Improving the HER activity of Ni3FeN to convert the superior OER electrocatalyst to an efficient bifunctional electrocatalyst for overall water splitting by doping with molybdenum

Abstract

Developing efficient and earth-abundant bifunctional electrocatalyst for overall water splitting to produce hydrogen is very important. Ni3FeN is always used as an excellent electrocatalyst for the oxygen evolution reaction (OER), but its hydrogen evolution reaction (HER) performance is always negative and seldom concerned. Here, we improve the HER activity and maintain the excellent OER activity of Ni3FeN to realize the efficient overall water splitting by doping with molybdenum. The Mo-doped Ni3FeN shows a significantly improved HER activity with a low overpotential of 69 mV at 10 mA cm−2 as well as an excellent OER activity with a low overpotential of 250 mV at 20 mA cm−2. The improved HER activity can be ascribed to the favorable absorption/desorption process of H intermediate and improved conductivity, which was verified by the density functional theory calculation results of free energy of adsorbed H (ΔGH*), the position of d-band center toward Fermi level and density of state near Fermi level. A two-electrode system that has Mo-doped Ni3FeN electrode as both cathode and anode requires only a low cell voltage of 1.554 V to reach the current density of 10 mA cm−2 and exhibits good stability for overall water splitting. The two-electrode system can also be powered by a commercial AA battery (∼1.5 V), which is better than most of the bifunctional electrocatalysts.