRD pattern after annealing are shown in Figure S5. Also the XPS spectra after annealing are shown in Figure S6. We can see that nanoparticles are uniformly deposited on C and the crystalline structure and chemical states are preserved in the annealing process. The ORR catalytic activity of the CZTS-AuAg heterodimers is first examined by cyclic voltammetry (CV) measurement in 0.1 M KOH solution, as shown in Figure 4a. The ORR catalytic activity of CZTS-AuAg can be clearly revealed from the comparison of the CV curves in O2- vs. Ar-saturated electrolytes. It shows an ORR onset potential at about 0.87 V vs. RHE and the peak current is arrived at the potential of 0.73 V vs. RHE (The onset potential is determined where 10 % of the current value at the peak current is reached.). Rotating disc electrode (RDE) experiments and Koutecky-Levich (K-L) analysis were used to study the ORR kinetics. Figure 4b shows the linear sweep voltammetry (LSV) curves of the CZTS-AuAg heterodimers modified electrode from 400 rpm to 1600 rpm. And the LSV curves show relatively wide plateaus of currents, indicating a diffusion-controlled process with an efficient four-electron dominant ORR pathway.41 At 1600 rpm, the half-wave potential (E1/2) observed at 2.75 mA cm−2 is 0.73 V vs. RHE. Specifically, the current density reaches 5.32 mA cm-2 at 0.6 V


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vs. RHE, which is superior to the reported B, N-codoped graphene, Au nanoparticle@zinc−iron embedded porous carbons and CoP under the same conditions (Table S1).42-45 Furthermore, these CZTS-AuAg heterodimers are supported on commercial carbon, which has the benefit of being cheaper than the graphene, carbon nanotube, etc. The corresponding K-L plots are shown in Figure 4c, and the linearity of each plot suggests its first-order reaction kinetics. The electron transfer number (n) is calculated to be ~3.9 at 0.1-0.5 V from the slopes of K-L plots, which further confirms it is a four-electron transfer route.46

Figure 4. (a) CV curves of CZTS-AuAg heterodimers modified electrode in Ar- and O2saturated 0.1 M KOH solution. (b) LSV curves of ORR at various rotation rates at a scan rate of


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10 mV s-1 and (c) Koutecky–Levich plots obtained from the data in 4b at various potentials. (d) Comparison of LSV curves in O2-saturated 0.1 M KOH solutions at the rotation rate of 1600 rpm. For comparison, we further carried out the LSV measurements for other electrode materials, including the single component of CZTS and AuAg nanocrystals and the commercial Pt/C catalyst. The TEM image of the AuAg nanocrystals is shown in Figure S7 with the diameter of 5~6 nm, which is similar as that in the CZTS-AuAg heterdimers. Figure S8 exhibit the LSV curves and K-L plots of AuAg and CZTS NCs, respectively. The impressive electrocatalytic activity of CZTS-AuAg heterodimers is confirmed by comparing the LSV curves at a rotation rate of 1600 rpm (Figure 4d). Obviously, the CZTS-AuAg heterodimers show the largest limiting current density (id) and the most positive half-wave potential (E1/2), which suggests that O2 is more easily reduced on CZTS-AuAg heterodimers than on the single component of CZTS or AuAg nanocrystals (details in Table S2). Furthermore, the id of CZTS-AuAg heterodimers is comparable with the commercial Pt/C catalyst, although the E1/2 was still lower than that of the Pt/C catalyst. Additionally, the excellent ORR activity of the CZTS-AuAg heterodimers was also confirmed from the much higher mass activity. For 0.01 mg of NP catalyst, the amount of Au in the CZTS-AuAg is 0.00055 mg (the weight ratio of Au in CZTS-AuAg was 5.5 % by the ICPAES). At 0.8 V vs. RHE, the mass activity for CZTS-AuAg was 148.4 mA/mg of Au, which was about 20 times of that of the AuAg catalyst (6.98 mA/mg of Au, the weight ratio of Au in AuAg was 60 % by the ICP-AES). All of these results indicate the synergistic effect of CZTS and AuAg in the heterodimers. The rotating ring-disk electrode (RRDE) technique was further used to verify the ORR pathway by monitoring the formation of intermediate peroxide species (HO2-).47 As shown in Figure 5a, the CZTS-AuAg heterodimers yield ∼3.1 %−6.2 % HO2- over a wide potential range


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from 0 to 0.7 V vs. RHE, with electron transfer number (n) ranging from 3.88 to 3.94 (Figure 5b). In contrast, as shown in Figure 5c and 5d, CZTS and AuAg NCs yield higher amounts of HO2under the same condition. For example, at 0.5 V vs. RHE, the HO2- yields and n values are 19.2 % (3.6), 7.1 % (3.86) and 3.6 % (3.93) for CZTS, AuAg and CZTS-AuAg, respectively. For the Pt/C, at 0.5 V vs. RHE, the HO2- yields and n value were calculated to be 4.2 % and 3.92, which are similar to those of CZTS-AuAg. All of these results are consistent with the RDE measurements, indicating the excellent electrocatalytic activity of CZTS-AuAg heterodimers.

Figure 5. (a) RRDE voltammograms and (b) the electron transfer number and peroxide yield for the CZTS-AuAg heterodimers electrode, (c) peroxide yield and (d) the corresponding electron transfer number of different samples. To shed light on the effect in CZTS-AuAg heterodimers for the enhanced ORR activity, the electronic structure of Au was studied by XPS measurement. As shown in Figure 6a, the binding


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energy of the Au 3d3/2 and 3d5/2 in CZTS-AuAg heterodimers obviously shifts to more positive value (0.4 eV) compared to that of Au 3d spectra in AuAg NCs. Considering that the reference level (C 1s, Figure S9) is at the same position, the change of binding energy is mostly induced by the electron transfer from AuAg to the CZTS part in CZTS-AuAg heterodimers.48 This electrondonating effect can be explained by the the energy-level of CZTS and AuAg nanoparticles.18 As we know, ORR activity is associated with the O2 adsorption and O-O bond cleavage in the following.4 This electron-donating effect will induce an increase of 5d vacancies in Au atom, thus increasing 2p electron donation from O2 to the Au surface and then resulting in enhanced O2 adsorption.28 This is consistent with the superior catalytic activity of CuS-Pt composites, in which the electron transfer from Pt to CuS reduces the electron density in Pt and accelerates the adsorption of C=C on the surface for the generation of hydrocinnamaldehyde.49


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Figure 6. (a) Au 4f XPS spectra in AuAg and CZTS-AuAg NCs. (b) Comparison of LSV curve in O2-saturated 0.1 M KOH solutions at the rotation rate of 1600 rpm. (c) LSV curves of CZTSAu at various rotation rates at a scan rate of 10 mV s-1, (d) Electron transfer number and peroxide yield for the CZTS-Au heterostructure. Besides the electronic coupling between metal and semiconductor in the heterodimers, the existence of Ag atoms also have great impact on the ORR activity. The molar ratio of Au to Ag was in consistent with the amount of HAuCl4 and AgNO3 introduced in the precursor mixture. Figure 6b shows the LSV curves of CZTS-Au and CZTS-AuAg alloy heterostructure with different Au/Ag molar ratios (details of CZTS-Au shown in Figure 6c and Figure S10). Obviously, along with the addition of Ag with the molar ratio of 1:0.5 and 1:1 in the precursor, a significant enhancement of the ORR catalytic activity is observed, including the higher limiting current density and more positive onset potential compared with monometallic CZTS-Au catalyst, which is mainly ascribed to the alloying effect of Au-Ag. Furthermore, as shown in Figure 6d, a significant drop of HO2− yield is observed on CZTS-AuAg heterodimer (6.2–3.1 %) than on CZTS-Au (17.5–13.0 %). And the corresponding electron transfer number of CZTSAuAg is also larger than that of CZTS-Au, indicating that the addition of Ag can also increase the four-electron selectivity of the catalysts. But further increasing the molar ratios of Au/Ag to 1:2 causes a drop in the ORR activity, probably because of the appropriate electron density with the molar ratio of 1:1.50 On the other hand, the increased number of Ag on the particle surface would decrease adsorption of O2 molecular that preferentially takes place on Au instead of Ag atoms. These results indicate that by controlling the optimal molar ratio of Au to Ag to form the alloy based heterostructure could not only reduce the used amount of high price noble metal but also enhance their electrocatalytic selectivity. All in all, the superior performance of CZTS-


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AuAg heterodimers can be attributed to the following two major factors: (i) the improved conductivity by noble metals to accelerate the charge transfer between electrode; (ii) the electronic coupling between CZTS and noble metals; and (iii) the alloying effect of Au-Ag. The stability and poison tolerance of the catalysts are also important for practical application. The stability of the CZTS-AuAg heterodimers catalyst was assessed by the current–time (i–t) chronoamperometric responses. These measurements revealed the catalytic activity showed no obvious attenuation during a 40000 s test (Figure 7a). The catalyst was then exposed to methanol to test its tolerance. When 1.2 mL of 3 M methanol solution was added, almost no change was observed for CZTS-AuAg heterodimers, but the catalytic activity of Pt/C severely drops in the same condition due to methanol oxidation reaction (Figure 7b). These results reveal that CZTSAuAg heterodimers own better long-term durability and stronger immunity to methanol crossover than Pt/C, which makes them highly promising as a Pt-substituted ORR electrocatalyst for practical application.

Figure 7. (a) The stability and (b) methanol-tolerance evaluation of CZTS-AuAg heterodimers tested by the current–time chronoamperometric responses. (commercial 20% Pt/C is used for comparison). 4. CONCLUSION


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In summary, we have demonstrated a facile strategy for the fabrication of CZTS-AuAg heterostructures using CZTS nanocrystals as seeds. At the beginning of the reaction, multiple AuAg nanoparticles can be formed on the CZTS nanocrystals. After a sufficient reaction time, CZTS-AuAg heterodimers are formed. The interaction between alloyed metal and CZTS results in lower electron population on Au, making it catalytically more active toward ORR than the single component of CZTS or AuAg catalyst and CZTS-Au heterostructure. The CZTS-AuAg heterodimers exhibit high limiting current density, which is superior to other potentially low-cost catalysts. Particularly, compared with the commercial Pt/C, the CZTS-AuAg heterodimers show better methanol tolerance but with much less consumption of precious metal. These results may open up a new route for the rational design of metal-semiconductor hybrid nanostructures as multifunctional electrocatalysts for energy conversion applications. ASSOCIATED CONTENT Supporting Information RDE measurements, XRD and Raman spectra of CZTS, XRD spectrum of CZTS-AuAg, XPS of CZTS-AuAg, TEM image and XRD pattern after supported on carbon, Comparison of the performances between CZTS-AuAg (this work) and other low cost catalysts reported in the literatures, LSV and K-L plots of carbon black, TEM image of AuAg, LSV and K-L plots of AuAg and CZTS. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author [email protected]


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Cu2ZnSnS4âAuAg Heterodimers and Their Enhanced Catalysis for

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