Key Takeaways & Executive Findings
- •• Reducing catalyst loading from 10 to 1.685 mg·cm−2 and increasing current density in concentrated bicarbonate solutions boosts formate faradaic efficiency to 88% at −30 mA·cm−2, while lowering costs and suppressing hydrogen evolution. • Applying Nafion as a surface coating rather than mixing it into the ink improves formate production, but binder-free systems still outperform due to the intrinsic activity of Sn catalysts. • PVDF binder shows promise for formate production (72% FE at −30 mA·cm−2) despite blocking active sites, owing to its stability, strength, and conductivity. • The study provides practical guidelines for optimizing catalyst ink formulations and binder use to enhance CO2-to-formate conversion, supporting cost-efficient high-current-density operations.
Abstract
Electrochemical CO2 reduction is a sustainable method for producing fuels and chemicals using renewable energy sources. Sn is a widely employed catalyst for formate production, with its performance closely influenced by the catalyst ink formulations and reaction conditions. The present study explores the influence of catalyst loading, current density, and binder choice on Sn-based CO2 reduction systems. Decreasing catalyst loading from 10 to 1.685 mg·cm−2 and increasing current density in highly concentrated bicarbonate solutions significantly enhances formate selectivity, achieving 88% faradaic efficiency (FE) at a current density of −30 mA·cm−2 with a cathodic potential of −1.22 V vs. reversible hydrogen electrode (RHE) and a catalyst loading of 1.685 mg·cm−2. This low-loading strategy not only reduces catalyst costs but also enhances surface utilization and suppresses the hydrogen evolution reaction. Nafion enhances formate production when applied as a surface coating rather than pre-mixed in the ink, as evidenced by improved faradaic efficiency and lower cathodic potentials. However, this performance still does not match that of binder-free systems because Sn-based catalysts intrinsically exhibit high catalytic activity, making the binder contribution less significant. Although modifying the electrode surface with binders leads to blocked active sites and increased resistance, polyvinylidene fluoride (PVDF) remains promising because of its stability, strength, and conductivity, achieving up to 72% FE to formate at −30 mA·cm−2 and −1.66 V vs. RHE. The findings of this research reveal methodologies for optimizing the catalyst ink formulations and binder utilization to enhance the conversion of CO2 to formate, thereby offering crucial insights for the development of a cost-efficient catalyst for high-current-density operations.
1. Introduction
Climate change has become a major environmental issue due to the release of harmful greenhouse gases. One of the main approaches for addressing this challenge involves converting CO2 emissions into value-added chemicals to achieve a sustainable economy [1–3]. The electrochemical reduction of CO2 (eCO2RR) provides a route for producing chemicals such as methane, formate, ethylene, and ethanol. Sn electrodes have gained attention for their catalytic properties in the transformation of CO2 to formate, a valuable intermediate for applications in various industries such as fuel cells, formic acid production, material synthesis, and energy generation and utilization [4–7]. Formate is a stable intermediate in several biological systems and a promising replacement for environmentally harmful compounds. Therefore, the design of efficient catalysts to enhance the conversion of CO2 to formate has been a matter of debate for several years [8–16].
Sn has garnered research attention as a catalyst owing to its electronic properties, cost, and availability. Moreover, Sn is more stable than other catalysts [17] and meets the essential catalytic requirements, such as low overpotential, good selectivity, and non-toxicity [18]. Recent studies demonstrated that Sn can successfully yield formate with high efficiency and stability [8,19–22]. Moreover, their catalytic properties can be optimized by doping or alloying with other elements [23–24]. SnO2 has been demonstrated to enhance this process [25–26]. SnO2/Sn interfaces, for example, are more selective towards formate and suppress the hydrogen evolution reaction (HER) [27]. In addition, Sn nanonization (in the form of nanoparticles, nanowires, nanosheets, or nanostructured alloys) increases the surface area, improving the response at the active sites [28–29].
The full potential of Sn-based catalysts depends on establishing a more efficient cathode material; therefore, the current density, energy efficiency, system stability, and faradaic efficiency (FE) must be considered [4–5,30–31]. The efficiency of an electrode is determined by the extension of the three-phase boundary (TPB), choice of the catalyst, and surface morphology [32]. The TPB, a crucial factor in catalyst design, is a specific region where three phases converge: the solid catalyst transports electrons, the liquid electrolyte carries ions, and the gas phase supplies reactants.
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Asier Grijalvo Rodriguez, Zhiyuan Chen, Deepak Pant, Jolien Dendooven (2025). Effect of catalyst ink preparation on formate production from CO2 electroreduction using Sn as electrocatalyst. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-025-3133-7
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Frequently Asked Questions
What is the optimal catalyst loading for formate production from CO2 electroreduction using Sn?
The study found that reducing the catalyst loading from 10 to 1.685 mg·cm−2 significantly enhances formate selectivity, achieving 88% faradaic efficiency at −30 mA·cm−2, while also reducing catalyst costs and improving surface utilization.
How does the choice of binder affect CO2 electroreduction to formate?
The binder choice impacts performance: Nafion applied as a surface coating improves formate production compared to pre-mixing, but binder-free systems still outperform. PVDF shows promise with 72% FE to formate, despite blocking some active sites, due to its stability and conductivity.
What current density and potential are needed for high formate selectivity?
High formate selectivity (88% FE) was achieved at a current density of −30 mA·cm−2 and a cathodic potential of −1.22 V vs. RHE with a catalyst loading of 1.685 mg·cm−2 in highly concentrated bicarbonate solutions.
Why is Sn considered a suitable catalyst for CO2 reduction to formate?
Sn is cost-effective, abundant, stable, and non-toxic, with good selectivity for formate. Its performance can be further enhanced through nanostructuring and the formation of SnO2/Sn interfaces, which suppress the hydrogen evolution reaction.
What are the practical implications of this research for industrial applications?
The findings provide guidelines for optimizing catalyst ink formulations and binder usage to enhance CO2-to-formate conversion, enabling cost-efficient operation at high current densities, which is crucial for industrial-scale electrochemical CO2 reduction.
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