Anti-corrosive mechanism of poly (N-ethylaniline)/sodium silicate electrochemical composites for copper: Correlated experimental and in-silico studies

doi:10.1016/j.jmst.2020.08.064

Abstract

Abstract:

Poly (N-ethylaniline) (PNEA) composites with varying silicate content were fabricated on copper through a novel electropolymerized strategy in acidic solution. Thickness, compactness, conductivity and adhesive strength of the composite (PNEA-10Si) were optimized as silicate content reached 10 mM. Electrochemical, morphological and solution analyses were employed to evaluate the protective performance of PNEA and PNEA-10Si coatings for copper in 3.5 % NaCl solution. Results of electrochemical analyses indicated that as-prepared coatings retarded the oxygen reduction process efficiently for copper in 3.5 % NaCl solution, drained corrosion current density and elevated interfacial charge transfer resistance. Due to favorable barrier effect, compact structure and low porosity index, PNEA-10Si composite exhibited superior anti-corrosive performance, which was more tolerant than PNEA during long-time immersion. PNEA-10Si coated sample exhibited a stable topography after 144 h immersion with the minimum concentration of released ions revealing the improved protection capacity. Electronic/atomic-multiscale calculations were conducted to clarify the deposition and protection mechanism of as-prepared coatings. Outcomes of density functional theory corroborated that silicate is stabilized in the PNEA layer via electrostatic force; and immobile silicate positively contributed to the charge transfer barrier of the composite. Molecular dynamics simulations evidenced that the favorable compatibility between PNEA and silicate facilitated polymer deposition and confined in-situ ions diffusion.

Key words: Electrochemical deposition, Composite coating, Anti-corrosion, Density-functional theory, Molecular dynamic simulation

Hao Liu, Baomin Fan, Guifeng Fan, Yucong Ma, Hua Hao, Wen Zhang. Anti-corrosive mechanism of poly (N-ethylaniline)/sodium silicate electrochemical composites for copper: Correlated experimental and in-silico studies[J]. J. Mater. Sci. Technol., 2021, 72: 202-216.

Figures/Tables 22

Fig. 1. Cyclic voltammograms for electropolymerized coatings on copper: (a) PNEA, (b) PNEA-5Si, (c) PNEA-10Si and (d) PNEA-15Si at 313 K.

Fig. 2. Thickness, conductivity (a) and adhesion strength (b) of PNEA, PNEA-5Si, PNEA-10Si and PNEA-15Si coatings on copper substrate.

Fig. 3. ATR-FTIR spectra of bare copper, PNEA and PNEA-10Si coatings.

Fig. 4. Surface morphologies of bare copper (a), PNEA (b) and PNEA-10Si (c) coatings.

Fig. 5. Polarization curves of bare and coated copper electrodes in 3.5 % NaCl solution at 298 K.

Table 1 Kinetic parameters for bare and coated copper in 3.5 % NaCl solution at 298 K.

Sample	E_corr (mV)	i_corr (μA/cm²)	-β_c (mV/dec)	βa (mV/dec)	SD^a ×10^-2	η₁ (%)
Bare copper	-241.70	12.59	89.35	92.34	0.19	—
PNEA	-246.94	2.23	90.95	106.18	1.28	82.29
PNEA-10Si	-247.18	0.65	103.36	109.25	0.89	94.84

Fig. 6. Nyquist (a) and Bode (b) spectra of bare and coated copper electrodes in 3.5 % NaCl solution at 298 K along with corresponding equivalent circuits (c and d).

Table 2 Impedance parameters for bare and coated copper electrodes in 3.5 % NaCl solution at 298 K.

Sample	R_f(Ω cm²)	R_ct(kΩ cm²)	W(Ω cm² s^1/2)	Q_f		Q_dl		chi-square(×10^-4)	η₂(%)
Sample	R_f(Ω cm²)	R_ct(kΩ cm²)	W(Ω cm² s^1/2)	C_f(μF/cm²)	n_f	C_dl(μF/cm²)	n_dl	chi-square(×10^-4)	η₂(%)
Bare copper	38.16	1.83	1.92 × 10^-2	298.62	0.79	79.28	0.59	6.24	—
PNEA	136.55	17.03	2.52 × 10^-3	30.13	0.83	68.75	0.89	5.58	89.12
PNEA-10Si	436.01	33.92	—	16.98	0.89	53.04	0.86	4.29	94.56

Fig. 7. Polarization curves of PNEA (a) and PNEA-10Si (b) coated copper with diversified immersion time in 3.5 % NaCl solution at 298 K.

Table 3 Kinetic parameters for coated copper with diversified immersion time in 3.5 % NaCl solution at 298 K.

Samples	Time (h)	E_corr (mV)	i_corr (μA/cm²)	-β_c (mV/dec)	βa (mV/dec)	SD^a ×10^-2
PNEA	24	-243.05	3.95	119.85	99.57	1.06
	48	-223.23	7.76	115.82	103.18	0.33
	96	-224.76	15.85	118.34	100.67	0.86
	144	-213.50	25.15	122.01	98.43	2.15
Composite	24	-270.02	0.57	110.92	101.74	1.14
	48	-261.90	0.69	118.54	99.38	0.97
	96	-252.82	0.21	113.09	127.96	3.12
	144	-256.61	0.61	115.62	109.35	1.88

Fig. 8. EIS spectra of PNEA (a and b) and PNEA-10Si (c and d) coatings on copper with diversified immersion time in 3.5 % NaCl solution at 298 K.

Table 4 Impedance parameters for coated copper in 3.5 % NaCl solution at 298 K.

Sample	Time(h)	R_f(Ω·cm²)	R_ct(kΩ·cm²)	W(Ω·cm²·s^1/2)	Q_f		Q_dl		chi-square(×10^-4)
Sample	Time(h)	R_f(Ω·cm²)	R_ct(kΩ·cm²)	W(Ω·cm²·s^1/2)	C_f(μF/cm²)	n_f	C_dl(μF/cm²)	n_dl	chi-square(×10^-4)
PNEA	24	155.39	9.01	8.19 × 10^-3	54.09	0.81	71.38	0.88	9.37
	48	122.61	8.17	1.02 × 10^-2	82.31	0.79	73.29	0.83	3.04
	96	98.34	4.20	6.67 × 10^-2	90.22	0.80	80.05	0.78	5.60
	144	100.27	1.93	9.33 × 10^-2	103.05	0.78	85.92	0.85	9.09
Composite	24	285.03	36.09	—	32.25	0.73	53.70	0.92	1.31
	48	338.20	27.98	—	92.06	0.76	65.13	0.66	6.92
	96	309.44	52.26	1.59 × 10^-3	18.93	0.78	39.30	0.80	2.11
	144	317.57	31.04	—	26.32	0.79	66.15	0.74	4.16

Fig. 9. Surface topographies of bare copper (a, d), PNEA (b, e) and PNEA-10Si (c, f) coatings before and after 144 h immersion in 3.5 % NaCl solution at 298 K.

Fig. 10. Average roughness for bare copper, PNEA and PNEA-10Si coatings before and after 144 h immersion in 3.5 % NaCl solution at 298 K.

Fig. 11. Concentration of copper ions released from coated and uncoated samples with time.

Fig. 12. Optimized configuration (a, b), mapping of molecular electrostatic potential (MEP, c and d), highest occupied (HOMO), (e) and (f)) and lowest unoccupied (LUMO, (g) and (h)) frontier orbitals for finite structure of PNEA (left) and its composite (right) under dominant solvent model.

Table 5 Reactive parameters for PNEA and its composite in dominant solvent model.

Samples	E_HOMO (eV)	E_LUMO (eV)	ΔE (eV)	γ(eV)	χ(eV)	E_back (eV)	μ (Debye)
PNEA	-3.114	-2.239	0.875	0.438	2.677	-0.110	9.075
Composite	-2.390	-1.434	0.956	0.478	1.192	-0.120	13.182

Fig. 13. Density of state analyses ((a), inset: Fermi levels for both models) and sigma-profiles (b) of PNEA and its composite.

Fig. 14. Top and side snapshots of equilibrium configurations for PNEA (a) and composite (b) deposited on Cu (1 1 1) plane at 313 K along with radial distribution function analyses for pristine (c) and composite systems (d).

Table 6 Interaction and binding energies of PNEA and composite layers on Cu (1 1 1) at 313 K.

Samples	E_inter (kJ/mol)	E_bind (kJ/mol)
PNEA	-9207.87	9207.87
Composite	-10145.28	10145.28

Fig. 15. Diffusion model for in-situ ions in PNEA (a) and composite (b) coatings along with the corresponding mean square displacement plots obtained under NVT ensemble at 298 K.

Table 7 Diffusion coefficients of in-situ species in deposited layers at 298 K.

Systems	Diffusion coefficient (D, m²/s)
Systems	Na⁺	Cl^-	SiO₃^2-
Pristine PNEA	6.93 × 10^-12	9.15 × 10^-12	—
Composite	1.89 × 10^-12	3.47 × 10^-12	1.03 × 10^-13

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