Concentrated zwitterion interfaces for the selective promotion of ionic electrocatalysis

The electrode/electrolyte interfacial structure is a seminal component that governs the activity of electrochemical reactions. Concentrated interfaces can typically retard the local electrocatalytic reactions to extend the voltage window for high-voltage batteries, whereas in this study we demonstrated that a dense interface constituting of zwitterionic betaine could selectively promote the electrocatalytic transformation of anionic species, especially electrocatalytic hydroxide oxidation in alkaline water splitting. Under concentrated betaines, the state-of-the-art oxygen evolution reaction (OER) electrocatalysts of nickel and nickel-iron oxyhydroxide exhibited overpotential gains of 138 mV and 97 mV, corresponding to two orders of magnitude higher current densities. The activity increment was stemmed from both the static dehydration effect that the hygroscopic betaine rips off the anionic hydration shell to promote its downstream reaction and the dynamic double layer effect that the ultra-dense betaine layer accelerates the accumulation of underhydrated anions in the inner Helmholtz plane. This enhancement is highly specific to ions for enabling the selective ionic transformation in complex media. The concentrated betaine interface effectively segregates the reactive zones to improve the durability of water electrolysis in aniline-containing electrolytes by at least an order of magnitude, opening up new possibilities for next-generation unconventional water splitting.