Molecular Self-Assembly in Conductive Covalent Networks for Selective Nitrate Electroreduction to Ammonia.

Electrochemical nitrate (NO) reduction in aqueous media provides a useful approach for ammonia (NH) synthesis. While efforts are focused on developing catalysts, the local microenvironment surrounding the catalyst centers is of great importance for controlling electrocatalytic performance. Here, we demonstrate that a self-assembled molecular iron catalyst integrated in a free-standing conductive hydrogel is capable of selective production of NH from NO at efficiencies approaching unity. With the electrocatalytic hydrogel, the NH selectivity is consistently high under a range of negative biases, which results from the hydrophobicity increase of the polycarbazole-based electrode substrate. In mildly acidic media, proton reduction is suppressed by electro-dewetting of the hydrogel electrode, enhancing the selectivity of NO reduction. The electrocatalytic hydrogel is capable of continuous production of NH for at least 100 h with NH selectivity of ∼89 to 98% at high current densities. Our results highlight the role of constructing an internal hydrophobic surface for electrocatalysts in controlling selectivity in aqueous media.