| 摘要: | 本研究利用循環伏安法(Cyclic Voltammetry，CV)和掃描式穿隧電子顯微鏡(Scanning Tunneling Microscope，STM)探討鎳薄膜於不同鹼性介質中的氫析出反應(HER)催化活性，在鹼性介質中開發高效且具成本效益的HER電催化劑，對於推動永續氫氣生產至關重要。儘管白金(Pt)仍是 HER 的標竿催化劑，但其在鹼性環境中的表現受限，主要因水分子解離動力學遲緩所致。透過修飾白金表面，特別是引入 3d 過渡金屬如鎳(Ni)，有望創造雙功能活性位點以提升催化活性。本研究系統性地探討了鎳覆蓋量對Pt(111)電極在鹼性條件下 HER 活性的影響。我們結合電化學測量與 STM 技術，分析了不同鎳覆蓋量的 Pt 電極樣品 (樣品 A、B 和 C)。其中，鎳覆蓋量為 1.53 單層(Monolayer; ML) 的樣品 B 展現最高 HER 活性，在僅需 -0.98 V 過電位的情況下即可達到 10 mA/cm² 的電流密度；相較之下，樣品 A (0.62 ML) 與樣品 C (3.95 ML)則分別需 -1.11 V 與 -1.15 V 的過電位。高解像 STM 影像顯示，在 HER 相關電位下，催化反應的活性相為金屬態 Ni，而非 Ni(OH)₂，這一結論來自於影像中觀察到的 moiré pattern，其為金屬 Ni 的特徵，並明顯區別於 Ni(OH)₂ 的結構。這些結果指出，鎳的化學狀態與覆蓋程度對 HER 活性具有關鍵影響。樣品 B 的催化表現已可媲美先前報導的 Pt/Ni 合金系統，顯示界面結構的精細調控在提升鹼性 HER 活性中扮演重要角色。第二部分探討不同陽離子對於HER催化活性的影響，Ni 修飾的 Pt(111) 電極在鹼性介質中進行HER時，其催化表現受到鹼金屬陽離子性質的顯著影響。本研究比較了在 0.1 M NaOH 與LiOH中催化劑的表面結構與電化學行為，藉由 STM 與 HER 活性測量進行分析。Li⁺ 具備較高的水合能與強電場，對於表面結構影響小，整齊結構與白金所提供的活性位點，進而使 HER 動力學略有改善(Tafel 斜率為 72 mV/dec)。相比之下，Na⁺ 的水合能力較弱，導致表面結構較為無序，水分解效率較低，反映於較高的 Tafel 斜率(87 mV/dec)，值得注意的是，我們的結果顯Na⁺在高覆蓋度的鎳中由於水合鈉離子的吸附，形成較大的原子間距，這種獨特結構是過往文獻中沒有報導過的。本研究強調了鹼金屬陽離子在調變催化表面結構與活性方面的細緻作用機制，對於未來在鹼性產氫活性研究有良好的前景。;Developing efficient and cost-effective electrocatalysts for the hydrogen evolution reaction (HER) in alkaline media is essential for advancing sustainable hydrogen production. While platinum remains the benchmark catalyst for HER, its performance under alkaline conditions is limited due to sluggish water dissociation kinetics. Modifying Pt surfaces with 3d transition metals like nickel offers a promising route to enhance activity by creating bifunctional active sites. In this study, we systematically investigated the effect of nickel (Ni) loading on the HER activity of Pt(111) electrodes in alkaline media. Using a combination of electrochemical measurements and in situ scanning tunneling microscopy (STM), we examined Ni-modified Pt electrodes with varying Ni coverages (sample A, B, and C). Sample B, with 1.53 monolayers (ML) of Ni, exhibited the highest HER activity, requiring only -0.98 V overpotential to reach 10 mA/cm², compared to -1.05 V and -1.15 V for samples A (0.62 ML) and C (3.95 ML), respectively. High-resolution STM revealed that the active phase under HER-relevant potentials is metallic Ni, not Ni(OH)₂, as evidenced by moiré patterns characteristic of metallic Ni and distinct from those of Ni(OH)₂. These findings indicate that both the chemical state and coverage of the Ni modifier critically influence HER activity. The performance of Sample B rivals that of previously reported Pt/Ni alloy systems, highlighting the role of finely tuned interfacial structures in enhancing alkaline HER catalysis. The second part investigates the influence of different alkali metal cations on HER catalytic activity. During the hydrogen evolution reaction (HER) in alkaline media, the performance of Ni-modified Pt(111) electrodes is significantly affected by the nature of the alkali cations. This study compares the surface structures and electrochemical behaviors of the catalyst in 0.1 M NaOH and LiOH solutions using STM imaging and HER activity measurements. Li⁺, with its higher hydration energy and stronger electric field, has minimal impact on the surface structure, allowing for the retention of an ordered morphology and effective exposure of platinum active sites, which slightly enhances HER kinetics (Tafel slope: 72 mV/dec). In contrast, Na⁺, with its weaker hydration ability, leads to a more disordered surface and reduced water dissociation efficiency, reflected by a higher Tafel slope (87 mV/dec). Notably, our results reveal that in Ni-rich surfaces, the adsorption of hydrated Na⁺ induces a significant increase in interatomic spacing—a unique structural feature not previously reported in the literature. This study highlights the nuanced role of alkali cations in modulating catalytic surface structures and activity, offering promising insights for the future design of efficient HER systems in alkaline environments. |
