Mass Activity Loss Research Articles

The key role of the second material's OER activity on MOR durability enhancement of the Pt alloys

Pt-based precious metal catalysts are generally regarded as the best catalyst materials for direct methanol fuel cells due to their high inherent methanol oxidation (MOR) activity. However, the commercial application of Pt catalyst is still facing with severe durability problem. The CO formed by the incomplete oxidation of methanol will occupy the Pt active site, hindering the further progress of the MOR reaction and causing the rapid attenuation of the activity. In this work, a MOR durability enhancement strategy that relation to the OER performance of the second materials M (M=Ni, Co, Fe and Cu) is reported. The precise electrochemical test results showed that the MOR durability of Pt-M alloy changes with the second material, which is related to the OER activity of M materials. The smaller the overpotential and tafel slopes of the M material, the better the MOR durability. Via M material screening, the Co element with the lowest OER overpotential among M promoted the Pt-Co alloy material with the highest MOR durability, resulting an excellent durability sustain 7000 times CV cycles with just 0.53 A mg−1Pt mass activity loss. According to the current generally accepted OER and MOR reaction mechanism, the association of MOR durability with OER activity is most likely derived from the same reaction step of M-OH formation, which played a key role on both reaction. This relationship between OER overpotential and MOR durability helps to screen the second material from the perspective of OER activity to improve the MOR durability of Pt catalysts, which is of great significance for the development of Pt-based CO-resistant MOR catalysts.

Ultrathin ternary PtNiRu nanowires for enhanced oxygen reduction and methanol oxidation catalysis via d-band center regulation

Direct methanol fuel cells rely on the efficiency of their anode/cathode electrocatalysts to facilitate the methanol oxidation reaction and oxygen reduction reaction, respectively. Platinum-based nanocatalysts are at the forefront due to their superior catalytic properties. However, the high-cost, scarcity, and low CO tolerance of platinum pose challenges for the scalable application of DMFCs. Herein, we report novel ultrathin ternary PtNiRu alloy nanowires to improve Pt utilization and CO tolerance. These novel electrocatalysts incorporate the oxophilic metal Ru into ultrathin PtNi nanowires, aiming to enhance the intrinsic activity of platinum while leveraging the long-term durability and high utilization efficiency provided by the bimetallic synergistic effect. The PtNiRu NWs significantly enhance both mass activity and specific activity for ORR, performing about 6.9 times and 3.9 times better than commercial Pt/C, respectively. After a rigorous durability test of 10,000 cycles, the PtNiRu NWs only exhibited a 25.2 % loss in mass activity. Additionally, for MOR, the MA and SA of PtNiRu NWs exceed that of Pt/C catalyst by 4.30 and 2.72 times, respectively, and exhibit exceptional resistance to CO poisoning. Theoretical insights from density functional theory calculations suggest that the introduction of Ru modulates the d-band center of the surface Pt atoms, which contributes to decreased binding strength of oxygenated species and an elevated dissolution potential, substantiating the enhanced performance metrics, and the durability enhancement stems from the stronger PtM bonds than those in PtNiRu NWs resulted from PtRu covalent interactions. These findings not only provide a new perspective on platinum-based nanocatalysts but also significantly advance the quest for more efficient and durable electrocatalysts for DMFCs, representing a substantial stride in fuel cell technology.

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.

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.

TiO2 Nanolayer–Coated Carbon as Pt Support for Enhanced Methanol Oxidation Reaction

Abstract To facilitate the large-scale application of direct methanol fuel cells (DMFCs), the issue of low Pt/C durability due to Pt degradation and carbon corrosion in harsh DMFC operating conditions must be addressed. A promising strategy is to hybridize metal oxides with carbon materials, resulting in a durable and conductive support that exhibits a strong metal-support interaction (SMSI) effect on platinum nanoparticles (Pt NPs). In this study, we introduced a TiO2 coating on carbon black, creating a TiO2 nanolayer between Pt and carbon black. The nanolayer not only protects the carbon black but also activates the SMSI effect on Pt. The resulting Pt/C@TiO2 electrocatalyst exhibits superior durability than commercial Pt/C. After the accelerated durability test, the mass activity loss of the methanol oxidation reaction (MOR) of Pt/C@TiO2 (32%) is significantly lower than that of Pt/C (46.8%). Moreover, the MOR activity of Pt/C@TiO2 is higher than Pt/C as well. It suggests that Pt/C@TiO2 shows great potential as a highly durable and active electrocatalyst for DMFCs.

Rational Design and Synthesis of Novel Catalyst Support for PEMFCs

Catalysts based on metal-organic frameworks (MOFs) are promising candidates to enable fuel cells with higher performance and durability. Our recently developed PtCo catalyst on porous carbon support produced by pyrolysis of Ce-doped-ZIF (PtCo/Ce-ZIF) shows record-high outstanding performance and durability in fuel cell testing. The cell was operated under the conditions prescribed by the Million Mile Fuel Cell Truck Consortium (M2FCT) consortium (250 kPa, 85% relative humidity (RH), 90 C cell temperature, and 15% oxygen). At application-relevant operating voltages of 0.7 V and higher, the PtCo/Ce-ZIF exhibited higher performance than the commercial catalyst. The PtCo/Ce-ZIF catalyst at 0.7 V achieved a life beginning-of-life (BOL) performance level of 1.38 A/cm2; even more importantly, it showed substantially higher durability. The PtCo/Ce-ZIF catalyst provided a current density of 1.25 A/cm2 at 0.7 V after 90K accelerated stress test (AST) cycles, exceeding the M2FCT target of >1.07 A/cm2. The PtCo/Ce-ZIF also showed higher mass activity and greatly improved retention of mass activity of 0.77 A/mgPt vs. 0.54 A/mgPt, at BOL and ending of life (EOL), respectively, ~34 % mass activity loss after 90K AST cycles, exceeding the DOE target of <40% loss after 30K AST cycles. This study demonstrates that MOF-based catalysts are the leading candidates to enable fuel cell commercialization and deployment in support of the global effort to reduce greenhouse gas emissions.

Fabrication and Scale-up of Highly Durable Heavy Duty Fuel Cell MEAs

Medium and heavy-duty PEM fuel cells operate under much harsher conditions than light duty fuel cells and are expected to last 25,000-30,000 hours in the field. These systems must operate successfully in the presence of impurities, starting and stopping, freezing and thawing, humidity and load cycling. Therefore, materials, components, and interfaces used in such systems must be highly resistant to severe mechanical and chemical stress.Novel, highly active stable Pt and ordered PtCo intermetallic nanoparticles with well-controlled particle size and composition have been synthesized on a highly efficient PGM-free single metal active site rich carbon, to maximize their synergistic effects for enhanced performance and durability. Integrating these catalysts integrated with high O2 permeability ionomer (HOPI) in membrane electrode assemblies (MEAs) improved their fuel cell performance and durability, allowing the MEAs to achieve >600 mA/mgPt at 0.9 VIR-free with a mass activity loss < 30% after 150k square wave accelerated stress test (AST) cycles; and > 600 mA/cm2 (~65% efficiency) at 0.8 V, with a performance loss < 40 mV after 150K AST cycles.In a PEM fuel cell, the catalyst ink formulation and mixing processes control catalyst layer coating quality, electrode morphology, and the resulting fuel cell performance and durability. Catalyst ink properties are a result of complex solvent-catalyst-ionomer interactions that depend on the mixing method employed. Here, we compare the performance and durability of electrodes made from bath sonicated inks for ultrasonic spray coating before and after the catalyst scale up. Ink rheology and catalyst particle size are used to correlate ink properties to electrode morphology and structure and ensure consistency from batch to batch, and from small lab scale to subsequent scale-up. We evaluate and discuss the challenges that arise when transitioning from spray coating catalyst ink on a small scale, directly on a membrane, to coating more viscous inks on gas diffusion layers (GDLs), made via Mayer rod coating of ball milled inks, in anticipation of developing a roll-to-roll (R2R) fabrication process. The MEA performance and durability of the novel catalyst was also evaluated under heavy duty operating conditions using M2FCT’s AST, i.e., in H2/Air, 90 ⁰C, and 50% RH.This work provides a comprehensive understanding of interactions between Pt, PtCo, carbon, ionomer, membrane, and GDLs and their impact on electrode structure, fuel cell performance and durability, as well as considerations for scale up to a R2R fabrication process. The attained information will be used to improve fuel cell electrode design, fabrication and scale-up.Acknowledgement: The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-SC0021671. Figure 1. (a) Comparison of H2-air fuel cell performance of HOPI-based CCMs prepared with different volume ratios of H2O to n-propanol (nPA). (b) Dependence of fuel cell performance at 0.8 and 0.7 V of the CCMs prepared with different volume ratios of H2O to nPA. (c) MEA performance of the best performing Pt (40 wt. %)/Mn-N-C MEA under various relative humidity. (d) The high-frequency resistance (HFR) of HOPI-based CCMs prepared with a volume ratio of 2:1. All of the tests were performed with a 5 cm2 differential cell with 14 parallel channels. The cell temperature was 80 ⁰C, the flow rates for H2 and air are 500 and 2000 sccm, and the backpressure is 250 kPaabs. The Pt loading in the anode and cathode are 0.1 and 0.2 mgPt/cm2, respectively. Figure 1

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.

A high-performance and anti-sulfur poisoning oxygen reduction reaction catalysts derive from molybdenum-doping on PtCo alloy nanoparticles surface

During the operation of fuel cell vehicles, sulfur dioxide (SO2) as a primary air pollutant can be transported to the cathode of the fuel cell with the air, leading to poisoning of the cathodic Pt-based catalyst, and subsequently, causing performance degradation and even shutdown. Therefore, there is an urgent need for SO2-tolerant Pt-based catalysts to mitigate poisoning in the cathodic oxygen reduction reaction (ORR). Herein, we report a carbon-supported Mo doped PtCo alloy catalyst with high-performance and anti-sulfur poisoning, termed as Mo-PtCo/C. Detailed investigations demonstrate that the Co in PtCo alloy nanoparticles (NPs) greatly promote ORR activity but do little to improve the SO2-tolerance. However, the PtCo alloy NPs doped with Mo not only exhibit a higher ORR activity, but also a superior SO2 poisoning resistance and a superior recovery performance. The optimal Mo-PtCo/C catalyst demonstrates a high initial mass activity of 871.0 mA mgPt−1, which is higher than that of the PtCo/C catalyst (initial value=558.8 mA mgPt−1) and 6.6 times higher than that of the commercial Pt/C (20 wt.% Pt, initial value=174.6 mA mgPt−1), along with a low mass activity loss of 36.19% after SO2 poisoning, which is much lower than 82.4% of the PtCo/C catalyst and 81.3% of the commercial Pt/C. More importantly, it is revealed that MoO3 formed on the PtCo NPs surface after Mo doping helps to reduce the electrooxidation potentials of SO2 to the operating potential of the fuel cell, thereby markedly boosting SO2-tolerance. Furthermore, the fuel cells test also confirmed that MoO3 improved the SO2-tolerance of the Mo-PtCo/C catalysts.

Multifunctional Pt3Rh–Co3O4 alloy nanoparticles with Pt-enriched surface and induced synergistic effect for improved performance in ORR, OER, and HER

Engineering high-performance electrocatalysts to improve the kinetics of parallel electrochemical reactions in low-temperature fuel cells, water splitting, and metal-air battery applications is important and inevitable. In this study, by employing a chemical co-reduction method, we developed multifunctional Pt3Rh–Co3O4 alloy with uniformly distributed ultrafine nanoparticles (2–3 nm), supported on carbon. The presence of Co3O4 and the incorporation of Rh led to a strong electronic and ligand effect in the Pt lattice environment, which caused the d-band center of Pt to shift. This shift improved the electrocatalytic performance of Pt3Rh–Co3O4 alloy. When Pt3Rh–Co3O4/C was used to catalyze the oxygen reduction reaction (E1/2: 0.75 V), oxygen evolution reaction (η10: 290 mV), and hydrogen evolution reaction (η10: 55 mV), it showed greater endurance (mass activity loss of only 7%–17%) than Pt–Co3O4/C and Pt/C catalysts up to 5000 potential cycles in perchloric acid. Overall, the as-prepared Pt3Rh–Co3O4/C showed high multifunctional electrocatalytic potency, as demonstrated by typical electrochemical studies, and its physicochemical properties endorse their extended performance for a wide range of energy storage and conversion applications.

Advanced nickel-based catalysts for the hydrogen oxidation reaction in alkaline media synthesized by reactive spray deposition technology: Study of the effect of particle size

Anion exchange membrane fuel cells (AEMFCs) have been regarded as a promising low-cost alternative to proton exchange membrane fuel cells (PEMFCs) due to their potential to utilize platinum group metal (PGM) free catalysts and their recently demonstrated improvement in power density. However, the development of highly active and stable PGM-free electrocatalysts for the hydrogen oxidation reaction (HOR) in alkaline solutions remains a significant challenge. In this study, reactive spray deposition technology (RSDT) is used to fabricate a set of Ni/CeO2/C catalysts, and their activity toward the HOR is investigated as a function of the nanoparticle size. The structural and morphological characterization of as synthesized Ni/CeO2/C catalysts confirms that the RSDT is capable of precise control of the nanoparticle size by adjusting the deposition parameters. The electrochemical rotating disk electrode study shows that the Ni/CeO2/C catalyst with an average particle size distribution of 3 nm has the highest mass activity of 14.8 A gNi−1, which is among the highest values reported in the literature for Ni-based catalysts. Moreover, the post-test characterization, performed after the accelerated stress test (AST) measurements, reveals that both the catalyst's corrosion and particle size increase are the main contributors to the mass activity loss. The measured electrocatalytic performance confirms the feasibility of the RSDT fabricated Ni/CeO2/C nanoparticles as an efficient PGM-free HOR catalyst for application in AMEFCs, with additional development required to improve their durability.

Stabilizing Fe in intermetallic L10-PtAuFe nanoparticles with strong Au-Fe bond to boost oxygen reduction reaction activity and durability

The intrinsic reactivity of PtM alloys during the catalysis of oxygen reduction reactions (ORRs) under acidic conditions is deactivated by the unavoidable leaching of cocatalyst M. Herein, we propose an unprecedented “Au-stabilized strategy” to stabilize the Fe atoms in L10-PtAuFe via a strong Au-Fe bond. Simultaneously, the introduction of Au atoms regulates the Pt atomic electronic structure and increases resistance to Pt atomic oxidation, which is beneficial to further boost ORR activity and stability. As a result, the as-obtained L10-PtAuFe exhibits minimal loss of mass activity after accelerated durability tests and is far superior to L10-PtFe and commercial Pt/C. In addition, L10-PtAuFe shows fantastic ORR activity, with a 7.3-fold improvement in mass activity and a 4.5-fold increase in specific activity compared to that of commercial Pt/C. This novel Au-stabilized strategy provides a new avenue to stabilize the M atoms in L10-PtM alloys and further enhance their ORR activity and stability.

Nitrogen doped titania stabilized Pt/C catalyst via selective atomic layer deposition for fuel cell oxygen reduction

The electrochemical dissolution of platinum (Pt) based nanoparticles and the consequent Pt active sites losses and particle aggregation have become a critical stability issue for the commercial proton exchange membrane fuel cell. Herein, nitrogen doped titania (N-TiO2) stabilized Pt low-coordinated sites on a commercial Pt/C catalyst is achieved by simply coupling selective atomic layer deposition of TiO2 and following nitrogen doping process. Selectively deposited N-TiO2 on Pt nanoparticles keeps the exposure of Pt sites on (111) facets and increases the reduction states of Pt, which results in 1.7 times improvement of mass activity than commercial Pt/C. Besides, N-TiO2 stabilized commercial Pt/C catalyst exhibits outstanding durability enhancement, showing only a 14.0% loss of mass activity after 30,000 potential cycles of rotating disk electrode tests and 91.7% retention after durability tests in humid fuel cell condition. The shielding role of N-TiO2 could effectively inhibit the degradation of low-coordinated sites on Pt nanoparticles and maintain Pt size distribution, which is a promising strategy to prolong the lifetime of commercial Pt/C catalysts.

Synthesis of Platinum Nanocrystals Dispersed on Nitrogen-Doped Hierarchically Porous Carbon with Enhanced Oxygen Reduction Reaction Activity and Durability.

Platinum-based catalysts are widely used for efficient catalysis of the acidic oxygen reduction reaction (ORR). However, the agglomeration and leaching of metallic Pt nanoparticles limit the catalytic activity and durability of the catalysts and restrict their large-scale commercialization. Therefore, this study aimed to achieve a uniform distribution and strong anchoring of Pt nanoparticles on a carbon support and improve the ORR activity and durability of proton-exchange membrane fuel cells. Herein, we report on the facile one-pot synthesis of a novel ORR catalyst using metal-nitrogen-carbon (M-N-C) bonding, which is formed in situ during the ion exchange and pyrolysis processes. An ion-exchange resin was used as the carbon source containing R-N+(CH3)3 groups, which coordinate with PtCl62- to form nanosized Pt clusters confined within the macroporous framework. After pyrolysis, strong M-N-C bonds were formed, thereby preventing the leaching and aggregation of Pt nanoparticles. The as-synthesized Pt supported on the N-doped hierarchically porous carbon catalyst (Pt/NHPC-800) showed high specific activity (0.3 mA cm-2) and mass activity (0.165 A mgPt-1), which are approximately 2.7 and 1.5 times higher than those of commercial Pt/C, respectively. The electrochemical surface area of Pt/NHPC-800 remained unchanged (~1% loss) after an accelerated durability test of 10,000 cycles. The mass activity loss after ADT of Pt/NHPC-800 was 18%, which is considerably lower than that of commercial Pt/C (43%). Thus, a novel ORR catalyst with highly accessible and homogeneously dispersed Pt-N-C sites, high activity, and durability was successfully prepared via one-pot synthesis. This facile and scalable synthesis strategy for high-efficiency catalysts guides the further synthesis of commercially available ORR catalysts.

Pt‐Anchored‐Zirconium Phosphate Nanoplates as High‐Durable Carbon‐Free Oxygen Reduction Reaction Electrocatalyst for PEM Fuel Cell Applications

AbstractCommercially available platinum‐supported carbon (Pt/C) catalysts are the most widely used oxygen reduction reaction (ORR) electrocatalysts in polymer electrolyte membrane fuel cells (PEMFCs). However, inadequate active triple‐phase boundary formation and carbon oxidation in Pt/C during PEMFC operation shorten its lifetime and efficiency. In this direction, a new class of carbon‐free electrocatalysts for ORR is prepared by dispersing Pt nanoparticles on ZrP (Zirconium phosphates) nanoplates. In one case (ZrP@Pt), the Pt nanoparticles are found to be closely distributed and completely covering the ZrP nanoplates, whereas in the second case (Pt/ZrP), the Pt nanoparticles selectively restrict dispersion along the edges of the support. ZrP as the support displays an intrinsic proton conductivity of ≈0.5 × 10−4 S cm−1 at 70 °C, with an activation energy (Ea) of 0.19 eV. Pt/ZrP shows better durability after 3000 start‐stop cycles. The mass activity of Pt/ZrP is increased by 4.6 times compared to Pt/C, which exhibits a loss in mass activity by 1.37 times. The single‐cell level validation of ZrP@Pt, Pt/ZrP, and Pt/C as the electrocatalysts in PEMFC at an operating potential of 0.60 V shows the achievable current densities of 0.600, 0.890, and 0.890 A cm−2.

Facile synthesis of L10-PtFe/C intermetallic catalysts with superior catalytic durability for the oxygen reduction reaction.

An o-PtFe/C intermetallic catalyst was prepared by a facile thermal reduction method with the average particle size of only 6.6 nm in the presence of urea. The loss of mass activity is only 25.9% after 50 000 cycles. This work provides guidance on the suppression of grain coarsening for high-temperature synthesis of Pt-based intermetallic catalysts.

N-Doped Carbon Nanotube Shell Encapsulating the NiFe Metal Core for Enhanced Catalytic Stability in Methanol Oxidation Reaction by the Structural Cooperation Mechanism.

Exploitation of high-efficiency catalysts toward methanol oxidation is a pivotal step to promote the commercialization of direct methanol fuel cells. Herein, a strategy is demonstrated to prepare nitrogen-doped carbon nanotubes with NiFe metal particles (NiFe@N-CNT) as the carrier material of Pt nanoparticles. Combining SEM and TEM, NiFe metal particles are fully encapsulated in N-CNTs, and they form the metal core and carbon nanotube shell structure based on the structural cooperation mechanism. Surprisingly, the as-prepared Pt/NiFe@N-CNT catalyst shows superior catalytic activity (1023 mA mg-1Pt) compared to commercial Pt/C (392 mA mg-1Pt), Pt/Ni@N-CNT (331 mA mg-1Pt), and Pt/Fe@N-CNT (592 mA mg-1Pt). After 1000 cycles, Pt/NiFe@N-CNT maintains the optimal catalytic activity (588 mA mg-1Pt), and its mass activity loss is 42.5%, which is better than those of commercial Pt/C (64.0%), Pt/Ni@N-CNT (67.7%), and Pt/Fe@N-CNT (59.6%) catalysts, indicating that the Pt/NiFe@N-CNT catalyst achieves excellent catalytic activity and stability, which stems chiefly from the homodispersed Pt nanoparticles and the generation of the metal core-carbon nanotube shell based on the structural cooperation mechanism. This study reports the facile construction of a metal core-carbon nanotube shell structure, which intrinsically ameliorates structural collapse of carrier material, thereby improving the catalytic stability of the Pt-based catalyst and broadening the view for design of other desire catalysts in methanol oxidation.

Ordered CoPt oxygen reduction catalyst with high performance and durability

A high-performance and durable polymer electrolyte membrane fuel cell cathode catalyst composed of an ordered L1 0 –CoPt core and a thin Pt shell was designed and prepared. Under practical fuel cell membrane electrode assembly testing conditions, the cathode catalyst showed an outstanding initial mass activity of 0.6 A/mg Pt , which satisfies the U.S. Department of Energy performance target while also meeting the durability target of less than 40% loss in mass activity after 30,000 accelerated stress test voltage cycles. The high structural stability of the L1 0 –CoPt@Pt-shell catalyst was confirmed by postmortem materials characterization, and the origin of this robustness was revealed by density functional theory calculations, where the barriers for diffusion of Co atoms were observed to be significantly increased in the ordered intermetallic core. • An intermetallic ORR catalyst was prepared through a scalable impregnation method • Mass activity of 0.6 A/mg Pt and high durability were achieved in fuel cell testing • H 2 /air power density of 0.87 W/cm 2 at 0.67 V was achieved with only 0.1 mgPt/cm 2 • Order-dependent energetics of vacancy-mediated diffusion were evaluated using DFT Fuel cells with high power density and high durability could contribute to the realization of net zero carbon emissions in the transportation sector. The catalyst reported here, which uses atomic-level ordering to stabilize Co within the intermetallic CoPt lattice, achieves higher Co retention and better durability compared with conventional CoPt catalysts. The origins of this high durability were investigated using density functional theory calculations, which revealed significantly higher barriers for Co diffusion in ordered catalysts compared with disordered ones. This new intermetallic catalyst is a promising candidate for deployment in transportation and other clean-energy fuel cell applications. An oxygen reduction reaction catalyst composed of core-shell CoPt nanoparticles possessing an ordered Co–Pt core and Pt shell shows excellent performance and durability in fuel cell testing.

Constructing uniform sub-3 nm PtZn intermetallic nanocrystals via atomic layer deposition for fuel cell oxygen reduction

The preparation of ultra-small structurally ordered Pt-based intermetallic nanocrystals (< 3 nm) is still challenging due to the sintering during high temperature ordering. We report a strategy to construct size and distribution controllable Pt-based intermetallic nanocrystals based on ultra-thin metal oxide coating on Pt nanoparticles via atomic layer deposition. The area-selective and thickness controllable metal oxide coatings can not only provide metal atoms for alloying, but also prevent the sintering of Pt nanoparticles during subsequently fast ordering reduction. The prepared uniform PtZn intermetallic nanocrystals with the size of 2.50 ± 0.65 nm achieve outstanding single-cell performance with the mass activity of 0.48 A mgPt−1 at 0.9 V and 10.42 % loss of mass activity after 30,000 voltage cycles, which is superior to commercial Pt/C. The enhanced activity and durability is attributed to the decreased binding energy of Pt-oxygen intermediates for weakly polarized surface Pt atoms and suppressed electrochemical Ostwald ripening.

Pt-Sn alloy shells with tunable composition and structure on Au nanoparticles for boosting ethanol oxidation.

Combining the core-shell structure with the optimization of surface composition and structure in the shell is a fantastic strategy to enhance the electrocatalytic performances. Here, we synthesized trimetallic Au@PtxSny core-shell nanoparticles (NPs) with tunable composition and structure of Pt-Sn alloyed shells. Impressively, the Au@PtSn core-shell NPs with hexagonal PtSn alloyed shells exhibited the highest mass activity and specific activity toward ethanol oxidation reaction (EOR) in alkaline electrolyte, which are 13.0 and 12.7 times higher than those of the commercial Pt/C. In addition, the Au@PtSn core-shell NPs displayed the best stability compared to commercial Pt/C, with only 44.8% loss vs. 86.8% loss in mass activity after 1,000 s due to the stronger anti-poisoning ability for reaction intermediates. The theory calculations reveal that the introduction of Au core and alloying Pt with Sn both endow Pt with an appropriate d-band center, and thus effectively boosting the EOR activity.