Direct Hydrogen Storage From Water to Diphenylmethane via Liquid Organic Hydrogen Carrier Electrochemical Hydrogenation System

This study presents a novel electrochemical hydrogenation (EH‐DPM) system that integrates clean hydrogen production and storage by utilizing a diphenylmethane (H0‐DPM, DPM) /dicyclohexylmethane (H12‐DPM, DCM) pair as a liquid organic hydrogen carrier (LOHC). The system operates in a full‐cell configuration, coupling a cathode for the electrochemical hydrogenation of H0‐DPM (EH‐DPM) with a proton exchange membrane water electrolyzer (PEMWE) anode, thereby enabling direct hydrogen storage in the LOHC during water splitting. The EH‐DPM system demonstrates higher energy efficiency than conventional PEMWE, achieving reaction currents at lower potentials. A comparative testing of Pt and Ru black electrocatalysts reveals that Ru black outperforms Pt black at higher voltages (> 1.5 V), achieving significantly higher selectivity (92.3% at 1.6 V) for the fully hydrogenated H12‐DPM. 1 H‐NMR and 13 C‐NMR analyses identifies cyclohexylmethylbenzene (H6‐DPM, CMB) as the sole hydrogenation intermediate, highlighting that optimal electrocatalyst selection is crucial for maximizing H12‐DPM yield and minimizing energy losses from intermediate formation. Density functional theory calculations elucidate catalyst‐dependent reaction pathways and show that distinct hydrogen migration barriers on Pt and Ru surfaces account for the observed voltage‐dependent selectivity. These findings suggest that Ru black is a promising electrocatalyst for developing commercially viable hydrogen storage technologies based on the EH‐DPM system.