Electrochemical Surface Area Quantification, CO 2 Reduction Performance, and Stability Studies of Unsupported Three-Dimensional Au Aerogels versus Carbon-Supported Au Nanoparticles.

The efficient scale-up of CO 2 -reduction technologies is a pivotal step to facilitate intermittent energy storage and for closing the carbon cycle. However, there is a need to minimize the occurrence of undesirable side reactions like H 2 evolution and achieve selective production of value-added CO 2 -reduction products (CO and HCOO - ) at as-high-as-possible current densities. Employing novel electrocatalysts such as unsupported metal aerogels, which possess a highly porous three-dimensional nanostructure, offers a plausible approach to realize this. In this study, we first quantify the electrochemical surface area of an Au aerogel (≈5 nm in web thickness) using the surface oxide-reduction and copper underpotential deposition methods. Subsequently, the aerogel is tested for its CO 2 -reduction performance in an in-house developed, two-compartment electrochemical cell. For comparison purposes, similar measurements are also performed on polycrystalline Au and a commercial catalyst consisting of Au nanoparticles supported on carbon black (Au/C). The Au aerogel exhibits a faradaic efficiency of ≈97% for CO production at ≈-0.48 V RHE , with a suppression of H 2 production compared to Au/C that we ascribe to its larger Au-particle size. Finally, identical-location transmission electron microscopy of both nanomaterials before and after CO 2 -reduction reveals that, unlike Au/C, the aerogel network retains its nanoarchitecture at the potential of peak CO production.