This study proposes a novel methodology for controlling syngas production from high-temperature CO2/steam co-electrolysis. The co-electrolysis of CO2/steam mixtures is one of the most promising methods to reduce CO2 emissions and mitigate climate change. CO2 and steam are reduced to produce synthetic gas (H-2 and CO) through thermo-electrochemical reactions occurring in a solid-oxide-cell fuel electrode. To make this technology viable, it is essential to improve electrochemical cell performance and obtain controllability of gas conversion and product gas selectivity. In this study, Fe infiltration to the Ni/YSZ fuel electrode and subsequent in situ alloying of Ni-Fe is used to enhance the cell performance and syngas productivity. Impregnation of Fe-oxide nanoparticles on the fuel electrode support of solid oxide cells and subsequent in situ alloying Ni-Fe is obtained. Their homogeneous morphology and distribution are obtained by using an advanced infiltration technique. Results show that the Ni-Fe/YSZ fuel electrode enhances CO selectivity and lowers an overvoltage imposed on the cell. This may result in syngas production with higher carbon contents and a higher co-electrolysis system efficiency. In addition, its long-term durability for 500-hour operation is also evidenced with stable syngas production and negligible cell degradation.