摘要

Ni-YSZ 陶金陽極微觀結構是影響固態氧化物燃料電池發
電效率的關鍵因素。本實驗在探討由化合物硝酸鎳、硝酸鈰以二甲基亞碸為溶劑，以適當的燒結溫度與持溫時間，亦可以製備奈米氧化鎳、氧化鈰。期望藉由奈米顆粒來促進Ni-YSZ 陶金陽極孔隙率與三相點。我們以YSZ纖維製備陽極，由樹枝狀YSZ 纖維搭配樹葉狀奈米鎳顆粒，先研究固態氧化物燃料電池Ni 含浸YSZ奈米纖維 陽極之製備與特性量測，並探討不同硝酸鎳溶液濃度3M、5M、7M、9M對於奈米鎳YSZ纖維陽極微觀結構與電池效率的影響。實驗研究結果顯示，隨著硝酸鎳濃度的增加，鎳顆粒披覆於YSZ纖維的厚度增加，卻未能促進三相點的增加，反被還原後散落的鎳顆粒減少陽極的孔隙，造成極化電阻的增加，電化學反應下降。由於其在700oK-1000oK易還原成Ce2O3在結晶相中仍維持立方C相，且同時產生為數眾多的氧空缺，使CeO2 在氧化還原反應中對氧離子發揮儲存與釋放的功能。在固態氧化物燃料電池陶金陽極中加入氧化鈰可以分散鎳的聚集降低極化電阻增進電池效率。本實驗探討奈米CeO2顆粒對於Ni-8YSZ纖維陽極催化能力的影響。實驗結果顯示，隨著氧化鈰含量的增加，8YSZ 纖維與鎳、氧化鈰顆粒更緊密的接合，因此產生更多的三相點，增進電化學反應區，電極極化電阻逐漸減少，增加交換電流密度，半電池效率增加。於800oC時，測得的功率密度是測得的功率密度在未添加奈米CeO2 之奈米Ni-YSZ纖維陽極是12.3mW/cm2。添加5wt%奈米CeO2 之奈米Ni-YSZ纖維陽極是28.8mW/cm2。添加10wt%奈米CeO2 之奈米Ni-YSZ纖維陽極是32.3mW/cm2。

Abstract

The micro structure of Ni-YSZ anode cermet is the most important feature which affect the SOFC property. We fabricate anode cermet by the continuous 8YSZ fiber and nano nickel particles to improve the porosity and triple phase boundary of anode. Combined 8YSZ fiber which was developed by older schoolmate and nano particles that identified by me. “ Fabrication and characterization of SOFC anode with Ni-YSZ fiber by impregnation method.”was published by older schoolmate on July 2007. Firstly, We fabricate the nano nickel particles and nano Ceria particles by Dimethyl sulfoxide solution which mixed with Nickel nitrate and Cerium nitrate and sintered on suitable temperature 1000oC and holding time 60mins. Due to the weight ratio percentage of Ni-YSZ was taken the wrong way to examine. Therefore I proposed the stoi-chemistry to calculate the weight ratio percentage of Ni-YSZ. In addition, We analyze the affection of micro structure and performance of SOFC by the concentration of nickel nitrate.

We learned by experiment with concentration of 3M、5M、7M、9M nickel nitrate (expressed by N3M、N5M、N7M、N9M ). The 8YSZ fiber was covered by layers nickel particles. As the thickness was added as the concentration of nickel nitrate increased. It does not improve TPB. In contrary, the over fitted nano particles blocked the gas tunnels to increase the over potential, polarization resistances and decrease the electrochemical reactions. The 3M nickel nitrate is the best concentration at all.

Ceria is one of the mixed conductor which consist electronic conductivity and ionic conductivity. It is affected with Oxygen partial pressure and doping substrate. The conductivities of ceria consist of electronic、electro-holes and oxygen vacancy. Ceria act as n-type semi-conductor under the high temperature and low oxygen partial pressure. The electronic conductivity of ceria is proportion to the reduction of ceria. Oxygen vacancy compensate the ion vacancy which is formed by Ce3+ instead of Ce4+ co-valent vacancy. The electronic mobility rate is several order of ionic mobility. In addition, Ceria act an important role in catalyst. It is remain C-phase from CeO2 reduce to Ce2O3 during the period of 700oC-1000oC. It is created oxygen vacancy in the crystal lattice. Therefore, the reduction and re-oxidation caused by oxygen release and storage results in a formation of oxygen vacancies on the ceria surface.

Ceria can disperse the nickel particles to decrease polarization resistances to improve the performance of solid oxide fuel cells. Dipping YSZ fiber in nickel nitrate and ceria nitrate. Adding 5wt% & 10wt% ceria to 3M nickel nitrate for experiment. It increase more triple phase boundary and reduce polarization to improve electrochemical reactions 、exchange current and performance as ceria increasing as 8YSZ fiber is tighten with nickel particle and ceria particles. In addition, due to the CeO2 create the function of store and release oxygen ions improve electrochemical reaction and performance during the period of CeO2 reduce to Ce2O3.It is increasing obviously that working temperature up to 800oC. We got the performances are 12.3mW/cm2, 28.8Mw/cm2 and 32.3mW/cm2 respected to N3M, N3MC5, and N3MC10.

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