Acidification of Polyphthalocyanine Boosts Solid-State Proton Battery Performance with High Specific Capacity and Robust Cycling Stability

Solid-state proton batteries are regarded as one of the most promising energy storage technologies. However, the shortage of efficient protonic electrolytes significantly hinders their development. In this study, a simple, efficient, and scalable method for synthesizing metal-free polyphthalocyanine (H₂PPc) with high purity and crystallinity is presented, which is subsequently integrated with methanesulfonic acid (MeSA) to give a solid protonic electrolyte, MeSA@H₂PPc, demonstrating great potential for application in proton batteries. Remarkably, MeSA@H₂PPc shows superior proton conduction exceeding 10^‒3 S cm^‒1 under ambient conditions, along with excellent long-term stability and the widest electrochemical stability window (ESW) reported to date for solid protonic electrolytes. More impressively, when used in solid-state proton batteries, MeSA@H₂PPc enables excellent rate performance, robust cycling durability, and a record-high specific capacity, surpassing previously reported solid-state systems and outperforming many proton batteries based on conventional liquid electrolytes.