Effect of phosphate variation on morphology and electrocatalytic activity (OER) of hydrous nickel pyrophosphate thin films

Simple, cost effective chemical bath deposition (CBD) method is used for synthesis of hydrous nickel pyrophosphate (Ni₂P₂O₇·8H₂O) thin films as an electrocatalyst on stainless steel (SS) substrate for OER application. The effect of phosphate variation is studied via preparing thin films with different nickel and phosphate molar weight ratio, as decreasing phosphate concentration in the reaction bath willow leaf like morphology changes to compact microflower with rectangular petals. As-prepared Ni₂P₂O₇·8H₂O at a molar weight ratio of 1:2 (nickel: phosphate) gives better results as an electrocatalyst with low overpotential of 308 mV at 25 mA cm⁻² current density, as compare to other molar weight ratios (1:1 and 1:0.5). This excellent electrocatalytic performance of hydrous nickel pyrophosphate thin film electrodes is credited to high ECSA and low impedance of electrocatalyst. Also, it exhibits good stability over 9 h in 1 M KOH at constant potential.