奈米材料/酵素共構生物陽極與葡萄糖燃料電池應用研究

Abstract

本研究結合奈米材料與酵素提升生物陽極之電流效率，並將奈米材料與酵素共構之陽極組裝成高功率葡萄糖生物燃料電池。電池陽極使用葡萄糖氧化酵素、媒介分子DHB（2, 5-dihydroxybenzaldehyde）、牛血清蛋白和戊二醛交聯，陰極使用漆氧化酵素和媒介分子ABTS。奈米材料部分選用奈米碳材和奈米金屬材料，前者包含酸化之多壁奈米碳管(MWCNT)、單壁奈米碳管(SWCNT)和白金碳黑(Pt/C)，後者包含釕金屬(Ru)、鉑金屬(Pt)和鉑釕金屬(PtRu)。奈米材料修飾於網印碳電極(SPCE)之間在於提升電流效率。本實驗先使用乙醇處理酸化之多壁奈米碳管，以去離子水當分散劑，修飾在網印碳電極(SPCE，面積0.2826 cm2)，放入100度烤箱15分鐘快速乾燥，防止奈米碳管聚集，此製備方式均勻且再現性高。利用線性掃描伏安法量測SPCE/MWCNT/DHB-BSA-GOx於葡萄糖溶液在25 oC和37 oC，催化電流值為497.6 ± 34.3 μA/cm2和681.7 ± 59.5 μA/cm2。比較不同奈米材料與酵素共構於葡萄糖生物燃料電池之功率分析中，以MWCNT電極為最佳，功率密度為 81.92 ± 1.48 μW/cm2，開環電位為0.65 V，短路電流為0.73 mA/cm2。葡萄糖生物燃料電池之最適化中，陰極以5 mM ABTS、80 unit/ml漆氧化酵素和奈米碳管修飾碳紙(2 cm × 1 cm)為最佳條件。在陽極部分，SPCE/MWCNT/DHB-BSA-GOx於不同緩衝溶液中會有不同的反應機制。在100 mM磷酸鹽緩衝溶液中，pKa大於葡萄糖酸，電極維持於中性環境，則DHB扮演唯一媒介分子，此時電流輸出平穩，短路電流為0.3 mA/cm2，功率為66.3 μW/cm2(0.4 V)於37 oC下。一旦於10 mM磷酸鹽緩衝溶液，葡萄糖氧化所產生的葡萄糖酸，會造成電極局部地區呈現酸性。此時推測酸化之多壁奈米碳管表面物質於酸性為陽極第二個媒介分子，催化電流值上升，短路電流為0.66 mA/cm2，功率為63.3 μW/cm2(0.2 V)於37oC下。最後將奈米碳管/酵素共構電極應用於膜電極組，需先將Nafion®117薄膜經由過氧化氫和硫酸前處理(P-Nafion)。在膜電極組設計中，電極間距離小可減低電子傳遞阻力，奈米碳管/酵素共構碳紙陰陽兩極(2 cm × 1 cm)組成葡萄糖生物燃料電池，電極以面對面形式擺放，輸出功率為36.29 μW於25 oC。

This thesis work aims at the development of high-efficiency glucose biofuel cells based on the bioanodes with both enzymes and nanomaterials. In my biofuel cell, the bioanode was made of a crosslinked matrix containing glucose oxidase (GOx), 2,5-dihydroxybenzaldehyde (DHB), bovine serum albumin (BSA) and glutaraldehyde. The biocathodic camber composed of non-immobilized laccase and ABTS. Nanomaterials made in this work were carbon and matel nanomaterials. The carbon nanomaterails include the carboxylated multi-walled carbon nanotube (MWCNT), single-walled carbon nanotube (SWCNT) and platinum on carbon (Pt/C). The matel nanomaterails include ruthenium (Ru), platinum (Pt) and platinum-ruthenium (PtRu). All of the nanomaterials were dropped on the screen-printing carbon electrode (SPCE). To develop a simple and reliable electrode, we prepared carbon nanotube/SPCE with ethanol pretreatment. Then, the MWCNT suspension, which used DIW as a dispersive agent, was dropped on SPCE. Finally, the electrode was placed in the oven for 15 minutes at 100oC to prevent the MWCNT aggregation. The SPCE/MWCNT bioanode was characterized by LSV, and the current density was 497.6± 34.3 μA/cm2 at 25oC and 681.7± 59.5 μA/cm2 at 37oC. In the nanomaterial/enzyme-based glucose biofuel cell, the SPCE/MWCNT/DHB-BSA-GOx bioanode showed better performance. The open-circuit voltage and short-circuit current of the biofuel cell at 50 oC are 0.65 V and 0.73 mA/cm2, respectively, and the maximum power output is 81.92± 1.48 μW/cm2.The optimal composition of the biocathodic chamber was 5 mM ABTS, 80 unit/ml laccase and 2 cm2 MWCNT-based carbon paper electrode. For the anodic chamber, the nanomaterial/enzyme-based bioanode showed different redox behavior at different buffer capacity. When the PBS concentration was 100 mM, it showed a stronger buffer effect for gluconic acid, and the current output was steadier. In comparsion, when 10 mM PBS was used, the vicinity of the bioanode turns acidic due to oxidization of glucose into gluconic acid. Afterward, the carboxylated multi-walled carbon nanotube (fulvic acid) was found to be a secondary mediator. In the final part of this work, the MWCNT/enzyme-based electrode was applied to a membrane electrode assembly, with a prior Nafion®117 membrane pretreated by hydrogen peroxide and sulfuric acid. The MWCNT/enzyme-based carbon paper (size 2 cm × 1 cm) bioanode in the 1 M glucose biofuel cell generated a power of 36.29 μW at 25oC with a face-to-face design.