Ti-based electrode coated with MnOx catalytic layer has presented superior electrochemical activity for degradation of organic pollution in wastewater, however, the industrial application of Ti-based MnOx electrode is limited by the poor stability of the electrode. In this study, the novel Ti-based MnOx electrodes co-incorporated with rare earth (Ce) and conductive carbon black (C) were prepared by spraying-calcination method. The Ti/Ce:MnOx-C electrode, with uniform and integrated surface and enhanced Mn(IV) content by C and Ce co-incorporation, could completely remove ammonia nitrogen (NH4+-N) with N2 as the main product. The cell potential and energy consumption of Ti/Ce:MnOx-C electrode during the electrochemical process was significantly reduced compared with Ti/MnOx electrode, which mainly originated from the enhanced electrochemical activity and reduced charge transfer resistance by Ce and C co-incorporation. The accelerated lifetime tests in sulfuric acid showed that the actual service lifetime of Ti/Ce:MnOx-C was ca. 25 times that of Ti/MnOx, which demonstrated the significantly promoted stability of MnOx-based electrode by Ce and C co-incorporation.

  • The Ti-based MnOx electrodes co-incorporated with Ce and C were prepared and served as electrocatalysts to remove ammonia nitrogen.

  • The cell potential and energy consumption of Ti/Ce:MnOx-C was reduced by 35% compared with Ti/MnOx, originating from the enhanced activity and reduced resistance.

  • The service lifetime of Ti/Ce:MnOx-C was improved by 25 times compared with Ti/MnOx, demonstrating the promoted stability.

Graphical Abstract

Graphical Abstract
Graphical Abstract

Well-developed methods, classified as physical technology, chemical technology and biological technology, have been applied to wastewater treatment. The physical technologies include coagulation/flocculation (Mamelkina et al. 2020), separation membrane (Tavangar et al. 2020) and adsorption (Bacelo et al. 2020; Choudhary et al. 2020; Imran et al. 2021). The biological treatments have been studied, including anaerobic process, activated sludge process and so on (Gopalakrishnan et al. 2019; Wu et al. 2021). The chemical technology, such as ozonation and oxidation with catalysts (Silva et al. 2019; Liu et al. 2021), as well as advanced oxidation processes (AOPs), has been widely used in wastewater treatment due to its effectiveness. Electrochemical oxidation (EO) technology, as one of the AOPs, has attracted considerable attention for wastewater remediation, because it could completely mineralize refractory organic pollutants and present several characteristics of environmental significance without generating secondary pollutants, such as mild operation conditions, strong adaptability, simple and reliable equipment, and so on (Brillas & Martínez-Huitle 2015; Dominguez et al. 2018; Garcia-Segura et al. 2018). In EO remediation of wastewater, anode materials play particularly important roles, which could determine the degradation efficiency and service lifetime of the electrodes. Dimensionally stable anode, an electrode prepared by active metal oxides coated on the titanium substrate, has been successfully employed to degrade various refractory pollutants, and shows potential to overcome the poor stability of traditional graphite electrodes (Zhu et al. 2019) and high cost of noble metal electrodes (Tavares et al. 2012). A variety of electrodes, such as Ti/PbO2 (Polcaro et al. 1999; Bian et al. 2019), Ti/SnO2 (Martínez-Huitle et al. 2008), Ti/RuO2 (Yue et al. 2017), and Ti/IrO2 (Baddouh et al. 2020) have been investigated as anode for the EO remediation of wastewater because they are effective in oxidizing pollutants with high oxygen overpotentials. However, the high cost and inefficient performance for high-chloride content wastewater limits their use (Kaur et al. 2017). And the large-scale application is also limited due to leakage of metal cations during preparation process and by electrochemical corrosion, which may cause secondary pollution (Li et al. 2016). Therefore, it is essential to develop electrodes with superior catalytic activity, high stability, low cost and mild toxicity.

Ti/MnOx anodes are regarded as promising candidates in EO remediation of wastewater because of the low cost and toxicity, ease of preparation, and high electro-catalytic activity. Yang et al. reported porous Ti/MnOx anode for degradation of phenol in electro-catalytic membrane reactor, and the phenol removal efficiency was 93%, with chemical oxygen demand (COD) and total organic carbon (TOC) removal efficiency of 79 and 68%, respectively (Yang et al. 2018). Massa's reports suggested that MnOx could promote the direct and indirect oxidation of phenol in EO remediation of wastewater (Massa et al. 2018). Hui et al. prepared porous Ti/MnOx anode for degradation of highly concentrated phenol in wastewater, and the phenol removal efficiency was 73% in fixed bed electro-catalytic reactor (Hui et al. 2019). Our previous results also demonstrated the superior activity of Ti/MnOx anodes in electrochemical degradation of Acid Red B, a typical azo dye in textile wastewater (Xu et al. 2019). Even though MnOx-based electrodes present superior electro-catalytic activity for removal of organic pollution, and have been widely studied in water oxidation, lithium-ion batteries and supercapacitors, the commercial application of Ti/MnOx electrode is still hindered by the short lifetime (Jiang & Kucernak 2002; Martínez-Huitle et al. 2008; Wiechen et al. 2012; Xiang et al. 2015; Wang et al. 2018).

Ammonia nitrogen (NH4+-N) in wastewater is an increasing problem, which can promote eutrophication and is toxic to aquatic organisms. Even though most of the NH4+-N can be removed by biological method in practical application (Del Moro et al. 2016), low concentration of NH4+-N is very difficult to remove, and the concentration of NH4+-N needs to be in accordance with a specified detection limit. Previous studies have demonstrated that NH4+-N could be decomposed to N2 mainly by electrochemical degradation process (Zöllig et al. 2015). To the best of our knowledge and according to the literature review, there is no report on the study of Ti/MnOx anodes in electrochemical degradation of NH4+-N from an aqueous solution. In the present work, we introduced conductive carbon black (C) and Ce into the MnOx catalytic layer to fabricate a Ti/Ce:MnOx-C electrode. The surface characteristics and electrochemical properties of Ti/Ce:MnOx-C electrode were studied, and the degradation efficiency, cell potential, energy consumption, and stability of Ti/Ce:MnOx-C electrode were compared with MnOx/Ti in electrochemical degradation of NH4+-N. Studies showed that Ti/Ce:MnOx-C electrode presented significantly improved lifetime and reduced energy consumption with the co-incorporation of C and Ce.

Materials and reagents

Titanium plate was purchased from Suzhou Shuertai Industrial Technology Co., Ltd (Suzhou, China). Isopropanol and oxalic acid were purchased from Tianjin Damao Chemical Reagent Factory (Tianjin, China). Conductive carbon black was purchased from Tianjin Yiborui Chemical Co. Ltd (Tianjin, China). Ammonia sulfate, manganese nitrate (50%), cerium nitrate hexahydrate, sulfuric acid, sodium hydroxide, sodium chloride and sodium sulfate were purchased from Sinopharm Group Chemical Reagent Co., Ltd (Shanghai, China). All chemical reagents employed were of analytical purity grade. Ultra-purified water with resistivity of 18.2 MΩ·cm was obtained from the Millipore-Q system for all of the solutions.

Electrode preparation

First, titanium plate was pretreated by polishing, caustic washing and acid etching. Then 5 mL of Mn(NO3)2 isopropanol solution (1 mmol) was sprayed onto the pretreated Ti substrate at pressure of 4 kPa by the spray gun (caliber: 0.2 mm). After that, the Ti plate was dried at 100 °C for 10 min and then thermally treated at 200 °C for 5 min. The above processes were repeated four times. Finally, the product was calcinated at 350 °C for 20 min to obtain Ti/MnOx electrode. Ti/MnOx-C electrode was prepared with a certain amount of conductive carbon black (C) added into the Mn(NO3)2 solution during the spraying process. The molar ratio of C/Mn was 14%. As for the Ti/Ce:MnOx-C electrode, the spraying solution was a mixture of conductive carbon black (C), Ce(NO3)2·6H2O and Mn(NO3)2 with C/Mn molar ratio of 14% and Ce/Mn molar ratio of 1%. The active area of the prepared electrodes was 4 cm2.

Electrode characterization

The powder X-ray diffraction (XRD) data were collected on X'PERT PRO type X-ray diffraction (Netherlands Spectris) with CuKα radiation (λ = 1.5418 Å) over the 2θ range of 5° to 80° with scan speed of 5°/min at room temperature. The scanning electron microscopy (SEM) was undertaken by JSM-7500F cold field emission scanning electron microscope (Japan Electronics Co., Ltd) at accelerating voltage of 20 kV. The X-ray photoelectron spectroscopy (XPS) was performed using ESCALAB250 (American Thermo VG Co., Ltd) equipped with an Al Kα source.

Electrochemical experiment

Electrochemical experiments were performed in a conventional three-electrode cell system at CHI660E electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd, China). The prepared electrodes were employed as working electrode with platinum electrode (20 mm × 30 mm × 0.1 mm) as the counter electrode, and Ag/AgCl/0.1 M KCl (Shanghai Ciyue Electronic Technology Co., Ltd, China) as the reference electrode. The cyclic voltammetry (CV) measurement was conducted in 0.1 mol/L sodium sulfate solution at scan rate of 50 mV/s with scan region from 0 to 2.5 V. The polarization curve (linear sweep voltammetry; LSV) was tested at scan rate of 10 mV/s in 0.1 mol/L sodium sulfate and 400 mg/L sodium chloride solution. The conductivity of the electrodes was tested by electrochemical impedance spectroscopy (EIS) with the frequency range from 1 × 105 to 1 × 10−2 Hz and the amplitude of 10 mV, which was conducted at open circuit potential. All of the electrodes were activated by cyclic voltammetry at 50 mV/s before the tests.

Electrode activity test

The electrochemical degradation of ammonia nitrogen, prepared by ammonia sulfate with concentration of 23 mg/L, was conducted in an electrochemical system with 0.1 mol/L sodium sulfate and 400 mg/L sodium chloride as supporting electrolyte at pH 9.0. The prepared electrode and pure titanium plate served as anode and cathode, respectively, with the distance of 1 cm between them. Constant current was chosen by a direct current power supply (DC stabilized power supply, KPS-3005D, Zhaoxin Electronic Equipment Co., Ltd, China) over reaction time of 90 min. The simulated wastewater was electrochemically degraded at 20 mA/cm2 with magnetic stirring at room temperature. The cell potentials were recorded by data recorder (34970A, Keithley Instruments, USA). The concentration of NH4+-N in the wastewater was analyzed on a DR3900 spectrophotometer (Hach Corporation, USA) equipped with a digestion system (DRB200) based on the principle of salicylic acid method. Then the degradation efficiency (DE) was calculated as Equation (1).
formula
(1)
where, and are the initial and final concentration of NH4+-N (mg/L), respectively.
The energy consumption (E, kW·h/g) during electrochemical process was calculated by Equation (2).
formula
(2)
where, U is the cell potential (V), I is the current (A), t is the degradation time (s), V is the volume of solution (L).
The accelerated service lifetime tests were carried out by anodic polarization of the prepared electrodes at 100 mA/cm2 in 0.5 mol/L H2SO4 solution at room temperature. The accelerated service lifetime of the electrode was defined as the duration from the initial value to the cell potential increasing to 5 V. The lifetime of electrode was calculated according to the empirical formula proposed by B. Correa-Lozano et al. shown as Equation (3) (Correa-Lozano et al. 1997).
formula
(3)
where, τ1 is the actual electrode lifetime, τ2 is the accelerated lifetime, i1 is the actual current density, i2 is the accelerated current density.

Surface properties of the electrodes

The surface morphology of the prepared electrodes was analyzed by SEM. As shown in Figure 1(a), the surface of Ti/MnOx electrode was rough with large particles, suggesting the aggregation of MnOx particles during preparation process. Ti/MnOx-C electrode possessed smooth surface without obvious cracks (Figure 1(b)), indicating that the introduction of conductive carbon black could significantly affect the morphology and improve the surface integrity of the electrode. However, pinholes with size of ca. 20 nm were observed on the surface of electrode. Ti/Ce:MnOx-C electrode displayed more dense and compact surface with smaller pinhole size (ca. 5 nm in Figure 1(c)). The surface evenness and compaction of electrode was important for electrochemical process, and might affect the lifetime of electrode (Santos et al. 2014). The SEM images suggested the significant improvement of surface evenness and compaction originated from carbon black and Ce addition.

Figure 1

SEM images of (a) Ti/MnOx, (b) Ti/MnOx-C, and (c) Ti/Ce:MnOx-C electrodes.

Figure 1

SEM images of (a) Ti/MnOx, (b) Ti/MnOx-C, and (c) Ti/Ce:MnOx-C electrodes.

Close modal

Typical XRD patterns of Ti/MnOx, Ti/MnOx-C and Ti/Ce:MnOx-C electrodes are shown in Figure S1 (Supporting Information). All of the diffraction peaks could be assigned to the hexagonal Ti (JCPDS No. 44-1294 and No. 89-3725) originating from Ti substrate without MnOx phase observed, which might be caused by the amorphous MnOx formed in the present conditions. Additionally, there was no diffraction peak of TiO2 in the XRD patterns, which suggested that the Ti substrate was not oxidized during the preparation process. Therefore, the conductivity of Ti substrate was maintained to facilitate the electrochemical reaction.

XPS measurement was performed to investigate the chemical state of the electrode surface elements. The XPS survey spectra are presented in Figure S2, and the Mn and O photoelectron peaks are clearly observed. The fine structure of Mn 2p and O 1 s was investigated because the Mn oxidation state and oxygen species play important roles in the electrochemical processes. As shown in Figure 2, the Mn 2p peaks were fitted by considering two resolved doublets, Mn 2p1/2 and Mn 2p3/2, located at 653.9 eV and 642.2 eV, respectively. The coexistence of Mn(II), Mn(III) and Mn(IV) was evidenced by fitting the peaks, which could be assigned to MnO, Mn2O3 and MnO2 as reported in the literature (Lee et al. 2011; Li et al. 2011; Wang et al. 2017a), even though there was no diffraction peak of manganese oxide found in the XRD results. The discrepancy might be caused by the poor crystallinity of manganese oxide formed in this study. The relative content of MnOx phase calculated by Mn 2p3/2 is displayed in Table 1. It has been reported that MnO2 was more beneficial for the electrochemical degradation of pollutants (Massa et al. 2018), and the results suggested that the introduction of Ce could enhance the Mn(IV) content while the addition of carbon black had little influence on the Mn oxidation state of Ti-based MnOx electrode. The O 1s peak could be deconvoluted into the signal of lattice oxygen (OL) and adsorbed oxygen (OA). According to the peak fitting results shown in Table 1, the relative content of OA, which has been reported as the most active oxygen and could play an important part in EO process, was similar for the three electrodes (Ramirez et al. 2014; Bian et al. 2019), suggesting the incorporation of carbon black and Ce had little effect on the relative OA content of Ti-based MnOx electrode.

Table 1

The characterization and electrochemical results of electrodes

ElectrodeRelative content of Mn species (%)
Relative content of O species (%)
Rs (Ω)Cell potential (V)Energy consumption (kW·h/g)Electrode lifetime (h)
Mn(II)Mn(III)Mn(IV)OLOA
Ti/MnOx 12 32 56 57 43 654 5.2 0.28 2.2 
Ti/MnOx-C 11 32 57 58 42 80 4.6 0.24 7.5 
Ti/Ce:MnOx-C 26 66 57 43 3.4 0.18 54.6 
ElectrodeRelative content of Mn species (%)
Relative content of O species (%)
Rs (Ω)Cell potential (V)Energy consumption (kW·h/g)Electrode lifetime (h)
Mn(II)Mn(III)Mn(IV)OLOA
Ti/MnOx 12 32 56 57 43 654 5.2 0.28 2.2 
Ti/MnOx-C 11 32 57 58 42 80 4.6 0.24 7.5 
Ti/Ce:MnOx-C 26 66 57 43 3.4 0.18 54.6 
Figure 2

The fine structure of (a, b, c) Mn 2p and (d, e, f) O 1s XPS spectra of (a, d) Ti/MnOx, (b, e) Ti/MnOx-C, and (c, f) Ti/Ce:MnOx-C electrodes.

Figure 2

The fine structure of (a, b, c) Mn 2p and (d, e, f) O 1s XPS spectra of (a, d) Ti/MnOx, (b, e) Ti/MnOx-C, and (c, f) Ti/Ce:MnOx-C electrodes.

Close modal

Electrochemical characterization of the electrodes

The influence of additive on the electrochemical behavior of the Ti-based MnOx electrode was investigated by voltammetry measurement. Typical CV curves of the Ti/MnOx, Ti/MnOx-C and Ti/Ce:MnOx-C electrodes in 0.1 mol/L sodium sulfate solution are shown in Figure 3(a). There was no obvious redox signal observed except for the oxygen evolution, indicating that Ti-based MnOx electrodes were electrochemically inactive in Na2SO4 solution (Duan et al. 2014). The electrochemical active surface area is related to the geometric area of the region enclosed by the CV curve, so the Ti/Ce:MnOx-C electrode with larger electrochemical active surface area will present higher electrochemical activity in EO degradation of pollution. Additionally, the oxygen evolution current of Ti/Ce:MnOx-C electrode was much higher than that of Ti/MnOx and Ti/MnOx-C at the same potential, which verified the superior electrochemical activity of Ti/Ce:MnOx-C electrode (Duan et al. 2012). It has been reported that the NH4+-N degradation mechanism could be direct oxidation and indirect oxidation (Siddharth et al. 2018). In this work, NH4+-N was completely removed in the presence of Cl and the degradation efficiency was only 6.1% in the absence of Cl in the electrolyte (Figure S3). The electrochemical degradation results verified that NH4+-N was mainly degraded by indirect oxidation in this work. Ti-based MnOx electrode showed enhanced performance for the electrochemical degradation of NH4+-N in the presence of Cl due to the generation of several chlorine-based oxidants, such as Cl2, HOCl and ClO (Siddharth et al. 2018). As shown by the LSV profiles of electrodes in the presence of Cl (Figure 3(b)), the onset potential of Ti/Ce:MnOx-C electrode was lower with higher current at the same potential, which indicated that Ce and C co-incorporation facilitated the electrochemical reaction of Ti-based MnOx electrode.

Figure 3

(a) Cyclic voltammetry of Ti/MnOx, Ti/MnOx-C and Ti/Ce:MnOx-C electrodes at a scan rate of 50 mV/s in a 0.1 mol/L Na2SO4 solution, and (b) linear sweep voltammetry of Ti/MnOx, Ti/MnOx-C and Ti/Ce:MnOx-C electrodes at a scan rate of 10 mV/s in 0.1 mol/L Na2SO4 and 400 mg/L NaCl solution.

Figure 3

(a) Cyclic voltammetry of Ti/MnOx, Ti/MnOx-C and Ti/Ce:MnOx-C electrodes at a scan rate of 50 mV/s in a 0.1 mol/L Na2SO4 solution, and (b) linear sweep voltammetry of Ti/MnOx, Ti/MnOx-C and Ti/Ce:MnOx-C electrodes at a scan rate of 10 mV/s in 0.1 mol/L Na2SO4 and 400 mg/L NaCl solution.

Close modal

In further investigation on the influence of additive on the electrochemical activity of Ti-based MnOx electrode, EIS was used to determine the charge transfer resistance of electrodes. The Nyquist and equivalent circuit model for Ti/MnOx, Ti/MnOx-C and Ti/Ce:MnOx-C electrodes are presented in Figure 4. In the equivalent circuit, the ohmic resistance and charge transfer resistance are presented as Rs and Rct, respectively. According to the fitting results, the value of Rct for Ti/MnOx-C electrode was 80 Ω, which was significantly reduced compared with that for the Ti/MnOx electrode (654 Ω), and the Rct value was further reduced to 9 Ω for Ti/Ce:MnOx-C electrode. The EIS measurement demonstrated that the Ce:MnOx-C coating layer exhibited a much lower charge transfer resistance, which indicated the great improvement of electron transfer rate and conductivity of electrodes. The improvement of electron transfer rate was beneficial for the reduction of cell potential and energy consumption during the electrochemical process, which provided economic feasibility for electrochemical degradation of pollutants in wastewater (Hernández et al. 2016).

Figure 4

Electrochemical impedance spectroscopy of Ti/MnOx, Ti/MnOx-C and Ti/Ce:MnOx-C electrodes in 0.1 mol/L Na2SO4.

Figure 4

Electrochemical impedance spectroscopy of Ti/MnOx, Ti/MnOx-C and Ti/Ce:MnOx-C electrodes in 0.1 mol/L Na2SO4.

Close modal

Electrochemical degradation of ammonia nitrogen

The catalytic performance of the Ti-based MnOx electrodes for electrochemical degradation of NH4+-N (23 mg/L) was investigated in Na2SO4 (0.1 mol/L) solution with NaCl concentration of 400 mg/L, current density of 20 mA/cm2 and pH of 9.0. Figure 5(a) illustrates the concentration of NH4+-N during the electrochemical degradation process with the prepared electrodes. The concentration of NH4+-N decreased gradually with the reaction proceed, and reached 0.2 mg/L at 90 min for Ti/MnOx electrode. The degradation efficiency of Ti/MnOx-C was comparable to that of Ti/Ce:MnOx-C electrode. For Ti/Ce:MnOx-C electrode, the NH4+-N could be completely removed within 90 min, and the residual total nitrogen was 2.0 mg/L with nitrate of 5.1% (1.2 mg/L) and dichloramine of 3.4% (0.8 mg/L), which suggested that most of the ammonia nitrogen (91.5%) was mineralized to N2. These results suggested that Ti-based MnOx electrode was efficient for NH4+-N degradation. Figure 5(b) illustrates the corresponding cell potential during the electrochemical degradation process, which kept stable for each electrode. The cell potential of Ti/MnOx-C electrode was lower than that of Ti/MnOx. It is noteworthy that the cell potential of Ti/Ce:MnOx-C electrode reduced by 35% compared to Ti/MnOx, which was 3.4 V versus 5.2 V. The significant decrease of cell potential might be caused by the improved conductivity of electrode by co-incorporation of carbon black and Ce verified by the EIS results (Song et al. 2007; Wang et al. 2017b). The corresponding energy consumption during electrochemical process was calculated by Equation (2) and shown in Figure 5(c). The energy consumption increased as electrochemical degradation proceeded and reached 0.18 kW·h/g for Ti/Ce:MnOx-C electrode when NH4+-N was totally degraded, which was reduced by 35% compared to the Ti/MnOx electrode (0.28 kW·h/g). The cost of energy consumption is reduced to ca. US$ 20/kg (NH4+-N) for Ti/Ce:MnOx-C electrode. These results indicated that the co-incorporation of carbon black and Ce could improve the conductivity of electrodes, leading to reduced cell potential and less energy consumption during electrochemical process (Jin et al. 2015).

Figure 5

(a) The concentration, (b) cell potential and (c) energy consumption of Ti/MnOx, Ti/MnOx-C and Ti/Ce:MnOx-C electrodes during the degradation of ammonia nitrogen.

Figure 5

(a) The concentration, (b) cell potential and (c) energy consumption of Ti/MnOx, Ti/MnOx-C and Ti/Ce:MnOx-C electrodes during the degradation of ammonia nitrogen.

Close modal

The stability of electrode determines the electrode performance and commercial application, so in order to evaluate the stability of electrode, accelerated service life experiments were carried out in 0.5 mol/L sulfuric acid solution at 100 mA/cm2. As displayed in Figure 6, the cell potential of Ti/MnOx electrode increased significantly, suggesting the poor stability of Ti/MnOx electrode, while the cell potential of Ti/Ce:MnOx-C electrode was lower and much more stable than that of Ti/MnOx. According to the empirical formula proposed by B. Correa-Lozano et al. (1997), the actual lifetime of Ti/Ce:MnOx-C electrode was 54.6 h calculated by Equation (3), which was ca. 25 times that of Ti/MnOx electrode (2.2 h). The improved stability of Ti/Ce:MnOx-C electrode mainly originated from the co-incorporation of carbon black and Ce, which not only enhanced the conductivity but also improved the surface evenness of the electrode (Gargouri et al. 2014; Jin et al. 2015).

Figure 6

Accelerated lifetime tests of Ti/MnOx, Ti/MnOx-C and Ti/Ce:MnOx-C electrodes in 0.5 M H2SO4 solution at 100 mA/cm2.

Figure 6

Accelerated lifetime tests of Ti/MnOx, Ti/MnOx-C and Ti/Ce:MnOx-C electrodes in 0.5 M H2SO4 solution at 100 mA/cm2.

Close modal

In summary, the Ti-based MnOx electrode co-incorporated with carbon black and Ce was successfully prepared by spraying-calcination method. The surface properties, electrochemical performance, degradation activity and stability of Ti/Ce:MnOx-C electrode were compared with those of the Ti/MnOx electrode. The electrochemical results demonstrated that Ti/Ce:MnOx-C electrode served as an efficient electrocatalyst to degrade NH4+-N completely with N2 formation of 91.5%. The cell potential and energy consumption of Ti/Ce:MnOx-C electrode were reduced by 35% and stability was improved by ca. 25 times. The superior performance of Ti/Ce:MnOx-C electrode might benefit from its flat and integrated surface and low charge transfer resistance by co-incorporation of carbon black and Ce. This research provided a novel method for the modification of Ti-based MnOx electrode, and would be helpful for the application of Ti-based MnOx electrode in electrochemical degradation of NH4+-N and other organic pollutants.

This research was financially supported by National Natural Science Foundation of China (No. 21905035), LiaoNing Revitalization Talents Program (XLYC1907093), Guide Plan of Key Research and Development Program of Liaoning Province (2019JH8/10100096) and Fundamental Research Funds for the Central Universities (No. 3132019334), and the Initial Scientific Research Fund of Young Teachers in Shenyang University of Technology under Grant No. 200005782.

All relevant data are included in the paper or its Supplementary Information.

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Author notes

Jiao Zhao and Xuelu Xu contributed equally to this work.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), which permits copying, adaptation and redistribution, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/).

Supplementary data