Electrocatalysts For Fuel Cells Research Articles

PtAu Thin Film as Anode Electrocatalyst in Methanol Fuel Cell

PtAu Thin Film as Anode Electrocatalyst in Methanol Fuel Cell

Nanoporous Copper–Metal Organic Framework Microneedles on Nickel Foam as a Bifunctional Electrocatalyst for Glycerol Fuel Cell and Electrochemical Glycerol Detection in Biodiesel

Nanoporous Copper–Metal Organic Framework Microneedles on Nickel Foam as a Bifunctional Electrocatalyst for Glycerol Fuel Cell and Electrochemical Glycerol Detection in Biodiesel

Impact of Heat Treatment on the Oxygen Reduction Reaction Performance of PtCo/C(N) Electrocatalyst in PEM Fuel Cell

AbstractThe synthesis of efficient and stable Pt alloy catalysts is a major challenge for the commercialization of PEMFC. Herein, we report a PtCo/C(N) electrocatalyst prepared by Na2CO3‐assisted urea liquid‐phase deposition strategy as an efficient cathodic oxygen reduction reaction electrocatalyst, and test its activity and stability in a rotating disc electrode and a single‐cell. The membrane electrode prepared with PtCo/C(N)‐800 °C catalyst has an output voltage of 0.652 V at 2 A/cm2 and a maximum power density of 1.501 W/cm2, which are 36 mV and 81 W/cm2 higher than those of commercial Pt/C catalyst, respectively. In addition, the mass activity and half‐wave potential of PtCo/C(N)‐800 °C are 2.44 times and 50 mV higher than those of commercial Pt/C, respectively. After 5000 voltammetric cycles, its mass activity and half‐wave potential only lose 35 A/gPt and 9 mV, respectively. XPS results show that the binding energy of Pt 4f is positively shifted relative to Pt/C‐TKK, and the d‐band center of Pt decreases, leading to weak chemical interaction between the oxygen‐containing intermediate and the surface of the electrocatalyst, which is conducive to the improvement of the ORR activity and stability of the catalyst.

Research progress of metal oxide supports for fuel cells electrocatalysts

AbstractFuel cell technology, as a new way of energy conversion, is widely used in various fields. At present, the electrocatalyst, as one of the key components of the electrochemical reaction of fuel cells, still suffers from the problems of high cost, low activity and poor stability. Excellent fuel cell electrocatalysts must have excellent catalytic activity, anti‐poisoning ability, electrical conductivity and stability. Metal oxides with corrosion resistance, electrochemical stability and strong metal support interaction effects have been intensively studied. The influence of the synthesis method on the catalytic performance is also crucial. In this review, the importance of fuel cells and their catalysts is introduced. The characteristics of catalysts with three metal oxides, titanium dioxide, cerium dioxide and tungsten oxide, as supports, preparation methods and applications in different fuel cells are reviewed. The synthesis of metal oxide supported catalysts by impregnation, precipitation and hydrothermal methods is described. Finally, the research on metal oxide supported catalysts is prospected.

CO-Tolerant Hydrogen Oxidation Electrocatalysts for Low-Temperature Hydrogen Fuel Cells.

The severe performance degradation of low-temperature hydrogen fuel cells upon exposure to trace amounts of carbon monoxide (CO) impurities in reformate hydrogen fuels is one of the challenges that hinders their commercialization. Despite significant efforts that have been made, the CO-tolerance performance of electrocatalysts for the hydrogen oxidation reaction (HOR) is still unsatisfactory. This Perspective discusses the path forward for the rational design of CO-tolerant HOR electrocatalysts. The fundamentals of the CO-tolerant mechanisms on commercialized platinum group metal (PGM) electrocatalysts via either promoting CO electrooxidation or weakening CO adsorption are provided, and comprehensive discussions based on these strategies are presented with typical examples. Given the recent progress, some emerging strategies, including blocking CO diffusion with a barrier layer and developing non-PGM HOR catalysts, are also discussed. We conclude with a discussion of the strengths and limitations of these strategies along with the perspectives of the major challenges and opportunities for future research on CO-tolerant HOR electrocatalysts.

Phosphorus doped PdMo bimetallene as a superior bifunctional fuel cell electrocatalyst

The commercialization of direct alcohol fuel cells (DAFCs) relies on the development of high performance electrocatalysts for both the alcohol oxidation reaction and the oxygen reduction reaction (ORR). In this study, a novel phosphorus-doped palladium-molybdenum (P-PdMo) bimetallene with a partially amorphous structure is demonstrated. The ultrathin and curved morphology of the nanosheets, combined with electronic regulation by phosphorus atoms, facilitates OH adsorption and CO desorption. Consequently, the catalyst exhibits significantly enhanced activity and durability in the electrooxidation of alcohols, including methanol, ethanol, ethylene glycol, and glycerol. Particularly toward ethanol oxidation, the P-PdMo bimetallene displays exceptional mass and specific activities up to 4.95 A mg-1Pd and 8.28 mA cm−2, respectively. Furthermore, the P-PdMo bimetallene demonstrates outstanding ORR performance, with an onset potential of 1.0 V and a half-wave potential of 0.88 V. Overall, this study opens new avenues in metallene electrocatalysts and advancing toward the practical implementation of DAFCs.

Atomically Dispersed Zn/Co-N-C as ORR Electrocatalysts for Alkaline Fuel Cells.

Hydrogen fuel cells have drawn increasing attention as one of the most promising next-generation power sources for future automotive transportation. Developing efficient, durable, and low-cost electrocatalysts, to accelerate the sluggish oxygen reduction reaction (ORR) kinetics, is urgently needed to advance fuel cell technologies. Herein, we report on metal-organic frameworks-derived nonprecious dual metal single-atom catalysts (SACs) (Zn/Co-N-C), consisting of Co-N4 and Zn-N4 local structures. These catalysts exhibited superior ORR activity with a half-wave potential (E1/2) of 0.938 V versus RHE (reversible hydrogen electrode) and robust stability (ΔE1/2 = -8.5 mV) after 50k electrochemical cycles. Moreover, this remarkable performance was validated under realistic fuel cell working conditions, achieving a record-high peak power density of ∼1 W cm-2 among the reported SACs for alkaline fuel cells. Operando X-ray absorption spectroscopy was conducted to identify the active sites and reveal catalytic mechanistic insights. The results indicated that the Co atom in the Co-N4 structure was the main catalytically active center, where one axial oxygenated species binds to form an Oads-Co-N4 moiety during the ORR. In addition, theoretical studies, based on a potential-dependent microkinetic model and core-level shift calculations, showed good agreement with the experimental results and provided insights into the bonding of oxygen species on Co-N4 centers during the ORR. This work provides a comprehensive mechanistic understanding of the active sites in the Zn/Co-N-C catalysts and will pave the way for the future design and advancement of high-performance single-site electrocatalysts for fuel cells and other energy applications.

Molybdenum–Based Electrocatalysts for Direct Alcohol Fuel Cells: A Critical Review

<p>Direct alcohol fuel cells (DAFCs) have gained much attention as promising energy conversion devices due to their ability to utilize alcohol as a fuel source. In this regard, Molybdenum-based electrocatalysts (Mo-ECs) have emerged as a substitution for expensive Pt and Ru–based co-catalyst electrode materials in DAFCs, owing to their unique electrochemical properties useful for alcohol oxidation. The catalytic activity of Mo-ECs displays an increase in alcohol oxidation current density by several folds to 1000–2000 mA mg<sub>Pt</sub><sup>−1</sup>, compared to commercial Pt and PtRu catalysts of 10–100 mA mg<sub>Pt</sub><sup>−1</sup>. In addition, the methanol oxidation peak and onset potential have been significantly reduced by 100–200 mV and 0.5–0.6 V, respectively. The performance of Mo-ECs in both acidic and alkaline media has shown the potential to significantly reduce the Pt loading. This review aims to provide a comprehensive overview of the bifunctional mechanism involved in the oxidation of alcohols and factors affecting the electrocatalytic oxidation of alcohol, such as synthesis method, structural properties, and catalytic support materials. Furthermore, the challenges and prospects of Mo-ECs for DAFCs anode materials are discussed. This in-depth review serves as valuable insight toward enhancing the performance and efficiency of DAFC by employing Mo-ECs.</p>

The role of high-resolution transmission electron microscopy and aberration corrected scanning transmission electron microscopy in unraveling the structure-property relationships of Pt-based fuel cells electrocatalysts.

Platinum-based fuel cell electrocatalysts are structured on a nano level in order to extend their active surface area and maximize the utilization of precious and scarce platinum. Their performance is dictated by the atomic arrangement of their surface layers atoms via structure-property relationships. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) are the preferred methods for characterizing these catalysts, due to their capacity to achieve local atomic-level resolutions. Size, morphology, strain and local composition are just some of the properties of Pt-based nanostructures that can be obtained by (S)TEM. Furthermore, advanced methods of (S)TEM are able to provide insights into the quasi-in situ, in situ or even operando stability of these nanostructures. In this review, we present state-of-the-art applications of (S)TEM in the investigation and interpretation of structure-activity and structure-stability relationships.

Local structures and robust oxygen reduction performances of TiN-supported bimetallic Pt–Cu electrocatalysts for fuel cells

The local structures and oxygen reduction reaction (ORR) performances of Pt–Cu fuel-cell electrocatalysts on robust TiN nanoparticles were investigated.

(Invited) The More Elements the Better? Studying Structure-Function Relations in High Entropy Alloy Nanoparticles As Fuel Cell Electrocatalysts

Low-temperature polymer electrolyte membrane fuel cells (PEMFCs), which convert chemical energy into electricity, are widely considered a suitable, sustainable technology to replace conventional combustion engines. However, fundamental issues such as fuel cell efficiency and durability still leave room for improvement, which could be achieved by finding more active and stable fuel cell electrocatalysts.[1] High entropy alloys (HEA) – solid solutions of five or more elements - are an emerging material class in the development of novel electrocatalysts. These multi-metallic compounds provide exciting new possibilities for catalyst design.[2] Recent theoretical analyses predict a great potential for HEAs as fuel cell catalysts due to the almost unlimited number of unique surface sites, which enables a wide distribution of adsorption energies. By changing the composition, the distribution of adsorption energies can be tailored toward the optimal binding energies of the catalytic intermediates.[3] The field of high entropy alloy catalysis enables a new, statistical approach to materials design. From an experimental viewpoint, however, HEAs come with new challenges regarding their synthesis and characterization.While HEA nanoparticles are essential for efficient catalysis to provide sufficiently large surfaces, their synthesis is only in its infancy. For a direct comparison between theoretically predicted properties and the performance of the prepared catalysts, single-phase HEA nanoparticles are essential.[4] Through studies of the synthesis pathways and in-depth structural characterization of the HEA nanoparticles with synchrotron X-ray techniques, it is possible to prepare model single-phase HEA nanoparticle catalysts. These well-mixed, multi-metallic materials allow us to study not only the different structure-activity properties of HEA nanoparticle fuel cell catalysts but to also explore the stability of these novel materials under reaction conditions. Studying the dissolution and degradation behaviour of model HEA catalysts in an acidic environment, the mechanisms that underly the degradation of multi-metallic PEMFC catalysts are explored. By relating structural characterization techniques with electrochemical analyses,[5] we can address the question of which role element mixing can play in the activation and stabilization of new fuel cell catalysts.[1] Schroeder, J.; Pittkowski, R. K.; Du, J.; Kirkensgaard, J. J. K.; Arenz, M. J. Electrochem. Soc. 2022, 169, 104504.[2] Löffler, T., Ludwig, A., Rossmeisl, J, Schuhmann, W. Angew. Chem. Int. Ed. 2021, 60, 2-12.[3] Batchelor, T. A. A, Pedersen, J. K., Winther, S.H., Castelli, I.E., Jacobsen, K. W., Rossmeisl, J. Joule 2019, 3, 834-845.[4] Pittkowski, R.; Clausen, C. M.; Chen, Q.; Stoian, D.; van Beek, W.; Bucher, J.; Welten, R. L.; Schlegel, N.; Mathiesen, J. K.; Nielsen, T. M.; Rosenkranz, A. W.; Bojesen, E. D.; Rossmeisl, J.; Jensen, K. M. Ø.; Arenz, M. ChemRxiv, 2022, https://doi.org/10.26434/chemrxiv-2022-khw4t.[5] Schroeder, J.; Pittkowski, R. K.; Martens, I.; Chattot, R.; Drnec, J.; Quinson, J.; Kirkensgaard, J. J. K.; Arenz, M. ACS Catalysis 2022, 12, 2077–2085

Non-PGM Cathode Electrocatalysts for PEM Fuel Cells

Polymer electrolyte membrane fuel cells, PEMFCs, are considered the most ideal next generation energy conversion device, able to provide power to a broad range of applications; automotive, combined heat and power, portable electronic devices. Pt-based electrocatalysts are regarded as ideal for promoting the desired redox reactions of a fuel cell, especially the sluggish oxygen reduction at the cathode, ORR. High expense and scarcity of Pt are the greatest impediments to successful commercialization of this technology. The replacement of unsustainable noble-metal catalysts with platinum group metal (PGM)-free catalysts for oxygen reduction reaction (ORR) is essential for material wise and market value viable PEMFCs.Among the different attempts towards non-PGM catalysts, incorporating atomically dispersed transition metal atoms (Fe, Mn, etc.) and heteroatoms (N, S, etc.) into carbon frameworks is the most promising [1,2]. Large specific surface area, high intrinsic ORR electrocatalytic activity, efficient porosity and sufficient stability in acid media and/or in the actual working environment are the least requirements to consider when designing the catalysts. So far, despite the tremendous efforts, many drawbacks still persist that include poor understanding of the nature of active centres and their control over the synthesis, as well as fast decay of the structure under operation.In this work, we will present a rationally designed strategy to prepare hybrid composite catalysts by developing Fe–N–C materials onto different 2D and 3D templates [3,4] with differentiated surface chemistry (silicon and heteroatom-doped carbon structures). Despite structural and physicochemical characterization, the study includes extensive electrochemical characterization in terms of activity and durability in relative to the application conditions. An example is depicted in Figure 1 for a single atom Fe-N-C catalyst synthesized using porous silica nanotubes as the sacrificial template resulting in a hierarchically porous structure with a surface area of 370 m2/g. Electrochemical study revealed a half-wave potential of 0.72 V and an onset potential of 0.88 V with high stability in acidic environment.Very importantly, the different findings are correlated to one another, thereby establishing a composition to function relationship to provide a pathway for the integrated engineering of novel structures with improved performance. Acknowledgments Funding from the Operational Program “Competitiveness, Entrepreneurship & Innovation” (EPAnEK), NSRF 2014-2020 through the project Solar2HyP Τ2ΕΔΚ-01877 References [1] L. Osmieri, et al., Current Opinion in Electrochemistry 25 (2020) 100627.[2] T. Asset, et al., Joule 4 (2019) 33-44.[3] Jin-Cheng Li et al., Asia Materials 10 (2018) e461[4] Nan Zhang et al., Energy Environ. Sci. 13 (2020) 111-118 Figure 1

Trimetallic Alloy as an Electrocatalyst for Direct Low Temperature Fuel Cells: The Case of MF Oxidation on Pt3Pd3Sn2

Methyl formate (MF) has been considered an attractive hydrogen carrier alternative fuel due to its high energy density, ease of storage and transport, and low boiling point (32o C @ 1 atmosphere) liquid. However, the low number of publications on efficient anodic catalysts is impeding the development of a direct methyl formate fuel cell (DMFFC).In this study, a first-principles density functional theory (DFT) calculation was performed to study the MF electro-oxidation on the surface of the Pt3Pd3Sn2 (111) alloy. This surface was proven to be the most active in the anodic oxidation of other small organic molecules1,2. A detailed thermochemistry and kinetics study of MF oxidation was carried out to determine the active sites, most probable reaction pathway for the oxidation of CH3OCHO to CO2, and analyzed the dehydrogenation steps via direct (HCOOH pathway) and indirect (CO pathway) mechanisms.The potential required for complete oxidation of MF to CO2 is 0.66 V. The study revealed that Sn plays an essential role in the mitigation of CO poisoning through water activation and surface oxide reaction mechanisms in a bifunctional manner. Furthermore, based on our findings, Pt and Pd work synergistically to enhance the utilization of active sites for the initiation of MF oxidation and promote HCOOH oxidation, which accelerates the kinetics of the electrochemical reaction.

Au-Based MOFs as Anodic Electrocatalysts for Direct Borohydride Fuel Cells

Researchers are exploring direct liquid fuel cells (DLFCs) as alternatives to proton-exchange membrane fuel cells because of their higher energy density and ease of storing and transporting the fuel. Direct borohydride fuel cells (DBFCs) are of particular interest as they offer a sustainable energy source with their high-power density output and the use of a highly alkaline NaBH4 medium [1]. Ensuring efficient and cost-effective catalysts for DBFCs is crucial for their commercial viability. Metal-organic frameworks (MOFs) have demonstrated significant potential as anodic electrocatalysts for BOR in DBFCs [2]. However, research should explore various modifications to MOFs, such as the incorporation of alternative metal ions or functional groups, to improve their catalytic efficiency and reduce cost. This study evaluated the performance of newly developed MOF-based electrocatalysts for DBFCs. Specifically, six MOF-based materials were synthesized and analyzed for their ability to facilitate borohydride oxidation (BOR) using cyclic voltammetry and chronoamperometry in alkaline media. MIL-101_Au@NH2 and MOF-808_Au@NH2 were found to be highly effective for BOR. The kinetic parameters for BOR with MOF-based electrocatalysts, including activation energy, reaction order, exchanged electrons, and anodic charge transfer coefficient, were determined. The activation energy for BOR was found to be 13.6 kJ mol−1 and 15.3 kJ mol−1 for MIL-101_Au@NH2 and MOF-808_Au@NH2, respectively. The number of transferred electrons, n, was found to be 7.0 and 3.1 for MIL-101_Au@NH2 and MOF-808_Au@NH2, respectively. This study demonstrates that MOF-based electrocatalysts can enhance DBFCs' performance, while offering insight into the potential usage of MOFs in other fuel cell technologies.[1] B. Šljukić, D.M.F. Santos, "Direct borohydride fuel cells", in: "Direct Liquid Fuel Cells: Fundamentals, Advances, and Future", 1st ed., R.G. Akay, A.B. Yurtcan (eds.), Academic Press, USA, 203-232 (2021)[2] G. Backovic, B. Šljukić, G.S. Kanberoglu, M. Yurderi, A. Bulut, M. Zahmakiran, D.M.F. Santos, Ruthenium (0) nanoparticles stabilized by the metal-organic framework as an efficient electrocatalyst for borohydride oxidation reaction, International Journal of Hydrogen Energy, 45, 27056-27066 (2020).

(Invited) Durable Hybrid Electrocatalysts for Fuel Cells

Proton exchange membrane fuel cell converts hydrogen and oxygen into electricity with zero emission. The high cost and low durability of Pt-based electrocatalysts for oxygen reduction reaction hinder its wide applications. The development of non-precious metal electrocatalysts also reaches the bottleneck because of the low activity and durability. Here we rationally design a hybrid electrocatalyst consisting of atomically dispersed Pt and Fe single atoms and Pt-Fe alloy nanoparticles. The Pt mass activity of the hybrid catalyst is 3.7 times higher than that of commercial Pt/C in a fuel cell. More importantly, the fuel cell with an ultra-low Pt loading in the cathode (0.015 mgPt cm-2) shows excellent durability, with 97 % activity retention after 100,000 cycles and no noticeable current drop at 0.6 V for over 200 h. These results highlight the importance of the synergistic effects among active sites in hybrid electrocatalysts and provide an alternative way to design more active and durable low-Pt electrocatalysts for electrochemical devices.

(Invited) Designing Advanced Low-PGM Core-Shell Electrocatalysts for Fuel Cells and Electrolyzers

The low-content Pt-based core-shell catalysts potentially alleviate the drawback in the existing Pt catalysts (i.e., high cost, slow kinetics, poor stability, etc.) and further improve the oxygen reduction reaction (ORR) activity and stability for the proton exchange membrane fuel cells (PEMFCs).1 There have been remarkable advances in both the development of promising core−shell catalysts and the understanding of the fundamental catalytic mechanisms, and it is clear that some of the low platinum-group-metal (PGM) core−shell catalysts with enhanced activity and stability have great potential for use in PEMFCs. Nevertheless, various issues still need to be clearly addressed for the advanced core−shell catalysts of the future. On the other hand, PEM electrolyzers (ELs) are desirable large-scale energy devices to produce green hydrogen toward a net-zero carbon economy. The technologies require the availability of effective catalysts, particularly for the oxygen evolution reaction (OER). However, Ir- and Ru-based catalysts are currently the best-performing OER catalysts and their cost and limited availability hamper the widespread commercialization/deployment of PEMELs. Therefore, there is also an urgent need for developing highly durable and inexpensive catalysts for the OER. This talk first focuses on synthetic strategies, catalytic mechanisms, and influencing factors of Pt- and Ir-based catalysts used for PEMFCs and PEMELs. We will then discuss effective and solid strategies/designs to employ transition-metal-nitride-based cores for the development of highly advanced low-PGM core-shell catalysts for the ORR, particularly in heavy-duty vehicle (HDV) PEMFC applications, and for the OER in PEMEL applications. R. Zhao and K. Sasaki, Advanced Pt-Based Core-Shell Electrocatalysts for Fuel Cell Cathodes, Accounts of Chemical Research. 55 (2022) 1226-1236.

Highly Durable Electrocatalyst with Low-Loading Pt-Co Dispersed over Graphene Nanofiber for Oxygen Reduction Reaction Under PEMFC Condition

Proton exchange membrane fuel cell (PEMFC) has been demonstrated as a highly efficient energy conversion technology. The sluggish oxygen reduction reaction (ORR) at the fuel cell cathode requires 3 to 5 times more catalysts than the hydrogen oxidation reaction at the anode (1). Currently, platinum is still the catalyst material of choice. However, the heavy use of scarce Pt in the electrodes represents a major cost barrier to the commercialization of PEMFCs. Tremendous efforts have been dedicated to reduce or remove Pt usage through the development of Pt-transition metal catalysts, as highlighted recently by dealloyed PtNi (2), Mo-doped PtNi(3), and ordered PtCo (4); or through the development of transition metals-nitrogen-carbon based PGM-free catalysts (5, 6).In the fuel cell, catalysts should be highly dispersed over the electrode surface to be easily accessible by the reactants, especially at the high fuel cell current density where a large influx of O2 must be converted. For the Pt alloy catalyst of large crystallites, there won’t be enough crystallites available to spread over the electrode surface to encounter the incoming O2 if the total loading of platinum has to be maintained ultralow. Furthermore, unprotected Pt nano-alloys may lose their nanostructure and crystallinity from the dissolution and agglomeration during the ORR process. The PGM-free catalysts, on the other hand, have high catalytic site density with uniform distribution when prepared by homogenous precursors such as metal-organic framework or porous organic polymer, rendering them highly efficient in interacting with O2 flux. Their key drawback, however, is the poor stability operated under PEMFC condition.In this presentation, we will describe a method of preparing highly active yet stable electrocatalysts containing ultralow Pt content using polymer fiber containing cobalt zeolitic imidazolate framework as precursor. The new catalyst contains Pt-Co nanoparticels situated over the PGM-free catalystically active support (7,8). The ORR activities of the new catalyst was first tested in O2 saturated acidic electrolyte by rotating ring disk electrode (RRDE) before fabricated into the membrane electrode assembly (MEA) and evaluated under fuel cell operating condition. The synergistic catalysis between PtCo NPs and the PGM-free active substrate led to an unprecedented oRR performance in both RRDE and fuel cell. For example, the fuel cell test demonstrated a mess activity of 2.43 A/mgPt for the new catalysts and > 80% retention of the initial mass activity after 60000 continuous voltage cycles from 0.6 – 1.0 V.The characterizations of the fresh and the post-electrochemical test samples were investigated by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), x-ray absorption near-edge structure (XANES), extended x-ray absorption fine structure (EXAFS), transmission electron microscopy (TEM), Raman spectroscopy and BET surface analysis. We also performed DFT calculation on the ORR thermodynamic barriers over both Pt-Co NPs and PGM-free site as the descriptors for reaction pathway. The results reveal that the synergistic interaction between Pt-Co and PGM active substrate contribute significantly to both activity and durability enhancements.Acknowledgments:This work was supported by Argonne National Laboratory through Maria Goeppert Mayer Fellowship, US; Overseas Outstanding Youth Fund project, shanghai Jiao Tong university, Shanghai, China, State Key Laboratory of Metal Matrix Composites, shanghai Jiao Tong university, Shanghai, China. The works performed at Argonne National Laboratory’s Center for Nanoscale Materials and Advanced Photo Source, and Hydrogen research center, shanghai Jiao Tong university.Reference: H. A. Gasteiger, N. M. Markovic, Just a Dream-or Future Reality? Science 324, 48-49 (2009).B. Han et al., Record activity and stability of dealloyed bimetallic catalysts for proton exchange membrane fuel cells. Energy & Environmental Science 8, 258-266 (2015).X. Huang et al., High-performance transition metal–doped Pt3Ni octahedra for oxygen reduction reaction. Science 348, 1230-1234 (2015).D. Wang et al., Structurally ordered intermetallic platinum-cobalt core-shell nanoparticles with enhanced activity and stability as oxygen reduction electrocatalysts. Nat Mater 12, 81-87 (2013).L. Chong et al., Investigation of Oxygen Reduction Activity of Catalysts Derived from Co and Co/Zn Methyl-Imidazolate Frameworks in Proton Exchange Membrane Fuel Cells. ChemElectroChem 3, 1541-1545 (2016).J. Shui, C. Chen, L. Grabstanowicz, D. Zhao, D. J. Liu, Highly efficient nonprecious metal catalyst prepared with metal-organic framework in a continuous carbon nanofibrous network. Proc Natl Acad Sci U S A 112, 10629-10634 (2015).L. Chong et al., Ultralow-loading platinum-cobalt fuel cell catalysts derived from imidazolate frameworks. Science, (2018).L. Chong et al., Highly durable fuel cell electrocatalyst with low-loading Pt-Co nanoparticles dispersed over single-atom Pt-Co-N-graphene nanofiber. Chem Catalysis 3, 100541.

Platinum recycling from fuel cell-spent electrocatalysts using oxidative leaching in HCl solution

The recovery of platinum (Pt) from electrocatalysts in spent proton exchange membrane fuel cells is promising and important for the sustainable development of such a noble metal. Conventional leaching of Pt in the aqueous phase typically requires the use of high concentration of mineral acids and the presence of strong oxidants owing to its thermodynamic stability and non-reactive properties. In the present study, the dissolution of Pt from a Pt/C fuel cell electrocatalyst was investigated using a simple and efficient process under moderate conditions in chloride media. Notably, the leachability of Pt was high ∼76% in a solution of low concentration HCl 2.0 M at 90 °C for 120 min in the absence of an oxidant. The enhancement of Pt leaching efficiency can be obtained using various oxidizing agents HNO3, H2O2, NaClO and NaClO3, and NaClO3 shown the most effective improvement from 76% to 88%. The dissolution of Pt in a solution of 2.0 M HCl and 3.0 wt% NaClO3 improved to 98% by the increase in leaching temperature from 50 to 90 °C. Kinetic studies indicated that Pt leaching in HCl in the presence of NaClO3 followed a chemical-controlled mechanism with an activation energy (Ea) of 40.6 kJ/mol. Based on the findings of this study, an efficient process is proposed to recover and reuse Pt from an electrocatalyst sample of spent fuel cells, including oxidative leaching, chemical precipitation and laser reduction.

ZIF-8-derived Fe-C catalysts: Relationship between structure and catalytic activity toward the oxygen reduction reaction

The oxygen reduction reaction (ORR) activity of carbonized ZIF-8 (CZ) and its Fe-doped derivatives, CZ-A (doped with ammonium iron (II) sulphate) and CZ-B (doped with iron (II) acetate), were examined in both acidic (0.5 M H2SO4) and basic (0.1 M KOH) electrolytes using a rotating disk electrode setup. These data show that the ORR activity of the Fe-doped catalysts is higher than that of pure CZ, with a higher activity in basic than acidic electrolyte. Extensive materials characterization highlights important differences in the sample crystallinity, morphology, porosity, and chemical composition as a function of the deployed precursor. The performance of the prepared catalysts is also impacted by the Fe precursor selection, highlighting the importance of such synthetic parameters in controlling the density and identify of Fe-Nx active sites. These results demonstrate the potential application of Fe-doped carbonized ZIF-8 catalysts for the ORR in basic electrolyte and offer important knowledge for the future design of non-precious metal fuel cell electrocatalysts.

Insight into Defect Engineering of Atomically Dispersed Iron Electrocatalysts for High-Performance Proton Exchange Membrane Fuel Cell.

Atomically dispersed and nitrogen coordinated iron catalysts (Fe-NCs) demonstrate potential as alternatives to platinum-group metal (PGM) catalysts in oxygen reduction reaction (ORR). However, in the context of practical proton exchange membrane fuel cell (PEMFC) applications, the membrane electrode assembly (MEA) performances of Fe-NCs remain unsatisfactory. Herein, improved MEA performance is achieved by tuning the local environment of the Fe-NC catalysts through defect engineering. Zeolitic imidazolate framework (ZIF)-derived nitrogen-doped carbon with additional CO2 activation is employed to construct atomically dispersed iron sites with a controlled defect number. The Fe-NC species with the optimal number of defect sites exhibit excellent ORR performance with a high half-wave potential of 0.83V in 0.5M H2 SO4 . Variation in the number of defects allows for fine-tuning of the reaction intermediate binding energies by changing the contribution of the Fe d-orbitals, thereby optimizing the ORR activity. The MEA based on a defect-engineered Fe-NC catalyst is found to exhibit a remarkable peak power density of 1.1W cm-2 in an H2 /O2 fuel cell, and 0.67W cm-2  in an H2 /air fuel cell, rendering it one of the most active atomically dispersed catalyst materials at the MEA level. This article is protected by copyright. All rights reserved.