Highly selective CO₂ electroreduction in an exsolution-induced flow cell using a hierarchical monolithic nano-Ag foam electrode

Electrochemical CO₂ reduction driven by renewable energy offers a promising route to carbon neutrality. The flow-through induced dynamic triple-phase boundary cell (FTDT cell) addresses the key challenges of conventional gas diffusion electrodes (GDEs), including salt precipitation and electrode flooding, by enabling direct electrolysis of CO₂-saturated solutions. However, the Ag catalyst with carbon cloth as a substrate in the FTDT cell exhibits the shortcomings of a few active sites and poor structural stability. Here, we reported a monolithic nano-Ag foam electrode featuring well-developed pores and a hierarchical nanostructure with a high electrochemically active surface area (ECSA), which is ten times that of the Ag NPs electrode, enhancing the CO₂ electroreduction performance of the FTDT cell significantly. Classical nucleation theory (CNT) clarified that the nanostructures accelerate bubble nucleation, and visualization experiments confirmed that the periodically connected pore structure provides abundant dynamic gas-liquid-solid triple-phase boundaries (TPBs). At an industrial current density of 200 mA cm^-2 and a cell voltage of 2.34 V, the nano-Ag foam electrode achieves a CO faradaic efficiency of 93% and an overall energy efficiency of 51.34%, presenting a promising approach for the commercialization of CO₂ electrolysis.