Structural defects on converted bismuth oxide nanotubes enable highly active electrocatalysis of carbon dioxide reduction

Abstract

Formic acid (or formate) is suggested to be one of the most economically viable products from electrochemical carbon dioxide reduction. However, its commercial viability hinges on the development of highly active and selective electrocatalysts. Here we report that structural defects have a profound positive impact on the electrocatalytic performance of bismuth. Bismuth oxide double-walled nanotubes with fragmented surface are prepared as a template, and are cathodically converted to defective bismuth nanotubes. This converted electrocatalyst enables carbon dioxide reduction to formate with excellent activity, selectivity and stability. Most significantly, its current density reaches ~288 mA cm −2 at −0.61 V versus reversible hydrogen electrode within a flow cell reactor under ambient conditions. Using density functional theory calculations, the excellent activity and selectivity are rationalized as the outcome of abundant defective bismuth sites that stabilize the *OCHO intermediate. Furthermore, this electrocatalyst is coupled with silicon photocathodes and achieves high-performance photoelectrochemical carbon dioxide reduction.

Promises of Main Group Metal–Based Nanostructured Materials for Electrochemical CO2 Reduction to Formate

“…Liquid products (such as formate, methanol, ethanol, acetate, and so on) accumulated in the catholyte at the end of tests can be measured using proton nuclear magnetic resonance ( 1 H NMR). Alternatively, we find that ion chromatography is an effective tool for quantifying the amount of formate in the catholyte . It has a lower detention limit (≈100 ppb) than NMR (1–10 ppm), and is easier to operate.…”

“…This is because the coupling to form C 2 –C 4 products requires the adsorption of multiple CO 2 molecules on surface and their concerted transformation, and is statistically challenged . Current state‐of‐the‐art electrocatalysts have the maximum selectivity of ≈100% for CO or formate, but only ≈60% for ethylene, ≈40% for acetate, and ≈15% for n ‐propanol . Poor selectivity not only results in ineffective utilization of electrolyzer electricity, but also incurs additional costs for the product separation.…”

“…When assessed in the flow‐cell configuration, this electrocatalyst sustained large current density up to 200 mA cm −2 and >90% formate selectivity in 1 m KHCO 3 . We very recently reported the use of double‐walled Bi 2 O 3 nanotubes with fragmented outer surface as the precatalyst (Figure d–f) . Electrochemical reduction transformed the precatalyst to defective Bi nanotubes.…”

“…f) Potential‐dependent Faradaic efficiency of formate, CO, and H 2 on metallic Bi nanotubes converted from Bi 2 O 3 double‐walled nanotubes. Reproduced with permission . Copyright 2019, Springer Nature.…”

“…f) Long‐term amperometric stability and the corresponding selectivity of NTD‐Bi in the flow cell. Reproduced with permission . Copyright 2019, Springer Nature.…”