Enhanced Charge Storage Performance and Electrocatalytic Oxygen Evolution Reaction Activity of Self-Grown Iron–Cobalt-Doped Nickel Oxide Nanoplates: An Example of the Synergistic Effect

Abstract

The synergistic electrochemical properties of a rational design transition metal oxide can improve its efficiency. However, the optimal synergistic effect of transition metal oxide nanostructures toward energy storage and conversion is still unsatisfactory. Herein, a simple, efficient wet chemical synthesis method is promoted for the incorporation of iron and cobalt ions into the nickel oxide matrix as (Fe–Co-doped NiO), with excellent high energy storage and electrocatalytic OER performance. Importantly, the correlation between varying amounts of Fe–Co-doped NiO electrodes and catalysts with different surface morphologies, crystallographic phases, and electrochemical activities was investigated. Benefiting from strong synergistic action, rich oxygen vacancies, oxidation behavior, transferred ion diffusion, and morphology, the 5 wt % Fe and Co-doped NiO electrode (5 wt % Fe–Co–NiO) exhibit a better specific capacitance of 5419.3 F g^–1 at a current density of 2 A g^–1, which is better than that of the pristine NiO (530.4 F g^–1). Similarly, a 5 wt % Fe–Co–NiO//5 wt % Fe–Co–NiO symmetric device provides a superb volumetric energy power density (47.9 Wh kg^–1/545.8 WK g^–1). It also demonstrates durable redox cycle life with 92.86% retention after 10,000 redox cycles scanned at a current density of 10 A g^–1. At the same time, a panel consisting of 42 red light-emitting diodes (LEDs) with a voltage of approximately 1.5 V has been successfully illuminated for five min, exhibiting a high level of illumination intensity. This was accomplished by connecting two symmetric supercapacitor devices in series. This demonstrates the significance of the as-grown 5 wt % Fe–Co-doped NiO electrode for commercial applications. Furthermore, compared to the pristine NiO (680 mV and 146 mV s^–1) catalyst, the 5 wt % Fe–Co–NiO electrocatalyst shows impressive intrinsic activity for the oxygen evolution reaction with an ultralow overpotential of 210 mV at 50 mA cm^–2 and a small Tafel slope of 85.6 mV dec^–1, approving the importance of bimetallic ion doping in water splitting activity. Additionally, the 5 wt % Fe–Co-doped NiO nanostructured catalyst presents the highest turn-on-frequency (1.64 s^–1) and electrochemically active surface area (84.75 mF cm^–2) values, thus indicating the specific efficacy of each active site. Also, a 5 wt % Fe–Co-doped NiO catalyst has maintained steady performance for more than 115 h. This work offers a deep understanding of the impact of optimal bimetallic doping through the synergistic effect on energy storage and water splitting performance of the NiO electrode/catalyst for commercial practices.