Developing high-density energy storage and lowering CO2 emissions have been considered as key issues in energy and environmental science. To tackle these issues simultaneously, syngas production from high-temperature thermo-electrochemical reduction of steam/CO2 mixtures utilizing renewable energy has been proposed. By doing so, renewable electrical energy can be stored in the form of chemical energy, and CO2 is converted to highly valuable syngas which can be processed further to produce liquid fuels. To make this technology viable, it is imperative to develop a cost-effective and efficient methodology for controlling syngas production given that this system is linked with fluctuating renewable electrical current and CO2 stream. Here we show that in-situ nano-alloying noble metals in solid oxide cells can provide such function by using substantially small amount of the expensive noble metals. Catalyzing selectively the reverse water gas shift reaction, this technique enables increasing the CO2 conversion rate, storing energy more efficiently, and controlling the syngas production rate and its quality. Consequently, it may enhance the syngas productivity and energy storage capacity and provide a capability for adjusting effectively the system to variable renewable electrical energy and CO2 sources. (C) 2016 Elsevier B.V. All rights reserved.