Effect of NaCu<sub>5</sub>S<sub>3</sub> composite Ni<sub><i>x</i></sub>Fe-LDH structure on hydrolysis oxygen evolution performance
Authors: Bai Cheng , Wu Yong , Xin Yu-Ci , Mou Jun-Feng , Jiang Jun-Ying , Ding Ding , Xia Lei , Yu Peng ,   Chongqing Key Laboratory of Photo-Electric Functional Materials, College of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 401331, China,   Institute of Materials, Shanghai University, Shanghai 200072, China
Published: March 2023

The oxygen evolution reaction (OER) plays a critical role in energy storage and conversion devices such as zinc-air batteries, fuel cells, and electrolysis water. However, the OER process involves a four-electron transfer, leading to slow reaction kinetics. Therefore, it is necessary to explore an efficient, inexpensive, and durable electrocatalysts to accelerate the OER process. Noble metal oxides are considered the most advanced OER electrocatalysts, but their high price and scarcity limit their commercial applications. Thus, researchers have started exploring other low-cost materials as alternatives. Nanocomposite materials have emerged as a promising alternative to expensive and scarce noble metal oxide electrocatalysts for OER. Therefore, this work synthesizes novel nanocomposite materials, NaCu<sub>5</sub>S<sub>3</sub>@Ni<sub><i>x</i></sub>Fe-LDH (<i>x</i> = 1, 2, 3, 4) nanosheet array via hydrothermal and water bath methods. The structure and morphology of each product are characterized, indicating a tightly integrated interface between NaCu<sub>5</sub>S<sub>3</sub> and Ni<sub>2</sub>Fe-LDH, which facilitates rapid charge transfer and enhancement of electron regulation at the interface. This changes the local structure characteristics and promotes the OER catalytic performance. Electrochemical characterization results show that in a 1.0 M KOH electrolyte, the overpotential of NaCu<sub>5</sub>S<sub>3</sub>@Ni<sub>2</sub>Fe-LDH for OER at a current density of 20 mA/cm<sup>2</sup> is only 227 mV, significantly lower than that of the original NaCu<sub>5</sub>S<sub>3</sub> (271 mV) and Ni<sub>2</sub>Fe-LDH (275 mV), with stability duration reaching 72 h. Electrochemical results also reveal that with the increase of overpotential, NaCu<sub>5</sub>S<sub>3</sub>@Ni<sub>2</sub>Fe-LDH shows a significant oxidation peak between 1.35–1.45 (V <i>vs.</i> RHE), which leads to the activation of Ni<sup>2+</sup> to Ni<sup>3+</sup> high oxidation state. The high oxidation state of Ni will promote the OER. The NaCu<sub>5</sub>S<sub>3</sub>@Ni<sub>2</sub>Fe-LDH composite electrocatalyst exhibits lower charge transfer resistance, higher double layer capacitance value (10.0 mF/cm<sup>2</sup>), and electrochemical active surface area (250 cm<sup>2</sup>), which are also beneficial to promoting OER. This study highlights the potential of nanocomposite materials as cost-effective alternatives to noble metal oxide electrocatalysts for OER. The NaCu<sub>5</sub>S<sub>3</sub>@Ni<sub>2</sub>Fe-LDH composite electrocatalyst exhibits excellent OER performance with a low overpotential, high stability, and favorable electrochemical properties. This research provides a valuable insight into the design and development of efficient and sustainable electrocatalysts for energy conversion and storage applications.