花朵狀氧化鎳摻雜磷作為電催化材料之能源應用

Abstract

本論文旨在發展花朵狀氧化鎳摻雜磷作為兩能源領域(染料敏化太陽能電池（染敏電池）和產氫反應)中所使用的電觸媒。該論文被分成兩部分：氧化鎳摻雜磷的材料表徵分析（第3章）和氧化鎳摻雜磷的能源應用，其中又被分成兩個小部分：當作對電極使用於染敏電池中（第4章）和當作陰極使用於水分解（第5章）。 在第三章中，透過XPS分析證明了氧化鎳摻雜磷的化學鍵結及組成。另外，從SEM圖像中觀察到由奈米片推疊成花朵狀的形貌。在合成時以較高的前驅物濃度所生成之產物（氧化鎳摻雜磷-1 (P-NiO-1)和P-NiO-0.75），它們會在退火過程中長成不規則的顆粒以及不完整且具有孔洞的奈米片，而P-NiO-0.5、P-NiO-0.25和P-NiO-0.1則是生長成完整的花朵狀結構。氧化鎳摻雜磷的花朵結構之直徑大小是依照前驅物濃度的高低而有次序地長成。此外，氧化鎳摻雜磷滴在不同的基材(碳布和多孔鎳片)上也會導致且影響氧化鎳摻雜磷的形狀外觀。還有，氧化鎳摻雜磷在碳布上和在多孔鎳片上，會由於它們本身具有弧度的表面而容易將小顆的氧化鎳摻雜磷聚集在某一個地方。 在第四章中，把氧化鎳摻雜磷做成薄膜當作對電極，應用於染敏電池上。花朵狀氧化鎳基本上是作為基體，其形狀可以提供二維傳遞途徑而促進電子傳導。而磷摻雜是為了在氧化鎳的表面上提供更多活性點，使得加速催化三碘化物離子與碘離子之間的反應，而提高其材料的催化能力。氧化鎳摻雜磷透過不同前驅物濃度來控制其生成，使得氧化鎳摻雜磷具有不同的形貌特徵。P-NiO-1因而呈現碎屑聚集，而P-NiO-0.75則是由不完整的奈米片推疊成花朵狀形貌。另外，P-NiO-0.5、P-NiO-0.25和P-NiO-0.1是以完整的花朵狀形態作為催化電極。具有P-NiO-0.5之對電極的染敏電池具有9.05%的光電轉換效率，比起白金對電極的染敏電池(光電轉換效率:8.51%)，有著更加優秀的表現。即使在背面照明和昏暗的光線條件下，它的表現都有比白金對電極的染敏電池還要更好。因此，氧化鎳摻雜磷的對電極具有取代昂貴的白金對電極的潛力。 在第五章中，是把氧化鎳摻雜磷電極拿去做水分解中的產氫反應。在所有的基板(FTO，碳布和多孔鎳片)上，氧化鎳摻雜磷皆以每平方公分面積之0.3毫克的負載量，測得最低過電位值。多孔鎳片的電催化能力是三種基板中最好的，所以氧化鎳摻雜磷在多孔鎳片上之電極得到最小值為230 mV（vs. RHE），以及最小的塔弗斜率為每電流為85 mV。此外，搭配第四章的染敏電池所組裝成的光電水分解系統，獲得良好的太陽能轉化氫氣之效率（5.42%）。因此，低成本的氧化鎳摻雜磷在多孔鎳片上作為電極，在水分解中是具有吸引力的產氫電極替代品

This dissertation aimed to develop the flower-like phosphorus-doped nickel oxide (P-NiO) as the electrocatalyst utilized in the two energy fields, dye-sensitized solar cells (DSSCs) and hydrogen evolution reaction (HER). The dissertation is divided into two part: the material characterizations of P-NiO (Chapter 3) and the energy applications of P-NiO, which are separated two section: the counter electrode (CE) for DSSCs (Chapter 4) and the cathode for water splitting (Chapter 5). In the case of the material characterizations of P-NiO, the chemical composition was proved via XPS analysis. The flower-like nanosheets morphology was observed from SEM images. The P-NiO was shattered to irregular particles and porous nanosheets after annealing process in the higher precursor concentrations (P-NiO-1 and P-NiO-0.75), while the P-NiO-0.5, P-NiO-0.25 and P-NiO-0.1 formed a complete flower-like morphology. The flower-like structure of P-NiO shrank sequential diameters according to the precursor concentrations. Furthermore, P-NiO dropped in the different substrates, carbon cloth (CC) and nickel foam (NF), also led to the variety of appearance. P-NiO-CC and P-NiO-NF easily clustered small units together because of their curved structures. In the case of P-NiO was designed for CEs in the DSSCs, the flower-like nickel oxide essentially serves as the matrix for the CE, which is expected to promote 2-dimensional electron transport pathway. The phosphorus is intended to improve the catalytic ability by creating more active sites in the NiO for the catalysis of triiodide ions (I3-) to iodide ions (I-) on the surface of the CE. The P-NiO was controlled by a sequencing of precursor concentration, which made the P-NiO possess different features. The debris aggregation occurred in the P-NiO-1, while it led to the incomplete flower-like nanosheets of the P-NiO-0.75. The complete flower-like morphology could be observed in the P-NiO-0.5, P-NiO-0.25 and P-NiO-0.1 catalytic electrodes. The DSSCs with P-NiO-0.5 CE has exhibited a power conversion efficiency (η) of 9.05%, which is better than that of the DSSC using a Pt CE (η = 8.51%); it also performs better than that with the Pt CE, even under rear illumination and dim light conditions. The results indicate the promising potential of P-NiO CE to replace the expensive Pt CE. In the case of P-NiO electrode of HER in water splitting, the lowest overpotential (η) all under the P-NiO loading of 0.3 mg cm-2 in the FTO, CC and NF substrates. The electrocatalytic ability of NF is the best among these substrates; thus, P-NiO-NF electrode obtains the smallest η of 230 mV (vs. RHE) and the smallest Tafel slope of 85 mV dec-1. In addition, the photoelectrochemical water splitting built with previous work (DSSC) obtained a good solar-to-hydrogen (ηSTH) of 5.42%. The low-cost P-NiO-NF electrode of HER is an attractive replacement for water splitting.