Electrocatalytic Properties of Binuclear Cu(II) Fused Porphyrins for Hydrogen Evolution

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 nonfused copper­(II) porphyrin complex, the fused species is reduced at significantly less applied bias potentials (ΔE 1/2 ∼ 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 nonfused copper­(II) porphyrins indicates extended macrocycles provide an advantageous structural motif and design element for preparing electrocatalysts that activate small molecules of consequence to renewable energy.