Interconnected-branched anodically oxidized tin nanowires: This electrode is produced via electrodeposition on aluminum anodic oxide (AAO) template followed by anodic oxidation. The electrode gave ~87 % Faradaic efficiency for formate with −14.55 mA cm⁻² current density. It preserved the product selectivity for 12 h with a slight decline in current density. (RE: Reference electrode).

Abstract

In this study, we used a specially designed aluminum anodic oxide (AAO) template technique to produce interconnected self-standing tin nanowire electrocatalysts having a high surface-to-volume ratio for CO₂ reduction toward formate. These electrodes consisted of interconnected tin nanowires with 150 nm diameter and 7 μm length supported on 70–100 μm thick tin film. As prepared electrodes produced 6 times higher formate than the flat tin sheets, yet Faradaic efficiencies (FE%) were unsatisfactory. The main reason for low FE% is determined as the etching of native oxide on tin nanowires during hot alkali treatment to remove AAO and remnant aluminum. Porous anodic oxidation in 1 M NaOH solution was realized to recover tin oxides on the surface. Anodized tin nanowire electrocatalysts produced higher formate than anodized tin sheets, reaching FE_formate% of ~87 at −1 V vs. RHE cathodic reduction potential. Moreover, while anodic oxide on flat tin flaked off the surface in 1 h, these electrodes preserved their integrity and formate production ability even after 12 h.