ISSN 1998-0124 CN 11-5974/O4 2019, 12(1): 000–000 https://doi.org/10.1007/s12274-019-2506-5 Research Article Research Self-powered electrochemical system by combining Fenton reaction and active chlorine generation for organic contaminant treatment Yawei Feng1,2,§, Kai Han1,2,§, Tao Jiang1,2,§, Zhenfeng Bian3, Xi Liang1,2, Xia Cao1,2 (), Hexing Li4 (), and Zhong Lin Wang1,2,5 () 1 CAS Center for Excellence in Nanoscience, Beijing Key Laboratory of Micro-nano Energy and Sensor, Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, China 2 School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing 100049, China 3 Education Ministry Key and International Joint Lab of Resource Chemistry and Shanghai Key Lab of Rare Earth Functional Materials, Shanghai Normal University, Shanghai 200234, China 4 School of Environmental and Chemical Engineering, Shanghai University of Electric Power, Shanghai 200090, China 5 School of Material Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA § Yawei Feng, Kai Han, and Tao Jiang contributed equally to this work. © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019 Received: 7 July 2019 / Revised: 18 August 2019 / Accepted: 22 August 2019 ABSTRACT Environmental deterioration, especially water pollution, is widely dispersed and could affect the quality of people’s life at large. Though the sewage treatment plants are constructed to meet the demands of cities, distributed treatment units are still in request for the supplementary of centralized purification beyond the range of plants. Electrochemical degradation can reduce organic pollution to some degree, but it has to be powered. Triboelectric nanogenerator (TENG) is a newly-invented technology for low-frequency mechanical energy harvesting. Here, by integrating a rotary TENG (R-TENG) as electric power source with an electrochemical cell containing a modified graphite felt cathode for hydrogen peroxide (H2O2) along with hydroxyl radical (•OH) generation by Fenton reaction and a platinum sheet anode for active chlorine generation, a self-powered electrochemical system (SPECS) was constructed. Under the driven of mechanical energy or wind flow, such SPECS can efficiently degrade dyes after power management in neutral condition without any O2 aeration. This work not only provides a guideline for optimizing self-powered electrochemical reaction, but also displays a strategy based on the conversion from distributed mechanical energy to chemical energy for environmental remediation. KEYWORDS self-powered electrochemistry, Fenton reaction, active chlorine, organic contaminant degradation 1 Introduction field, photocatalytic hydrogen generation and organic compounds degradation in aqueous condition can be significantly promoted Distributed mechanical energy from wind blow, water flow, animal [18–20]. An insulating featured photocatalyst-loaded electrostatic motion and human action, is widely existed around. Triboelectric filter can achieve a doubled efficiency of gaseous formaldehyde nanogenerator (TENG) is a newly-invented technology for low- degradation, when a peak voltage of 1,110 V is applied on the filter frequency mechanical energy harvesting at a high efficiency [1, 2]. By by a single electrode TENG [21]. coupling of triboelectrification and electrostatic induction, mechanical On the other hand, environmental deterioration, especially water vibration or relative displacement of metal electrode and dielectric pollution, is widely dispersed [22, 23]. Though the sewage treatment materials can be converted into electricity [3, 4]. This electricity plants are used to meet the demands of cities, distributed treatment generation origins from Maxwell’s displacement current, which is units are still in request for the supplementary of centralized essentially different from traditional electromagnetic generator [5, 6]. purification beyond the range of plants. Electro-Fenton (EF) reaction, The efficient conversion by TENGs makes it possible to power a derivatived advanced oxidation processes from Fenton reaction and light-emitting diodes, wireless transmitters, sensors, even to realize electrochemistry, is widely used for organic contaminant treatment the world of internet of things [7, 8]. The design of TENGs is rather [24, 25]. The main reactions are hydrogen peroxide (H2O2) electro- flexible due to the utilization of various dielectric and conductive generation over cathode and decomposition under the catalytic materials, which have found applications in the fields of tribotronics, effect of Fe2+ ions, forming hydroxyl radical (•OH), along with the self-powered systems and hybrid energy harvesting devices [9–12]. regenation of Fe2+ ions through Fe3+ reduction on cathode [24, 26, 27]. The electric energy translated from TENGs can also be used in •OH is a kind of active oxygen species with higher oxidation 0 + electrochemistry and photo-electrochemistry [13–16]. For example, potential (E (•OH,H /H2O) = 2.72 V), than the standard one of ozone efficient self-powered water splitting can be directly realized at a under acidic conditions [28, 29]. The traditional EF process is rate of 6.25 × 10−3 mL/min by integrating an electrolysis cell and conducted by an extra power source in an electrochemical cell, thus flowing-water-driven TENG [17]. Assisted with the induced electric electric circuit design needs to be considered for large-scale application Address correspondence to Zhong Lin Wang, [email protected]; Hexing Li, [email protected]; Xia Cao, [email protected] 2 Nano Res. outdoors. Hence, EF process powered by distributed energy source, in the three-electrode system. Linear sweep voltammetry (LSV) was such as wind blow or water flow, is more prospective for the recorded at a scanning rate of 10 mV/s. The modified graphite felt applications in the water area beyond the sewage treatment plants. was used as cathode electrode, a platinum sheet (10 mm × 20 mm × Besides, electrolyte is needed for electric conductivity enhancement 0.1 mm) as counter electrode and an Ag/AgCl electrode as reference in the aqueous phase. Chloride-based salt electrolyte can produce electrode. NaCl aqueous solution (0.1 M) with or without Fe2+ ions active chlorine species, like hypochlorous (HClO), hypochlorite ion (0.2 mM FeSO4) was used as electrolyte. − (ClO ), via dissolving the evolved chlorine (Cl2) in aqueous solution [30, 31]. The generated active chlorine species can also contribute 2.4 Generation and measurement of H2O2 and •OH to the degradation of organic compounds coordinated with •OH The electro-generation of H2O2 was carried out in a single chamber species generated in the EF process. cell (100 mL) at 22 °C. In this process, direct current (DC) was In this work, a self-powered electrochemical system (SPECS) was applied by Keithley 2410 SourceMeter, platinum sheet was used as constructed by a rotary TENG (R-TENG) driving electrochemical the anode electrode, 50 mL of 0.1 M NaCl aqueous solution was cell for the generation of H2O2, •OH and active chlorine species. used as the electrolyte, and constant stirring was employed for the Modified graphite felt (GF) cathode with mesoporous carbon black diffusion of the generated H2O2. The pH value of electrolyte was and polytetrafluoroethylene (PTFE) nanopowder was prepared, adjusted by H2SO4 or NaOH, N2 or O2 was introduced at a flow rate which can efficiently generate H2O2 by making full use of dissolved of 0.6 L/min to determain the effect of atmosphere. At an interval oxygen (O2) in neural condition. Platinum sheet was used as the anode of 2 min, 1 mL solution was pipette out for the quantitative detection for the generation of active chlorine species. With power management, of H2O2. The analysis method was referenced to spectrophotometric this constructed SPECS can efficiently degrade Rhodamine B (RhB) determination (Shimadzu UV3600) using titanium reagent (20 mM and methylene blue (MB) in neutral condition without any O2 potassium titanium(IV) oxalate, 1 M sulphuric acid) [33]. •OH aeration and external electric power supply. A wind-driven rotary generated from H2O2 via Fenton process (0.2 mM FeSO4) was TENG (WR-TENG) was also fabricated for the demo application of quantitatively measured by determination of the fluorescence intensity SPECS. The SPECS presented in this work would not only extend (Edinburgh instruments, FLS980-S2S2-stm) of 2-hydroxyterephthalic the application of TENGs in electrochemistry, but also provide a acid evolved from hydroxylated terephthalic acid [34]. promising strategy for the treatment of distributed water pollution via the conversion from distributed mechanical energy to chemical 2.5 Degradation of RhB and MB energy. The degradation tests of RhB and MB were carried out in the same chamber cell as the H2O2 electro-generation. 0.1 M NaCl aqueous 2 Experimental section solution with 0.2 mM FeSO4 was used as the electrolyte. The electrolyte solution was neutral. DC current (Keithley 2410 SourceMeter) 2.1 Fabrication of the R-TENG or R-TENG was used as power source for the degradation. The concentration of RhB or MB dye was determined by spectrophotometer The R-TENG consists of two well fixed coaxial parts. For the stator, (Shimadzu UV 3600) at the characteristic absorption peak. The 1 oz Cu was deposited on a disk-shape printed circuit board (PCB). removal rate η was calculated by η = 1 − (At/A0), where At denotes The whole PCB was divided into 12