The catalytic valorization of carbon dioxide (CO2) has attracted extensive attention as a promising route to mitigate greenhouse gas emissions while producing value-added chemicals. Significant progress has been achieved in the selective reduction of CO2 to C1 and C2 products such as CO, CH4, HCOO-, C2H4, and C2H5OH through precise control of catalysts and reaction environments within single-batch systems. However, the formation of higher-order carbon products (C3+) remains a major challenge because it requires complex multielectron and multiproton transfer steps, typically involving 18-20 electrons and protons for intermediates such as propanol or propylene. These demanding reaction pathways lead to sluggish C-C-C coupling kinetics and limited energy utilization under conventional single-cell configurations. Recent advances have focused on multibatch cascade catalytic systems that integrate thermochemical, photochemical, and electrochemical processes to overcome these intrinsic barriers. By enabling the stepwise conversion of CO2-derived intermediates, such hybrid platforms improve selectivity and efficiency toward C3+ products that are difficult to achieve in single-batch systems. Nevertheless, the integration of distinct reaction environments introduces challenges, including intermediate loss between reactors and reduced overall energy efficiency. This review provides a comprehensive overview of cascade strategies for CO2 conversion, emphasizing mechanistic understanding, reactor design, and operando characterization. The discussion aims to guide the rational design of next-generation catalytic architectures capable of achieving efficient and scalable C3+ production from CO2 through improved control of multistep extended hybrid reaction pathways and interfacial energy management.
Keywords: CO2 electroreduction; copper-based catalyst; density functional theory (DFT); formate-mediated mechanism; in situ spectroscopy; machine-learning-assisted catalyst design; multicarbon (C2+/C3+) products; tandem reactor design.