CoPt Alloy Research Articles

Synaptic Modulation of Conductivity and Magnetism in a CoPt‐Based Electrochemical Transistor

Among various types of neuromorphic devices toward artificial intelligence, the electrochemical synaptic transistor emerges, in which the channel conductance is modulated by the insertion of ions according to the history of gate voltage across the electrolyte. Despite the striking progress in exploring novel channel materials, few studies report on the ferromagnetic metal‐based synaptic transistors, limiting the development of spin‐based neuromorphic devices. Herein, synaptic modulation of both conductivity and magnetism based on an electrochemical transistor with a metallic channel of ferromagnetic CoPt alloy is presented. Its essential synaptic functionalities in the transistor are demonstrated, including depression and potentiation of synaptic weight and paired‐pulse facilitation (PPF). Then, short‐to‐long‐term plasticity transition induced by different gate parameters, such as amplitude, duration, and frequency, is shown. Furthermore, the device presents multilevel and reversible nonvolatile states in both conductivity and coercivity. The results demonstrate simultaneous modulation of conductivity and magnetism, paving the way for building future spin‐based multifunctional synaptic devices.

Exploring the Function of Nitrogen-Doped Carbon Shell on Ordered and Disordered PtCo Alloy Catalysts in Oxygen Reduction Reaction By X-Ray Absorption Spectroscopy

The development of proton exchange membrane fuel cells (PEMFCs) has received increasing attention for its potential to get rid of dependence on fossil fuels and curb carbon emissions[1]. However, the application of PEMFC has been limited by the consumption of platinum due to the sluggish kinetics of the cathode reaction and limiting platinum reserves. So far, forming Pt-M (M = non-precious metal) alloying phase catalysts has been regarded as an efficient method to improve the activity and decrease the cost of platinum. However, the introduction of the non-precious metal content will decrease the stability of the catalysts by accelerating the dissolution of metal atoms and agglomeration of the nanoparticles[2]. In this research, the nitrogen-doped carbon coating structure was applied to protect the PtCo nanoparticles. And both ordered (I-PtCo@CNx) and disordered (D-PtCo@CNx) PtCo alloy phase core was synthesized to further explore the role of nitrogen-doped carbon shell in improving the activity and stability. To study the electronic statement and structure changes of the catalysts, both in-situ and ex-situ X-ray absorption spectroscopy (XAS) was applied at BL36XU at SPring-8.The synthesis of order PtCo catalysts, generally, requires a high temperature to overcome the energy barrier of forming the ordering phase, which will cause severe Ostwald ripening and get larger nanoparticles[3]. However, in the participation of nitrogen-doped carbon shells, the particle size could be limited to less than 5 nm. The I-PtCo@CNx exhibited high mass activity and specific activity at 1.08 A mgPt -1 and 1.51 mA cmPt -2, respectively. The XAS and X-ray photoelectron spectroscopy (XPS) analysis showed the decreased electronic density on the I-PtCo@CNx compared with I-PtCo catalysts, which suggested the increase of the activity might be originated from the interaction from the nitrogen-doped carbon shell. Furthermore, the accelerate durability tests (ADTs) were applied to measure the stability of the catalysts. In the rotating disk electrode and fuel cell condition, after 30,000 cycles ADTs, the activity of I-PtCo@CNx showed less decrease compared with other samples. The EXAFS analysis confirmed the high stability of I-PtCo@CNx might come from the less oxygen species generation during the ADTs, especially for the Co, and the confined structure benefits to maintaining the structure. In addition, the operando XAS analysis of the membrane electrode assemblies (MEA) samples also showed the high stability of I-PtCo@CNx after polarization at 1.1 V for 1 h. Figure 1. The Pt L3 edge and Co K edge FT-EXAFS spectra of disordered-PtCo, ordered-PtCo, and ordered-PtCo@CNx in different ADTs cycles at 80 °C in MEA operation condition. Acknowledgement This work was supported by the project (JPNP20003) and a NEDO FC-Platform project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). And China Scholarship Council (CSC) was acknowledged for the doctoral scholarship of Yunfei Gao (202006270046). Reference s : [1] Zhao L.; Zhu J.; Zheng Y.; Xiao M.; Gao R.; Zhang Z.; et al. Adv. Energy Mater. 2022, 12, 2102665.[2] Sun Y.; Polani S.; Luo F.; Ott S.; Strasser P.; Dionigi F. Nat. Commun. 2021, 12 (1), 5984.[3] Yang C.; Wang L.; Yin P.; Liu J.; Chen M.; Yan Q.; et al. Science 2021, 374 (6566), 459-64. Figure 1

Improvements in Oxygen Diffusivity, ORR Activity and Durability of Pt-Based Catalysts By Mesoporous Carbon Support and Melamine Decoration

1. Introduction In Japan, an extremely high I-V performance is required for polymer electrolyte fuel cells (PEFCs) used in fuel cell electric vehicles after 2030 (red line in Figure 1) [1]. Therefore, we have to design Pt-based catalysts that have a high ORR activity and a durability as well as a high oxygen diffusivity [2]. In this study, the Pt-based catalysts were supported on a mesoporous carbon to increase oxygen diffusivity and the catalysts were decorated with melamine to improve ORR activity and durability [3, 4]. 2. Experimental Ketjen Black EC-300J (KB-300J: SBET: 922 m2/g, LION), Ketjen Black EC-600JD (KB-600JD: SBET: 1,345 m2/g, LION) and a mesoporous carbon (CNovel MH-18, SBET 1,334 m2/g, TOYO TANSO [5]) were used as carbon supports in the synthesis of PtCo alloy and Pd@Pt core-shell catalysts. A commercially available Pt/KB-300J catalyst (TEC10E50E, Pt size: 2.5 nm, Pt metal loading: 46.3 wt.%, TKK) was used as a reference catalyst. The PtCo alloy catalyst was synthesized by an oleylamine reduction method [6] and the Pd@Pt core-shell catalyst was synthesized by a direct displacement reaction method [7]. The metal loadings of Pt and Co in the alloy catalysts were 41 wt.% and 3 wt.%, respectively, and those of Pt and Pd in the Pd@Pt core-shell catalyst were 20 wt.% and 30 wt.%, respectively. The particle sizes of the PtCo alloy and the Pd@Pt core-shell catalyst NPs were 3.0 nm and 5.5 nm, respectively. CV of the catalyst was recorded at 25oC in Ar-saturated 0.1 M HClO4 with a potential scan rate of 50 mV/s and LSV was measured by RDE method at 25oC in O2-saturated 0.1 M HClO4 with a potential scan rate of 10 mV/s at a rotation speed of 1,600 rpm. An accelerated durability test (ADT) of the catalysts was conducted by a square wave potential cycling of 0.6 V (3 s)-1.0 V (3 s) vs. RHE performed in Ar-saturated 0.1 M HClO4 at 80oC for 10,000 cycles with and without melamine addition (10 µM to the electrolyte). MEA was fabricated by a decal method using a reinforced membrane (12 µm in thickness, Gore) and a GDL (TORAY). Nafion® DE2020 was used as an ionomer for the catalyst ink preparation (I/C: 0.83). I-V performance of a single cell was evaluated at 80oC, 75% RH by using the MEA with an active area of 1 cm2 in which the Pt loading in the cathode catalyst layer was set to 0.1 mg-PGM/cm2. H2 gas (418 NmL) and air (998 NmL) were supplied to the anode and the cathode, respectively, and the H2 gas was pressurized to 150 kPa at the gas-outlet (H2 utilization: 5% at a current density of 3.0 A/cm2). 3. Results and Discussion Pore size distribution of the carbon supports is summarized in Figure 2. KB-300J has no clear mesopores, while KB-600JD and CNovel MH-18 have the mesopores. Figure 1 shows I-V performance of Pd@Pt core-shell catalysts, indicating that Pt/Pd/CNovel MH-18 catalyst exhibits a superior cell performance to that of Pt/Pd/KB-600JD catalyst. Connectivity of mesopores in KB-600JD and CNovel MH-18 supports analyzed by 3D-TEM is shown in Figure 3. It is clear that the connectivity in CNovel MH-18 support is much higher than that in KB-600JD support, which is considered to contribute to the superior I-V performance of Pt/Pd/CNovel MH-18 catalyst observed in Figure 1.Figures 4 depicts morphological change of PtCo/CNovel MH-18 alloy catalyst by ADT performed at 80oC for 10,000 cycles. A very small amount of melamine addition to the electrolyte (10 µM) notably suppressed the catalyst NPs agglomeration in ADT, which significantly mitigated ECSA decay of the catalysts. More importantly, Co dealloying of the PtCo alloy catalyst in ADT was remarkably suppressed by the melamine addition, and thus the alloy catalyst retained a high ORR mass activity even after ADT. Therefore, we believe that the target cell performance as well as the high durability of the Pt-based catalysts can be realized by combination of the mesoporous carbon support and the decoration with melamine or melamine derivatives.This study was partly supported by NEDO, Japan.

Atomic-Scale Strucural Analysis of Pt-Based Nanoparticles Using Scanning Transmission Electron Microscopy

Polymer electrolyte fuel cells (PEFCs) is proposed as an alternative to the power generation system in fuel cell vehicles. The performance of the PEFCs is significantly affected by the catalytic activity of the cathode, which contains platinum in general. Recent theoretical studies show that the Pt-Pt interatomic distance at the subsurface of the Pt-based catalysts might considerably influence the catalytic activity. However, experimental evidence remains a challenge due to the requirement of measurement accuracy in picometers at the subsurface. The present work attempts to achieve precise measurements on the Pt-Pt interatomic distance of Pt particles by high-angle annular dark-field (HAADF) imaging in scanning transmission electron microscopy (STEM). Further, we also aim to understand the effects of the change in Pt-Pt interatomic distance on the catalytic activity.A catalyst of 10 wt.% Pt-loaded on graphitized carbon (Sigma-Aldrich) was used in this work. TEM specimen was prepared by dispersing the catalyst on a carbon film supported copper grid. Structural characterizations were examined by a spherical aberration corrected scanning transmission electron microscope (JEM-2100F, JEOL) operated at 200 kV.In order to determine the Pt atomic coordinate accurately, images were first taken under the optimized conditions. Further, a series of images were taken and integrated to form one image with high signal-to-noise ratio and minimized drifting. Finally, the Pt atomic coordinates were extracted precisely on a picometer scale by fitting of the individual atomic columns to two-dimensional Gaussian functions using a custom code developed by MatLab software. To gain insight into the atomic changes in Pt particle, a map of Pt-Pt interatomic displacement vector was constructed and superimposed on the HAADF-STEM image. Intriguingly, a significant Pt-Pt interatomic displacement occurs at the surface of the Pt particle, corresponding to changes in surface morphology and particle size.The state-of-the-art methodology demonstrated here could greatly advance our understanding of surface chemistry of Pt-based catalysts such as Pt3Co alloys. Further understanding of the correlation between the interatomic distances on the catalyst surface and the catalytic activity may give considerable interests and guidelines for future developments of PEFCs.

First-Principles Study on Pt-Based Sub-Nanocluster Carbon-Metal Hybrid Catalysts for the Oxygen Reduction Reaction

Recently, the polymer electrolyte membrane fuel cell (PEMFC) has been drawing huge attention as an eco-friendly energy conversion device which can replace an internal combustion engine without environmental contaminant such as CO2 and NOx. However, the use of expensive noble metal catalysts such as Pt is essential for the cathode because the oxygen reduction reaction (ORR) at cathode are kinetically much slower than the hydrogen oxidation at anode. For this reason, many of researchers have vigorously worked on the development of Pt-based alloy catalysts such as Pt-Co and Pt-Ni alloys to reduce noble metal usage, but there are still limitations in catalytic activity and durability for the commercialization. Herein, to overcome the limitations, we developed Pt-based carbon-metal hybrid catalyst showing high performance for ORR using density functional theory (DFT) calculation. The slab model of Pt-based carbon-metal hybrid catalyst was constructed by Pt sub-nanocluster supported on graphite with graphene-shaped carbon shell on top of the Pt sub-nanocluster. The most stable geometry of the hybrid catalyst was determined by the formation energy, and the ORR mechanism on surface of hybrid catalyst as well as electrochemical activity was investigated. As a result of investigation, we confirmed that the oxygen reduction occurs on active graphene-shaped carbon shell sites. On pure Pt sub-nanocluster hybrid catalyst, once the hydrogen superoxide (OOH) is adsorbed on carbon shell surface after the oxygen adsorption and protonation, the hydrogen peroxide (H2O2) is preferentially formed at higher onset potential than that of four-electron O2 reduction, which the final product is water (H2O). However, the formation of hydrogen peroxide in PEMFC should be avoided owing to creation of radical, resultant degradation of membrane and low energy conversion efficiency. Surprisingly, we identified that the hydrogen peroxide formed on pure Pt sub-nanocluster hybrid catalyst can be decomposed into OH and H2O with low energy barrier, whose value is much lower than desorption energy of produced hydrogen peroxide, so that subsequent reduction reaction can occur. When this four-electron ORR via hydrogen peroxide decomposition takes place, the ORR activity is improved compared to Pt(111) catalyst, where the onset potential of pure Pt sub-nanocluster hybrid catalyst presents is higher than that of Pt(111). Moreover, we introduced Pt-based alloy sub-nanocluster to reduce Pt usage further. The Pt-based alloy sub-nanocluster hybrid catalyst also exhibited increased ORR activity. For Pt-based alloy sub-nanocluster hybrid catalyst, we carried out analysis of density of state and figured out that the more orbital overlap between carbon shell and sub-nanocluster is generated, the higher catalytic activity is shown due to enrichment of electrons on carbon shell surface. We expect this work can help understanding the mechanism of activity improvement of carbon metal hybrid catalyst, suggesting promising way to design high-performance ORR catalyst with low Pt loadings.

Electronic Perturbation of Platinum Alloy By Transition Metal-Doping Towards Improved ORR Activity and Stability

As of today, Pt-based catalysts are the predominant ORR catalysts that meet the desired activity requirements of ORR in fuel cells. However, their broader applications are still challenging due to highly sluggish ORR kinetics, limited stability and higher cost of Pt. In order to develop novel electrocatalyst materials, herein we report surface tuning of binary PtCo alloy through transition metal doping, which reveals superior ORR activity achieving a mass activity of 2.07 A mgPt -1 at 0.9 V vs. reversible hydrogen electrode (RHE) and excellent durability with minor degradation after 30000 cycles. The ternary PtCoMn@NGNS alloy prepared through facile molten salt pyrolysis reveals a strong metal-support interaction via metal-nitrogen-graphene coordination.Furthermore, Mn dopants alter the electronic structure of Pt alloy, which improves the oxygen-intermediate binding energy on the interface and suppress the Co dissolution through unique configuration, resulting in enhanced activity and durability of the catalyst. According to the DFT calculations, the surface Mn extensively adsorbs an OH, resulting in increased surface Co stability and overall ORR catalytic performance. Therefore, it is understandable that the development of ternary Pt alloy results in considerable changes in the structural and electrical characteristics of metal overlayer, which varies dramatically from monometallic surfaces.Our experimental results corroborated by theoretical calculations show that electronic perturbation of PtCo by Mn doping stabilizes the Co and causes significant strain in the Pt(111), which accounts for the increased ORR performance. The strained lattice of Pt caused by Co alloying and surface segregation of Mn both play important roles in the increased ORR activity. Similarly, the Pt3CoMn-OH configuration diminishes Co dissolution and improves overall stability. It is anticipated that such a facile preparation of high-performance electrocatalysts will advance the practical applications of ORR catalysts.Figure 1: Figure 1

Synthesis of Single-Atom and Dual-Atom Catalyst Using N-Defective C3N4

Single-atom catalysts, which have been studied tremendously in the past decade, are emerging as a new class of heterogeneous catalysts. It is now generally known that defect sites play an important role in forming single-atomic structures. In the case of SACs, defective sites provide not only space for fixation of metal precursor, but also electrons for stabilizing positive metal ions. Graphitic carbon nitride (g-C3N4) is one of the ideal 2D materials for the synthesis of SACs. C3N4 has enough anchoring sites which originate from the ordered structure of tri-s-triazines connected together. Furthermore, abundant nitrogen atoms in C3N4 can provide electrons to single metal atoms. however, C3N4 is unsuitable as support for electrochemical catalysts due to its low electrical conductivity. Therefore, we made a C3N4 shell on the outer surface of carbon black (Ketjen Black EC-600JD) to obtain conductive support (C@C3N4).[1] Pt was supported on C@C3N4 at 1, 2, 4, and 8 wt% by wetness impregnation method. Through XRD, HAADF-STEM, and XAFS analysis, it was confirmed that a single-atomic structure was formed only when the Pt content was 1 or 2 wt%. In addition, I confirmed that the H2O2 selectivity (%) in the electrochemical oxygen reduction reaction was different according to the Pt content of the catalysts.In terms of controlling reaction sites at the atomic level, the challenge above creating single-atomic structures is creating structures in which two or three atoms are formed as dimer or trimer. Unlike single-atom catalysts, in a dimer or trimer structure, two or more atoms are adjacent to each other, so they can exhibit completely different catalytic properties. Finely controlling the defect site of the support can be a good strategy. Therefore, I adopted the strategy of making a defect in C3N4 to synthesize a dimer structure. It has been reported that N-vacancy can be selectively formed on C3N4 by additional heat treatment with NaBH4.[2, 3] In addition, DFT calculation results have been reported that Pd-Cu dimer structure can be stably formed on nitrogen-defective C3N4.[4]In this work, I create N-vacancy on a Pt1/C@C3N4 by additional heat treatment with NaBH4, and Co atoms were deposited as a secondary transition metal. The research strategy was to anchor the Co atom to the N-vacancy formed around the Pt single-atom, resulting in the formation of a dimer structure. First of all, the formation of N-vacancy on C@C3N4 support was clearly confirmed by FT-IR and XPS analysis. To confirm the dimer structure of Pt and Co, XAFS analysis was conducted. As a result, although not all Pt and Co atoms formed a dimer structure due to the limitation of the synthesis method, the intended structure of Co atom connected to a Pt atom was confirmed. In the Pt L3 edge EXAFS, a peak arising from Pt-Co scattering was observed at 2.4 Å. Furthermore, to confirm that PtCo alloy particles were not formed, high-result HAADF-STEM images were taken. All metal atoms were atomically dispersed, and nanoparticles were not found. This research demonstrated that defect engineering on support material can successfully modify active site on the atomic scale.

Ordered PtCo Intermetallics Featuring Nitrogen‐Doped Carbon Prepared by Surface Coating Strategy for Oxygen Reduction Reaction

AbstractImproving the activity and stability of Pt‐based electrocatalysts is essential for large‐scale commercial applications of fuel cells. The ordered Pt‐based alloy nanomaterials encapsulated by coating have attracted significant attention. Here, we displayed a surface coating strategy to synthesize structurally ordered PtCo alloy catalysts featuring nitrogen‐doped carbon (NC). Experimental results reveal that the sample with appropriate dopamine feeding content shows enhanced oxygen reduction activity and stability, which exhibits a mass activity of 1.36 mA ⋅ mg−1Pt and specific activity of 1.98 mA ⋅ cm−2, superior to those of excessive or low dopamine adding content samples and commercial Pt/C catalyst. The enhanced electrocatalytic performance of this catalyst was attributed to the combined effect including the protection of suitable thickness NC shells, strong electronic interaction and high ordering degree. In this work, the surface coating strategy provides available references to further improve the oxygen reduction performance of PtM alloy catalysts.

Portable and Label-Free Sensor Array for Discriminating Multiple Analytes via a Handheld Gas Pressure Meter.

Cross-reactive sensor arrays are useful for discriminating multiple analytes in a complex sample. Herein, a portable and label-free gas pressure sensor array was proposed for multiplex analysis via a handheld gas pressure meter. It is based on the interaction diversity of analytes with catalase-like nanomaterials, including Pt nanoparticles (PtNP), Co3O4 nanosheets (Co3O4NS), and Pt-Co alloy nanosheets (PtCoNS), respectively. Thus, the diverse influence of analytes on the catalase-like activity could be output as the difference in the gas pressure. By using principal component analysis, eight proteins were well distinguished by the gas pressure sensor array at the 10 nM level within 12 min. Moreover, different concentrations of proteins and mixtures of proteins could likewise be discriminated. More importantly, the effective discrimination of proteins in human serum and discrimination of five kinds of cells further confirmed the potential of the gas pressure sensor array. Therefore, it provides a portable, cheap, sensitive, and label-free gas pressure sensor array, which is totally different from the reported sensor arrays and holds great potential for portable and cheap discrimination of multiple analytes.

Compositional gradient induced enhancement of Dzyaloshinskii–Moriya interaction in Pt/Co/Ta heterostructures modulated by Pt–Co alloy intralayers

The Dzyaloshinskii–Moriya interaction (DMI) is an antisymmetric exchange in magnetic structures with broken inversion symmetry. In magnetic heterostructures, the bulk DMI may coexist with the conventional interfacial DMI contributing to the chiral magnetic behavior of the system. Here, we report the enhancement of DMI in Pt/Co heterostructures wherein Pt-Co alloy intralayers with compositional gradients are sandwiched between Pt and Co. Due to the composition gradient-induced bulk magnetic asymmetry and the face-centered cubic (fcc) (111) multilayer crystal structure, the DMI shows a complex behavior attributed to both the interfacial (i-DMI) and bulk-like (b-DMI) contributions. While the b-DMI is defined by the presence of composition differences and structure symmetry, the i-DMI hosts the interfacial contributions in the multilayer structure. Our approach allows the creation of graded magnetic thin films, where the structural inversion symmetry is broken solely due to the predefined compositional gradient of an intralayer, thereby giving rise to an ‘all-interface-bulk’ DMI with the controllable spatial distribution.

One-Dimensional Numerical Simulation of Pt-Co Alloy Catalyst Aging for Proton Exchange Membrane Fuel Cells

The service life of catalysts is a key aspect limiting the commercial development of proton exchange membrane fuel cells (PEMFCs). In this paper, a one-dimensional degradation model of a Pt-Co alloy catalyst in the cathode catalytic layer (CCL) of a PEMFC is proposed, which can track the catalyst size evolution in real time and demonstrate the catalyst degradation during operation. The results show that severe dissolution of particles near the CCL/membrane leads to uneven aging of the Pt-Co alloy catalyst along the CCL thickness direction. When the upper potential limit (UPL) is less than 0.95 V, it does not affect the catalyst significantly; however, a slight change may cause great harm to the catalyst performance and service life after UPL > 0.95 V. In addition, it is found that operating temperature increases the Pt mass loss on the carbon support near the CCL/membrane side, while it has little effect on the remaining Pt mass on the carbon support near the CCL/GDL side. These uncovered degradation mechanisms of Pt-Co alloy provide guidance for its application in PEMFCs.

Effect of the Preparation Conditions on the Catalytic Properties of CoPt for Highly Efficient 4-Nitrophenol Reduction.

CoPt alloys with Pt contents from 15 to 90% were prepared using low-cost electrochemical deposition. Different samples were synthesized from electrochemical baths at pH = 2.5 and 5.5 in a solution with and without saccharin as an additive. The morphology, composition and crystalline structure of the as-prepared samples were investigated by High Resolution—Scanning Electron Microscopy (HR-SEM), Atomic Force Microscopy (AFM), Ultra-high Resolution—Transmission Electron Microscopy (UHR-TEM), Energy-Dispersive X-ray Spectroscopy (EDX), and X-ray Diffraction (XRD). XRD investigations revealed that fcc crystalline structure transforms into hcp crystalline structure when the pH of the electrochemical bath is increased from 2.5 to 5.5 as well as when saccharin is added to the electrochemical bath. The catalytic performance of the CoPt alloys for the nitro to amino phenol compounds conversion was investigated for all the prepared samples, and the results show that the conversion degree increases (from 11.4 to 96.5%) even though the Pt content in the samples decreases. From the samples prepared from the electrochemical bath with saccharin, a study regarding the effect of contact time was performed. The results indicated that after only 5 min, the CoPt sample prepared at pH = 5.5 in the presence of saccharin completely converted the nitro compound to an amino compound.

Structural regulation of Fe–Co prussian blue analogues by incorporation of Pt for enhanced electrocatalytic overall water splitting

The specific properties of easy manufacturing, open frameworks, and high specific surface area endow prussian blue analogues (PBAs) as promising electrode materials for water splitting. Herein, we reported the successful application of interface engineering strategy to introduce low content of Pt species to boost the electrocatalytic activity of FeCo PBAs by ammonia etching and subsequent calcination. The resulting PtCo alloy modified FeCo PBAs (PtCo–FeCo PBAs) complex reveals modest electrocatalytic activity with low overpotentials (η) of 139 mV for hydrogen evolution reaction (HER) and 310 mV for oxygen evolution reaction (OER) at 10 mA cm−2 in alkaline electrolyte. Remarkably, the PtCo–FeCo PBAs only required small cell voltage of 1.68 V to drive 10 mA cm−2 for overall water splitting and the ideal electrocatalytic activity can be maintained for more than 50 h at a current density of 10 mA cm−2. The structural analysis unveils that the strong interaction between FeCo PBAs host and PtCo alloy resulting in charge redistribution and ultimately lead to high electrocatalytic activity and stability of PtCo–FeCo PBAs for both HER and OER.

Manipulation of micromagnetic structure of thin Co/Pt multilayer films by precise variation of Co and Pt thicknesses

We have investigated the magnetic properties and micromagnetic structure of multilayer Co/Pt films with the variation of bilayer thickness ([Co(0.3 × t nm)/Pt(0.5 × t nm)]10). The films represent Co-Pt alloys with periodic Co vs Pt composition. The magnetic force microscopy and Lorentz transmission electron microscopy have demonstrated the presence of N é el-type skyrmions in the films. The density of skyrmions was found to be strongly dependent on the bilayer thickness parameter (t). The effect is attributed to Dzyaloshinskii–Moriya interaction which is known to be strongly dependent on the regularities of magnetic and nonmagnetic layers alternation. We emphasize that the investigated system represents an intermediate case between unalloyed multilayer films and uniformly mixed alloys. Despite that it demonstrates similar micromagnetic behavior with skyrmion density very well controllable by modulation of technological parameters.

Electron-enriched Pt induced by CoSe2 promoted bifunctional catalytic ability for low carbon alcohol fuel electro-reforming of hydrogen evolution

Alcohol fuel electro-reforming is promising for green hydrogen generation while developing efficient bifunctional catalysts for alcohol fuel electrolysis is still very tricky. Herein, we for the first time proposed the electron-enriched Pt induced by CoSe2 has an efficient bi-functional catalytic ability for alcohol fuels electro-reforming of hydrogen in acid electrolytes. The theoretical calculation revealed the advantages of electron-enriched Pt surface for the adsorption of intermediate, which is well supported by spectroscopic analysis and CO-stripping techniques. Largely improved catalytic performances of activity, durability, and kinetics are demonstrated compared to the conventional alloy system and commercial Pt/C catalyst, due to the efficient synergism of Pt and CoSe2; the peak current density of Pt/CoSe2 for methanol (ethanol) oxidation is 87.61 (48.27) mA cm−2, which is about 3.3 (2.0) times higher than that of Pt/C catalyst and 2.0 (1.5) times that of the traditional PtCo alloy catalysts. Impressively, about 80% of the initial current was found after 1000 cycles of stability test for alcohol fuel oxidation of Pt/CoSe2 catalyst, higher than that of Pt/C (ca. 50%) and PtCo catalyst (65%). When Pt/CoSe2 catalyst serviced as bi-functional catalysts for electrolyzer, a low cell potential of 0.65 (0.78) V for methanol (ethanol) electrolysis was required to reach 10 mA cm−2, which was about 1030 (900) mV less than that of conventional water electrolysis using Pt/C as the catalyst. The current result is instructive for the design of novel bifunctional catalyst and the understanding of hydrogen generation via alcohol fuel electro-reforming.

Tuning the Cobalt–Platinum Alloy Regulating Single‐Atom Platinum for Highly Efficient Hydrogen Evolution Reaction

AbstractDesigning atomically dispersed metal catalysts for the electrocatalytic hydrogen evolution reaction (HER) is a promising strategy to efficiently convert electrical energy to chemical fuels. This strategy, however, still faces the challenge of finding a catalyst with high activity and long‐term durability. Here, single‐atom platinum and cobalt–platinum‐alloy nanocrystals in a nitrogen‐doped porous‐carbon framework (CoPt‐PtSA/NDPCF) is confined. The electrocatalyst exhibits ultralow overpotentials under both alkaline and acidic conditions at a high current density of −300 mA cm−2 and excellent long‐term durability up to 100 h or 10 000 cycles, which are attributed to the synergetic effects of PtSA and tuning of the CoPt alloy in the NDPCF. First‐principles calculations suggested that PtSA aided by the CoPt alloy has high d‐band occupation for promoting the reaction kinetics. This study opens a new avenue for designing heterostructures with the synergic effects of single metal atoms and metal alloys with outstanding performance in the HER.

Revealing the Role of Mo Doping in Promoting Oxygen Reduction Reaction Performance of Pt3Co Nanowires

Highly active and durable electrocatalysts towards oxygen reduction reaction (ORR) are imperative for the commercialization application of proton exchange membrane fuel cells. By manipulating ligand effect, structural control, and strain effect, we report here the precise preparation of Mo-doped Pt3Co alloy nanowires (Pt3Co-Mo NWs) as the efficient catalyst towards ORR. The as-prepared Pt3Co-Mo NWs deliver high specific activity (0.596 mA cm-2) and mass activity (MA, 0.84 A mg -1Pt), much higher than those of undoped counterparts. Besides activity, Pt3Co-Mo NWs also demonstrate excellent structural stability and cyclic durability even after 50,000 cycles (76% MA retain), again surpassing control samples without Mo dopants. The superior catalytic performance can be attributed to several structural advantages. First, both ultrafine nanowire morphology and controlled growth ensure the exposure of abundant highly active high-index facets, resulting in increased electrochemical active surface area (ECSA, 141 m2 g−1 Pt). Second, one dimensional (1D) Pt nanostructure, particularly ultrafine Pt nanowires, are less subject to dissolution, aggregation, and even Ostwald ripening than nanoparticles, leading to much-improved durability. Third and most importantly, the Mo doping directly changes the local electronic structure of both element Pt and Co, not only effectively endowing the Pt3Co electrocatalysts with an enhanced activity but also efficiently preventing element Co from leaching leading to improved durability.The geometric phase analysis (GPA) strain maps and the density function theory (DFT)calculations were conducted to further analyze the role of Mo dopants. GPA strain maps reveal that Mo dopants are inclined to be the tensile strain cores, generating local lattice expansion to adjust the excessively compressive strain effect introduced by Co alloying. Benefiting from the optimized d-band center, the oxygen binding energy (Eo) on Pt3Co-Mo slabs is closest to the optimal value compared with those of undoped counterparts. Moreover, the energy required to remove Co atoms from Pt3Co slab with Mo doping is increased by 0.195 eV compared to the slab without Mo doping, indicating the electronic effect of Mo dopants to stabilize Co. This work provides not only a facile methodology but also an in-depth investigation of the relationship between structure and properties to provide general guidance for future design and optimization.

Interfacial perpendicular magnetic anisotropy in Co2FeSi alloy films sandwiched by Pt and MgAl2O4

Co2FeSi (CFS) alloy film is one of promising ferromagnetic electrodes and MgAl2O4 (MAO) spinel is an attractive oxide barrier. In this work, we fabricate a series of Pt/CFS/MAO/Pt stacks using sputtering method. For the as-deposited stacks the easy axis lies in the in sample plane. After annealing at 350 °C perpendicular magnetic anisotropy is shown to build in the stacks with CFS thickness ranged from 3.5 to 5.5 nm. A high saturation magnetization of 908 emu/cm3, close to the bulk CFS, is achieved. The perpendicular magnetic anisotropy constant of 105 erg/cm3 in the order of magnitude is witnessed. A large interfacial perpendicular magnetic anisotropy of 1.32 ± 0.18 erg/cm2 is obtained in the annealed stacks. Positive contributions to the PMA from the Pt/CFS and CFS/MAO/Pt interfaces are experimentally confirmed. Significantly improved crystallinity of Pt layers and (111)-oriented CoPt alloy were revealed by X-ray diffractometry measurements on the annealed stacks, which may be additionally responsible for the PMA.

Co‐N as a Promoter towards Modulation Surface Chemistry of PtCo Alloy on 2D Thin Layer Hierarchical Porous Nitrogen‐Carbon for the Efficient Oxygen Reduction Reaction

AbstractTo clarify the mechanism of active site conversion and utilization of the Pt−M alloy complexed with nitrogen‐doped carbon (NC) catalysts (Pt−M/NC) for oxygen reduction reaction (ORR), we synthesized the two‐dimensions thin‐layer hierarchical porous nitrogen‐carbon for supporting PtCo nanoparticles (2D PtCo/TNC) and applied to alkaline ORR. The self‐assembled thin layer of carbon nitride (TL‐C3N4) was thermally fused with commercial carbon black (C) to form a 2D‐TNC, which can conduct the optimal mass transfer. Therewith, PtCo nanoparticles were anchored on this carrier through a thermal injection strategy, promoting the formation of Co−N and achieving low Pt loading (2 wt%). As a promoter, the Co−N favours the lattice distortion of PtCo alloys and facilitates the in‐situ adsorption‐diffusion process of oxygen‐containing species. Thus, the obtained catalyst demonstrates an excellent ORR activity in alkaline electrolytes, with a half‐wave potential (E1/2) of 0.885 V and electrochemical active surface area (ECSA) of 111 m2/g, lower Tafel slope of 66 mV/dec.

Synergistic Promotion of Single-Atom Co Surrounding a PtCo Alloy Based On a g-C3N4 Nanosheet for Overall Water Splitting

Synergistic Promotion of Single-Atom Co Surrounding a PtCo Alloy Based On a g-C₃N₄ Nanosheet for Overall Water Splitting