Rechargeable nickel reservoir enables nitrile production in organic solvents

Researchers at National Taiwan University have created a nickel-based redox reservoir that enables the spontaneous production of nitriles in organic solvents, while simultaneously generating hydrogen gas. Nitriles are crucial building blocks found in pharmaceuticals, agrochemicals, dyes, electronic materials and polymers. However, traditional methods for creating nitriles often involve hazardous substances or harsh reaction conditions, prompting the search for greener, more controllable approaches.

One promising method involves using an electrochemical process to convert benzylamine into benzonitrile, with the added benefit of hydrogen production. In conventional setups, this reaction typically occurs in strongly alkaline aqueous electrolytes, but this can lead to unwanted side reactions and degradation of the desired products. The new nickel-based redox reservoir, developed by a team led by Professor Chih-Jung Chen, addresses this issue by separating nitrile synthesis from hydrogen production.

The NiOOH/Ni(OH)₂ electrode acts as a rechargeable redox reservoir, temporarily storing and releasing oxidizing power, similar to pumped-storage hydropower. When placed in a benzylamine solution, the nickel-based reservoir spontaneously converts benzylamine into benzonitrile in an open-circuit condition, without an external electrical bias. The reduced reservoir can then be recharged electrochemically to NiOOH, while simultaneously generating hydrogen gas at the cathode.

This separation allows for nitrile synthesis to occur in organic solvents, avoiding the hydrolysis reactions that degrade benzylimine and benzonitrile. Hexane proved to be the best solvent for this process, maintaining high benzonitrile yield, selectivity, and Faradaic efficiency even at benzylamine concentrations above 100 mM. Since the organic reaction does not require supporting electrolyte salts, product separation becomes simpler.

The researchers emphasize that this approach is not limited to benzylamine, as it can also be applied to convert several benzylamine derivatives containing different functional groups into their corresponding nitriles. This flexibility suggests that the strategy could be adapted to produce various chemicals according to demand. Moreover, by using a rechargeable material as an intermediate reservoir, nitrile synthesis and hydrogen production can be independently optimized, opening up new possibilities for renewable-electricity-driven chemical manufacturing.