具二維 Ag–S 結構的新型金屬有機硫化物應用於染料敏化太陽能電池之電催化觸媒

Abstract

本研究成功以低溫水熱法合成兩種新穎的金屬–有機硫族化合物奈米晶體，分別為 Ag-BDT（BDT = 1,4-苯二硫醇；pKa = 5.92）與 Ag-DMTD（DMTD = 2,5-二硫基-1,3,4-噻二唑；pKa = 5.77）。其中Ag-BDT的晶體結構預期由準六方排列的網狀結構所構成，形成二維的Ag–S平面。該結構中Ag1中心呈三角平面構型，與三個硫醇配體配位；而硫醇基則以擬四面體構型，與三個銀原子配位。每一層Ag–S平面之間透過 BDT 串聯，形成堆疊式的層狀結構。藉由配基輔助的原位合成法，可將片狀的 Ag-BDT 與棒狀的 Ag-DMTD 奈米粒子均勻修飾於導電碳布表面（CC）。作為染料敏化太陽能電池中的陰極時，這兩種 Ag-MOCs 均可作為電催化劑，有效促進 [Cu(dmp)2]1+/2+（其中 dmp = 2,9-二甲基-1,10-菲囉啉；新銅試劑）氧化–還原對的還原反應。相較於傳統貴金屬鉑電極（CC/Pt；Jpc = 2.61 mA cm-2；Esep = 369 mV），CC/Ag-BDT 與 CC/Ag-DMTD 電極展現更高的陰極峰電流密度（Jpc 分別為 4.11 與 4.21 mA cm-2）以及更低的峰對峰電位差（Esep 分別為 361 與 356 mV），顯示其具備優異的電化學活性。在類似的電催化活性下，搭載 CC/Ag-BDT陰極的染敏電池，其光電轉換效率可達 7.45%，優於搭載 CC/Ag-DMTD陰極的染敏電池（6.75%）。此結果歸因於 BDT 配體具較高的 pKa 值，能與金屬中心形成較強的共價鍵結，有助於提升薄膜的覆蓋性與穩定性，並有效抑制電化學掃描過程中的薄膜脫落。此外Ag-BDT 與 Ag-DMTD 電極皆展現優於傳統鉑與銀電極的電化學穩定性，顯示其在多元電化學應用中具有良好的發展潛力。Two novel metal-organic chalcogenide (MOC) nanocrystals, i.e., Ag-BDT (BDT= 1,4-benzenedithiol; pKa = 5.92) and Ag-DMTD (DMTD= 2,5-dimercapto-1,3,4-thiadiazole; pKa = 5.77), were successfully synthesized by a low-temperature hydrothermal process. The proposed crystal structure of Ag-BDT is constructed by a quasi-hexagonal network of two-dimensional (2D) Ag-S plane. The trigonal-planar Ag1 center is coordinated by three thiolates, and the pseudo-tetrahedral thiolate is coordinated by three Ag atoms. Each Ag-S layer is linked to another by the BDT ligands. Via a ligand-assisted bottom-up method, both sheet-like Ag-BDT and rod-like Ag-DMTD nanoparticles were well covered on the conducting surface of carbon cloth (CC). As a cathode in dye-sensitized solar cells (DSSCs), each type of Ag-MOC functioned as an electrocatalyst to trigger the reduction of CuII-neocuproine (denoted as [Cu(dmp)2]1+/2+). The higher cathodic peak current density (Jpc) and the lower peak-to-peak separation (Esep) values are obtained by both CC/Ag-BDT (Jpc = 4.11 mA cm–2; Esep = 361 mV) and CC/Ag-DMTD (Jpc = 4.21 mA cm–2; Esep = 356 mV), in comparison to the noble CC/Pt electrode (Jpc = 2.61 mA cm–2; Esep = 369 mV). With the comparable electrochemical activity, the DSSC with the cathode of CC/Ag-BDT reached a better solar-to-electricity conversion efficiency of 7.45% than the cell with CC/Ag-DMTD (6.75%). It is attributed to the stronger covalent-bond is established by BDT with the higher pKa, leading to the better film coverage and suppressing the film detachment during electrochemical scanning. Moreover, both Ag-MOCs electrodes provides a better electrochemical stability than the noble Pt and Ag metals, indicating their robust potentials in various electrochemical applications.