The Critical Role of Initial/Operando Oxygen Loading in General Bismuth-Based Catalysts for Electroreduction of Carbon Dioxide

Abstract

Operando reconstruction of solid catalyst into a distinct active state frequently occurs during electrocatalytic processes. The correlation between initial and operando states, if ever existing, is critical for the understanding and precise design of a catalytic system. Inspired by recently established intermediate metallic state of Bi-based catalysts during electrocatalytic carbon dioxide reduction (CO2RR), here we investigate a series of Bi oxide catalysts (Bi, Bi2O3, BiO2) and demonstrate that the operando surface/subsurface oxygen loading, positively correlated to the initial oxygen content, plays a critical role in determining Bi-based CO2RR performance. Higher initial oxygen loading indicates a better electrocatalytic efficiency. Further analysis shows that this conclusion generally applies to all Bi-based electrocatalysts reported up to date. Following this principle, cost-effective BiO2 nanocrystals demonstrated the highest formate Faradaic efficiency (FE) and current density compared to Bi/Bi2O3, further allowing a pair-electrolysis system with 800 mA/cm2 current density and an overall 175% FE for formate production.

Ampere-Level Electrolytic Coproduction of Formate with Coupled Carbon Dioxide Reduction and Selective Methanol Oxidation

“…When paired with anodic methanol oxidation using a Au/NiOOH@Ni foam anode, a CO 2 RR/MOR full-cell electrolyzer (Li-Bi 2 S 3 ||Au/NiOOH@Ni foam) was assembled, as illustrated in Figure c. The total cell voltage (without iR correction) is only 3.14 V when the coelectrolysis is conducted at 200 mA/cm 2 current density (Figure d), demonstrating a 230 mV reduction as compared to the previous work . We further evaluated the performance of the CO 2 RR/MOR full-cell electrolyzer under different and up to industrial-level current densities.…”

“…The total cell voltage (without iR correction) is only 3.14 V when the coelectrolysis is conducted at 200 mA/cm 2 current density (Figure 5d), demonstrating a 230 mV reduction as compared to the previous work. 15 We further evaluated the performance of the CO 2 RR/MOR full-cell electrolyzer under different and up to industrial-level current densities. As shown in Figure 5e, the coelectrolysis reaction obtained ampere-level current density (1.2 A/cm 2 ) with total Faraday efficiency of formate of up to 182%, and chronopotentiometry results are provided in Figure S19.…”

“…As shown in Figure 5g, the formate Faraday efficiencies of both CO 2 RR and MOR were kept at a high level at 200 mA/cm 2 or even 1.0 A/cm 2 during 20 h of operation, with a stable electrode potential (200 mA/cm 2 ) and cell voltage (1.0 A/ cm 2 ), demonstrating an unprecedented full-cell stability under high current densities. Figure 5h summarizes the total FEs and the working current densities of coupled coelectrolysis pairs reported to date, 14,15,17,33,71,72 and the Li−Bi 2 S 3 ||Au/ NiOOH@Ni cell shows an obvious advantage in performance over state-of-the-art systems, demonstrating great promise for the potential industrial production.…”

“…In the search for alternative anode reactions that can replace OER to better couple with the CO 2 RR, the oxidation of methanol, alcohol, urea, amines, biomass, and glucose has been considered suitable because of the relatively lower overpotentials and higher value-added products, yet the development of an ultrafast reaction kinetics that complements the state-of-the-art ampere-level cathodic CO 2 RR , is crucial for practical considerations. The selective oxidation of methanol to formic acid is a promising process as the product unit value is increased 3–5 times after conversion, , and formic acid is a valuable source of hydrogen-rich fuels, with a high hydrogen content of 53 g L –1 or 4.4 wt % . More importantly, this anodic reaction is a natural complement to cathodic CO 2 RR, in which the same formate/formic acid product can be obtained with high catalytic efficiency, energy efficiency, and cost-effectiveness. , …”