Cobalt phthalocyanine (CoPc) is a modestly-active electrocatalyt for the CO2 reduction reaction (CO2RR) in aqueous solution. When adsorbed onto edge-plane graphite surfaces, CoPc reduces CO2 to CO along with significant co-generation of H2 due to concurrent water reduction. However, upon immobilization within a poly-4-vinylpridine (P4VP) film, the resulting CoPc-P4VP system shows dramatically enhanced activity and selectivity for CO generation compared to the parent system, operating with a turnover frequency of ~4.8 s-1 at just -0.75 V vs RHE with ~90% Faradaic efficiency for CO production. We propose that two properties of the P4VP polymer contribute to this catalytic enhancement: 1) axial coordination of individual pyridine residues to the square planar cobalt center of CoPc increases the activity of the catalyst, and 2) the uncoordinated pyridine residues enable secondary and outer-coordination sphere effects that increase the selectivity of the system for CO production from CO2. These effects were independently investigated by studying the electrocatalytic performance of the CoPc catalyst immobilized in non-coordinating poly-2-vinylpyridine films and as polymer-free, five coordinate CoPc-pyridine films. We also report initial investigations into other polymer-immobilized catalyst systems for electrocatalytic CO2 reduction.

Immobilization of molecular electrocatalysts in a coordinating membrane to enhance their activity and selectivity for CO2 reduction

251st National Meeting (2016)

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