Rodrigues Pinto Maria, Vos Rafaël E, Nagao Raphael, Koper Marc T M
Institute of Chemistry, University of Campinas, Campinas, São Paulo 13083-970, Brazil.
Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, Leiden 2300 RA, The Netherlands.
J Phys Chem C Nanomater Interfaces. 2024 Dec 5;128(50):21421-21429. doi: 10.1021/acs.jpcc.4c06361. eCollection 2024 Dec 19.
Understanding the electrolyte factors governing the electrochemical CO reduction reaction (CORR) is fundamental for selecting the optimized electrolyte conditions for practical applications. While noble metals are frequently studied, the electrolyte effects on the CORR on Sn catalysts are not well explored. Here, we studied the electrolyte effect on Sn metallic electrodes, investigating the impact of electrolyte concentration, cation identity, and anion properties, and how it shapes the CORR activity and selectivity. The activity for formic acid and carbon monoxide increases with the cation concentration and size at mild acid conditions. In contrast, hydrogen production is not strongly influenced by the cathodic potential, electrolyte concentration, and cation size. Furthermore, we have compared the CORR performance at a constant cation concentration in KSO (pH 4) and KHCO (pH 7), where we show that the reaction rate toward HCOOH and CO are minimally impacted by the anion identity on the SHE scale, while being affected by the cations in solution, which we attribute to the reaction being limited by cation-coupled electron transfer steps rather than by a proton-coupled electron transfer step. We propose that the HCOOH forms via adsorbed hydrides leading to *OCHO intermediate, while CO forms through an electron transfer step, producing *CO . Cations facilitate both processes by stabilizing the negatively charged intermediates, and the difference in the extent of the promotion of HCOOH over CO formation would stem from the stronger cation effects on *H compared with *CO species. Additionally, the presence of HCO at high concentrations (1.0 mol L) is shown to significantly enhance the production of H at high overpotentials (>-1.0 V vs RHE) due to bicarbonate ions acting as protons donors, outcompeting water reduction. These findings underscore the significance of electrolyte engineering for enhanced formic acid synthesis, offering valuable insights for optimizing the CORR processes on Sn electrocatalysts.
了解控制电化学CO还原反应（CORR）的电解质因素对于选择实际应用中的优化电解质条件至关重要。虽然贵金属经常被研究，但电解质对Sn催化剂上CORR的影响尚未得到充分探索。在此，我们研究了电解质对Sn金属电极的影响，考察了电解质浓度、阳离子种类和阴离子性质的影响，以及它们如何塑造CORR活性和选择性。在温和酸性条件下，甲酸和一氧化碳的活性随阳离子浓度和尺寸的增加而增加。相比之下，析氢受阴极电位、电解质浓度和阳离子尺寸的影响不大。此外，我们比较了在KSO（pH 4）和KHCO（pH 7）中恒定阳离子浓度下的CORR性能，结果表明，在标准氢电极（SHE）标度上，HCOOH和CO的反应速率受阴离子种类的影响最小，而受溶液中阳离子的影响，我们将其归因于反应受阳离子耦合电子转移步骤而非质子耦合电子转移步骤的限制。我们提出，HCOOH通过吸附氢化物形成，生成OCHO中间体，而CO通过电子转移步骤形成，生成CO。阳离子通过稳定带负电荷的中间体促进这两个过程，HCOOH形成相对于CO形成的促进程度差异源于阳离子对H物种的影响强于CO物种。此外，高浓度（1.0 mol L）HCO的存在表明，由于碳酸氢根离子作为质子供体，在高过电位（>-1.0 V vs RHE）下显著增强了析氢，从而胜过水的还原。这些发现强调了电解质工程对增强甲酸合成的重要性，为优化Sn电催化剂上的CORR过程提供了有价值的见解。
