Potential-controlled Deposition of Multilayer CO₂ Reduction Catalyst Films onto Silicon Photoelectrodes Demonstrates Thickness-dependent Catalytic Rate

Covalently attaching molecular catalysts to semiconductor surfaces yields promising hybrid photoelectrode architectures for reducing CO₂ to higher-value carbon products. Polymeric molecular catalyst films have higher loading densities than their monolayer counterparts, promising greater rates of solar fuel production. Using photoassisted diazonium electrografting, multilayered films of a Re(apbpy)(CO)₃Cl CO₂-reduction catalyst were attached to low-doped p-type Si (pSi). Parallel characterization of the newly formed films with ellipsometry, XPS, and ICP-MS revealed that catalyst loading increased with increasingly negative applied grafting potentials (V_graft), providing us an experimental test bed to study the effects of film thickness on photocatalytic performance. Controlled-potential electrolysis experiments showed enhanced CO evolution rates on all photoelectrodes with increasingly negative applied potentials (V_app), with thicker films exhibiting the greatest rates of enhancement. Competitive proton reduction reactions at the Si surface were not strongly linked to V_app but dependent on film thickness, with thicker films showing increased CO-to-H₂ production ratios.

Teitsworth, T. S.; Rotundo, L.; Harvey, A. K.; Fang, H.; Tanwar, M.; Orr, A.; Robinson, T.; Seigel, D. J.; Sampaio, R.; Donley, C.; Atkin, J.; Fakhraai, Z.; Manbeck, G.; Lockett, M. Potential-controlled Deposition of Multilayer CO2 Reduction Catalyst Films onto Silicon Photoelectrodes Demonstrates Thickness-dependent Catalytic Rate, ACS Appl. Mater. Interfaces, 2025, In press. https://doi.org/10.1021/acsami.5c15759