Synthesis, microstructure and electrochemical properties of Ni-P-based alloy coatings for hydrogen evolution reaction in alkaline media

Abstract

Alkaline water electrolysis driven by renewable energy is a promising technology for green hydrogen generation. The cathode half-cell reaction i.e., the hydrogen evolution reaction (HER) in alkaline water electrolysis suffers from slow kinetics. Ni-P-based alloys have shown to be an efficient and cost-effective electrocatalyst to accelerate the HER rate. In this study, three Ni-P alloy coatings are prepared via electrodeposition by varying the deposition currents viz. 10 mA cm-2 direct, 10 mAcm-2 and 100 mAcm-2 pulsed currents. The XRD patterns of all the Ni-P coatings exhibited the formation of crystalline deposits and confirmed the alloying of P in Ni. The SEM images suggested that the microstructures of the Ni-P alloy deposits are highly dependent on the magnitude and waveform of the applied current employed during preparation of the alloy coatings. The composition of the alloy surface is Ni-rich in all three cases but exhibited local variations as evaluated by EDX. The surface distributions of Ni and P in the pulsed deposited samples are more uniform and homogeneous. The cyclic voltammetry patterns of the Ni-P coatings in KOH media exhibit characteristic peaks due to Ni/Ni3+ redox phenomenon. The Ni2+/Ni3+ oxidation peak area is lowest for the direct deposited sample and highest for the pulsed deposited one (100 mAcm-2). The Ni-P alloy electrocatalyst deposited under pulsed mode at 100 mAcm-2 exhibits a current density of −10 mAcm-2 at 0.09 V overpotential and is most active among all samples. The remarkable electrocatalytic activity of this sample is attributed to its smaller crystallite size, better morphological characteristics and lesser resistances to charge transfer and porosity.