Surface carbon layer controllable Ni3Fe particles confined in hierarchical N-doped carbon framework boosting oxygen evolution reaction

Developing high-efficiency and low-cost catalysts towards oxygen evolution reaction (OER) is extremely important for overall water splitting and rechargeable metal−air batteries. Herein we propose a promising organometallic coordination polymer (OCP) induced strategy to construct hierarchical N-doped carbon framework with NiFe nanoparticles encapsulated inside (Nx[email protected]–C) as a highly active and stable OER catalyst. The synthesis of OCP precursor depends on the unique molecular structure of iminodiacetonitrile (IDAN), which can coordinate with metal ions to form Ni2Fe(CN)6 with prussian blue analogs (PBA) structure. Unlike previous PBA-induced methods, the thickness of the carbon layer covering the surface of the metal core can be well controlled during the pyrolysis through adjusting the amount of IDAN, which builds a wonderful bridge for investigating the relationship between carbon layer thickness and catalytic performance. Both the experimental characterizations and theoretical studies validate that a suitable carbon layers thickness leads to optimal OER activity and stability. By optimizing the structure and composition, the optimized Ni3[email protected]–C with hierarchical framework exhibits the low overpotentials (260 ​mV at 10 ​mA ​cm−2; 320 ​mV at 50 ​mA ​cm−2), improved kinetics (79 ​mV dec−1), and robust long-term stability, which exceeds those of benchmark RuO2.