Insights into the structure-property relationships of activated carbon derived from phenolic resin for electrochemical storage of green hydrogen using proton battery

Electrochemical hydrogen storage in porous activated carbons is a rapidly advancing technology, yet the composition and role of oxygen-containing surface functionalities in hydrogen storage remain underexplored. This study provides a detailed investigation of the surface and bulk properties of porous activated carbon derived from phenolic resin (aC PR) using a comprehensive multi-technique approach, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The aC PR exhibits an exceptional BET surface area of approximately 4400 m 2 /g, with a well-balanced distribution of mesopores, micropores, and ultra-micropores. Quantitative analyses reveal that aC PR is composed of 95.45 % carbon and 4.55 % oxygen, with oxygen functionalities distributed as carboxylic acid (~8 %), anhydride (~28 %), phenol (~17 %), carbonyl and quinones (~21 %), and lactones (~23 %). Post-TPD treatment, the oxygen content reduces to 2.25 %, with minimal impact on the material's hydrogen storage capacity, which remains at ~0.60 ± 0.05 wt% H. H-storage was measured using Proton Battery. In the proton battery, protons are generated by water splitting towards the oxygen side and are stored towards the C side in the negatively charged ac PR electrode. Ab initio molecular dynamics simulations demonstrate that both acidic and basic oxygen-containing groups have similar proton affinities, suggesting that the type of oxygen functional group plays a minimal role in hydrogen storage capacity. This work underscores the critical role of oxygen functionalities in hydrogen storage and offers new insights into the design and optimization of next-generation carbon materials for scalable hydrogen storage technologies. • aC PR has a high BET surface area (~4,400 m 2 /g) with mesopores, micropores, and ultra-micropores, for H-storage. • O-based groups in aC PR: carboxylic acid (7.7 %), anhydride (28 %), phenol (17 %), carbonyl/quinones (21 %), and lactones (23 %). • Both acidic and basic O-based groups enable H-storage (~0.60 ± 0.05 wt% H), confirmed by AIMD simulations and experiments.