Grafted AuCu Electrodes with Aryldiazonium Salts: Materials Chemistry Route to Efficient Hydrogen Evolution Reaction Catalysis

In the search for hydrogen evolution reaction (HER) electrocatalysts, copper-based systems offer a cost-effective route by incorporating surface grafting strategies to enhance their durability and performance in alkaline water splitting. Here, we utilized the surface grafting of flexible copper films using aryldiazonium gold(III) salts, [HOOC-4-C 6 H 4 –N≡N]AuCl 4, via an electroless dipping strategy, forming nanostructured aryl–AuCu interfaces. This effective approach introduces a nanoscale aryl–gold texture and tunes the Cu oxidation state. Upon electrochemical activation, the modified films exhibit a pronounced enhancement in HER performance by decreasing the overpotential from 0.23 to 0.17 V at 10 mA/cm 2 and increasing the current density from 153 to 364 mA/cm 2 at −0.46 V. Further, the electrocatalyst exhibited a Faradaic efficiency (FE%) of 86.1%. These improvements resulted from reduced charge transfer resistance, increased double-layer capacitance, increased electrochemically active surface area, grafted superhydrophilic aryl layer, structural reorientation of Cu lattice, and the formation of catalytically active Cu(I) species. Electrochemical delamination experiments confirmed the durability of the aryl–AuCu interface, demonstrating outstanding stability after continuous electrolysis for 115 h at a current density of 100 mA/cm 2 . This study highlights the potential of aryldiazonium gold chemistry as a promising approach for engineering Cu-based HER interfaces, providing a pathway toward cost-effective and durable alkaline water-splitting technologies.