End-capping of hydrogen bonds: A strategy for blocking the proton conduction pathway in aqueous electrolytes

Sustainable battery development is becoming a key goal for storing renewable energy on a large scale. Toward this goal, great hopes are placed on the use of aqueous electrolytes. However, with high expectations, come increasing challenges, represented by the parasitic hydrogen evolution reaction (HER) on the anode of aqueous batteries. Here, we propose a new strategy to mitigate HER in aqueous batteries by the regulation of mass transfer kinetics, namely blocking the pathway of proton conduction by the end-capping of H-bond using N-methyl-2-pyrrolidone (NMP). The NMP structure possesses the H-bond acceptor but no H-bond donor sites, a feature that can effectively cut off H-bond propagation, and further block the pathway of proton transport in aqueous electrolytes. Hence, the modulated electrolyte confers a combination of enhanced cathodic and anodic stability, dendrite-free metal plating/stripping, and a high average Coulombic efficiency (CE) of 99.2%. Further, the end-capping of the H-bond network in electrolytes results in substantially more stable full-cell batteries that pair the metal anode with Prussian blue analogue (PBA) and polyaniline (PANI) cathodes at both room and low temperature. The “end-capping” concept in polymers is broadened to aqueous solutions for the first time here, providing a potential direction to revolutionize aqueous batteries for efficient energy storage.