Room temperature preparation of NiFe-phytic acid composite and its electrocatalytic performance for overall water splitting

The preparation of bifunctional catalysts with high stability and high activity for hydrogen production from water is one of the important step in the large-scale commercial application of hydrogen energy. Herein, the flake amorphous phytic acid-nickel iron bimetallic composite (NiFe-PA) has been prepared on foamed nickel (NF) by two-step room temperature impregnation using phytic acid (PA), ferric chloride hexahydrate (FeCl₃·6H₂O) and nickel chloride hexahydrate (NiCl₂·6H₂O) as the starting materials. The electrocatalytic performance of NiFe-PA modified NF electrode (NiFe-PA/NF) for water electrolysis in alkaline condition (1.0 mol/L KOH) was investigated by linear sweep voltammetry (LSV). The results show that NiFe-PA/NF, as a bifunctional catalyst, has excellent oxygen and hydrogen evolution properties due to the synergistic effect between Ni and Fe. The overpotentials are only 220 mV at 50 mA·cm⁻² for oxygen evolution reaction (OER) and 135 mV at 10 mA·cm⁻² hydrogen evolution reaction (HER). The NiFe-PA/NFs were then assembled into a two-electrode system for overall water splitting, and the cell voltage required to reach the current density of 10 mA·cm⁻² was only 1.61 V, which is lower than the precious metal catalyst system of RuO₂/NF||Pt-C/NF (1.64 V). It can also satisfy the hydrogen production driven by solar panels (2 V) under solar illumination conditions. Furthermore, owing to the high stability and corrosion resistance of the PA-metal complex, the catalytic stability of NiFe-PA/NF can be maintained at least for 175 h and 75 h, respectively, for the OER and HER at 100 mA·cm⁻², indicating the high catalytic stability of NiFe-PA/NF at high current densities.