CoPt Alloy Research Articles

Hydrogen Adsorption on Ordered and Disordered Pt-Fe and Pt-Co Alloys.

The bulk properties and surface chemical reactivity of compositionally disordered Pt-Fe and Pt-Co alloys in the fcc A1 phase have been investigated theoretically in comparison to the ordered alloys of the same compositions. The results are analyzed together with our previously reported findings for Pt-Ni. Nonlinear variation is observed in lattice constant, d band center, magnetic moment, and hydrogen adsorption energy across the composition range (0-100 atomic % of Pt, x Pt). The Pt 5d states are strongly perturbed by the 3d states of the base metals, leading to notable density of states above the Fermi level and residual magnetic moments at high x Pt. Surface reactivity in terms of average H adsorption energy varies continuously with composition between the monometallic Fe-Pt and Co-Pt limits, going through a maximum around x Pt = 0.5-0.75. Close inspection reveals a significant variation in site reactivity at x Pt < 0.75, particularly with disordered Pt-Fe alloys due in part to the inherent disparity in chemical reactivity between Fe and Pt. Furthermore, the strong interaction between Fe and Pt causes Pt-rich sites to be less reactive toward H than Pt-rich sites on disordered Pt-Ni alloy surfaces, despite less compressive strain caused. These results provide theoretical underpinnings for conceptualizing and understanding the performance of these Pt-base metal alloys in key catalytic applications and for efforts to tailor Pt-alloys as catalysts.

Magneto-optical properties of superparamagnetic CoPt alloy nanoparticles in the UV–visible range

Superparamagnetic CoPt alloy nanoparticles were synthesized via a wet chemical method and exhibited intense magnetic circular dichroism (MCD) in the UV–visible range. The dissymmetry factor of MCD, gMCD, for the CoPt nanoparticles was 0.034 at room temperature in a magnetic field of ±1.6 T. The MCD responses may be due to plasmonic circular currents generated in the metallic CoPt nanoparticles by circularly polarized light. The responses were higher than those of the Co nanoparticles, likely due to the chemical stability and spin–orbit coupling.

PtCo-ZIF-derived hybrid electrocatalysts comprising an ordered PtCo alloy and a single-atoms-decorated carbon shell for the oxygen reduction reaction

Recent research on hybrid catalysts showed that Pt-based alloy particles surrounded by a single-atoms-decorated carbon shell exhibit promising oxygen reduction reaction catalytic activity and durability owing to the synergistic effect. However, the structural complexity of these hybrid catalysts renders their synthesis challenging. This study synthesized a mixed-metal zeolitic imidazolate framework (ZIF) containing Pt and Co ions coordinated with a benzimidazole ligand, which was used as a scaffold to fabricate hybrid catalysts comprising uniform PtCo intermetallic alloy particles coated with a thin N-doped carbon shell containing numerous Pt and Co single atoms via one-step annealing. Without post-treatment, the mass and specific activities of the synthesized catalyst were significantly higher than those of the commercial Pt/C catalyst. Additionally, the synthesized catalyst exhibited ultra-long-term durability, meeting the 2025 target of the U.S. Department of Energy, even after 300 000 cycles of an accelerated durability test.

Optimized porous nanostructure of carbon fibers enabling excellent stability of Pt-based catalysts for oxygen reduction reaction

Facile synthesis of highly-dispersed Pt-based electrocatalysts on porous carbon supports with strong durability is extremely desirable for oxygen reduction reaction but remains challenging. The influence of pores in carbon supports on the stability and activity of catalysts is ambiguous and needs to be elucidated. Targeting this aim, herein, we prepared a series of carbon nanofibers with tunable pore diameter and specific surface area using the resorcinol-formaldehyde (RF) resins as a model system. Homogeneous composite precursors composed of RF resins and silica colloids were synthesized by the surfactant-assisted simultaneous polycondensation of RF resins and tetraethylorthosilicate (TEOS). The diameter of the pores induced by removal of silica could be controllable tailored through thermal treatment of the composite under various target temperatures. Pt3Co alloy nanoparticles loaded on the as-synthesized porous carbon nanofibers were prepared by an optimized wet-impregnation method. The experimental results indicated that the carbon nanofibers with pore size distribution focused on ∼1.27 nm and ∼2.34 nm provided the best stability without limiting current density decay, and negative shift of half-wave potential (E1/2) and mass activity (MA) loss of Pt after 20000 potential cycles are relatively mild. Conversely, negative shift of 21 mV, 15 mV and 22 mV in E1/2 and mass activity loss of 51.8%, 30.2% and 33.0% were observed for the Pt3Co nanoparticles supported on MC-60, MC-100 and MC-140 matrices which have pore size distribution focused on ∼2.73 nm, ∼2.73 nm as well as ∼4.66 nm, and ∼4.66 nm, respectively. This work demonstrates the importance of micropores and small mesopores for activity and long-term stability enhancement of carbon supported Pt-based electrocatalysts.

Strategies for Achieving Ultra‐Long ORR Durability—Rh Activates Interatomic Interactions in Alloys

AbstractThe stability of platinum‐based alloy catalysts is crucial for the future development of proton exchange membrane fuel cells, considering the potential dissolution of transition metals under complex operating conditions. Here, we report on a Rh‐doped Pt3Co alloy that exhibits strong interatomic interactions, thereby enhancing the durability of fuel cells. The Rh−Pt3Co/C catalyst demonstrates exceptional catalytic activity for oxygen reduction reactions (ORR) (1.31 A mgPt−1 at 0.9 V vs. the reversible hydrogen electrode (RHE) and maintaining 92 % of its mass activity after 170,000 potential cycles). Long‐term testing has shown direct inhibition of Co dissolution in Rh−Pt3Co/C. Furthermore, tests on proton exchange membrane fuel cells (PEMFC) have shown excellent performance and long‐term durability with low Pt loading. After 50,000 cycles, there was no voltage loss at 0.8 A cm−2 for Rh−Pt3Co/C, while Pt3Co/C experienced a loss of 200 mV. Theoretical calculations suggest that introducing transition metal atoms through doping creates a stronger compressive strain, which in turn leads to increased catalytic activity. Additionally, Rh doping increases the energy barrier for Co diffusion in the bulk phase, while also raising the vacancy formation energy of the surface Pt. This ensures the long‐term stability of the alloy over the course of the cycle.

Strategies for Achieving Ultra-Long ORR Durability-Rh Activates Interatomic Interactions in Alloys.

The stability of platinum-based alloy catalysts is crucial for the future development of proton exchange membrane fuel cells, considering the potential dissolution of transition metals under complex operating conditions. Here, we report on a Rh-doped Pt3Co alloy that exhibits strong interatomic interactions, thereby enhancing the durability of fuel cells. The Rh-Pt3Co/C catalyst demonstrates exceptional catalytic activity for oxygen reduction reactions (ORR) (1.31 A mgPt -1 at 0.9 V vs. the reversible hydrogen electrode (RHE) and maintaining 92 % of its mass activity after 170,000 potential cycles). Long-term testing has shown direct inhibition of Co dissolution in Rh-Pt3Co/C. Furthermore, tests on proton exchange membrane fuel cells (PEMFC) have shown excellent performance and long-term durability with low Pt loading. After 50,000 cycles, there was no voltage loss at 0.8 A cm-2 for Rh-Pt3Co/C, while Pt3Co/C experienced a loss of 200 mV. Theoretical calculations suggest that introducing transition metal atoms through doping creates a stronger compressive strain, which in turn leads to increased catalytic activity. Additionally, Rh doping increases the energy barrier for Co diffusion in the bulk phase, while also raising the vacancy formation energy of the surface Pt. This ensures the long-term stability of the alloy over the course of the cycle.

Optimized Pt-Co Alloy Nanoparticles for Reverse Water-Gas Shift Activation of CO2.

Different Co contents were used to tune bimetallic Pt-Co nanoparticles with a diameter of 8 nm, resulting in Pt:Co ratios of 3.54, 1.51, and 0.96. These nanoparticles were then applied to the MCF-17 mesoporous silica support. The synthesized materials were characterized with HR-TEM, HAADF-TEM, EDX, XRD, BET, ICP-MS, in situ DRIFTS, and quasi in situ XPS techniques. The catalysts were tested in a thermally induced reverse water-gas shift reaction (CO2:H2 = 1:4) at atmospheric pressure in the 200-700 °C temperature range. All bimetallic Pt-Co particles outperformed the pure Pt benchmark catalyst. The nanoparticles with a Pt:Co ratio of 1.51 exhibited 2.6 times higher activity and increased CO selectivity by 4% at 500 °C. Experiments proved that the electron accumulation and alloying effect on the Pt-Co particles are stronger with higher Co ratios. The production of CO followed the formate reaction pathway on all catalysts due to the face-centered-cubic structure, which is similar to the Pt benchmark. It is concluded that the enhanced properties of Co culminate at a Pt:Co ratio of 1.51 because decreasing the ratio to 0.96 results in lower activity despite having more Co atoms available for the electronic interaction, resulting in the lack of electron-rich Pt sites.

P and O Co‐Doped Pt‐Co Octahedral Nanocrystals as Highly Active and Stable Electrocatalysts for Oxygen Reduction Reaction

The development of high active and stable Pt‐M (M = transition metals) electrocatalysts for oxygen reduction reaction (ORR) is crucial for the commercialization of proton exchange membrane fuel cells (PEMFCs). The main challenge of Pt‐M electrocatalysts is their instability, mainly due to the leaching of M. In this study, we report the design of P and O co‐doped octahedral PtCo alloy on Ketjen carbon black (Px‐Oct PtCo/C) through a seed‐mediated synthesis. In‐situ FTIR spectroscopy revealed that P0.61‐Oct PtCo/C has the lowest d‐band center, thereby enhancing the catalytic activity. The strong interaction formed by chemical bond between O and Co in Px‐Oct PtCo/C, observed by EXAFS spectra effectively inhibited the dissolution of Co and improved the ORR stability. The mass activity and specific activity of P0.61‐Oct PtCo/C can reach 0.61 A mgPt‐1 and 2.4 mA cm‐2, respectively, which is 4.1 times and 10.9 times higher than that of commercial Pt/C. After 50,000 potential cycles, the loss of mass activity is only 25%, surpassing the DOE 2025 target of less than 40% loss after 30,000 cycles. This study offers an alternative approach to enhancing the activity and durability of Pt‐M electrocatalysts for the ORR.

Numerical simulation for non-uniform PtCo catalyst degradation under different coolant conditions and its effect on PEMFC performance

Long-term non-uniform temperature, pressure and reaction rates distributions in the proton exchange membrane fuel cells (PEMFCs) may result in local catalyst degradation and deteriorate PEMFC performance. However, the problem of non-uniform catalyst degradation in PEMFC stacks is still incompletely understood due to the lacking of advanced experimental methods and three-dimensional (3D) catalyst aging models. In this study, a 3D PtCo alloy catalyst degradation model under voltage cycles is built and a 25 cm2 PEMFC stack containing realistic cathode, anode as well as coolant flow fields is used as the computational domain to analyze in detail the influence of non-uniform catalyst degradation on the performance of the PEMFC during different coolant conditions. The simulation results show that the non-uniform catalyst degradation is strongly dependent on the cathode flow field structure. It can alleviate non-uniform catalyst degradation as well as contribute to improving PEMFC performance when the coolant flow direction is the same as the air, and both coolant flow rate and inlet temperature also are found to significantly affect the local catalyst degradation behavior. Therefore, an optimally designed cathode flow fields structure as well as good water and heat management during operation can help to extend the service life of the PEMFC.

Engineering a High-Loading Sub-4 nm Intermetallic Platinum-Cobalt Alloy on Atomically Dispersed Cobalt-Nitrogen-Carbon for Efficient Oxygen Reduction in Fuel Cells.

Developing a high-performance membrane electrode assembly (MEA) poses a formidable challenge for fuel cells, which lies in achieving both high metal loading and efficient catalytic activity concurrently for MEA catalysts. Here, we introduce a porous Co@NC carrier to synthesize sub-4 nm PtCo intermetallic nanocrystals, achieving an impressive Pt loading of 27 wt %. The PtCo-CoNC catalyst demonstrates exceptional catalytic activity and remarkable stability for the oxygen reduction reaction. Advanced characterization techniques and theoretical calculations emphasize the synergistic effect between PtCo alloys and single Co atoms, which enhances the desorption of the OH* intermediate. Furthermore, the PtCo-CoNC-based cathode delivers a high power density of 1.22 W cm-2 in the MEA test owing to the enhanced mass transport, which is verified by the simulation results of the O2 distributions and current density inside the catalyst layer. This study lays the groundwork for the design of efficient catalysts with practical applications in fuel cells.

Morphology engineering of self-assembled bimetallic PtCo alloy nanofoams as efficient multifunctional electrocatalysts for oxygen reduction and alcohol oxidation

The exploration of high properties of electrocatalysts is imperative for the commercialization application of fuel cells. Enhancing the catalytic activity and stability of Pt-based catalysts can be achieved by rationally designing their morphology and composition. Here, we synthesized self-assembled PtCo alloy nanofoams (ANs) catalysts with controllable surface composition and porous network. The experimental results show that prepared PtxCo1-ANs catalysts display excellent electrochemical performance in oxygen reduction reaction (ORR), methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR). Interestingly, the mass activities of Pt2Co1-ANs with optimized surface composition for ORR, MOR, and EOR are 6.41, 6.64, and 7.71-fold higher than commercial Pt/C catalysts, respectively. Meantime, it also maintains high electrocatalytic durability in ORR, MOR, and EOR. Such results ascribe to the modified surface composition, optimized electronic structure, and porous interconnected nanofoam structure. These findings provide valuable insights into the design of highly active and durable multifunctional electrocatalysts with controllable shapes and composition.

Low-temperature diffusion in thin-film Pt-(Au-)-Co heterostructures: a structural and magnetic characterization

Formation of functional thin films for nanoelectronics and magnetic data storage via thermally induced diffusion-driven structural phase transformations in multilayer stacks is a promising technology-relevant approach. Ferromagnetic thin films based on Co Pt alloys are considered as a material science platform for the development of various applications such as spin valves, spin orbit torque devices, and high-density data storage media. Here, we study diffusion processes in Pt–Co-based stacks with the focus on the effect of layers inversion (Pt/Co/substrate versus Co/Pt/substrate) and insertion of an intermediate Au layer on the structural transitions and magnetic properties. We demonstrate that the layer stacking has a pronounced effect on the diffusion rate at temperatures, where the diffusion is dominated by grain boundaries. We quantify effective diffusion coefficients, which characterize the diffusion rate of Co and Pt through the interface and grain boundaries, providing the possibility to control the homogenization rate of the Pt–Co-based heterostructures. The obtained values are in the range of 10−16–10−13 cm2 s−1 for temperatures of 150 °C–350 °C. Heat treatment of the thin-film samples results in the coercivity enhancement, which is attributed to short-range chemical ordering effects. We show that introducing an additional Au intermediate layer leads to an increase of the coercive field of the annealed samples due to a modification of exchange coupling between the magnetic grains at the grain boundaries.

Ligand carbonization in-situ derived ultrathin carbon shells enable high-temperature confinement synthesis of PtCo alloy catalysts for high-efficiency fuel cells

High-temperature reduction technology significantly improves the alloying process but inevitably causes the sintering of metal. Herein, we report the high-temperature confinement synthesis of PtCo nanoparticles encapsulated with N-doped graphitic carbon shells (NGCS) in porous Ketjenblack (KB) carbon architectures (PtCo@NGCS/KB) for fuel cells via ligand carbonization strategy. The optimal PtCo@NGCS/KB-800 exhibits outstanding mass and specific activities (840.2 mA/mgPt and 0.94 mA/cm2, respectively) for oxygen reduction reaction (ORR), and possesses excellent stability with a smaller peak power density loss rate of 7.1 % than commercial benchmark Pt/C (23.7 %) after the accelerated durability test (ADT) in practical H2/air fuel cells. Experimental and theoretical investigations reveal that carbon shell reconstruction improves the accessibility of surface sites, and PtCo and NGCS synergically promote the enhancement of ORR performance. The NGCS encapsulation significantly reduces the energy level of the d-band center of Pt, promotes the desorption of intermediates, and lowers the reaction barrier for efficient ORR.

Magnetic Field Enhanced Oxygen Reduction Reaction via Oxygen Diffusion Speedup.

The mass-transfer of oxygen in liquid phases (including in the bulk electrolyte and near the electrode surface) is a critical step to deliver oxygen to catalyst sites (especially immersed catalyst sites) and use the full capacity of oxygen reduction reaction (ORR). Despite the extensive efforts of optimizing the complex three-phase reaction interfaces to enhance the gaseous oxygen transfer, strong limitations remain due to oxygen's poor solubility and slow diffusion in electrolytes. Herein, a magnetic method for boosting the directional hydrodynamic pumping of oxygen toward immersed catalyst sites is demonstrated which allows the ORR to reach otherwise inaccessible catalytic regions where high currents normally would have depleted oxygen. For Pt foil electrodes without forced oxygen saturation in KOH electrolytes, the mass-transfer-limited current densities can be improved by 60% under an external magnetic field of 435mT due to the synergistic effect between bulk- and surface-magnetohydrodynamic (MHD) flows induced by Lorentz forces. The residual magnetic fields are further used at the surface of magnetic materials (such as CoPt alloys and Pt/FeCo heterostructures) to enhance the surface-MHD effect, which helps to retain part of the ORR enhancement permanently without applying external magnetic fields.

Ultrafine PtCo alloy by pyrolysis etching-confined pyrolysis for enhanced hydrogen evolution

Zeolitic imidazolate framework-67 (ZIF-67) has been widely used as a precursor to developing efficient PtCo alloy catalysts for hydrogen evolution reaction (HER). However, traditional in-situ pyrolysis strategies involve complicated interface structure modulating processes between ZIF-67 and Pt precursors, challenging large-scale synthesis. Herein, a “pyrolysis etching-confined pyrolysis” approach is developed to design confined PtCo alloy in porous frameworks of onion carbon derived from ZIF-67. The confined PtCo alloy with Pt content of only 5.39 wt% exhibits a distinct HER activity in both acid (η10: 5 mV and Tafel: 9 mV dec−1) and basic (η10: 33 mV and Tafel: 51 mV dec−1) media and a drastic enhancement in stability. Density functional theory calculations reveal that the strong electronic interaction between Pt and Co allows favorable electron redistribution, which affords a favorable hydrogen spillover on PtCo alloy compared with that of pristine Pt(111). Operational electrochemical impedance spectroscopy demonstrates that the Faraday reaction process is facilitated under acidic conditions, while the transfer of intermediates through the electric double-layer region under alkaline conditions is accelerated. This work not only offers a universal route for high-performance Pt-based alloy catalysts with metal–organic framework (MOF) precursors but also provides experimental evidence for the role of the electric double layer in electrocatalysis reactions.

Ultrafine PtCo alloy nanoparticles integrated into porous N-doped nanosheets for durable oxygen reduction reaction.

Here, we propose a sub-3 nm small-size PtCo alloy catalyst integrated into a porous nitrogen-doped nanosheet through a space-confined and interfacial induction strategy. The designed PtCo-CoNC-P catalyst exhibits exceptional durability, with only a minimal 2 mV decline in half-wave potential after 30 000 cycles of accelerated durability tests.

Hollow PtCo alloy nanostructures for efficient oxygen reduction electrocatalysis in polymer electrolyte membrane fuel cells

The construction of hollow architecture in ∼5 nm PtCo core–shell nanostructures ensures an improved oxygen reduction electrocatalysis and minimizes electrochemical Co leaching, promoting its activity and durability in fuel cells.

Highly dispersed ultrafine PtCo alloy nanoparticles on unique composite carbon supports for proton exchange membrane fuel cells.

The design of highly efficient and robust platinum-based electrocatalysts is pivotal for proton exchange membrane fuel cells (PEMFC). One of the long-standing issues for PEMFC is the rapid deactivation of the catalyst under working conditions. Here, we report a simple synthesis strategy for ultrafine PtCo alloy nanoparticles loaded on a unique carbon support derived from a zeolitic imidazolate framework-67 (ZIF-67) and Ketjen Black (KB) composite, exhibiting a remarkable catalytic performance toward the oxygen reduction reaction (ORR) and PEMFC. Benefitting from the N-doping and wide pore size distribution of the composite carbon supports, the growth of PtCo nanoparticles can be evenly restricted, leading to a uniform distribution. The Pt-integrated catalyst delivers an outstanding electrochemical performance with a mass activity that is 8.6 times higher than that of the commercial Pt/C catalyst. Impressively, the accelerated durability test (ADT) demonstrates that the hybrid carbon support can significantly enhance the durability. Theoretical simulations highlight the synergistic contribution between the supports and the PtCo nanoparticles. Moreover, hydrogen-oxygen fuel cells assembled with the catalyst exhibited a high power density of 1.83 W cm-2 at 4 A cm-2. These results provide a new opportunity to design advanced catalysts for PEMFC.

Electronic Structure Effect of PtCo Alloy with Adjustable Compositions for Efficient Methanol Electrooxidation.

Various efficient strategies have been developed to overcome the anodic electrocatalyst issue of methanol-based fuel cells owing to their complicated methanol electrooxidation mechanism. In this work, PtCo nanoparticles with adjustable compositions supported on multiwalled carbon nanotubes (Pt1Cox/MWCNTs) through the adsorbing-coating-annealing-etching route were synthesized. Compared with the Pt/C catalyst, Pt1Co3/MWCNTs exhibit better electrocatalytic MOR activity in both activity and durability. Notably, the electrochemical mass and specific activity of the as-prepared catalyst are 1.04 mA μg-1Pt and 2.18 mA cm-2, respectively, which are higher than those of the Pt/C catalyst. Moreover, the as-prepared sample revealed lower onset potential during the CO stripping test. Furthermore, the Pt1Co3/MWCNTs possess a lower current density decrease rate in chronoamperometry and cyclic durability tests. The enhancement of activity and stability of Pt1Co3/MWCNTs could be ascribed to their ordered morphological structure, the electronic interaction between MWCNTs and PtCo nanoparticles, and the suitable electronic structure effect between Pt/Co ratios. The concept of the catalyst design in this study offers a different guideline for constructing the novel methanol electrooxidation catalyst, which will accelerate the widespread fuel cell practical application.

Improvement of the Electrocatalytic Properties for the Methanol Oxidation Reaction (MOR) of the CoPt Alloy

The commercialization of the Direct Methanol Fuel Cell (DMFC) is limited due to the high cost and low efficiency of the electrocatalysts. In this context, the development of new electrocatalysts able to efficiently oxidize the methanol and to have at the same time low price and high stability is one of the researcher’s milestones. In this work, CoPt alloys with different Pt content were prepared, and the efficiency of the alloys to be used as electrocatalysts for the methanol oxidation reaction (MOR) was investigated. Our data show that the electrocatalytic performance of the CoPt electrodeposited alloys is strongly influenced by the synthesis conditions, mainly by the potential applied during the synthesis. The best electrocatalytic activity was obtained for the samples prepared at −0.8 V/SCE.