Why CO₂ capture via supercapacitive swing adsorption needs a theory, not just tweaks

Supercapacitive Swing Adsorption (SSA) is an emerging electrochemical approach to CO₂ capture that uses the charging and discharging of aqueous supercapacitors with a gas-exposed electrode. Its appeal lies in low-energy operation, long cycle lifetime, humidity tolerance and the use of sustainable and abundant materials. Yet, despite a rapidly growing literature and extensive efforts to optimise the process, CO₂ adsorption capacities remain modest compared with more established capture technologies, and the underlying capture mechanism remains unresolved. Here, we argue that further optimisation is increasingly limited by this lack of mechanistic understanding. We first map the empirical landscape of SSA, summarising robust trends across electrolytes, electrode materials, charging protocols, and gas composition. From these trends, we derive mechanistic constraints that any theory of SSA must be able to explain, and assess their compatibility with the leading mechanistic proposals (gas-solid, molecular liquid-solid, ionic liquid-solid, and pH-swing-based mechanisms), highlighting tensions and open questions. Finally, we outline possible strategies for closing these gaps and resolving the operative capture mechanism and driving forces, with the aim of enabling a transition from empirical optimisation toward predictive design of SSA systems as a viable carbon capture technology.