| 摘要: | 近年來，隨著科技日新月異的發展，社會對於能源的依賴程度亦日益提升，導致傳統化石燃料的消耗迅速增加，其對環境所造成的衝擊也逐漸受到各界關注。為了因應全球能源轉型與減碳需求，氫能的開發已成為新興替代能源中的重要一環。氫氣可透過電解水方式進行製備，並具備零碳排放的潛力，符合未來潔淨能源的發展趨勢。
在產氫氣過程中，析氫反應往往受到其緩慢動力學的限制，故需藉由高效能觸媒促進反應進行，以提升產氫效率。本研究以油胺法成功合成出負載於炭黑上的PdxTa奈米顆粒作為HER觸媒，並藉由恆電位儀對其HER電化學性能進行評估。此外，亦結合感應耦合電漿光學發射光譜、X光繞射光譜、高解析度穿透式電子顯微鏡及X光光電子能譜等材料分析技術，探討觸媒之元素組成比例、晶體結構、晶格影像與元素價態等特徵。
初步將Pd及不同比例的PdxTa(X=1、3、5、7、9)觸媒在0.5 M H2SO4溶液中進行析氫反應性能評估。後續則針對Pd及性能差異較為顯著的PdxTa(x = 1、3、7)樣品進行進一步的電化學測試與材料分析。其中，Pd7Ta展現出最佳的析氫反應性能，其在10 mA cm-2時的過電位為41 mV，Tafel斜率為45 mV dec-1；經5000圈加速降解測試後，過電位為51 mV，Tafel斜率為48 mV dec-1，相比之下，電化學活性與穩定性皆比Pd更為優異。進一步探討Pd7Ta觸媒的劣化機制，透過感應耦合電漿光學發射光譜與拉曼光譜的分析結果顯示，活性位點Pd無溶解至電解液中，而是於ADT後氧化為PdO，此現象是導致析氫反應性能下降的主要原因。然而，經-0.5 V(vs. RHE)定電位還原處理(2分鐘)後，可恢復至其原始電化學性能，間接驗證了PdO的生成為其劣化主因。最後，利用H-cell進行配對電解實驗，將陽極傳統之析氧反應替換為甲醇氧化反應，以此降低整體能耗。結果顯示，在30 mA cm-2電流密度下，MOR||HER相較OER||HER可降低約300 mV反應電位，顯示甲醇氧化反應在提升整體反應效率與經濟效益上具有高度優勢。最後，於電解器中進行4 A定電流條件下之150小時長時間穩定性測試，結果顯示該觸媒具備良好的穩定性，展現其於實際應用中的潛力。
本研究顯示，透過摻雜適量Ta元素可有效提升Pd基觸媒之析氫反應活性與穩定性，並具備可逆的再活化特性。此外，結合甲醇氧化反應於陽極作為配對電解策略，顯著降低了整體反應電位，有助於提高能量轉換效率與經濟性，展現其在未來氫能應用中的發展潛力與實用價值。;With the rapid advancement of technology in recent years, global energy demand has increased significantly, leading to the accelerated consumption of traditional fossil fuels and growing concerns over their environmental impact. In response to the need for energy transition and carbon reduction, hydrogen energy has emerged as a promising alternative due to its potential for zero carbon emissions when produced via water electrolysis.
However, the hydrogen evolution reaction (HER) is often hindered by sluggish kinetics, necessitating the development of efficient catalysts. In this study, PdxTa nanoparticles supported on carbon black were successfully synthesized via a simple oleylamine method and evaluated as HER catalysts in acidic media. Their electrocatalytic performance was assessed using a potentiostat, and comprehensive characterization ¬- including inductively coupled plasma optical emission spectroscopy (ICP-OES), X-Ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), and X-ray photoelectron spectroscopy (XPS) - was employed to analyze composition, structure, lattice features, and oxidation states.
The HER performance of pure Pd and a series of PdxTa (x = 1, 3, 5, 7, 9) catalysts was initially evaluated in 0.5 M H2SO4 solution. Based on preliminary results, further electrochemical measurements and material characterizations were conducted on selected samples with significant performance differences, including pure Pd, PdTa, Pd3Ta, and Pd7Ta. Among them, Pd7Ta exhibited the best HER activity, delivering a low overpotential of 41 mV at a current density of 10 mA cm-2 and a Tafel slope of 45 mV dec-1.After 5000 cycles of accelerated degradation testing (ADT), its performance remained stable with only slight increases to 51 mV and 48 mV dec-1, respectively - outperforming pure Pd in both activity and durability. ICP-OES and Raman spectroscopy confirmed that Pd degradation was primarily due to surface oxidation to PdO rather than dissolution. Remarkably, the catalytic activity could be fully restored via a 2-minute electrochemical reduction at -0.5 V (vs. RHE), verifying the reversibility of the oxidation process.Furthermore, a paired electrolysis strategy using a two-chamber H-cell was adopted to replace the sluggish anodic oxygen evolution reaction (OER) with the methanol oxidation reaction (MOR). This substitution significantly reduced the overall cell voltage. At a current density of 30 mA cm-2, the MOR||HER configuration exhibited a ~300 mV lower reaction potential compared to OER||HER, highlighting MOR’s potential in enhancing system efficiency and economic feasibility. Finally, a 150-hour long-term stability test was conducted in an electrolyzer under a constant current of 4 A. The results demonstrated excellent durability of the catalyst, highlighting its potential for practical applications.
In conclusion, the incorporation of Ta into Pd catalysts effectively enhanced HER activity and stability, while demonstrating reversible reactivation behavior. Coupling HER with MOR offers a viable strategy to improve energy efficiency and reduce operating costs, underscoring the potential of this system in future hydrogen energy applications. |
