This study aimed to use a functionally graded (FG) Ni-Cu-Fe coating as an electrocatalyst for oxygen evolution reaction (OER) applications. The coating was applied on a mild carbon steel substrate by an electrodeposition technique, with the current density being progressively increased from 0.5 A/dm to 5 A/dm at a steady rate of 0.2 (A/dm)/min during the coating operation. Using this specific method, the Ni content of the FG Ni-Cu-Fe coating changed along the cross-section when increasing the current density, 17 % more than the constant current coating. This technique also affected the surface morphology of the FG Ni-Cu-‌Fe coating and changed it from cauliflower to micro/nanocones when the current density was linearly increased, enhancing active sites significantly and thereby improving electrocatalytic activity. The coating's electrocatalytic behavior was studied by electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and cyclic voltammetry (CV). results showed that the FG Ni-Cu-Fe coating had the smallest overpotential (134 mV) at the current density of 10 . Also, it had the smallest Tafel slope (24.3 mV.dec) and smallest resistance (598 Ω.cm) compared to all of the other coatings. The FG Ni-Cu-‌‌Fe coating had higher OER performance because of high Ni content, micro/nanocones morphology with many active sites, and FG nature. The FG Ni-Cu-Fe coating is finally concluded to be a promising and economical catalyst with high OER activity.

中文翻译：

---

电沉积功能梯度Ni-Cu-Fe涂层的增强析氧反应

本研究旨在使用功能梯度 (FG) Ni-Cu-Fe 涂层作为析氧反应 (OER) 应用的电催化剂。通过电沉积技术将涂层涂覆在低碳钢基材上，在涂层操作过程中，电流密度以 0.2 (A/dm)/min 的稳定速率从 0.5 A/dm 逐渐增加到 5 A/dm。采用这种特定方法，当增加电流密度时，FG Ni-Cu-Fe涂层的Ni含量沿横截面变化，比恒流涂层高17%。该技术还影响了FG Ni-Cu-Fe涂层的表面形貌，当电流密度线性增加时，其从菜花状变为微米/纳米锥状，显着增强了活性位点，从而提高了电催化活性。通过电化学阻抗谱（EIS）、线性扫描伏安法（LSV）和循环伏安法（CV）研究了涂层的电催化行为。结果表明，FG Ni-Cu-Fe涂层在电流密度为10 时具有最小的过电势（134 mV）。此外，与所有其他涂层相比，它具有最小的塔菲尔斜率 (24.3 mV.dec) 和最小的电阻 (598 Ω.cm)。由于高镍含量、具有许多活性位点的微/纳米锥形态以及 FG 性质，FG Ni-Cu-Fe 涂层具有更高的 OER 性能。 FG Ni-Cu-Fe 涂层最终被认为是一种有前途且经济的催化剂，具有高 OER 活性。