Full paper Ultrafine and highly disordered Ni 2 Fe 1 nanofoams enabled highly efficient oxygen evolution reaction in alkaline electrolyte

Highlights • Amorphous NiFe NFs were synthesized with facile method. • Ni 2 Fe NFs show excellent OER performance. • The catalytic mechanism was studied. Abstract Nickel iron hydroxides are the most promising non-noble electrocatalysts for oxygen evolution reaction (OER) in alkaline media. By in situ reduction of metal precursors, compositionally controlled three-dimensional Ni x Fe y nanofoams (NFs) are synthesized with high surface area and uniformly distributed bimetallic networks. The resultant ultrafine and highly disordered amorphous Ni 2 Fe 1 NFs exhibit extraordinary electrocatalytic performance toward OER and overall water splitting in alkaline media. At a potential as low as 1.42 V (vs. RHE), Ni 2 Fe 1 NFs can deliver a current density of 10 mA/cm2 and show negligible activity loss after 12 h stability test. Even at large current flux of 100 mA/cm2, an ultralow overpotential of 0.27 V is achieved, which is about 0.18 V more negative than benchmark RuO 2 . Both ex-situ Mӧssbauer spectroscopy and X-ray Absorption Spectroscopy reveal a phase separation and transformation for the Ni 2 Fe 1 catalyst during OER process. The evolution of oxidation state and disordered structure of Ni 2 Fe 1 might be a key to the high catalytic performance for OER. Graphical abstract

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Keywords Porous nanostructures NiFe alloys Amorphous catalysts Oxygen evolution reaction Water splitting

Shaofang Fu received her Master's degree from Department of Materials Science and Engineering at The University of Tennessee-Knoxville in August 2014. She is currently a doctoral graduate student supervised by Prof. Yuehe Lin in the School of Mechanical and Materials Engineering at Washington State University. Her research is focused on nanostructured materials for electrochemical energy storage and conversion.

Junhua Song is a Ph.D. student from Washington State University and currently works at Pacific Northwest National Laboratory. His research is focused on designing functional materials for rechargeable batteries and electrocatalytic applications. He received his Master's degree from Columbia University in 2015.

Dr. Chengzhou Zhu received his Ph.D. degree in January 2013 at the Changchun Institute of Applied under the supervision of Prof. Shaojun Dong. Since then, he did postdoctoral work with Prof. Alexander Eychmüller supported by the Alexander von Humboldt Foundation in Dresden University of Technology. Currently, he is an Assistant Research Professor at Washington State University. He has coauthored over 110 peer-reviewed publications, with citations of ∼ 6000, and an h-index of 36, according to Google Scholar. His scientific interests focus on nanomaterial-based electrochemical energy and analytical applications.

Gui-Liang Xu received his Bachelor in July 2009 and Ph.D. degree in June 2014 from Department of Chemistry of Xiamen University. He is now a post-doctoral fellow at Argonne national laboratory. He mainly focuses on the research of advanced battery materials and their study by in-situ synchrotron X-ray techniques.

Dr. Khalil Amine is a Distinguished Fellow and the Manager of the Advanced Battery Technology programs at Argonne National Laboratory, where he is responsible for directing the research and development of advanced materials and battery systems for HEV, PHEV, EV, satellite, military and medical applications. Dr. Amine currently serves a member of the U.S. National Research Consul on battery related technologies. Among his many awards, Dr. Khalil is 2017 Fellow of the Electrochemical Society, 2003 recipient of Scientific America's Top Worldwide Research 50 Research Award, a 2009 recipient of the US Federal Laboratory Award for Excellence in Technology Transfer, and is the five-time recipient of the R & D 100 Award, which is considered as the Oscar of technology and innovation. In addition, he was recently awarded the ECS battery technology award and the international battery association award. Dr. Amine holds or has filed over 140 patents and patent applications and has over 450 publications. From 1998–2008, Dr. Amine was the most cited scientist in the world in the field of battery technology.

Cheng-Jun Sun is a physicist in the X-ray Science Division at Argonne National Laboratory, his research interests include X-ray absorption spectroscopy (XAFS), X-ray emission spectroscopy, high-energy-resolution fluorescence-detected XAFS, application of advanced spectroscopy on energy materials, and magnetic thin films and multiferroic materials.

Dr. Xiaolin Li is a scientist at Pacific Northwest National Laboratory. He received his Ph.D. degree in 2005 from Department of Chemistry, Tsinghua University and conducted his postdoctoral research in Hongjie Dai's group at Stanford University. He has extensive experience with carbon nanotubes, graphene, and is an expert in designing nanostructured functional materials for various applications. His current research interest is on battery materials and renewable energy. He has authored/co-authored more than 70 papers, which have been cited for more than 20,000 times. His h-index is 50.

Dr. Dan Du received her Ph.D. in Analytical Chemistry from Nanjing University in 2005. She joined Central China Normal University in 2005 and was promoted to Full Professor in 2011. Currently she is a Research Professor at Washington State University. Her research interests include functional nanomaterials for fuel cells and electrochemical biosensing.

Dr. Yuehe Lin is a professor at Washington State University and a Laboratory Fellow at Pacific Northwest National Laboratory. He has been actively working in the nanotechnology area, particularly in the synthesis of functional nanomaterials for energy and environmental applications. His other research activities include development of new biosensors and bioelectronic devices and nanomaterials for biomedical diagnosis and drug delivery. Dr. Lin has published 430 papers, with 38,500 total citations and an h-index of 102, according to Google Scholar. He was listed as a highly cited researcher in chemistry on Thompson Reuters and Clarivate Analytics's lists in 2014, 2015, 2016, and 2017.

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