Two-in-One Integrated CO2/N2 Conversion and Related Systems: Potential, Status, and Future

Abstract Electro-conversion of CO 2 , N 2 , or NO x into valuable chemicals, e.g., CO, HCOOH, and NH 3 , has become a favorite for mitigating environmental pollution and addressing the energy crisis. Typical electrolysis systems, which pair a cathodic CO 2 , N 2 , or NO x reduction reaction (CO 2 RR, NRR, or NO x RR) with an anodic oxygen evolution reaction (OER), hinder the economic viability and efficiency of the overall system due to the energy-intensive OER process. Innovative “Two-in-One” systems that integrate CO 2 RR, NRR, or NO x RR with a value-added oxidation process or energy storage unit, rather than OER, within a single device have emerged as promising alternatives. However, these “Two-in-One” integrated systems still face numerous pressing challenges in advancing the industrialization of CO 2 -, N 2 -, and NO x -related conversion technologies, such as limited application scenarios, low efficiency, and restricted products. Herein, we discuss the technological breakthroughs of “Two-in-One” systems from the perspective of value-added chemical co-production, environmental remediation, and energy storage, aiming to provide readers with fresh research viewpoints to improve efficiency, increase product variety and selectivity, maximize product value, and reduce costs. Specifically, the design principles of “Two-in-One” systems, specific design strategies for dual-value-added chemical co-production, environmental pollutant recycling, and energy storage applications, along with techno-economic and environmental impacts, are discussed in detail. Finally, key research opportunities and challenges are highlighted to facilitate further developments. Graphical Abstract From the perspectives of value-added chemical synthesis, environmental remediation, and energy storage, we discuss innovative “Two-in-One” systems that integrate CO 2 , N 2 , or NO x reduction reactions with a value-added oxidation process or energy storage unit, rather than oxygen evolution reaction (OER), within a single device, as promising alternatives for solving the problem of high energy consumption and meeting real-world sustainability needs.