NSF-DFG: Strategies to Overcome Contemporary Limitations of Reductive Electrosynthetic Conversions in Aqueous Media

Iowa State University, Ames IA

Investigators

Abstract

Reductive electrosynthesis is an inherently green, safe, and sustainable technology for chemical reductions as it replaces hazardous chemicals and/or harsh reaction conditions by electrons supplied by renewable wind/solar energy. Reductive electrosynthesis also offers unique opportunities for increasing conversion efficiencies and for synthesizing new molecules that are not accessible thermochemically or photochemically. However, the implementation of this technology for chemical manufacturing is hampered by the parasitic hydrogen evolution reaction and by the corrosion of conventional cathode materials. This project will introduce highly disruptive concepts that address these severe shortcomings. This effort is timely as it will advance the American power and chemical manufacturing industries, and provide unique outreach and training opportunities for building a locally-rooted STEM workforce in the Midwest. The parasitic hydrogen evolution reaction (HER) and corrosion of contemporary cathode materials will be addressed through the investigation and development of two innovative approaches, namely cationic hydrogen inhibitors and unconventional metal and metal alloy cathode materials. Novel cationic hydrogen inhibitors will be designed to selectively increase the overvoltage for the hydrogen evolution reaction, which will enable reactions that are inaccessible by the current state-of-the-art methods. These cations will interact with the negatively charged cathode and self-assemble to create a protective ionic layer that hampers corrosion and HER while enabling the desired tunneling of electrons to the substrates in solution. Cations with various molecular structures will be synthesized and investigated to establish structure-performance relationships. In addition to self-assembly, the research team will also explore the electrografting of selected cations to suitable electrode materials. This approach is expected to grant a high flexibility as the organic cationic inhibitors can be further tailored for specific requirements, for instance using chiral additives to transfer stereogenic information to desired substrates. The stated shortcomings will also be tackled from a different perspective by designing unconventional electrode materials such as Ga/In mixtures, ternary alloys of zinc and lead, bismuth, and bismuth alloys as cathodes. These materials are expected to excel in many aspects. For example, in addition to exhibiting high hydrogen overpotentials, some of them should also show increased biocompatibility and resistance to biobased corrosive compounds compared to existing metal electrodes used in reductive electrochemistry. The performance of such alloys for reductive electrosynthesis in aqueous media has not been carefully investigated yet and it is anticipated that doing so will open new avenues for organic electrosynthesis. The synergistic combination of both approaches, i.e. cationic hydrogen inhibitors and novel metal alloys, is also expected to yield unmatched performance and durability for challenging transformations. The technological advances achieved through this project will promote the adoption of green electrochemistry in the chemical industry and facilitate the implementation of electrochemical manufacturing processes at commercial scale. This research was funded under the NSF-DFG Lead Agency Activity in Electrosynthesis and Electrocatalysis (NSF-DFG EChem) opportunity NSF 20-578. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.