Designing Biomimetic NADH-Analogs for Artificial Photosynthesis

Over the past few decades, numerous homogenous organometallic catalysts have been studied for electrocatalytic CO2RR. While superior in their activity, they often suffer from low selectivity and durability. Metal-free hydrides are emerging as promising cost- effective substitutes for selective CO2 reduction, where the selectivity is achieved via hydride transfers. Initial studies on metal-free CO2 reduction focused on B-H and Si-H based hydrides, but despite being successful in conversion to the formate-stage and beyond, the oxophilic nature and consequent formation of Si-O and B-O bonds limit them to the application as stoichiometric reagents. This work focuses on less oxophilic reagents, carbon-based hydride donors – NADH analogs, as potential catalysts in CO2 reduction. NADH analogs are designed to be strong enough hydride donors, capable of performing a hydride transfer reaction to CO2. The structural design is governed by the concept of thermodynamic hydricity, which is obtained using DFT calculations and then tested using experimental methods. Apart from the hydride donor ability, an important requirement for any type of catalyst is to have a relatively easy regeneration of the active form. To test this, we employ electrochemical methods (such as cyclic voltammetry and preparative electrolysis) often coupled with spectroscopic techniques to gain insights on regeneration pathways. The principles obtained here give a perspective of utilizing metal- free motifs in electrocatalytic selective CO2 reduction.