Water splitting with solid oxide electrolysis cells (SOECs) has gained increasing attention as an efficient, affordable, and sustainable technology for hydrogen production. Since electricity represents the bulk of projected hydrogen cost for operating SOECs, enhancing the utilization efficiency of electricity (electrochemical energy efficiency) is critical to reach the cost-effective milestone for cell/electrolyzer development. In this study, we present a SOEC design with an ultra-thin solid electrolyte (based on an yttria-stabilized zirconia material) layer as well as an electrode support layer with reduced thickness to minimize the cell resistance. The thin electrolyte and electrode-support layers were fabricated with our optimized tape casting process. In addition to reducing the cell resistance, the implementation of thin electrolyte and electrode-support layers offers a facile and short path for gas diffusion, which can reduce the efficiency loss caused by diffusion. With our optimized cell configuration design, a high electrolysis current density was achieved at 750 ^oC. Over the process of cell-configuration optimization, electrochemical impedance spectroscopy (EIS) and microscopic analysis were systematically performed on the cell and cell components to rationalize the cell architecture toward accessing high electrochemical performance and high energy efficiency of the SOEC. The relevant analysis strategies and results will be presented as well.