Selectivity is another critical factor to consider when assessing a molecular catalyst. Catalyst that produces one product over the other selectively enables a good control of the reaction outcome. An established strategy to implement selectivity on a catalyst in a homogenous system is to modulate the supporting ligand. In a heterogenized system, tuning the selectivity of products can be achieved by modifying the surface loading of the metal complex. An example of selective production of CO over formate in CO2 reduction was demonstrated with a carbon nanotube electrode surface functionalized with a Mn(bipyridine)-pyrene complex (Figure ). The molecular species was immobilized via π-π interactions between the pyrene moiety of the Mn complex and the electrode. The successful immobilization was confirmed electrochemically and spectroscopically. The hybrid electrode showed high activity for CO2 reduction with turnover numbers (TONs) up to 1790 ± 290 for CO and 3920 ± 230 for formate at an applied potential of -1.1 V vs. standard hydrogen electrode (SHE). The selectivity was tuned by controlling the surface loading of the molecular catalyst. A Mn hydride was responsible for converting CO2 to formate at low catalyst loading. In contrast, at high loading, a Mn dimer intermediate was proposed after reduction, leading to the production of CO. Catalytically active species were identified by in situ UV-vis and attenuated total reflectance infrared spectroscopy (ATR-IR). These results showcase the possibility of achieving selectivity with an electrode surface-attached metal complex catalyst. However, the rate for CO2 reduction decreased due to the deactivation of the immobilized Mn electrocatalyst after a few hours while the rate for H2 evolution was less influenced. Therefore, challenges remain on increasing stability and durability of the designed immobilized system.