Effect of catalyst ink preparation on formate production from CO₂ electroreduction using Sn as electrocatalyst

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.