Electrocatalytic Properties of Binuclear Cu(II) Fused Porphyrins for Hydrogen Evolution KhusnutdinovaDiana WadsworthBrian L. FloresMarco BeilerAnna M. Reyes CruzEdgar A. ZenkovYegor MooreGary F. 2018 Binuclear copper­(II) porphyrins in which two copper­(II) porphyrin macrocycles are doubly fused at the <i>meso</i>-beta positions are shown to be active electrocatalysts for the hydrogen evolution reaction (2H<sup>+</sup> + 2e<sup>–</sup> → H<sub>2</sub>). 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 (Δ<i>E</i><sub>1/2</sub> ∼ 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<sup>–1</sup>. 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.