以理論計算探討甲酸在鈀金屬團簇上電氧化反應及脫氫步驟對反應選擇性之影響

Formic Acid Electrooxidation on Graphene Supported Pd Cluster and the Selectivity of Reaction Pathway by the Influence of Hydrogen Ratio

吳亘曜(Shiuan-Yau Wu) ； 陳欣聰(Hsin-Tsung Chen)

《化學》 78卷2期 (2020/06) Pp. 127-134

https://doi.org/10.6623/chem.202006_78(2).007

摘要

本研究利用理論計算來探討以石墨烯支撐的鈀金屬團簇對於甲酸電催化形成二氧化碳的反應機構。在電催化的環境之下，鈀金屬團簇會佈滿吸附態的氫原子，而逐步提升外部電壓會讓表面的H*透過Volmer step（H*→*+H^++e^-）釋放，當外在電壓為0.41V的時候會將表面所有H*釋放，然在團簇上的脫氫反應是階段性的，而非到達一定的電位下全部釋放，因此利用這樣的特性在低電位的情況之下脫氫反應及甲酸氧化反應會同時的發生，而團簇在不同的含氫數量下，產生HCOO*及COOH*中間體的起始電位逐漸的改變。透過逐一地去計算不同含氫的鈀金屬團簇對於甲酸的氧化脫氫反應，我們發現在0.02V的情況下HCOO*路徑會在飽和的10H鈀金屬團簇開始進行，一直提升電位至0.23V後，COOH*中間體的路徑才會開始發生。而COOH*中間體很容易分解成CO*+OH*或脫水形成CO*+H_2O。一旦形成CO*中間體則需要一直提升至0.67V才能將CO*移除。因此，如果要提升HCOO*的選擇性避免COOH*的生成，我們需要保留部分H*在表面上讓G_(HCOO*)的能量落在最理想的區間。而透過計算的結果我們可以得到在0.02到0.22之間主要以HCOO*產物為主，同時避免COOH*中間體的生成。

關鍵字

金屬團簇 ； 甲酸氧化 ； 選擇性

並列摘要

With the thermotical calculation and the computational hydrogen electrode (CHE) model, we investigated the formic acid oxidation on graphene supported nH-Pd_(10) and clean Pd_(10) clusters. Under the electrochemical conditions, the Pd cluster would be hydrogenation to Pd hydride cluster without applied potential. With the gradually enhance of applied, the hydrogen desorption via Volmer step (H* → * + H^+ + e^-) and completely release at applied potential of 0.41 V. However, the H release is a gradual process and could H* ratio could be controlled by the applied potential. While theformic acid electrooxidation would proceed simultaneously and the selectivity of reaction pathway could be affected of the H-ratio for different nH-Pd_(10)-grahene. According to our results, the on-set potential of formate (HCOO*) path is 0.02 V on 10H-Pd_(10)-grahene, and carboxyl path would be proceeded at the on-set potential of 0.23 V on 6H-Pd_(10)-grahene. Therefore, controlling the applied potential between 0.02 to 0.22 V could enhance the selectivity of HCOO* path and avoid the COOH* formation.

並列關鍵字

Formic acid electrooxidation ； Pd cluster ； Reaction selectivity