高温共电解技术利用可再生能源或核能，通过高温固体氧化物电解池将H2O/CO2共电解生成H2/CO，并进一步合成各种清洁液态碳氢燃料，是一种很有前景的清洁燃料生产和CO2减排新技术。论文针对高温共电解H2O/CO2制备H2/CO的关键环节，构建了SOEC共电解运行和测试系统，分析了NiO-YSZ支撑电解池的共电解特性、产物合成气成分和电极极化规律，初步研究了高温固体氧化物电解池共电解H2O/CO2制备合成燃料工艺的可行性，主要研究成果如下：1. 设计并建立了单体SOEC共电解测试系统，成功将该系统用于SOEC高温共电解实验研究。共电解测试系统具有多功能性，不仅能满足SOEC单体电解池共电解制合成气的性能测试要求，还能进行电解池电极材料的相关测试。2. 建立了共电解具体的研究方法和测试手段，并确立了共电解体系能斯特电压和开路电压的关系；摸索出色谱测试的工作参数并实现了色谱对共电解产物的理想分离及测量。3. 初步确定850℃为本论文的共电解运行温度，SOEC共电解性能与高温电解水蒸气相当，但要远远好于纯CO2的高温电解性能。初步推断：共电解过程发生的电解过程主要是水蒸气电解，而CO主要通过水汽可逆转化生成，具体的反应机理还需要进一步研究说明。4. 确定恒流共电解更适合共电解的研究，电流密度对SOEC共电解性能稳定性的影响较大。反应过程中的极化阻抗随电流密度的增大而不断增大，较低电流密度（<400mA/cm2）下，电极的极化阻抗主要体现为电极活化阻抗；当电解电流增大时，极化阻抗渐渐由扩散过程占主导地位；当电流密度增大到600mA/cm2时，阻抗谱中扩散过程（低频部分）呈现发散状。所以在较大工作电流下保持SOEC较高的共电解性能也是目前对新型SOEC的更高要求。5. 在无电流通过时，由于在高温下存在水汽可逆反应，也检测出CO的生成；随着电解电流密度增大，反应物中CO2的浓度持续下降，而H2和CO都在稳定增加，但总体来讲电解电流的利用率还较低，所以共电解产物浓度随电解电流的变化还不是很显著，主要是由于SOEC自身性能的局限性，所以需要开发高性能的SOEC，提高电解电流利用率，进而提高共电解的产率。
The technology of clean fuel production through co-electrolysis of H2O and CO2 simultaneously at high temperature (High temperature co-electrolysis, HTCE), is a promising method for large scale clean fuels production and a new technology for the reduction of CO2 emission. It makes full use of renewable energy or nuclear energy to split H2O and CO2 in SOEC (Solid Oxide Electrolysis Cell) to produce synthesis gas (H2+CO), which are raw materials of liquid synthetic hydrocarbon fuels for the current transport infrastructure. In this work, the research focused on the key issues associated with high temperature coelectrolysis of H2O and CO2 for the preparation of H2/CO. A high temperature electrochemical testing system had been self-designed and self-developed in the lab. The electrochemical property, the product compositions and the polarization principles of NiO/YSZ supported SOEC single button cells were analyzed. Also, the technological feasibility of preparing sythetic fuel process through high temperature coelectrolysis of H2O and CO2 was investigated, which is the solid foundation for the further research on HTCE and industrial application of massive clean fuels production. The main results of this study are as follows:1. The high temperature co-electrolysis testing systems of single button cells had been successfully developed. The system was muti-functional, which could not only meet the testing requirements of electrochemical property of the cells, but also be used to analysize the performance of the electrode materails.2. The specific research and testing methods were establised, including the relationship with the open-circuit voltage. The detailed parameters for the set of chromatographic test were explored, which could realize the effective separation of the products for co-electrolysis.3. 850℃ was determined as the operating temperature of coelectrolysis in this work. The initial co-electrolysis performance was similar to that of HTSE (High temperature steam electrolysis), and both of them were much better than the performance of pure CO2 electrolysis by SOEC. It could be preliminarily concluded that steam electrolysis maybe the the main process of co-electrolysis H2O/CO2, and the CO production mainly come from water vapor reversible reaction. The detailed reaction mechanism needs further study.4. Constant-current electrolysis was more suitable for the research of HTCE by SOEC than the constant-voltage electrolysis. At lower current density (<400mA/cm2), the electrode polarization resistance was mainly from electrode activation impedance. As the current increases, the diffusion processes dominated the electrode polarization impedances gradually. Especially, when the current density reaches 600mA/cm2, the diffusion process spectroscopy (low frequency of EIS) will present divergent patterns. Therefore, how to maintain the SOECs with higher performance under larger operating current is the new issue for the development of SOEC currently.5. CO could bedetected from the production even in the absence of electrolysis current due to the presence of water vapor reversible reaction at high temperature. As the electrolysis current density increased, the CO2 concentration continued to decline, while both of H2 and CO increased steadily. But the electrolytic production rate was relatively low due to the unfavorable performance of SOECs. Therefore, it is of great importance to develop high performance SOECs and the yield of the production will improve with the promotion of the electrolysis current.
