Commercial Pt-based Catalysts Research Articles

Mechanistic study of Eu single atoms occupying four vacancy centers as potential electrocatalysts for the oxygen reduction reaction.

The oxygen reduction reaction (ORR) on the oxygen electrode plays a critical role in rechargeable metal-air batteries, and the development of electrochemical energy storage and conversion technologies for the ORR is of great significance. In this study, the catalytic performance of rare earth-doped graphene (EuNxC6-x-Gra) as an electrocatalyst for the ORR was investigated. The results showed that a majority of the catalysts exhibited good ORR catalytic activity under acidic conditions, with some approaching or even surpassing commercial Pt-based catalysts (ηORR = 0.45 V). Particularly, EuN2C4-2-Gra demonstrated an ηORR of 0.38 V. It has been observed that the f-band center of Eu atoms increases with an increasing number of N atoms, and the charge distribution exhibits a "U" shape. There is a decreasing trend from N0 to N3 and an increasing trend from N4 to N6. By incorporating the proportional relationship of the adsorption free energies of reaction intermediates (ΔG*ads), a volcano diagram was constructed to rapidly assess catalytic activity. Finally, an intrinsic characteristic descriptor φ was formulated to quantitatively describe the relationship between φ and ηORR, providing a new tool for predicting and designing catalysts. This will provide guidance for the development and design of high-performance rare earth single atom catalysts.

Multi-dimensional PtRu/Co3O4-Activated carbon Nano-Electrocatalyst: Metal–Support Interaction, and electronic contributions towards methanol electrooxidation in alkaline fuel cells

In this work, we report PtRu alloy system supported on Co3O4-activated carbon (Co3O4-C) prepared by direct reduction of H2PtCl6 and RuCl3 solutions as a highly active and durable electrocatalyst for methanol oxidation reaction. The electrochemical activity of the electrocatalysts was evaluated using electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), cyclic voltammetry (CV), and chronoamperometry (CA). The formation of PtRu alloy on the Co3O4-C matrix, as well as their electronic interactions, is confirmed by employing X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques. The electrocatalysts showed distinct electrocatalytic activity in alkaline medium, depending on whether the catalysts contained PtRu alloy and whether they were supported on the hybrid Co3O4-C, proving their unique contributions to the electrocatalytic reaction. Benefiting from the strong metal-support interaction (SMSI) and electronic interaction between Pt and Ru, the PtRu/Co3O4-C displayed a highly efficient electrocatalytic performance with a mass activity of 6709 mAmgPt-1, a substantial improvement compared to the commercial Pt-based benchmark catalyst, which achieved only 212 mAmgPt-1. Furthermore, the PtRu/Co3O4-C showed excellent stability after 10 000 s, high durability after 500 cycles retaining 94 % of current density, and higher tolerance for CO. This enhanced catalytic performance can be attributed to the small nanoparticle sizes, high dispersion, large ECSA of 102.1 m2/g, and the synergy resulting from electronic coupling interactions.

A single site ruthenium catalyst for robust soot oxidation without platinum or palladium

The quest for efficient non-Pt/Pd catalysts has proved to be a formidable challenge for auto-exhaust purification. Herein, we present an approach to construct a robust catalyst by embedding single-atom Ru sites onto the surface of CeO2 through a gas bubbling-assisted membrane deposition method. The formed single-atom Ru sites, which occupy surface lattice sites of CeO2, can improve activation efficiency for NO and O2. Remarkably, the Ru1/CeO2 catalyst exhibits exceptional catalytic performance and stability during auto-exhaust carbon particle oxidation (soot), rivaling commercial Pt-based catalysts. The turnover frequency (0.218 h−1) is a nine-fold increase relative to the Ru nanoparticle catalyst. We further show that the strong interfacial charge transfer within the atomically dispersed Ru active site greatly enhances the rate-determining step of NO oxidation, resulting in a substantial reduction of the apparent activation energy during soot oxidation. The single-atom Ru catalyst represents a step toward reducing dependence on Pt/Pd-based catalysts.

Atomic-Level Regulation of Cu-Based Electrocatalyst for Enhancing Oxygen Reduction Reaction: From Single Atoms to Polymetallic Active Sites.

The slow kinetics of cathodic oxygen reduction reactions (ORR) in fuel cells and the high cost of commercial Pt-based catalysts limit their large-scale application. Cu-based single-atom catalysts (SACs) have received increasing attention as a promising ORR catalyst due to their high atom utilization, high thermodynamic activity, adjustable electronic structure, and low cost. Herein, the recent research progress of Cu-based catalysts is reviewed from single atom to polymetallic active sites for ORR. First, the design and synthesis method of Cu-based SACs are summarized. Then the atomic-level structure regulation strategy of Cu-based catalyst is proposed to improve the ORR performance. The different ORR catalytic mechanism based on the different Cu active sites is further revealed. Finally, the design principle of high-performance Cu-based SACs is proposed for ORR and the opportunities and challenges are further prospected.

The graphene-supported Lanthanum oxide cluster as efficient bifunctional electrocatalyst for oxygen reaction

The development of bifunctional oxygen electrode electrocatalysis for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) plays a vital role in the solution of the energy crisis as well as the environmental pollution. The purpose of this paper is to investigate the potential of graphene-supported lanthanum oxide clusters (La2O3-Gra) as a bifunctional electrocatalyst; the results show that the optimal catalytic site (up-down1) of the most stable configuration (O-Gra-1) modified by OH group shows outstanding bifunctional catalytic activity with ηORR of 0.51 V and ηOER of 0.52 V, which can be compared to the commercial Pt-based ORR catalysts and the Ru/Ir-oxides OER catalysts. Furthermore, there is a strong scale-dependent relationship between the adsorption free energy (ΔGads) of reaction intermediates, resulting in volcano plots between the catalytic activity and ΔGads, which provides a valuable description for future performance prediction of structurally similar catalysts.

(Invited) Catalyst Challenges for Ion-Pair High Temperature Proton Exchange Membrane Fuel Cells

High temperature proton exchange membrane fuel cells (HT-PEMFCs) have several merits over low temperature PEMFCs, including simplified fuel cell systems and high CO tolerance. Recently developed ion-pair HT-PEMFCs1 has a significantly lower concentration of phosphoric acids in the membrane-electrode assembly (MEA) that allows ion-conducting binders (ionomers) in the electrodes. Here, we first explain the difference in MEA configurations and fuel cell performance between conventional polybenzimidazole-based and ion-pair HT-PEMFCs2. Next, we discuss catalyst challenges for ion-pair HT-PEMFCs by comparing half-cell and single-cell results.We focus on three critical areas in that electrocatalysts face challenges: i) phosphate anion poisoning on oxygen reduction reaction catalysts, ii) phenyl adsorption on hydrogen oxidation reaction catalysts and iii) phosphoric acid flooding. Research progress mitigating those adverse effects is demonstrated using various commercial Pt-based catalysts and homemade ionomers. Lastly, we provide general directions for designing high-performing catalysts of ion-pair HT-PEMFCs.References Lee, K. S.; Spendelow, J. S.; Choe, Y. K. Fujimoto, C.; Kim, Y. S. An Operationally Flexible Fuel Cell Based on Quaternary Ammonium-Biphosphate Ion Pairs, Nature Energy, 1, 16120 (2016).Lim, K. H.; Lee, A. S.; Atanasov, V.; Kerres, J.; Park, E. J.; Adhikari, S.; Maurya, S.; Manriquez, L. D.; Jung, J.; Fujimoto, C.; Matanovic, I.; Jankovic, J.; Hu, Z.; Jia, H.; Kim, Y. S. Protonated phosphonic acid electrodes for high power heavy-duty vehicle fuel cells, Nature Energy, 7, 248 (2022).

General Carbon-Supporting Strategy to Boost the Oxygen Reduction Activity of Zeolitic-Imidazolate-Framework-Derived Fe/N/Carbon Catalysts in Proton Exchange Membrane Fuel Cells.

The oxygen reduction reaction (ORR) activity of the Fe/N/Carbon catalysts derived from the pyrolysis of zeolitic-imidazolate-framework-8 (ZIF-8) has been still lower than that of commercial Pt-based catalysts utilized in the proton exchange membrane fuel cells (PEMFCs) due to low density of accessible active sites. In this study, an efficient carbon-supporting strategy is developed to enhance the ORR efficiency of the ZIF-derived Fe/N/Carbon catalysts by increasing the accessible active site density. The enhancement lies in (i) improving the accessibility of active sites via converting dodecahedral particles to graphene-like layered materials and (ii) enhancing the density of FeNx active sites via suppressing the formation of nanoparticles as well as providing extra spaces to host active sites. The optimized and efficient Fe/N/Carbon catalyst shows a half-wave potential (E1/2) of 0.834 V versus reversible hydrogen electrode in acidic media and produces a peak power density of 0.66 W cm-2 in an air-fed PEMFC at 2 bar backpressure, outperforming most previously reported Pt-free ORR catalysts. Finally, the general applicability of the carbon-supporting strategy is confirmed using five different commercial carbon blacks. This work provides an effective route to derive Fe/N/Carbon catalysts exhibiting a higher power density in PEMFCs.

Efficient and cost-effective ORR electrocatalysts based on low content transition metals highly dispersed on C3N4/super-activated carbon composites

Oxygen reduction reaction (ORR) is one of the most important electrochemical reactions for fuel cells. However, commercial Pt-based catalysts used have important limitations such as their deactivation by carbon monoxide and Pt scarcity. In the present work, small and highly-dispersed copper and iron clusters were anchored onto composite supports based on carbon nitride (C3N4) nanostructures and a highly porous carbon material. Catalysts with a moderate carbon nitride content showed an interesting catalytic behaviour because of the combination of the metallic active sites and the availability of micropores, which play an active role in ORR. The presence of either Fe or Cu in the synthesis affected the structure of the resulting composite materials, as well as their electrocatalytic activity. Copper-based materials showed superior catalytic activity, which is supported by the information obtained from the evaluation of the system using DFT computational calculations.

Highly dispersed and ultrafine Co3O4@N-doped carbon catalyst derived from metal-organic framework for efficient oxygen reduction reaction

Electrocatalysts are composed of transition metal/metal oxide and N-doped carbon can overcome the sluggish kinetics of oxygen reduction reaction (ORR). Herein, The Co3O4/ketjen black (KB) @MOF-derived with uniformly dispersed and ultrafine Co3O4 nanoparticles (1-5 nm) is synthesized by a facile in-suit method and subsequent mild pyrolysis process. It exhibits enhanced activity with onset potential (Eonset) of 0.96 V (vs. RHE) and a half-wave potential (E1/2) of 0.86 V (vs. RHE) in 0.1 M KOH solution, the excellent durability with E1/2 a small negative shift of 10 mV after 5000 continuous cycles and good methanol-tolerance property. The ultrahigh catalytic performance of Co3O4/KB@MOF-derived can be ascribed to the small particle size range of 1-5 nm of Co3O4, as well as the strong interaction between the in-situ formed N-Co3O4 active sites and substrate under the mild calcination temperature. Above all, these indicate that the as-prepared Co3O4/KB @MOF-derived may be a good alternative to commercial Pt-based catalysts.

Fast and Facile Synthesis of Pt Nanoparticles Supported on Ketjen Black by Solution Plasma Sputtering as Bifunctional HER/ORR Catalysts

Hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) are two core electrochemical processes involved in hydrogen fuel cell (HFC) technology. ORR is a cathodic reaction occurring in HFC, whereas HER can convert the H2O byproduct from HFCs into H2 gas via water splitting. Platinum (Pt)-based catalysts are the most effective catalysts for both reactions. In this work, we used a fast, facile, and chemical-free method, called solution plasma sputtering (SPS), to synthesize Pt nanoparticles supported on Ketjen Black (KB). The discharge time was varied (5, 10, and 20 min) to alter the Pt loading. Characterization results revealed that the plasma did not affect the morphology of KB, and the Pt loading on KB increased with increasing discharge time (5.5–17.9 wt%). Well-crystallized Pt nanoparticles, ~2–5 nm in diameter, were obtained. Electrochemical measurements revealed that Pt/KB exhibited bifunctional catalytic activity toward HER and ORR in 0.5 M H2SO4 solution. Both HER and ORR activities enhanced as the loading of Pt nanoparticles increased with a longer discharge time. Moreover, Pt/KB exhibited better HER and ORR stability than a commercial Pt-based catalyst, which was attributed to the stronger adhesion between Pt nanoparticles and KB support. Thus, SPS can be applied as an alternative synthesis method for preparing Pt/KB catalysts for HER and ORR.

N-Doped porous carbon nanosheets decorated with graphitized carbon layer encapsulated Co9S8 nanoparticles: an efficient bifunctional electrocatalyst for the OER and ORR.

Electrocatalysts with highly effective activity for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are considered to be the key factor of renewable energy technologies. Herein, we designed and synthesized bi-functional electrocatalyst Co9S8/C nanosheets (NSs) by reducing the Co3O4/C NS precursor with sodium sulfide. From the structural characterization, Co9S8 is anchored on the graphitized carbon NSs homogeneously. According to the electrochemical measurements, the Co9S8/C NSs show excellent electrocatalytic activity towards both the ORR (Eonset = 0.892 V vs. RHE and E1/2 is 0.778 V vs. RHE) and OER (Eonset = 1.50 V vs. RHE and the overpotential is 0.434 V vs. RHE at 10 mA cm-2) in 0.1 M KOH solution. In the ORR, Co9S8/C catalyzes through a 4-electron process like the commercial Pt-based catalyst. In addition, the Co9S8/C NSs show great long-term stability. The Co9S8/C NSs show excellent catalytic performance due to the rich active sites and two-dimensional sheet structure. The developed strategy offers an effective method for preparing bi-functional electrocatalysts for both the OER and ORR.

On the challenges and constrains of ultra-low emission limits: Formaldehyde oxidation in catalytic sinusoidal-shaped channels

This paper presents the results of a study on kinetics and mass transfer in a catalytically coated metallic monolith converter with sinusoidal-shape channels. Hereby, experimental and modelling studies are performed on a commercial Pt-based oxidation catalyst for total oxidation of formaldehyde applicable in after-treatment system of lean-burn gas engines. For the description of flow field and mass transport inside the channel as well as species diffusion and chemical reaction inside the porous washcoat, a three-dimensional approach is applied and the calculations are performed, using ANSYS-FLUENT. Three different computational models representing different washcoat distribution are compared. The effects of washcoat distribution and mass transfer on kinetics and catalyst activity are investigated in detail and the numerically obtained results are compared with experimental data.Despite of a very high intrinsic reaction rate at operation temperature, the complete conversion of formaldehyde could not be achieved experimentally. All three models have shown to operate in mass transport limited regime, where the diffusion distance from bulk to catalyst surface as well as reactant concentration play a significant role. Thus, very low levels of formaldehyde emissions are technically hard to achieve and a long catalyst is required to overcome the low diffusion rate due to the small concentration gradient. The computational results indicate also that due to individual structure of each channel of metallic monolith in real applications, they can behave distinctly from each other and one channel does not represent the entire monolith. It is also evident from simulated data that the lack of knowledge of washcoat properties and distribution may bring about misleading results since apparent reaction rates can be highly sensitive to this parameter for particularly catalytic reactions under mass-transfer-controlled conditions.

Effect of surface morphology on catalytic activity for NO oxidation of SmMn2O5 nanocrystals

SmMn2O5 has been reported to be a promising alternative to substitute the current commercial Pt-based catalysts for NO oxidation. In this work, single-crystalline orthorhombic SmMn2O5 nanorods and nanoparticles are successfully synthesized through a tunable hydrothermal route. The pH value of the precursor solution is a decisive factor for morphology control of SmMn2O5 nanocrystals, with decreasing pH value the morphology of SmMn2O5 nanocrystals converts from nanoparticles to nanorods. The nanoparticles exhibit a better catalytic activity for NO oxidation than the nanorods, because they can efficiently convert NO at lower temperature. By the analysis of X-ray photoelectron spectrum and high-resolution transmission electron microscope, the oxidation activity is found to be dependent on the high specific surface area and surface crystal planes of SmMn2O5 nanocrystals, which widens and deepens the oxygen chemistry and NO oxidation mechanism on the surfaces of SmMn2O5. This work could not only provide new insights into the morphology control of SmMn2O5 nanocrystals, but also pave a new way for the crystal planes modification of SmMn2O5 nanocrystals as NO oxidation catalyst to achieve an enhanced performance for environmental applications.

Highly Dispersed Carbon Supported PdNiMo Core with Pt Monolayer Shell Electrocatalysts for Oxygen Reduction Reaction

The development of low-cost, durable, and high-performance materials that could substitute for the current platinum-based electrocatalysts would accelerate the commercialization of polymer electrolyte membrane fuel cells as an alternative power source. We report herein a new fabrication approach of carbon-supported platinum monolayer (ML) on ternary palladium-nickel-molybdenum core electrocatalysts (PtML/PdNiMo/C) by a sonochemical method using ionic liquid (IL) as a dispersion medium. The sonolysis technique can control the size and distribution of the ternary-metal nanoparticles on different carbon supports without addition of any external reducing agents, surfactants or capping agents. Depositing Pt MLs using under-potential deposition method on the ternary PdNiMo nanoparticle cores could enhance activity and durability of the cathode during the oxygen reduction reaction of the fuel cell. Herein, we show that the described sonolysis method produces more reliable and cost-effective electrocatalysts that outperforms a commercial Pt-based catalyst.

Highly Dispersed Carbon Supported PdNiMo Core with Pt Monolayer Shell Electrocatalysts for Oxygen Reduction Reaction

The development of low-cost, durable, and high-performance materials that could substitute for the current platinum-based electrocatalysts would accelerate the commercialization of polymer electrolyte membrane fuel cells as an alternative power source. We report herein a new fabrication approach of carbon-supported platinum monolayer (ML) on ternary palladium-nickel-molybdenum core electrocatalysts (PtML/PdNiMo/C) by a sonochemical method using ionic liquid (IL) as a dispersion medium. The sonolysis technique can control the size and distribution of the ternary-metal nanoparticles on different carbon supports without addition of any external reducing agents, surfactants or capping agents. Depositing Pt MLs using under-potential deposition method on the ternary PdNiMo nanoparticle cores could enhance activity and durability of the cathode during the oxygen reduction reaction of the fuel cell. Herein, we show that the described sonolysis method produces more reliable and cost-effective electrocatalysts that outperforms a commercial Pt-based catalyst.

A nitrogen-doped electrocatalyst from metal–organic framework-carbon nanotube composite

Abstract

Pyrolysis-induced synthesis of iron and nitrogen-containing carbon nanolayers modified graphdiyne nanostructure as a promising core-shell electrocatalyst for oxygen reduction reaction

Low-cost facile fabrication of highly efficient non-precious-metal catalysts to replace commercial Pt-based catalysts for oxygen reduction reaction (ORR) has attracted great attentions, because it is significant for rapid commercialization of fuel cells. Based on a fact that graphdiyne, another member of the carbon family, has not been systematically investigated as a new carbon support to ORR catalysts. We here report an effective strategy for easy synthesis of a cheap iron-nitrogen-doped carbon nanolayers wrapped around graphdiyne core-shell electrocatalyst (Fe-PANI@GD-900) for ORR from one-step pyrolysis of iron and polyaniline loaded onto graphdiyne nanocomposite at 900 °C. Electrochemical results indicate that the catalyst exhibits unexpectedly high ORR activity with onset and half-wave potentials of 1.05 V and 0.82 V (vs. RHE), while its mass activity at given potentials is lower than that of the Pt/C catalyst. Moreover, Fe-PANI@GD-900 follows a direct four-electron reduction pathway, and its long-term stability is superior to Pt/C and other graphdiyne-based catalysts previously reported in the literature. The relatively excellent ORR performance may be largely attributed to the formation of high contents of graphitic-N and FeN compounds, and the addition of graphdiyne facilitating to absolutely accelerate ORR charge transfer and fully expose more N-doped active sites on the surface.

A novel octahedral MnO/RGO composite prepared by thermal decomposition as a noble-metal free electrocatalyst for ORR

Octahedral MnO/reduced graphene oxide (RGO) composite was synthesized by thermal decomposition method and characterized by XRD, Raman, XPS, TGA/DSC, TEM and SEM. The analysis results show that GO was reduced to RGO, and the octahedral MnO nanoparticles disperse on the RGO sheet by thermal decomposition process. It is important that the as-prepared composite exhibits excellent electrocatalytic performance for oxygen reduction reaction. The onset potential of the octahedral MnO/RGO composite is about 100 and 200 mV positive-shifted compared with that of MnO and RGO, respectively. The current density of O2 reduction for the MnO/RGO composite is also much higher than that of MnO and RGO, respectively. In addition, the composite shows better stability and tolerance ability toward CH3OH and CO poisoning than that of commercial Pt-based catalyst. The enhanced electrocatalytic performance of octahedral MnO/RGO may make it available to be an efficient and cheap noble-metal free cathodic catalyst for fuel cells and metal–air batteries.

Facile Synthesis of Co-N4-Doped Mesoporous Carbon for Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is a critical factor in fuel cells that has attracted significant research attention. Non-precious metal catalysts have improved the ORR activity considerably, but they still exhibit poorer ORR performance than commercial Pt-based catalysts. In this study, Co-N4-doped mesoporous carbon (Co-N4-MC) was prepared for the ORR using cobalt-azides as the Co-N4-containing precursor, and ordered mesoporous silica SBA-15 as a template for achieving mesoporous structures. The Co-N4-MC electrode exhibited remarkable ORR activity in an alkaline medium (a half-wave potential of −0.15 V vs. MMO, only ∼19 mV deviation from the commercial Pt/C catalyst), high selectivity (electron-transfer number ∼4) and excellent electrochemical stability (∼8 mV negative shift of the half-wave potential after 1000 cycles). The good performance of the Co-N4-MC electrode was attributed to the synergetic effects of N4, C and Co. In particular, the existence of graphitic pores in the Co-N4-MC catalyst facilitated the diffusion of O2 to the catalytic active sites, which benefited the progression of the ORR on the Co-N4-MC catalyst.

A graphene-based electrocatalyst co-doped with nitrogen and cobalt for oxygen reduction reaction

The development of low cost, active and stable non-precious metal (Co-N/C) catalysts to replace commercial Pt-based catalysts for oxygen reduction reaction (ORR) is a hot topic to this day. In this work, we have synthesized a new graphene-based catalyst (Co-N/C-A) doped by cobalt and nitrogen atoms with high contents of pyridinic- and pyrrolic-nitrogen (planar nitrogen), which exhibits ORR electrocatalytic activity with onset and peak potentials of 0.035 and −0.082 V (versus Hg/HgO) in 0.1 mol l−1 KOH solution, respectively. Besides, it has much higher stability and tolerance to methanol compared to the commercial Pt/C catalyst. The overall electron transfer number is calculated to be about 3.8. The transition-metal (Co) in the precursor can promote the formation of active sites during pyrolysis process and the followed acid-treatment may effectively expose the active sites on the surface of the catalyst, helping to enhance the ORR activity. It can be also proposed that pyridinic- and pyrrolic-nitrogen groups may play a key role in the ORR process and serve as the ORR active centers.