Preparation and Electro-catalytic Mechanisms for Nitrate Ion Reduction of Ti(100-δ)Cuδ(δ=0.02, 0.09, 0.28, 1.39, 5.65) Cathodes†

doi:10.7503/cjcu20170229

Abstract

Abstract:

The ectopic electro-deposition method was used to prepare Ti_(100-_δ₎Cu_δ cathodes with various mass fraction(δ) of 0.02, 0.28, 1.39 and 5.65, respectively, over titanium plates under different electro-deposition time. The scanning electron microscope(SEM), X-ray diffraction(XRD), electrochemical tests including cyclic voltammetry, linear sweep voltammetry and Tafel plots on an electrochemical workstation and nitrate ion reduction experiments were performed to characterize and investigate the microstructure, physical composition, electro-catalytic reduction performance, corrosion resistance and the products selectivity. The experimental results indicate that the active layer existing on the surface of Ti_(100-_δ₎Cu_δ cathodes presents as lattice pattern (111) if the value of δ is no less than 0.28, which can effectively improve the stability of the active layer. The existence of the active layer provides additional active sites for adsorption of nitrate ion(N $O 3 -$ ), which enhances the electro-catalytic performance of cathodes; however, the involvement of copper element would reduce the corrosion resistance of cathodes compared with that of Ti electrode. Besides, Cu exhibits a certain negative effect on the adsorption of nitrite ion while enhances the reduction activity of nitrite ion thus improving selectivity of nitrogen gas. The results of nitrate treatment experiments using Ti_(100-_δ₎Cu_δ(δ=5.65) cathodes at current density of 20 mA/cm² and reaction time of 6 h illustrate that nitrate removal and the selectivity of N₂ were 75.47% and 32.65%, respectively, but as a comparison only 39.89% and 2.19% of those variables were obtained on a titanium electrode at the same experimental conditions.

Key words: Ti(100-δ)Cuδ cathode, Electro-catalytic reduction, Nitrate ion(N $O 3 -$ ), Mechanism, Selectivity coefficient

CLC Number:

O646

TrendMD:

KONG Yan, WANG Lizhang, YANG Shengxiang, ZHAO Peng. Preparation and Electro-catalytic Mechanisms for Nitrate Ion Reduction of Ti_(100-_δ₎Cu_δ(δ=0.02, 0.09, 0.28, 1.39, 5.65) Cathodes^†[J]. Chem. J. Chinese Universities, 2018, 39(1): 132.

Figures/Tables 11

Fig.1 SEM images of the prepared Ti(100-δ)Cuδ cathodes under different electro-deposition time(A) t=0 min(δ=0); (B) t=0.5 min(δ=0.02); (C) t=6 min(δ=0.28); (D) t=30 min(δ=1.39).

Fig.2 XRD patterns of the prepared Ti(100-δ)Cuδ cathodes under different electro-deposition timea. t=0(δ=0); b. t=0.5 min(δ=0.02); c. t=6 min(δ=0.28); d. t=30 min(δ=1.39); e. t=120 min(δ=5.65).

Table 1 Effects of electro-deposition time(t) on the mass fraction(δ), crystallinity and grain size(D) of Cu on Ti(100-δ)Cuδ cathodes

t/min	δ	Crystallinity(%)	D/nm	t/min	δ	Crystallinity(%)	D/nm
0	0			30	1.39	74.71	>100
0.5	0.02	3.03	35.7	120	5.65	15.93	>100
6	0.28	41.69	73.1

Table 2 Calculated results of the texture coefficient(TC) of Cu coating on Ti(100-δ)Cuδ cathodes from XRD patterns

δ	TC(%)				δ	TC(%)
δ	(111)		(200)	(220)	(311)	(111)	(200)	(220)	(311)
0.02	20.8	19.9	41.7	17.5	1.39	34.9	23.5	23.5	18.1
0.28	32.0	24.8	24.5	18.7	5.65	38.0	27.3	22.4	12.3

Fig.3 CV curves of the prepared Ti(100-δ)Cuδ cathodes in hybrid of NaNO3(0.01 mol/L) and Na2SO4(3%, mass fraction) at a scanning rate of 10 mV/sδ: (A) 0; (B) 0.02; (C) 0.28; (D) 1.39; (E) 5.65.

Fig.4 Tafel plots of the prepared Ti(100-δ)Cuδ cathodes and copper in hybrid of NaNO3(0.01 mol/L) and Na2SO4(3%) at a scanning rate of 5 mV/sδ: a. 0; b. 0.02; c. 0.28; d. 1.39; e. 5.65; f. 100.

Table 3 Tafel constants(a,b) of Ti(100-δ)Cuδ cathodes in NaNO3(0.01 mol/L) solution

δ	a/mV	b/mV	δ	a/mV	b/mV
0	81.82	75.99	1.39	61.93	108.29
0.02	66.29	97.14	5.65	91.54	69.17
0.28	60.15	114.20	100	105.66	62.83

Fig.5 NO3- removal efficiency and product selectivity during electro-catalytic reduction on the prepared Ti(100-δ)Cuδ cathodesCurrent density: 20 mA/cm2; electrolysis time: 6 h.

Fig.6 pH values during electro-catalytic reduction of N O 3 - on the prepared Ti(100-δ)Cuδ cathodesCurrent density: 20 mA/cm2; electrolysis time: 6 h.

Fig.7 LSV curves of the prepared Ti(100-δ)Cuδ cathodes in 0.01 mol/L NaNO3(a) and 0.01 mol/L NaNO2(b) solutionsScanning rate: 10 mV/s. δ: (A) 0; (B) 0.02; (C) 0.28; (D) 1.39; (E) 5.65; (F) the enlarged panel in NaNO3 solution. P1 and P2 represent the reduction peaks of the nitrate and nitrite ions, respectively; the subscripts of A, B, C, D and E denote the peaks at δ values of 0, 0.02, 0.28, 1.39, 5.65, respectively.

Fig.8 Linear relationship between concentration and peak currents obtained by recorded LSV data in NaNO3(0.01 mol/L) solutionScanning rate: 10 mV/s. δ: a. 0; b. 0.02; c. 0.28; d. 1.39; e. 5.65.

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