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In the photoelectrochemical water splitting reaction system, bubbles will cover the reaction area on the photoelectrode surface, affecting the reaction impedance and gas-liquid mass transfer. A laser irradiation system is built and it is coupled with an electrochemical workstation and high-speed microscopic imaging system. The evolution behavior and mass transfer characteristics of single O2 bubble on the TiO2 photoelectrode are studied at different electrolyte concentrations (Na2SO4, 0.1–2.0 mol/L). With the increase of electrolyte concentration from 0.1 mol/L to 2.0 mol/L, the solution resistance and bubble additional resistance decrease, and the overpotential in the stable growth stage of bubble decreases from 0.113 V to –0.089 V. The bubble will cause the fluctuation of overpotential in the nucleation, growth and detachment stages, which is consistent with the impedance change caused by the change of dissolved oxygen concentration in the liquid phase. By analyzing the correlation between gas evolution efficiency and bubble coverage, it is found that the increase of electrolyte concentration will lead the bubble coverage and gas evolution efficiency to decrease simultaneously. By calculating the Sherwood dimensionless number, the results show that the total convective mass transfer coefficient increases with the electrolyte concentration increasing. Single-phase natural convection plays a dominant role in the process of gas product transfer, and its mass transfer coefficient is one order of magnitude larger than that of bubble-induced convection. In summary, by adjusting the electrolyte concentration, the bubble on the gas evolution photoelectrode surface can be effectively removed and the mass transfer of the system can be optimized, which is of great significance in improving the efficiency of photoelectrochemical water splitting.
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图 1 光电化学分解水实验系统图(1-紫外激光发生器; 2-光束扩展器; 3-透镜; 4-Ag/AgCl参比电极; 5-铂片对电极; 6-纳米棒状TiO2薄膜工作电极; 7-石英反应池; 8-电化学工作站; 9-计算机; 10-高速摄像机; 11-显微镜头; 12-LED照明光源)
Figure 1. Experimental measurement system diagram (1-UV laser generator; 2-beam expander; 3-lens; 4-Ag/AgCl reference electrode; 5-platinum counter electrode; 6-nanorod TiO2 film working electrode; 7-quartz reaction cell; 8-electrochemical workstation; 9-computer; 10-high speed camera; 11-micro-lens; 12-LED lighting source).
图 2 MATLAB程序处理气泡图像 (a)裁剪高速相机拍摄的气泡图像; (b)将图像转换为黑白二值图; (c)在黑白二值图上识别气泡直径的像素点; (d)在黑白二值图上识别气泡的接触直径和接触角
Figure 2. Bubble images processed by Matlab program: (a) Cutting bubble image; (b) converting image into a black and white binary image; (c) identifying pixels of bubble diameter on the black and white binary image; (d) identifying contact diameter and contact angle of bubble.
图 3 气泡演化引起的过电势波动
Figure 3. Bubble evolution corresponding to overpotential at different moments (concentration of 0.3 mol/L).
图 4 气泡直径随生长时间的变化 (a)线性坐标; (b)双对数坐标
Figure 4. Bubble diameter at different concentrations with growth time: (a) The linear coordinate; (b) the logarithmic coordinate.
图 5 (a) 0.1—2.0 mol/L电解液浓度下的过电势波动曲线; (b)稳态氧浓度与稳态过电位的关系
Figure 5. (a) Overpotential fluctuation curves with time during bubble growth at 0.1–2.0 mol/L electrolyte concentration; (b) the relationship between steady-state oxygen concentration and steady-state overpotential.
图 6 (a)平均气泡周期和脱离直径随电解液浓度的变化; (b)气泡产量随电解液浓度的变化
Figure 6. (a) Variations of average bubble period and departure diameter with electrolyte concentration; (b) the variation of bubble production with electrolyte concentration.
图 7 不同电解液浓度下的析气效率和气泡覆盖率 (a)电解液浓度为0.5 mol/L时析气效率和气泡覆盖率随气泡生长时间的变化; (b)平均析气效率和气泡覆盖率随电解液浓度的变化
Figure 7. Gas evolution efficiency fg and bubble coverage Θ at different electrolyte concentration: (a) The variation curves of fg and Θ with bubble growth time when the electrolyte concentration is 0.5 mol/L; (b) the variation curves of $ {{\bar f}_{{\mathrm{g}}}} $ and $ \overline{\varTheta } $ with electrolyte concentration.
图 8 不同电解液浓度下, 瞬态析气效率(a)、气泡覆盖率(b)和光电流密度(c)的变化曲线
Figure 8. Variation of transient gas evolution efficiency (a), gas bubble coverage (b) and photocurrent density (c) at different electrolyte concentrations.
图 9 平均单相自然对流传质系数$ {{\bar k}_{{\mathrm{s}}}} $、气泡诱导对流传质系数$ {{\bar k}_{{\mathrm{b}}}} $和总对流传质系数$ {{\bar k}_{{\mathrm{e}}}} $随电解液浓度的变化
Figure 9. Variation curves of average mass transfer coefficients of single-phase natural convection $ {{\bar k}_{{\mathrm{s}}}} $, bubble-induced convection $ {{\bar k}_{{\mathrm{b}}}} $ and total convection ${{\bar k}_{{\mathrm{e}}}} $ with electrolyte concentration.
图 10 不同电解液浓度下, 单相自然对流传质系数ks、气泡诱导对流传质系数kb和总对流传质系数ke随气泡生长时间的变化
Figure 10. Variation curves of mass transfer coefficients of single-phase natural convection ks, bubble-induced convection kb and total convection ke with bubble growth time at different electrolyte concentrations.
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[1] Fujishima A, Honda K 1972 Nature 238 37
Google Scholar
[2] Wang R, Hashimoto K, Fujishima A, Chikuni M, Kojima E, Kitamura A, Shimohigoshi M, Watanabe T 1997 Nature 388 431
Google Scholar
[3] 黄柏标, 王朋, 张晓阳, 秦晓燕, 戴瑛 2009 科学通报 54 847
Google Scholar
Huang B B, Wang P, Zhang X Y, Qin X Y, Dai Y 2009 Sci. Bull. 54 847
Google Scholar
[4] 陈娟雯, 郭烈锦, 胡晓玮, 曹振山 2018 工程热物理学报 39 550
Chen J W, Guo L J, Hu X W, Cao Z S 2018 J. Eng. Thermophys. 39 550
[5] 郭烈锦, 曹振山, 王晔春, 张博, 冯雨杨, 徐强 2023 西安交通大学学报 57 1
Google Scholar
Guo L J, Cao Z S, Wang Y C, Zhang B, Feng Y Y, Xu Q 2023 J. Xi'an Jiaotong Univ. 57 1
Google Scholar
[6] Tawfik M E, Diez F J 2014 Electrochim. Acta 146 792
Google Scholar
[7] Matsushima H, Iida T, Fukunaka Y 2012 J. Solid State Electrochem. 16 617
Google Scholar
[8] Li Y J, Zhang H C, Xu T H, Lu Z Y, Wu X C, Wan P B, Sun X M, Jiang L 2015 Adv. Funct. Mater. 25 1737
Google Scholar
[9] Chen J W, Guo L J 2019 Appl. Phys. Lett. 115 101602
Google Scholar
[10] Lu X, Lalwani S, Yuan L, Abdelsalam M A, AlMarzooqi F, Zhang T 2022 Int. J. Hydrogen Energ. 47 36504
Google Scholar
[11] Ansari S A, Khan M M, Ansari M O, Cho M H 2016 New J. Chem. 40 3000
Google Scholar
[12] Piontek S, Andronescu C, Zaichenko A, Konkena B, Puring K J, Marler B, Antoni H, Sinev I, Muhler M, Mollenhauer D, Roldan Cuenya B, Schuhmann W, Apfel U P 2018 ACS Catal. 8 987
Google Scholar
[13] Ye X, Xu Q, Nie T F, Luo X Y, Jiang S, Guo L J 2023 J. Phys. Chem. C 127 22085
Google Scholar
[14] Bashkatov A, Yang X, Mutschke G, Fritzsche B, Hossain S S, Eckert K 2021 Phys. Chem. Chem. Phys. 23 11818
Google Scholar
[15] Matsushima H, Fukunaka Y, Kuribayashi K 2006 Electrochim. Acta 51 4190
Google Scholar
[16] Lubetkin S D, Akhtar M 1996 J. Colloid Interf. Sci. 180 43
Google Scholar
[17] Baczyzmalski D, Karnbach F, Yang X, Mutschke G, Uhlemann M, Eckert K, Cierpka C 2016 J. Electrochem. Soc. 163 E248
Google Scholar
[18] Cao Z S, Zhang B, Feng Y Y, Xu Q, Wang Y C, Guo L J 2022 Electrochim. Acta 434 141293
Google Scholar
[19] Wang H P, Xu Z X, Lin W, Yang X, Gu X R, Zhu W, Zhuang Z B 2023 Nano Res. 16 420
Google Scholar
[20] Obata K, Stegenburga L, Takanabe K 2019 J. Phys. Chem. C 123 21554
Google Scholar
[21] Liu Y, Jiang J G, Xu Q, Li M T, Guo L J 2013 Mater. Res. Bull. 48 4548
Google Scholar
[22] Hu X W, Cao Z S, Wang Y C, Shen S, Guo L J, Chen J W 2016 Electrochim. Acta 202 175
Google Scholar
[23] Thoroddsen S T, Etoh T G, Takehara K 2008 Annu. Rev. Fluid Mech. 40 257
Google Scholar
[24] Rox H, Bashkatov A, Yang X, Loos S, Mutschke G, Gerbeth G, Eckert K 2022 Int. J. Hydrog. Energ. 48 2892
Google Scholar
[25] Vogt H 1993 Electrochim. Acta 38 1421
Google Scholar
[26] Lubetkin S, Blackwell M 1988 J. Colloid Interf. Sci. 126 610
Google Scholar
[27] Scriven L E 1959 Chem. Eng. Sci. 10 1
Google Scholar
[28] Chandran P, Bakshi S, Chatterjee D 2015 Chem. Eng. Sci. 138 99
Google Scholar
[29] Vogt H, Balzer R J 2005 Electrochim. Acta 50 2073
Google Scholar
[30] Wei J J, Xue Y F, Zhao J F, Li J 2011 Chin. Phys. Lett. 28 016401
Google Scholar
[31] Chen J W, Guo L J, Hu X W, Cao Z S, Wang Y C 2018 Electrochim. Acta 274 57
Google Scholar
[32] Wang M S, Nie T F, She Y, Tao L, Luo X Y, Xu Q, Guo L J 2023 Int. J. Hydrog. Energ. 48 23387
Google Scholar
[33] Bashkatov A, Hossain S S, Yang X, Mutschke G, Eckert K 2019 Phys. Rev. Lett. 123 214503
Google Scholar
[34] Vogt H 1993 Electrochim. Acta 38 1427
Google Scholar
[35] Vogt H 2017 Electrochim. Acta 235 495
Google Scholar
[36] Vogt H 2013 Electrochim. Acta 87 611
Google Scholar
[37] Shah A, Jorne J 1989 J. Electrochem. Soc. 136 144
Google Scholar
[38] Lochiel A C, Calderbank P H 1964 Chem. Eng. Sci. 19 471
Google Scholar
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