NiO-Nanoparticle-Embedded Polyaniline for Enhanced Ammonia and Water Oxidation Reactions
Pratiksha D. Tanwade, Ajay V. Munde, Balaji B. Mulik, Arindam Adhikari, Rajkumar Patel, Bhaskar R. Sathe
Abstract
Electrochemical ammonia and water oxidation has proven to be a practical substitute for hydrogen and oxygen in low-temperature fuel cell reactions. Herein, this work describes highly dispersed nickel oxide nanoparticles (NiO NPs) on polyaniline (NiO–PANI) that were synthesized by the chemical method. The synthesized electrocatalysts were characterized by X-ray diffraction (XRD) confirming the face-centered cubic (FCC) structure, and morphological features were analyzed using transmission electron microscopy (TEM) to show crumpled nanosheets of PANI decorated by NiO NPs (∼14.97 nm). X-ray photoelectron spectroscopy (XPS) showed variable oxidation states of Ni 2+ /Ni 3+ in NiO–PANI. Raman spectra demonstrate efficient support of the C framework and more defect formation in NiO–PANI compared to PANI and incorporation of NiO into the network. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) studies of NiO–PANI demonstrate higher electrochemical activity and feasible electron transfer corresponding to the ammonia oxidation reaction (AOR) and oxygen evolution reaction (OER). An excellent activity for the AOR on NiO–PANI at 10 mA/cm 2 is shown at an ultralow potential of E = 1.25 V versus reversible hydrogen electrode (RHE), and a dominant OER is present at an anodic peak potential of E = 1.53 V versus RHE. Chronoamperometric ( i – t ) measurement shows NiO–PANI having stability at 1.35 V (peak potential) and long-term, i.e., 15 h, current performance toward the AOR. An excellent result for the electrocatalytic AOR and OER was from the availability of additional anchoring sites, cooperative interactions of both NiO with PANI, and increased overall conductivity of nanocomposite material. This work offers a synthetic method for the fabrication of noble-metal-free electrocatalytic systems for remarkable outcomes, like H 2 production from ammonia oxidation for direct fuel-cell-based energy production.