| 摘要: | 隨著化石燃料造成的環境污染與日俱增，尋求清潔與可再生的能源已成為當務之急。氫能，為傳統能源的一種有前途的替代品，它在生產及使用過程中幾乎不會產生有害排放物。經由電解水之析氫反應 (hydrogen evolution reaction, HER) ，是目前製氫的最佳方式之一，然而，其緩慢的反應動力學阻礙了整體反應效率，故通過使用適當的觸媒以降低HER中的過電位對於提升反應效率至關重要。鉑 (Pt) 基觸媒在酸性電解質中有著快速的反應動力學以及優異的氫吸附能，但其在鹼性環境下的活性不佳，且鉑具有稀缺性，限制了其廣泛運用的可能性。因此，為了實現高效的HER，研究並開發具有高活性及耐用性的非鉑基觸媒勢在必行。
鈀 (Pd) 是鉑族金屬之一，具有與鉑相似的電子結構以及僅次於鉑的高氫吸附能，使其成為鉑的潛在替代品，然而鈀對氫的吸附力極強，因此弱化其氫吸附能，才能有效促進其產氫步驟。本研究製備鈀-鈷 (Pd-Co) 雙金屬觸媒 (Pd-Co2/NC) ，利用沸石咪唑酯骨架- 67 (ZIF-67) 衍生物代替碳黑作為觸媒的支撐物。ZIF-67 獨特的結晶和多孔結構可以通過高溫熱解轉化為具有眾多活性位點的奈米結構。這些高度分散的活性位點嵌入具有相互連通孔隙的高導電性氮摻雜碳中，能促進質傳並增強奈米結構的催化活性和穩定性。除此之外，ZIF-67 中固有的鈷可作為水解位點並調節鈀的氫吸附能。 Pd-Co2/NC 在酸性和鹼性電解質中均表現出優異的HER活性，分別是在電流密度為10 mA cm-2時的過電位為23 和 13 mV，Tafel 斜率為11 和 54 mV dec-1 ，質量活性為745 和 186 A gPd-1，以及轉換頻率 (turnover frequency, TOF) 7.89和1.80 H2 s-1。值得注意的是，透過感應耦合電漿放射光譜儀 (Inductively coupled plasma optical emission, ICP-OES) 對進行了5000圈穩定度測試的電解液進行分析，發現鈀-鈷的合金化有助於降低觸媒於電解液中的溶解率，提升其結構穩定性，進而保留高HER效能。此外，也透過 X 射線光電子能譜儀 (X-ray photoelectron spectroscopy, XPS)確認了觸媒的表面組成，證明了鈷的添加會改變觸媒的電子結構，並增加鈀的抗氧化能力。另一方面，透過毒化試驗與 X 射線吸收光譜儀 (X-ray absorption spectroscopy, XAS) 分析，得知觸媒的活性位點主要是由金屬，特別是鍵結比例最高的鈀-鈀配位所提供，驗證了結構對 HER 性能的影響。本研究之觸媒結合了過渡金屬的引入以及多孔性氮摻雜碳做為支撐物的優點，並對其結構與電化學結果進行了一系列分析，為開發高性能 HER 觸媒提供了一個有前景的新方向。
;With the escalating environmental pollution caused by fossil fuels, the pursuit of clean and renewable energy has become an urgent priority. One promising alternative to traditional energy sources is hydrogen, which produces almost no harmful emissions during its production and utilization. Among the various methods, hydrogen evolution reaction (HER) from electro-splitting of water has emerged as a leading approach for hydrogen production. However, the sluggish reaction kinetics of HER impede overall efficiency, so it is crucial to utilize appropriate catalysts to reduce the overpotential in HER and enhance reaction efficiency. Pt-based catalysts exhibit rapid reaction kinetics and excellent hydrogen adsorption in acidic electrolytes, however, the limited activity in alkaline electrolytes, and the scarcity limit their widespread application. Therefore, to achieve efficient HER, it is essential to research and develop non-Pt-based catalysts with high activity and durability.
Pd is a member of the platinum group metals and shares similar electronic structure with Pt. It exhibits high hydrogen adsorption energy second only to platinum, which makes it a potential substitute for Pt. Nevertheless, the hydrogen binding energy of Pd is extremely strong. Therefore, it is essential to weaken its hydrogen adsorption energy so that the hydrogen generation step can be effectively promoted. Pd-Co bimetallic catalyst (Pd-Co2/NC), utilizing zeolitic imidazolate framework-67 (ZIF-67)-derivative as a support instead of carbon black has been prepared. The unique crystalline and porous structure of ZIF-67 can be transformed into nanostructures with numerous active sites through high-temperature pyrolysis. These highly dispersed active sites are embedded in a highly conductive nitrogen-doped carbon matrix with interconnected pores, promoting mass transfer and enhancing the catalytic activity and stability of the nanostructures. Moreover, the inherent Co presented in ZIF-67 can serve as hydrolysis sites and modulate the hydrogen binding energy of Pd. Pd-Co2/NC demonstrates excellent HER activity in both acidic and alkaline electrolytes, exhibiting low overpotentials of 23 and 13 mV at a current density of 10 mA cm–2, Tafel slopes of 11 and 54 mV dec-1, high mass activity (MA) values of 745 and 186 A gPd-1, and impressive turnover frequency (TOF) values of 7.89 and 1.80 H2 s-1 in 0.5 M H2SO4 and 1.0 M KOH solutions, respectively. It is worth noting that the analysis of the electrolytes after 5000 cycles of stability tests through inductively coupled plasma optical emission (ICP-OES) revealed that the alloying of Pd and Co helps reduce the dissolution rate of the catalyst in the electrolyte, enhancing its structural stability and thereby preserving high HER performance. Furthermore, the surface composition of the catalyst was confirmed through X-ray photoelectron spectroscopy (XPS), demonstrating that the addition of cobalt alters the electronic structure of the catalyst and enhances the oxidation resistance of Pd. On the other hand, through poisoning tests and X-ray absorption spectroscopy (XAS) analysis, it was found that the active sites of the catalyst are primarily provided by the metal, especially the Pd-Pd bonds with the highest coordination number, confirming the influence of the structure on HER performance. were conducted to verify the impact of structures on the HER performance. The catalyst developed in this study combines the advantages of introducing transition metals and utilizing porous nitrogen-doped carbon as a support. A series of analyses were conducted on its structure and electrochemical results, providing a promising new direction for the development of high-performance HER catalysts. |
