Electrocatalytic hydrogen evolution with gallium hydride and ligand-centered reduction

Ga(III) chloride tetrakis(pentafluorophenyl)porphyrin (1) was synthesized and shown to be a highly active and stable post-transition metal-based electrocatalyst for the hydrogen evolution reaction (HER). Electrochemical and spectroscopic studies indicate that both the first and second reduction events of 1 are ligand-centered. The 2e-reduced form 1(2–) reacts with a proton to give Ga(III)–H species (1–H), which undergoes protonolysis with Brønsted acids to produce H(2). The identification of key intermediates 1(–), 1(2–), and 1–H leads to a catalytic cycle, which is valuable for the fundamental understanding of the HER. This study presents a rare but highly active HER electrocatalyst with unusual features, including ligand-centered electron transfer and formation of post-transition metal hydride.