Abstract
The Ni(P2N2)2 catalysts are among the most efficient non-noble-metal based molecular catalysts for H2 cycling. However, these catalysts are O2 sensitive and lack long term stability under operating conditions. Here, we show that in a redox silent polymer matrix the catalyst is dispersed into two functionally different reaction layers. Close to the electrode surface is the “active” layer where the catalyst oxidizes H2 and exchanges electrons with the electrode generating a current. At the outer film boundary, insulation of the catalyst from the electrode forms a “protection” layer in which H2 is used by the catalyst to convert O2 to H2O, thereby providing the “active” layer with a barrier against O2. This simple but efficient polymer-based electrode design solves one of the biggest limitations of these otherwise very efficient catalysts enhancing its stability for catalytic H2 oxidation as well as O2 tolerance.
Highlights
The Ni(P2N2)[2] catalysts are among the most efficient non-noble-metal based molecular catalysts for H2 cycling
We demonstrated in a previous study that the electrocatalytic H2 oxidation activity of the DuBois catalyst CyGly was lost irreversibly after 10 min when 2% O2 was added to the H2 gas feed[15]
When H2 is flushed through the electrochemical cell, a catalytic current appears starting at the redox potential of the complex (Fig. 2b)
Summary
The Ni(P2N2)[2] catalysts are among the most efficient non-noble-metal based molecular catalysts for H2 cycling. Extension of the proton channel with a carboxylic acid moiety between the metal center and the solvent by attachment of an amino acid to the pendant amine, allows the DuBois catalyst to operate at very low overpotentials at low pH and at room temperature in aqueous systems[10,11,12], or even reversibly[13,14]. These catalysts show tolerance towards CO, a common contaminant of H2 feedstocks and a strong inhibitor of hydrogenases and of platinum used for catalysis[5,15,16]. Crystallographic and nuclear magnetic resonance (NMR) spectroscopic studies showed that the Ni-(bis)diphosphine complexes in low oxidation states react with O2 to oxidize the phosphine ligands, inactivating the OH
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