Prussian blue/ZIF-67-derived carbon layers-encapsulated FeCo nanoparticles for hydrogen and oxygen evolution reaction

Abstract

In this work, FeCo nanoparticles encapsulated in graphitic carbon layers are derived by direct pyrolysis of Prussian blue/ZIF-67. First, the Prussian blue nanocubes with size of 100–150 nm are selected as cores for growth of ZIF-67 metal organic frameworks. Subsequent direct pyrolysis of Prussian blue/ZIF-67 in nitrogen atmosphere enables the formation of carbon nanospheres with FeCo nanoparticles embedded into the nitrogen-doped graphitic carbon layers. The encapsulation of FeCo nanoparticles into the nitrogen-doped carbon layers favors the electron penetration from the underlying FeCo nanoparticles to the nitrogen-doped graphitic carbon layers, tuning the electron density and the electronic properties at the carbon overlayers and then promoting the both hydrogen and oxygen evolution reaction activity. By optimizing the ratio between the Prussian blue and ZIF-67, the active and inexpensive carbon layers-encapsulated FeCo nanoparticles achieve high activity towards the hydrogen evolution reaction, exhibiting a low overpotential of 106 mV at 10 mA cm−2 as well as a low Tafel slope of 90.0 mV dec−1. As oxygen evolution reaction electrocatalysts, the carbon layers-encapsulated FeCo nanoparticles deliver an overpotential of 312 mV at 10 mA cm−2 and a low Tafel slope of 40.6 mV dec−1. Severing as both anode and cathode, the carbon layers-encapsulated FeCo nanoparticles show a potential of 1.495 V at 10 mA cm−2 for water splitting, which is close to the noble metal benchmarks of Pt/C and RuO2 counterparts. The carbon layers-encapsulated FeCo nanoparticles can be used as an attractive replacement for electrocatalytic water splitting.