表面改性水热自生长SnO_(2)碳布电极电化学还原CO_(2)性能

Performance of CO_(2) electrochemical reduction with surface modified self-growing SnO_(2) on carbon cloth electrode prepared by hydrothermal method

电化学还原CO_(2)是一种有效的CO_(2)转化及利用方法,但是由于CO_(2)在电解质溶液中溶解度较低,限制了其电化学还原性能.为增加电极-溶液-CO_(2)的三相反应界面,本文通过水热自生长的方法在碳布基底上制备SnO_(2)纳米片催化剂,利用三甲氧基硅烷修饰电极使其表面具有疏水性,研究了疏水电极与亲水电极的微观形貌和元素价态,对比了疏水电极与亲水电极的表面浸润性、双电层电容、塔菲尔斜率和电化学阻抗,并在不同电位下进行了电化学还原性能测试.实验结果表明,与亲水电极相比,表面改性后的疏水电极具有更低的塔菲尔斜率和传质阻力,表现出更优的电化学还原性能;在-1.8 V(vs.Ag/AgCl)电解电位下,电流密度为(28.0±0.6)mA cm^(-2),法拉第效率为77.2%±1.9%,比亲水电极的法拉第效率提高了14.7%;经12 h的电解测试后仍可维持72.6%的法拉第效率.

Over the past 100 years,the consumption of a large amount of fossil energy has led to an increase in CO_(2)in the atmosphere,triggering a serious greenhouse effect.In response to the energy crisis and global climate change,some strategies have been proposed to reduce CO_(2)emissions and convert CO_(2),such as biotransformation,photochemical process,thermochemical and electrochemical reduction.Among these technologies,electrocatalytic reduction of CO_(2)is an effective method for the conversion and utilization of CO_(2)and mitigation of greenhouse effect.Sn-based catalysts are widely used in electrocatalytic reduction of CO_(2)due to its non-toxicity,abundant reserves,low cost and high selectivity.However,the low solubility of CO_(2)in electrolyte solution(only 0.33 mol/L at room temperature and ordinary pressure)limits the electrochemical reduction performance.Herein,the SnO_(2)nanosheet catalyst was prepared on the carbon cloth substrate by hydrothermal self-growing method.Then,trimethoxysilane was used to modify the wettability of the electrode surface to make it hydrophobic,increasing the contact surface of the electrode-solution-CO_(2)three-phase reaction.The surface modified electrode was denoted as SnO_(2)/CC-HB and the unmodified one was SnO_(2)/CC-HL.The micromorphology and element valence states of hydrophobic and hydrophilic electrodes were studied by physical characterization.The results show that SnO_(2)nanosheets grow successfully on the carbon cloth for both SnO_(2)/CC-HB and SnO_(2)/CC-HL electrodes.By measuring the contact angle,it is found that SnO_(2)/CC-HB electrode shows hydrophobicity while SnO_(2)/CC-HL electrode is completely hydrophilic.The electrochemical reduction performance of SnO_(2)/CC-HB and SnO_(2)/CC-HL electrodes,including electrochemical active surface area,Tafel slope and electrochemical impedance were measured in an H-cell with three-electrode system.The electrolyte was 0.5 mol/L potassium bicarbonate CO_(2)saturated solution(pH 7.3).The results show that although the electrochemical activity of SnO_(2)/CC-HB electrode is lower than that of SnO_(2)/CC-HL electrode,the CO_(2)transfer and the three-phase reaction interface are increased because of the hydrophobicity.The Tafel slope of both electrodes is greater than 120 mV/dec,indicating that the restricted process of the electrochemical reduction of CO_(2)reaction is the process of CO_(2)gaining electrons.Moreover,the Tafel slope of SnO_(2)/CCHB electrode is smaller,indicating that SnO_(2)/CC-HB electrode has a better reaction kinetics.In addition,although the charge transfer resistance of SnO_(2)/CC-HB electrode is higher,the mass transfer resistance is lower,suggesting enhanced mass transfer for SnO_(2)/CC-HB electrode.Compared with SnO_(2)/CC-HL electrode,SnO_(2)/CC-HB electrode exhibits a better electrochemical reduction performance.The current density is(28.0±0.6)mA cm^(-2)and Faradaic efficiency is 77.2%±1.9%at-1.8 V(vs.Ag/AgCl)electrolytic potential,which is 14.7%higher than that of SnO_(2)/CC-HL electrode.After 12 hours of electrochemical reaction,the SnO_(2)/CC-HB electrode still shows good hydrophobicity,and the Faradaic efficiency remains 72.6%,which proves that the electrode has a good durability.In summary,tuning the wettability of the electrode can improve the mass transfer of CO_(2)and effectively enhance the performance of CO_(2)electrochemical reduction.