Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation.

It remains a grand challenge to replace platinum group metal (PGM) catalysts with earth-abundant materials for the oxygen reduction reaction (ORR) in acidic media, which is crucial for large-scale deployment of proton exchange membrane fuel cells (PEMFCs). Here, we report a high-performance atomic Fe catalyst derived from chemically Fe-doped zeolitic imidazolate frameworks (ZIFs) by directly bonding Fe ions to imidazolate ligands within 3D frameworks. Although the ZIF was identified as a promising precursor, the new synthetic chemistry enables the creation of well-dispersed atomic Fe sites embedded into porous carbon without the formation of aggregates. The size of catalyst particles is tunable through synthesizing Fe-doped ZIF nanocrystal precursors in a wide range from 20 to 1000 nm followed by one-step thermal activation. Similar to Pt nanoparticles, the unique size control without altering chemical properties afforded by this approach is able to increase the number of PGM-free active sites. The best ORR activity is measured with the catalyst at a size of 50 nm. Further size reduction to 20 nm leads to significant particle agglomeration, thus decreasing the activity. Using the homogeneous atomic Fe model catalysts, we elucidated the active site formation process through correlating measured ORR activity with the change of chemical bonds in precursors during thermal activation up to 1100 °C. The critical temperature to form active sites is 800 °C, which is associated with a new Fe species with a reduced oxidation number (from Fe3+ to Fe2+) likely bonded with pyridinic N (FeN4) embedded into the carbon planes. Further increasing the temperature leads to continuously enhanced activity, linked to the rise of graphitic N and Fe-N species. The new atomic Fe catalyst has achieved respectable ORR activity in challenging acidic media (0.5 M H2SO4), showing a half-wave potential of 0.85 V vs RHE and leaving only a 30 mV gap with Pt/C (60 μgPt/cm2). Enhanced stability is attained with the same catalyst, which loses only 20 mV after 10 000 potential cycles (0.6-1.0 V) in O2 saturated acid. The high-performance atomic Fe PGM-free catalyst holds great promise as a replacement for Pt in future PEMFCs.

[1]  S. Karakalos,et al.  3D polymer hydrogel for high-performance atomic iron-rich catalysts for oxygen reduction in acidic media , 2017 .

[2]  Gang Wu Current challenge and perspective of PGM-free cathode catalysts for PEM fuel cells , 2017 .

[3]  Shuhong Yu,et al.  Metal-Organic Framework-Derived FeCo-N-Doped Hollow Porous Carbon Nanocubes for Electrocatalysis in Acidic and Alkaline Media. , 2017, ChemSusChem.

[4]  X. Bao,et al.  Surface functionalization of ZIF-8 with ammonium ferric citrate toward high exposure of Fe-N active sites for efficient oxygen and carbon dioxide electroreduction , 2017 .

[5]  Michael J. Workman,et al.  Fe–N–C Catalyst Graphitic Layer Structure and Fuel Cell Performance , 2017 .

[6]  Feng Wang,et al.  Biomass Derived N-Doped Porous Carbon Supported Single Fe Atoms as Superior Electrocatalysts for Oxygen Reduction. , 2017, Small.

[7]  M. Engelhard,et al.  Self-Assembled Fe-N-Doped Carbon Nanotube Aerogels with Single-Atom Catalyst Feature as High-Efficiency Oxygen Reduction Electrocatalysts. , 2017, Small.

[8]  Hui Xu,et al.  Engineering Favorable Morphology and Structure of Fe-N-C Oxygen-Reduction Catalysts through Tuning of Nitrogen/Carbon Precursors. , 2017, ChemSusChem.

[9]  Jingxiang Zhao,et al.  Metal–Organic-Framework-Derived Fe-N/C Electrocatalyst with Five-Coordinated Fe-Nx Sites for Advanced Oxygen Reduction in Acid Media , 2017 .

[10]  Zheng Hu,et al.  From Carbon-Based Nanotubes to Nanocages for Advanced Energy Conversion and Storage. , 2017, Accounts of chemical research.

[11]  H. Barkholtz,et al.  Advancements in rationally designed PGM-free fuel cell catalysts derived from metal–organic frameworks , 2017 .

[12]  Gang Wu,et al.  Engineering nanostructures of PGM-free oxygen-reduction catalysts using metal-organic frameworks , 2017 .

[13]  Shiva Gupta,et al.  Carbon nanocomposite catalysts for oxygen reduction and evolution reactions: From nitrogen doping to transition-metal addition , 2016 .

[14]  Hui Xu,et al.  Transition metal (Fe, Co, Ni, and Mn) oxides for oxygen reduction and evolution bifunctional catalysts in alkaline media , 2016 .

[15]  M. Samoć,et al.  Co/ZIF-8 Heterometallic Nanoparticles: Control of Nanocrystal Size and Properties by a Mixed-Metal Approach , 2016 .

[16]  Bo-Qing Xu,et al.  Is Ammonium Peroxydisulate Indispensable for Preparation of Aniline-Derived Iron-Nitrogen-Carbon Electrocatalysts? , 2016, ChemSusChem.

[17]  A. Mahmood,et al.  Metal‐Organic Framework‐Based Nanomaterials for Electrocatalysis , 2016 .

[18]  Cheng Wang,et al.  Directly converting Fe-doped metal–organic frameworks into highly active and stable Fe-N-C catalysts for oxygen reduction in acid , 2016 .

[19]  Yao Zheng,et al.  Determination of the Electron Transfer Number for the Oxygen Reduction Reaction: From Theory to Experiment , 2016 .

[20]  Jaephil Cho,et al.  High‐Performance Direct Methanol Fuel Cells with Precious‐Metal‐Free Cathode , 2016, Advanced science.

[21]  Hsing-lin Wang,et al.  Is reduced graphene oxide favorable for nonprecious metal oxygen-reduction catalysts? , 2016 .

[22]  L. Wan,et al.  Understanding the High Activity of Fe-N-C Electrocatalysts in Oxygen Reduction: Fe/Fe3C Nanoparticles Boost the Activity of Fe-N(x). , 2016, Journal of the American Chemical Society.

[23]  Kai Zhou,et al.  Core–Shell Nanocomposites Based on Gold Nanoparticle@Zinc–Iron-Embedded Porous Carbons Derived from Metal–Organic Frameworks as Efficient Dual Catalysts for Oxygen Reduction and Hydrogen Evolution Reactions , 2016 .

[24]  M. Bedzyk,et al.  Atomic-scale cation dynamics in a monolayer VOX/α-Fe2O3 catalyst , 2015 .

[25]  Yongfeng Hu,et al.  A single iron site confined in a graphene matrix for the catalytic oxidation of benzene at room temperature , 2015, Science Advances.

[26]  Edward F. Holby,et al.  Experimental Observation of Redox-Induced Fe-N Switching Behavior as a Determinant Role for Oxygen Reduction Activity. , 2015, ACS nano.

[27]  Frédéric Jaouen,et al.  Identification of catalytic sites for oxygen reduction in iron- and nitrogen-doped graphene materials. , 2015, Nature materials.

[28]  S. Mukerjee,et al.  Highly active oxygen reduction non-platinum group metal electrocatalyst without direct metal–nitrogen coordination , 2015, Nature Communications.

[29]  J. Baek,et al.  Metal-free catalysts for oxygen reduction reaction. , 2015, Chemical reviews.

[30]  Gang Wu,et al.  Oxygen-deficient BaTiO3−x perovskite as an efficient bifunctional oxygen electrocatalyst , 2015 .

[31]  Jaephil Cho,et al.  Metal-organic framework-derived bamboo-like nitrogen-doped graphene tubes as an active matrix for hybrid oxygen-reduction electrocatalysts. , 2015, Small.

[32]  U. Ozkan,et al.  A comparison of N-containing carbon nanostructures (CNx) and N-coordinated iron–carbon catalysts (FeNC) for the oxygen reduction reaction in acidic media , 2014 .

[33]  Li An,et al.  Well-defined carbon polyhedrons prepared from nano metal–organic frameworks for oxygen reduction , 2014 .

[34]  Lijun Yang,et al.  A New Catalytic Site for the Electroreduction of Oxygen? , 2014 .

[35]  Alexey Serov,et al.  Fe‐N‐C Oxygen Reduction Fuel Cell Catalyst Derived from Carbendazim: Synthesis, Structure, and Reactivity , 2014 .

[36]  Piotr Zelenay,et al.  Structure of Fe–Nx–C Defects in Oxygen Reduction Reaction Catalysts from First-Principles Modeling , 2014 .

[37]  Jaephil Cho,et al.  Graphene/Graphene‐Tube Nanocomposites Templated from Cage‐Containing Metal‐Organic Frameworks for Oxygen Reduction in Li–O2 Batteries , 2014, Advanced materials.

[38]  Lauren R. Grabstanowicz,et al.  Highly Efficient Non‐Precious Metal Electrocatalysts Prepared from One‐Pot Synthesized Zeolitic Imidazolate Frameworks , 2014, Advanced materials.

[39]  Guofeng Wang,et al.  Reaction Pathway for Oxygen Reduction on FeN4 Embedded Graphene. , 2014, The journal of physical chemistry letters.

[40]  Gang Wu,et al.  Stability of iron species in heat-treated polyaniline–iron–carbon polymer electrolyte fuel cell cathode catalysts , 2013 .

[41]  Guofeng Wang,et al.  A density functional theory study of oxygen reduction reaction on Me–N4 (Me = Fe, Co, or Ni) clusters between graphitic pores , 2013 .

[42]  Lauren R. Grabstanowicz,et al.  A highly active and support-free oxygen reduction catalyst prepared from ultrahigh-surface-area porous polyporphyrin. , 2013, Angewandte Chemie.

[43]  Piotr Zelenay,et al.  Nanostructured nonprecious metal catalysts for oxygen reduction reaction. , 2013, Accounts of chemical research.

[44]  Hsing-lin Wang,et al.  A carbon-nanotube-supported graphene-rich non-precious metal oxygen reduction catalyst with enhanced performance durability. , 2013, Chemical communications.

[45]  J. Baldwin,et al.  Nitrogen-doped graphene-rich catalysts derived from heteroatom polymers for oxygen reduction in nonaqueous lithium-O2 battery cathodes. , 2012, ACS nano.

[46]  K. Artyushkova,et al.  Multitechnique Characterization of a Polyaniline–Iron–Carbon Oxygen Reduction Catalyst , 2012 .

[47]  T. Regier,et al.  Direct observation of tetrahedrally coordinated Fe(III) in ferrihydrite. , 2012, Environmental science & technology.

[48]  J. Spendelow,et al.  Progress in PEMFC MEA Component R&D at the DOE Fuel Cell Technologies Program , 2011 .

[49]  P. Shen,et al.  Synthesis of nitrogen-doped onion-like carbon and its use in carbon-based CoFe binary non-precious-metal catalysts for oxygen-reduction , 2011 .

[50]  Juan Herranz,et al.  Iron-based cathode catalyst with enhanced power density in polymer electrolyte membrane fuel cells. , 2011, Nature communications.

[51]  Gang Wu,et al.  High-Performance Electrocatalysts for Oxygen Reduction Derived from Polyaniline, Iron, and Cobalt , 2011, Science.

[52]  Minhua Shao,et al.  Electrocatalysis on platinum nanoparticles: particle size effect on oxygen reduction reaction activity. , 2011, Nano letters.

[53]  Ann V. Call,et al.  Cobalt imidazolate framework as precursor for oxygen reduction reaction electrocatalysts. , 2011, Chemistry.

[54]  Piotr Zelenay,et al.  Titanium Dioxide-supported Non-precious Metal Oxygen Reduction Electrocatalystw , 2022 .

[55]  Matthew Thorum,et al.  Electroreduction of dioxygen for fuel-cell applications: materials and challenges. , 2010, Inorganic chemistry.

[56]  C. Sangregorio,et al.  A Structural and Magnetic Investigation of the Inversion Degree in Ferrite Nanocrystals MFe2O4 (M = Mn, Co, Ni)” , 2009 .

[57]  Frédéric Jaouen,et al.  Iron-Based Catalysts with Improved Oxygen Reduction Activity in Polymer Electrolyte Fuel Cells , 2009, Science.

[58]  Jong-Won Lee,et al.  Nitrogen-modified carbon-based catalysts for oxygen reduction reaction in polymer electrolyte membrane fuel cells , 2009 .

[59]  Jong-Won Lee,et al.  Development of high performance carbon composite catalyst for oxygen reduction reaction in PEM Proton Exchange Membrane fuel cells , 2008 .

[60]  K. Ota,et al.  Stability and electrocatalytic activity for oxygen reduction in WC + Ta catalyst , 2004 .