Exploring the frontiers of catholyte in hybrid Na-CO₂ batteries

Abstract

Metal-carbon dioxide (M-CO₂) batteries are a promising dual-function technology for addressing the urgent need for high-energy-density storage and the imperative of carbon capture and utilization. Among them, hybrid Na-CO₂ batteries belonging to the alkali metal-CO₂ family offer unique advantages of resource abundance, enhanced safety, and reaction pathways toward valuable chemicals through a proton-coupled electron transfer mechanism. Among battery components, the catholyte and its nature influence ion transport, establish the micro-reaction environment at the catalyst interface, and directly determine the discharge product speciation and overall cell performance. However, despite growing interest in hybrid Na-CO₂ batteries, review reports thoroughly examining design principles of catholytes, along with their challenges and advances, are still lacking. In this paper, we systematically review the latest progress in catholyte development for hybrid Na-CO₂ batteries, covering aqueous electrolytes, water-in-salt electrolytes, gel electrolytes, molten-salt electrolytes, and solid-state electrolytes. We critically analyze the fundamental electrochemical reaction mechanisms, discharge product characteristics, and the corresponding advantages and limitations for each system. Key challenges, such as the narrow electrochemical stability window (ESW), interface compatibility issues, sluggish CO₂ reduction kinetics, and the trade-off between product selectivity and long-term stability, are highlighted. Finally, future research perspectives and directions, emphasizing in-depth mechanistic understanding through advanced operando characterization, rational design of electrolyte-catalyst interfaces, and the development of multifunctional electrolyte systems, are proposed to achieve efficient, durable, and economically viable hybrid Na-CO₂ batteries for practical carbon-neutral energy applications.

Keywords

Hybrid Na-CO₂ battery / CO₂ electrochemistry / working mechanism / catholyte engineering / electrochemical performance

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