Next Article in Journal
Electrogeneration and Characterization of Poly(methylene blue) Thin Films on Stainless Steel 316 Electrodes—Effect of pH
Next Article in Special Issue
NiS2/NiS/Mn2O3 Nanofibers with Enhanced Oxygen Evolution Reaction Activity
Previous Article in Journal
Constituents from Dolichos lablab L. Flowers and Their Anti-Inflammatory Effects via Inhibition of IL-1β Release
Previous Article in Special Issue
Heteronuclear Dual Metal Atom Electrocatalysts for Water-Splitting Reactions
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Molecules
Volume 29
Issue 16
10.3390/molecules29163753
molecules-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Aqueous Synthesis of Au10Pt1 Nanorods Decorated with MnO2 Nanosheets for the Enhanced Electrocatalytic Oxidation of Methanol

by
Ting Li
1,*,
Yidan Liu
2,
Yibin Huang
1,
Zhong Yu
1 and
Lei Huang
3,*
1
Jiangxi Province Key Laboratory of Applied Optical Technology (2024SSY03051), School of Physical Science and Intelligent Education, Shangrao Normal University, Shangrao 334001, China
2
International Institute of Silk, College of Textile Science and Engineering, Zhejiang Sci-Tech University, Hangzhou 310018, China
3
Research Center of Nano Science and Technology, College of Sciences, Shanghai University, Shanghai 200444, China
*
Authors to whom correspondence should be addressed.
Molecules 2024, 29(16), 3753; https://doi.org/10.3390/molecules29163753
Submission received: 26 June 2024 / Revised: 29 July 2024 / Accepted: 2 August 2024 / Published: 7 August 2024
(This article belongs to the Special Issue Synthesis and Applications of Novel Low-Dimensional Nanomaterials in Catalysis)
Browse Figures
Versions Notes

Abstract

:
Developing novel catalysts with high activity and high stability for the methanol oxidation reaction (MOR) is of great importance for the ever-broader applications of methanol fuel cells. Herein, we present a facile technique for synthesizing Au10Pt1@MnO2 catalysts using a wet chemical method and investigate their catalytic performance for the MOR. Notably, the Au10Pt1@MnO2-M composite demonstrated a significantly high peak mass activity of 15.52 A mg(Pt)−1, which is 35.3, 57.5, and 21.9 times greater than those of the Pt/C (0.44 A mg(Pt)−1), Pd/C (0.27 A mg(Pt)−1), and Au10Pt1 (0.71 A mg(Pt)−1) catalysts, respectively. Comparative analysis with commercial Pt/C and Pd/C catalysts, as well as Au10Pt1 HSNRs, revealed that the Au10Pt1@MnO2-M composite exhibited the lowest initial potential, the highest peak current density, and superior CO anti-poisoning capability. The results demonstrate that the introduction of MnO2 nanosheets, with excellent oxidation capability, not only significantly increases the reactive sites, but also promotes the reaction kinetics of the catalyst. Furthermore, the high surface area of the MnO2 nanosheets facilitates charge transfer and induces modifications in the electronic structure of the composite. This research provides a straightforward and effective strategy for the design of efficient electrocatalytic nanostructures for MOR applications.

1. Introduction

The exceptional performance exhibited by the precious metal Pt in direct methanol fuel cells has established it as a preferred choice among researchers [1,2,3,4]. However, its extensive application is hindered by inherent limitations, including the scarcity of Pt, sluggish reaction kinetics, and its susceptibility to CO poisoning [5,6,7,8]. To address these limitations, the integration of Pt-based nanostructures with suitable carriers has emerged as a cost-effective and efficient strategy [9,10,11,12,13,14]. Manganese-based materials, recognized for their oxidation capabilities and economic viability, are often employed as catalytic oxidation agents [15,16,17,18]. Furthermore, the amalgamation of two-dimensional materials with precious metals holds significant importance in catalysis [19,20]. Notably, MnO2 nanosheets are frequently paired with select precious metals to fabricate composite catalysts owing to their affordability, extensive specific surface area, and abundant binding sites [21,22,23,24]. The strong binding affinity and numerous electron transfer pathways exhibited by MnO2 nanosheets towards the loaded material enable the maximization of their compositional and electronic structural effects [25,26,27].
In recent years, researchers have noted that the strong interaction between active noble metal elements and MnO2 nanosheets exerts a significant promotional effect on catalytic performance [28,29,30]. Li et al. incorporated Au nanoparticles (NPs), synthesized via a hydrothermal method, into metal organic frameworks (Au@MOFs) and immobilized them onto ultra-thin MnO2 nanosheets to fabricate MnO2UNs/Au@Pd^Pt nanocube composite nanostructures, featuring ultra-thin MnO2 nanosheets with a high surface area [24]. These nanosheets serve to enhance the dispersibility of Au@Pd^Pt nanocube, elevate atomic utilization efficiency, and provide a greater number of catalytically active sites. Additionally, Zhang et al. developed Pt NPs@MnO2 by cultivating MnO2 nanosheets on the surface of Pt nanoparticles that were pre-reduced with citric acid using KMnO4 and ethane sulfonic acid in aqueous solution medium, with the surface of the Pt nanoparticles being enveloped by citrate ions [31]. The utilization of citric acid ions as both a template to facilitate the attachment of MnO2 nanosheets and a reducing agent to promote their formation underscores the multifunctional role of citric acid in the synthesis process.
The challenges associated with the existing composite structures and synthesis methods of MnO2 nanosheets and metals include the need for numerous synthesis steps, lengthy processing times, non-mild reaction conditions, and unfriendly reactant environments [32,33,34]. Furthermore, the limited research regarding the composites of one-dimensional noble metal nanostructures and two-dimensional MnO2 nanosheets highlights the importance of developing a simpler and milder pathway for preparing composites of precious metals and two-dimensional MnO2 nanosheets. By addressing these challenges and emphasizing the optimization of the synthesis process, researchers can pave the way for the development of novel composite nanostructures with improved properties and applicability in various catalytic applications.
Motivated by the above considerations, in this work, we developed a facile wet chemical technique to prepare Au10Pt1@MnO2, based on the structure of the Au10Pt1 heterostructure nanorods (HSNRs) prepared in our work [35]. By leveraging the excess reducing agent Na3C6H5O7 present in the Au10Pt1 HSNRs sol, the addition of KMnO4 solution triggers a redox reaction at 60 °C in an incubator, leading to the formation of the Au10Pt1@MnO2 composite catalyst. When compared with commercial Pt/C catalysts, commercial Pd/C catalysts, and Au10Pt1 HSNRs, the Au10Pt1@MnO2-M sample exhibits the lowest initial potential and the highest peak current density in the catalytic methanol oxidation reaction (MOR). This superior performance can be attributed to the unique electronic structure and oxidation capacity of manganese dioxide present in the composite catalyst, highlighting its potential for catalytic applications.

2. Results and Discussion

2.1. Characterization of Pt/Au@MnO2 Nanostructures

The MnO2 nanosheets were synthesized via a wet chemical method, as illustrated in Figure S1. At 45 °C, a specific amount of KMnO4 and Na3C6H5O7 solutions were mixed and reacted for 2 h, resulting in the formation of MnO2 nanosheets. The UV–VIS absorption spectrum of KMnO4, depicted in Figure S2a, exhibits an absorption peak in the range of 500–600 nm, which is characteristic of the KMnO4 solution. Upon the reduction of KMnO4 to produce MnO2 nanosheets, the absorption peak observed in the 500–600 nm range dissipates. Instead, a new prominent absorption peak (Figure S2b) emerges within the 300–400 nm range, indicative of the presence of the MnO2 nanosheet. The TEM in Figure S2c reveal the lamellar structure of the MnO2 nanosheets.
A wet chemical approach strategy based on the localized surface plasmon resonance (LSPR) effect was used to synthesize Au10Pt1 HSNRs [35]. The synthesis methodology encompasses two distinct stages: light nucleation and dark heat reaction. Upon photoexcitation, the LSPR effect of Au NPs facilitates the initial reduction of Pt nucleation on the Au NPs (Figure 1b). Subsequently, the reduction of the Pt precursor occurs in a dark environment at 45 °C, promoting the gradual connection of Au NPs and ultimately leading to the formation of Au10Pt1 HSNRs, as depicted in Figure 1c. Next, the reduction of KMnO4 was employed to synthesize the Au10Pt1@MnO2 composites, as shown in Figure 1d. The morphological evolution from Au NPs to Au10Pt1 HSNRs and ultimately, to the Au10Pt1@MnO2-M composite material (the amount of KMnO4 added in the preparation process is designated as Au10Pt1@MnO2-L, Au10Pt1@MnO2-M, and Au10Pt1@MnO2-H, respectively, as described in the Section 3.4), is illustrated in Figure 1b–d, demonstrating the successful combination of Au10Pt1 HSNRs with MnO2. Throughout this synthesis process, the UV–VIS absorption spectrum of the sample undergoes changes, as shown in Figure 1a. With the formation of the Au10Pt1@MnO2-M composite material, a strong absorption peak in the range of 600–1300 nm is observed, along with a distinct absorption peak representing MnO2 between 300–400 nm. This indicates the reduction of KMnO4 to generate MnO2 nanosheets. TEM images in Figure 1d reveal that the morphology and structure of MnO2 are largely consistent with those shown in Figure S2c. Locally magnified HRTEM images (Figure 1e) demonstrate that the Au10Pt1 HSNRs retain their original appearance, with a lattice spacing of 0.221 nm in HRTEM confirming the formation of MnO2 nanosheets (Figure 1f). Furthermore, at this stage, the two-dimensional structure of the MnO2 nanosheet is predominantly integrated on the surface of the Au10Pt1 HSNRs, as evidenced by the HRTEM image in Figure 1f. The diffraction ring in the selected electron diffraction pattern in Figure 1g further confirms the presence of Au10Pt1 HSNRs and MnO2 in the composite material.
The STEM images in Figure S3a demonstrate a mosaic combination of Au10Pt1 HSNRs and MnO2 nanosheets. The element mapping in Figure S3b–e clearly indicates the presence of Au, Pt, Mn, and O elements in the Au10Pt1@MnO2-M composite. The similar distribution of Mn and O elements indicates the formation of a compound (MnO2) that is evenly distributed on the surface of Au10Pt1 HSNRs, resulting in the creation of the Au10Pt1@MnO2-M composite material. The EDS analysis in Figure S3f confirms the presence of elements such as Au, Pt, Mn, and O in the Au10Pt1@MnO2-M composites.
XPS analysis was conducted on the Au10Pt1@MnO2-M composite material to investigate the chemical valence states of each element, as shown in Figure 2. The XPS spectra revealed characteristic peaks of Au, Pt, and Mn elements in the samples. There are peaks of O 1s, C 1s, and Na Auger in the XPS pattern (Figure 2a), in which Na may be derived from the residual ions after the reaction of sodium citrate and then adsorbed on the MnO2 nanosheets. Peaks at binding energies of 83.8 eV and 87.45 eV, corresponding to Au0 4f7/2 and Au0 4f5/2, respectively [36], indicate the presence of Au in a zero valence state. Similarly, peaks at 72.05 eV and 75.45 eV are attributed to Pt0 4f7/2 and Pt0 4f5/2, while peaks at 73.45 eV and 76.8 eV correspond to Pt2+ 4f7/2 and Pt2+ 4f5/2, respectively [37]. In the previous work [35], the Pt element in the structure of Au10Pt1 HSNRs is mainly in a zero-valence state, while in the Au10Pt1@MnO2-M composite, the larger peak area of Pt2+ (73.9%, as shown in Table S1) suggests that Pt2+ is the predominant form, likely due to the oxidation by KMnO4 during the preparation of the material. For Mn 2p, three valence states were observed: Mn2+ 2p3/2 and Mn2+ 2p1/2 at 640.8 eV and 652.05 eV, Mn3+ 2p3/2 and Mn3+ 2p1/2 at 641.8 eV and 653.05 eV, and Mn4+ 2p3/2 and Mn4+ 2p1/2 at 642.8 eV and 654.05 eV [36]. The largest peak area corresponding to Mn4+ (37.6%, as Table S1 shown) suggests that the Mn elements primarily exist in the form of MnO2, with a portion of the KMnO4 precursors being reduced to the lower valence states of Mn3+ and Mn2+ [38]. The presence of the lower oxidation Mn states (Mn3+ and Mn2+), as described by Wei et al., may result in the creation of cationic vacancies, which can serve as anchor points for nanoparticles [39].
The TEM image analysis in Figure 3a illustrates the impact of KMnO4 additions on the formation of MnO2 nanosheets. When the addition of KMnO4 is reduced, only a small quantity of MnO2 nanosheets are observed. In this scenario, the surface of Au10Pt1 HSNRs interacts with the positively charged cations (e.g., potassium ions) and negatively charged anions (e.g., citrate ions) through electrostatic attraction. This interaction facilitates the formation of connections, resulting in the development of partially longer chain-like structures. Upon increasing the addition of KMnO4, a more significant reaction occurs with Na3C6H5O7, resulting in the generation of MnO2 nanosheets that cover the surface of the Au10Pt1 HSNRs, forming an Au10Pt1@MnO2 composite structure, as depicted in Figure 3b. With an increased addition of KMnO4, a substantial quantity of MnO2 nanosheets is generated, which subsequently nearly envelop the Au10Pt1 HSNRs, as depicted in Figure 3c. This extensive wrapping of MnO2 nanosheets around the Au10Pt1 HSNRs could potentially result in the complete coverage of the active sites of noble metals. Such complete coverage is not favorable for catalytic reactions, as it may hinder the accessibility of reactants to the active sites, thereby impacting the catalytic efficiency of the Au10Pt1@MnO2 composite structure.
XPS analysis was conducted on the Au10Pt1@MnO2-H composite sample with the increased addition KMnO4, as depicted in Figure S4. In Figure S4b, the presence of Au in the zero-valent state is observed. The appearance of O 1s, C 1s, and Na Auger is consistent with that in Figure 2a. At this point, Pt in the sample is found to exist in three valence states: Pt0, Pt2+, and Pt4+, as shown in Figure S4c. Notably, Pt4+ exhibits the largest area (46.7%, as shown in Table S2) in Figure S4c, indicating a higher prevalence of tetravalent Pt. This suggests that with an increase in the amount of KMnO4 addition, Pt elements tend to undergo further oxidation to higher valence states. Mn exists in three valence states: Mn2+, Mn3+, and Mn4+, as illustrated in Figure S4d. In the Au10Pt1@MnO2-H composite material, the excess MnO2 content can cover some of the active sites of Pt, which may result in a decrease in catalytic performance.
After optimizing the addition of KMnO4, the effect of different reaction temperatures on the morphology of the composite material was investigated. In the TEM image presented in Figure 4a, it is evident that at a low reaction temperature of 35 °C, MnO2 nanosheets are not formed. However, the increases in the length of the nanorod structures, possibly due to the electrostatic attraction between the positively charged cations (e.g., potassium ions) and the negatively charged anions (e.g., citrate ions) on the surface of Au10Pt1 HSNRs, led to the formation of secondary connections. Upon increasing the temperature to 45 °C, well-defined MnO2 nanosheets are generated, as shown in Figure 4b. Further elevation of the reaction temperature to 60 °C accelerates the reaction rate, promoting increased interactions between the MnO2 nanosheets and resulting in the formation of a large interconnected area in the Au10Pt1@MnO2 composite structure, as shown in Figure 4c. At this elevated temperature, the oxidation of Pt elements to higher valence states is enhanced, which could potentially have a detrimental effect on the catalytic performance of the material.
Based on the experimental findings and analysis, the proposed formation mechanism of the Au10Pt1@MnO2 composite structure is illustrated in Figure S5. In a one-dimensional sol of Au10Pt1 HSNRs containing Na3C6H5O7, the addition of KMnO4 solution triggers a reaction at 45 °C, as follows:
C6H5O73− + MnO4− → H2O + MnO2 + CO2
Here, C6H5O73− is oxidized to CO2 and H2O, while MnO4− is reduced to form MnO2 nanosheets. The citrate ion protectants present on the surface of Au10Pt1 HSNRs facilitate the growth of MnO2 nanosheets on their surface. As the MnO2 nanosheets continue to grow, the distance between the dispersed Au10Pt1 HSNRs gradually diminishes, ultimately resulting in the formation of an Au10Pt1@MnO2 two-dimensional composite structure by connecting individual Au10Pt1 HSNRs through MnO2 nanosheets.

2.2. Electrocatalytic Hydrogen Evolution Performance

The Au10Pt1@MnO2 composite structure was evaluated for its performance in methanol electrooxidation. As shown in Figure 5a, the cyclic voltammetry (CV) curves of different electrocatalysts in a mixed electrolyte of 1 M KOH and 1 M CH3OH at a scan rate of 10 mV/s were compared. The Au10Pt1@MnO2-M composite structure showed the best catalytic activity, achieving an onset potential of 0.31 V vs RHE and a peak current density of 21.95 mA/cm2. In Figure 5b, CV curves normalized by the mass of Pt and Pd elements indicated that the Au10Pt1@MnO2-M composite structure exhibits the best mass activity. The forward scan peak mass activity of the Au10Pt1@MnO2-M composite structure in Figure 5c was 15.52 A mg(Pt)−1, which was 35.3, 57.5, and 21.9 times higher than that of Pt/C (0.44 A mg(Pt)−1), Pd/C (0.27 A mg(Pd)−1), and Au10Pt1 (0.71 A mg(Pt)−1), respectively, indicating the highest mass activity for MOR. The chronoamperometry (CA) test on the Au10Pt1@MnO2-M composite structure at the potential of the forward scan peak current demonstrated its durability. As shown in Figure 5d, after 4000 s, the MOR mass activity of the Au10Pt1@MnO2-M composite structure was 1.59 A mg(Pt)−1, which was 12.6, 79.5, and 8.4 times higher than that of Pt/C (0.13 A mg(Pt)−1), Pd/C (0.02 A mg(Pt)−1), and Au10Pt1 (0.19 A mg(Pt)−1), respectively. This indicates the excellent stability of the Au10Pt1@MnO2-M composite structure for methanol electrooxidation.
The study evaluated the ability of the catalyst to resist CO poisoning in the electrocatalytic MOR by analyzing the ratio of If/Ib as forward and reverse current densities [40]. In Figure S6, the histogram of the If/Ib ratio of each catalyst is presented. The If/Ib ratio of Au10Pt1@MnO2-M was found to be 7.23, which is notably higher than that of commercial Pt/C (5.44), commercial Pd/C (1.93), and Au10Pt1 (4.71). This result indicates that Au10Pt1@MnO2-M exhibits better anti-CO poisoning performance compared to the other catalysts, thereby contributing to improved stability in the MOR reaction.
The study investigated the morphology and structure of composite materials with varying ratios of Au10Pt1 and MnO2 to determine the optimal combination for enhanced electrocatalytic MOR performance. The samples denoted as Au10Pt1@MnO2-L, Au10Pt1@MnO2-M, and Au10Pt1@MnO2-H contained varying amounts of MnO2 nanosheets. As illustrated in Figure S7a, the electrode area–normalized CV curve indicated that the specific activity of the Au10Pt1-MnO2 composite initially increased with the MnO2 content and then decreased with the MnO2 content, the Au10Pt1@MnO2-M showing the highest performance. Figure S7b presents the Pt element quality normalization results, revealing that the peak mass activity of the Au10Pt1@MnO2-M composite was 15.52 A mg(Pt)−1, which was 1.43 and 2.06 times higher than that of Au10Pt1@MnO2-L (10.83 A mg(Pt)−1) and Au10Pt1@MnO2-H (7.55 A mg(Pt)−1), respectively. The introduction of MnO2 nanosheets influenced the electronic structure of the composite structure and enhanced its oxidation ability. The study highlighted the synergistic effect of the composite material, leading to improved electrocatalytic methanol oxidation performance. Additionally, the strong interaction between one-dimensional Au10Pt1 HSNRs and MnO2 contributed to enhancing the MOR properties [36]. In the case of Au10Pt1@MnO2-L, the limited number of MnO2 nanosheets resulted in a minimal effect on the methanol oxidation process, demonstrating insufficient enhancement of catalytic activity. Conversely, Au10Pt1@MnO2-H contained excessive numbers of MnO2 nanosheets, which could hinder the performance of the composite by covering active Pt sites and affecting the composition and electronic structure. Ultimately, Au10Pt1@MnO2-M demonstrated the optimal ratio of Au10Pt1 to MnO2, exhibiting the best electrocatalytic methanol oxidation performance among the samples studied.
Figure S8 presents a histogram illustrating the If/Ib ratio of the catalyst for MOR. The If/Ib ratio of the Au10Pt1@MnO2-L sample was the highest at 9.52, indicating a strong ability to resist CO poisoning. However, this sample exhibited lower activity. The If/Ib ratio of Au10Pt1@MnO2-M was higher than that of Au10Pt1@MnO2-H, indicating that it possessed better resistance to CO poisoning compared to that of the latter sample. Therefore, when the ratio of Au10Pt1 to MnO2 nanosheets is moderate, the overall performance is better. This finding underscores the importance of balancing CO poisoning resistance and activity in catalyst design. The Au10Pt1@MnO2-M sample, with its moderate ratio of components, demonstrated improved comprehensive performance in terms of CO poisoning resistance and activity for the MOR.

3. Materials and Methods

3.1. Materials

All the reagents were used directly as received from the suppliers, without further treatment. Hydrogen tetrachloroaurate tetrahydrate (HAuCl4·4H2O, ≥99.9%), chloroplatinic acid hexahydrate (H2PtCl6·6H2O, ≥99.9%), potassium permanganate (KMnO4, ≥ 99%), sodium borohydride (NaBH4, ≥98%), hydrochloric acid (HCl, 36.0–38.0%), sodium citrate dihydrate (Na3C6H5O7·2H2O, ≥99.5%), and methanol (CH3OH, ≥99.7%) were purchased from Sinopharm Chemical Reagent Company (Shanghai, China). The 5 wt. % Nafion solution was purchased from Sigma-Aldrich. Carbon black (Vulcan XC−72) was purchased from Cabot Limited. The commercial Pt/C, Pd/C catalysts were purchased from Johnson Matthey Chemicals Limited (London, UK).

3.2. Synthesis of Au NPs

The synthesis of Au NPs was carried out through a citrate reduction process [41]. In a typical procedure, 1 mL Na3C6H5O7 solution (0.01 M/L) and 415 μL of HAuCl4 solution (0.024 M) were added to 37 mL of ultrapure water and vigorously stirred. Subsequently, 1 mL of ice-bathed NaBH4 solution (0.1 M) was added after 5 min, resulting in a color change in the solution from pale yellow to ruby red upon completion of the reaction. The solution was then left undisturbed for 2 h to age, yielding Au NPs sol (0.05 mg/mL) with a particle size of 6–8 nm.

3.3. Synthesis of Au10Pt1 HSNRs

In a quartz photoreactor, 40 mL of Au NPs sol was introduced into 10 mL of ultrapure water and stirred vigorously to achieve a homogeneous mixture. Subsequently, 50 μL of NaOH (0.1 M) and 53 μL of H2PtCl6 (0.019 M) were added to the solution. The mixture was then subjected to visible light irradiation (≥400 nm) for 0.5 h in a water bath at 15 °C. Subsequently, the solution was allowed to react at 45 °C in the dark for 24 h, without agitation, to yield Au10Pt1 HSNRs. The experimental setup employed an Xe lamp (PLS-SXE300 +/UV), sourced from Beijing Perfect Light Technology Co., Ltd. (Beijing, China).

3.4. Synthesis of Au10Pt1@MnO2 Composites

The synthesis procedure for the Au10Pt1@MnO2 composite involves several steps. Initially, 50 mL Au10Pt1 HSNRs is stirred in a beaker. Subsequently, 0.5 mL of KMnO4 (0.014 M) solution is introduced. The mixture is stirred and homogenized in a 45 °C water bath for 2 h. Upon completion of this process, the resulting composite material is designated as Au10Pt1@MnO2-M. Additional samples incorporating varying amounts of KMnO4, specifically 0.25 mL and 1 mL, are labeled as Au10Pt1@MnO2-L and Au10Pt1@MnO2-H, respectively.

3.5. Materials Characterization

The X-ray photoelectron spectra (XPS) were acquired using the K-Alpha+ XPS system on a thermo ESCALAB250Xi instrument (Axis Ultra DLD Kratos AXIS SUPRA; PHI5000versaprobeIII) outfitted with an X-ray source of Al Kα radiation and calibrated with respect to C 1s at a binding energy (BE) of 284.6 eV from contaminant carbon. The XPS sample was prepared using the drop-casting method, and the sol sample was directly cast on a 5 × 5 cm2 monocrystalline silicon sheet with a dropper. The structure and morphologies of the samples were examined using field emission high resolution transmission electron microscopy (FE-HRTEM, JEM-2010F and Tecnai G2 F20). For the preparation of the TEM test samples, a drop-casting method was employed, and the sol was directly deposited onto a standard carbon support film using an eyedropper. After allowing the sample to dry, it was subsequently placed in the sample holder for analysis. Energy dispersive X-ray (EDX) analysis and elemental mapping were performed using the X-max T80 system from Oxford instruments. The ultraviolet−visible (UV−VIS, diffuse reflection absorption spectra) data were recorded in the spectral region of 200–1400 nm using a unico UV-2600 spectrophotometer (Shimadzu, Japan). All the UV−VIS samples in this work are sols, which can be tested directly in quartz colorimetric dishes.

3.6. Evaluation of Electrocatalytic Activity

The fabrication process of the working electrode involved the following steps: Initially, 0.02 g of conductive carbon black (Vulcan XC-72, Cabot) was combined with the Au10Pt1@MnO2 solutions and subjected to ultrasonic agitation for adsorption over 24 h. The mixture was then filtered and dried. Subsequently, 1 mg of the catalyst obtained in the previous step (or commercial Pt/C, Pd/C catalyst) was added to a spiral glass bottle containing 0.48 mL water, 0.5 mL ethanol and 20 μL Nafion solution (5.0 wt. %), and ultrasonically stirred for 2 h to obtain the uniformly dispersed catalyst slurry ink. Finally, the 5 μL catalyst paste was dropped five times onto a 3 mm diameter, polished, and cleaned L-shaped glass carbon electrode. After natural drying, a uniform catalyst film was formed on the electrode surface.
The evaluation of the electrochemical methanol oxidation reaction (MOR) was conducted at a controlled temperature of 25 °C using a single-chamber electrolytic cell equipped with a three-electrode system and a CHI660E electrochemical workstation from Shanghai CH Instrument Co., Ltd., Shanghai, China. A platinum sheet electrode and a saturated calomel electrode (SCE) were selected as the counter electrode and the reference electrode, respectively. The electrochemical tests for the MOR were performed in 1 M KOH and 1 M CH3OH electrolytes saturated with N2. Prior to the electrochemical test, the activated working electrode underwent 20 cycles of voltammetric scanning at a rate of 50 mV/s. The performance assessment was carried out at a scanning rate of 5 mV/s, and the cyclic voltammetry curve was recorded. The stable test voltage corresponded to the overpotential at the maximum current density. All potentials mentioned in this study are referenced to the SCE reference electrode. Commercial Pt/C and Pd/C (JM, 20%) were utilized as the reference catalysts.

4. Conclusions

In summary, the study focused on synthesizing Au10Pt1@MnO2 composites using a wet chemical method, successfully maintaining the one-dimensional structure of Au10Pt1 HSNRs while incorporating lamellar MnO2. The quantity of the KMnO4 added and the reaction temperature were crucial factors in the formation of MnO2. The inclusion of MnO2 nanosheets significantly influenced the electronic structure of the composite, with MnO2 contributing to the oxidation capacity and enhancing the overall material properties, leading to improved electrocatalytic MOR performance. Comparative analyses using a commercial Pt/C catalyst and a commercial Pd/C catalyst, as well as Au10Pt1 HSNRs, revealed that the Au10Pt1@MnO2-M composite exhibited the lowest initial potential, highest peak current density, and superior CO anti-poisoning ability. Notably, the Au10Pt1@MnO2-M composite demonstrated a significantly high peak mass activity of 15.52 A mg(Pt)−1. This was 35.3, 57.5, and 21.9 times that of Pt/C (0.44 A mg(Pt)−1), P/C (0.27 A mg A mg(Pt)−1), and Au10Pt1 (0.71 A mg(Pt)−1), respectively.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/molecules29163753/s1, Figure S1. Schematic diagram of the preparation process of Au10Pt1@MnO2 composites. Figure S2. UV–VIS absorption spectra of (a) KMnO4 and (b) MnO2 nanosheets; (c) TEM image of MnO2 nanosheets. Figure S3. (a) STEM image of Au10Pt1@MnO2 composites; (b–e) mapping images; (f) EDS spectra diagram. Figure S4. XPS spectra of Au10Pt1@MnO2-H: (a) survey; (b) Au; (c) Pt; (d) Mn. Figure S5. Formation mechanism of Au10Pt1@MnO2 composite structure. Figure S6. The If/Ib ratio of MOR with different catalysts. Figure S7. The electrocatalytic MOR of different catalysts in 1 M KOH and 1 M CH3OH solutions: (a) CV curve of mass activity; (b) mass activity at the highest current density. Figure S8. The If/Ib ratio of MOR with different catalysts. Table S1. The ratios of different states of elements from XPS analysis about Au10Pt1@MnO2-M. Table S2. The ratios of different states of elements from XPS analysis about Au10Pt1@MnO2-H.

Author Contributions

Conceptualization, T.L. and L.H.; methodology, T.L.; validation, formal analysis, investigation, resources and data curation, T.L. and Y.L.; writing—original draft preparation, T.L.; writing—review and editing, T.L., Y.H., Z.Y. and L.H.; project administration and funding acquisition, T.L. and L.H. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Science and Technology Project of Jiangxi Provincial Education Department (GJJ2201812), Shanghai Municipal Science and Technology Commission (18520744500).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article and the Supplementary Materials.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Hu, S.; Wang, B.; Ma, Y.; Li, M.; Zhang, L.; Huang, Z. Ultrathin bismuth tungstate nanosheets as an effective photo-assisted support for electrocatalytic methanol oxidation. J. Colloid Interf. Sci. 2019, 552, 179–185. [Google Scholar] [CrossRef] [PubMed]
  2. Selivanova, A.V.; Demina, V.G.; Aydakov, E.E.; Saraev, A.A.; Kaichev, V.V.; Bukhtiyarov, V.I. Mechanistic study of methanol oxidation on Pt(1 1 1) single crystal. Appl. Surf. Sci. 2022, 579, 152140–152147. [Google Scholar] [CrossRef]
  3. Wang, X.; Xi, S.; Lee, W.S.V.; Huang, P.; Cui, P.; Zhao, L.; Hao, W.; Zhao, X.; Wang, Z.; Wu, H.; et al. Materializing efficient methanol oxidation via electron delocalization in nickel hydroxide nanoribbon. Nat. Commun. 2020, 11, 4647. [Google Scholar] [CrossRef] [PubMed]
  4. Lu, Z.; Zou, L.; Song, W. Hierarchical Pt-In nanowires for efficient methanol oxidation electrocatalysis. Molecules 2023, 28, 1502. [Google Scholar] [CrossRef] [PubMed]
  5. Gong, W.; Jiang, Z.; Wu, R.; Liu, Y.; Huang, L.; Hu, N.; Tsiakaras, P.; Shen, P.K. Cross-double dumbbell-like Pt–Ni nanostructures with enhanced catalytic performance toward the reactions of oxygen reduction and methanol oxidation. Appl. Catal. B Environ. 2019, 246, 277–283. [Google Scholar] [CrossRef]
  6. Liu, Y.; Hu, B.; Wu, S.; Wang, M.; Zhang, Z.; Cui, B.; He, L.; Du, M. Hierarchical nanocomposite electrocatalyst of bimetallic zeolitic imidazolate framework and MoS2 sheets for non-Pt methanol oxidation and water splitting. App. Catal. B Environ. 2019, 258, 117970. [Google Scholar] [CrossRef]
  7. Feng, Q.; Zhao, S.; He, D.; Tian, S.; Gu, L.; Wen, X.; Chen, C.; Peng, Q.; Wang, D.; Li, Y. Strain engineering to enhance the electrooxidation performance of atomic-layer Pt on intermetallic Pt3Ga. J. Am. Chem. Soc. 2018, 140, 2773–2776. [Google Scholar] [CrossRef] [PubMed]
  8. Huang, L.; Zhang, X.; Wang, Q.; Han, Y.; Fang, Y.; Dong, S. Shape-control of Pt-Ru nanocrystals: Tuning surface structure for enhanced electrocatalytic methanol oxidation. J. Am. Chem. Soc. 2018, 140, 1142–1147. [Google Scholar] [CrossRef] [PubMed]
  9. Huang, S.; Jin, Z.; Ning, P.; Gao, C.; Wu, Y.; Liu, X.; Xin, P.; Chen, Z.; Jiang, Y.; Hu, Z.; et al. Synergistically modulating electronic structure of NiS2 hierarchical architectures by phosphorus doping and sulfur-vacancies defect engineering enables efficient electrocatalytic water splitting. Chem. Eng. J. 2021, 420, 127630. [Google Scholar] [CrossRef]
  10. Chen, G.; Dai, Z.; Sun, L.; Zhang, L.; Liu, S.; Bao, H.; Bi, J.; Yang, S.; Ma, F. Synergistic effects of platinum–cerium carbonate hydroxides–reduced graphene oxide on enhanced durability for methanol electro-oxidation. J. Mater. Chem. A 2019, 7, 6562–6571. [Google Scholar] [CrossRef]
  11. Wu, Y.P.; Tian, J.W.; Liu, S.; Li, B.; Zhao, J.; Ma, L.F.; Li, D.S.; Lan, Y.Q.; Bu, X. Bi-microporous metal-organic frameworks with cubane [M4(OH)4] (M=Ni, Co) clusters and pore-space partition for electrocatalytic methanol oxidation reaction. Angew. Chem. Int. Ed. Engl. 2019, 58, 12185–12189. [Google Scholar] [CrossRef] [PubMed]
  12. Szliszka, E.; Czuba, Z.P.; Domino, M.; Mazur, B.; Zydowicz, G.; Krol, W. Pt2CeO2 heterojunction supported on multiwalled carbon nanotubes for robust electrocatalytic oxidation of methanol. Molecules 2023, 14, 2995–3007. [Google Scholar]
  13. Chen, Z.; Wang, W.; Huang, S.; Ning, P.; Wu, Y.; Gao, C.; Le, T.T.; Zai, J.; Jiang, Y.; Hu, Z.; et al. Well-defined CoSe2@MoSe2 hollow heterostructured nanocubes with enhanced dissociation kinetics for overall water splitting. Nanoscale 2020, 12, 326–335. [Google Scholar] [CrossRef]
  14. Zhou, X.; Yu, X.; Peng, L.; Luo, J.; Ning, X.; Fan, X.; Zhou, X.; Zhou, X. Pd(II) coordination molecule modified g-C3N4 for boosting photocatalytic hydrogen production. J. Colloid Interf. Sci. 2024, 671, 134–144. [Google Scholar] [CrossRef] [PubMed]
  15. Bigiani, L.; Andreu, T.; Maccato, C.; Fois, E.; Gasparotto, A.; Sada, C.; Tabacchi, G.; Krishnan, D.; Verbeeck, J.; Morante, J.R.; et al. Engineering Au/MnO2 hierarchical nanoarchitectures for ethanol electrochemical valorization. J. Mater. Chem. A 2020, 8, 16902–16907. [Google Scholar] [CrossRef]
  16. Salarizadeh, P.; Azizi, S.; Beydaghi, H.; Bagheri, A.; Askari, M.B. Electrocatalytic performance of MnMoO4-rGO nano-electrocatalyst for methanol and ethanol oxidation. Molecules 2023, 28, 4613. [Google Scholar] [CrossRef]
  17. Feng, Y.-Y.; Song, G.H.; Zhang, Q.; Lv, J.-N.; Hu, X.-Y.; He, Y.-L.; Shen, X. Morphology effect of MnO2 promoter to the catalytic performance of Pt toward methanol electrooxidation reaction. Int. J. Hydrogen Energy 2019, 44, 3744–3750. [Google Scholar] [CrossRef]
  18. Liu, R.; Zhou, H.; Liu, J.; Yao, Y.; Huang, Z.; Fu, C.; Kuang, Y. Preparation of Pd/MnO2-reduced graphene oxide nanocomposite for methanol electro-oxidation in alkaline media. Electrochem. Commun. 2013, 26, 63–66. [Google Scholar] [CrossRef]
  19. Lu, Z.; Li, S.; Ning, L.; Tang, K.; Guo, Y.; You, L.; Chen, C.; Wang, G. Nickel–iron-layered double hydroxide electrocatalyst with nanosheets array for high performance of water splitting. Molecules 2024, 29, 2092. [Google Scholar] [CrossRef]
  20. González-Ingelmo, M.; Rocha, V.G.; González, Z.; Sierra, U.; Barriga, E.D.; Álvarez, P. Graphene materials from coke-like wastes as proactive support of Nickel–Iron electro-catalysts for water splitting. Molecules 2024, 29, 1391. [Google Scholar] [CrossRef]
  21. Zhao, Y.; Jiang, P. MnO2 nanosheets grown on the ZnO-nanorod-modified carbon fibers for supercapacitor electrode materials. Colloid Surf. A Physicochem. Eng. Asp. 2014, 444, 232–239. [Google Scholar] [CrossRef]
  22. Li, J.; Peng, Y.; Zhang, W.; Shi, X.; Chen, M.; Wang, P.; Zhang, X.; Fu, H.; Lv, X.; Dong, F.; et al. Hierarchical Pd/MnO2 nanosheet array supported on Ni foam: An advanced electrode for electrocatalytic hydrodechlorination reaction. Appl. Surf. Sci. 2020, 509, 145369. [Google Scholar] [CrossRef]
  23. Bi, H.; Dai, Y.; Yang, P.; Xu, J.; Yang, D.; Gai, S.; He, F.; An, G.; Zhong, C.; Lin, J. Glutathione and H2O2 consumption promoted photodynamic and chemotherapy based on biodegradable MnO2–Pt@Au25 nanosheets. Chem. Eng. J. 2019, 356, 543–553. [Google Scholar] [CrossRef]
  24. Ma, E.; Wang, P.; Yang, Q.; Yu, H.; Pei, F.; Zheng, Y.; Liu, Q.; Dong, Y.; Li, Y. Electrochemical immunosensors for sensitive detection of neuron-specific enolase based on small-size trimetallic Au@Pd^Pt nanocubes functionalized on ultrathin MnO2 nanosheets as signal labels. ACS Biomater. Sci. Eng. 2020, 6, 1418–1427. [Google Scholar] [CrossRef]
  25. Begum, H.; Ahmed, M.S.; Jeon, S. δ-MnO2 nanoflowers on sulfonated graphene sheets for stable oxygen reduction and hydrogen evolution reaction. Electrochim. Acta 2019, 296, 235–242. [Google Scholar] [CrossRef]
  26. Hu, Q.; Liu, X.; Zhu, B.; Li, G.; Fan, L.; Chai, X.; Zhang, Q.; Liu, J.; He, C. Redox route to ultrathin metal sulfides nanosheet arrays-anchored MnO2 nanoparticles as self-supported electrocatalysts for efficient water splitting. J. Power Sources 2018, 398, 159–166. [Google Scholar] [CrossRef]
  27. Wang, M.; Zhang, L.; Huang, W.; Zhou, Y.; Zhao, H.; Lv, J.; Tian, J.; Kan, X.; Shi, J. Pt/MnO2 nanosheets: Facile synthesis and highly efficient catalyst for ethylene oxidation at low temperature. RSC Adv. 2017, 7, 14809–14815. [Google Scholar] [CrossRef]
  28. Hu, X.; Chen, J.; Li, S.; Chen, Y.; Qu, W.; Ma, Z.; Tang, X. The Promotional Effect of Copper in Catalytic Oxidation by Cu-Doped α-MnO2 Nanorods. J. Phys. Chem. C 2019, 124, 701–708. [Google Scholar] [CrossRef]
  29. Du, H.; Wang, Y.; Wan, T.; Arandiyan, H.; Chu, D. Highly efficient and selective Cu/MnOx catalysts for carbon dioxide reduction. ACS Appl. Energy Mater. 2018, 1, 3035–3041. [Google Scholar] [CrossRef]
  30. Chen, D.; Zhang, G.; Wang, M.; Li, N.; Xu, Q.; Li, H.; He, J.; Lu, J. Pt/MnO2 nanoflowers anchored to boron nitride aerogels for highly efficient enrichment and catalytic oxidation of formaldehyde at room temperature. Angew. Chem. Int. Ed. Engl. 2021, 60, 6377–6381. [Google Scholar] [CrossRef]
  31. Liu, J.; Meng, L.; Fei, Z.; Dyson, P.J.; Zhang, L. On the origin of the synergy between the Pt nanoparticles and MnO2 nanosheets in wonton-like 3D nanozyme oxidase mimics. Biosens. Bioelectron. 2018, 121, 159–165. [Google Scholar] [CrossRef] [PubMed]
  32. Xu, J.; Gu, P.; Birch, D.J.S.; Chen, Y. Plasmon-promoted electrochemical oxygen evolution catalysis from gold decorated MnO2 nanosheets under green light. Adv. Funct. Mater. 2018, 28, 1801573–1801579. [Google Scholar] [CrossRef]
  33. Yusuf, A.; Sun, Y.; Ren, Y.; Snape, C.; Wang, C.; Jia, H.; He, J. Opposite effects of Co and Cu dopants on the catalytic activities of birnessite MnO2 catalyst for low-temperature formaldehyde oxidation. J. Phys. Chem. C 2020, 124, 26320–26331. [Google Scholar] [CrossRef]
  34. Peng, X.; Chen, Y.; Mi, Y.; Zhuo, L.; Qi, G.; Ren, J.; Qiu, Y.; Liu, X.; Luo, J. Efficient electroreduction CO2 to CO over MnO2 Nanosheets. Inorg. Chem. 2019, 58, 8910–8914. [Google Scholar] [CrossRef] [PubMed]
  35. Li, T.; Liu, Y.; Huang, S.; Jia, R.; Shi, L.; Huang, L. Photochemical fabrication of bimetal wormlike heterostructured nanorods for enhanced electrochemical hydrogen evolution reaction. J. Alloys Compd. 2022, 910, 164913–195921. [Google Scholar] [CrossRef]
  36. Liu, B.; Mosa, I.M.; Song, W.; Zheng, H.; Kuo, C.H.; Rusling, J.F.; Suib, S.L.; He, J. Unconventional structural and morphological transitions of nanosheets, nanoflakes and nanorods of AuNP@MnO2. J. Mater. Chem. A 2016, 4, 6447–6455. [Google Scholar] [CrossRef]
  37. Hong, W.; Shang, C.; Wang, J.; Wang, E. Bimetallic PdPt nanowire networks with enhanced electrocatalytic activity for ethylene glycol and glycerol oxidation. Energy Environ. Sci. 2015, 8, 2910–2915. [Google Scholar] [CrossRef]
  38. Yang, S.; Song, X.; Zhang, P.; Gao, L. Facile synthesis of nitrogen-doped graphene-ultrathin MnO2 sheet composites and their electrochemical performances. ACS Appl. Mater. Interfaces 2013, 5, 3317–3322. [Google Scholar] [CrossRef] [PubMed]
  39. Wei, J.-X.; Cao, M.-Z.; Xiao, K.; Guo, X.-P.; Ye, S.-Y.; Liu, Z.-Q. In situ confining Pt clusters in ultrathin MnO2 nanosheets for highly efficient hydrogen evolution reaction. Small Struct. 2021, 2, 2100047–2100055. [Google Scholar] [CrossRef]
  40. Zhang, W.; Yang, Y.; Huang, B.; Lv, F.; Wang, K.; Li, N.; Luo, M.; Chao, Y.; Li, Y.; Sun, Y.; et al. Ultrathin PtNiM (M = Rh, Os, and Ir) nanowires as efficient fuel oxidation electrocatalytic materials. Adv. Mater. 2019, 31, 1805833–1805841. [Google Scholar] [CrossRef]
  41. Li, T.; Jiang, W.; Liu, Y.; Jia, R.; Shi, L.; Huang, L. Localized surface plasmon resonance induced assembly of bimetal nanochains. J. Colloid Interf. Sci. 2022, 607, 1888–1897. [Google Scholar] [CrossRef] [PubMed]
Molecules 29 03753 g001
Figure 1. (a) UV–VIS absorption spectra of the samples; (b) TEM image of Au NPs, (c) Au10Pt1 HSNRs, and (d) Au10Pt1@MnO2-M; local amplification of HRTEM images of (e) Au10Pt1 HSNRs and (f) MnO2 nanosheets; (g) selected area electron diffraction (SAED) image.
Figure 1. (a) UV–VIS absorption spectra of the samples; (b) TEM image of Au NPs, (c) Au10Pt1 HSNRs, and (d) Au10Pt1@MnO2-M; local amplification of HRTEM images of (e) Au10Pt1 HSNRs and (f) MnO2 nanosheets; (g) selected area electron diffraction (SAED) image.
Molecules 29 03753 g001
Molecules 29 03753 g002
Figure 2. XPS spectra of Au10Pt1@MnO2-M: (a) survey; (b) Au; (c) Pt; (d) Mn.
Figure 2. XPS spectra of Au10Pt1@MnO2-M: (a) survey; (b) Au; (c) Pt; (d) Mn.
Molecules 29 03753 g002
Molecules 29 03753 g003
Figure 3. TEM images of different KMnO4 additions: (a) Au10Pt1@MnO2-L; (b) Au10Pt1@MnO2-M; (c) Au10Pt1@MnO2-H.
Figure 3. TEM images of different KMnO4 additions: (a) Au10Pt1@MnO2-L; (b) Au10Pt1@MnO2-M; (c) Au10Pt1@MnO2-H.
Molecules 29 03753 g003
Molecules 29 03753 g004
Figure 4. TEM images of Au10Pt1@MnO2-M at different reaction temperatures: (a) 35 °C; (b) 45 °C; (c) 60 °C.
Figure 4. TEM images of Au10Pt1@MnO2-M at different reaction temperatures: (a) 35 °C; (b) 45 °C; (c) 60 °C.
Molecules 29 03753 g004
Molecules 29 03753 g005
Figure 5. The performance of different catalysts for MOR in 1 M KOH and 1 M CH3OH solutions: (a) CV curve of specific activity; (b) CV curve per mass of noble metals; (c) mass activity at the highest current density; (d) chronoamperometry measurement curves.
Figure 5. The performance of different catalysts for MOR in 1 M KOH and 1 M CH3OH solutions: (a) CV curve of specific activity; (b) CV curve per mass of noble metals; (c) mass activity at the highest current density; (d) chronoamperometry measurement curves.
Molecules 29 03753 g005
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Li, T.; Liu, Y.; Huang, Y.; Yu, Z.; Huang, L. Aqueous Synthesis of Au10Pt1 Nanorods Decorated with MnO2 Nanosheets for the Enhanced Electrocatalytic Oxidation of Methanol. Molecules 2024, 29, 3753. https://doi.org/10.3390/molecules29163753

AMA Style

Li T, Liu Y, Huang Y, Yu Z, Huang L. Aqueous Synthesis of Au10Pt1 Nanorods Decorated with MnO2 Nanosheets for the Enhanced Electrocatalytic Oxidation of Methanol. Molecules. 2024; 29(16):3753. https://doi.org/10.3390/molecules29163753

Chicago/Turabian Style

Li, Ting, Yidan Liu, Yibin Huang, Zhong Yu, and Lei Huang. 2024. "Aqueous Synthesis of Au10Pt1 Nanorods Decorated with MnO2 Nanosheets for the Enhanced Electrocatalytic Oxidation of Methanol" Molecules 29, no. 16: 3753. https://doi.org/10.3390/molecules29163753

APA Style

Li, T., Liu, Y., Huang, Y., Yu, Z., & Huang, L. (2024). Aqueous Synthesis of Au10Pt1 Nanorods Decorated with MnO2 Nanosheets for the Enhanced Electrocatalytic Oxidation of Methanol. Molecules, 29(16), 3753. https://doi.org/10.3390/molecules29163753

Article Metrics

Back to TopTop