Atomic-scale Ni₃Ti/CNT interface modulation enables fast electron transport for bifunctional water splitting and supercapacitors

The development of robust, binder-free electrodes with bifunctional capabilities for energy conversion and storage is essential for advancing sustainable energy technologies. Here, a scalable strategy is reported to synthesize a binder-free Ni₃Ti/CNT electrocatalyst on a Kovar alloy substrate via screen-printing and vacuum annealing. During annealing, a solid-state reaction between nickel (Ni) and titanium (Ti) nanoparticles yields a Ni₃Ti intermetallic alloy, which establishes strong metallurgical bonding with the substrate, greatly improving electrode adhesion and enabling long-term electrochemical durability. Strong interfacial coupling between Ni₃Ti and carbon nanotubes (CNTs) modulates the local electronic structure, accelerates charge-transfer kinetics, and optimizes adsorption of reaction intermediates. As a result, the Ni₃Ti/CNT hybrid achieves a low cell voltage of 1.51 V at 10 mA cm⁻² for overall water splitting and enables an asymmetric supercapacitor with a high energy density of 34.09 μWh cm⁻² at 750 μW cm⁻² and 87.9% capacitance retention after 5000 cycles. Density functional theory (DFT) calculations reveal that interfacial charge transfer (~0.17 e⁻) activates carbon sites at the Ni₃Ti/CNT heterojunction, optimizing hydrogen adsorption (ΔG_H* = −0.32 eV), and lowers the oxygen evolution reaction (OER) free-energy barrier from 6.44 eV (Ni₃Ti) to 3.21 eV (Ni₃Ti/CNT). Furthermore, the Ni₃Ti/CNT interface substantially increases the quantum capacitance to 3848 μF cm⁻², compared to 3229 μF cm⁻² for Ni₃Ti. These results demonstrate an industrially compatible route to high-performance, dual-functional Ni₃Ti/CNT electrodes and provide atomic-level insight into alloy–CNT interface engineering for next-generation energy systems.