Key Takeaways & Executive Findings
- •• • The pre-doped Bi catalyst achieves >95% Faradaic efficiency (FE) for formate across a current density range of 100–500 mA cm−2 in a flow cell, demonstrating industrial relevance for high-rate production. • • Long-term stability is proven with >95% FE maintained for over 70 hours at 100 mA cm−2 in a membrane electrode assembly (MEA), addressing the sulfur leaching failure of conventional Bi2S3. • • A solar-driven system achieves a solar-to-formate conversion efficiency of 4.4%, validating the potential for renewable-powered carbon valorization. • • Mechanistic studies confirm that trace sulfur doping increases electron density, stabilizes the *OCHO intermediate, and suppresses hydrogen evolution, providing a design principle for selective CO2RR catalysts.
Abstract
Electrocatalytic CO2 reduction reaction (CO2RR) to formate offers a promising pathway for storing renewable electricity in chemical fuels and enabling carbon recycling. The development of efficient and stable catalysts for this specific pathway, however, remains a central challenge. Heteroatom doping can significantly tune the interaction between active sites and key intermediates, boosting catalytic performance. Conventional doping in Bi-based catalysts often relies on uncontrollable in-situ electrochemical processes, leading to ineffective bulk incorporation. Here, we present a simple pre-doping strategy that enables precise doping at surface active sites, thereby enhancing electrochemical performance. The resulting catalyst achieves >95% Faradaic efficiency for formate across 100–500 mA cm−2 in a flow cell and maintains >95% efficiency for over 70 h at 100 mA cm−2 in a membrane electrode assembly, outperforming pure Bi and Bi2S3. A solar-driven system further demonstrates a 4.4% solar-to-formate conversion efficiency. Mechanistic studies reveal that sulfur doping increases electron density, stabilizes the key *OCHO intermediate, and suppresses hydrogen evolution. These findings provide valuable insights into the precise pre-doping modulation of surface active sites for designing highly efficient and stable CO2RR catalysts.
1. Introduction
The electrochemical conversion of CO2 to formate via CO2 reduction reaction (CO2RR) offers a sustainable pathway for renewable energy storage and carbon utilization, yet its industrial deployment is hindered by low selectivity and limited production efficiency. The large energy barrier for activating CO2 to *OCHO species and the competitive hydrogen evolution reaction (HER) in aqueous systems have historically constrained performance. Bismuth-based catalysts are promising due to their optimal binding with *OCHO and weak hydrogen adsorption, but conventional doping methods rely on uncontrollable in-situ electrochemical processes, leading to ineffective bulk incorporation and poor stability.
This study introduces a simple pre-doping strategy that precisely incorporates trace sulfur at surface active sites of bismuth, overcoming the limitations of in-situ doping. The resulting catalyst demonstrates exceptional activity, selectivity, and stability, achieving >95% Faradaic efficiency for formate across a wide current density range (100–500 mA cm−2) and maintaining performance for over 70 hours in a membrane electrode assembly. This approach not only addresses the sulfur leaching issue of Bi2S3 but also provides a scalable pathway for industrial CO2-to-formate conversion.
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Zhengjie Yao, Yitao Wang, Chenglong Qiu, Yiwen Wang, Lijia Liu, Wei Chen, Zhenjie Cheng, Jiacheng Wang, Lili Zhang (2026). Trace Sulfur Pre-Doped Bismuth Electrocatalysts for Stable and Efficient CO2 Reduction to Formate. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-4035-5
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Frequently Asked Questions
What is the maximum current density at which the catalyst maintains >95% Faradaic efficiency for formate?
The catalyst maintains >95% Faradaic efficiency for formate across a current density range of 100–500 mA cm−2 in a flow cell, as reported in the study.
How does the pre-doping strategy prevent sulfur leaching compared to conventional Bi2S3?
The pre-doping strategy incorporates trace sulfur at surface active sites, which stabilizes the catalyst structure. In contrast, conventional Bi2S3 suffers from sulfur leaching during operation, leading to performance degradation. The pre-doped catalyst maintains >95% efficiency for over 70 hours at 100 mA cm−2 in a membrane electrode assembly, demonstrating enhanced stability.
What is the solar-to-formate conversion efficiency achieved in the integrated photovoltaic system?
The solar-driven system achieves a solar-to-formate conversion efficiency of 4.4%, as demonstrated in the study.
What mechanistic insights explain the enhanced catalytic performance?
Mechanistic studies reveal that sulfur doping increases electron density on the bismuth surface, which stabilizes the key *OCHO intermediate and suppresses the competing hydrogen evolution reaction (HER). This leads to improved selectivity and activity for formate production.
What are the key performance metrics that make this catalyst suitable for industrial applications?
The catalyst achieves >95% Faradaic efficiency for formate at current densities up to 500 mA cm−2, maintains >95% efficiency for over 70 hours in a membrane electrode assembly, and demonstrates a 4.4% solar-to-formate conversion efficiency. These metrics meet industrial requirements for high-rate, stable, and efficient CO2-to-formate conversion.
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