Modulating Ammonium-Driven Hydrogen Evolution on Silver Electrodes in Amine-CO ₂ Capture Solutions

Integrating CO2 capture with direct electrochemical conversion has been proposed to address key challenges with the current decoupled paradigm but exhibits low CO2 conversion selectivity due to the high hydrogen evolution reaction (HER) activity. In amine-based electrolytes, disentangling HER contributions is particularly challenging because solution pH and the speciation of multiple possible proton donors (ammonium, bicarbonate, water) are strongly coupled. Here, we address this complexity by developing model solutions that replicate the individual pH-concentration trends of the full capture solutions but contain only amine/ammonium or bicarbonate/carbonate. On Ag electrodes, ammonium solutions exhibit high intrinsic HER activity facilitated by high buffer capacity across several structurally distinct primary amines. However, this activity is strongly attenuated in CO2-containing amine capture solutions. This suggests that bicarbonate and/or carbamate, with potassium cations, strongly suppresses ammonium-driven HER through a competitive surface adsorption process that will be critical to further understand and exploit to support the CO2 reduction pathways.