Highly dispersed Pt–Fe–Ru nanoparticles on mesoporous bio-based hydrochar for effective oxygen reduction reactions in acidic and alkaline electrolytes

• Cellulose-based activated hydrochar is a sustainable support for high-performance catalysts. • Ultralow Pt mass loading (2 %) has limited ORR activity, significantly enhanced with Fe and Ru. • Pt-Fe-Ru catalysts are highly efficient for ORR in alkaline and acidic media. • Integration of Fe and Ru with Pt on N-doped carbon leads to efficient and durable catalysts. This study aims to develop a cost-effective, high-performance electrocatalyst using mesoporous bio-derived hydrochar support. The mesoporous hydrochar was synthesized from cellulose through hydrothermal carbonization followed by H 3 PO 4 activation, yielding a material with a high specific surface area (1137 m 2 g −1 ), mesoporosity (537 m 2 g −1 ), abundant defect sites (I D /I G = 1.9), and diverse surface functionalities. These properties enabled the uniform dispersion of low-load (≤ 2 wt%) platinum, iron, and ruthenium nanoparticles through wet impregnation and thermal reduction, forming synergistic trimetallic nanoparticles on the hydrochar surface. Electrochemical evaluations demonstrated highly efficient 4 e − ORR activity of a trimetallic Pt-Ru-Fe catalyst in both acidic and alkaline media. In 0.1 M HClO 4 , the catalyst exhibited an onset potential of 0.91 V vs. RHE and a Tafel slope of 69 mV dec −1 , while in 0.1 M KOH, the onset potential and Tafel slope improved to 0.94 V vs. RHE and 47 mV dec −1 , respectively, highlighting its versatility across different electrolytes. Overall, this work provides a pathway to significantly reduce PEMFC costs while maintaining high catalytic performance, offering a sustainable and economically viable solution for the advancement of fuel cell technologies.