Hydrochar Produced from Orange Peel Essential Oil Extraction Residues as a Support for Nanoparticles in Hydrogen Evolution Catalysis from NaBH4.

This work explores the valorization of orange peel residues from essential oil extraction as support for Co/Pt nanoparticles in the catalytic hydrolysis of sodium borohydride (NaBH4) for hydrogen production. Hydrochar was produced via hydrothermal carbonization at 130 °C for 6 h, preserving surface functional groups that facilitate metal nanoparticle dispersion. Co/Pt nanoparticles were successfully deposited on the hydrochar, as confirmed by TEM, SEM, EDS, and XRD analyses, revealing homogeneous distribution and nanoscale size. FTIR, TGA and BET characterization demonstrated a chemically rich, mesoporous structure, conducive to high catalytic performance. The catalytic activity was evaluated through NaBH4 hydrolysis under varying metal loadings, NaOH concentrations, NaBH4 concentrations, and temperatures. Monometallic Pt and Co achieved hydrogen generation rates (HGR) of 2573 and 4074 mL·min-1·g-1, respectively, while a 50:50 Co/Pt bimetallic composition showed a synergistic effect, reaching 3359 mL·min-1·g-1. Durability assays indicated that the catalyst retained approximately 95% of its initial activity over ten consecutive cycles. Kinetic isotope effect (KIE) experiments using H2O and D2O revealed a high KIE value of 4.97, indicating that water activation is the rate-determining step. This work demonstrates that orange peel residues can be efficiently repurposed as a sustainable catalyst support, combining waste valorization with environmentally friendly hydrogen production. The approach offers a cost-effective and green strategy for generating hydrogen while contributing to circular economy initiatives.