Electrocatalytic Performance of Interconnected Self‐Standing Tin Nanowire Network Produced by AAO Template Method for Electrochemical CO₂ Reduction**

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 FEformate% 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.

Electro-Coloring Mechanism of Aluminum Anodic Oxides in Tin-Based Electrolytes

“…The shift in the cathodic breakdown potential to more negative values with cycling and thickening of the tin oxide layer may indicate that the second mechanism better explains this shift. The observation of lower cathodic currents at point 2 is due to the well-known high overvoltage of HER on tin oxides [63][64][65]. With the increase in cycle numbers beyond 20, the reduction and oxidation current increases (points A and B) and stabilizes after 50 cycles.…”

Electro-Coloring Mechanism of Aluminum Anodic Oxides in Tin Based Electrolytes

“…After the deposition of tin in the pores, the potential at point 4 also starts to change in a positive direction towards the corrosion potential of tin in alkaline electrolytes [53][54][55]. With the change of potential towards anodic direction, oxidation of deposited tin starts to commence at point B [54][55][56][57][58][59]. After the oxidation of metallic tin, a very low anodic current is recorded even beyond the anodic oxidation potential (oxygen evolution reaction) (point5), similar to the anodic behavior of tin in alkaline solutions anodized at high anodic potentials.…”

“…• At Point B; Primary, secondary passivation of metallic tin and dehydration of anodic oxide occurs [59].…”