The global climate crisis, driven by the depletion of fossil fuels and rising atmospheric CO2 levels, has intensified the need for sustainable energy solutions. Among these, the electrochemical CO2 reduction reaction (CO2RR), particularly when integrated with renewable energy sources, has emerged as a promising approach. This process not only mitigates CO2 emissions but also addresses energy storage challenges by converting CO2 into high-value, carbon-neutral fuels. One of the standout products of CO2RR is formic acid (HCOOH), valued for its versatility in industries such as tanning, textiles, and pharmaceuticals, as well as its role as a high-energy-density liquid hydrogen storage medium.
"Formic acid is an indispensable chemical in various industries, and its potential as a hydrogen carrier makes it a critical component for a sustainable energy future," said Xue Jia, an assistant professor at Tohoku University's Advanced Institute for Materials Research (WPI-AIMR). Recent techno-economic analyses have also highlighted the practicality and economic feasibility of synthesizing formic acid through CO2RR, emphasizing its adaptability for future industrial applications.
To advance the development of efficient CO2RR catalysts, Jia and her colleagues conducted a comprehensive study, analyzing over 2,300 experimental reports from the past decade. Their findings underscored the superior activity and selectivity of tin-based catalysts, such as Sn−N4−C single-atom catalysts (SAC) and polyatomic Sn, for HCOOH production. These catalysts consistently outperformed others, including metal-nitrogen-carbon (M−N−C) catalysts and various metals, in terms of formic acid Faradaic efficiency (FE).
A significant aspect of the study was the influence of pH on catalyst performance. The team's analysis revealed that the selectivity and activity of HCOOH production increase with pH levels, as demonstrated in catalysts like SnO2 and Bi0.1Sn. However, conventional theoretical models that treat pH-dependent energetic corrections as constants failed to accurately predict activity at the reversible hydrogen electrode (RHE) scale.
"By incorporating electric field effects and pH-dependent free energy formulations, we were able to analyze the selectivity and activity of catalysts under actual working conditions, which is a significant step forward," explained Hao Li, associate professor at WPI-AIMR. This advanced modeling approach provided critical insights into the reaction mechanism, enabling a deeper understanding of the pH-dependent behavior of Sn-based catalysts.
The study also addressed a longstanding challenge: understanding how the structural differences between single-atom and polyatomic Sn catalysts impact their performance. The team discovered that Sn−N4−C SAC exhibits a monodentate adsorption mode, while polyatomic Sn adopts a bidentate mode. These distinct adsorption modes result in opposite dipole moments for the intermediate OCHO, significantly influencing the catalysts' activity and selectivity for CO2RR.
"This structural sensitivity, combined with pH-dependent modeling, has provided a comprehensive understanding of Sn-based catalysts and aligned our predictions with experimental observations," said Linda Zhang, Assistant Professor at Tohoku University's Frontier Institute Frontier Research Institute for Interdisciplinary Sciences (FRIS). The research highlights the importance of considering structural and kinetic factors, beyond conventional thermodynamic models, for precise catalyst design.
The implications of this work extend beyond CO2RR. By employing advanced computational techniques, such as density functional theory (DFT) and machine learning force fields (MLFF), the researchers demonstrated the potential of tailoring catalysts for specific reaction conditions. This approach is expected to drive the development of high-performance systems for a range of electrocatalytic processes.
"Precise modeling and advanced computational techniques are enabling us to design catalysts tailored for specific reaction conditions, paving the way for more efficient CO2 reduction technologies," adds Li. The study's integration of experimental and theoretical perspectives marks a significant step toward addressing climate challenges through innovative catalyst design.
The findings were published in the journal Angewandte Chemie International Edition, with the authors expressing their gratitude to the Tohoku University Support Program for covering the article processing charge.
- Publication Details:
Title: Divergent Activity Shifts of Tin-Based Catalysts for Electrochemical CO2 Reduction: pH-Dependent Behavior of Single-Atom versus Polyatomic Structures
Authors: Yuhang Wang, Di Zhang, Bin Sun, Xue Jia, Linda Zhang,, Hefeng Cheng, Jun Fan, and Hao Li
Journal: Angewandte Chemie International Edition
