Natural Assembly of Electroactive Metallopolymers on the Electrode Surface: Enhanced Electrocatalytic Production of Hydrogen by [2Fe-2S] Metallopolymers in Neutral Water

A molecularcatalyst attached to an electrode surfacecan offerthe advantages of both homogeneous and heterogeneous catalysis. Unfortunately,some molecular catalysts constrained to a surface lose much or allof their solution performance. In contrast, we found that when a smallmolecule [2Fe-2S] catalyst is incorporated into metallopolymersof the form PDMAEMA-g-[2Fe-2S] (PDMAEMA =poly(2-dimethylamino)ethyl methacrylate) and adsorbed to the surface,the observed rate of hydrogen production increases to k (obs) > 10(5) s(-1) per activesite with lower overpotential, increased lifetime, and tolerance tooxygen. Herein, the electrocatalytic performances of these metallopolymerswith different length polymer chains are compared to reveal the factorsthat lead to this high performance. It was anticipated that smallermetallopolymers would have faster rates due to faster electron andproton transfers to more accessible active sites, but the experimentsshow that the rates of catalysis per active site are independent ofthe polymer size. Molecular dynamics modeling reveals that the highperformance is a consequence of adsorption of these metallopolymerson the surface with natural assembly that brings the [2Fe-2S]catalytic sites into close contact with the electrode surface whilemaintaining exposure of the sites to protons in solution. The assemblyis conducive to fast electron transfer, fast proton transfer, anda high rate of catalysis regardless of the polymer size. These resultsoffer a guide to enhancing the performance of other electrocatalystswith incorporation into a polymer that provides an optimal interactionof the catalyst with the electrode and solution.