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Development of inexpensive and efficient oxygen evolution reaction (OER)catalysts in acidic environment is very challenging, but important for practical proton exchange membrane (PEM) water electrolyzers. Here we develop a molecular iron-nitrogen coordinated carbon nanofiber supported on electrochemically exfoliated graphene (FeN 4 /NF/EG) electrocatalyst through carbonizing the precursor composed of iron ions absorbed on polyaniline-electrodeposited EG. Benefitting from the unique 3D structure, the FeN 4 /NF/EG hybrid exhibits a low overpotential of ~294 mV at 10 mA cm -2 for the OER in This article is protected by copyright. All rights reserved. 5precursor was uniformly electrodeposited on EG surface that was constructed by electrochemical exfoliation of graphite (Figure S1). After soaking in iron nitrate solution, carbonization, and acid etching treatments, the precursor was in situ converted into FeN x /NF/EG catalyst, which is supported by Fourier-transform infrared spectroscopy (FTIR) results (Figure S2). We systematically explored the influence of annealing at different temperatures (800-1000 o C) affecting the OER activity. The optimized carbonization temperature was 900 o C (FeN x /NF/EG), which exhibited the best electrocatalytic performance for OER in acid (Figure S3-S4). Moreover, this synthesis method can be further This article is protected by copyright. All rights reserved. 13 support from U.S. DOE fuel cell technologies Offices. M. Qiu thanks the support of Self-determined Research Funds of CCNU from Colleges' Basic Research and Operation of MOE ( 23020205170456). This research was supported by Dr. Y. Hu (Yongfeng Hu) to provide valuable discussion about the XAS analysis.Received: ((will be filled by the editorial staff))Revised: ((will be filled by the editorial staff))

Sluggish kinetics of the methanol oxidation reaction (MOR) at the anode of direct methanol fuel cells (DMFCs) is primarily due to adsorbed CO poisoning of precious metal catalysts. CeO2 is known to provide oxygen containing species to adjacent precious metal sites for facilitating CO removal during the MOR. In this work, highly dispersed Pd nanoparticles surrounded by CeO2 dots were deposited on a core–shell structured and nitrogen-doped mesoporous carbon sphere (NMCS) support, which exhibited encouraging electrocatalytic activity, CO tolerance, and stability for the MOR in alkaline media. The ratios of Pd to CeO2 were found crucial for overall catalytic performance enhancement. When compared to a commercial PtRu/C catalyst, an optimized Pd(20%)-CeO2(20%)/NMCS catalyst presented a comparable CO stripping onset potential, ∼6 times higher peak current density, and enhanced cyclic stability. The unique mesoporous carbon with nitrogen doping also benefits for uniform dispersion of Pd nanoparticles and CeO2 dots. In good agreement with experimental spectroscopy analysis, density functional theory calculations suggest that the strong electronic interactions between Pd and surrounding CeO2, as well as nitrogen dopants in supports, dramatically reduce the adsorption energy of CO at the Pd surface, therefore enhancing CO tolerance of the Pd-CeO2/NMCS catalyst and further improving MOR activity. Using a polymer fiber membrane-based alkaline DMFC, the Pd(20%)-CeO2 (20%)/NMCS anode catalyst further demonstrated encouraging performance when a NiCo2O4 catalyst was used for the oxygen cathode.

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