Controllable growth of branched silver crystals over a rod of the same material as an efficient electrode in CO₂ reduction at high current densities

Ultrathin Ag nanosheets (ANS), rice spike-like Ag dendrites (ADD) and porous Ag dendrites foam (ADDF) are synthesized respectively via a capping agent and electric field-induced Ag crystals growth approach. Compared with ANS and ADD, ADDF catalysts possess significantly increased CO Faradaic efficiency (FE) and can be operated at a broader applied current range due to the inter-connective porous macrostructure of ADDF catalysts with more abundant active sites, which can afford plenty of pore channels to substantially impel CO₂ diffusion to reaction sites, therefore maintaining a high rate of CO₂ reduction. Furthermore, unique conical microstructure can intensify the local electric field to raise the CO₂ concentration at the reaction sites. ADDF-2 exhibits a CO Faradaic efficiency of 96.84% at −28.8 mA cm⁻² in a membrane microchannel reactor at an optimal gas–liquid ratio of 1:2. To increase the CO₂ concentration, by increasing the CO₂ pressure (3∼9.5 bar), so that CO partial current density can reach −288.68 mA cm⁻², which is the highest one achieved so far in the liquid phase with neutral pH.