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Article

Self-Assembly of Pt3Co Superlattice as a Catalyst for Oxygen Reduction Reaction

by
Quan Wang
1,
Chang Jiang
1,
Baosen Mi
1 and
Hongbin Wang
1,2,*
1
School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China
2
H2E Technology Zhejiang Co., Ltd., Jinhua 321000, China
*
Author to whom correspondence should be addressed.
Catalysts 2023, 13(2), 406; https://doi.org/10.3390/catal13020406
Submission received: 18 January 2023 / Revised: 7 February 2023 / Accepted: 13 February 2023 / Published: 14 February 2023
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Versions Notes

Abstract

:
Pt-based binary alloy catalysts with different structures have been designed to boost the catalytic activity of oxygen reduction reaction (ORR), however, the dissolution of the transition metals leads to insufficient catalyst durability. In order to solve this problem, a self-assembly Pt3Co superlattice catalyst is reported in this paper, which exhibits enhancement in both activity and durability towards ORR. Compared with commercial Pt catalyst, the mass activity and specific activity of Pt3Co superlattice are significantly improved. The Pt3Co superlattice dropped only 9.2% and 12.4% in the mass activity and specific activity after 5000 cycles of durability tests. Moreover, the mechanistic studies find that the improvement of the catalyst performance is mainly dominated by reducing the energy of oxygen adsorption to a more suitable energy, optimizing the electronic structure of d-band, and suppressing the leaching of Co. This work provides a strategy to prepare superlattice catalyst with great activity and durability toward ORR.

1. Introduction

It is known that the slow kinetics of oxygen reduction reaction (ORR) on the cathode is the key issue in the development of Proton Exchange Membrane Fuel Cells (PEMFC) [1,2]. In order to solve this problem, binary alloy catalysts, especially Pt-based catalysts, have been proposed. It was proved that with the addition of moderate amount of the second element, the 5d vacancies of surface increased and the adsorption of O2 increased, leading to the improvement of ORR performance [3]. To date, many researchers have prepared Pt-based binary catalysts (mainly alloy with Fe, Co, Ni) with various structures, and all of them showed better ORR performance [4,5,6,7,8,9,10]. Moreover, there has also been a lot of recent work to propose solutions for improving ORR performance of cathode catalyst. For example, Zhang et al. successfully synthesized single cobalt atom catalysts embedded in nitrogen-doped carbon, Co–N/C, by adopting a precursor modulation strategy [11]. The XPS, XAS, and WT EXAFS analysis have been used to prove the formation of single Co atoms embedded in carbon matrix. In addition, it displayed superior activity and stability in the ORR process. Furthermore, density functional theory calculation indicated that the down-shift d-band center of Co-N4 significantly promotes catalytic kinetics and thermodynamics for ORR. It is known that the microstructure of catalyst directly affects the performance of catalyst. According to recent research, many novel methods have been proposed to synthesis catalysts for the ORR process. Xu et al. reviewed a variety of methods for synthesizing catalysts with different nanostructures [12]. Methods include the sol–gel process, precipitation methods, hydrothermal synthesis, physical vapor deposition, chemical vapor deposition, electrodeposition, template-assisted synthesis, electrospinning method, infiltration method, exsolution method, and other synthetic methods. All these methods can prepare catalysts with specific structures and improve the performance of ORR. Recent studies showed that there were many ways to improve the performance of Pt-based binary catalyst ORR, however, the second element of these Pt-based binary catalysts may dissolve in an acidic environment and induce Ostwald ripening of Pt, resulting in lower stability [13].
In addition, increasing the surface areas and active sites of the catalyst is also a way to improve the ORR performance of catalysts. The particle size and distribution of catalysts affect the surface areas and active sites [14]. Therefore, many methods, such as chemical vapor deposition, colloidal technique, impregnation, and buffer-layer assisted growth, have been devoted to enhancing the catalytic performance by controlling the size and distribution of catalysts [15]. However, the homogeneous distribution of particle size was difficult to control, which will lead to the degradation of the ORR performance [16].
The superlattice structure is a macroscopic structure composed of ordered and close-packed nanoparticles which have high surface areas and active sites [17,18]. The structure has demonstrated a better catalytic performance than isolated/disordered nanoparticles due to superior electron transport properties [19]. Additionally, the superlattice can also be resistant to agglomeration, and Ostwald ripening possesses a higher stability [20,21]. It seems that this structure qualified all the requirements for excellent catalytic activity. Therefore, it has the potential to be utilized to improve the ORR performance of catalysts.
It was reported that the superlattice structure can be achieved by nanoparticle self-assembly technique under near or complete thermodynamic equilibrium [22,23]. Nanoparticles assembled into stable superlattices due to the interparticle interactions, such as van der Waals and dipole–dipole interactions [24,25]. In general, the technique depends on surface effects such as air–liquid surface [26]. Accordingly, the commonly used methods for synthesizing superlattice structure include solvent evaporation, template-directed growth, and anti-solvent destabilization [27].
Impressively, it was found that the superlattice has been successfully used in some catalytic processes. For example, Wang et al. prepared bimetallic PtAu superlattice arrays via hydrogen bonding-induced self-assembly, which enhanced the catalytic activities for methanol oxidation reaction and oxygen reduction reaction as compared to Pt/C in alkaline fuel cells [20]. Zheng et al. synthesized an ordered CoMnO@CN superlattice structure catalyst as an excellent hydrogen evolution reaction and oxygen evolution reaction catalysts for water splitting. It also proved that the ordered superlattice structure increased the catalytic sites and prevented nanoparticles from aggregation or dissolution [28]. In addition, there were many studies devoted to enhancing the catalytic performance of superlattice structures [19,29,30,31,32]. However, the superlattice structures with such advantages were rarely used in ORR catalytic processes for PEMFC.
Herein, a self-assembly superlattice catalyst was synthesized via the solvent evaporation as a catalyst for ORR. The Pt3Co was used as the catalytic nanoparticles, which has been proved to be a mature method for preparing nanoparticles with uniform size and homogeneous composition [33,34]. The ORR activity and durability were determined by electrochemical experiments. In addition, the characterization was evaluated by XRD, TEM, and XPS. Combining the density functional theory (DFT) calculations with the experimental results, the improvement of ORR performance is further explained.

2. Results

2.1. Structure and Charaterization of Pt3Co Superlattice

The morphology of the as-prepared superlattice catalyst is shown in Figure 1a via transmission electron microscopy (TEM). It shows that the Pt3Co nanoparticles are self-assembled by solvent evaporation, which is different from Pt3Co nanoparticles (Figure S1, Supplementary Materials). As is shown, the superlattice catalyst is composed of highly ordered Pt3Co nanoparticles with diameters of 4.0–6.5 nm, and the average size is about 5.2 nm. The HRTEM image of a single nanoparticle is shown in Figure 1b. It displays clear lattice fringes with interplanar spacing distances of 0.23 nm, which corresponds to the (111) facet of Pt3Co superlattice catalyst. It was also proved by the fast Fourier transform (FFT) pattern. The energy dispersive spectrometer (EDS) line scan profiles (Figure 1c) show that the Pt and Co are uniformly distributed with an atom ratio of 3:1. The Pt ratio of Pt3Co superlattice catalyst is found to be 90.6 wt% determined by ICP-OES. The EDS mapping (Figure S7, Supplementary Materials) shows that the Pt and Co element is uniform in each nanoparticle. The X-ray diffraction (XRD) pattern is shown in Figure 1d. The catalyst exhibited four characteristic diffraction peaks at 40.5, 47.1, 68.6, and 83.2 degree, corresponding to the (111), (200), (220), and (311) planes. It corresponds to a face-centered cubic (fcc) Pt3Co crystal. In addition, all peaks shift to higher 2θ angles, indicating that the incorporation of Co in the fcc structure of Pt results in the contraction of the lattice. It can be calculated that the distance of Pt-Pt in the Pt3Co superlattice is 2.72 Å, which suggests that the distance of Pt-Pt is decreased. The short Pt-Pt distance profits the reduction of oxygen [35]. In addition, the particle size calculated by Scherer formula agrees with that obtained by HRTEM in Figure 1c. To evaluate the surface electron structure and the composition of the product, the X-ray photoelectron spectroscopy (XPS) analysis was adopted. Figure 1e shows the Pt 4f and Co 2p spectra of Pt3Co superlattice. The Pt 4f spectra shows that double peaks at the binding energy of 70.9 and 74.23 eV are assigned to Pt0, and double shoulder peaks at the binding energy of 71.6 and 75.02 eV are assigned to Pt2+. For Co 2p spectra, the peaks at 781.9 eV, 779.5 eV, and a weak shoulder at 777.9 eV are associated with Co3+, Co2+, and Co0, respectively. The results indicate that the Pt is mainly in the metallic state and the Co is mainly in the oxidized state. The result is consistent with the literature [36]. Additionally, the percentage of Pt0 is 59.5% by calculating the corresponding peak, and a high ratio of Pt0 indicates that there are more active sites, which improves the catalytic performance. Moreover, the Pt0 peak of Pt3Co superlattice is 0.8 eV negatively shifted compared to the Pt 4f spectra of Pt/C (Figure S2, Supplementary Materials), which indicates that the electron density of Pt atom on the surface is increased and the binding energy of oxygen adsorption is reduced [37]. As a result, it down-shifted the d-band center and promoted the oxygen reduction reaction, improving the catalytic activity.

2.2. Electrochemical Characterization Analysis

To evaluate the catalytic performance of the Pt3Co superlattice, the cyclic voltammetry (CV), liner sweep voltammetry (LSV), and accelerated durability tests (ADT) were adopted. In addition, the Pt3Co nanoparticles and the Pt/C catalyst are taken for comparison under the identical electrochemical test conditions. Figure 2a shows the cyclic voltammograms of Pt3Co superlattice and the comparison catalysts in 0.1 M HClO4 at a scan rate of 20 mV s−1. The electrochemically active surface area (ECSA) of catalysts are obtained according to total charges (Qh, μC) collected in the hydrogen adsorption region from 0.05 V to 0.4 V versus reversible hydrogen electrode (RHE), and 210 μC cm−2 is the charge required for monolayer adsorption of hydrogen on Pt surface [38]. The ECSAs are calculated to be 25.6, 17.4, and 58.8 m2 g−1 for Pt3Co superlattice, Pt3Co nanoparticles, and Pt/C catalysts, respectively. The results show that the ECSA of Pt/C catalyst is highest compared with that of contrast catalysts. It mainly ascribed to the size effect, which has been reported to affects ECSA [39]. Figure 2b shows the linear sweep voltammograms of Pt3Co superlattice and comparison catalysts in O2-saturated 0.1M HClO4 at the sweep rate of 10 mV s−1 under 1600 rpm. In order to evaluate the ORR activity of catalysts, the kinetic current (Ik) at 0.9 V versus RHE is normalized to both the Pt loading and ECSA to obtain mass activity (MA) and specific activity (SA). The results indicate that the superlattice has the highest ORR activity among these catalysts. It exhibits that the SA and MA are 2.10 mA cm−2 and 0.54 A mg−1, respectively. Moreover, the Pt/C catalyst exhibits the lowest half-wave potential among the three catalysts, while the Pt3Co superlattice catalyst shows the highest half-wave potential with a value of 0.934 V vs. RHE. It shows the same activity law, which was obtained from LSV curves. It is obvious that the ORR activities are sharply increased compared to that of the Pt/C catalyst shown in Figure 3c, and all data of the LSV experiment are in Table S1 in the Supplementary Materials. Impressively, the ORR activity of Pt3Co superlattice is better than the Pt3Co nanoparticles with a similar particle size. The reason is that, unlike isolated nanoparticles, interactions of nanoparticles contribute to improve catalytic performance [40]. The Tafel slope is calculated to further understand the kinetic characteristics of the Pt3Co superlattice catalyst. The Tafel plot of Pt/C commercial catalyst, Pt3Co nanoparticles, and Pt3Co superlattice catalyst are shown in Figure S6 (Supplementary Materials). The Tafel slope of Pt/C, Pt3Co nanoparticles, and Pt3Co superlattice catalyst are 72.56, 61.43, and 58.96 mV dec−1, respectively. The Pt3Co superlattice catalyst has the lowest Tafel slope. It is known that the Tafel slope can be reduced due to the acceleration of ORR kinetics [41]. Therefore, combined with the results of the previous LSV experiment, it is further proved that Pt3Co superlattice catalyst has better ORR activity. The performance was also compared with some research, and the details are shown in Table S2 (Supplementary Materials).
To evaluate the durability of Pt3Co superlattice catalyst, ADT is adopted by cyclic potential sweeps between 0.6 V and 1.1 V versus RHE in 0.1 M HClO4 at sweep rate 100 mV s−1 for 5000 cycles at room temperature according to previous work [42]. Figure 2d shows the LSV curves of the Pt3Co superlattice catalyst before and after 5000 cycles ADT. The results show that compared with the initial MA and SA values of the Pt3Co superlattice structure catalyst, the MA and SA values only decrease by 9.2% and 12.4%, respectively. In comparison, the Pt/C suffers considerable losses in the ORR activities under similar conditions (Figure S3, Supplementary Materials). The results demonstrate that the Pt3Co superlattice catalyst has the best durability toward ORR among the comparison catalysts. In addition, to reveal the reason for the enhanced durability of Pt3Co superlattice, the catalysts after ADT are collected and observed by TEM (Figure S4, Supplementary Materials). It is obvious that both Pt3Co nanoparticles and Pt/C particle size grew after 5000 cycles ADT, and agglomeration occurred due to the aggregation and Ostwald ripening of the catalyst particles [43]. On the contrary, although the ordered structure of Pt3Co superlattice nanoparticles disappeared, the size of the individual particles had little change. It indicates that the as-prepared catalyst is more stable during the ORR.

2.3. DFT Calculation of Pt3Co Superlattice Catalyst

It is known that the electronic structures and the d-band center of the catalysts govern the catalytic properties. Accordingly, to understand the enhancement of the ORR activity of Pt3Co superlattice arrays, the density functional theory (DFT) calculations were carried out to disclose the oxygen adsorption energy and the d-band center of the (111) surface of the catalysts. The oxygen atom tends to adsorb in the hollow sites of the catalyst surface [44]. Thus, possible adsorption sites are represented by green dots, as shown in Figure 3a,b, and the adsorption energy of the oxygen (Eo) on the (111) surface is calculated to describe the ORR activity (Pt (111) and Pt3Co (111) model slabs are shown in Figure S5, Supplementary Materials). According to the calculation results, the Eo of site 1 in Pt (111) surface is −4.48 eV and the Eo of site 1 to site 4 in Pt3Co (111) surface are −4.00, −3.47, −4.20, and −3.46 eV, respectively. In addition, the Eo on Pt3Co (111) in all sites shows weaker value than that on Pt (111). It has reported that the Eo, which is 0.0–0.4 eV weaker than Pt (111), exhibits a better ORR activity [45]. The results indicate that the oxygen adsorbed on the Pt3Co (111) has a weaker binding energy, which promotes the ORR. Comparing the Eo of these adsorption sites, the adsorption of O at site 3 has the lowest Eo value, suggesting that the O prefers to be adsorbed at the site. It can conclude that the incorporation of Co helps to enhance the ORR activity. When the alloy is formed, the d-band center will be changed according to the stretching or compression of the atomic spacing. Consequently, the projected d-density of states (PDOS) of surface Pt atoms are adopted to estimate the d-band center. The results are shown in Figure 3c. It shows that the Pt3Co slab presented the lower d-band center toward the Pt slab. According to the d-band center theory, the lower d-band center exhibits the weaker binding strength of oxygenated species, which promoted the ORR activity considering the too-strong binding on pure Pt [45,46,47]. The results also agree with the ORR activity observed by LSV experiments. In addition, the vacancy formation energies of Pt are calculated to explain the durability of Pt3Co superlattice arrays. As shown in Figure 3d, the Pt3Co (111) slab exhibits an obvious increase in vacancy formation energy compared with the Pt (111) slab. The Pt vacancy formation energy represents the dissolute tendency of Pt atoms, and it has been proved that the catalysts slab with higher vacancy formation energy show higher structure stability [48]. In addition, the leaching of Co was inhibited, and the composition of catalyst was stabilized. Therefore, such an increase in vacancy formation energy of Pt3Co superlattice improves the stability of the structure, which has the same tendency as the ADT experiments.

3. Materials and Methods

3.1. Chemicals and Materials

The chemical reagents used in the synthesis were of analytical grade and used without further purification.
For the self-assembled superlattice catalyst preparation process: Pt(acac)2 (Macklin, Shanghai, China), Co2(CO)8, oleylamine, benzyl ether, 1,2-tetradecanediol, 1-adamantanecarboxylic acid, dichlorobenzene, iso-propanol, ethanol, hexane, and squalene (All the chemical reagent above except Pt(acac)2 are purchase from Rhawn, Shanghai, China).
For the electrochemical evaluation: perchloric acid (HClO4) (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), 5% Nafion solution (Wilmington, DE, USA). In addition, 20% Pt/C was used as a commercial catalyst for the comparison in this paper (Jiping New Energy Technology Co., Ltd., Shanghai, China). The water used in this paper is deionized water with an electrical resistivity greater than 18 MΩ·cm.

3.2. Synthesis of Pt3Co Superlattice Catalyst

The synthesis of the Pt3Co superlattice arrays was carried out by solvent evaporation method. 62.9 mg Pt(acac)2 (0.16 mmol) was dissolved in 10 mL oleylamine and 5 mL benzyl ether, and then 230.39 mg 1,2-tetradecanediol (1 mmol) and 504.68 mg 1-adamantanecarboxylic acid (2.8 mmol) were added. The solution was heated to 473 K under N2 flow. After that, 85.5 mg Co2(CO)8 (0.25 mmol) and 1 mL dichlorobenzene was added into the as-prepared solution. Then, the temperature was raised to 533 K and kept for 30 min by refluxing with constant stirring. The solution was cooled to room temperature after the reaction. The iso-propanol and the ethanol (volume ratio was 2:1) were added to precipitate the nanoparticles and then collected by centrifugation. The precipitates were dispersed in 10 mL hexane to form a stable colloidal solution. The solution was mixed with squalene (1 wt%) and then deposited on a conductive substrate, allowing the solvent to evaporate slowly to obtain the superlattice arrays.

3.3. Electrochemical Characterization

The electrochemical characterization was carried out by an electrochemical workstation (Reference 600, Gamry Instrments, Warminster, PA, USA) to evaluate the ORR activities. A typical three-electrode cell was used. A carbon stick was a counter electrode, a saturated calomel electrode was a reference electrode, and a glassy carbon electrode with the area of 0.196 cm2 was the working electrode, respectively. The catalyst ink was dropped onto the surface of glassy carbon electrodes and dried at room temperature. The catalyst ink was prepared as follows. Pt3Co superlattice was dispersed in 0.8 mL H2O, 0.2 mL iso-propanol, and 10 μL Nafion solution (5 wt%), then the homogeneous dispersion was obtained by ultrasound for 1 h. Before measurements, 50 cycles of activation were performed at a sweep rate of 100 mV s−1 in N2-saturated HClO4 electrolyte solution. CV measurement was performed in 0.1 M N2-saturated HClO4 solution at a sweep rate of 20 mV s−1 and the ORR measurement was performed in O2-saturated electrolyte solution at a sweep rate of 10 mV s−1 under a rotation speed of 1600 rpm. Then, the mass activity and specific activity were calculated by kinetic current at 0.9 V versus RHE. Since the reference electrode selected in this paper is SCE, it is necessary to convert the voltage during the experiment into the voltage of versus RHE. The calculation method of voltage conversion is shown in Formula (1).
E vs .   RHE = E vs .   SCE + 0.241 + 0.059 pH
In this paper, the electrolyte solution is 0.1 M HClO4, therefore the pH is 1.
The accelerated durability test (ADT) was performed by cyclic potential sweeps between 0.6 V and 1.1 V vs. RHE at a sweep rate of 100 mV/s for 5000 cycles in 0.1 M HClO4 electrolyte solution at room temperature. The same three-electrode system was used, except a carbon stick was utilized as the counter electrodes. It can prevent the Pt counter electrode from dissolving and depositing on the working electrode in acidic electrolyte solution, which will affect the experimental results. Then, the ECSA and ORR activities were obtained and compared with the performance of 20% Pt/C catalyst and Pt3Co nanoparticles after the durability test.

3.4. Catalyst Characterization

The morphology and the structure of the superlattice arrays were obtained by transmission electron microscopy (TEM, JEM-2100F, JEOL Co., Akishima, Japan) and high-resolution transmission electron microscope (HRTEM, JEM-2100F, JEOL Co., Akishima, Japan) with an accelerating voltage of 100 kV. The XRD pattern was obtained by D/MAX2200V (Riken Electric Co., Ltd., Tokyo, Japan) with Cu Kα radiation at 40 KV. The catalyst surface characterization was investigated by X-ray photoelectron spectroscopy (XPS, Escalab 250Xi, Thermo Fisher Scientific, Waltham, MA, USA). The composition of catalyst was obtained by ICP-OES (PerkinElmer 8300, PerkinElmer, Waltham, MA, USA).

4. Conclusions

A Pt3Co superlattice structure catalyst was successfully synthesized by a self-assembly method, which highly improved the ORR performance. The as-prepared catalyst showed that the mass activity and specific activity were higher than those of commercial Pt/C catalysts, respectively. Moreover, the catalyst also showed good stability during the ADT process. The mass activity and specific activity were only decreased by 9.2% and 12.4% after 5000 cycles ADT. The DFT and experimental results showed that the improvement of the catalyst performance is mainly due to the reduction of the energy of oxygen adsorption to a more suitable energy, the optimization of d-band electronic structure, and suppressing the leaching of Co. This work provides a design strategy for preparing high-performance catalysts for ORR.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal13020406/s1, Figure S1: TEM image of Pt3Co nanoparticles and Pt/C catalyst; Figure S2: Pt 4f XPS spectra pattern of Pt/C and the comparison of Pt3Co and Pt/C; Figure S3: CV and LSV curves of Pt3Co nanoparticles and Pt/C before and after 5000 cycles ADT; Figure S4: TEM image of Pt/C, Pt3Co nanoparticles and Pt3Co superlattice before and after ADT; Figure S5: theoretical model of Pt (111) and Pt3Co (111); Figure S6: Tafel plot of Pt/C, Pt3Co nanoparticles, and Pt3Co superlattice catalyst; Figure S7: EDS mapping of Pt3Co superlattice catalyst; Table S1: detail electrochemical data of all the catalyst in this paper; Table S2: Performance of catalyst in this work and several representative results with high performance from recent published work [4,6,49,50,51,52,53,54,55,56,57,58].

Author Contributions

Conceptualization, Q.W. and H.W.; methodology, Q.W.; validation, Q.W. and H.W.; formal analysis, Q.W. and C.J.; investigation, Q.W., C.J. and B.M.; resources, H.W.; writing—original draft preparation, Q.W.; writing—review and editing, Q.W.; supervision, H.W.; project administration, H.W.; funding acquisition, H.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data generated or analyzed during the study are included in the article.

Acknowledgments

This research was supported by Shanghai Engineering Research Center of Metal Parts Green Remanufacture (No. 19DZ2252900) from Shanghai Engineering Research Center Construction Project.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (a) TEM image of Pt3Co superlattice structure. (b) HRTEM image of a single Pt3Co particle, and the corresponding FFT patterns are also shown. (c) EDS line scan profile of a single nanoparticle. (d) XRD pattern of Pt3Co superlattice, Pt3Co nanoparticles, and Pt/C. (e) Pt 4f and Co 2p spectra pattern of Pt3Co superlattice.
Figure 1. (a) TEM image of Pt3Co superlattice structure. (b) HRTEM image of a single Pt3Co particle, and the corresponding FFT patterns are also shown. (c) EDS line scan profile of a single nanoparticle. (d) XRD pattern of Pt3Co superlattice, Pt3Co nanoparticles, and Pt/C. (e) Pt 4f and Co 2p spectra pattern of Pt3Co superlattice.
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Figure 2. (a) Cyclic voltammograms of Pt3Co superlattice arrays, Pt3Co nanoparticles, and Pt/C. (b) Liner sweep voltammograms of Pt3Co superlattice arrays, Pt3Co nanoparticles, and Pt/C. (c) MA and SA of all the catalysts at 0.9 V versus RHE. (d) CV and LSV curves of Pt3Co superlattice arrays before and after 5000 cycles ADT.
Figure 2. (a) Cyclic voltammograms of Pt3Co superlattice arrays, Pt3Co nanoparticles, and Pt/C. (b) Liner sweep voltammograms of Pt3Co superlattice arrays, Pt3Co nanoparticles, and Pt/C. (c) MA and SA of all the catalysts at 0.9 V versus RHE. (d) CV and LSV curves of Pt3Co superlattice arrays before and after 5000 cycles ADT.
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Figure 3. (a) DFT models and the adsorption sites of Pt (111). (b) Pt3Co (111) superlattice arrays. The smaller atom means the atom in the second layer of the catalyst, and the possible adsorption site of O atom is represented by the green dot. (c) The projected d-density of states (PDOS) of surface Pt atoms for Pt (111) and Pt3Co (111). (d) Pt vacancy formation energies for Pt (111) and Pt3Co (111) slabs.
Figure 3. (a) DFT models and the adsorption sites of Pt (111). (b) Pt3Co (111) superlattice arrays. The smaller atom means the atom in the second layer of the catalyst, and the possible adsorption site of O atom is represented by the green dot. (c) The projected d-density of states (PDOS) of surface Pt atoms for Pt (111) and Pt3Co (111). (d) Pt vacancy formation energies for Pt (111) and Pt3Co (111) slabs.
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Wang, Q.; Jiang, C.; Mi, B.; Wang, H. Self-Assembly of Pt3Co Superlattice as a Catalyst for Oxygen Reduction Reaction. Catalysts 2023, 13, 406. https://doi.org/10.3390/catal13020406

AMA Style

Wang Q, Jiang C, Mi B, Wang H. Self-Assembly of Pt3Co Superlattice as a Catalyst for Oxygen Reduction Reaction. Catalysts. 2023; 13(2):406. https://doi.org/10.3390/catal13020406

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Wang, Quan, Chang Jiang, Baosen Mi, and Hongbin Wang. 2023. "Self-Assembly of Pt3Co Superlattice as a Catalyst for Oxygen Reduction Reaction" Catalysts 13, no. 2: 406. https://doi.org/10.3390/catal13020406

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