| 摘要: | 迄今為止，Pt和Pt基合金催化劑由於其優異的效能和穩定性，已被廣泛應用於全pH值的電化學反應。但是，對於乙醇氧化反應(ethanol oxidation reaction, EOR)而言，由於Pt較難打斷C-C鍵，因此無法實現完全的12個電子轉移。此外，儘管事實證明Pt具有很高的析氫反應(hydrogen evolution reaction, HER)效能，但其昂貴和稀缺性使Pt無法大規模被使用。因此為了在成本和效能之間取得平衡，設計低Pt含量且高效EOR和HER的觸媒為燃料電池發展的重要議題。
本研究透過簡便的沉澱沉積法製備超低Pt負載量的Pt、Rh、PtRh2 和PtRh2Ni0.3奈米團簇(nanocluster, NCs)。經由高解析穿透式電子顯微鏡(high-resolution transmission electron microscopy, HRTEM)證實NCs的平均粒徑約為1.5±0.5奈米。並藉由X光吸收光譜(X-ray absorption spectroscopy, XAS)結果表明添加銠/鎳(Rh/Ni)會改變Pt的電子結構並提高催化活性。
對於EOR效能，相較於Pt和PtRh2-NCs，PtRh2Ni0.3-NCs顯示出在全pH值的環境下之最佳催化效能。值得注意的是，在所有催化劑中，PtRh2Ni0.3-NCs在電位為0.6V時擁有最高的電流密度(I0.6)，其在0.5 M 硫酸和1.0 M氫氧化鉀電解液中，分別為181.5和3295.7 A/g，約為Pt-NCs的2.8和6.1倍(64.3和536.0 A/g)。經穩定度測試後，在0.5 M 硫酸和1.0 M氫氧化鉀電解液中，相較於Pt-NCs(3.5和11.5 A/g)，PtRh2Ni0.3-NCs的I0.6仍然高達33.3和227.4 A/g。
另一方面，對於HER效能，在酸性和鹼性電解液中，PtRh2Ni0.3-NC具有最小的過電位(28和29 mV)、出色的塔佛斜率(30和73 mV dec-1)和最高的質量活性(mass activity, MA)(4489和1663 A/gPt or Rh)。經長時間的CA測試後，在所有催化劑中，PtRh2Ni0.3-NCs在酸性和鹼性電解液中仍具有最高的MA值分別為3513和1366 A/gPt or Rh。本研究揭示了Rh/Ni的添加會改變Pt的電子結構，並提高EOR和HER的效能和穩定度。更重要的是，這項研究提供了一種有潛力的方法，可通過精確控制Pt的添加量和透過添加Rh/Ni來提高Pt-NCs的效能，並增加Pt的利用率和改善在全pH值條件下EOR和HER的性能。
關鍵詞: 奈米團簇、沉澱沉積、乙醇氧化反應、析氫反應、鉑銠觸媒、鉑銠鎳觸媒
;Up to date, Pt and Pt-based alloy catalysts have been widely used for all electrochemical reactions, owing to its outstanding activity and excellent stability under all pH-universal condition. However, for the application as ethanol oxidation reaction (EOR) catalysts, the total 12 electron transfer is not attainable on Pt due to the difficulty of the C-C bond cleavage. Moreover, despite the fact that Pt shows high hydrogen evolution reaction (HER) performance, the high cost and scare supply make it far away from the large-scale application. In order to have a balance between cost and performance, the design of low Pt content and highly efficient electrocatalyst EOR and HER is important tasks for the development of fuel cells.
In this study, Pt, Rh, PtRh2 and PtRh2Ni0.3 nanocluster (NCs) with ultra-low Pt loading were prepared by a facile deposition-precipitation method. High-resolution transmission electron microscopy (HRTEM) confirms that NCs with an average particle size of about 1.5±0.5nm. The X-ray absorption spectroscopy (XAS) result demonstrates that the addition of Rh/Ni will change the electronic structure of Pt and improve catalytic activity.
For the EOR performance, PtRh2Ni0.3-NCs show clearly superior catalytic performance under the pH-universal environment to Pt and PtRh2 NCs. It is worth noting that among all catalyst, PtRh2Ni0.3-NCs display the highest I0.6 of 181.5 and 3295.7 A/g, which is ~2.8 and 6.1 folds higher than that of Pt- NCs (64.3 and 536.0 A/g) in the 0.5 M H2SO4 and 1.0 M KOH electrolyte, respectively. After the durability test, I0.6 of PtRh2Ni0.3-NCs in 0.5 M H2SO4 and 1.0 M KOH is still as high as 33.3 and 227.4 A/g, which is higher than that of Pt-NCs (3.5 and 11.5 A/g).
On the other side, for the HER performance, PtRh2Ni0.3-NCs have the smallest overpotential at 10 mA cm-2 (28 and 29 mV), outstanding Tafel slope (30 and 73 mV dec-1) and the highest mass activity (MA) (4489 and 1663 A/gPt or Rh) in acidic and alkaline electrolyte, respectively. After long-term CA test, among all catalysts, PtRh2Ni0.3-NCs still has the highest MA of 3513 and 1366 A/gPt or Rh in acidic and alkaline electrolyte. This study reveals that the addition of Rh/ Ni will change the electronic structure of Pt and enhance the EOR and HER performance and stability, which is proved by XAS. More importantly, this study provides a promising method to enhance the Pt utilization and improve EOR and HER performance under the pH-universal conditions for Pt-NCs by precisely controlling the Pt loading and adding Rh and Ni.
Keywords: nanoclusters (NCs), deposition-precipitation method (DP), ethanol oxidation reaction (EOR), hydrogen evolution reaction (HER), PtRh, PtRhNi |
