Wanhua Wang

Date of Award

Fall 2023

Document Type

Open Access Dissertation

Department

Mechanical Engineering

First Advisor

Fanglin Chen

Abstract

There has been an increasing interest in clean and renewable energy generation for highlighted energy and environmental concerns. Solid oxide cell (SOC) has been considered as one of the most promising technologies since it can convert chemical energy to electricity in the fuel cell mode and store electricity to chemicals in the electrolysis mode. The present work is devoted to materials development in both oxygen ion conducting SOC (O-SOC) and proton conducting SOC (P-SOC). The objective of this study is to design and optimize the electrolyte and electrode materials for SOC in energy conversion and energy storage applications. One major focus of this work is developing cathode materials for direct CO2 electrolysis via solid oxide electrolysis cells (SOECs). In addition, the potential issues of proton-conducting electrolytes during the preparation process of the single cells are also revealed. Direct CO2 electrolysis using SOECs holds the promise to efficiently convert carbon dioxide to carbon monoxide and oxygen. Cathodes with desirable catalytic activity and chemical stability play a critical role in the development of direct CO2-SOECs. Sr2Fe1.5Mo0.5O6-δ has exhibited promises for direct CO2-SOECs due to its reliability and stability but suffers from insufficient activity for CO2 reduction reaction (CO2RR). In the second chapter, we report interface engineering of nanosized Pr6O11 on the Sr1.9Fe1.5Mo0.5O6-δ (SFM) cathode obtained through infiltration to promote the CO2RR performance for direct CO2-SOECs. The effect of Pr6O11 loading on the performance of CO2RR has been systematically investigated. At 800°C, the current density of the Pr6O11 infiltrated SFM cathode with an optimum Pr6O11 loading of 14.8wt.% reaches 1.61 A/cm2 at 1.5V, more than double that of the SFM cathode (0.76 A/cm2) at the same operating conditions. In addition, the polarization resistance of SFM cathode has significantly decreased with the addition of Pr6O11. These results demonstrate that the formation of Pr6O11 through infiltration is a promising approach for increasing CO2RR activity. Furthermore, in the third chapter, we designed novel dual-phase material (Pr0.4Ca0.6)xFe0.8Ni0.2O3-δ (PCFN, x=1, 0.95, and 0.9) as the cathode for a pure CO2-SOEC by A-site deficiency methods. Among all these compositions, (Pr0.4Ca0.6)0.95Fe0.8Ni0.2O3-δ (PCFN95) exhibited the lowest polarization resistance of 0.458 Ω cm2 at open circuit voltage and 800℃. The application of PCFN95 as the cathode in a single cell yields an impressive electrolysis current density of 1.76 A cm-2 at 1.5 V and 800℃, which is 76% higher than that of single cells with non-deficient Pr0.4Ca0.6Fe0.8Ni0.2O3-δ (PCFN100) cathode. The effects of A-site deficiency on materials’ phase structure and physicochemical properties are also systematically investigated. Such an enhancement in electrochemical performance is attributed to the promotion of effective CO2 adsorption, as well as the improved electrode kinetics resulting from A-site deficiency. The proton-conducting electrolyte is one of the dominant factors to dictate performance, efficiency, and durability of P-SOCs. The commonly used proton-conducting electrolyte compositions are based on Ba(Ce,Zr)O3 perovskite with Y or/and Yb dopants for a tradeoff of conductivity, chemical stability, and ionic transference number. In the fourth chapter, the phenomenon of surface and grain-boundary precipitation during the aging of protonic ceramics has been studied to understand the effects on conductivity and relevant mechanisms. Systematical studies have been performed to understand the impact of NiO introduction and Ba volatilization on the Y single-doping and Y/Yb co-doping BaZr(Ce)O3-based electrolyte materials. Additionally, the underlying mechanism for element surface precipitation has been proposed.

Rights

© 2024, Wanhua Wang

Download

Share

COinS