Carbon fibers as active substrates for engineering Ni/Au interfaces toward enhanced hydrogen evolution in ammonia-containing alkaline electrolytes.

The development of material-efficient electrode platforms for controlling metal dispersion and interfacial charge transfer is central to advanced electrochemical technologies. Here, carbon fibers are used as active substrates for engineering metal-carbon interfaces via thermal activation and sequential electrodeposition. Surface modification exposes graphitic domains and increases roughness, enabling uniform metal nucleation and strong interfacial bonding of the deposited nickel-gold layers, resulting in a hierarchical and highly accessible surface architecture. Electrochemical analysis reveals enhanced charge-transfer behavior and increased electrochemical accessibility, highlighting the role of the carbon scaffold in facilitating electron transport and interfacial charge transfer. The modified fibers exhibit reduced overpotential (168.2 mV at - 10 mA cm⁻²), a Tafel slope of 57 mV dec⁻¹, and decreased charge-transfer resistance (~ 651 Ω), indicating improved interfacial kinetics and more efficient utilization of deposited metals. In an ammonia-containing alkaline electrolyte, a further increase in current response (~ 14-15%) is observed, consistent with a modification of the interfacial reaction environment. The findings demonstrate that carbon fibers function beyond passive supports, acting as conductive and structurally adaptive frameworks that govern metal dispersion, interfacial bonding, and charge-transfer behavior. This work highlights carbon fibers as scalable, material-efficient substrates for designing high-performance metal-carbon hybrid systems for ammonia-containing alkaline electrochemical systems and future alkaline wastewater technologies.