| 摘要: | 化石燃料的廣泛使用導致了嚴重的能源危機和環境挑戰，促使人們需要探索可持續和清潔的能源。氫氣因其高能量密度、運輸和儲存的可行性以及用於燃料電池時的能量轉換效率而受到高度重視。然而，用於電解水的陰極析氫反應(HER)和陽極析氧反應(OER)的緩慢反應動力學導致高過電位，對大規模產氫構成了重大障礙。因此，設計優異的電催化觸媒以實現最佳的過電位和高效的水電解是目前研究的主要目標。Pd 具有與Pt相似的電子結構，使其成為Pt最有利的替代品。然而，Pd 和氫原子之間的強相互作用通常會使氫脫附變得困難，導致 HER 表現較差。
本研究透過氫的引入和第二金屬的合金化，利用應變效應和配體效應有效削弱Pd和H之間的強親和力，改善HER過程。我們使用簡單的油胺法合成Pd基觸媒形成氫化物，且透過Ir的添加適當的調節觸媒的氫吸附能，除了提升觸媒在酸性環境中的HER效能，Ir優異的抗腐蝕能力也為觸媒在酸性HER穩定度中有良好表現。在酸性環境下(0.5 M H2SO4)，PdIr0.1H0.2/C和PdIr0.15/C表現出優異的HER電化學效能，在電流密度為10 mA cm-2時的過電位為25和28 mV，Tafel斜率為14 和18 mV dec-1，質量活性為1025及1064 mA/mg Pd+Ir，經過5000圈循環加速測試的穩定度後，PdIr0.15/C的質量活性仍保留76%，而PdIr0.1H0.2/C的質量活性僅剩下33%。雖然PdIr0.1H0.2/C初始效能表現出較低的過電位和Tafel斜率，凸顯了 H 和Ir添加的提高 HER性能的關鍵作用。然而，與PdIr相比，PdIr氫化物並不穩定。此外，通過原位X光吸收光譜(In-situ X-ray absorption spectroscopy, XAS)和感應耦合電漿放射光譜儀(Inductively coupled plasma optical emission, ICP-OES)分析提供了對PdIr氫化物觸媒(PdIr0.1H0.2/C)穩定性的分析。In-situ XAS結果顯示穩定度測試後Pd-Pd和Pd-Ir配位數與初始狀態相比變得更大，且Pd-Pd鍵長變回與Pd箔一樣，表明最初存在的氫原子經過穩定度後會從Pd晶格中離開。從ICP結果得知，在PdIr中添加氫原子會了造成Ir溶解。從上述結果總結，H的添加導致PdIr觸媒結構不穩並造成Ir的溶解，使觸媒穩定度不好。
另一方面，H的添加除了減弱觸媒的氫吸附能，還能提高觸媒鹼性模擬海水電解質(1 M KOH+3.5wt% NaCl)中的穩定性，PdH0.4/C在電流密度為10 mA cm-2時的過電位為25 mV，Tafel斜率為40 mV dec-1，質量活性為207 mA/mg Pd`，經過5000圈循環加速測試的穩定度後，PdH0.4/C的質量活性仍保留96%，顯示出優異的效能和穩定性。本篇研究結合了Ir和H的引入改善Pd基觸媒在HER的效能，且透過進一步的分析了解了其出色性能背後的機制。為合理設計更有效率的電催化觸媒提供了新的見解。
;The extensive use of fossil fuels has led to a severe energy crisis and environmental challenges, prompting the need to explore sustainable and clean energy sources. Hydrogen is highly valued for its high energy density, feasibility of transport and storage, and energy conversion efficiency in fuel cells. However, the slow reaction kinetics of the cathodic hydrogen evolution reaction (HER) and the anodic oxygen evolution reaction (OER) in water electrolysis result in high overpotentials, posing significant barriers to large-scale hydrogen production. Therefore, designing superior electrocatalysts to achieve optimal overpotentials and efficient water electrolysis is a primary research goal. Pd, with an electronic structure similar to Pt, is a promising alternative to Pt. However, the strong interaction between Pd and hydrogen atoms usually makes hydrogen desorption difficult, leading to poor HER performance.
This study improves the HER process by introducing hydrogen and alloying with a second metal, effectively weakening the strong affinity between Pd and H through strain and ligand effects. We synthesized Pd-based catalysts using a simple oleylamine method to form hydrides, and by adding Ir, we appropriately tuned the catalyst′s hydrogen adsorption energy, enhancing HER performance in acidic environments and improving stability due to Ir′s excellent corrosion resistance. In an acidic environment (0.5 M H2SO4), PdIr0.1H0.2/C and PdIr0.15/C showed excellent HER electrochemical performance with overpotentials of 25 and 28 mV at a current density of 10 mA cm-2, Tafel slopes of 14 and 18 mV dec-1, and mass activities of 1025 and 1064 mA/mg Pd+Ir, respectively. After 5000 cycles of accelerated durability testing, PdIr0.15/C retained 76% of its mass activity, while PdIr0.1H0.2/C retained only 33%. Despite PdIr0.1H0.2/C showing lower initial overpotential and Tafel slope, highlighting the crucial role of H and Ir in enhancing HER performance, PdIr hydrides proved unstable compared to PdIr. Additionally, in-situ X-ray absorption spectroscopy (XAS) and inductively coupled plasma optical emission spectrometry (ICP-OES) analyses provided insights into the stability of PdIr hydride catalysts (PdIr0.1H0.2/C). In-situ XAS results indicated that after stability testing, the coordination numbers of Pd-Pd and Pd-Ir increased compared to the initial state, and the Pd-Pd bond length reverted to that of Pd foil, indicating the departure of initially present hydrogen atoms from the Pd lattice. ICP results revealed that adding hydrogen to PdIr caused Ir dissolution. These findings suggest that hydrogen addition destabilizes the PdIr catalyst structure and leads to Ir dissolution, deteriorating the catalyst stability.
On the other hand, hydrogen addition not only reduces the catalyst′s hydrogen adsorption energy but also enhances stability in alkaline simulated seawater electrolyte (1 M KOH + 3.5 wt% NaCl). PdH0.4/C exhibited an overpotential of 25 mV at 10 mA cm-2, Tafel slope of 40 mV dec-1, and mass activity of 207 mA/mg Pd, retaining 96% of its mass activity after 5000 cycles, demonstrating excellent performance and stability. This study combines the introduction of Ir and H to improve the HER performance of Pd-based catalysts and provides insights into the mechanisms behind their superior performance, offering new perspectives for the rational design of more efficient electrocatalysts. |
