Conversion of aqueous CO₂ into CO through the electrochemical reduction reaction (ERR) suffers from poor selectivity and low current density with the classic Ag-based catalysts due to the inert nature of CO₂ and the low activity of the active sites. Recently, it has been reported that nanostructured catalysts can display very distinctive behavior compared to their bulk counterparts. To explore the reasons behind this, the latest developments in Ag-based nanostructured materials in the CO₂ ERR are summarized into six aspects in this review: (1) the size effect, (2) the morphology effect, (3) the porous effect, (4) the alloying effect, (5) the support effect, and (6) the surface modification effect. In particular, Ag-based alloy catalysts could exhibit a superior catalytic activity and long-term stability owing to the synergistic effect. Besides, the morphology of Ag-based alloy catalysts could also be controlled through adjusting their compositions. From the current literature survey we find that the maximum FE for CO obtained from Ag-based nanocatalysts reaches as high as 99.3%, which is a breakthrough over that from the traditional Ag foil. This review aims to offer a comprehensive understanding of Ag-based nanostructured catalysts in the CO₂ ERR and consequently improve the catalyst design for active and selective electro-reduction of CO₂ to CO.

Carbon dioxide (CO₂) electroreduction offers an attractive pathway for converting CO₂ to valuable fuels and chemicals. Despite the existence of some excellent electrocatalysts with superior selectivity for specific products, these reactions are conducted at low current densities ranging from several mA cm⁻² to tens of mA cm⁻², which are far from commercially desirable values. To extend the applications of CO₂ electroreduction technology to an industrial scale, long-term operations under high current densities (over 200 mA cm⁻²) are desirable. In this paper, we review recent major advances toward higher current density in CO₂ reduction, including: (1) innovations in electrocatalysts (engineering the morphology, modulating the electronic structure, increasing the active sites, etc.); (2) the design of electrolyzers (membrane electrode assemblies, flow cells, microchannel reactors, high-pressure cells, etc.); and (3) the influence of electrolytes (concentration, pH, anion and cation effects). Finally, we discuss the current challenges and perspectives for future development toward high current densities.

To increase the specific surface area, high-density (i.e. number per unit area) Ag nanosheets (ANS) with large electrochemically active surface area and rich edge active sites over Ag plates were synthesized via a facile electrodeposition approach in a double electrode system at a constant current of −1 mA for 1800 s. By adjusting the concentration of H ₃ BO ₃ (0.5 M, 0.1 M and 0.05 M), which is used to control the growth direction of ANS, ANS-20, -50, -350 were obtained with varying thickness of 20 nm, 50 nm, and 350 nm, respectively. Notably, ANS-20 showed a remarkable current density of −6.48 mA cm ⁻² at −0.9 V versus the reversible hydrogen electrode (RHE), which is almost 1.6 and 2.4 times as high as those of ANS-50 and -350, respectively. Furthermore, ANS-20 exhibits the best CO selectivity of 91.2% at −0.8 V versus RHE, while the other two give 84.6% and 77.9% at the same potential. The excellent performance of ANS-20 is attributed to its rich edge active sites and large electrochemically active surface area (ECSA).