Aqueous H+ and NH4+ Batteries

This chapter provides a comprehensive overview of two emerging aqueous battery technologies: proton (H+) batteries and ammonium-ion (NH4+) batteries. It examines their working principles, intrinsic advantages, ion transport mechanisms, and the electrode and electrolyte materials enabling their operation. Both systems employ a rocking-chair (intercalation) mechanism with H+ or NH4+ charge carriers in aqueous media, leveraging intrinsic safety and sustainable, and metal-free resources. Aqueous proton batteries benefit from the ultra-small size and exceptional mobility of protons (via both vehicular diffusion and Grotthuss hopping) to achieve high power densities. Conversely, ammonium-ion batteries exploit the lightweight, minimal hydrated radius, and mild acidity of NH4+ to facilitate rapid ion diffusion with fewer side reactions. The chapter surveys a broad spectrum of advanced electrodes optimized for reversible H+/NH4+ insertion, as well as electrolyte innovations. These range from optimized acidic or concentrated “water-in-salt” electrolytes that expand voltage windows to quasi-solid-state gels that enhance safety and thermal stability. Together, these developments illustrate the progress and promise of H+ and NH4+ batteries as high-performance, sustainable energy storage alternatives.