Ligament size-dependent electrocatalytic activity of nanoporous Ag network for CO₂ reduction

Electrochemical CO2 reduction (ECR) depends significantly on the nanostructures of electrocatalysts. Here we show a nanoporous Ag network catalyst (np-Ag) for efficient electrochemical reduction of CO2. The np-Ag samples with an average ligament size of 21 nm (denoted by np-Ag (21 nm)) and 87 nm (denoted by np-Ag (87 nm)) were fabricated by dealloying the rapidly solidified Mg80Ag20 (wt%) alloy ribbons in 1 wt% citric acid and 5 wt% phosphoric acid, respectively. The ligament size effect on the electrocatalytic activity and selectivity of CO2 conversion into CO is investigated. When catalysing CO2 reduction in 0.1 M KHCO3, the np-Ag (21 nm) catalyst exhibits a significantly enhanced selectivity with a faradaic efficiency for CO formation of 85.0% at -0.8 V versus RHE, about two times that (41.2%) over the np-Ag (87 nm). Additionally, a superior catalytic activity is also achieved over the np-Ag (21 nm), with a >2.5-fold increase in the CO partial current density relative to the np-Ag (87 nm). The improved selectivity and activity of np-Ag (21 nm) are attributed to the enhanced electrochemical surface area, higher local pH derived from ligament size effect, as well as more defect sites (i.e., grain boundaries) in ligaments.