Binuclear copper(II) porphyrins in which two copper(II) porphyrin macrocycles are doubly fused at the meso-beta positions are shown to be active electrocatalysts for the hydrogen evolution reaction (2H+ + 2e- → H2). Structural characterization, including use of electron paramagnetic resonance and x-ray photoelectron spectroscopies, verifies the fused species contains two copper(II) metal centers in its resting state. In comparison to the non-fused copper(II) porphyrin complex, the fused species is reduced at significantly less applied bias potentials (δE ~ 570 mV for the first reduction process). Electrochemical characterization in the presence of substrate protons confirms the production of hydrogen with near-unity Faradaic efficiency, and kinetic analysis shows the catalyst achieves a maximum turnover frequency above 2,000,000 s-1. The enhancement in catalytic performance over analogous non-fused copper(II) porphyrins indicates extended macrocycles provide a structural motif and design element for preparing electrocatalysts that activate small molecules consequence to renewable energy.
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