Tuning d-Band Center of Pt by PtCo-PtSn Heterostructure for Enhanced Oxygen Reduction Reaction Performance

Metalloid tellurium-induced electron-deficient NiFe alloys awakening efficient oxygen electroreduction

Transition metal alloys catalysts have been extensively studied in oxygen reduction reactions (ORR); however, their suboptimal catalytic activity presents a significant challenge. Modifying the local electronic configuration of the catalytic active site by heteroatom doping is an effective strategy to enhance the electrocatalytic performance. Herein, an ORR Te/NiFe@NCNFs electrocatalyst, featuring with Te modified NiFe alloys nanoparticles and anchored on N-doped carbon nanofibers (NCNFs), was constructed via a surface-modified synthesis strategy. The introduction of Te leads to electron transfer on the surface of Te/NiFe@NCNFs, forming an electron-deficient NiFe site with high catalytic activity. Theoretical calculations confirm that Te regulates an electron redistribution and reduces the d-band centers of Fe and Ni, which help to facilitate the desorption of ORR intermediate oxides. As a result, Te/NiFe@NCNFs exhibit a half-wave potential of 0.86 V, superior to that of Pt/C (0.84 V) and most reported modified-NiFe-based catalysts. When assembled into a zinc-air battery, Te/NiFe@NCNFs deliver remarkable power density of 158.8 mW cm-2-2 and specific capacity of 778.1 mA h gZn-1. The present study presents new insights into the modulation of electronic structure in transition metal alloys, providing a feasible and innovative approach for the design of unrivaled ORR electrocatalysts.

Asymmetry Spin-Orbit of Single Iron Active Site Enhance Oxygen Reduction Reaction

Asymmetric electron distribution of single-atom catalysts (SAC) is an important means of regulating intrinsic catalytic activity. However, limited by synthetic preparation methods, understanding of the mechanism of asymmetrically coordinated single-atom catalysis is restricted. In this study, leveraging the micropore confinement effect, nitrogen and phosphorus-doped microporous carbon is used as a substrate to successfully anchor singly dispersed Fe atoms, constructing the asymmetrically coordinated single-atom Fe site coordinated with N and P atoms (Fe-SAs/NPC). The existence of the Fe-N3P1 site structure breaks the symmetry Fe-N4 in Fe-SAs/NC, which would optimize the adsorption strength of intermediates. The resulting Fe-SAs/NPC exhibits excellent ORR activity with a half-wave potential of 0.91 V (0.1 m KOH), which is 40 mV higher than that of Fe-SAs/NC (0.87 V). Combined with theoretical calculations, an in-depth understanding of the asymmetric electronic configuration from the perspective of spin orbitals can enhance the electronic activity near the Fermi level and strengthen the adsorption of oxygen-containing intermediates. This work provides new perspectives and ideas for understanding spin-electronic behavior in catalytic processes. Furthermore, the Zn-air battery constructed using Fe-SAs/NPC exhibits a high power density of 187.7 mW cm-2 and a specific capacity of 819.6 mAh gZn -1 at 10 mA cm-2.

A review of ordered PtCo3 catalyst with higher oxygen reduction reaction activity in proton exchange membrane fuel cells

This review is devoted to the potential advantages of ordered alloy catalysts in proton exchange membrane fuel cells (PEMFCs), specifically focusing on the development of the low Pt content, high activity, and durability ordered PtCo3 catalyst. Due to the sluggish oxygen reduction reaction (ORR) kinetics and poor durability, the overall performance of the fuel cell is affected, and its application and promotion are limited. To address this issue, researchers have explored various synthetic strategies, such as element doping, morphology adjusting, structure controlling, ordering and support/metal interaction enhancement. This article extensively discussed the Pt related ORR catalysts and follows an in-depth analysis of ordered PtCo3. The introduction briefly discusses the direction of development of fuel cell catalysts and frontier progress, including theoretical mechanism, practical preparation, and Pt-containing electrode structures, etc. The subsequent chapter focuses on the Pt-Co catalyst, the evolution process of Pt alloy to Pt-Co alloy and the improvement scheme are introduced. The next chapter describes the properties of PtCo3. Although the ordered PtCo3 catalyst has a wide range of applicability due to low cost and high activity catalyst. However, besides the common agglomeration and sintering problems of Pt-Co alloy, its commercial application still faces unique problems of oversized crystal size, phase segregation, ordering transformation and transition metal dissolution. Therefore, in Chapter 4, this overview provides some possible improvement methods for three specific functions: crystal refinement, enhancing the effect of support and active substances, and anti-dissolution.

Facilitating charge transfer via a Semi-Coherent Fe(PO3)2-Co2P2O7 heterointerface for highly efficient Zn-Air batteries

Developing reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial for achieving high-performance rechargeable Zn-air batteries (ZABs). This study introduced an nitrogen-doped carbon confined with a semi-coherent Fe(PO3)2-Co2P2O7 heterojunction for bifunctional oxygen electrocatalysis. This nanocomposite yielded an ORR half-wave potential of 0.908 V and an OER overpotential of 291 mV at 10 mA/cm2. ZABs incorporating this catalyst yielded impressive performance, including a peak power density of 203 mW/cm2, a specific capacity of 737 mAh/gZn, and promoted stability. Both experimental and theoretical simulations demonstrated that the unique electric field between Fe(PO3)2 and Co2P2O7 promoted efficient charge transport across the heterointerface. This interaction likely modulated the d-band center of the heterojunction, expedite the desorption of oxygen intermediates, thus improving oxygen catalysis and, consequently, ZAB performance. This work illustrates a significant design principle for creating efficient bifunctional catalysts in energy conversion technologies.

A Janus Platinum/Tin Oxide Heterostructure for Durable Oxygen Reduction Reaction

Designing efficient and durable electrocatalysts for oxygen reduction reaction (ORR) is essential for proton exchange membrane fuel cells (PEMFCs). Platinum-based catalysts are considered efficient ORR catalysts due to their high activity. However, the degradation of Pt species leads to poor durability of catalysts, limiting their applications in PEMFCs. Herein, a Janus heterostructure is designed for high durability ORR in acidic media. The Janus heterostructure composes of crystalline platinum and cassiterite tin oxide nanoparticles with carbon support (J-Pt@SnO2/C). Based on the synchrotron fine structure analysis and electrochemical investigation, the crystalline reconstruction and charge redistribution at the interface of Janus structure are revealed. The tightly coupled interface could optimize the valance states of Pt and the adsorption/desorption of oxygenated intermediates. As a result, the J-Pt@SnO2/C catalyst possesses distinguishing long-term stability during the accelerated durability test without obvious degradation after 40 000 cycles and keeps the majority of activity after 70 000 cycles. Meanwhile, the catalyst exhibits outstanding activity with half-wave potential at 0.905 V and a mass activity of 0.355 A mgPt -1 (2.7 times higher than Pt/C). The approach of the Janus catalyst paves an avenue for designing highly efficient and stable Pt-based ORR catalyst in the future implementation.

Electrospinning-derived transition metal/carbon nanofiber composites as electrocatalysts for Zn-air batteries

The sluggish kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) significantly impede the broader implementation of Zn-air batteries (ZABs), underscoring the necessity for advanced high-efficiency materials to catalyze these electrochemical processes. Recent advancements have highlighted the potential of transition metal/carbon nanofiber (TM/CNF) composite materials, synthesized via electrospinning technology, due to their expansive surface area, profusion of active sites, and elevated catalytic efficacy. This review comprehensively examines the structural characteristics of TM/CNFs, with a particular emphasis on the pivotal role of electrospinning technology in fabricating diverse structural configurations. Additionally, it delves into the mechanistic underpinnings of various strategies aimed at augmenting the catalytic activity of TM/CNFs. A meticulous discourse is also presented on the application scope of TM/CNFs in the realm of electrocatalysis, with a special focus on their impact on the performance of assembled ZABs. Lastly, this review encapsulates the challenges and future prospects in the development of TM/CNF composite materials via electrospinning, aiming to provide an exhaustive understanding of the current state of research in this domain and to foster further advancements in the commercialization of ZABs.

Recent Progress of Transition Metal Selenides for Electrochemical Oxygen Reduction to Hydrogen Peroxide: From Catalyst Design to Electrolyzers Application

Hydrogen peroxide (H2O2) is a highly value-added and environmental-friendly chemical with various applications. The production of H2O2 by electrocatalytic 2e- oxygen reduction reaction (ORR) has emerged as a promising alternative to the energy-intensive anthraquinone process. High selectivity Catalysts combining with superior activity are critical for the efficient electrosynthesis of H2O2. Earth-abundant transition metal selenides (TMSs) being discovered as a classic of stable, low-cost, highly active and selective catalysts for electrochemical 2e- ORR. These features come from the relatively large atomic radius of selenium element, the metal-like properties and the abundant reserves. Moreover, compared with the advanced noble metal or single-atom catalysts, the kinetic current density of TMSs for H2O2 generation is higher in acidic solution, which enable them to become suitable catalyst candidates. Herein, the recent progress of TMSs for ORR to H2O2 is systematically reviewed. The effects of TMSs electrocatalysts on the activity, selectivity and stability of ORR to H2O2 are summarized. It is intended to provide an insight from catalyst design and corresponding reaction mechanisms to the device setup, and to discuss the relationship between structure and activity.

Pt nanoparticles anchored by oxygen vacancies in MXenes for efficient electrocatalytic hydrogen evolution reaction

The improvement of the hydrogen evolution reaction (HER) performance of nanomaterials is associated with the interfacial synergistic interaction and their hydrogen adsorption kinetics. Nevertheless, it is still a challenge to accelerate the proton transfer and optimize the HER kinetics by constructing Pt-supported heterostructures based on the hydrogen spillover phenomenon. Herein, oxygen vacancies on the surface of MXene nanosheets were constructed via a high-temperature annealing method, which was employed to anchor/stabilize Pt nanoparticles and fabricate a Pt/MXene heterostructure. EPR and XPS analyses verified the presence of oxygen vacancies, which could enhance the intrinsic HER activity of the MXene. The HER catalytic performance was investigated by taking into account the surface structure of the MXene affected by the annealing temperature, the concentration of Pt and the number of deposition cycles. Electrochemical results showed that Pt/MXene with higher utilization of Pt was obtained at 900 °C and 0.05 mgPt mL-1. The 0.05-Pt/MXene-900 obtained at deposition of 60 cycles in 0.5 M H2SO4 solution exhibited the optimized HER activity. The overpotential was 22 mV at a current density of 10 mA cm-2 and the Tafel slope was 42.41 mV dec-1. Furthermore, the accelerated HER kinetics was mainly due to the electron trapping ability of the MXene, small particles of Pt, as well as the enhanced charge transfer between the oxygen vacancies of the MXene and Pt. This strategy for constructing Pt-supported heterostructures based on the vacancy anchoring effects provides new ideas for the design of well-defined electrocatalysts toward the HER.

Manipulation of Electronic States of Pt Sites via d-Band Center Tuning for Enhanced Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells

Expediting the torpid kinetics of the oxygen reduction reaction (ORR) at the cathode with minimal amounts of Pt under acidic conditions plays a significant role in the development of proton exchange membrane fuel cells (PEMFCs). Herein, a novel Pt-N-C system consisting of Pt single atoms and nanoparticles anchored onto the defective carbon nanofibers is proposed as a highly active ORR catalyst (denoted as Pt-N-C). Detailed characterizations together with theoretical simulations illustrate that the strong coupling effect between different Pt sites can enrich the electron density of Pt sites, modify the d-band electronic environments, and optimize the oxygen intermediate adsorption energies, ultimately leading to significantly enhanced ORR performance. Specifically, the as-designed Pt-N-C demonstrates exceptional ORR properties with a high half-wave potential of 0.84 V. Moreover, the mass activity of Pt-N-C reaches 193.8 mA gPt-1 at 0.9 V versus RHE, which is 8-fold greater than that of Pt/C, highlighting the enormously improved electrochemical properties. More impressively, when integrated into a membrane electrode assembly as cathode in an air-fed PEMFC, Pt-N-C achieved a higher maximum power density (655.1 mW cm-2) as compared to Pt/C-based batteries (376.25 mW cm-2), hinting at the practical application of Pt-N-C in PEMFCs.

High stability copper clusters anchored on N-doped carbon nanosheets for efficient CO2 electroreduction to HCOOH

Cu-based nanomaterials is crucial for electrochemical CO2 reduction reaction (CO2RR), but they inevitably undergo performance degradation due to structural self-reconstruction at a large current density during CO2RR. Here, we developed a pre-synthetic atomically dispersed Cu source strategy to fabricate a catalyst of stable Cu clusters anchored on N-doped carbon nanosheets (c-Cu/NC), which exhibited an exceptional electroreduction for CO2 to HCOOH with a Faradaic efficiency of up to 96.2 % at current density of 276.4 mA cm-2 at - 0.96 V vs. RHE, which surpasses most reported catalysts. Especially, there was no any decay in stability during a 100 h continuous test, attributed to a strong interaction of Cu-C for restraining its self-reconstruction during CO2RR. DFT calculations indicated that N-doped carbon can strongly stabilize Cu clusters for keeping stability and cause the downshift of d-band center of Cu on c-Cu/NC for reducing the desorption energy between c-Cu/NC and OCHO* intermediates. This work provides an effective way to construct stable Cu clusters catalysts, and unveil the origin of catalyticmechanism over Cu clusters anchored on N-doped carbon towards electrochemical conversion ofCO2 to HCOOH.

Spatial separation strategy to construct N/S co-doped carbon nanobox embedded with asymmetrically coupled Fe-Co pair-site for boosted reversible oxygen electrocatalysis

The fabrication of a remarkably efficient iron-metal-based pair-site, constrained within carbon support, presents a significant and intricate undertaking, primarily attributable to the propensity of proximate metallic entities to amalgamate into the alloy state. In response to this challenge, a spatial segregation approach was conceptualized, aiming to synthesize an N/S co-doped carbon nanobox hosting an asymmetrically coupled Fe-Co pair-site. This engineered nanostructure manifested remarkable electrocatalytic properties, notably featuring a superb half-wave potential of 0.903 V for the oxygen reduction reaction (ORR) and a commendable overpotential of 0.296 V at 10 mA/cm2 for the oxygen evolution reaction (OER). Additionally, a homemade Zn-air battery incorporating this nanohybrid catalyst demonstrated a discharge capacity of 737 mAh/g, a specific maximum power density of 239 mW/cm2 as well as notable durability. Work-function calculations suggested that the electronic interaction between Fe and Co phases, along with the synergetic catalysis of N/S co-doped carbon substrate, could facilitate charge redistribution at the interface, create abundant active sites, and optimize the adsorption-desorption energy of oxygen species on the active center, thus markedly reducing the ORR/OER catalytic reaction barriers. These findings highlight a new strategy for designing and synthesizing efficient bifunctional carbon-based catalysts for energy storage and conversion devices.

Defect-Engineered Charge Transfer in a PtCu/PrxCe1-xO2 Carbon-Free Catalyst for Promoting the Methanol Oxidation and Oxygen Reduction Reactions

Platinum (Pt) and Pt-based alloys have been extensively studied as efficient catalysts for both the anode and cathode of direct methanol fuel cells (DMFC). Defect engineering has been revealed to be practicable in tuning the charge transfer between Pt and transition metals/supports, which leads to the charge density rearrangement and facilitates the electrocatalytic performance. Herein, Pr-doped CeO2 nanocubes were used as the noncarbon support of a PtCu catalyst. The concentration and structure of oxygen vacancy (Vo) defects were engineered by Pr doping. Besides the Vo monomer, the oxygen vacancy with a linear structure is also observed, leading to the one-dimensional PtCu. The Vo concentration shows the volcanic scenario as Pr increased. Accordingly, the activities of PtCu/PrxCe1-xO2 toward methanol oxidation and oxygen reduction reactions exhibit the volcanic scenario. PtCu/Pr0.15Ce0.85O2 exhibits the optimal catalytic performance with the specific activity 3.57 times higher than that of Pt/C toward MOR and 1.34 times higher toward ORR. The MOR and ORR mass activities of PtCu/Pr0.15Ce0.85O2 reached 1.05 and 0.12 A·mg-1, which are 3.09 and 0.92 times the values of Pt/C, respectively. The abundant Vo afforded surplus electrons, which tailored the electron transfer between PtCu and PrxCe1-xO2, leading to enhanced catalytic performance of PtCu/PrxCe1-xO2. DFT calculations on PtCu/Pr0.15Ce0.85O2 revealed that Pr doping reduced the band gap of CeO2 and lowered the overpotential.

Surface-structure tailoring of Dendritic PtCo nanowires for efficient oxygen reduction reaction

Platinum-based alloy nanowire catalysts demonstrates great promise as electrocatalysts to facilitate the cathodic oxygen reduction reaction (ORR) of proton exchange membrane fuel cells (PEMFCs). However, it is still challenge to further improve the Pt atom utilization of Pt based nanowires featuring inherent structural stability. Herein, a new structure of PtCo nanowire with nanodendrites was developed using CO-assistance solvent thermal method. The dendrite structure with an average length of about 7 nm are characterized by a Pt-rich surface and the high-index facets of {533}, {331} and {311}, and grows from the ultra-fine wire structure with an average diameter of about 3 nm. PtCo nanowires with nanodendrites developed in this work shows outstanding performance for ORR, in which its mass activity of 1.036 A/mgPt is 5.76 times, 1.74 times higher than that of commercial Pt/C (0.180 A/mgPt) and PtCo nanowires without nanodendrites (0.595 A/mgPt), and its mass activity loss is only 18% under the accelerated durability tests (ADTs) for 5k cycles. The significant improvement is attributed to high exposure of active sites induced by the dendrite structure with Pt-rich surface with the high-index facets and Pt-rich surface. This structure may provide a new idea for developing novel 1D Pt based electrocatalysts.

Materials Strategies Tackling Interfacial Issues in Catalyst Layers of Proton Exchange Membrane Fuel Cells

The most critical challenge for the large-scale commercialization of proton exchange membrane fuel cells (PEMFCs), one of the primary hydrogen energy technologies, is to achieve decent output performance with low usage of platinum (Pt). Currently, the performance of PEMFCs is largely limited by two issues at the catalyst/ionomer interface, specifically, the poisoning of active sites of Pt by sulfonate groups and the extremely sluggish local oxygen transport toward Pt. In the past few years, emerging strategies are derived to tackle these interface problems through materials optimization and innovation. This perspective summarizes the latest advances in this regard, and in the meantime unveils the molecule-level mechanisms behind the materials modulation of interfacial structures. This paper starts with a brief introduction of processes and structures of catalyst/ionomer interfaces, which is followed by a detailed review of progresses in key materials toward interface optimization, including catalysts, ionomers, and additives, with particular emphasis on the role of materials structure in regulating the intermolecular interactions. Finally, the challenges for the application of the established materials and research directions to broaden the material library are highlighted.

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

Electrocatalysis underpins the renewable electrochemical conversions for sustainability, which further replies on metallic nanocrystals as vital electrocatalysts. Intermetallic nanocrystals have been known to show distinct properties compared to their disordered counterparts, and been long explored for functional improvements. Tremendous progresses have been made in the past few years, with notable trend of more precise engineering down to an atomic level and the investigation transferring into more practical membrane electrode assembly (MEA), which motivates this timely review. After addressing the basic thermodynamic and kinetic fundamentals, we discuss classic and latest synthetic strategies that enable not only the formation of intermetallic phase but also the rational control of other catalysis-determinant structural parameters, such as size and morphology. We also demonstrate the emerging intermetallic nanomaterials for potentially further advancement in energy electrocatalysis. Then, we discuss the state-of-the-art characterizations and representative intermetallic electrocatalysts with emphasis on oxygen reduction reaction evaluated in a MEA setup. We summarize this review by laying out existing challenges and offering perspective on future research directions toward practicing intermetallic electrocatalysts for energy conversions.

Exploring The Synergistic Effect Of CoSeP/CoP Interface Catalyst For Efficient Urea Electrolysis

Electrocatalytic oxidation of urea (UOR) is a potential energy-saving hydrogen production technology that can replace oxygen evolution reaction (OER). Therefore, CoSeP/CoP interface catalyst is synthesized on nickel foam using hydrothermal, solvothermal, and in situ template methods. The strong interaction of tailored CoSeP/CoP interface promotes the hydrogen production performance of electrolytic urea. During the hydrogen evolution reaction (HER), the overpotential can reach 33.7 mV at 10 mA cm-2 . The cell voltage can reach 1.36 V at 10 mA cm-2 in the overall urea electrolytic process. Notably, the overall urine electrolysis performance of the catalyst in the human urine medium can reach 1.40 V at 10 mA cm-2 and can exhibit durable cycle stability at 100 mA cm-2 . Density functional theory (DFT) proves that the CoSeP/CoP interface catalyst can better adsorb and stabilize reaction intermediates CO* and NH* on its surface through a strong synergistic effect, thus enhancing the catalytic activity.

Theoretical Study on B-doped FeN4 Catalyst for Potential-Dependent Oxygen Reduction Reaction

Electrochemical reactions mostly take place at a constant potential, but traditional DFT calculations operate at a neutral charge state. In order to really model experimental conditions, we developed a fixed-potential simulation framework via the iterated optimization and self-consistence of the required Fermi level. The B-doped graphene-based FeN4 sites for oxygen reduction reaction were chosen as the model to evaluate the accuracy of the fixed-potential simulation. The results demonstrate that *OH hydrogenation gets facile while O2 adsorption or hydrogenation becomes thermodynamically unfavorable due to the lower d-band center of Fe atoms in the constant potential state than the neutral charge state. The onset potential of ORR over B-doped FeN4 by performing potential-dependent simulations agree well with experimental findings. This work indicates that the fixed-potential simulation can provide a reasonable and accurate description on electrochemical reactions.

Toward the Long-Term Stability of Cobalt Benzoate Confined Highly Dispersed PtCo Alloy Supported on a Nitrogen-Doped Carbon Nanosheet/Fe3C Nanoparticle Hybrid as a Multifunctional Catalyst for Zinc-Air Batteries

This work reports a new type of platinum-based heterostructural electrode catalyst that highly dispersed PtCo alloy nanoparticles (NPs) confined in cobalt benzoate (Co-BA) nanowires are supported on a nitrogen-doped ultra-thin carbon nanosheet/Fe₃C hybrid (PtCo@Co-BA-Fe₃C/NC) to show high electrochemical activity and long-term stability. One-dimensional Co-BA nanowires could alleviate the shedding and agglomeration of PtCo alloy NPs during the reaction so as to achieve satisfactory long-term durability. Moreover, the synergistic effect at the interface optimizes the surface electronic structure and prominently accelerates the electrochemical kinetics. The oxygen reduction reaction half-wave potential is 0.923 V, and the oxygen evolution reaction under the condition of 10 mA•cm^-2 is 1.48 V. Higher power density (263.12 mW•cm^-2), narrowed voltage gap (0.49 V), and specific capacity (808.5 mAh•g^-1) for PtCo@Co-BA-Fe₃C/NC in Zn-air batteries are achieved with long-term cycling measurements over 776 h, which is obviously better than the Pt/C + RuO₂ catalyst. The interfacial electronic interaction of PtCo@Co-BA-Fe₃C/NC is investigated, which can accelerate electron transfer from Fe to Pt. Density functional theory calculations also indicate that the interfacial potential regulates the binding energies of the intermediates to achieve the best performance.

Introduction of Surface Modifiers on the Pt-Based Electrocatalysts to Promote the Oxygen Reduction Reaction Process

The design of Pt-based electrocatalysts with high efficiency towards acid oxygen reduction reactions is the priority to promote the development and application of proton exchange membrane fuel cells. Considering that the Pt atoms on the surfaces of the electrocatalysts face the problems of interference of non-active species (such as OH_ad, OOH_ad, CO, etc.), high resistance of mass transfer at the liquid-solid interfaces, and easy corrosion when working in harsh acid. Researchers have modified the surfaces' local environment of the electrocatalysts by introducing surface modifiers such as silicon or carbon layers, amine molecules, and ionic liquids on the surfaces of electrocatalysts, which show significant performance improvement. In this review, we summarized the research progress of surface modified Pt-based electrocatalysts, focusing on the surface modification strategies and their mechanisms. In addition, the development prospects of surface modification strategies of Pt-based electrocatalysts and the limitations of current research are pointed out.

Ultrathin Ultralow-Platinum Catalyst Coated Membrane for Proton Exchange Membrane Fuel Cells

Catalyst coated membrane (CCM) is the core component of proton exchange membrane fuel cells and is routinely fabricated by spraying Pt/C slurries onto membrane, resulting in low activity and thick catalyst layer (CL, 5-10 µm) with an unaffordable Pt loading of 0.2-0.4 mg cm^-2 and a large mass transfer resistance at cathode. Highly active ultrathin ultralow-Pt CL (UUCL) is urgently required, but remains rare. Herein, wet-chemical direct growth of UUCLs on both sides of membrane to achieve integrated ultrathin ultralow-Pt catalyst coated membranes (UUCCMs) with a cathodic CL thickness of 79.7 ± 15.0 nm and a Pt loading of 20.2 ± 1.6 µg cm^-2 is reported. The key to this unique fabrication is the release of proton from membrane to regioselectively initiate the growth of interconnected Pd nanoneedle clusters array on membrane, followed by high-density deposition of Pt nanoparticles on Pd (Pt/Pd UUCLs). The single cell of UUCCMs exhibits the highest mass peak power density of 59.9 W mg_Pt,Cathode ^-1 in the literature. The exceptional activity originates from high electrochemically active surface area, remarkable oxygen reduction reaction activity closely correlated with strain, and electronic effect at Pt/Pd interface, as well as improved mass transfer and optimal water management.

Low-Loading Sub-3 nm PtCo Nanoparticles Supported on Co-N-C with Dual Effect for Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells

Developing low-loading Pt-based catalysts possessing glorious catalytic performance can accelerate oxygen reduction reaction (ORR) and hence significantly advance the commercialization of proton exchange membrane fuel cells. In this report, we propose a hybrid catalyst that consists of low-loading sub-3 nm PtCo intermetallic nanoparticles carried on Co-N-C (PtCo/Co-N-C) via the microwave-assisted polyol procedure and subsequent heat treatment. Atomically dispersed Co atoms embedded in the Co-N-C carriers diffuse into the lattice of Pt, thus forming ultrasmall PtCo intermetallic nanoparticles. Owing to the dual effect of the enhanced metal-support interaction and alloy effect, as-fabricated PtCo/Co-N-C catalysts deliver an extraordinary performance, achieving a half-wave potential of 0.921 V, a mass activity of 0.700 A mg_Pt^-1@0.9 V, and brilliant durability in the acidic medium. The fuel cell employing PtCo/Co-N-C as the cathode catalyst with an ultralow Pt loading of 0.05 mg cm^-2 exhibits an impressive peak power density of 0.700 W cm^-2, higher than that of commercial Pt/C under the same condition. Furthermore, the enhanced intrinsic ORR activity and stability are imputed to the downshifted d-band center and the strengthened metal-support interaction, as revealed by density functional theory calculations. This report affords a facile tactic to fabricate Pt-based alloy composite catalysts, which is also applicable to other alloy catalysts.

Recent Advances in Anode Electrocatalysts for Direct Formic Acid Fuel Cell-II-Platinum-Based Catalysts

Platinum-based catalysts have a long history of application in formic acid oxidation (FAO). The single metal Pt is active in FAO but expensive, scarce, and rapidly deactivates. Understanding the mechanism of FAO over Pt important for the rational design of catalysts. Pt nanomaterials rapidly deactivate because of the CO poisoning of Pt active sites via the dehydration pathway. Alloying with another transition metal improves the performance of Pt-based catalysts through bifunctional, ensemble, and steric effects. Supporting Pt catalysts on a high-surface-area support material is another technique to improve their overall catalytic activity. This review summarizes recent findings on the mechanism of FAO over Pt and Pt-based alloy catalysts. It also summarizes and analyzes binary and ternary Pt-based catalysts to understand their catalytic activity and structure relationship.

Rare earth Y doping induced lattice strain of mesoporous PtPd nanospheres for alkaline oxygen reduction electrocatalysis

The synthesis of catalysts with controllable morphology and composition is important to enhance the catalytic performance for oxygen reduction reaction (ORR). Herein, trimetallic PtPdY mesoporous nanospheres (PtPdY MNs) are produced via a one-step chemical reduction method applying F127 as soft temple under acidic condition. The mesoporous structure provides a large contact area and also stimulates the diffusion and mass transfer of reactants and products. Besides, synergistic effect among Pt, Pd and Y elements effectively alters their electronic structure, enhancing the catalytic activity. Therefore, the PtPdY MNs show excellent ORR permanence to Pt/C under the alkaline solution. This study offers an effective channel for the preparation of mesoporous metals with rare earth metal doping towards promising electrocatalytic applications.

Pt-Co Electrocatalysts: Syntheses, Morphologies, and Applications

Pt-Co electrocatalysts have attracted significant attention because of their excellent performance in many electrochemical reactions. This review focuses on Pt-Co electrocatalysts designed and prepared for electrocatalytic applications. First, the various synthetic methods and synthesis mechanisms are systematically summarized; typical examples and core synthesis parameters are discussed for regulating the morphology and structure. Then, starting with the design and structure-activity relationship of catalysts, the research progress of the morphologies and structures of Pt-Co electrocatalysts obtained based on various strategies, the structure-activity relationship between them, and their properties are summarized. In addition, the important electrocatalytic applications and mechanisms of Pt-Co catalysts, including electrocatalytic oxidation/reduction and bifunctional catalytic reactions, are described and summarized, and their high catalytic activities are discussed on the basis of their mechanism and active sites. Moreover, the advanced electrochemical in situ characterization techniques are summarized, and the challenges and direction concerning the development of high-performance Pt-Co catalysts in electrocatalysis are discussed.

d-sp orbital hybridization: a strategy for activity improvement of transition metal catalysts

Orbital hybridization to regulate the electronic structures and surface chemisorption properties of transition metals has been extensively investigated for searching high-performance catalysts toward various reactions. Unlike conventional d-d hybridization, the d-sp hybridization interaction between transition metals and p-block elements could result in surprising electronic properties and catalytic activities. This feature article highlights the recent progress in the development of high-performance transition metal-based catalysts through the extraordinary d-sp hybridization strategy, particularly for energy-related electrocatalytic applications. We start by giving an introduction of fundamental concepts associated with electronic structures of transition metal catalysts, including the Sabatier principle, d-band theory, electronic descriptor, as well as the comparison of d-d hybridization and d-sp hybridization strategies. Then, we summarize the theoretical and experimental advances in d-sp hybridization catalysts, including p-block element-doped metal catalysts, intermetallic catalysts and supported metal catalysts, with emphasis on the important roles of d-sp hybridization in tuning catalytic performances. Finally, we present existing challenges and future development prospects for the rational design of advanced d-sp hybridization catalysts.