应用固体氧化物电解池（SOEC）将CO2和H2O转化为合成气和烃类燃料，可望成为同时实现CO2资源化利用和可再生能源电力储存的有效途径。明确CO2/H2O共电解反应机理和性能，对SOEC电极开发、性能优化、产物调控以及系统集成等具有重要意义。本文采用图案电极、多孔电极和管式单元三种不同类型的SOEC，系统地研究了SOEC CO2/H2O共电解机理及性能规律。 首先，本文开发了Ni-单晶YSZ图案电极，实现反应活性面积的定量调控，获得了本征电化学动力学数据。图案电极SOEC电化学性能均与温度、极化电压和载气分压呈正相关。电解CO2的速率控制步骤为O(Ni)+(YSZ)→(Ni)+O2-(YSZ)，极化电压较小时还包括O(Ni)的表面扩散过程。电解H2O的速率控制步骤为H2O(YSZ)+(Ni)+e-→H(Ni)+OH-(YSZ)，极化电压较小时还包括H2O(YSZ)的表面扩散过程。图案电极电解H2O的速率约是电解CO2的12-15倍，因此CO2/H2O共电解电化学性能与电解H2O十分接近。通过原位检测Ni条纹表面积碳程度和结构的空间分布特性，成功鉴别了电化学积碳/消耗碳CO(Ni)+(YSZ)+2e-?C(Ni)+O2-(YSZ)反应机理。 其次，通过多孔电极SOEC CO2/H2O共电解实验，掌握了操作条件参数对电化学性能的影响规律，获得了共电解制取合成气和甲烷特性。增大电压可显著提高CH4浓度，650℃可提高9-12倍。C(s)+2H2→CH4是甲烷生成的反应路径之一。综合考虑非均相基元反应、电化学反应、电极微观几何结构、质量传递和电荷传递过程，建立了一维SOEC基元反应模型，分析了燃料极和氧气极反应和传递过程的耦合特性。提出非均相化学反应和电化学反应分区概念，统一了实验现象分歧。两种反应区域大小分别受质量传递通量D?c和电荷传递通量σ?V控制。由于氧气极SOEC模式的O2传递和电化学反应方向与SOFC模式相反，SOEC的浓差极化可为SOFC的1/7。 最后，应用管式SOEC单元实现了CO2/H2O共电解制取合成气和甲烷的稳定运行，单管共电解功率可大于4.15W，功率密度可大于2817W/m2，550℃电解产物中CH4浓度可达10%。在实验基础上，建立了二维轴对称管式SOEC稳态模型，分析了管内流动和传热过程对性能的影响规律。
The electrochemical conversion of CO2 and H2O to fuel in solid oxide electrolysis cells (SOEC) provides a pathway for renewable electricity storage while utilizing greenhouse gas CO2 at the same time. In order to optimize the SOEC performance, it is crucial to investigate the kinetic mechanisms and characteristics of CO2/H2O co-electrolysis. This dissertation presented systematic researches on patterned, porous and tubular SOEC in different scales. Firstly, button cells with patterned Ni electrode and single crystal YSZ electrolyte were fabricated to investigate the electrochemical performance of H2O electrolysis, CO2 electrolysis and co-electrolysis. Patterned electrode is an effective approach to avoid complexities associated with porous electrodes and obtain the intrinsic kinetics of electrochemical reactions due to the well-defined length of TPB. The electrochemistry was positively related to temperature, polarization voltage and gas partial pressure. The possible rate-controlling step was O(Ni)+(YSZ)→(Ni)+O2-(YSZ) for CO2 electrolysis or H2O(YSZ)+(Ni)+e-→H(Ni)+OH-(YSZ) for H2O electrolysis. The surface diffusion of O(Ni) or H2O(YSZ) also could respectively controls the reaction rate for CO2 or H2O electrolysis when the polarization voltage was not high. The electrochemical reaction rate of patterned Ni electrode for H2O electrolysis was 12-15 times higher than that for CO2 electrolysis, thus the reaction rate of co-electrolysis was very close to that of H2O electrolysis. The distribution and structural feature of carbon deposition on patterned Ni for both SOEC and SOFC were observed to clarify the electrochemical reaction CO(Ni)+(YSZ)+2e-?C(Ni)+ O2-(YSZ) at TPB. Secondly, the electrochemical performance and product compositions of porous button SOEC were studied. CH4 could be detected in the gas products and significantly promoted more than 9-12 times by electricity. C(s+2H2→CH4 was proposed as one of reaction pathways for CH4 generation of co-electrolysis. A one-dimensional elementary reaction model of SOEC was developed, coupled with heterogeneous elementary reactions, electrochemical reactions, electrode microstructure, mass transport and charge transport. The model was utilized to predict the effect of operating parameter and electrode microstructure on co-electrolysis performance, and analyze the coupling properties of reaction and transfer in electrode. The concept of main zones for heterogeneous chemical reaction and electrochemical reaction was proposed and successfully explained the different experimental phenomena. The mass transfer flux D?c determined the heterogeneous chemical reaction while the charge transfer flux σ?V determined the electrochemical reaction. Due to the opposite directions of O2 diffusion and electrochemical reaction in the oxygen electrode, the concentration polarization of SOFC could be 7 times higher than SOEC. At last, a tubular SOEC was built to directly convert the CO2 and H2O to syngas and CH4. The power and power density of single tube could achieve 4.15 W and 2817 W/m2, the CH4 yield could reach 10% at 550oC. A two-dimensional tubular SOEC model was developed to study the effects of fluid and heat transfer on performance.
