(4a) Nanostructuring Electrocatalysts Using Atomic Layer Deposition

For the energy transition of the chemical industry, we foresee an important role for electrocatalytic conversion of CO₂ into hydrocarbons. However, making highly active and highly stable electrocatalysts is a major challenge. Here, we will demonstrate how atomic layer deposition (ALD) can help in this. ALD is a cyclic gas phase coating process that can deposit sub-nanometer coatings per cycle. This approach combine nanoscales precision with good scalability. We will illustrate this with two examples:

1. Making a nanostructured Pt-Pd bimetallic electrocatalyst to convert CO₂ into formate;
2. Protecting silver nanoparticles by a silica nanocoating for conversion of CO₂ into CO with SO₂ impurities in the feed stream.

For example 1, we synthesize well-controlled core-shell and alloy catalysts by ALD on the surface of carbon powder in a fluidized bed reactor. It is shown using an H-cell setup that the Pt−Pd alloy catalyst displays a 46 % faradaic efficiency toward formic acid, outperforming Pt@Pd and Pd@Pt core-shell structures that show faradaic efficiencies of 22 % and 11 %, respectively. Moreover, both core-shell bimetallic catalysts (Pd@Pt and Pt@Pd) are not stable under electroreduction conditions.

For example 2, we studied the effect of SO₂ impurities (various concentrations, up to 1000 ppm) in a CO₂ feed to an H-cell setup, operated at various potentials. We observed that the silver catalyst stayed stable for 20 hours of operation when fed with pure CO₂. However, after 1 hour of operation with 1000 ppm SO₂ added, the faradaic efficiency for CO already dropped from about 60% to about 40%, depending on the potential. Catalysts protected with 4 or 8 ALD cycles SiO₂ kept the original performance. This is likely due to the SO₂ and CO₂ permeability differences through the SiO₂ coatings.

Both examples clearly show the strength of nanostructuring electrocatalysts using ALD to control their performance.