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TEM (A1, A2, B1, B2, C1, and C2) and HRTEM (A3, B3, and C3) images of Pt grown on G@(PEI/Au NP) 3.5 at different Pt loading amounts. (A1-A3) 30%, (B1-B3) 50%, and (C1-C3) 60%. A2, B2, and C2 are high magnification images of A1, B1, and C1, respectively.
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Controllable growth of highly dense and uniform Pt nanostructures on graphene could greatly increase the electrocatalytic activity and Pt utilization for methanol oxidation in direct methanol fuel cells (DMFCs), but still presents a great challenge. This study reports a novel strategy of combining self-assembly with in-situ seeded growth to fabrica...
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... making further assembly impossible. This should be due to the low charge density of PEI at high assembly pH inducing aggregation between both Au nanoparticles and graphene. [21][22][23] The unique graphene-based 2-D assembly process reported here could provide a new route to the fabrication of various freestanding uniform 2-D nanoparticle arrays. Fig. 5 shows TEM images of Pt nanostructures grown on the graphene supported Au nanoparticle array aer the in situ seeded growth at different magnications. Different Pt loadings were studied for more understanding of the growth mechanism. The metal nanoparticles on graphene are as uniform and dense as those before Pt growth ( Fig. 5A1-C1). ...
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... of G@(PEI/Au NP) 3.5 @Pt is 0.189 A mg À1 based on the total mass of metal, which is 4.50 times that of PEI-G@Pt and 9.45 times that of G@Pt. These results clearly indicate the importance of Au nanoparticles assembled on graphene, which can not only signicantly increase the Pt dispersion and direct the Pt growth into the nanodendritic structure (Fig. 5, 6 and 9), but also increase the tolerance toward CO (Fig. 12). Moreover, it is found that the number of deposition cycles has a great effect on the electrocatalytic activity. The forward peak current density for the reaction on G@(PEI/Au NP) 3.5 @Pt is $4.4 times higher than that on G@(PEI/Au) 1.5 @Pt (0.083 A mg À1 ) based on Pt, and 3.78 ...
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Citations
... To improve fuel cell performance, extensive research has been conducted on structural design, material improvement, MEA membrane catalyst preparation, and parameters optimization [7,8], where the operating and structural parameters of DMFC showed significant effects on power density and energy efficiency [9]. The operating parameters mainly include methanol concentration, flow rate, air flow rate, and temperature [10]. ...
The operating parameters of the active direct methanol fuel cell (DMFC) are essential factors that affect cell performance. However, it is challenging to maintain the optimal maximum output power density due to the system’s complexity, the operating conditions variation, and the correlations between those parameters. This paper proposes an adaptive joint optimization method for fuel cell operating parameters. The methods include the adaptive numerical simulation of the operation parameters and the optimization for fuel cell performance. Based on orthogonal tests, a BP neural network is used to build a performance evaluation model that can quantify the influence of the operating parameters on fuel cell performance. The optimal combination of operating parameters for the fuel cell is obtained by a whale optimization algorithm (WOA) through the evaluation model. The experimental results show that the evaluation model could respond accurately and adaptively to the cell operating conditions under different operating conditions. The optimization algorithm improves the maximum power density of the fuel cell by 8.71%.
... The EOR current density of catalyst Pt 27 Co 73 /C (118.88 mA mg −1 ) and Pt 53 Co 47 /C (86.48 mA mg −1 ) catalyst were 5.47 and 3.98 times that of commercial Pt/C (21.73 mA mg −1 ) after 5000 s, respectively (Figure 5b). Moreover, compared with recently reported electrocatalysts [42][43][44][45][46][47], the Pt 53 Co 47 NWs/C catalyst and Pt 27 Co 73 NWs/C catalyst also exhibited excellent stability under the same conditions (Tables 3 and 4). CA tests of the Pt 53 Co 47 /C for MOR were extended to 7500 s at 0.65 V vs. RHE. ...
... The EOR current density of catalyst Pt27Co73/C (118.88 mA mg −1 ) and Pt53Co47/C (86.48 mA mg −1 ) catalyst were 5.47 and 3.98 times that of commercial Pt/C (21.73 mA mg −1 ) after 5000 s, respectively ( Figure 5b). Moreover, compared with recently reported electrocatalysts [42][43][44][45][46][47], the Pt53Co47 NWs/C catalyst and Pt27Co73 NWs/C catalyst also exhibited excellent stability under the same conditions (Tables 3 and 4). CA tests of the Pt53Co47/C for MOR were extended to 7500 s at 0.65 V vs. RHE. ...
The compositions and surface facets of platinum (Pt)-based electrocatalysts are of great significance for the development of direct alcohol fuel cells (DAFCs). We reported an approach for preparing ultrathin PtnCo100−n nanowire (NW) catalysts with high activity. The PtnCo100−n NW alloy catalysts synthesized by single-phase surfactant-free synthesis have adjustable compositions and (111) plane and strain lattices. X-ray diffraction (XRD) results indicate that the alloy composition can adjust the lattice shrinkage or expansion of PtnCo100−n NWs. X-ray photoelectron spectroscopy (XPS) results show that the electron structure of Pt is changed by the alloying effect caused by electron modulation in the d band, and the chemical adsorption strength of Pt is decreased, thus the catalytic activity of Pt is increased. The experimental results show that the activity of PtnCo100−n for the oxidation of methanol and ethanol is related to the exposed crystal surface, strain lattice and composition of catalysts. The PtnCo100−n NWs exhibit stronger electrocatalytic performance for both methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR). The dominant (111) plane Pt53Co47 exhibits the highest electrocatalytic activity in MOR, which is supported by the results of XPS. This discovery provides a new pathway to design high activity, stability nanocatalysts to enhance direct alcohol fuel cells.
... On the other hand, Figure 1c shows that Pt NPs were not uniformly distributed on the TG surface of the TG/Pt 0.241 catalyst, evidenced by strong aggregation of a numerous amount of Pt NPs to form nondispersive Pt clusters (see Figure 1c). This is due to the ultra-flat surface and scarce functional groups of the TG [36]. Pt NPs had diameters of 2 to 4 nm, which were much smaller than those of Au NPs (see Figure 1e). ...
... XRD measurement was performed to identify crystallographic structures of the TG mesh, TG/Au 0.258 , and TG/Pt 0.241 catalysts (see Figure 1f). The sharp peaks at approximately 26.4 • in the three XRD patterns are attributed to the hexagonal phase of graphite (see the PDF#41-1487), which is originated from the multi-layered feature of the TG mesh [36]. The main peaks (111) in the XRD patterns of the TG/Au 0.258 and TG/Pt 0.241 are approximately at 38.23 and 39.90 • , respectively. ...
... Moreover, no Fe element was found in the EDS analyses ( Figures S3, S4 and S6), confirming the total removal of Fe traces. The TEM-EDS element-mapping data of the TG/Au 52 Pt 48 catalyst ( Figure 2b) shows a spatial well overlapping of Au and Pt elements in both big particle (~100 nm) and small particle (~20 nm), indicating that Pt NPs grew at Au NP sites to form binary AuPt mixing NPs [17,36]. The TEM-EDS element-mapping result also rules out the formation of the core-shell Au@Pt NPs. ...
Pt-based alloy or bimetallic anode catalysts have been developed to reduce the carbon monoxide (CO) poisoning effect and the usage of Pt in direct methanol fuel cells (DMFCs), where the second metal plays a role as CO poisoning inhibitor on Pt. Furthermore, better performance in DMFCs can be achieved by improving the catalytic dispersion and using high-performance supporting materials. In this work, we introduced a free-standing, macroscopic, interwoven tubular graphene (TG) mesh as a supporting material because of its high surface area, favorable chemical inertness, and excellent conductivity. Particularly, binary AuPt nanoparticles (NPs) can be easily immobilized on both outer and inner walls of the TG mesh with a highly dispersive distribution by a simple and efficient chemical reduction method. The TG mesh, whose outer and inner walls were decorated with optimized loading of binary AuPt NPs, exhibited a remarkably catalytic performance in DMFCs. Its methanol oxidation reaction (MOR) activity was 10.09 and 2.20 times higher than those of the TG electrodes with only outer wall immobilized with pure Pt NPs and binary AuPt NPs, respectively. Furthermore, the catalyst also displayed a great stability in methanol oxidation after 200 scanning cycles, implying the excellent tolerance toward the CO poisoning effect.
... On the other hand, Figure 1c shows that Pt NPs were not uniformly distributed on the TG surface of the TG/Pt 0.241 catalyst, evidenced by strong aggregation of a numerous amount of Pt NPs to form nondispersive Pt clusters (see Figure 1c). This is due to the ultra-flat surface and scarce functional groups of the TG [36]. Pt NPs had diameters of 2 to 4 nm, which were much smaller than those of Au NPs (see Figure 1e). ...
... XRD measurement was performed to identify crystallographic structures of the TG mesh, TG/Au 0.258 , and TG/Pt 0.241 catalysts (see Figure 1f). The sharp peaks at approximately 26.4 • in the three XRD patterns are attributed to the hexagonal phase of graphite (see the PDF#41-1487), which is originated from the multi-layered feature of the TG mesh [36]. The main peaks (111) in the XRD patterns of the TG/Au 0.258 and TG/Pt 0.241 are approximately at 38.23 and 39.90 • , respectively. ...
... Moreover, no Fe element was found in the EDS analyses ( Figures S3, S4 and S6), confirming the total removal of Fe traces. The TEM-EDS element-mapping data of the TG/Au 52 Pt 48 catalyst ( Figure 2b) shows a spatial well overlapping of Au and Pt elements in both big particle (~100 nm) and small particle (~20 nm), indicating that Pt NPs grew at Au NP sites to form binary AuPt mixing NPs [17,36]. The TEM-EDS element-mapping result also rules out the formation of the core-shell Au@Pt NPs. ...
Pt-based alloy or bimetallic anode catalysts have been developed to reduce the carbon monoxide (CO) poisoning effect and the usage of Pt in direct methanol fuel cells (DMFCs), where the second metal plays a role as CO poisoning inhibitor on Pt. Furthermore, better performance in DMFCs can be achieved by improving the catalytic dispersion and using high-performance supporting materials. In this work, we introduced a free-standing, macroscopic, interwoven tubular graphene (TG) mesh as a supporting material because of its high surface area, favorable chemical inertness, and excellent conductivity. Particularly, binary AuPt nanoparticles (NPs) can be easily immobilized on both outer and inner walls of the TG mesh with a highly dispersive distribution by a simple and efficient chemical reduction method. The TG mesh, whose outer and inner walls were decorated with optimized loading of binary AuPt NPs, exhibited a remarkably catalytic performance in DMFCs. Its methanol oxidation reaction (MOR) activity was 10.09 and 2.20 times higher than those of the TG electrodes with only outer wall immobilized with pure Pt NPs and binary AuPt NPs, respectively. Furthermore, the catalyst also displayed a great stability in methanol oxidation after 200 scanning cycles, implying the excellent tolerance toward the CO poisoning effect.
Keywords: direct methanol fuel cells; tubular graphene; supporting material; binary AuPt nanoparticles; anode catalyst; CO poisoning effect
... V (vs. RHE) after 10 cycles are shown in Fig. 5a and b, with a similar shape to those previously reported [37][38][39]. Herein, the current was normalized using the metal mass to obtain the mass activity of PtTiMg alloy catalysts [40]. According to metal, mass normalized CV curves, the EOR peak potential at the PtTiMg alloy catalysts shifted positively ca. ...
Although nanostructures based on noble metal alloys are widely used in the anode catalysts of direct ethanol fuel cells, their commercialization remains a remarkable challenge due to their high cost and poor durability. We describe the successful synthesis of trimetallic PtTiMg alloy nanoparticles with adjustable composition using a simple one-step three-target magnetron co-sputtering method. Various physical characterization and electrochemical methods were used to investigate the structure/composition and electrochemical properties of the obtained PtTiMg alloy catalysts toward ethanol oxidation reaction (EOR). The PtTiMg alloy catalyst demonstrated excellent electrocatalytic activity and high durability when the Mg content was 2.76%, (after 3000 cycles, retained 91% of its electrochemical surface area). Furthermore, the electrochemically active surface area and peak current density of the PtTiMg alloy catalyst are 1.5 and 0.8 times higher than those of the commercial pure Pt catalyst, respectively. Furthermore, the long-term strong acid immersion test demonstrated that the PtTiMg alloy catalysts retain high electrocatalytic activity in harsh environments, demonstrating the potential application of the obtained PtTiMg alloy catalysts for EOR.
... Similarly, the tensile Pt shell in the Au@Pt and Ag@Pt electrocatalysts exhibited satisfied MOR performance. [46,222,223] When the metal in the shell is changed to a PtNi alloy, the tensile strain effect appears. An Au core thus further facilitates the MOR activity of the PtNi electrocatalysts. ...
Strain engineering of nanomaterials, namely, designing, tuning, or controlling surface strains of nanomaterials is an effective strategy to achieve outstanding performance in different nanomaterials for their various applications. This article summarizes recent progress and achievements in the development of strain‐rich electrocatalysts (SREs) and their applications in the field of electrochemical energy conversion technologies. It starts from the definition of lattice strains, followed by the classification of lattice strains where the mechanisms of strain formation and the reported methods to regulate related strains are elaborated. The SRE characterization techniques are overviewed, focusing deeply on the clarification of the strain‐property relationship of these SREs. Their applications for different electrocatalytic reactions are further highlighted, including the hydrogen evolution reaction, oxygen reduction reaction, oxygen evolution reaction, alcohol oxidation reaction, electrochemical carbon dioxide reduction reaction, and nitrogen reduction reaction. Related reaction mechanisms of the SREs are interpreted after taking catalytic performance, as well as the relationship between the SRE properties and their strains into account. The challenges and future opportunities to regulate SREs are finally outlined and discussed together with their potential applications in different fields.
... The area of weak polyelectrolyte-based multilayers was previously focused mainly on the linear growth of all-weak-polyelectrolyte multilayers [23,24,43]. More recently, however, LbL assembly of weak polyelectrolytes and other components including strong polyelectrolytes [44,45], neutral polymers [9,46] and NPs [47,48] has been investigated. These multilayers can inherit the advantages of weak polyelectrolytes as well as incorporate unique characteristics of the other components; therefore, they may have novel structures, properties and applications [9,32,47,49]. ...
... Weak polyelectrolyte-based multilayers have the great ability to introduce and tailor nanostructures on various substrates, and thus are highly promising for energy conversion and storage. We have assembled PEI/Au NP multilayers on pristine graphene with uniformly distributed Au NPs by controlling the assembly pH of PEI [48]. Pt nanodendrites have been subsequently grown on Au NPs with controlled loading to form Au@Pt nanodendrites on the graphene substrate ( Fig. 17A1-C3). ...
... The current density for the MOR shows an initial rapid decay mainly due to the poisoning of CO or CO-like intermediates and remains almost unchanged after 1800 s (Fig. 17E and inset); the steady-state mass-specific current density for the MOR on G@(PEI/Au NP) 3.5 @Pt is 0.009 A mg −1 based on Pt, which is 4.5 times higher than those on commercial Pt/C (0.002 A mg −1 ) (Fig. 17E and inset). This performance is also among the highest reported for other state-of-the-art commercial Pt/C and PtRu/C as well as for Pt and PtRu catalysts on non-covalently polyelectrolytefunctionalized carbon [48]. ...
... Self-assembly is a facile, economical, and scalable approach for fabrication of various nanostructures on solid substrates [5,29,33]. Polymer-mediated self-assembly is particularly versatile since it can be applied on various substrates with complex geometries and specifically chosen polymers can strongly interact with the substrates for high-density assembly and efficiently stabilize precursors/products to form small and well-dispersed NPs [4,5,34]. In this work, ultra-small, highly dispersed, and high-density cobalt oxide (CoO x ) NPs were directly grown on TiO 2 NWAs via the polymer-mediated self-assembly strategy. ...
... 38,39 Graphene oxide (GO)/strongly oxidized graphene could serve as the support due to its relatively rich functional groups, but it would compromise the performance even after complicated reduction processes using strong reductants since the electronic stucture has been damaged irreversibly leading to 2−3 orders of magnitude lower electronic conductivity of chemically reduced GO than that of pristine graphene. 36,37 In addition, there are not enough surface functional groups on GO for the in situ assembly of NiFe alloy NPs since strong reductants conventionally used for the reduction will make the nucleation so fast that they easily grow in solution rather than on the support. 30,40 To date, it remains elusive to fabricate pristine graphene supported small and well-dispersed NiFe alloy NPs, and it is even more challenging to controllably assemble these NPs on the pristine graphene. ...
... It is noteworthy that the growth of other nanostructures such as Au@Pt core−shell nanodendrites and MnO 2 nanowires on pristine graphene has been reported. 7,37 Tannic acid (TA) is a naturally occurring polyphenol with high-density galloyl groups, and it possesses a high affinity to essentially all substrates via a combination of electrostatic interactions, hydrophobic interactions, hydrogen bonding, and π−π stacking, and a strong capability to coordinate with various metal ions and reduce them. 41−43 Therefore, this molecule could not only interact with pristine graphene via the hydrophobic and π−π interactions to introduce rich functional groups on its surface while maintaining its chemical and electronic structures but also act as a linker to bind with Ni 2+ and Fe 2+ for the in situ controlled growth of small and dispersed NiFe-based NPs; additionally, it could serve as a strong reductant for the in situ reduction of NiFe-based compounds into NiFe alloys. ...
... It is noteworthy that the pristine graphene has been characterized in our previous studies. 37 Figure 2 displays FESEM, TEM, and HRTEM images of G@Ni 9 Fe. The FESEM result shows that the morphology of the sample does not change significantly after calcination, and therefore, only the images of the sample after calcination are shown in Figure 2 (see Figure S3 for the FESEM image of the sample before calcination). ...
... Tsang et al. reported that Pd loaded graphene aerogel deposited on nickel foam exhibited satisfactory performance in methanol electrooxidation in alkaline media [25]. Yuan et al. reported that well-dispersed Au@Pt bimetallic nanodendrites supported on graphene demonstrated greatly enhanced electrocatalytic activity and durability toward methanol oxidation in DMFCs [26]. However, these previous works did not get rid of the negative effects caused by the aggregation of chemically reduced graphite oxide (rGO) sheets [27e29]. ...
Palladium (Pd) nanoparticles (NPs) prepared by gas phase cluster deposition demonstrated excellent electrocatalytic activity. Herein, a series of Pd NPs modified freestanding electrodes with a super clean surface and easy repeating process for methanol oxidation reaction is reported. Pd NPs with different coverage were deposited on Ni foams and three-dimensional graphene-Ni foams, respectively. Owning to the special three-dimensional structure of Ni foam, the Pd NPs-Ni foam composite exhibited remarkable activity and unusually long-term stability for methanol electro-oxidation. The introduced three-dimensional graphene prepared by conventional chemical vapour deposition improved the electrocatalytic performance. The results can be attributed to the Pd NPs with high electrochemical activity and unique properties for three-dimensional supports.
