Multifunctional Photoelectroactive Platform for CO2 Reduction toward C2+ Products─Programmable Selectivity with a Bioinspired Polymer Coating

In recent years, CO 2 photo/electroreduction has received great attention due to the urges and concerns to solve problems connected with global warming, for example, reducing the consumption of fossil fuels as energy sources and switching to renewable energy sources. The realization of this technology depends on efficient photo/electrocatalysts with high selectivity for the products. Herein, we report a programmable, bifunctional, scalable, high-performance, and low-cost bioinspired catalyst for photo/electrochemical CO 2 reduction (P/EC-R). We synthesized hydroxyapatite (HAP) needle-like nanoparticles coated with a functional polydopamine polymer (HAP/P(DOPA)) and then modified them with copper nanoparticles (HAP/P(DOPA)/Cu NPs). It was expected that HAP and P(DOPA), due to their plentiful functional groups such as hydroxyl (−OH – ), oxygen (−O •– and ═O), and amines (−NH 2 and −NH−), provide extensive active catalytic sites, participate in the capture, maintenance, and hydrogenation of the CO 2 intermediate, and offer a combination of efficient electrical conduction and photoactivity and synergistic effect together with Cu nanoparticles, thus potentially empowering CO 2 P/EC-R. Interestingly, varying the polymerization time of the coating layer (P(DOPA)) leads to different product selectivities in both photoelectrochemical and electrochemical reactions. In a shorter polymerization period (2 h), CO (>83%) is the main product, while for 5 and 15 h, C 2 H 6 (>70%) and CH 4 (>74%) are the main products, respectively. It is noteworthy to mention that as the applied potential increased (>−1.2 V vs RHE), propanal (C 3 H 6 O, FE > 35%) and surprisingly ethyl acetate (C 4 H 8 O 2, FE > 67%) have been detected. This is the first report on the C 4 product.