Coordination Polymer-Derived Fe3N Nanoparticles for Efficient Electrocatalytic Oxygen Evolution

Based on a coordination polymer, FeCl2(4,4'-bpy) (4,4'-bpy = 4,4'-bipyridine) and the carbon nanotube (CNT)/NaCl dual template, Fe3N nanoparticles (NPs) were synthesized via chemical thermolysis in the absence of an extra nitrogen source. The decomposition of 4,4'-bpy under high temperature produces thin carbon coating for Fe3N NPs. Also, the CNT template anchors the Fe3N NPs to avoid aggregation. The sample (denoted as Fe3N-C N) exhibits excellent electrocatalytic oxygen evolution reaction (OER) behavior even with a small molar ratio of Fe3N (Fe: 4.9 at. %), which can deliver a current density of 10 mA cm(-2) at an overpotential of 218 mV with a Tafel slope of 84 mV dec(-1) and long-term OER activity during 60 h electrolysis at 20 mA cm(-2). Furthermore, the sample after 20 h electrolysis, denoted as Post-Fe3N-C N (20 h), displays enhanced OER activity with a smaller Tafel slope of 41 mV dec(-1) and overpotentials of 195 and 327 mV at 10 and 100 mA cm(-2), respectively, which is mainly due to the partial transformation of Fe3N into FeOOH. The OER mechanism is investigated by density functional theory calculations, and it is found that the surface partial oxidation of Fe3N leads to the effective OER electrolysis, which changes the electron density of the superficial atoms and induces the moderate adsorption for the intermediates.