Molecular Modification of Cu-Based Electrodes via Electrografting: Effects of Modifier Structure on CO ₂ Electroreduction Selectivity

CO₂ electroreduction to multicarbon products using Cu-based catalysts is one of the strategies currently developed in order to valorize CO₂ and store electricity. Molecular modification of material surfaces has been recently explored in order to tune the reactivity of Cu catalysts and improve their selectivity toward C₂₊ products, in particular ethylene and ethanol. Here, we compare four classes of precursors of aryl radicals, namely, aryl-iodoniums, -diazoniums, -sulfoniums, and -silicates, which are used for grafting an aromatic layer onto the surface of Cu nanoparticles via electroreduction or electrooxidation. In all cases, the surface modification promotes CO-CO coupling and C₂₊ product formation, leading to a much higher FE_C2+/FE_CO (FE = Faradaic efficiency) ratio. However, we show that the composition of the layer is more complex and diverse than anticipated and likely explains the unexpectedly large variations in selectivity, even though the Cu catalysts were functionalized with presumably the same aromatic layer derived from the same aryl radical generated by the four different precursors. These classes of precursor salts are thus not interchangeable and provide a much larger scope of Cu surface modifications and Cu catalysts than anticipated to be studied independently.