Effect of the electrochemically induced surface annealing on corrosion behaviors of 304L stainless steel in an acidic environment

Abstract

The corrosion behaviour of electrochemically induced surface annealed (EISA) 304L stainless steel was analysed using a range of electrochemical methods, such as polarisation, impedance and Mott–Schottky techniques. Secondary ion mass spectroscopy was used to examine the elemental distribution around the surface of an EISA-treated specimen. The results showed that the EISA treatment increases the resistance to pitting corrosion due to surface densification caused by the absorption of NO and/or N₂, which had been reduced under cathodic polarisation during the EISA process. Owing to the limited annealing depth, however, the prolonged corrosion process (i.e. Fe dissolution) can lead to the dissolution of NO and/or N₂ species, which had been absorbed on the outer surface, and only smaller portions remained with an uneven distribution at the surface. This can make the EISA-treated steel more vulnerable to corrosion.

Keywords

304L stainless steel electrochemically induced surface annealing corrosion secondary ion mass spectroscopy polarisation

Introduction

Austenitic stainless steels are used widely in a variety of industrial fields, such as the petroleum, chemical and food industries, because of their superior corrosion resistance [1]. When the steels are applied in the afore-mentioned fields, a mechanical forming process is necessarily involved. Under heavily plastically deformed conditions, such as rolling and grounding, the metastable austenite matrix was transformed to martensite by mechanical-phase transformation [2 -10]. The high levels of residual stress in martensite causes degradation in the mechanical properties and corrosion resistance [11–14]. In general, heat treatment of mechanically deformed austenitic stainless steel is carried out at several hundreds of degrees Celsius to remove the martensitic phase [2]. At several hundreds of degrees, however, carbides, such as chromium carbides, can be precipitated, which result in a decrease in bulk properties, particularly the mechanical properties and corrosion resistance of steel [15–19]. Therefore, a surface treatment of steel without affecting their bulk properties is essential for a range of applications. Burstein et al. [20] proposed a novel concept of an EISA treatment to remove the martensite phase from the steel surface without altering the bulk properties of the steel. They reported that the martensite phase that had formed by a grinding process had decreased significantly after the EISA treatment involving a series of electrochemical pulses composed of anodic and cathodic overpotentials in a sodium nitrite solution. Based on the contraction of the γ-phase lattice parameter [21], they suggested that the surface annealing effect might be due to an austenite-stabilizing element, such as nitrogen. On the other hand, precise analytical evidence was not presented, and the underlying mechanism was not provided. Furthermore, the influence of EISA on the corrosion behaviours of the austenitic stainless steel is still unclear. Although Li et al. [22] evaluated the resistance of the EISA-treated stainless steel to pitting corrosion using a potentiodynamic polarisation test in a 3.5% NaCl solution, it was not enough to determine the prolonged corrosion behaviours of the steel with the limited information available. Therefore, potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS), Mott–Schottky, and secondary ion mass spectroscopy (SIMS) measurements were employed to gain a better understanding of the effects of EISA treatment on the surface characteristics, including the corrosion behaviours. Based on the experimental results, a possible corrosion mechanism of the EISA-treated stainless steel in acidic environments is proposed.

Experimental

Specimen preparation

The material tested in this paper was a SUS 304L type stainless steel sheet. Table 1 lists the chemical composition of the steel. For a sufficient area of the electrochemical experiment, the specimens with a 1 mm thickness were cut into 2 cm² using a linear cutting machine. Each of the surfaces was ground with silicon carbide abrasive paper at 220-2400 grit. They were then polished with 3 and 1 μm diamond paste, cleaned and rinsed with ethanol.

Table 1

Chemical composition of the tested specimen.

	C	Si	Mn	P	S	Ni	Cr
SUS304L	∼0.03	∼1.00	∼2.00	∼0.045	∼0.030	8.00-10.50	18.00-20.00

EISA treatment

The surfaces were subjected to the same conditions of the EISA treatment. The surfaces were treated with a series of anodic and cathodic electrochemical pulses, −1.8 V for 277 s and +0.28 V for 56 s (vs. SCE), for 33 cycles in an 8 M aqueous solution of sodium nitrite at 80°C. Equivalent results can be achieved using a two-electrode cell with a voltage pulse of −4.1 V and +1.2 V for 277 and 56 s, respectively [20]. Figure 1(a) shows a schematic diagram of the three-electrode cell subjected to the EISA treatment. The saturated calomel electrode and graphite cylinder were used as the reference and counter electrodes, respectively.

Figure 1

Schematic diagram of an electrochemical test cell: (a) for the EISA treatment cell and (b) for the electrochemical corrosion test cell.

X-ray diffraction analysis

The phases of the EISA-treated and untreated samples were examined by X-ray diffraction (XRD) using Cu-Kα radiation (λ = 1.542 Å).

Electrochemical test

To evaluate the electrochemical corrosion behaviour according to the EISA treatment, a potentiodynamic polarisation test was employed for two different immersion times: 0 and 24 h. The different immersion times were used in the potentiodynamic polarisation test to examine the effects of the immersion time on the EISA-tested sample. The specimens were polarised dynamically from −0.3 to 1 V vs. open circuit potential (OCP) at a scan rate of 0.3 mV s⁻¹.

EIS was used to determine the change in the electrochemical corrosion resistance. The EIS measurements were conducted at the OCP, applying a 10 mV amplitude sinusoidal voltage in 0.01-100 000 Hz frequency intervals. The impedance test was performed at different exposure times ranging from 3 to 96 h after the specimen was immersed in the electrolyte.

In addition, the Mott–Schottky measurement was conducted to evaluate the stability of the passive film on the steel surface. The tested specimens were polarised from −0.194 to 0.3003 V vs. OCP at a scan rate of 0.5 mV s⁻¹. The potential range was applied in the passivity potential range of the anodic parts based on the potentiodynamic polarisation curves.

The reference and the counter electrodes for the electrochemical corrosion test were the saturated calomel electrode and platinum grid, respectively. A 0.1 N HCl solution was used as the electrolyte for all electrochemical tests. Figure 1(b) presents a schematic diagram of the electrochemical corrosion test cell.

All of the electrochemical tests were conducted in aerated and unstirred solutions at ambient temperature.

SIMS analysis

SIMS analysis using a Cs⁺ gun was used in the tested specimens before and after the EISA treatment, and after 24 h immersion in a 0.1 N HCl solution after the EISA treatment, to identify the presence of nitrogen on the steel surface. The detection area was 33 μm (ϕ) and the ions detected were carbon, nickel, nitrogen, chromium, iron and oxygen.

Results and discussion

Potentiodynamic polarisation measurement and SIMS analysis after EISA

Figure 2 presents the potentiodynamic polarisation test results before and after the EISA treatments, and Table 2 lists the corrosion parameters of the OCP, pitting potential (E _p) and passivity current density (i _pass). After the EISA treatment, the OCP and E _p were increased, but the i _pass was decreased, suggesting that the EISA treatment can contribute to the increase in resistance to pitting corrosion. This agrees well with the previous finding [22], showing that the deepest pit and the pit area of the EISA-treated specimen were shallower and smaller, respectively, than those of the untreated specimen. Actually, the appearance of multiple potentials of zero current during the anodic sweep was caused by the background oxygen reduction current. Nevertheless, it is also worth making a relative comparison of pitting potentials between the two specimens exposed to an acidic environment with oxygen. Anyway, the increase in resistance to the pitting corrosion of the EISA-treated specimen may be associated closely with the phase transition from α’-martensite to γ-austenite during the EISA treatment [2 -10]. In addition, the improvement of the pitting corrosion resistance after the EISA treatment may have resulted from a significant decrease in the amount of martensite phase, which was confirmed by XRD (Figure 3). On the other hand, the decrease in or elimination of the martensite phase does not always increase the corrosion resistance [23–28]. Chunchun et al. [23 -31] examined the effects of the martensite contents on the pitting and stress corrosion sensitivities and found that the sensitivities were not proportional to the martensite content. This suggests that the critical factor may not be the fraction of the martensite phase in the microstructure, but densification of the matrix caused by absorption of an element into the lattice [21]. Based on the XRD pattern (i.e. contraction of the γ-phase lattice parameter [21]), reported previously, the element was assumed to be nitrogen, which was reduced cathodically on the steel surface in a solution containing NaNO₂ under the cathodic polarisation condition. In principle, the water reduction reaction could be a dominant cathodic reaction in a weakly alkaline solution under cathodic polarisation [32–37], and the H⁺ released can be reduced to atomic hydrogen, as shown in the following equations: (1) (2) dissociated from NaNO₂ in water () could be reduced cathodically, and finally, NO_(ads) could be produced [38,39], as expressed by the following equation: (3) Under a cathodic overpotential, the electrochemical reduction of NO to oxygen and nitrogen is also possible, as shown in the following equation [40–45]: (4)

Figure 2

Potentiodynamic polarisation measurements of the EISA-treated and -untreated specimens.

Figure 3

XRD test result of the EISA-treated and -untreated specimens.

Table 2

Potentiodynamic polarisation test results of the EISA-treated and -untreated specimens.

		OCP (V_SCE)	E _p (V_SCE)	i _pass (A cm⁻²)
Immediately after immersion	Before EISA	−0.19	0.16	1.69 × 10⁻⁶
After EISA	−0.10	0.32	1.16 × 10⁻⁷
After 24 h immersion	Before EISA	−0.25	0.19	2.63 × 10⁻⁶
After EISA	−0.31	0.30	1.82 × 10⁻⁶

Considering the (electro) chemical processes, described above, it could be expected that several species of H, NO and/or N₂ were produced and adsorbed on the surface. On the other hand, only H could be oxidised at the sub-surface under the anodic polarisation process in the EISA (Equation (4)). Therefore, H may not diffuse into the lattice, and the possible diffusing species were NO and/or N₂, which may have resulted in the contraction of the γ-phase lattice parameter [21]. The proposed mechanism was supported in part by SIMS analysis, as shown in Figure 4. Because the high peak intensities at the outermost surface (approximately 200 nm) were due to the imperfect vacuum condition in the SIMS analysis equipment, the data can be neglected. The noticeable features in this analysis are that both nitrogen and oxygen peaks appeared at approximately 1.8-6.5 μm of the depth profile after the EISA treatment. In addition, the peaks from the two elements appeared at the same depth, suggesting that most diffusing species into the lattice were NO_(ads), which was produced by Equation (3), and the diffusing depth was approximately 6.5 μm from the surface, which corresponds to the annealed depth reported by Burstein et al. [20]. Indeed, it is still unclear if the nitrogen existed as single NO or co-existed as NO and N₂, and further attempts to clarify the existing form are needed. Nevertheless, it is worthy of note that the species that forms can lead to densification of the matrix, resulting in an increase in pitting corrosion resistance. The change in the characteristics of the passive film was analysed because the characteristics of the thin passive film formed on the outermost surface are one of the critical factors for the corrosion resistance of stainless steel, which will be discussed in the following section.

Figure 4

SIMS analysis of EISA (a) -untreated and (b) -treated specimens.

Mott–Schottky analysis

Figure 5 presents the Mott–Schottky plots of the specimens before and after the EISA treatments. Both plots showed positive slopes (i.e. characteristics of n-type semiconductor) within the range of passivity potential. On the other hand, they have different slopes, meaning that the density of donor sites, which are regarded simply as the defect density, in the passive film changed after the EISA treatment. The slope of the Mott–Schottky plots of the n-type semiconductor was calculated by the following equation [46,47]: (5) where e is the electron charge (1.6 × 10⁻¹⁹ C); N _D is the density of donor sites (m⁻³); ε ₀ is the vacuum permittivity (8.854 × 10⁻¹² Fm⁻¹), and ε _r is the dielectric constant of passivity (15.6 for stainless steel).

Figure 5

Mott–Schottky measurement of the EISA-treated and -untreated specimens.

Table 3 lists the donor density of the passive film formed on the specimens before and after the EISA treatment; the donor density of the EISA-treated specimen was lower than that of the untreated specimen. This indicates that the EISA treatment improved the stability of the passive film. This could be due to the filling of defects in the passive film by NO and/or N₂, which had been reduced and adsorbed on the surface during the EISA treatment.

Table 3

Defect density of the EISA-treated and -untreated specimens.

n-type	Before EISA	After EISA
Donor density (N _D, cm³)	5.03 × 10²¹	2.51 × 10²¹

Changes in corrosion behaviours of the EISA-treated specimen after pre-immersion

Figure 6 presents the potentiodynamic polarisation test results of the EISA-treated specimen which had been immersed in a 0.1 N HCl for 24 h. Although E _p, which is known as a critical parameter for the localised corrosion resistance, was relatively unchanged, the OCP and i _pass decreased and increased, respectively, suggesting that the passivity had degraded somewhat. The polarisation resistance (R _p), which is inversely proportional to i _corr, was also measured using an EIS test. As shown in Figure 7, the R _p of the specimen without the EISA treatment increased progressively with increasing immersion time, from 0 to 96 h. On the other hand, the R _p of the EISA-treated specimen tended to increase at an early stage of immersion, but it decreased significantly after 24 h immersion, and it was relatively constant with further immersion. This showed a similar trend with the polarisation behaviour: an increase in i _pass of the EISA-treated specimen after 24 h immersion. These results were attributed to the decrease in thickness of the specimen by the corrosion process (i.e. Fe dissolution: Fe → Fe²⁺ + 2e⁻) with the immersion time. The strain-induced α′ phase at the outermost surface of the untreated specimen might have disappeared gradually by surface dissolution, showing a slight improvement in corrosion resistance at around the OCP with increasing immersion time. On the other hand, at the early stage of dissolution for the EISA-treated specimen, the desorption of NO and/or N₂, which had absorbed on the surface, could make the specimen more resistive to corrosion by the formation of NH₄ ⁺, leading to an increase in local pH [48–53]. With further immersion at approximately 24 h, however, the specimen became much thinner and lots of NO and/or N₂ species had dissolved, leaving only smaller portions remaining with an uneven distribution at the surface. This may weaken the corrosion resistance due to the formation of local galvanic cells between the NO- and/or N₂-enriched and -depleted regions. To measure the dissolved thickness indirectly, the Wagner–Traud equation was used to fit the potentiodynamic polarisation curves; Table 4 lists kinetic parameters for corrosion. For the curve-fitting to the potentiodynamic polarisation data, the Wagner–Traud equation (Equation (6)) and Stern–Geary equation (Equation (7)) were employed. (6) (7) where i is the calculated total current density (A cm⁻²); i _corr is the corrosion current density (A cm⁻²); β _a is the anodic Tafel slope (V decade⁻¹); β _c is the cathodic Tafel slope (V decade⁻¹); E _corr is the corrosion potential (V); E is the calculated potential (V) and R _p is the polarisation resistance (Ω cm²).

Figure 6

Potentiodynamic polarisation measurements of the EISA-treated specimens before and after 24 h immersion in 0.1 M HCl solution.

Figure 7

Nyquist plots, obtained by EIS, of (a) EISA-treated, (b) -untreated specimens and (c) polarisation resistance values of the tested specimens with immersion time.

Table 4

Various corrosion kinetic parameter values obtained by curve-fitting to potentiodynamic polarisation data.

	i _corr (A cm⁻²)	E _corr (V)	R _p (Ω cm²)	β _a (V decade⁻¹)	β _c (V decade⁻¹)
0 h	3.048 × 10⁻⁸	−0.0112	2.52 × 10⁵	0.0329	0.0382
24 h	1.841 × 10⁻⁶	−0.3118	1.216 × 10⁴	0.12	0.0903

The value of mpy, which was obtained by the following equation [54], for the EISA-treated samples at two different immersion times, 0 and 24 h, were 0.01375 and 0.83064, which are equal to 0.09569 and 5.78042 in μm/day, respectively. (8) where ρ is the density (7.86 g cm⁻³ for iron); ε is the equivalent weight (27.56 g (equivalent for iron)⁻¹) and Λ is 1.2866 × 10⁵ (equivalents s mil)(Coulombs cm year)⁻¹.

The proposed mechanism described above was supported in part by SIMS analysis of the EISA-treated specimen, which had been conducted after 24 h immersion. As shown in Figure 8, some of the peaks from nitrogen and oxygen, which appeared at approximately 2.4-6.2 μm in the depth profile before immersion, disappeared due to Fe dissolution at the outer surface, and only one peak remained. Based on this analysis, the dissolution depth was approximately 4 μm, which agrees with the value of mpy to a certain degree.

Despite the several strengths of the EISA treatment, the significant reduction of α’ martensite and high hardness of the surface without heat treatment at several hundreds of degrees Celsius, the treatment has a technical limitation in that the surface characteristics, including the higher corrosion resistance, can only last for a limited period. Therefore, a significant increase in the electrochemical annealing depth in the short EISA treatment time can be one of the technical issues in this field, and further study on this issue will be required (Figure 8).

Figure 8

SIMS analysis of the EISA-treated specimen measured after 24 h immersion.

Conclusion

The changes in corrosion behaviour of the EISA-treated 304L stainless steel were evaluated using a range of electrochemical methods, and the results were supported in part by SIMS. The major findings on this study can be summarised as follows:

The EISA treatment composed of a series of anodic and cathodic electrochemical pulse increases the corrosion resistance in a 0.1 N HCl solution (i.e. increase in E _p from potentiodynamic polarisation measurement and decrease in N _D from the Mott–Schottky measurement). This may be associated closely with the surface densification effect caused by the absorption of NO and/or N₂, which had been reduced cathodically during the EISA treatment.

The improved corrosion resistance after the EISA treatment did not last long. In contrast to the early stages of immersion, with increasing immersion time exceeding 24 h, the R _p of the EISA-treated specimen became smaller than that of the untreated specimen. This change in R _p was closely related to the dissolution of NO and/or N₂ in the outer surface, which was caused by the decrease in steel thickness via the corrosion process (i.e. Fe dissolution: Fe → Fe²⁺ + 2e⁻) with increasing immersion time. Therefore, despite the several strengths of the EISA treatment, it has a technical limitation in that the surface characteristics, including a higher corrosion resistance, can last only a limited time.

Disclosure statement

No potential conflict of interest was reported by the authors.

Footnotes

Data availability statement

The data supporting the findings of this study are available from the corresponding author upon reasonable request.

References

Hedberg

Odnevall

WI.

Metal release from stainless steel in biological environments: a review. Biointerphases. 2016; 11: 018901-1-17. doi: 10.1116/1.4934628

Sumitomo

Investigation of the development of cold-rolling and annealing textures in SUS304 austenitic stainless steel. J Iron Steel Inst Jpn. 1991; 77: 558–565. doi: 10.2355/tetsutohagane1955.77.4_558

Angel

Formation of martensite in austenitic stainless steel. J Iron Steel Inst. 1954; 177: 165–174.

Ludwigson

Berger

JA.

Plastic behaviour of metastable austenitic stainless steels. J Iron Steel Inst. 1969; 207: 63–69.

Olson

Cohen

Kinetics of strain-induced martensitic transformation. Metall Trans A. 1975; 6: 791–795. doi: 10.1007/BF02672301

Olson

Cohen

Stress-assisted isothermal martensitic transformation: application to TRIP steels. Metall Trans A. 1982; 13: 1907–1914. doi: 10.1007/BF02645934

Huang

Matlock

Krauss

Martensite formation, strain rate sensitivity and deformation behaviour of type 304 stainless steel sheet. Metall Trans A. 1989; 20: 1239–1246. doi: 10.1007/BF02647406

Tomimura

Takaki

Tokunaga

Reversion mechanism from deformation induced martensite to austenite in metastable austenitic stainless steels. ISIJ Int. 1991; 31: 1431–1437. doi: 10.2355/isijinternational.31.1431

Takaki

Tomimura

Ueda

Effect of pre-cold-working on diffusional reversion of deformation induced martensite in metastable austenitic stainless steel. ISIJ Int. 1994; 34: 522–527. doi: 10.2355/isijinternational.34.522

10.

Petersen

Mataya

Matlock

DK.

The formability of austenitic stainless steels. J Mater. 1997; 49: 54–58.

11.

Gleidys

Asuncion

Susana

. Influence of the cold working induced martensite on the electrochemical behavior of AISI 304 stainless steel surfaces. J Mater Res Tech. 2019; 8 (1): 1335–1346. doi: 10.1016/j.jmrt.2018.10.004

12.

Gravier

Vignal

Bissey-Breston

Influence of residual stress, surface roughness and crystallographic texture induced by machining on the corrosion behaviour of copper in salt-fog atmosphere. Corr Sci. 2012; 61: 162–170. doi: 10.1016/j.corsci.2012.04.032

13.

Xue

Fei

Dan

. Effect of residual and external stress on corrosion behaviour of X80 pipeline steel in sulphate-reducing bacteria environment. Eng Fail Anal. 2018; 91: 275–290. doi: 10.1016/j.engfailanal.2018.04.016

14.

Nazarov

Vivier

Thierry

. Effect of mechanical stress on the properties of steel surfaces: scanning kelvin probe and local electrochemical impedance study. J Electrochem Soc. 2017; 164: C66–C74. doi: 10.1149/2.1311702jes

15.

Grabke

HJ.

Carburization, carbide formation, metal dusting, coking. J Mater Technol. 2002; 36: 297–305.

16.

Babakr

Habiby

Lengthening, cracking and weld ability problems of Fe-Ni-Cr alloy tube. J Miner Mater Charact Eng. 2009; 8: 133–148.

17.

Rashid

MWA

Gakim

Rosli

. Formation of Cr₂₃C₆ during the sensitization of AISI 304 stainless steel and its effect to pitting corrosion. Int J Electrochem Sci. 2012; 7: 9465–9477.

18.

Punburi

Tareelap

Post weld heat treatment to reduce intergranular corrosion susceptibility of dissimilar welds between austenitic 304 and ferritic 430 stainless steels. Proceedings of the 1st Mae Fah Luang University International Conference; Bangkok, Thailand; 2012. p. 1-9.

19.

Shao

Thermodynamic modeling of the Cr-Nb-Si system. J Intermet. 2005; 13: 69–78. doi: 10.1016/j.intermet.2004.06.003

20.

Burstein

Hutchings

Sasaki

Electrochemically induced annealing of stainless-steel surfaces. Nature. 2000; 407: 885–887. doi: 10.1038/35038040

21.

Burstein

Sasaki

Hutchings

IM.

Lattice changes generated by electrochemically induced surface annealing of austenitic stainless steel. Electrochem Solid State Lett. 2003; 6: D13–D15. doi: 10.1149/1.1612013

22.

Liu

The effect of electrochemically induced annealing on the pitting resistance of metastable austenite stainless steel. Metall Mater Trans A. 2006; 37: 435–439. doi: 10.1007/s11661-006-0014-1

23.

Chunchun

Yongxin

. Deformation-induced martensite phase transition and its effect on pitting susceptibility for 1Cr18Ni9Ti stainless steel. J Chin Soc Corr Protect. 1996; 16: 47–52.

24.

Gang

Chunchun

Xingsheng

. Effect of cold working on pitting susceptibility of 304 stainless steel. J Chin Soc Corr Protect. 2002; 22: 198–201.

25.

Guangjie

Yulin

Yurong

. Correlation between pit corrosive sensitivity of metastable austenite stainless steel and its content of ferromagnetic phases. Iron Steel. 1996; 31: 48–52.

26.

Ruifen

Chunchun

Huiyong

. Relation between deformation induced martensite and pitting susceptibility of 1Cr18Ni9Ti. Corr Sci Protect Technol. 1998; 10: 197–201.

27.

Chunchun

Ruifen

Weizhen

. EIS study of the effect of deformation induced α′ martensite on pitting sensibility of 1Cr18Ni9Ti stainless steel in acidic NaCl solution. Corr Sci Protect Technol. 1997; 9: 95–102.

28.

Ruifen

Chunchun

Weizhen

. Effect of the martensite phase transition of austenitic stainless steel on the corrosion resistance. J Beijing Univ Chem Technol. 1998; 25: 57–63.

29.

Chunchun

Xinsheng

Gang

. Deformation induced martensite of cold worked stainless steel and its corrosion behaviors. Mater Protect. 2002; 35: 15–17.

30.

Chunchun

Weizhen

Ruifen

An investigation of the relationship between SCC susceptibility and ferromagnetic content of 1Cr18Ni9Ti stainless steel in chloride solution. J Chin Soc Corr Protect. 1997; 17: 73–76.

31.

Chunchun

Weizhen

Baowen

. The effect of martensite induced by deformation on stress corrosion cracking of 1Cr18Ni9Ti stainless steel. Corr Sci Protect Technol. 1996; 8: 267–270.

32.

Maximilian

Alexandar

Olaga

. A perspective on low-temperature water electrolysis-challenges in alkaline and acidic technology. Int J Electorchem Sci. 2018; 13: 1173–1226.

33.

Durst

Siebel

Simon

. New insights into the electrochemical hydrogen oxidation and evolution reaction mechanism. Energy Environ Sci. 2014; 7: 2255–2260. doi: 10.1039/C4EE00440J

34.

Neyerlin

Jorne

. Study of the exchange current density for the hydrogen oxidation and evolution reactions. J Electrochem Soc. 2007; 154: B631–B635. doi: 10.1149/1.2733987

35.

Sheng

Gasteiger

Shao-Horn

Hydrogen oxidation and evolution reaction kinetics on platinum: acid vs. alkaline electrolytes. J Electrochem Soc. 2010; 157: B1529–B1536. doi: 10.1149/1.3483106

36.

Sheng

Zhuang

Gao

. Correlating hydrogen oxidation and evolution activity on platinum at different pH with measured hydrogen binding energy. Nat Commun. 2015; 6: 1–6. doi: 10.1038/ncomms6848

37.

Zheng

Sheng

Zhuang

. Universal dependence of hydrogen oxidation and evolution reaction activity of platinum-group metals on pH and hydrogen binding energy. Sci Adv. 2016; 2: 1–8.

38.

Brian

Sayed

Todd

CH.

NO₂ ⁻ activation and reduction to NO by a nonheme Fe(NO₂)₂ complex. J Am Chem Soc. 2014; 136: 10230–10233. doi: 10.1021/ja505236x

39.

Maia

Moura

JJG.

How biology handles nitrite. Chem Rev. 2014; 114: 5273–5357. doi: 10.1021/cr400518y

40.

Bhaduri

Verma

Preparation of asymmetrically distributed bimetal ceria CeO₂ and copper (Cu) nanoparticles in nitrogen-doped activated carbon micro/nanofibers for the removal of nitric oxide (NO) by reduction. J Colloid Interface Sci. 2014; 436: 218–226. doi: 10.1016/j.jcis.2014.08.030

41.

Zhou

. Microwave-assisted catalytic reduction of NO into N₂ by activated carbon supported Mn₂O₃ at low temperature under O₂ excess. Fuel Process Technol. 2014; 127: 1–6. doi: 10.1016/j.fuproc.2014.06.005

42.

Zhang

. Efficient selective catalytic reduction of NO by novel carbon-doped metal catalysts made from electroplating sludge. Environ Sci Technol. 2014; 48 (19): 11497–11503. doi: 10.1021/es502391y

43.

Aarna

Suuberg

EM.

The role of carbon monoxide in the NO-carbon reaction. Energy Fuels. 1999; 13 (6): 1145–1153. doi: 10.1021/ef9900278

44.

Wey

MY.

Simultaneous removal of VOC and NO by activated carbon impregnated with transition metal catalysts in combustion flue gas. Fuel Process Technol. 2007; 88 (6): 557–567. doi: 10.1016/j.fuproc.2007.01.004

45.

Goncalves

Figueiredo

JL.

Development of carbon supported metal catalysts for the simultaneous reduction of NO and N₂O. Appl Catal B. 2004; 50 (4): 271–278. doi: 10.1016/j.apcatb.2004.01.014

46.

Zeng

Pang

. Effects of hydrogen and tensile stress on passivity of carbon steel. Corr Eng Sci Technol. 2015; 50: 186–190. doi: 10.1179/1743278215Y.0000000020

47.

Simoes

AMP

Ferreira

MGS

Rondot

. Study of passive films formed on AISI 304 stainless steel by impedance measurements and photoelectrochemistry. J Electrochem Soc. 1990; 137: 82–87. doi: 10.1149/1.2086444

48.

Jing

Guo

Hour

. Catalytic role of vanadium (V) sulfate on activated carbon for SO₂ oxidation and NH₃-SCR of NO at low temperatures. Catal Commun. 2014; 56: 23–26. doi: 10.1016/j.catcom.2014.06.017

49.

Wang

Yan

Liu

. In situ DRIFTS investigation on the SCR of NO with NH₃ over V₂O₅ catalyst supported by activated semi-coke. Appl Surf Sci. 2014; 313: 660–669. doi: 10.1016/j.apsusc.2014.06.043

50.

Huang

Hou

Zhu

. Study on the NO reduction by NH₃ on a SO₄ ²⁻/AC catalyst at low temperature. Catal Commun. 2014; 50: 83–86. doi: 10.1016/j.catcom.2014.03.008

51.

Liu

ZY.

Carbon supported vanadia for multi-pollutants removal from flue gas. Fuel. 2013; 108: 149–158. doi: 10.1016/j.fuel.2011.05.015

52.

Xie

Sun

Xiong

. Effects of surface chemical properties of activated coke on selective catalytic reduction of NO with NH₃ over commercial coal-based activated coke. Int J Min Sci Technol. 2014; 24: 471–475. doi: 10.1016/j.ijmst.2014.05.009

53.

Wang

Zhan

. Effect of SO₂ on activated carbon honeycomb supported CeO^2-MnO_x catalyst for NO removal at low temperature. Ind Eng Chem Res. 2015; 54 (8): 2274–2278. doi: 10.1021/ie504074h

54.

Mehta

Trivedi

Chandra

. Miner effect of silicon on the corrosion behavior of powder-processed phosphoric irons. Mater Charact Eng. 2010; 9: 855–865.