Exploring affordable and efficient electrocatalysts is crucial for advancing fuel cell, supercapacitor, and water-splitting

technologies. This study introduces a high-performance tri-functional composite, Cu@FeEu-N-C/porous graphitic carbon

nitride (pCN), for electrochemical water splitting, the oxygen reduction reaction (ORR), and supercapacitor applications.

The Cu@FeEu-N-C/pCN electrocatalyst exhibits remarkable efficiency, requiring only 369 mV and 420 mV of overpotential

for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, at a current density

of 10 mA cm⁻². The onset potentials are − 0.12 V vs. the reversible hydrogen electrode (RHE) for HER and 1.45 V vs.

RHE for OER. Additionally, in the ORR, it proceeds predominantly via the four-electron (4e⁻) pathway, with an electron

transfer number of 3.32, indicating minor contribution from the two-electron pathway. The incorporation of porous graphitic

carbon nitride (pCN) appears to enhance the overall catalytic performance, likely due to synergistic effects such

as improved electrical conductivity, better dispersion and accessibility of active sites, and facilitated electron transfer.

The Metal-Nitrogen-Carbon (M-N-C) structure in the composite plays a crucial role in boosting the activity by creating

abundant active sites and stabilizing the catalyst under operating conditions. These combined effects result in faster reaction

kinetics, lower onset potentials, and superior durability. Furthermore, as a supercapacitor electrode, the composite

achieves a specific capacitance of 226 F.g⁻¹ at 1 A.g⁻¹, emphasizing its multifunctionality for energy storage and conversion

applications. In summary, Cu@FeEu-N-C/pCN exhibits promising tri-functional capability for HER, OER, and ORR,

with performance approaching that of noble-metal-based catalysts, while also excelling in supercapacitor performance.