As determined by high-resolution transmission electron microscopy (HR-TEM), X-ray absorption spectroscopy (XAS), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), this benign aqueous synthesis strategy facilitates the formation of homogeneous atomic nitrogen-coordinated iron sites embedded in a popcorn-like porous more » graphitic carbon matrix. Herein, we report a self-assembly method in an aqueous solution to develop an atomically-dispersed iron catalyst with high oxygen reduction reaction (ORR) activity and stability in acidic electrolytes. « lessĪtomically-dispersed iron-nitrogen-carbon (Fe-N-C) catalysts have arisen as promising candidates for replacing the costly precious metal catalysts in fuel cells but still face some grand challenges, such as insufficient site density and durability. These differences suggest that the nature of the interactions between the ionomer and catalyst is highly dependent on the H 2O % in the DM. In contrast, the H 2O-rich inks exhibited a significant increase in viscoelasticity with increasing I/C, suggesting flocculation of the catalyst by the ionomer. The nPA-rich inks remained predominantly stable-ink viscosity only weakly increased with I/C and the Newtonian behavior was maintained for I/C up to 0.9. In dilute inks ( 0.35), interesting differences were observed between nPA-rich inks (H 2O % ≤ 50%) and H 2O-rich (82% H 2O) inks. In concentrated inks (≥2 wt % catalyst), increasing H 2O % was found to increase agglomeration because of the hydrophobic nature of the catalysts. The effect of H 2O % in the DM on particle agglomeration was found to vary with particle concentration. In the absence of the ionomer, the inks were significantly agglomerated, approaching a gel-like microstructure more » for catalyst concentrations as low as 2 wt %. Steady-shear and dynamic-oscillatory-shear rheology, in combination with synchrotron X-ray scattering, was utilized to understand interparticle interactions and the level of agglomeration of the inks. The effects of the ionomer-to-catalyst (I/C) ratio and weight percentage of water (H 2O %) in the DM on the ink microstructure were studied. In this paper, we present an investigation of the microstructure and rheological behavior of catalyst inks consisting of Fe–N–C platinum group metal-free catalysts and a perfluorosulfonic acid ionomer in a dispersion medium (DM) of water and 1-propanol ( nPA). Publication Date: Wed Mar 13 00:00: Sponsoring Org.: USDOE OSTI Identifier: 1499203 Alternate Identifier(s): OSTI ID: 1499204 Resource Type: Published Article Journal Name: Advanced Science Additional Journal Information: Journal Name: Advanced Science Journal Volume: 6 Journal Issue: 10 Journal ID: ISSN 2198-3844 Publisher: Wiley Blackwell (John Wiley & Sons) Country of Publication: Germany Language: English

Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge TN 37831 USA.

Department of Energy Conversion and Storage Technical University of Denmark Lyngby 2800 Denmark.

Faculty of Science, Health, Education and Engineering University of Sunshine Coast Maroochydore DC Queensland 4558 Australia, School of Chemistry and Molecular Biosciences The University of Queensland Brisbane Queensland 4072 Australia.

School of Molecular and Life Sciences/Curtin Institute of Functional Molecules and Interfaces Curtin University Perth Western Australia 6102 Australia.Centre for Microscopy Characterization and Analysis (CMCA) and School of Molecular Sciences The University of Western Australia Perth Western Australia 6009 Australia.Australian Synchrotron Clayton Victoria 3168 Australia.

John de Laeter Centre Curtin University Perth Western Australia 6102 Australia.Beijing Key Laboratory of Bio‐inspired Energy Materials and Devices School of Space and Environment Beihang University Beijing 100191 P.Fuels and Energy Technology Institute &, Western Australia School of Mines: Minerals, Energy and Chemical Engineering Curtin University Perth Western Australia 6102 Australia.Department of Environmental Engineering School of Metallurgy and Environment Central South University Changsha 410083 China.

Arloy nonprecious high fusing metal