電解水是常見的產氫方法，而為了避免氣體產物的混合常在電解器中增加的隔膜，但會導致額外的電阻，反應產生的氣泡也會使溶液電阻上升，影響電解效率。為了改善以上問題，本實驗設計一個循環式無膜電解器，但去除隔膜將使氣相產物的分離成為難題，因此本實驗以流動的電解液對反應施加流場，探討電解液流動對氣相產物收集效率與分離效果。
本實驗藉由電解液的流動進行氣相產物分離與電化學表現改善，因此確認雷諾數所對應電解液的流動狀態十分重要，我們使用染劑進行流態可視化，結果顯示雷諾數在1250以內，流態看起來屬於層流，大於1250則看起來像過渡態與湍流。而為了探討電解液流動對此電解裝置的收集效率與氣相產物分離效果影響，在陰、陽極下游分別設置的氣體收集管並以GC分析氣體組成。結果顯示，於電解液靜止狀態下進行反應收集效率可達97.3%，但會隨雷諾數上升而下降，而氣相產物分離效果在層流(Re<1250)範圍最佳，陰極收集管內的氧氣佔比僅不到2%。
除了藉由流場解決氣相產物分離問題，我們也可以添加甘油至電解液中，將電解水的陽極產氧反應以甘油氧化反應取代，不但解決了分離問題，也能得到甘油氧化後的高經濟價值產物(dihydroxyacetone, DHA)。緊接著探討甘油氧化反應受電解液在各參數(不同NaOH/甘油體積莫耳濃度比、黏度、pH)對電化學表現影響。結果顯示，儘管提高NaOH體積莫耳濃度會使導電度上升導致電化學表現的提升，但有其臨界點，因為過高的NaOH會造成黏度的上升而導致導電度下降，OH基也會佔據電極表面活性點，使甘油分子無法有效反應。接著我們將電解液導電度調整至同為50 mS cm-1，並以交流阻抗法分別測定1.1 cp與6.6 cp電解液之溶液電阻值並計算其差值，以探討流場對黏度影響的改善。結果顯示溶液電阻值差值會隨雷諾數提高而下降，電解液由靜止狀態提高至Re=2500時，溶液電阻值差值下降45%，代表電解液的流動可以降低黏度影響的反應的程度。我們還探討了流速對於液相產物選擇率的影響。結果表明，在三個電壓(2.8 V、3 V、3.2 V)下進行反應六小時後，DHA選擇率與產量皆會隨雷諾數提高而提高，而在Re=2500且施加3 V進行反應，不但DHA選擇率達60%，也可以達到相對較高的產量。

Electrolysis of water is a common method of hydrogen generation, and to avoid the mixing of gas products often added membrane in the electrolyzer. But membrane will lead to additional resistance, and the gas bubbles generated by the reaction will also increase the resistance of the solution, affecting the electrolysis efficiency. In order to improve the above problems, we design a circulating membrane-less electrolyzer, but the removal of the membrane will make the separation of the gas phase products difficult, so we use the flowing electrolyte to impose a flow field on the reaction to investigate the effect of electrolyte flow on the Collection efficiency and separation of the gas phase products.
In this experiment, the gas phase separation and electrochemical performance are improved by the flow of electrolyte, so it is important to confirm the flow state of the electrolyte corresponding to the Reynolds number. In order to investigate the effect of electrolyte flow on the Collection efficiency and gas phase separation of this electrolysis device, gas collection tubes were set up downstream of the cathode and anode, and the gas composition is analyzed by GC. The results show that the collection efficiency of the electrolyte reaction at stagnant could reach 97.3%, but would decrease with the increase of Reynolds number, while the gas phase product separation effect is best in the laminar flow (Re<1250) range, and the percentage of oxygen in the cathode collection tube is less than 2%.
In addition to solving the gas phase product separation problem by flow field, we can also add glycerol to the electrolyte and replace the oxygen evolution reaction (OER) with glycerol electrooxidation reaction (GEOR), which not only solves the separation problem, but also obtains the high economic value product (DHA) after glycerol electrooxidation. The effect of the glycerol electrooxidation reaction on the electrochemical performance of the electrolyte in terms of various parameters (NaOH/glycerol molarity ratio, viscosity, and pH) is then investigated. The results show that although the increase of NaOH volume molar concentration led to the increase of conductivity and electrochemical performance, there is a critical point because too much NaOH would cause the decrease of conductivity due to the increase of viscosity, and the OH- will occupy the active point on the electrode surface, which prevent the effective reaction of glycerol molecules. Then, we adjust the conductivity of electrolyte to the same level of 50 mS cm-1, and measure the solution resistance values of 1.1 cp and 6.6 cp electrolyte by AC impedance method and calculate the difference to investigate the improvement of the flow field on the viscosity. The results show that the difference of solution resistance decreased with the increase of Reynolds number. When the electrolyte is raised from the stagnant state to Re=2500, the difference of solution resistance decrease by 45%, which represents the extent to which the flow of electrolyte can reduce the response of viscosity effect. We also investigate the effect of flow rate on the selectivity of liquid phase products. The results show that after six hours of reaction at three voltages (2.8 V, 3 V, and 3.2 V), the selectivity and yield of DHA increase with increasing Reynolds number, and the reaction at Re=2500 with 3 V not only resulted in 60% DHA selectivity but also achieved relatively high yield.

[1] H.Wang, L.Gao, Recent developments in electrochemical hydrogen evolution reaction, Curr. Opin. Electrochem. 7 (2018) 7–14.
[2] X.Zou, Y.Zhang, Noble metal-free hydrogen evolution catalysts for water splitting, Chem. Soc. Rev. 44 (2015) 5148–5180.
[3] M.Pagliaro, R.Ciriminna, H.Kimura, M.Rossi, C.DellaPina, From glycerol to value-added products, Angew. Chemie - Int. Ed. 46 (2007) 4434–4440.
[4] J.Schnaidt, M.Heinen, D.Denot, Z.Jusys, R.Jürgen Behm, Electrooxidation of glycerol studied by combined in situ IR spectroscopy and online mass spectrometry under continuous flow conditions, J. Electroanal. Chem. 661 (2011) 250–264.
[5] M.Simões, S.Baranton, C.Coutanceau, Electrochemical valorisation of glycerol, ChemSusChem. 5 (2012) 2106–2124.
[6] A.Direct, G.Fuel, Alkaline Direct Glycerol Fuel Cells, (2019).
[7] M.S.E.Houache, K.Hughes, E.A.Baranova, Study on catalyst selection for electrochemical valorization of glycerol, Sustain. Energy Fuels. 3 (2019) 1892–1915.
[8] M.Guschakowski, U.Schröder, Direct and Indirect Electrooxidation of Glycerol to Value-Added Products, ChemSusChem. 14 (2021) 5216–5225.
[9] B.Katryniok, H.Kimura, E.Skrzyńska, J.S.Girardon, P.Fongarland, M.Capron, R.Ducoulombier, N.Mimura, S.Paul, F.Dumeignil, Selective catalytic oxidation of glycerol: Perspectives for high value chemicals, Green Chem. 13 (2011) 1960–1979.
[10] G.D.O.Neil, J.E.Soc, G.D.O.Neil, C.D.Christian, D.E.Brown, D.VEsposito, Hydrogen Production with a Simple and Scalable Membraneless Electrolyzer FOR I NCREASED Hydrogen Production with a Simple and Scalable Membraneless Electrolyzer, (2016) 1–9.
[11] J.R.Selman, C.W.Tobias, By the Limiting-Current Technique, (n.d.).
[12] P.Coñizares, J.García-Gómez, I.Fernández de Marcos, M.A.Rodrigo, J.Lobato, Measurement of mass-transfer coefficients by an electrochemical technique, J. Chem. Educ. 83 (2006) 1204–1207.
[13] P.Hadikhani, S.M.H.Hashemi, G.Balestra, L.Zhu, M.A.Modestino, F.Gallaire, D.Psaltis, Inertial manipulation of bubbles in rectangular microfluidic channels, Lab Chip. 18 (2018) 1035–1046.
[14] R.J.Thorne, C.Sommerseth, A.P.Ratvik, S.Rørvik, E.Sandnes, L.P.Lossius, H.Linga, A.M.Svensson, Bubble Evolution and Anode Surface Properties in Aluminium Electrolysis, J. Electrochem. Soc. 162 (2015) E104–E114.
[15] H.Vogt, The Quantities Affecting the Bubble Coverage of Gas-Evolving Electrodes, Electrochim. Acta. 235 (2017) 495–499.
[16] S.DeLi, C.C.Wang, C.Y.Chen, Water electrolysis in the presence of an ultrasonic field, Electrochim. Acta. 54 (2009) 3877–3883.
[17] Y.Yu, X.Qiu, Y.Zhong, High Centrifugal Field Coupling with Electrolyte Circulation Internals : Process Intensification toward Efficient Water Electrolysis for Hydrogen Storage via Power-to-Gas High Centrifugal Field Coupling with Electrolyte Circulation Internals : Process Int, (2021).
[18] M.M.Bakker, D.A.Vermaas, Gas bubble removal in alkaline water electrolysis with utilization of pressure swings, Electrochim. Acta. 319 (2019) 148–157.
[19] S.Liang, Y.Cao, X.Liu, X.Li, Y.Zhao, Y.Wang, Y.Wang, Insight into pressure-swing distillation from azeotropic phenomenon to dynamic control, Chem. Eng. Res. Des. 117 (2017) 318–335.
[20] S.Sircar, T.C.Golden, Purification of hydrogen by pressure swing adsorption, Sep. Sci. Technol. 35 (2000) 667–687.
[21] M.T.Ho, G.W.Allinson, D.E.Wiley, Reducing the cost of CO2 capture from flue gases using pressure swing adsorption, Ind. Eng. Chem. Res. 47 (2008) 4883–4890.
[22] M.Y.Lin, L.W.Hourng, Ultrasonic wave field effects on hydrogen production by water electrolysis, J. Chinese Inst. Eng. Trans. Chinese Inst. Eng. A. 37 (2014) 1080–1089.
[23] K.M.Cho, P.R.Deshmukh, W.G.Shin, Hydrodynamic behavior of bubbles at gas-evolving electrode in ultrasonic field during water electrolysis, Ultrason. Sonochem. 80 (2021) 105796.
[24] L.M.A.Monzon, J.M.D.Coey, Magnetic fields in electrochemistry: The Lorentz force. A mini-review, Electrochem. Commun. 42 (2014) 38–41.
[25] H.Matsushima, D.Kiuchi, Y.Fukunaka, Measurement of dissolved hydrogen supersaturation during water electrolysis in a magnetic field, Electrochim. Acta. 54 (2009) 5858–5862.
[26] M.Y.Lin, L.W.Hourng, C.W.Kuo, The effect of magnetic force on hydrogen production efficiency in water electrolysis, Int. J. Hydrogen Energy. 37 (2012) 1311–1320.
[27] T.Iida, H.Matsushima, Y.Fukunaka, Water Electrolysis under a Magnetic Field, J. Electrochem. Soc. 154 (2007) E112.
[28] J.A.Koza, S.Mühlenhoff, P.Zabiński, P.A.Nikrityuk, K.Eckert, M.Uhlemann, A.Gebert, T.Weier, L.Schultz, S.Odenbach, Hydrogen evolution under the influence of a magnetic field, Electrochim. Acta. 56 (2011) 2665–2675.
[29] H.Matsushima, T.Iida, Y.Fukunaka, Gas bubble evolution on transparent electrode during water electrolysis in a magnetic field, Electrochim. Acta. 100 (2013) 261–264.
[30] M.F.Kaya, N.Demir, M.S.Albawabiji, M.Taş, Investigation of alkaline water electrolysis performance for different cost effective electrodes under magnetic field, Int. J. Hydrogen Energy. 42 (2017) 17583–17592.
[31] M.Atobe, S.Hitose, T.Nonaka, Chemistry in centrifugal fields: Part 1. Electrooxidative polymerization of aniline, Electrochem. Commun. 1 (1999) 278–281.
[32] H.Cheng, K.Scott, Improvement in methanol oxidation in a centrifugal field, J. Power Sources. 123 (2003) 137–150.
[33] P.Mandin, J.M.Cense, B.Georges, V.Favre, T.Pauporté, Y.Fukunaka, D.Lincot, Prediction of the electrodeposition process behavior with the gravity or acceleration value at continuous and discrete scale, Electrochim. Acta. 53 (2007) 233–244.
[34] C.Ramshaw, The opportunities for exploiting centrifugal fields, Heat Recover. Syst. CHP. 13 (1993) 493–513.
[35] M.Wang, Z.Wang, Z.Guo, Water electrolysis enhanced by super gravity field for hydrogen production, Int. J. Hydrogen Energy. 35 (2010) 3198–3205.
[36] A.Angulo, P.van derLinde, H.Gardeniers, M.Modestino, D.Fernández Rivas, Influence of Bubbles on the Energy Conversion Efficiency of Electrochemical Reactors, Joule. 4 (2020) 555–579.
[37] H.Vogt, R.J.Balzer, The bubble coverage of gas-evolving electrodes in stagnant electrolytes, Electrochim. Acta. 50 (2005) 2073–2079.
[38] S.M.H.Hashemi, P.Karnakov, P.Hadikhani, E.Chinello, S.Litvinov, C.Moser, P.Koumoutsakos, D.Psaltis, A versatile and membrane-less electrochemical reactor for the electrolysis of water and brine, Energy Environ. Sci. 12 (2019) 1592–1604.
[39] D.Chen, L.M.Pan, S.Ren, Prediction of bubble detachment diameter in flow boiling based on force analysis, Nucl. Eng. Des. 243 (2012) 263–271.
[40] Y.Li, G.Yang, S.Yu, Z.Kang, J.Mo, B.Han, D.A.Talley, F.Y.Zhang, In-situ investigation and modeling of electrochemical reactions with simultaneous oxygen and hydrogen microbubble evolutions in water electrolysis, Int. J. Hydrogen Energy. 44 (2019) 28283–28293.
[41] A.Coskun Avci, E.Toklu, A new analysis of two phase flow on hydrogen production from water electrolysis, Int. J. Hydrogen Energy. 47 (2022) 6986–6995.
[42] J.M.Meléndez, M.Désilets, G.Lantagne, E.Oliaii, Effect of Bubbles and Liquid Drops Fluid Dynamics on the Lithium Recombination inside a Lithium Electrolytic Cell with Diaphragm, J. Electrochem. Soc. 169 (2022) 026516.
[43] D.Zhang, K.Zeng, Evaluating the behavior of electrolytic gas bubbles and their effect on the cell voltage in alkaline water electrolysis, Ind. Eng. Chem. Res. 51 (2012) 13825–13832.
[44] J.F.Klausner, R.Mei, D.M.Bernhard, L.Z.Zeng, Vapor bubble departure in forced convection boiling, Int. J. Heat Mass Transf. 36 (1993) 651–662.
[45] © 1961 Nature Publishing Group, (1961).
[46] J.M.Martel, M.Toner, Inertial focusing in microfluidics, Annu. Rev. Biomed. Eng. 16 (2014) 371–396.
[47] M.N.& B.A.Samuel Raymond, © 1962 Nature Publishing Group, Nat. Int. J. Sci. 196 (1962) 1048–1050.
[48] L.F.Arenas, C.Ponce de León, F.C.Walsh, Critical Review—The Versatile Plane Parallel Electrode Geometry: An Illustrated Review, J. Electrochem. Soc. 167 (2020) 023504.
[49] S.A.Grigoriev, V.N.Fateev, D.G.Bessarabov, P.Millet, Current status, research trends, and challenges in water electrolysis science and technology, Int. J. Hydrogen Energy. 45 (2020) 26036–26058.
[50] S.Shiva Kumar, V.Himabindu, Hydrogen production by PEM water electrolysis – A review, Mater. Sci. Energy Technol. 2 (2019) 442–454.
[51] P.Hadikhani, S.M.H.Hashemi, S.A.Schenk, D.Psaltis, A membrane-less electrolyzer with porous walls for high throughput and pure hydrogen production, Sustain. Energy Fuels. 5 (2021) 2419–2432.
[52] S.A.Mousavi Shaegh, N.T.Nguyen, S.H.Chan, A review on membraneless laminar flow-based fuel cells, Int. J. Hydrogen Energy. 36 (2011) 5675–5694.
[53] J.W.Lee, M.A.Goulet, E.Kjeang, Microfluidic redox battery, Lab Chip. 13 (2013) 2504–2507.
[54] M.A.Goulet, E.Kjeang, Co-laminar flow cells for electrochemical energy conversion, J. Power Sources. 260 (2014) 186–196.
[55] D.V.Esposito, Membraneless Electrolyzers for Low-Cost Hydrogen Production in a Renewable Energy Future, Joule. 1 (2017) 651–658.
[56] J.T.Davis, D.E.Brown, X.Pang, D.V.Esposito, High Speed Video Investigation of Bubble Dynamics and Current Density Distributions in Membraneless Electrolyzers, J. Electrochem. Soc. 166 (2019) F312–F321.
[57] O.O.Talabi, A.E.Dorfi, G.D.O’Neil, D.V.Esposito, Membraneless electrolyzers for the simultaneous production of acid and base, Chem. Commun. 53 (2017) 8006–8009.
[58] X.Pang, J.T.Davis, A.D.Harvey, D.V.Esposito, Framework for evaluating the performance limits of membraneless electrolyzers, Energy Environ. Sci. 13 (2020) 3663–3678.
[59] D.Pletcher, R.A.Green, R.C.D.Brown, Flow Electrolysis Cells for the Synthetic Organic Chemistry Laboratory, Chem. Rev. 118 (2018) 4573–4591.
[60] F.C.Walsh, L.F.Arenas, C.Ponce de León, Developments in plane parallel flow channel cells, Curr. Opin. Electrochem. 16 (2019) 10–18.
[61] E.R.Choban, L.J.Markoski, A.Wieckowski, P.J.A.Kenis, Microfluidic fuel cell based on laminar flow, J. Power Sources. 128 (2004) 54–60.
[62] A.Taqieddin, R.Nazari, L.Rajic, A.Alshawabkeh, Review—Physicochemical Hydrodynamics of Gas Bubbles in Two Phase Electrochemical Systems, J. Electrochem. Soc. 164 (2017) E448–E459.
[63] N.Elgrishi, K.J.Rountree, B.D.McCarthy, E.S.Rountree, T.T.Eisenhart, J.L.Dempsey, A Practical Beginner’s Guide to Cyclic Voltammetry, J. Chem. Educ. 95 (2018) 197–206.
[64] P.Chooto, Cyclic Voltammetry and Its Applications, Voltammetry. (2019).
[65] D.H.Evans, K.M.O’Connell, R.A.Petersen, M.J.Kelly, Cyclic voltammetry, J. Chem. Educ. 60 (1983) 290–293.
[66] T.Kim, W.Choi, H.C.Shin, J.Y.Choi, J.M.Kim, M.S.Park, W.S.Yoon, Applications of voltammetry in lithium ion battery research, J. Electrochem. Sci. Technol. 11 (2020) 14–25.
[67] J.Li, C.Arbizzani, S.Kjelstrup, J.Xiao, Y. yaoXia, Y.Yu, Y.Yang, I.Belharouak, T.Zawodzinski, S.T.Myung, R.Raccichini, S.Passerini, Good practice guide for papers on batteries for the Journal of Power Sources, J. Power Sources. 452 (2020) 227824.
[68] W.Choi, H.C.Shin, J.M.Kim, J.Y.Choi, W.S.Yoon, Modeling and applications of electrochemical impedance spectroscopy (Eis) for lithium-ion batteries, J. Electrochem. Sci. Technol. 11 (2020) 1–13.
[69] S.Wang, J.Zhang, O.Gharbi, V.Vivier, M.Gao, M.E.Orazem, Electrochemical impedance spectroscopy, Nat. Rev. Methods Prim. 1 (2021).
[70] H.S.Magar, R.Y.A.Hassan, A.Mulchandani, Electrochemical impedance spectroscopy (Eis): Principles, construction, and biosensing applications, Sensors. 21 (2021).
[71] F.Iturbide Jiménez, A.J.Mendoza Jasso, A.Antonio García, A.Santiago Alvarado, Design and construction of an apparatus to visualize incompressible fluid flow in several regimes, Rev. Mex. Fis. E. 64 (2018) 133–138.
[72] J.dePaula, D.Nascimento, J.J.Linares, Influence of the anolyte feed conditions on the performance of an alkaline glycerol electroreforming reactor, J. Appl. Electrochem. 45 (2015) 689–700.
[73] H.Miao, L.Lu, Z.Huang, Flammability limits of hydrogen-enriched natural gas, Int. J. Hydrogen Energy. 36 (2011) 6937–6947.
[74] S.M.H. Hashemi, M.A.Modestino, D.Psaltis, A membrane-less electrolyzer for hydrogen production across the pH scale, Energy Environ. Sci. 8 (2015) 2003–2009.
[75] H.Amini, W.Lee, D.DiCarlo, Inertial microfluidic physics, Lab Chip. 14 (2014) 2739–2761.
[76] P.Kováts, D.Thévenin, K.Zähringer, Influence of viscosity and surface tension on bubble dynamics and mass transfer in a model bubble column, Int. J. Multiph. Flow. 123 (2020).
[77] J.Qi, L.Xin, Z.Zhang, K.Sun, H.He, F.Wang, D.Chadderdon, Y.Qiu, C.Liang, W.Li, Surface dealloyed PtCo nanoparticles supported on carbon nanotube: Facile synthesis and promising application for anion exchange membrane direct crude glycerol fuel cell, Green Chem. 15 (2013) 1133–1137.
[78] K.Mansouri, K.Ibrik, N.Bensalah, A.Abdel-Wahab, Anodic dissolution of pure aluminum during electrocoagulation process: Influence of supporting electrolyte, initial pH, and current density, Ind. Eng. Chem. Res. 50 (2011) 13362–13372.
[79] A.Dave, K.L.Gering, J.M.Mitchell, J.Whitacre, V.Viswanathan, Benchmarking Conductivity Predictions of the Advanced Electrolyte Model (AEM) for Aqueous Systems, J. Electrochem. Soc. 167 (2020) 013514.
[80] A.M.Verma, L.Laverdure, M.M.Melander, K.Honkala, Mechanistic Origins of the pH Dependency in Au-Catalyzed Glycerol Electro-oxidation: Insight from First-Principles Calculations, ACS Catal. 12 (2022) 662–675.
[81] C.Liu, M.Hirohara, T.Maekawa, R.Chang, T.Hayashi, C.Y.Chiang, Selective electro-oxidation of glycerol to dihydroxyacetone by a non-precious electrocatalyst – CuO, Appl. Catal. B Environ. 265 (2020) 118543.
[82] L.Roquet, E.M.Belgsir, J.M.Léger, C.Lamy, Kinetics and mechanisms of the electrocatalytic oxidation of glycerol as investigated by chromatographic analysis of the reaction products: Potential and pH effects, Electrochim. Acta. 39 (1994) 2387–2394.
[83] T.Li, D.A.Harrington, An Overview of Glycerol Electrooxidation Mechanisms on Pt, Pd and Au, ChemSusChem. 14 (2021) 1472–1495.
[84] W.A.Braff, C.R.Buie, M.Z.Bazant, Boundary Layer Analysis of Membraneless Electrochemical Cells, J. Electrochem. Soc. 160 (2013) A2056–A2063.
[85] Y.S.Muzychka, M.M.Yovanovich, Convective heat transfer, Handb. Fluid Dyn. Second Ed. (2016) 14.1-14.58.