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Volume 15
Issue 2
10.3390/coatings15020138
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Article

Electrochemical Fabrication of Ni–Co Alloy over a Wide pH Range Using Sodium Citrate as a Complexing Agent

by
Évany Silva dos Santos
1,
Josiane Dantas Costa
2,*,
Arthur Filgueira de Almeida
2,
Aureliano Xavier dos Santos
3,
Lincoln Rodrigues Sampaio de Araújo
4,
Renato Alexandre Costa de Santana
2 and
Ana Regina Nascimento Campos
1
1
Department of Chemical Engineering, Federal University of Campina Grande, Av. Aprígio Veloso, 882, Campina Grande 58429-970, Brazil
2
Department of Mechanical Engineering, Federal University of Campina Grande, Av. Aprígio Veloso, 882, Campina Grande 58429-970, Brazil
3
Academic Unit of Cabo de Santo Agostinho, Rural Federal University of Pernambuco, Cabo de Santo Agostinho 54518-430, Brazil
4
Department of Physics, Federal University of Campina Grande, Av. Aprígio Veloso, 882, Campina Grande 58429-970, Brazil
*
Author to whom correspondence should be addressed.
Coatings 2025, 15(2), 138; https://doi.org/10.3390/coatings15020138
Submission received: 31 December 2024 / Revised: 20 January 2025 / Accepted: 22 January 2025 / Published: 24 January 2025
(This article belongs to the Special Issue Surface Modification of Advanced Transition Metal-Based Materials for Electrochemical Energy Storage)
Versions Notes

Abstract

In this study, nickel–cobalt (Ni–Co) coatings were fabricated via electrodeposition using a 22 central composite factorial design with two central and two axial points, totaling ten experiments. The effects of pH and current density on the coatings’ chemical composition and properties were evaluated. Coatings were characterized by microstructure, morphology, magnetic properties, and corrosion resistance. The results showed that pH significantly influenced chemical composition, while current density had no notable effect. Acidic pH produced cobalt-rich coatings (43–81 at.%), with uniform morphology, higher saturation magnetization, and lower corrosion resistance. Maximum cobalt content (81 at.%) resulted in a mixed face-centered cubic (fcc) + hexagonal close-packed (hcp) phase. Alkaline pH yielded nickel-rich coatings (89–95 at.%), featuring nodular morphology, lower magnetization, higher corrosion resistance, and, exclusively, the fcc phase. The highest polarization resistance (66.1 kΩ) occurred at pH 8.83 and 60 mA/cm2, while resistance decreased with increasing cobalt content. The pH effect on deposition was linked to the formation of citrate complexes: ammonia and citrate complexes promoted nickel deposition under alkaline conditions, while stable cobalt complexes dominated in an acidic pH. These findings highlight the potential to tailor Ni–Co coatings for applications such as corrosion-resistant coatings (nickel-rich) or magnetic devices (cobalt-rich).
Keywords: electrodeposition; Ni–Co; corrosion electrodeposition; Ni–Co; corrosion

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MDPI and ACS Style

Santos, É.S.d.; Costa, J.D.; Filgueira de Almeida, A.; Santos, A.X.d.; Araújo, L.R.S.d.; Santana, R.A.C.d.; Campos, A.R.N. Electrochemical Fabrication of Ni–Co Alloy over a Wide pH Range Using Sodium Citrate as a Complexing Agent. Coatings 2025, 15, 138. https://doi.org/10.3390/coatings15020138

AMA Style

Santos ÉSd, Costa JD, Filgueira de Almeida A, Santos AXd, Araújo LRSd, Santana RACd, Campos ARN. Electrochemical Fabrication of Ni–Co Alloy over a Wide pH Range Using Sodium Citrate as a Complexing Agent. Coatings. 2025; 15(2):138. https://doi.org/10.3390/coatings15020138

Chicago/Turabian Style

Santos, Évany Silva dos, Josiane Dantas Costa, Arthur Filgueira de Almeida, Aureliano Xavier dos Santos, Lincoln Rodrigues Sampaio de Araújo, Renato Alexandre Costa de Santana, and Ana Regina Nascimento Campos. 2025. "Electrochemical Fabrication of Ni–Co Alloy over a Wide pH Range Using Sodium Citrate as a Complexing Agent" Coatings 15, no. 2: 138. https://doi.org/10.3390/coatings15020138

APA Style

Santos, É. S. d., Costa, J. D., Filgueira de Almeida, A., Santos, A. X. d., Araújo, L. R. S. d., Santana, R. A. C. d., & Campos, A. R. N. (2025). Electrochemical Fabrication of Ni–Co Alloy over a Wide pH Range Using Sodium Citrate as a Complexing Agent. Coatings, 15(2), 138. https://doi.org/10.3390/coatings15020138

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