Abstract: Electro-conversion of CO2, N2, or NOx into valuable chemicals, e.g., CO, HCOOH, and NH3, has become a favorite for mitigating environmental pollution and addressing the energy crisis. Typical electrolysis systems, which pair a cathodic CO2, N2, or NOx reduction reaction (CO2RR, NRR, or NOxRR) 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 CO2RR, NRR, or NOxRR 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 CO2-, N2-, and NOx-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.

Key words: Integrated dual-function systems, CO2RR, NRR/NOxRR, Alternative oxidation, Chemical synthesis, Environmental remediation, Metal-CO2/metal-N2 batteries