Hydrogen bond-mediated pH-universal electrocatalytic hydrogen production by conjugated porous poly-indigo

High-performing catalysts for the hydrogen evolution reaction (HER) via water electrolysis are of great importance for producing carbon-free green fuels. Compared to the routinely used metal-based systems under acidic conditions, metal-free pH-universal HER catalysts are smarter options taking into account the practical usability, sustainability, biocompatibility, and nominal cytotoxicity. Herein, we present an indigo-based organic conjugated porous polymer featuring a pronounced 2D few-layered morphology with surface-decorated hydrogen bonding sites for a deep catalyst-water contact and promising electrochemical HER activity. Indigo, being a vat dye, reduces in situ to its anionic leuco analogue and further promotes catalytic activity. The material manifested equipotent activity in acidic, alkaline, and neutral media superior to the contemporary metal-free carbonaceous electrocatalysts and comparable to the state-of-the-art metal-based catalytic systems. Under appropriate conditions, the material showed an overpotential of only 28 mV at 10 mA cm(-2) current density.