Catalyst Support Effect on the Activity and Durability of Magnetic Nanoparticles: toward Design of Advanced Electrocatalyst for Full Water Splitting.

Earth-abundant element-based inorganic-organic hybrid materials are attractive alternatives for electrocatalyzing energy conversion reactions. Such material structures do not only increase the surface area and stability of metal nanoparticles (NPs) but also modify the electrocatalytic performance. Here, we introduce, for the first time, multiwall carbon nanotubes (MWNTs) functionalized with nitrogen-rich emeraldine salt (ES) (denoted as ES-MWNT) as a promising catalyst support to boost the electrocatalytic activity of magnetic maghemite (γ-Fe2 O3 ) NPs. The latter component has been synthesized by a simple and upscalable one-step pulsed laser ablation method on Ni core forming the core-shell Ni@γ-Fe2 O3 NPs. The catalyst (Ni@γ-Fe2 O3 /ES-MWNT) is formed via self-assembly as strong interaction between ES-MWNT and Ni@γ-Fe2 O3 results in NPs' encapsulation in a thin C-N shell. We further show that Ni does not directly function as an active site in the electrocatalyst but it has a crucial role in synthesizing the maghemite shell. The strong interaction between the NPs and the support improves notably the NPs' catalytic activity toward oxygen evolution reaction (OER) in terms of both onset potential and current density, ranking it among the most active catalysts reported so far. Furthermore, this material shows a superior durability to most of the current excellent OER electrocatalysts as the activity, and the structure, remains almost intact after 5000 OER stability cycles. On further characterization, the same trend has been observed for hydrogen evolution reaction, the other half-reaction of water splitting.