Quinoline reversible electrochemical hydrogen storage on phosphide transition metal catalysts

Liquid Organic Hydrogen Carriers (LOHCs) are recognized as promising candidates for hydrogen storage due to their compatibility with the existing oil and gas infrastructure, which facilitates large-scale and long-distance storage and transportation. However, the hydrogenation and dehydrogenation processes of traditional organic hydrogen carriers necessitate an external supply of hydrogen and are conducted under high temperature and pressure conditions, raising safety concerns for their practical implementation. This paper introduces a reversible electrochemical hydrogen storage system utilizing quinoline, a nitrogen heterocyclic organic compound, as the hydrogen carrier. In this system, water serves as both the solvent and the hydrogen source for quinoline hydrogenation, with self-supported lamellar NiCoP/NF electrodes function as electrocatalysts. The catalytic performance of NiCoP/NF electrode for electrochemical hydrogenation of quinoline and dehydrogenation of 1,2,3,4-tetrahydroquinoline (THQ) was evaluated in 1 M KOH solution under mild conditions. The findings revealed that the hydroconversion yield of quinoline was 95 % with a selectivity of 99 %. The dehydroconversion yield of THQ was 81.4 % with a selectivity of 81 %. These results suggest that the system is capable of effectively facilitating reversible hydrogen storage. The NiCoP/NF electrode maintained high catalytic activity even after five cycles, which underscores its excellent stability. The electrochemical hydrogenation of quinoline does not necessitate exogenous hydrogen, thereby conferring the system with superior safety performance. This study presents a sustainable and efficient approach to hydrogen storage within nitrogen heterocyclic organic compounds.