A research team has gone through thousands of reports from the last ten years to find a tin-based catalyst that supports the production of formic acid—a vital chemical used in many industries—while also making the production process more environmentally friendly.
The global climate crisis, which is fueled by dwindling fossil fuel supplies and increasing CO2 levels in the atmosphere, has made the quest for sustainable energy solutions more urgent than ever. One promising method in this regard is the electrochemical CO2 reduction reaction (CO2RR), especially when it works in tandem with renewable energy sources. This technique not only helps reduce CO2 emissions but also solves energy storage challenges by turning CO2 into valuable, carbon-neutral fuels. Formic acid (HCOOH) is one of the key products from CO2RR, prized for its flexibility in industries like tanning, textiles, and pharmaceuticals, and it also serves as a high-energy-density medium for hydrogen storage.
“Formic acid is a crucial chemical across various sectors, and its role as a hydrogen carrier makes it essential for a sustainable energy future,” expressed Xue Jia, an assistant professor at Tohoku University’s Advanced Institute for Materials Research (WPI-AIMR). Recent economic assessments have confirmed that producing formic acid through CO2RR is practical and economically viable, making it suitable for future industrial uses.
To improve the efficiency of CO2RR catalysts, Jia and her team performed an extensive analysis of over 2,300 experimental reports from the last decade. Their research highlighted the exceptional effectiveness and selectivity of tin-based catalysts like Sn−N4−C single-atom catalysts (SAC) and polyatomic Sn for producing formic acid. These catalysts consistently outperformed others, such as metal-nitrogen-carbon (M−N−C) catalysts and various metals, in terms of formic acid Faradaic efficiency (FE).
A key finding of the study was the impact of pH on catalyst performance. The analysis showed that the productivity and selectivity for formic acid increased with higher pH levels, particularly in catalysts like SnO2 and Bi0.1Sn. However, traditional theoretical models that treated pH-related energy adjustments as fixed failed to accurately predict performance at the reversible hydrogen electrode (RHE) scale.
“By factoring in electric field impacts and pH-dependent free energy calculations, we successfully evaluated the selectivity and performance of catalysts under real-world conditions, marking a significant breakthrough,” explained Hao Li, associate professor at WPI-AIMR. This refined modeling method provided valuable insights into the reaction mechanisms, offering a better understanding of the pH-related behaviors of Sn-based catalysts.
The research also tackled a long-standing question about how the structural variations between single-atom and polyatomic Sn catalysts affect their effectiveness. The team found that Sn−N4−C SAC displays a monodentate adsorption configuration, while polyatomic Sn uses a bidentate mode. These differing adsorption modes create opposing dipole moments for the intermediate OCHO, which greatly influences the catalysts’ activity and selectivity in CO2RR.
“This dependency on structure, coupled with pH-based modeling, has given us a thorough understanding of Sn-based catalysts and allowed our predictions to align with experimental findings,” said Linda Zhang, Assistant Professor at Tohoku University’s Frontier Research Institute for Interdisciplinary Sciences (FRIS). The research underscores the need to consider structural and kinetic components, in addition to standard thermodynamic models, for designing effective catalysts.
The significance of this research goes beyond CO2RR alone. Utilizing advanced computational methods like density functional theory (DFT) and machine learning force fields (MLFF), the team illustrated the potential to customize catalysts for specific reaction environments. This method is anticipated to enhance the creation of high-performance systems for numerous electrocatalytic tasks.
“Advanced modeling and computational techniques are allowing us to engineer catalysts tuned for specific reaction settings, which is crucial for developing more efficient CO2 reduction technologies,” Li remarked. The combination of experimental and theoretical approaches in this study is a major advancement in tackling climate issues through innovative catalyst development.
The study’s outcomes were published in the journal Angewandte Chemie International Edition, with the authors expressing their appreciation to the Tohoku University Support Program for covering the article processing costs.
