Functional hyper-crosslinked polymers as advanced materials for hydrogen generation via sodium borohydride methanolysis

Abstract

Air pollution caused by fossil fuels is the biggest problem humanity has ever created, and clean energy sources like hydrogen are seriously needed to solve it. Therefore, in this study, four phenanthrene-based hyper-crosslinked polymers (PTHCP-1–4) were synthesized via Friedel–Crafts alkylation and characterized by FTIR, BET, SEM, XPS, TGA, and zeta potential measurements. The BET surface areas ranged from 518.9 to 908.8 m2 g-1, with PTHCP-4 showing the highest value, while pore volumes varied between 0.24 and 1.60 cm3 g-1. SEM revealed uniform nanoscale particles for PTHCP-2 (mean size 54 nm) and aggregated morphologies for PTHCP-3/4. XPS confirmed incorporation of pyridinic-N (399.3 eV) and phenolic –OH groups, and TGA demonstrated high thermal stability with main degradation above 400 °C. Zeta potentials shifted from +36.3 mV (PTHCP-3) or −6.48 mV (PTHCP-1) to more negative values after reaction, indicating surface interaction with BH4- species. Catalytic tests showed hydrogen generation rates (HGR) up to 34600 mL H2 min-1 gcat-1 (PTHCP-3) with the lowest activation energy (27.22 kJ mol-1). PTHCP-4 retained 95 % of its activity after five cycles, confirming excellent reusability. These results highlight the synergy between surface area, pore structure, and heteroatom functionality in optimizing metal-free catalysts for NaBH4 methanolysis.