Carbon supported chemically ordered nanoparicles with stable Pt shell and their superior catalysis toward the oxygen reduction reaction

L10-PtCo and L12-Pt3Co Intermetallics for Oxygen Reduction Reaction: The Influence of Composition and Structure on Properties

Pt-based intermetallics are regarded as highly efficient electrocatalysts for oxygen reduction reaction (ORR). However, Pt-based intermetallics with different Pt: M atomic ratios have different atomic arrangements and crystal structures, which will change the electronic structure and coordination environment of Pt, thus affecting the electrocatalytic activity. In this work, we prepared L12-Pt3Co and L10-PtCo intermetallic catalysts by modulating the molar ratio of Pt and Co precursors using a thermal annealing method. The mass activity (MA) of L10-PtCo is 0.52 A mg-1 Pt at 0.9 V, which is 1.44 times larger than that of L12-Pt3Co (0.36 A mg-1 Pt). In addition, the MA of L10-PtCo decreases by 17.31 % after 10,000 CV cycles, which is smaller than that of L12-Pt3Co (25.00 % loss in MA), showing excellent structural stability. Theoretical calculations reveal that compared to L12-Pt3Co, L10-PtCo has more electrons transferred to the Pt sites, which further optimizes the electronic structure of Pt and reduces the d-band center, leading to the increase of the electrocatalytic performance. This work provides new insights into the study of Pt-based intermetallics with different Pt: M ratios, which is helpful for the screening and preparation of high-performance Pt-based intermetallics.

Pt3(CoNi) Ternary Intermetallic Nanoparticles Immobilized on N-Doped Carbon Derived from Zeolitic Imidazolate Frameworks for Oxygen Reduction

Pt-based intermetallic compound (IMC) nanoparticles have been considered the most promising catalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC). Herein, we propose a strategy for producing ordered Pt3(CoNi) ternary IMC nanoparticles supported on N-doped carbon materials. Particularly, the Co and Ni are originally embedded into ZIF-derived carbon, which diffuse into Pt nanocrystals to form Pt3(CoNi) nanoparticles. Moreover, a thin layer of carbon develops outside of Pt3(CoNi) nanoparticles during the cooling process, which contributes to stabilizing the Pt3(CoNi) on carbon supports. The optimal Pt3(CoNi) nanoparticle catalyst has achieved significantly enhanced activity and stability, exhibiting a half-wave potential of 0.885 V vs reversible hydrogen electrode (RHE) and losing only 16 mV after 10,000 potential cycles between 0.6 and 1.0 V. Unlike the direct-use commercial carbon (VXC-72) for depositing Pt, we utilized ZIF-derived carbon containing dispersed Co and Ni nanocluster or nanoparticles to prepare ordered Pt3(CoNi) intermetallic catalysts.

Gram-Scale Synthesis of CoO/C as Base for PtCo/C High-Performance Catalysts for the Oxygen Reduction Reaction

The composition, structure, catalytic activity in the ORR and stability of PtCo/C materials, obtained in two stages and compared with commercial Pt/C analogs, were studied. At the first stage of the synthesis performed by electrodeposition of cobalt on a carbon support, a CoOx/C composite containing 8% and 25 wt% cobalt oxide was successfully obtained. In the second step, PtCoOx/C catalysts of Pt1.56Co and Pt1.12Co composition containing 14 and 30 wt% Pt, respectively, were synthesized based on the previously obtained composites. According to the results of the composition and structure analysis of the obtained PtCoOx/C catalysts by X-ray diffraction (XRD), X-ray fluorescence analysis (XRF), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) methods, the formation of small bimetallic nanoparticles on the carbon support surface has been proved. The resulting catalysts demonstrated up to two times higher specific catalytic activity in the ORR and high stability compared to commercial Pt/C analogs.

Subsize Pt-based intermetallic compound enables long-term cyclic mass activity for fuel-cell oxygen reduction

Pt-based alloy catalysts may promise considerable mass activity (MA) for oxygen reduction but are generally unsustainable over long-term cycles, particularly in practical proton exchange membrane fuel cells (PEMFCs). Herein, we report a series of Pt-based intermetallic compounds (Pt₃Co, PtCo, and Pt₃Ti) enclosed by ultrathin Pt skin with an average particle size down to about 2.3 nm, which deliver outstanding cyclic MA and durability for oxygen reduction. By breaking size limitation during ordered atomic transformation in Pt alloy systems, the MA and durability of subsize Pt-based intermetallic compounds can be simultaneously optimized. The subsize scale was also found to enhance the stability of the membrane electrode through preventing the poisoning of catalysts by ionomers in humid fuel-cell conditions. We anticipate that subsize Pt-based intermetallic compounds set a good example for the rational design of high-performance oxygen reduction electrocatalysts for PEMFCs. Furthermore, the prevention of ionomer poisoning was identified as the critical parameter for assembling robust commercial membrane electrodes in PEMFCs.

Pt-Based Intermetallic Nanocrystals in Cathode Catalysts for Proton Exchange Membrane Fuel Cells: From Precise Synthesis to Oxygen Reduction Reaction Strategy

Although oxygen reduction reaction (ORR) catalysts have been extensively investigated and developed, there is a lack of clarity on catalysts that can balance high performance and low cost. Pt-based intermetallic nanocrystals are of special interest in the commercialization of proton exchange membrane fuel cells (PEMFCs) due to their excellent ORR activity and stability. This review summarizes the wide range of applications of Pt-based intermetallic nanocrystals in cathode catalysts for PEMFCs and their unique advantages in the field of ORR. Firstly, we introduce the fundamental understanding of Pt-based intermetallic nanocrystals, and highlight the difficulties and countermeasures in their synthesis. Then, the progress of theoretical and experimental studies related to the ORR activity and stability of Pt-based intermetallic nanocrystals in recent years are reviewed, especially the integrated strategies for enhancing the stability of ORR. Finally, the challenges faced by Pt-based intermetallic nanocrystals are summarized and future research directions are proposed. In addition, numerous design ideas of Pt-based intermetallic nanocrystals as ORR catalysts are summarized, aiming to promote further development of commercialization of PEMFC catalysts while fully understanding Pt-based intermetallic nanocrystals.

Synthesis of catalysts with fine platinum particles supported by high-surface-area activated carbons and optimization of their catalytic activities for polymer electrolyte fuel cells

Herein, we demonstrated that carbon-supported platinum (Pt/C) is a low-cost and high-performance electrocatalyst for polymer electrolyte fuel cells (PEFCs). The ethanol reduction method was used to prepare the Pt/C catalyst, which was realized by an effective matching of the carbon support and optimization of the Pt content for preparing a membrane electrode assembly (MEA). For this, the synthesis of Pt/C catalysts with different Pt loadings was performed on two different carbons (KB1600 and KB800) as new support materials. Analysis of the XRD pattern and TEM images showed that the Pt nanoparticles (NPs) with an average diameter of ca. 1.5 nm were uniformly dispersed on the carbon surface. To further confirm the size of the NPs, the coordination numbers of Pt derived from X-ray absorption fine structure (XAFS) data were used. These results suggest that the NP size is almost identical, irrespective of Pt loading. Nitrogen adsorption-desorption analysis indicated the presence of mesopores in each carbon. The BET surface area was found to increase with increasing Pt loading, and the value of the BET surface area was as high as 1286 m2 gcarbon -1. However, after 40 wt% Pt loading on both carbons, the BET surface area was decreased due to pore blockage by Pt NPs. The oxidation reduction reaction (ORR) activity for Pt/KB1600, Pt/KB800 and commercial Pt/C was evaluated by Koutecky-Levich (K-L) analysis, and the results showed first-order kinetics with ORR. The favourable surface properties of carbon produced Pt NPs with increased density, uniformity and small size, which led to a higher electrochemical surface area (ECSA). The ECSA value of the 35 wt% Pt/KB1600 catalyst was 155.0 m2 gpt -1 higher than that of the Pt/KB800 and commercial Pt/C (36.7 wt%) catalysts. A Higher ECSA indicates more available active sites for catalyst particles. The single cell test with MEA revealed that the cell voltage in the high current density regions depends on the BET surface area, and the durability of the 35 wt% Pt/KB1600 catalyst was superior to that of the 30 wt% Pt/KB800 and commercial Pt/C (46.2 wt%) catalysts. This suggests that an optimal ratio of Pt to Pt/KB1600 catalyst provides adequate reaction sites and mass transport, which is crucial to the PEFC's high performance.

High-Loading Pt-Co/C Catalyst with Enhanced Durability toward the Oxygen Reduction Reaction through Surface Au Modification

Carbon-supported Pt-Co (Pt-Co/C) nanoparticles with a high Pt loading are regarded as promising cathode catalysts for practical applications of proton exchange membrane fuel cells (PEMFCs). Unfortunately, with high loading, it is difficult to improve the catalytic durability while maintaining the particle size between 2 and 5 nm to ensure the initial catalytic activity. Thus, it is of great significance to prepare high-loading Pt-Co/C catalysts with enhanced activity and durability. Herein, we proposed an efficient way to prepare high-Pt-loading (>50 wt %) Pt-Co/C catalysts without using any further surfactants. Furthermore, due to the one-step selective acid etching and surface Au modification, the as-prepared catalysts only need to undergo thermal treatment at as low as 150 °C to achieve a surface structure rich of Pt and Au. The average particle size of the as-prepared Au-Pt-Co/C-0.015 is 3.42 nm, and the Pt loading of it is up to 50.2 wt %. The atomic ratio of Pt, Co, and Au is 94:5:1. The mass activity (MA) is nearly 1.9 times that of Pt/C (60 wt %, JM) and the specific activity is also improved. The MA loss after the 30,000-cycle accelerated degradation test (ADT) is only 9.4%. The remarkable durability is mainly due to the surface Au modification, which can restrict the dissolution of Pt and Co. This research provides an effective synthesis strategy to prepare high-loading carbon-supported Pt-based catalysts beneficial to practical PEMFC applications.

Interface-tuned Mo-based nanospheres for efficient oxygen reduction and hydrogen evolution catalysis

Developing earth-abundant materials for efficient oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) catalysis in both alkaline and acidic media is of significance for hydrogen fuel cell application.

Alloy Nanocatalysts for the Electrochemical Oxygen Reduction (ORR) and the Direct Electrochemical Carbon Dioxide Reduction Reaction (CO2 RR)

In the face of the global energy challenge and progressing global climate change, renewable energy systems and components, such as fuel cells and electrolyzers, which close the energetic oxygen and carbon cycles, have become a technology development priority. The electrochemical oxygen reduction reaction (ORR) and the direct electrochemical carbon dioxide reduction reaction (CO₂ RR) are important electrocatalytic processes that proceed at gas diffusion electrodes of hydrogen fuel cells and CO₂ electrolyzers, respectively. However, their low catalytic activity (voltage efficiency), limited long-term stability, and moderate product selectivity (related to their Faradaic efficiency) have remained challenges. To address these, suitable catalysts are required. This review addresses the current state of research on Pt-based and Cu-based nanoalloy electrocatalysts for ORR and CO₂ RR, respectively, and critically compares and contrasts key performance parameters such as activity, selectivity, and durability. In particular, Pt nanoparticles alloyed with transition metals, post-transition metals and lanthanides, are discussed, as well as the material characterization and their performance for the ORR. Then, bimetallic Cu nanoalloy catalysts are reviewed and organized according to their main reaction product generated by the second metal. This review concludes with a perspective on nanoalloy catalysts for the ORR and the CO₂ RR, and proposes future research directions.

Ordered Pt3Co Intermetallic Nanoparticles Derived from Metal-Organic Frameworks for Oxygen Reduction

Highly ordered Pt alloy structures are proven effective to improve their catalytic activity and stability for the oxygen reduction reaction (ORR) for proton exchange membrane fuel cells. Here, we report a new approach to preparing ordered Pt₃Co intermetallic nanoparticles through a facile thermal treatment of Pt nanoparticles supported on Co-doped metal-organic-framework (MOF)-derived carbon. In particular, the atomically dispersed Co sites, which are originally embedded into MOF-derived carbon, diffuse into Pt nanocrystals and form ordered Pt₃Co structures. It is very crucial for the formation of the ordered Pt₃Co to carefully control the doping content of Co into the MOFs and the heating temperatures for Co diffusion. The optimal Pt₃Co nanoparticle catalyst has achieved significantly enhanced activity and stability, exhibiting a half-wave potential up to 0.92 V vs reversible hydrogen electrode (RHE) and only losing 12 mV after 30 000 potential cycling between 0.6 and 1.0 V. The highly ordered intermetallic structure was retained after the accelerated stress tests made evident by atomic-scale elemental mapping. Fuel cell tests further verified the high intrinsic activity of the ordered Pt₃Co catalysts. Unlike the direct use of MOF-derived carbon supports for depositing Pt, we utilized MOF-derived carbon containing atomically dispersed Co sites as Co sources to prepare ordered Pt₃Co intermetallic catalysts. The new synthesis approach provides an effective strategy to develop active and stable Pt alloy catalysts by leveraging the unique properties of MOFs such as 3D structures, high surface areas, and controlled nitrogen and transition metal dopings.

Scalable Preparation of the Chemically Ordered Pt-Fe-Au Nanocatalysts with High Catalytic Reactivity and Stability for Oxygen Reduction Reactions

Carbon-supported Au-Pt _xFe _y nanoparticles were synthesized via microwave heating polyol process, followed by annealing for the formation of the ordered structure. The structure characterizations indicate that Au is alloyed with intermetallic Pt-Fe nanoparticles and therefore the surface electronic properties are tuned. The electrochemical tests show that the microwave heating polyol process is more effective than oil bath heating polyol process for synthesizing the highly active catalysts. The introduction of trace Au (0.2 wt % Au) significantly improves the oxygen reduction reaction (ORR) catalytic activity of Pt _xFe _y catalysts. Au-PtFe/C-H (0.66 A/mg_Pt) and Au-PtFe₃/C-H (0.63 A/mg_Pt) prepared in a batch of 10.0 g show significantly improved catalytic activities than their counterparts (PtFe/C-H and PtFe₃/C-H) as well as commercial Johnson Matthey Pt/C (0.17 A/mg_Pt). In addition, the as-prepared Au-PtFe/C-H and Au-PtFe₃/C-H display highly enhanced stability toward the ORR compared to the commercial Pt/C. The superior catalytic performance is attributed to the synergistic effect of chemically ordered intermetallic structure and Au. This work provides a scalable synthesis of the multimetallic chemically ordered Au-Pt _xFe _y catalysts with high ORR catalytic performance in acidic condition.