| 摘要: | 近年來由於嚴重的碳排放與工業汙染，發展替代性的再生能源受到相當重視。氫氣為一有潛力之再生能源，因其燃燒過程可產生高能量且無二氧化碳排放。氫氣可由電化學水分解產生 (hydrogen evolution reaction, HER)，然而需要有效的催化劑以最小過電位來提高HER的活性。貴金屬由於其極佳之催化活性被認為是酸性條件下的最佳材料，但其效能及穩定性仍有待提升並克服。
本研究分成兩個部分，第一部分透過結構設計，以油胺法合成氫化鈀 (palladium hydride, PdH) 並以X光繞射儀 (X-ray diffraction, XRD)證明其結構，氫化鈀與商用鈀和鉑觸媒相比在HER反應中具有最小的過電位 (27 mV (vs. RHE))，且有與鉑相同的塔佛斜率 (23 mV dec-1)，經過5000圈的穩定性測試，PdH展現最佳的穩定性，和最少的電化學活性面積(electrochemical active surface area, ECSA) 損失 (0.7 %)，穩定度測試後之過電位 (39 mV (vs. RHE)) 和塔佛斜率 (29 mV dec-1) 都最小，並具有最高的質量活性 (mass activity, MA) (144A gPd-1) 。
第二部分則是以油胺還原出不同比例的鈀銅觸媒 (Pd5Cu1, Pd3Cu1, Pd1Cu2及Pd1Cu9)，透過第二金屬銅添加以及氫化物的形成改善反應過程中氫原子的吸脫附能力並提升穩定性，利用X光繞射儀證明鈀銅合金化的形成及X光電子能譜儀 (X-ray photoelectron spectroscopy, XPS) 的結果證明適量的銅添加減少表面鈀的氧化，其中Pd5Cu1在表面具有最高的金屬態 (Pd0 84 % 和Cu0 69 %)。在HER反應中Pd5Cu1展現與PdH相近的過電位 (28mV (vs. RHE)) 和塔佛斜率 (23mV dec-1)，此外經過5000圈穩定性測試，Pd5Cu1展現最優異的效能和穩定性，呈現最小的過電位 (31 mV (vs. RHE)) 和塔佛斜率 (23 mV dec-1) 以及最高的ECSA (298 m2 g-1) 和 MA (406 A g Pd-1) 為PdH的1.3倍。本研究揭示了氫化鈀的形成可提升析氫反應之效能，並且透過適量的銅添加可經由電子修飾效應在析氫反應中具有更卓越的活性和穩定性。更重要的是，這項研究也為優化鈀銅觸媒的析氫反應提供新的見解，即結合結構設計和電子修飾，為開發高效和穩定的電催化劑之可行的方法。
;Due to severe carbon emission and industrial pollution in recent years, development of an alternative renewable energy has received much attention. Hydrogen is one of the most important renewable energy because its combustion process can produce high energy without carbon dioxide emissions. Hydrogen can be produced through electrochemical water splitting (hydrogen evolution reaction, HER) provides an effective way to store energy in the form of chemical energy. However, an effective catalyst is required to increase the activity of HER with a minimum overpotential. Due to the high catalytic activity, precious metals are considered to be the best materials under acidic conditions, but the performance and stability still needs to be improved and overcome
This study is divided into two parts. In the first part, through structural-design, palladium hydride (PdH) is synthesized by oleylamine method and its structure is proved by X-ray diffraction (XRD). When compared with commercial Pd/C and Pt/C, the HER performance of PdH has the lowest overpotnetial at 10 mA cm-2 (27 mV (vs. RHE)) and the same Tafel slope with commercial Pt/C (23 mV dec-1). After 5000 cycles of ADT test, PdH reveals the best HER stability, the smallest ECSA decay (0.7 %), the smallest overpotential (39 mV (vs. RHE)), the smallest Tafel slope (29 mV dec-1), and the highest MA (144A gPd-1) after ADT.
In the second part, PdxCuy (Pd5Cu1, Pd3Cu1, Pd1Cu2及Pd1Cu9) are prepared by oleylamine method. Through the addition of copper and the formation of hydride, the absorption and desorption of hydrogen atoms can be ameliorated so that the stability can be improved. XRD confirms the alloy formation and the X-ray photoelectron spectroscopy (XPS) results demonstrate that with proper Cu addition, surface Pd oxidation can be retarded. Among all samples, Pd5Cu1 reveals the highest metallic state on the surface (Pd0 84 % and Cu0 69 %). During HER, the current density at 10 mA cm-2 (28 mV (vs. RHE)) and Tafel slope (23 mV dec-1) of Pd5Cu1 is similar and identical to those of PdH. Besides, Pd5Cu1 shows the best performance and stability after 5000 cycles of ADT test, with the smallest overpotential at 10 mA cm-2 (31 mV (vs. RHE)), the smallest Tafel slope (23 mV dec-1), the highest ECSA (298 m2 g-1), and the highest MA (406 A g Pd-1) which is 1.3 times higher than that of PdH catalyst. This study reveals that the hydride formation can enhance the HER performance and with proper Cu addition, both HER activity and stability can be improved through electronic modification. More importantly, this work also provides new insight for the HER performance optimization of PdCu catalysts, in which the combination of structural design and electronic modification can offer a feasible approach to develop the highly effective and stable electrocatalysts. |
