Vol. 3, No. 4 (Fall 2016) 54-59   

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  Investigation of Hydroxylated Carbon Felt Electrode in a Vanadium Redox Flow Battery Used Optimized Supporting Electrolyte
M. Zarei Jelyani, M. Babaiee, A. Ghasemi and R. Eqra
( Received: February 15, 2017 – Accepted: August 16, 2017 )

Abstract    Traditional vanadium batteries use pure sulfuric acid as electrolyte, but H2SO4 does not absorb enough vanadium ions to make the electrolyte an efficient energy source. This study investigates the effect of hydroxylation process on electrochemical and operational properties of carbon felt electrode in VOSO4 solution with an optimized supporting electrolyte (a mixture of six parts HCl and 2.5 parts H2SO4). Carbon felt electrode was hydroxylated with mixed acids of H2SO4 and HNO3 in a stainless steel autoclave for 6 h. Then thermal treatment of electrode was performed at 400 oC for 5h. Obtained results of cyclic voltammograms showed that when the carbon felt was hydroxylated, both oxidation and reduction peak currents were increased remarkably and the peak potential separation is decreased from 356 mV to 246 mV, suggesting that the electrochemical activity and the kinetic reversibility on HCF electrode were improved compared to the pristine one. According to results of electrochemical impedance spectra, charge transfer resistance (Rct) was calculated to be 648 Ω for pristine carbon felt. The obtained Rct at hydroxylated electrode (176 Ω) shows a decrease of about 73 % in Rct. Charge-discharge profiles of two cells assembled with the pristine carbon felt (cell A), and hydroxylated carbon felt (cell B) showed that energy, voltage and coulombic efficiencies were significantly improved by using the hydroxylated electrodes inside the cell of vanadium redox flow battery.


Keywords    Vanadium redox flow battery, Carbon felt, Hydroxylation, Supporting electrolyte, Wettability


چکیده    باتری­های وانادیومی مرسوم از سولفوریک­اسید خالص به­عنوان الکترولیت استفاده می­کنند، اما H2SO4 نمی­تواند یون­های وانادیوم را به اندازه کافی جذب کند تا یک منبع انرژی کارآمد باشد. مطالعه حاضر اثر فرایند هیدروکسیلاسیون روی خواص الکتروشیمیایی الکترود نمدکربنی در محلول VOSO4 به همراه الکترولیت کمکی بهینه­شده (ترکیب 6 جزء حجمی HCl و 5/2 جزء حجمی H2SO4 ) را بررسی می­کند. الکترود نمدکربنی به­وسیله اسیدهای H2SO4 و HNO3 در اتوکلاو به مدت 6 ساعت هیدروکسیل شده است. سپس تیمار حرارتی به مدت 5 ساعت در دمای 400 درجه سانتی­گراد روی الکترود انجام شده است. نتایج ولتاموگرام­های چرخه­ای نشان می­دهد که با اعمال فرایند هیدروکسیلاسیون، هر دو جریان قله اکسایشی و کاهشی به­طور قابل­توجهی افزایش می­یابد و فاصله پتانسیل دو قله از mV 356 به mV 246 کاهش می­یابد. این موضوع نشان­دهنده بهبود فعالیت الکتروشیمیایی و برگشت­پذیری سینتیکی الکترود نمدکربنی هیدروکسیل­شده (HCF) در مقایسه با الکترود برهنه است. طبق نتایج طیف­های امپدانس الکتروشیمیایی، هیدروکسیلاسیون توانسته است مقاومت انتقال بار الکترود نمدکربنی برهنه را از 648 اهم به 176 اهم کاهش دهد. پروفایل­ شارژ- دشارژ سل­های باتری وانادیومی مونتاژشده با الکترودهای نمدکربنی برهنه (سل A) و نمدکربنی هیدروکسیل­شده (سل B)، افزایش قابل­ملاحظه راندمان­های کولمبیک، ولتاژ و انرژی را نشان می­دهد.

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